JP6328945B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  In recent years, due to the demand for higher compression and higher output of internal combustion engines, the applied voltage to the spark plug has been increased, and hence the spark plug is required to have improved withstand voltage performance. The spark plug has an insulator and a cylindrical metal shell that surrounds a part of the insulator. The spark plug is provided on the inner peripheral surface of the metal shell and on the outer peripheral surface of the insulator. The step portion has a structure facing the metal plate packing. Since the inner diameter of the metal shell is small at the step portion, the distance between the metal shell and the center electrode (interelectrode distance) is short at the step portion. For this reason, there existed a possibility that dielectric breakdown might arise in the vicinity of the step part of a metal shell, and an insulator might be damaged. Moreover, in the above-mentioned part, since the electric field strength is increased by the edge of the step portion of the metal shell, the withstand voltage performance may be lowered. For this reason, the spark plug which improves a withstand voltage performance by forming a step part in the curved shape which does not have an edge is proposed (refer patent document 1).

Japanese Patent No. 3432102

  Even in the spark plug described in Patent Document 1 described above, when the metal shell and the insulator are assembled by performing caulking processing on the metal shell at the time of manufacture, the plate packing is deformed and the inner diameter direction ( There is a risk of protruding in a direction approaching the insulator. In such a case, there is a problem that the electric field strength is increased by the protruding plate packing and the withstand voltage performance is lowered.

The present invention has been made to solve the above-described problems, and can be realized as the following forms.
The first aspect of the present invention is:
A rod-shaped center electrode extending in the axial direction;
A first through hole is formed along the axial direction, the center electrode is held in the first through hole, and an insulator-side reduced diameter portion whose outer diameter decreases toward the distal end side along the axial direction. An insulator having,
A second through hole is formed along the axial direction, the insulator is held in the second through hole, and a metal fitting side reduced diameter portion having a smaller inner diameter toward the distal end side along the axial direction. Having a metal shell,
A seal member disposed between the insulator-side reduced diameter portion and the metal shell-side reduced diameter portion;
A spark plug comprising:
The metal shell further includes:
A protruding portion that is in contact with the end portion on the distal end side of the metal shell-side reduced diameter portion and protrudes in a direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion;
The length of the protrusion in the direction along the surface of the metal shell side reduced diameter portion is Tw, and the height of the protrusion in the direction perpendicular to the surface of the metal shell side reduced diameter portion is Th. When the distance between the metal shell side reduced diameter part and the insulator side reduced diameter part in the direction perpendicular to the surface of the metal part reduced diameter part is Ph,
Tw ≧ Th and Th ≧ (1/2) × Ph
It is a spark plug characterized by satisfying the following conditions.
The second aspect of the present invention is:
A rod-shaped center electrode extending in the axial direction;
A first through hole is formed along the axial direction, the center electrode is held in the first through hole, and an insulator-side reduced diameter portion whose outer diameter decreases toward the distal end side along the axial direction. An insulator having,
A second through hole is formed along the axial direction, the insulator is held in the second through hole, and a metal fitting side reduced diameter portion having a smaller inner diameter toward the distal end side along the axial direction. Having a metal shell,
A seal member disposed between the insulator-side reduced diameter portion and the metal shell-side reduced diameter portion;
A spark plug comprising:
The metal shell further includes:
A protruding portion that is in contact with the end portion on the distal end side of the metal shell-side reduced diameter portion and protrudes in a direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion;
The metallic shell is
A first constant diameter portion that is in contact with the end portion on the distal end side of the protruding portion and has a constant inner diameter at any position along the axial direction;
A second constant diameter portion that is in contact with an end portion on the base end side of the metal shell-side reduced diameter portion and has a constant inner diameter at any position along the axial direction;
Have
A first intersection line where a surface virtually extending the inner peripheral surface of the metal shell-side reduced diameter portion toward the distal end side and an inner peripheral surface of the first constant-diameter portion, and an inside of the metal shell-side reduced diameter portion The shortest distance between the peripheral surface and the second intersecting line where the inner peripheral surface of the second constant diameter portion intersects is L1, and the inner peripheral surface of the metal shell-side reduced diameter portion and the protruding portion intersect with each other. When the shortest distance between the intersection line and the second intersection line is L2,
L2 ≧ (1/2) × L1
It is a spark plug characterized by satisfying the following conditions. The present invention can also be realized as the following forms.

  (1) According to one aspect of the present invention, a rod-shaped center electrode extending in the axial direction and a first through hole are formed along the axial direction, and the center electrode is held in the first through hole, An insulator having an insulator-side reduced diameter portion whose outer diameter decreases along the axial direction toward the distal end side, and a second through hole is formed along the axial direction, and the insulation is formed in the second through hole. A metal shell having a metal shell-side reduced diameter portion that holds the body and has an inner diameter that decreases toward the distal end side along the axial direction, and between the insulator metal diameter-reduced portion and the metal shell-side reduced diameter portion. A spark plug is provided. In the spark plug, the metal shell is further in contact with the end portion on the distal end side of the metal shell-side reduced diameter portion, and protrudes in a direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion. It has the part. According to the spark plug of this embodiment, the metal shell is in contact with the end portion on the tip side of the metal shell-side reduced diameter portion, and the protruding portion protruding in the direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion. Therefore, the seal member disposed between the insulator-side reduced diameter portion and the metal shell-side reduced diameter portion has an inner diameter direction (a direction perpendicular to the direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion). Can be prevented from protruding. For this reason, it is possible to suppress a decrease in withstand voltage due to the projecting of the seal member and the increase in electric field strength.

  (2) In the spark plug of the above aspect, the metal shell has a first constant diameter portion that is in contact with the end portion on the distal end side of the protruding portion and has a constant inner diameter at any position along the axial direction. In the projecting portion, the inner peripheral surface from the apex in the direction from the metal shell-side reduced diameter portion to the insulator-side reduced diameter portion to the end portion on the distal end side in contact with the first constant diameter portion is convex. It may be a curved surface. According to this form of the spark plug, the inner peripheral surface from the top of the projecting portion to the end on the tip side in contact with the first constant diameter portion is a curved surface, so there is no edge. An increase in electric field strength can be suppressed.

  (3) In the spark plug of the above aspect, the length of the protruding portion in the direction along the surface of the metal shell-side reduced diameter portion is Tw, and the protrusion in the direction perpendicular to the surface of the metal shell-side reduced diameter portion is When the length of the portion is Th and the distance between the metal shell side reduced diameter portion and the insulator side reduced diameter portion in the direction perpendicular to the surface of the metal shell side reduced diameter portion is Ph, Tw ≧ The condition of Th and Th ≧ (1/2) × Ph may be satisfied. According to the spark plug of this embodiment, by satisfying Tw ≧ Th, the protruding portion has a long external shape in the direction along the surface of the reduced diameter portion of the metal shell, so that the protruding portion applies a pressing force from the seal portion. When received, deformation of the protrusion can be suppressed. In addition, by satisfying Th ≧ (1/2) × Ph, the gap between the protruding portion and the insulator (insulator-side reduced diameter portion) is narrowed, and the tip end side (inner diameter side) end surface of the seal portion is reduced. Many of these areas can be supported by protrusions. For this reason, it can suppress that a seal part gets over a protrusion part, and protrudes to the front end side (inner diameter side).

  (4) In the spark plug of the above aspect, the metal shell is in contact with the end portion on the distal end side of the protruding portion and has a first constant diameter portion having a constant inner diameter at any position along the axial direction; A second constant diameter portion having a constant inner diameter at any position along the axial direction in contact with the base end side end portion of the metal shell side reduced diameter portion; A first intersection line where a surface virtually extending the inner peripheral surface toward the distal end side and an inner peripheral surface of the first constant diameter portion, an inner peripheral surface of the metal shell side reduced diameter portion, and the second constant diameter The shortest distance between the second intersecting line intersecting the inner peripheral surface of the part is L1, and the third intersecting line and the second intersecting line intersecting the inner peripheral surface of the metal shell side reduced diameter portion and the protruding portion When the shortest distance between and is L2, the condition of L2 ≧ (1/2) × L1 may be satisfied. According to the spark plug of this embodiment, by satisfying L2 ≧ (1/2) × L1, it is interposed between the metal shell and the insulator as compared with the configuration in which L2 is less than (1/2) × L1. The volume of the sealing portion to be increased can be increased. In other words, since the contact area between the seal portion and the metal shell and the contact area between the insulator and the seal portion can be increased, the airtightness between the metal shell and the insulator can be improved.

  (5) In the spark plug of the above aspect, the distance along the radial direction between the tip end portion of the protruding portion and the insulator may be 0.5 mm or less. According to this form of the spark plug, the withstand voltage can be improved while realizing a reduction in the size and diameter of the spark plug.

  (6) In the spark plug of the above aspect, a threaded portion having a nominal diameter of M12 or less may be formed on the outer peripheral portion of the metal shell. According to the spark plug of this embodiment, withstand voltage can be improved in a relatively small spark plug having a threaded portion having a nominal diameter of M12 or less.

  The present invention can be realized in various forms other than the spark plug. For example, it can be realized in the form of an internal combustion engine equipped with a spark plug, a method for manufacturing a spark plug, or the like.

It is a fragmentary sectional view showing spark plug 100 as one embodiment of the present invention. It is explanatory drawing which shows the detailed structure of the board packing 8 vicinity. It is explanatory drawing which shows the detailed structure of the plate packing 8 vicinity in the spark plug of 2nd Embodiment. It is explanatory drawing which shows the test result of the withstand voltage evaluation test according to the presence or absence of a protrusion part. It is explanatory drawing which shows the 1st test result of the withstand voltage evaluation test according to the presence or absence of satisfaction of 1st conditions (Tw> = Th and Th> = (1/2) * Ph). It is explanatory drawing which shows the 2nd test result of the withstand voltage evaluation test according to the presence or absence of satisfaction of 1st conditions. It is explanatory drawing which shows the 1st test result of the airtightness evaluation test according to the presence or absence of satisfaction of 2nd conditions (L2> = (1/2) * L1). It is explanatory drawing which shows the test result of the withstand voltage improvement evaluation test according to the presence or absence of satisfaction of 3rd conditions (length D <= 0.5mm).

A. First embodiment:
A1. Spark plug configuration:
FIG. 1 is a partial cross-sectional view showing a spark plug 100 as an embodiment of the present invention. In FIG. 1, the left side of the spark plug 100 shows a cross-sectional shape passing through the axis OL of the spark plug 100, and the right side of the spark plug 100 shows the external shape of the spark plug 100. Hereinafter, the direction along the axis OL is referred to as the axis direction OD. Also, with the axial direction OD as the vertical direction in the drawing, the lower side (side where a ground electrode 30 to be described later is disposed) is called the distal end side, and the upper side (side where the terminal fitting 40 to be described later is disposed) is the base end. Call the side.

  The spark plug 100 includes an insulator 10, a center electrode 20, a terminal metal fitting 40, a metal shell 50, and a ground electrode 30. Among these, all the components other than the ground electrode 30 have the same axis as the axis OL of the spark plug 100.

  The insulator 10 is a cylindrical member formed by firing a ceramic material such as alumina. A through-hole 12 extending along the axial direction OD is formed in the insulator 10, and the insulator 10 holds the center electrode 20 and the terminal fitting 40 in the through-hole 12. In the insulator 10, a flange portion 19 having the largest outer diameter is formed at the central portion in the axial direction OD, and a proximal end body portion 18 is formed at the proximal end side. A distal end side body portion 17 having an outer diameter smaller than that of the proximal end side body portion 18 is formed on the distal end side of the flange portion 19, and further on the distal end side with respect to the distal end side body portion 17, more than the distal end side body portion 17. A long leg portion 13 having a small outer diameter is formed. The long leg portion 13 is reduced in diameter toward the tip side, and is exposed to the combustion chamber when the spark plug 100 is attached to the engine head 200 of the internal combustion engine. A reduced diameter portion 15 is formed between the leg long portion 13 and the distal end side body portion 17. The outer diameter of the reduced diameter portion 15 becomes smaller toward the tip side along the axial direction OD.

  The center electrode 20 has a rod-like appearance shape extending in the axial direction OD. The center electrode 20 is accommodated in the through hole 12 of the insulator 10 so that the tip portion is exposed from the insulator 10. The center electrode 20 has a structure in which a core material 25 is embedded in an electrode base material 21. The electrode base material 21 is made of nickel such as Inconel (trade name) 600 or 601 or an alloy containing nickel as a main component. The core material 25 is made of copper or an alloy containing copper as a main component, which is superior in thermal conductivity to the electrode base material 21. A center electrode tip 90 is joined to the tip of the center electrode 20. The center electrode tip 90 has a substantially cylindrical shape extending in the axial direction OD, and is formed of a high melting point noble metal such as iridium (Ir) or platinum (Pt) in order to improve the spark wear resistance. . The center electrode 20 is electrically connected to the terminal fitting 40 via the seal body 4 and the ceramic resistor 3. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown), and a high voltage is applied.

  The metal shell 50 is a cylindrical metal fitting formed of a low carbon steel material, and fixes the spark plug 100 to the engine head 200 of the internal combustion engine. A through hole 65 is formed in the metal shell 50 along the axial direction OD, and the metal shell 50 holds the insulator 10 in the through hole 65.

  The metal shell 50 includes a tool engaging portion 51 and a mounting screw portion 52 on the outer peripheral portion. The tool engaging part 51 is a part into which a spark plug wrench (not shown) is fitted. The mounting screw portion 52 of the metal shell 50 is a portion where a screw thread is formed, and is screwed into a mounting screw hole 201 of the engine head 200 provided in the upper part of the internal combustion engine. In this embodiment, the nominal diameter of the mounting screw portion 52 is M12.

  Between the tool engaging portion 51 and the mounting screw portion 52 of the metal shell 50, a bowl-shaped seal portion 54 is formed. An annular gasket 5 formed by bending a plate is fitted into a screw neck 59 between the attachment screw portion 52 and the seal portion 54. When the spark plug 100 is attached to the engine head 200, the gasket 5 is crushed and deformed between the seat surface 55 of the seal portion 54 and the opening peripheral edge portion 205 of the attachment screw hole 201. Due to the deformation of the gasket 5, the gap between the spark plug 100 and the engine head 200 is sealed, and airtight leakage in the engine through the mounting screw hole 201 is prevented.

  A thin caulking portion 53 is provided on the rear end side of the metal shell 50 from the tool engaging portion 51. In addition, a thin buckled portion 58 is provided between the seal portion 54 and the tool engaging portion 51, similarly to the caulking portion 53. Between the inner peripheral surface of the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the outer peripheral surface of the base end side body portion 18 of the insulator 10, annular ring members 6 and 7 are interposed. Has been. Further, a powder of talc (talc) 9 is filled between the ring members 6 and 7. When the crimping portion 53 is bent inwardly, the insulator 10 is pressed toward the front end side in the metal shell 50 via the ring members 6 and 7 and the talc 9. Thus, the reduced diameter portion 15 of the insulator 10 is supported by the step portion 56 formed on the inner periphery of the metal shell 50, and the metal shell 50 and the insulator 10 are integrated. At this time, the airtightness between the metal shell 50 and the insulator 10 is maintained by the annular plate packing 8 interposed between the reduced diameter portion 15 of the insulator 10 and the step portion 56 of the metal shell 50, Outflow of combustion gas is prevented. The plate packing 8 is formed of a material having high thermal conductivity such as copper or aluminum. When the thermal conductivity of the plate packing 8 is high, the heat of the insulator 10 is efficiently transmitted to the step portion 56 of the metal shell 50, so that the heat extraction of the spark plug 100 is improved and the heat resistance can be improved. A detailed configuration in the vicinity of the plate packing 8 will be described later. A clearance CL having a predetermined dimension is provided between the front end side of the stepped portion 56 of the metal shell 50 and the insulator 10.

  The ground electrode 30 is made of a metal having high corrosion resistance, and is made of, for example, a nickel alloy such as Inconel (trade name) 600 or 601. The base 32 of the ground electrode 30 is joined to the tip 57 of the metal shell 50 by welding. The ground electrode 30 is bent, and a ground electrode tip 95 is bonded to the tip 33 of the ground electrode 30. The ground electrode chip 95 faces the center electrode chip 90, and a spark discharge gap G is formed between the ground electrode chip 95 and the center electrode chip 90. The ground electrode tip 95 can be formed of the same material as the center electrode tip 90.

A2. Detailed configuration near the plate packing 8:
FIG. 2 is an explanatory view showing a detailed configuration in the vicinity of the plate packing 8. As shown in FIG. 2, the step portion 56 of the metal shell 50 includes a reduced diameter portion 62, a first constant diameter portion 63, an enlarged diameter portion 64, and a protruding portion 70.

  The reduced diameter portion 62 is located on the most proximal side in the step portion 56, is in contact with the second constant diameter portion 61 at the proximal end, and is in contact with the protrusion 70 at the distal end. The inner diameter of the reduced diameter portion 62 becomes smaller toward the tip side along the axial direction OD. An inner peripheral surface S51 of the reduced diameter portion 62 is in contact with the plate packing 8. Further, the inner peripheral surface S51 of the reduced diameter portion 62 faces the outer peripheral surface S11 of the reduced diameter portion 15 of the insulator 10 via the plate packing 8. The above-mentioned second constant diameter portion 61 is a portion having a substantially constant inner diameter at any position along the axial direction OD.

  The first constant diameter portion 63 is located at the approximate center along the axial direction OD in the step portion 56, contacts the protruding portion 70 at the proximal end, and contacts the expanded diameter portion 64 at the distal end. The inner diameter of the first constant diameter portion 63 is constant at any position along the axial direction OD. The inner peripheral surface S52 of the first constant diameter portion 63 faces the outer peripheral surface 14 of the insulator 10 (leg long portion 13).

  The enlarged diameter portion 64 is located on the most distal end side in the stepped portion 56, and contacts the first constant diameter portion 63 at the proximal end side. The inner diameter of the enlarged diameter portion 64 becomes larger toward the tip side along the axial direction OD. The clearance CL described above is formed between the inner peripheral surface of the enlarged diameter portion 64 and the outer peripheral surface 14 of the insulator 10 (leg long portion 13).

  The protruding portion 70 is in contact with the end portion on the distal end side of the reduced diameter portion 62 and protrudes from the reduced diameter portion 62 of the metal shell 50 in the direction toward the reduced diameter portion 15 of the insulator 10. As shown in FIG. 2, the inner peripheral surface 71 of the protruding portion 70 is a convex curved surface that is convex in the inner diameter direction, and is continuous with the inner peripheral surface S <b> 52 of the first constant diameter portion 63. The inner peripheral surface 71 of the protrusion 70 means a surface exposed in the direction toward the axis OL. In other words, the inner peripheral surface 71 of the protruding portion 70 is a surface from the top in the direction from the reduced diameter portion 62 to the reduced diameter portion 15 to the end portion on the distal end side in contact with the first constant diameter portion 63 in the protruding portion 70. Means. The outer peripheral surface 72 of the protruding portion 70 is a flat surface that is substantially perpendicular to the inner peripheral surface S51 of the reduced diameter portion 62, and is in contact with the end surface on the front end side of the plate packing 8. In addition, the outer peripheral surface 72 of the protrusion part 70 is a surface exposed in the direction away from the axis line OL in the protrusion part 70.

  As shown in FIG. 2, the plate packing 8 is disposed in a space surrounded by the inner peripheral surface S <b> 51 of the reduced diameter portion 62 and the outer peripheral surface S <b> 11 of the reduced diameter portion 15. Further, the end face (inner diameter side) end face of the plate packing 8 is in contact with the outer peripheral face 72 of the protrusion 70. In the manufacturing process of the spark plug 100, when the crimping portion 53 is crimped, the plate packing 8 is crushed by the inner peripheral surface S51 and the outer peripheral surface S11 and tends to extend. However, since the protruding portion 70 is disposed on the front end side of the plate packing 8, the extension of the plate packing 8 to the front end side is suppressed. More specifically, when the plate packing 8 is to be extended, the end surface (inner diameter side) of the plate packing 8 abuts against the outer peripheral surface 72 of the projecting portion 70, so that the front end side (inner diameter side) of the plate packing 8. ) Is suppressed. For this reason, it is suppressed that the plate packing 8 protrudes more to the front end side (inner diameter side) than the protrusion part 70 in the space | gap between the metal shell 50 (step part 56) and the insulator 10 (reduced diameter part 15). It is done. Therefore, the withstand voltage performance can be improved by suppressing an increase in electric field strength. Moreover, since the inner peripheral surface 71 of the protrusion part 70 is a curved surface which is continuously in contact with the inner peripheral surface S52 of the first constant diameter part 63 and there is no edge portion, an increase in electric field strength due to the protrusion part 70 is also suppressed. it can.

Here, in the present embodiment, the length of the protruding portion 70 in the direction along the inner peripheral surface S51 of the reduced diameter portion 62 is Tw, and the length of the protruding portion 70 in the direction perpendicular to the inner peripheral surface S51 is Th. When the distance between the reduced diameter portion 62 and the reduced diameter portion 15 in the direction perpendicular to the inner peripheral surface S51 is Ph, the condition shown in the following formula 1 (hereinafter referred to as “first condition”) is satisfied. It is preferable.
Tw ≧ Th and Th ≧ (1/2) × Ph (1)

  When the length Tw is equal to or longer than the length Th, the shape becomes a horizontally long shape along the inner circumferential surface S51 of the reduced diameter portion 62. Therefore, when force is applied to the protruding portion 70 during caulking, When the residual stress is received, the deformation of the protrusion 70 is suppressed. In addition, since the length Th is ½ or more of the distance Ph, the gap between the projecting portion 70 and the insulator 10 (the reduced diameter portion 15) is narrowed, and the front end side of the plate packing 8 ( Many regions of the end surface on the inner diameter side can be supported by the outer peripheral surface 72. For this reason, it can suppress that the plate packing 8 gets over the protrusion part 70, and protrudes to the front end side (axis line OL side).

In the present embodiment, the line of intersection between the surface virtually extending the inner peripheral surface S51 of the reduced diameter portion 62 and the inner peripheral surface S52 of the first constant diameter portion 63 is defined as an intersection line A. A line of intersection between the inner peripheral surface S51 of the reduced diameter portion 62 and the inner peripheral surface of the second constant diameter portion 61 is defined as an intersection line B, and an intersection line between the inner peripheral surface S51 of the reduced diameter portion 62 and the protruding portion 70 is defined. When the intersection line C, the shortest distance between the intersection line A and the intersection line B is L1, and the shortest distance between the intersection line B and the intersection line C is L2, the condition shown in the following formula 2 is satisfied. (Hereinafter referred to as “second condition”) is preferably satisfied.
L2 ≧ (1/2) × L1 (2)

  When the distance L2 is equal to or greater than ½ of the distance L1, the volume of the plate packing 8 interposed between the metal shell 50 and the insulator 10 can be increased as compared with the configuration of less than ½. For this reason, the contact area between the plate packing 8 and the metal shell 50 and the contact area between the plate packing 8 and the insulator 10 can be increased, and the sealing performance can be improved.

  Moreover, in this embodiment, the length D along the radial direction (direction perpendicular to the axial direction OD) between the distal end side end portion of the protrusion 70 and the outer peripheral surface 14 of the insulator 10 is 0.5 mm or less. Is preferably satisfied (hereinafter referred to as “third condition”). By satisfying the third condition, the radial length of the spark plug 100 can be reduced. For this reason, withstanding the miniaturization of the spark plug 100, it is possible to suppress the protrusion of the plate packing 8 toward the tip side and improve the voltage resistance. In addition, as a minimum of length D, it can be set to 0.1 mm, for example.

  Moreover, in this embodiment, although the nominal diameter of the attachment screw part 52 of the spark plug 100 was M12, it is preferable that it is M12 or less. A spark plug having a nominal diameter of M12 or less is a relatively small spark plug, the thickness of the insulator 10 is small, and the possibility of dielectric breakdown is relatively high. However, like the spark plug 100 of the first embodiment described above, by providing the protruding portion 70, it is possible to suppress the protrusion of the plate packing 8 toward the distal end side (inner diameter side) and improve the withstand voltage performance.

  In the first embodiment described above, the insulator 10 corresponds to an insulator in claims. The through hole 12 is the first through hole in the claims, the reduced diameter portion 15 is the insulator-side reduced diameter portion in the claims, the through hole 65 is the through hole in the claims, and the reduced diameter portion 62 is in the claims. In the metal shell side reduced diameter portion, the plate packing 8 corresponds to the seal member in the claims, and the mounting screw portion 52 corresponds to the screw portion in the claims.

B. Second embodiment:
FIG. 3 is an explanatory view showing a detailed configuration in the vicinity of the plate packing 8 in the spark plug of the second embodiment. The spark plug according to the second embodiment is different from the spark plug 100 according to the first embodiment in that a protrusion 70 a is provided instead of the protrusion 70. Since the other structure in the spark plug of 2nd Embodiment is the same as the spark plug 100 of 1st Embodiment, it attaches | subjects the same code | symbol and abbreviate | omits detailed description.

  As shown in FIG. 3, the protrusion 70a of the spark plug of the second embodiment is the protrusion of the first embodiment in that the outer peripheral shape is a stepped shape in which two planes are connected. Unlike 70, the other structure is the same as the protrusion part 70 of 1st Embodiment. Specifically, the inner peripheral surface of the protruding portion 70a is constituted by a first surface 73 and a second surface 74 that are in contact with each other. The first surface 73 is a flat surface that is in contact with the proximal end portion of the inner peripheral surface S52 of the first constant diameter portion 63 and is continuous with the inner peripheral surface S52 at the end portion on the distal end side. In addition, the proximal end of the first surface 73 is in contact with the second surface 74. The second surface 74 is a flat surface in contact with the outer peripheral surface 72 at the proximal end portion and in contact with the first surface 73 at the distal end portion. The second surface 74 is a plane parallel to the inner peripheral surface S51 of the reduced diameter portion 62.

  Also in the spark plug according to the second embodiment having the above-described configuration, since the protruding portion 70a is provided in contact with the end portion on the tip end side of the reduced diameter portion 62, the plate packing 8 is extended to the tip end side (inner diameter side). Is suppressed. For this reason, it is suppressed that the plate packing 8 protrudes more to the front end side (inner diameter side) than the protrusion part 70a in the space | gap between the metal shell 50 (step part 56) and the insulator 10 (reduced diameter part 15). It is done. For this reason, the spark plug of 2nd Embodiment has an effect similar to the spark plug 100 of 1st Embodiment.

C. Test example of withstand voltage according to the presence or absence of protrusions:
FIG. 4 is an explanatory diagram showing test results of a withstand voltage evaluation test according to the presence or absence of protrusions. In this test, the sample of the spark plug 100 of the first embodiment (hereinafter referred to as “first sample group”) and the sample of the spark plug of the second embodiment (hereinafter referred to as “second sample group”). ) And 10 spark plug samples (hereinafter referred to as “third sample group”) each having no protrusion 70 and no protrusion 70a. And withstand voltage performance evaluation test was done about each sample.

The withstand voltage performance evaluation test was performed in the order of the following procedure 1 to procedure 3.
(Procedure 1) The ground electrode 30 of each sample is removed, and each sample is disposed so that the mounting screw portion 52 is accommodated in a silicon tube, and then the center electrode tip 90 of the center electrode 20 is electrically insulating liquid. The inside of the tube is filled with an electrically insulating liquid so as to be located inside. As the electrically insulating liquid, for example, insulating oil or a fluorine-based inert liquid can be used.
(Procedure 2) The metal shell 50 of each sample is connected to the ground (GND), and the potential of the spark plug is set to 0 (zero).
(Procedure 3) The voltage applied to the sample is increased at a predetermined speed (for example, 0.1 kV / 3 sec), and the limit voltage (withstand voltage) at which the leg portion 13 of the insulator 10 breaks down is measured. To do.

  FIG. 4 shows the average withstand voltage (kV) of 10 samples for each sample group. As shown in FIG. 4, the first sample group (first embodiment) has the highest withstand voltage, the second sample group (second embodiment) has the second highest withstand voltage, and the third sample group has the withstand voltage. Was the lowest. From this result, it can be understood that the withstand voltage is improved by providing the protrusions 70 and 70a as compared to the configuration without the protrusions 70 and 70a. Further, the inner peripheral surface of the protrusion (the surface exposed in the direction toward the axis OL, in other words, the surface facing the insulator 10) is a curved surface that is convex in the inner diameter direction. It can be understood that the withstand voltage is high. This is presumed to be because an increase in the electric field strength due to the protrusion is suppressed because there is no edge because the inner peripheral surface of the protrusion is a curved surface.

D. Test example of withstand voltage according to whether the first condition is satisfied:
FIG. 5 is an explanatory diagram showing a first test result of a withstand voltage evaluation test according to whether or not the first condition (Tw ≧ Th and Th ≧ (1/2) × Ph) is satisfied. . FIG. 6 is an explanatory diagram illustrating a second test result of the withstand voltage evaluation test according to whether or not the first condition described above is satisfied. In this test, in the spark plug 100 of the first embodiment, the length Th of the protrusion 70 (the length Th in the direction perpendicular to the inner peripheral surface S51) and the length Tw of the protrusion 70 (on the inner peripheral surface S51). Samples having different lengths (Tw) in the direction along the sample and samples having no protrusion 70 were manufactured, and a withstand voltage performance evaluation test was performed on each sample.

  Specifically, as shown in FIG. 5, 10 samples each having a length Th of 0.05 mm and a length Tw of 0.05 mm, 0.10 mm, 0.15 mm, and 0.20 mm are provided. Made one by one. In addition, 10 samples each having a length Th of 0.10 mm and a length Tw of 0.05 mm, 0.10 mm, 0.15 mm, and 0.20 mm were manufactured. In addition, 10 samples each having a length Th of 0.15 mm and a length Tw of 0.05 mm, 0.10 mm, 0.15 mm, and 0.20 mm were manufactured. In addition, ten samples having no protrusions 70 were manufactured. In each sample described above (the sample from which the test result shown in FIG. 5 was obtained), the distance Ph (the distance between the reduced diameter portion 62 and the reduced diameter portion 15 in the direction perpendicular to the inner peripheral surface S51) is: It was 0.20 mm. Since the specific procedure of the withstand voltage performance evaluation test is the same as (Procedure 1) to (Procedure 3) described above, the description thereof is omitted.

  FIG. 5 shows the average withstand voltage (kV) of 10 samples with the same length Th and Tw. As shown in FIG. 5, the withstand voltage (35 kV) of the sample without the protrusion 70 was lower than that of the other samples. In addition, the withstand voltage (36V) of the sample having a length Th of 0.05 mm was higher than that of the sample without the protrusion 70, but was lower than that of the other samples. As described above, when the length Th is less than ½ of the distance Ph, the plate packing 8 protrudes from between the protruding portion 70 and the outer peripheral surface S11 of the reduced diameter portion 15, and the electric field strength is increased and the voltage resistance is improved. Presumed to be lower. In other words, when the length Th is ½ or more of the distance Ph, the plate packing 8 is suppressed from protruding between the protruding portion 70 and the outer peripheral surface S11 of the reduced diameter portion 15, and the voltage resistance is improved. Presumed to be.

  Regarding the sample with the length Th of 0.10 mm, the withstand voltage of the sample with the length Tw of 0.05 mm was 37 kV, but the withstand voltage of the sample with the length Tw of 0.10 mm or more is all It was a relatively high value of 38 kV. When the length Tw is equal to or longer than the length Th, when the force is applied to the projecting portion 70 during caulking, or when a residual stress is subsequently applied, deformation of the projecting portion 70 (the tip side and the insulation) Since the deformation in the direction toward the insulator 10 is suppressed, it is presumed that the voltage resistance is relatively high.

  For samples with a length Th of 0.15 mm, the withstand voltage of the samples with the length Tw of 0.05 mm and 0.10 mm was 37 kV, but the withstand voltage of the samples with the length Tw of 0.15 mm or more All were relatively high values of 38 kV. As described above, the reason why the withstand voltage is relatively high when the length Tw is 0.15 mm or more is that the withstand voltage is obtained when the length Tw is 0.10 mm or more in the above-described sample having the length Th of 0.10 mm. Is presumed to be the same as the reason for the high.

  In the test example of FIG. 6, ten samples each having a length Th of 0.10 mm and a length Tw of 0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm were manufactured. In addition, 10 samples each having a length Th of 0.15 mm and a length Tw of 0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm were manufactured. Further, ten samples each having a length Th of 0.20 mm and a length Tw of 0.10 mm, 0.15 mm, 0.20 mm, and 0.25 mm were manufactured. In each sample described above (the sample from which the test result shown in FIG. 6 was obtained), the distance Ph (the distance between the reduced diameter portion 62 and the reduced diameter portion 15 in the direction perpendicular to the inner peripheral surface S51) is as shown in FIG. Unlike the example, it was 0.30 mm. Since the specific procedure of the withstand voltage performance evaluation test is the same as (Procedure 1) to (Procedure 3) described above, the description thereof is omitted.

  FIG. 6 shows the average withstand voltage (kV) of 10 samples under the same conditions for the lengths Th and Tw, as in FIG. In the test example of FIG. 6, the same tendency as the test example of FIG. 5 was obtained. That is, the withstand voltage of the sample whose length Th is 1/2 or more of the distance Ph is higher than the withstand voltage of a sample whose length Th is smaller than 1/2 of the distance Ph. Moreover, the voltage resistance of the sample whose length Tw is equal to or longer than the length Th was higher than the voltage resistance of the sample whose length Tw was lower than the length Th. From the above test results, the withstand voltage of the spark plug was improved by satisfying the first condition (Tw ≧ Th and Th ≧ (1/2) × Ph).

E. Test example of airtightness depending on whether the second condition is satisfied:
FIG. 7 is an explanatory diagram showing a first test result of an airtightness evaluation test according to whether or not the second condition (L2 ≧ (1/2) × L1) is satisfied. In this test, in the spark plug 100 of the first embodiment, the distance L1 (the shortest distance between the intersection line A and the intersection line B) is equal, and the distance L2 (the shortest distance between the intersection line B and the intersection line C). ) Were produced from different samples, and a confidential performance evaluation test was conducted on each sample.

  Specifically, five samples with a distance L2 of 0.15 mm were manufactured. Similarly, five samples each having a distance L2 of 0.20 mm, a sample having a distance L2 of 0.25 mm, and a sample having a distance L2 of 0.30 mm were manufactured. In any sample, the distance L1 was 0.50 mm.

  As an airtightness evaluation test, a test based on a JIS (Japanese Industrial Standard) test method (JIS B8031 7.5) was performed. The torque when tightening the spark plug 100 was 15 N · m, which is the lower limit value of the nominal diameter M12. Then, after maintaining the spark plug 100 in an atmosphere of 150 ° C. for 30 minutes, an air pressure of 1.5 MPa was applied in that state, and the amount of air leakage from the inside of the spark plug 100 was measured. “Leakage amount” in FIG. 7 represents an average value of air leakage amounts (cc / min) of five samples having the same distance L2. Then, “OK” was determined when the leakage amount was 10 cc / min or less, and “NG” was determined when the leakage amount was greater than 10 cc / min.

  As shown in FIG. 7, the determination for the samples having the distance L2 of 0.15 mm and 0.20 mm was NG. On the other hand, the determination about the sample whose distance L2 is 0.25 mm and 0.30 mm was OK. Since the distance L1 is 0.50 mm, in other words, the test result is NG when the distance L2 is smaller than 1/2 of the distance L1, and the determination is OK when the distance L1 is 1/2 or more of the distance L1. Met.

  In the sample whose distance L2 is 1/2 or more of the distance L1, the inner peripheral surface S51 of the metal shell 50 and the outer peripheral surface S11 of the insulator 10 are compared with the sample whose distance L2 is smaller than 1/2 of the distance L1. The volume of the plate packing 8 interposed therebetween can be increased. In other words, the contact area between the inner peripheral surface S51 of the metal shell 50 and the plate packing 8 and the contact area between the outer peripheral surface S11 of the insulator 10 and the plate packing 8 can be further increased. For this reason, it is estimated that the sealing performance between the inner peripheral surface S51 of the metal shell 50 and the outer peripheral surface S11 of the insulator 10 can be improved, and a better airtightness evaluation test result was obtained.

F. Test example of withstand voltage according to whether the third condition is satisfied:
FIG. 8 is an explanatory diagram showing test results of a withstand voltage improvement evaluation test according to whether or not the third condition (length D ≦ 0.5 mm) is satisfied. In this test, first, in the spark plug 100 of the first embodiment, the length D (the length along the radial direction between the distal end side end of the protruding portion 70 and the outer peripheral surface 14 of the insulator 10) is set. Three different samples were produced. Specifically, 10 samples with a length D of 0.3 mm, 10 samples with a length D of 0.5 mm, and 10 samples with a length D of 0.7 mm were manufactured. And the withstand voltage was measured about each sample. Since the withstand voltage measurement method at this time is the same as the procedure of the withstand voltage performance evaluation test described above, the description thereof is omitted. Then, the withstand voltage is measured in the same manner for the spark plug without the projecting portion 70, and the withstand voltage value obtained for the spark plug without the projecting portion 70 is subtracted from the withstand voltage value obtained for each sample. Thus, the withstand voltage improvement value for each sample was obtained. In FIG. 8, the horizontal axis represents the length D, and the vertical axis represents the withstand voltage improvement value (kV). In addition, the withstand voltage improvement value of FIG. 8 represents the average value of the withstand voltage improvement values of five samples having the same length D.

  As shown in FIG. 8, the withstand voltage improvement value of the sample having the length D of 0.3 mm is the highest, the withstand voltage of the sample having the length D of 0.5 mm is the second highest, and the length D is 0. The withstand voltage of the sample that was .7 mm was the lowest. This is because the smaller the length D, the greater the deterioration of the withstand voltage due to the protrusion of the plate packing 8 toward the tip side (inner diameter side). In other words, the smaller the length D, the greater the effect of improving the withstand voltage by the protrusion 70.

G. Variations:
The configuration of the spark plug of the present invention is not limited to the configuration of the spark plug 100 in each embodiment, and can be changed as appropriate. For example, the plate packing 8 has an annular outer shape, but instead, it may have an annular outer shape partially missing along the circumferential direction. Further, for example, a plurality of plate packings having an arcuate appearance may be used instead of the plate packing 8.

  Further, the spark plug 100 of each embodiment may be replaced with a lateral discharge type spark plug.

  The present invention is not limited to the above-described embodiments, test examples, and modifications, and can be realized with various configurations without departing from the spirit of the present invention. For example, the technical features in the present embodiment and the modified examples corresponding to the technical features in the embodiments described in the column of the summary of the invention are to solve part or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be appropriately performed. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 3 ... Ceramic resistance 4 ... Sealing body 5 ... Gasket 6 ... Ring member 8 ... Plate packing 9 ... Talc 10 ... Insulator 12 ... Through-hole 13 ... Leg long part 14 ... Outer peripheral surface 15 ... Reduced diameter part 17 ... Tip side trunk | drum 18 ... Base end side body part 19 ... Gutter part 20 ... Center electrode 21 ... Electrode base material 25 ... Core material 30 ... Ground electrode 32 ... Base part 33 ... Tip part 40 ... Terminal metal fitting 50 ... Main metal fitting 51 ... Tool engagement part 52 ... Mounting screw portion 53 ... Clamping portion 54 ... Sealing portion 55 ... Seat surface 56 ... Step portion 57 ... Tip portion 58 ... Buckling portion 59 ... Neck 61 ... Second constant diameter portion 62 ... Reduced diameter portion 63 ... First constant diameter Part 64 ... Diameter-enlarged part 65 ... Through hole 70, 70a ... Projection part 71 ... Inner peripheral surface 72 ... Outer peripheral surface 73 ... First surface 74 ... Second surface 90 ... Central electrode tip 95 ... Ground electrode tip 100 ... Spark plug 200 ... Engine head 201 ... Hole 20 5 ... Opening peripheral edge G ... Spark discharge gap A, B, C ... Intersection line L1 ... Distance L2 ... Distance OD ... Axial direction OL ... Axis line CL ... Clearance Ph ... Distance S11 ... Outer peripheral surface M12 ... Diameter S51 ... Inner peripheral surface S52 ... Inner peripheral surface Th ... Length Tw ... Length

Claims (5)

A rod-shaped center electrode extending in the axial direction;
A first through hole is formed along the axial direction, the center electrode is held in the first through hole, and an insulator-side reduced diameter portion whose outer diameter decreases toward the distal end side along the axial direction. An insulator having,
A second through hole is formed along the axial direction, the insulator is held in the second through hole, and a metal fitting side reduced diameter portion having a smaller inner diameter toward the distal end side along the axial direction. Having a metal shell,
A seal member disposed between the insulator-side reduced diameter portion and the metal shell-side reduced diameter portion;
A spark plug comprising:
The metal shell further includes:
The metal shell-side contact with the distal end of the reduced diameter portion, have a protrusion from the metal shell side reduced-diameter portion projecting in a direction towards the insulator side reduced diameter portion,
The length of the protrusion in the direction along the surface of the metal shell side reduced diameter portion is Tw, and the height of the protrusion in the direction perpendicular to the surface of the metal shell side reduced diameter portion is Th. When the distance between the metal shell side reduced diameter part and the insulator side reduced diameter part in the direction perpendicular to the surface of the metal part reduced diameter part is Ph,
Tw ≧ Th and Th ≧ (1/2) × Ph
A spark plug characterized by satisfying the following conditions . The spark plug according to claim 1, wherein
The metal shell has a first constant diameter portion that is in contact with the end portion on the distal end side of the protruding portion and has a constant inner diameter at any position along the axial direction.
In the protruding portion, an inner peripheral surface from a top in a direction from the metal shell side reduced diameter portion toward the insulator side reduced diameter portion to an end portion on the distal end side in contact with the first constant diameter portion is a convex shape. A spark plug characterized by a curved surface. A rod-shaped center electrode extending in the axial direction;
A first through hole is formed along the axial direction, the center electrode is held in the first through hole, and an insulator-side reduced diameter portion whose outer diameter decreases toward the distal end side along the axial direction. An insulator having,
A second through hole is formed along the axial direction, the insulator is held in the second through hole, and a metal fitting side reduced diameter portion having a smaller inner diameter toward the distal end side along the axial direction. Having a metal shell,
A seal member disposed between the insulator-side reduced diameter portion and the metal shell-side reduced diameter portion;
A spark plug comprising:
The metal shell further includes:
A protruding portion that is in contact with the end portion on the distal end side of the metal shell-side reduced diameter portion and protrudes in a direction from the metal shell-side reduced diameter portion toward the insulator-side reduced diameter portion;
The metallic shell is
A first constant diameter portion that is in contact with the end portion on the distal end side of the protruding portion and has a constant inner diameter at any position along the axial direction;
A second constant diameter portion that is in contact with an end portion on the base end side of the metal shell-side reduced diameter portion and has a constant inner diameter at any position along the axial direction;
Have
A first intersection line where a surface virtually extending the inner peripheral surface of the metal shell-side reduced diameter portion toward the distal end side and an inner peripheral surface of the first constant-diameter portion, and an inside of the metal shell-side reduced diameter portion The shortest distance between the peripheral surface and the second intersecting line where the inner peripheral surface of the second constant diameter portion intersects is L1, and the inner peripheral surface of the metal shell-side reduced diameter portion and the protruding portion intersect with each other. When the shortest distance between the intersection line and the second intersection line is L2,
L2 ≧ (1/2) × L1
A spark plug characterized by satisfying the following conditions. In the spark plug according to any one of claims 1 to 3 ,
A spark plug characterized in that a distance along a radial direction between a tip side end portion of the protruding portion and the insulator is 0.5 mm or less. The spark plug according to any one of claims 1 to 4 , wherein
A spark plug, wherein a threaded portion having a nominal diameter of M12 or less is formed on an outer peripheral portion of the metal shell.

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