WO2011118087A1

WO2011118087A1 - Spark plug

Info

Publication number: WO2011118087A1
Application number: PCT/JP2010/071433
Authority: WO
Inventors: かおり岸本; 裕之亀田
Original assignee: 日本特殊陶業株式会社
Priority date: 2010-03-25
Filing date: 2010-12-01
Publication date: 2011-09-29
Also published as: JPWO2011118087A1; JP5271420B2

Abstract

The disclosed sparkplug (1) is provided with a central electrode (5) extending in the direction of an axis line (CL1), an insulator (2) and a main metal fitting (3). The main metal fitting (3) has an annular protrusion (21); the insulator (2) is provided with a step portion (14) which engages with an annular protrusion (13), and a long leg portion (13) extending from the end of the step portion (14). Defining that in the tip position of the main metal fitting (3), the inner diameter of the main metal fitting (3) is A (mm) and the outer diameter of the insulator (2) is B (mm), that 4mm from the tip of the main metal fitting (3) along the axis line (CL1) towards the rear, the inner diameter of the main metal fitting (3) is C (mm) and the outer diameter of the insulator is D (mm), and that more than 4mm along the axis line (CL1) from the end of the main metal fitting (3) on the rear side, the outer diameter of the long leg portion (13) is Y, the following expressions are satisfied: 0.472 ? B / A ? 0.570, 0.472 ? D / C ? 0.660, B < Y, and A ? 8.7. By this means, the sparkplug achieves excellent resistance to pre-ignition.

Description

Spark plug

The present invention relates to a spark plug used for an internal combustion engine or the like.

A spark plug is attached to a combustion device such as an internal combustion engine (engine) and used to ignite a mixture in a combustion chamber. In general, a spark plug is provided at an insulator having an axial hole, a center electrode inserted into the axial hole, a metal shell provided on the outer periphery of the insulator, and a tip end of the metal shell. And a ground electrode that forms a spark discharge gap therebetween. Also, in general, the metal shell and the insulator are directly or indirectly engaged with the annular projection projecting toward the axial line on the inner peripheral surface of the metal shell and the stepped portion provided on the outer peripheral surface of the insulator. It fixes in the state which was carried out (for example, refer patent document 1 grade | etc.,).

By the way, if the tip temperature of the insulator is overheated to a predetermined temperature (for example, 1100 ° C.) or more, the tip of the overheated insulator may become an ignition source. That is, there is a possibility that a phenomenon (so-called pre-ignition) of igniting to air-fuel mixture may occur even though the spark plug is before ignition.

Therefore, in order to improve the pre-ignition resistance, the heat at the tip of the insulator can be conducted smoothly to the center electrode by reducing the difference in diameter between the outer diameter of the center electrode and the inner diameter of the insulator. Thus, a method has been proposed to prevent the overheating of the insulator tip and the occurrence of preignition resulting from this.

JP 2008-123989 A

However, when the above method is adopted, there is a possibility that the insulator is pushed and split with the thermal expansion of the center electrode. If the insulator is broken, current leakage may occur between the center electrode and the metal shell, which may make it impossible to perform normal spark discharge.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a spark plug which can realize excellent pre-ignition resistance without changing the difference in diameter between the center electrode and the insulator. It is to do.

Hereinafter, each configuration suitable for solving the above object will be described in terms of terms. In addition, the operation effect peculiar to a corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration comprises: a rod-like center electrode extending in an axial direction;
An insulator provided on an outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A spark plug including a ground electrode extending from a front end portion of the metal shell;
The metal shell has an annular projection projecting toward the axis on the inner peripheral portion of the metal shell,
The insulator is
A step which is directly or indirectly locked to the annular projection;
And a long leg extending from the tip of the step toward the tip,
The inner diameter of the metal shell at the end position of the metal shell is A (mm), and the outer diameter of the insulator is B (mm),
The inner diameter of the metal shell is C (mm) and the outer diameter of the insulator is D (mm) at a position 4 mm from the front end of the metal shell along the axis.
Assuming that the outer diameter of the long leg portion is Y (mm) at a position on the rear end side exceeding 4 mm from the front end of the metal shell along the axis, the following formulas (1) to (4) are satisfied. It is characterized by

0.472 ≦ B / A ≦ 0.570 (1)
0.472 ≦ D / C ≦ 0.660 (2)
B <Y (3)
A ≦ 8.7 (4)
When the front end surface of the metal shell and the inner peripheral surface are formed in a tapered shape or a curved surface, the “inner diameter A of the metal shell” means the inner peripheral surface of the metal shell as the axial direction front end It means the inside diameter of the circle formed by the virtual surface extended to the side and the virtual surface extended to the axial line side of the end surface of the metal shell.

According to the above configuration 1, the inner diameter A of the metal shell at the tip position of the metal shell and the outer diameter B (mm) of the insulator satisfy B / A ≦ 0.570, and the metal shell along the axis line CL1 With respect to the inner diameter C of the metal shell and the outer diameter D (mm) of the insulator at a position 4 mm from the front end of the rear end, D / C ≦ 0.660 is satisfied. That is, the heat at the tip of the insulator is drawn to the metal shell side from the step portion of the insulator and the like via the annular projection and the like. According to the above configuration 1, the insulator tip particularly easily heated (insulator Among the above, the amount of heat received from the front end to a position 4 mm from the front end according to the size of the inner diameter of the metal shell (that is, the ability to draw the heat of the insulator by the metal shell) It can be suppressed to a minute.

Further, in view of the fact that the heat at the front end of the insulator is conducted to the metal shell side through the leg length portion, according to the above configuration 1, the rear end side exceeds 4 mm from the front end of the metal shell along the axis. The outer diameter Y of the leg length portion at the position of (1) is configured to satisfy B <Y. That is, a portion of the leg length portion that corresponds to the heat drawing path of the insulator tip portion is configured to have a sufficiently large cross-sectional area. Therefore, the heat of the insulator tip can be effectively conducted to the metal shell side.

Furthermore, while the inner diameter A at the end of the metal shell is relatively small so as to satisfy A ≦ 8.7, by satisfying B / A ≦ 0.570, between the metal shell and the insulator. The opening of the space formed in is configured to have a certain size. For this reason, in the combustion cycle, where the high temperature combustion gas and the low temperature fresh air intrude alternately into the space (so-called gas volume), the insulator is heated and cooled in a well-balanced manner by the combustion gas and the new air. It will be done. As a result, overheating of the insulator can be prevented more reliably.

As described above, according to the above-described configuration 1, by satisfying A ≦ 8.7 or the like, B / A ≦ 0.570 and D / C ≦ 0.660 are prevented while preventing overheating of the tip of the insulator. As a result, the amount of heat received by the insulator tip can be reduced to the amount corresponding to the heat transfer performance of the metal shell, and by satisfying B <Y, the heat at the insulator tip can be effectively transferred to the metal shell side. Can be As a result, the pre-ignition resistance can be dramatically improved.

Further, according to the above configuration 1, the preignition resistance is improved by changing the diameter difference between the metal shell and the insulator without changing the diameter difference between the center electrode and the insulator. Can. Therefore, it is possible to more reliably prevent a situation such as cracking of the insulator due to thermal expansion of the center electrode.

In order to realize sufficient withstand voltage performance in the insulator, it is necessary to secure the thickness of the insulator to a certain extent. Therefore, it is desirable to configure the insulator to satisfy 0.472 ≦ B / A and 0.472 ≦ D / C.

Configuration 2. In the spark plug of this configuration, in the above configuration 1, B / A ≦ 0.540
It is characterized by satisfying.

According to the above-mentioned configuration 2, the amount of heat received at the insulator tip can be further suppressed, and the pre-ignition resistance can be further improved.

Configuration 3. In the spark plug of this configuration, in the

above configuration

1 or 2, when a distance from the tip of the metal shell along the axis to the tip of the center electrode is E (mm),
2.0 ≦ E ≦ 5.0
It is characterized by satisfying.

From the viewpoint of improving the ignition performance, it is effective to dispose the tip of the center electrode so as to project toward the tip in the axial direction so that the ignition position is closer to the center of the combustion chamber. However, if the tip of the center electrode is disposed in a protruding manner, the center electrode having the function of drawing the heat of the insulator as in the case of the metal shell will be heated more, and thus the heat of the tip of the insulator will not be drawn easily. I will. Furthermore, since the insulator can also be disposed so as to protrude toward the end in the axial direction along with the protrusion of the center electrode, the insulator tip end is further heated. That is, when the tip of the center electrode is disposed so as to protrude toward the tip end side in the axial direction, there is a possibility that the pre-ignition resistance is lowered.

In this respect, according to Configuration 3, the distance E (mm) from the tip of the metal shell along the axis to the tip of the center electrode is 2.0 ≦ E. Therefore, while the improvement of the ignition performance can be expected, there is a concern about the reduction of the pre-ignition resistance, but the adoption of the configuration 1 and the like makes it possible to more effectively improve the pre-ignition resistance. In other words, the operation and effect of the configuration 1 and the like are particularly effective when the center electrode is disposed to be protruded and there is a concern that the pre-ignition resistance is lowered.

If the center electrode is disposed so as to protrude excessively, the durability of the center electrode is reduced. In addition, since the center electrode is extremely heated, the heat buildup of the insulator via the center electrode is deteriorated, and by adopting the configuration 1 or the like, the preignition resistance can be improved. There is a risk that the effect will be slightly reduced. Therefore, it is preferable to configure the center electrode or the like so as to satisfy E ≦ 5.0 in order to exhibit the effects of the configuration 1 and the like more remarkably while preventing the deterioration in the durability of the center electrode.

Configuration 4. In any one of the above configurations 1 to 3, the spark plug according to the present configuration has a cross section including the axis,
An outline of a portion of the leg length facing the annular projection extends along the axis,
When the shortest distance between the leg long portion and the annular projection along the direction orthogonal to the axis is F (mm),
F ≦ 0.5
It is characterized by satisfying.

According to the above configuration 4, the proximal end portion of the leg length portion and the annular projection sufficiently approach, and the surface area of the proximal end portion of the leg length portion approaching the annular projection is increased. it can. For this reason, heat is conducted more smoothly from the leg length portion to the metal shell, and as a result, the pre-ignition resistance can be further improved.

By the way, for example, in the case where a portion of the leg length facing the annular protrusion is tapered toward the tip end side in the axial direction, the surface area of the portion approaching the annular protrusion of the base end of the leg length If it is going to increase, the boundary part of the step part and leg length part of the insulator or its vicinity part may contact with a metallic shell. When the boundary portion or the like comes in contact with the metal shell, there is a risk that a crack starting from the boundary portion may occur in the insulator.

In this respect, according to the above configuration 4, the portion of the leg length facing the annular projection is formed to extend along the axis, so that the portion of the proximal end of the leg that approaches the annular projection is It is possible to prevent the contact of the boundary portion and the like with the metal shell more reliably while increasing the surface area. That is, by adopting the above-mentioned configuration 4, it is possible to further improve the pre-ignition resistance while preventing damage to the insulator.

Configuration 5. In the spark plug of this configuration, in any one of the above configurations 1 to 4, the metal shell is
A screw for screwing into a mounting hole of the combustion device;
And a seat portion provided on the rear end side of the screw portion and formed larger in diameter than the screw diameter of the screw portion,
The distance between the front end of the metal shell and the seat along the axis is 17.5 mm or more.

According to the above configuration 5, the distance from the end of the metal shell along the axis to the seat portion (so-called screw reach) is 17.5 mm or more, and a sufficient contact area of the metal shell to the combustion device is secured. be able to. Therefore, the heat of the metal shell can be more smoothly transferred to the combustion device side, and thus the heat of the insulator can be more effectively drawn. As a result, the pre-ignition resistance can be further improved.

Configuration 6. In any one of the above configurations 1 to 5, the spark plug according to this configuration is characterized in that a protrusion length of the tip of the center electrode with respect to the tip of the insulator along the axis is 1.8 mm or less.

According to the above configuration 6, since the protrusion length is 1.8 mm or less, it is possible to reduce the amount of heat received by the center electrode, and it is possible to effectively suppress the reduction in the heat transfer performance of the insulator. As a result, the pre-ignition resistance can be further improved.

Configuration 7. In any one of the above configurations 1 to 6, in the spark plug having this configuration, the center electrode bulges radially outward to the rear end side of itself, and the flange portion engaged with the inner circumferential surface of the insulator Have
A difference in diameter between the outer diameter of the center electrode and the inner diameter of the insulator may be 0.06 mm or more on the tip end side in the axial direction with respect to the tip end of the flange portion.

According to the seventh aspect, the difference in diameter between the outer diameter of the center electrode and the inner diameter of the insulator is sufficiently large, 0.06 mm or more. Therefore, even when the center electrode thermally expands, the gap between the center electrode and the insulator can be sufficiently maintained. As a result, damage to the insulator due to the thermal expansion of the center electrode can be prevented more reliably.

It is a partially broken front view which shows the structure of a spark plug. FIG. 4 is a partial enlarged cross-sectional view showing the configuration of the tip end portion of the spark plug. It is a partial expanded sectional view for demonstrating another example of an insulator. It is a partial expanded sectional view for demonstrating another example, such as a center electrode. It is a partial expanded sectional view which shows the diameter difference etc. of the outer diameter of a center electrode, and the internal diameter of an insulator. It is a graph which shows the result of the preignition test in the sample which changed B / A variously. It is a graph which shows the result of the preignition test in the sample which changed B / A variously. It is a graph which shows the result of the preignition test in the sample which changed D / C variously. It is a graph which shows the result of the preignition test in the sample which changed D / C variously. It is a graph which shows the result of the preignition test in the sample which changed the internal diameter A of the front-end | tip of a main metal fitting variously. It is a partial expanded sectional view which shows the structure of a sample provided with a straight part. It is a cross-sectional schematic diagram for demonstrating the test apparatus used by the withstand voltage test. It is a graph which shows the advance angle improvement value with respect to the conventional product sample in the sample which changed the distance E variously. It is a graph which shows an advance angle change value in a sample which changed variously the shortest distance F. It is a graph which shows the temperature of the insulator tip part in the sample which changed protrusion length PL variously. It is a graph which shows the stress which generate | occur | produced in the insulator in the sample which changed diameter difference DS variously. (A), (b) is a partially broken enlarged front view which shows the structure of the spark plug in another embodiment. (A), (b) is a partially broken enlarged front view which shows the structure of the spark plug in another embodiment. (A), (b) is a partially broken enlarged front view which shows the structure of the spark plug in another embodiment. (A), (b) is a partially broken enlarged front view which shows the structure of the metal shell etc. in another embodiment.

Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL1 of the spark plug 1 is referred to as the vertical direction in the drawing, and the lower side is referred to as the front end side of the spark plug 1 and the upper side is referred to as the rear end.

The spark plug 1 is composed of an insulator 2 as a tubular insulator and a tubular metal shell 3 for holding the insulator 2.

As is well known, the insulator 2 is formed by firing alumina or the like, and in the outer shape portion thereof, the rear end side body portion 10 formed on the rear end side and the front end than the rear end side body portion 10 A large diameter portion 11 formed to project radially outward on the side, a middle body portion 12 formed smaller in diameter on the tip side than the large diameter portion 11, and a tip end than the middle body portion 12 And a leg length portion 13 formed smaller in diameter on the side. In addition, of the insulator 2, the large diameter portion 11, the middle body portion 12, and most of the leg length portions 13 are accommodated in the metal shell 3. Further, a step portion 14 is formed at a connecting portion between the middle body portion 12 and the leg length portion 13, and the insulator 2 is engaged with the metal shell 3 at the step portion 14.

Furthermore, an axial hole 4 is formed through the insulator 2 along the axis line CL 1, and the center electrode 5 is inserted and fixed to the tip end side of the axial hole 4. The center electrode 5 is composed of an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Further, the center electrode 5 has a bar-like (cylindrical) shape as a whole, and its tip end face is formed flat, and protrudes from the tip of the insulator 2.

In addition, the center electrode 5 is provided with a noble metal tip 31 made of a noble metal alloy (for example, a platinum alloy, an iridium alloy, etc.) at its tip. Furthermore, the front end portion of the center electrode 5 is formed to have a diameter slightly smaller than that of its own rear end side portion, and an annular space between the front end side of the axial hole 4 and the center electrode 5 Pocket portion 30 is formed. The thermo pocket portion 30 can make the distance from the center electrode 5 to the metal shell 3 along the surface of the insulator 2 and the distance between the center electrode 5 and the tip of the insulator 2 relatively large. For this reason, it is possible to more reliably prevent an abnormal spark discharge, such as a so-called side spark, etc., which crawls the surface of the insulator 2. The center electrode 5 may be configured without the thermo pocket portion 30. Further, the center electrode 5 may be configured without providing the noble metal tip 31.

In addition, as shown in FIG. 2, the center electrode 5 has a collar 5F formed radially outward at the rear end side of itself and substantially the same as extending from the tip of the collar 5F along the axis line CL1 And an outer diameter main body 5M. In the present embodiment, the outer diameter DC of the rearmost end of the main body 5M is relatively small (e.g., 2.6 mm or less).

Returning to FIG. 1, the terminal electrode 6 is inserted and fixed to the rear end side of the shaft hole 4 in a state of projecting from the rear end of the insulator 2.

Furthermore, a cylindrical resistor 7 is disposed between the center electrode 5 of the axial hole 4 and the terminal electrode 6. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 via the conductive glass seal layers 8 and 9 respectively.

In addition, the metal shell 3 is formed of a metal such as low carbon steel in a cylindrical shape, and a screw for attaching the spark plug 1 to a combustion device such as an internal combustion engine or a fuel cell reformer on the outer peripheral surface thereof. A portion (male screw portion) 15 is formed. Further, a seat portion 16 having a diameter larger than that of the screw portion 15 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted in the screw neck 17 of the screw portion 15 rear end. There is. When the spark plug 1 is attached to the combustion device, the seat portion 16 is pressed against the combustion device via the gasket 18. In addition, the rear end side of the metal shell 3 is provided with a tool engagement portion 19 having a hexagonal cross section for engaging a tool such as a wrench when attaching the spark plug 1 to the combustion device, and the rear end portion A caulking portion 20 for holding the insulator 2 is provided in FIG.

In the present embodiment, when the spark plug 1 is attached to the combustion device, in order to secure a sufficient contact area between the combustion device and the spark plug 1, from the end of the metal shell 3 along the direction of the axis CL1. The distance ML to the seat portion 16 is 17.5 mm or more.

Further, on the inner peripheral surface of the metal shell 3, an annular protrusion 21 which protrudes toward the axis line CL1 and which forms an annular shape centering on the axis line CL1 is formed. Then, the insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the step portion 14 of the insulator 2 is engaged with the annular projection 21 of the metal shell 3. The end openings are fixed by radially inward crimping, that is, by forming the crimped portions 20. An annular plate packing 22 is interposed between the step portion 14 of the insulator 2 and the annular projection 21 of the metal shell 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg length 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 does not leak to the outside.

Furthermore, in order to make the sealing by caulking more complete, on the rear end side of the metal shell 3,

ring members

23 and 24 are interposed between the metal shell 3 and the insulator 2, and the

ring member

23 , 24 are filled with a powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the

ring members

23 and 24, and the talc 25.

Further, at the front end portion 26 of the metal shell 3, a ground electrode 27 whose end face is bent to the front end portion of the center electrode 5 is joined. A spark discharge gap 33 is formed between the noble metal tip 31 bonded to the center electrode 5 and the tip of the ground electrode 27. In the spark discharge gap 33, the spark discharge gap 33 is exposed to air substantially along the axis CL1. Spark discharge is to be performed.

In addition, as shown in FIG. 2, when the inside diameter of the metal shell 3 at the end position of the metal shell 3 along the direction of the axis line CL1 is A (mm), 8.0 ≦ A ≦ 8.7 There is.

Furthermore, the outer diameter of the insulator 2 (leg length 13) at the tip end position of the metal shell 3 along the direction of the axis CL1 is set to correspond to the inner diameter of the metal shell 3, and in the present embodiment, the metal shell 3 So that 0.472 ≦ B / A ≦ 0.570 (more preferably 0.472 ≦ B / A ≦ 0.540), where B (mm) is the outer diameter of the insulator 2 at the tip position of Is configured.

Furthermore, while the front end side hole part 28 located in the front end side rather than the said cyclic | annular protrusion 21 among the metal shell 3 is made into the substantially identical internal diameter, the said leg long part 13 is the rear end side in the axis line CL1 direction It has a tapered shape that gradually expands in diameter. However, in the present embodiment, on the rear end side of the metal shell 3 from the front end of the metal shell 3 along the axis line CL1, the ratio of the outer diameter of the leg length 13 to the inner diameter of the metal shell 3 does not become excessively large. It is formed. That is, the inner diameter of the metal shell 3 is C (mm) and the outer diameter of the insulator 2 (leg length 13) is D (mm) at a position 4 mm from the front end of the metal shell 3 along the axis CL1. When doing, the leg length 13 is formed to satisfy 0.472 ≦ D / C ≦ 0.660. Further, when the outer diameter of the leg long portion 13 at this position is Y (mm) at a position of 4 mm from the front end of the metal shell 3 along the axis line CL1 and at the rear end side, B <Y . The inner diameter C of the metal shell 3 is set to 8.0 mm or more and 8.7 mm or less.

Furthermore, in the present embodiment, the length KL of the leg length 13 along the direction of the axis CL1 is relatively large (for example, 15 mm or more) in order to improve the contamination resistance.

In addition, the end of the center electrode 5 is disposed so as to protrude from the end of the metal shell 3 toward the end in the direction of the axis CL1 and from the end of the metal shell 3 along the axis CL1 to the center electrode 5 (noble metal tip 31) It is assumed that 2.0 ≦ E ≦ 5.0 is satisfied, where E (mm) is the distance to the tip of the lens.

Further, a cylindrical equal diameter portion 13A having substantially the same outer diameter is formed at the rear end portion of the leg length portion 13, and the outer peripheral surface of the equal diameter portion 13A corresponds to the inner periphery of the annular protrusion 21. It faces to the surface extending along the axis line CL1 among the surfaces. That is, in the cross section including the axis line CL1, an outline of a portion of the leg length portion 13 (equal diameter portion 13A) facing the annular protrusion 21 extends along the axis line CL1.

Furthermore, the equal diameter portion 13A is configured to be relatively close to the annular protrusion 21, and is located between the equal diameter portion 13A and the annular protrusion 21 along a direction orthogonal to the axis line CL1. When the shortest distance is F (mm), F ≦ 0.5.

At the same time, the projection length PL of the tip of the center electrode 5 (the noble metal tip 31) with respect to the tip of the insulator 2 along the axis line CL1 is set to 1.8 mm or less.

As shown in FIG. 3, the leg length portion 53 may be configured and the base end portion of the leg length portion 53 may be tapered without providing the equal diameter portion 13A.

Further, as shown in FIG. 4, an annular gap may be provided between the outer peripheral surface of the main portion 5 M of the center electrode 5 and the inner peripheral surface of the insulator 2. In this case, as shown in FIG. 5, the diameter difference DS between the outer diameter of the center electrode 5 (main portion 5M) and the inner diameter of the insulator 2 is 0.06 mm or more (DS / 2 is 0.03 mm or more). It is preferable to do.

As described above in detail, according to the present embodiment, B / A ≦ 0.570 for the inner diameter A of the metal shell 3 and the outer diameter B (mm) of the insulator 2 at the tip end position of the metal shell 3 D / C ≦ 0.660 for the inner diameter C of the metal shell 3 and the outer diameter D (mm) of the insulator 2 at a position 4 mm from the front end of the metal shell 3 along the axis line CL1 It is configured to meet the For this reason, the amount of heat received at the tip of the insulator 2 which is particularly easily heated is suppressed according to the size of the inner diameter of the metal shell 3 (that is, the ability to draw the heat of the insulator 2 by the metal shell 3). Can.

Further, the outer diameter Y of the leg long portion 13 at a position on the rear end side exceeding 4 mm from the front end of the metal shell 3 along the axis line CL1 is configured to satisfy B <Y. That is, the portion of the leg length portion 13 corresponding to the path for drawing heat at the tip of the insulator 2 is configured to have a sufficiently large cross-sectional area. Therefore, the heat of the tip portion of the insulator 2 can be effectively conducted to the metal shell 3 side.

Furthermore, the inner diameter A at the end of the metal shell 3 has a relatively small diameter so as to satisfy A ≦ 8.7, while the metal shell 3 and the insulator 2 are satisfied by satisfying B / A ≦ 0.570. The opening of the space formed between (the leg length 13) is configured to have a certain size. Therefore, in the combustion cycle, the combustion gas and the fresh air allow the insulator 2 to be heated in a well-balanced manner since the combustion gas and the fresh air alternately enter the space (so-called gas volume) into which the high temperature combustion gas and the low temperature fresh air intrude. It will be cooled. As a result, overheating of the insulator 2 can be prevented more reliably.

As described above, according to the present embodiment, B / A ≦ 0.570 and D / C ≦ 0.660 while preventing overheating of the tip portion of the insulator 2 by satisfying A ≦ 8.7 or the like. By satisfying the above, the amount of heat received at the tip of the insulator 2 can be suppressed to the amount corresponding to the heat transfer performance of the metal shell 3. Further, by satisfying B <Y, the heat at the tip of the insulator 2 can be reduced. It can be effectively pulled to the metal shell 3 side. As a result, the pre-ignition resistance can be dramatically improved.

Further, according to the present embodiment, the preignition resistance is improved by changing the diameter difference between the metal shell 3 and the insulator 2 without changing the diameter difference between the center electrode 5 and the insulator 2. Can be improved. Therefore, it is possible to more reliably prevent a situation such as a crack in the insulator 2 due to the thermal expansion of the center electrode 5.

Furthermore, since the insulator 2 is configured to satisfy 0.472 ≦ B / A and 0.472 ≦ D / C, sufficient withstand voltage performance can be secured in the insulator 2.

In addition, the distance E (mm) from the end of the metal shell 3 along the axis line CL1 to the end of the center electrode 5 is 2.0 ≦ E ≦ 5.0. Therefore, the ignition performance is improved, and the above-described effect of improving the pre-ignition resistance is significantly exhibited.

In addition, since the shortest distance F between the leg length 13 and the annular projection 21 is 0.5 mm or less, heat is more efficiently conducted from the insulator 2 (leg length 13) to the metal shell 3 be able to. As a result, the pre-ignition resistance can be further improved.

In addition, an equal diameter portion 13A is provided at the base end portion of the leg length portion 13, and it is possible to increase the surface area of the portion of the leg length portion 13 which approaches the annular protrusion 21. Therefore, heat can be conducted more smoothly from the leg portion 13 to the metal shell 3. Furthermore, by providing the equal diameter portion 13A, the shortest portion of the insulator 2 while preventing the boundary portion between the step portion 14 and the leg length portion 13 or the vicinity thereof from coming into contact with the metal shell 3, It is possible to make the distance F smaller, and it is possible to further improve the pre-ignition resistance.

In addition, since the protrusion length PL is set to 1.8 mm or less, the amount of heat received by the center electrode 5 can be reduced, and a decrease in the heat transfer performance of the insulator 2 can be effectively suppressed. As a result, the pre-ignition resistance can be further improved.

In the case where the diameter difference DS between the outer diameter of the center electrode 5 (main portion 5M) and the inner diameter of the insulator 2 is sufficiently large to be 0.06 mm or more, the center electrode 5 is thermally expanded. Also, the gap between the center electrode 5 and the insulator 2 can be sufficiently maintained. Therefore, breakage of the insulator 2 due to the thermal expansion of the center electrode 5 can be prevented more reliably.

Incidentally, although the abnormal discharge can be suppressed by providing the thermo pocket portion 30, since the tip of the insulator 2 and the center electrode 5 are separated, the insulator 2 with the center electrode 5 interposed therebetween There is concern that the heat buildup of the In this respect, according to the present embodiment, the amount of heat received by the end portion of the insulator 2 is suppressed to a level corresponding to the ability of the metal shell 3 to draw the heat of the insulator 2. Even if the pulling is aggravated, overheating at the tip of the insulator 2 can be prevented more reliably. That is, it is particularly effective in the plug including the thermo pocket portion 30 to satisfy B / A ≦ 0.570, D / C ≦ 0.660, and the like for the insulator 2 and the metal shell 3.

Next, in order to confirm the operation and effect exhibited by the above embodiment, the length KL of the leg length along the axis is 11 mm or 15 mm, and the outer diameter DC of the tip of the center electrode is 2.1 mm or 2.. After setting the diameter to 6 mm, prepare a spark plug sample in which the ratio (B / A) of the outer diameter B (mm) of the insulator to the inner diameter A (mm) of the metal shell at the tip position of the metal shell The preignition test based on JISD1606 was done about each sample. The outline of the preignition test is as follows. That is, after each sample is attached to a 1.6 L displacement, 4-cylinder DOHC engine, the ignition timing is advanced by a predetermined angle from the regular ignition timing, and the operation is continued for 2 minutes for each ignition timing. The Then, based on the waveform of the current applied to the sample, the ignition timing (preignition generation advance angle) at which the preignition occurred was specified. It should be noted that, as the preignition occurrence advance angle is larger, preignition is less likely to occur, that is, excellent in preignition resistance.

FIG. 6 shows test results of a preignition test on a sample in which the length KL of the leg length portion is 11 mm and the outer diameter DC of the center electrode tip portion is 2.6 mm. Further, FIG. 7 shows the test results of the sample in which the length KL of the leg length is 15 mm and the outer diameter DC is 2.6 mm in triangles, the length KL of the leg length is 15 mm, and the outer diameter DC is The test results of the sample of 2.1 mm are shown by squares. The longer the leg length is or the smaller the outer diameter of the tip of the center electrode, the more difficult it is to draw heat from the tip of the insulator, which tends to be disadvantageous in terms of pre-ignition resistance. In each sample, the inner diameter A of the metal shell was 8.4 mm, and the outer diameter B of the insulator was changed to change the value of B / A. Furthermore, the ratio (D / C) of the outer diameter D (mm) of the insulator to the inner diameter C (mm) of the metallic shell at a position 4 mm from the front end of the metallic shell along the axis was 66% or less . In addition, in the following tests, a thermo pocket was provided between the center electrode and the tip of the axial hole in each sample. Further, in the sample in which the outer diameter DC is 2.6 mm, in the sample in which the outer diameter of a portion corresponding to the thermo pocket portion in the center electrode is 2.5 mm and the outer diameter DC is 2.1 mm, the center electrode The outer diameter of the portion corresponding to the thermo pocket portion was 2.0 mm.

Furthermore, the sample which changed said D / C variously was produced, and the above-mentioned preignition test was done about each sample. FIG. 8 shows test results for a sample in which the length KL of the leg length portion is 11 mm and the outer diameter DC of the center electrode tip portion is 2.6 mm. Also, in FIG. 9, the test results of the sample in which the length KL of the leg length is 15 mm and the outer diameter DC of the center electrode tip is 2.6 mm are shown by triangles, the length KL of the leg length is 15 mm, and the center is The test results of the sample in which the outer diameter DC of the electrode tip portion is 2.1 mm are shown by squares. In each test, the inner diameter A of the metal shell was 8.4 mm, and B / A was 53.3%.

In addition, while the B / A is 57.0%, the D / C is 66.0%, or the B / A is 53.3%, and the D / C is 63.8%, the inner diameter of the end of the metal shell The samples of the spark plug which changed A variously were produced, and the above-mentioned preignition test was done about each sample. In FIG. 10, the test result of the sample which made B / A 57.0% and D / C 66.0% is shown by a circle, B / A 53.3%, D / C 63.8% Test results of the samples taken are shown by triangles. In each sample, the length KL of the leg length was 15 mm, and the outer diameter DC of the tip of the center electrode was 2.6 mm.

As shown in FIGS. 6 to 10, samples in which the inner diameter A of the tip of the metal shell is 8.7 mm or less while B / A is 57.0% or less and D / C is 66.0% or less It has been found that the ignition advance angle is relatively large, and the pre-ignition resistance is excellent. This is because the inner diameter A is set to 8.7 mm or less, the insulator is heated and cooled in a well-balanced manner by the combustion gas and fresh air entering the space between the metal shell and the leg length, and the insulator tip portion By suppressing the overheat of B, and setting B / A to 57.0% or less, and D / C to 66.0% or less, the amount of heat received at the tip of the insulator depends on the heat transfer performance by the metal shell. It is thought that it is attributable to the fact that the

Moreover, as shown in FIG.6 and FIG.7, it was confirmed that the further outstanding pre-ignition resistance can be implement | achieved by B / A being 54.0% or less.

Next, as shown in FIG. 11, a straight portion with a constant outer diameter extending from the front end toward the rear end is provided at the front end of the insulator, and the length along the axial direction of the straight portion (straight length) Spark plug samples with various changes in SL were prepared, and the above-described preignition test was performed on each sample. Here, on the basis of the test results of the preignition test on the sample in which the straight portion was not provided at the tip of the insulator (taper-shaped), the samples for which test results equal to or higher than the standard were obtained To give an evaluation. On the other hand, samples which were inferior in preignition resistance to the above criteria were evaluated as “×”. Table 1 shows the test results of the test. In each sample, the amount of protrusion of the end of the insulator with respect to the end of the metal shell along the axis was 1.5 mm, and the inner diameter A of the end of the metal shell was 8.4 mm. Furthermore, it is made into the taper shape which diameter-expands the site | part of the rear end side from a straight part gradually toward a rear end side among insulators. In the reference sample, B / A is 53.3% and D / C is 63.8%, and for the other samples, B / A ≦ 57.0% and D / C ≦ 66. It was configured to satisfy .0%.

As shown in Table 1, a sample having a straight length SL of more than 5.5 mm, in other words, a sample having a straight portion length of more than 4 mm from the front end of the metal shell toward the rear end, is B / A. It became clear that the effect by making D / C into the said predetermined numerical range is not fully acquired. It is considered that this is because it has become difficult to conduct the heat of the distal end portion of the insulator to the metal shell side through the leg length portion because the volume of the proximal end portion of the leg length portion decreases.

On the other hand, a sample with a straight length SL of 5.5 mm or less, in other words, a portion of the insulator exceeding 4 mm from the front end to the rear end of the metal shell is the insulation at the front end position of the metal shell It has been found that the sample having a diameter larger than the outer diameter B (mm) of the insulator sufficiently exerts the effect by making B / A, D / C, etc. into the above-mentioned predetermined numerical range.

Taking the above test results into consideration comprehensively, let A (mm) be the inner diameter of the metal shell at the tip position of the metal shell, B (mm) be the outer diameter of the insulator, and lead the metal shell along the axis The inner diameter of the metal shell is C (mm) and the outer diameter of the insulator is D (mm) at a position 4 mm from the rear end, and the position at the rear end beyond 4 mm from the front end of the metal shell along the axis When the outer diameter of the insulator (leg length) in Y is Y (mm), B / A ≦ 0.570 (57.0%), D / C ≦ 0.660 (66.0%), B < By satisfying Y and A ≦ 8.7, it can be said that very excellent pre-ignition resistance can be realized.

Further, from the viewpoint of further improving the pre-ignition resistance, it can be said that it is more preferable to be configured to satisfy B / A ≦ 0.540.

Next, after making the length KL of the leg length part 11 mm or 15 mm, the sample of the insulator which changed the value of B / A variously was produced, and the withstand voltage test was done about each sample. The outline of the withstand voltage test is as follows. That is, as shown in FIG. 12, the insulating oil IO is filled in a predetermined case CA, and the ring RG connected to the ground is disposed in the insulating oil IO. Then, after the electrode bar ES for high voltage application is inserted into the axial hole of the sample, the sample is disposed so that the outer periphery of the portion corresponding to the tip of the metal shell in the sample faces the inner periphery of the ring RG. did. Then, a high voltage of 20 kV was applied to the electrode bar ES, and it was confirmed whether penetration by discharge occurred in the sample. Here, a sample in which penetration did not occur was evaluated as "o" because of excellent withstand voltage performance, while a sample in which penetration occurred was evaluated as "x" as poor in withstand voltage performance. I decided. Table 2 shows the test results of the sample in which the length KL of the leg length portion is 11 mm, and Table 3 shows the test results of the sample in which the length KL of the leg length portion is 15 mm. Each sample has an axial hole into which the center electrode with an outer diameter DC at the tip of 2.6 mm can be inserted almost without a gap, and can be inserted into the metal shell with an inner diameter A of 8.4 mm. It has an outer shape.

As shown in Tables 2 and 3, regardless of the length of the leg length, it is clear that the sample having B / A of 47.2% or more has excellent withstand voltage performance without occurrence of penetration. It became. This is considered to be due to the fact that the thickness of the insulator can be sufficiently secured by setting B / A to 47.2% or more.

From the above test results, in order to improve the withstand voltage performance, it can be said that it is preferable to configure so as to satisfy 0.472 ≦ B / A. From the above test results, it is preferable that 0.472 ≦ D / C be satisfied for the inner diameter C of the metal shell and the outer diameter D of the insulator.

Next, the spark is obtained by variously changing the distance E from the end of the metal shell along the axis to the end of the center electrode, with B / A being 57.0%, 53.3%, or 51.3%. The above-described pre-ignition test was performed on a plug sample (inventive product sample) and a spark plug sample (conventional product sample) in which B / A was 60.7% and the distance E was variously changed. . Then, a value (advance angle advance value) obtained by subtracting the preignition occurrence advance angle in the conventional sample from the preignition occurrence advance angle in the invention sample was calculated for each distance E. The test result of the said test is shown in FIG. In FIG. 13, the lead angle improvement value in a sample in which B / A is 57.0% is indicated by a circle, and the lead angle improvement value in a sample in which B / A is 53.3% is indicated by a triangle. The advance improvement value in the sample in which B / A is 51.3% is indicated by a square. In each sample, the inner diameter A of the end of the metal shell was 8.4 mm, and the amount of protrusion of the end of the center electrode with respect to the end of the insulator was 1.5 mm. In addition, D / C ≦ 0.660 is satisfied at least for the inventive product samples.

As shown in FIG. 13, although each invention sample had excellent pre-ignition resistance compared to the conventional sample, the sample with a distance E of less than 2.0 mm or more than 5.0 mm It was found that the improvement effect of the pre-ignition resistance due to the B / A being 57.0% or less is relatively small. This is because when the distance E is less than 2.0 mm, the tip of the insulator is not heated so much, so that even the conventional sample had some degree of pre-ignition resistance, and If the distance E is larger than 5.0 mm, it is considered that the heat dissipation of the insulator by the center electrode is deteriorated because the center electrode is extremely heated.

On the other hand, in the sample in which the distance E is 2.0 mm or more and 5.0 mm or less, the improvement effect of the preignition resistance by satisfying B / A ≦ 0.570, D / C ≦ 0.660, etc. It became clear that it was exhibited remarkably.

From the above test results, in the spark plug satisfying 2.0 mm E E 5.0 5.0 mm, satisfying B / A 0.5 0.570, D / C 0.6 0.660, etc. improves the pre-ignition resistance. It can be said that this is particularly effective.

Then, a sample (straight sample) of a spark plug provided with an equal diameter portion at the base end portion of the leg length portion and extending along the axis the outline of the portion of the leg length portion facing the annular projection And a sample of the spark plug (taper-shaped sample) configured to have a tapered shape expanding toward the rear end side without providing an equal diameter portion at the base end of the leg length portion, along the direction orthogonal to the axis. What changed variously the shortest distance F (mm) between a leg long part and an annular projection was produced, and the above-mentioned preignition test was done about each sample. And the value (advancing angle fluctuation value) which subtracted the preignition generation advance angle in the taper-shaped sample which made the shortest distance F 0.45 mm from the preignition generation advance angle in each sample was computed for every sample. The test result of the said test is shown in FIG. In FIG. 14, the test results of the straight sample are shown by circles, and the test results of the tapered sample are shown by triangles. In each sample, the inside diameter A of the end of the metal shell was 8.4 mm, and the outside diameter DC of the end of the center electrode was 2.6 mm. Furthermore, B / A was 53.3%, and D / C was 63.8%.

As shown in FIG. 14, as the shortest distance F is reduced, the preignition resistance is further improved, and in particular, by setting the shortest distance F to 0.5 mm or less, the effect of improving the preignition resistance is obtained. It became clear that it was exhibited remarkably.

Moreover, it was confirmed that the straight sample can realize more excellent pre-ignition resistance as compared to the tapered sample. This is considered to be due to the fact that the heat of the insulator is conducted more smoothly to the metal shell side because the portion approaching the annular protrusion is increased on the surface of the base end portion of the leg length portion.

From the above test results, it is preferable to provide an equal diameter portion at the base end portion of the leg length portion and to set the shortest distance F to 0.5 mm or less in order to further improve the preignition resistance.

Next, the distance from the end of the metal shell along the axis to the center of the spark discharge gap (ignition position distance) is 3 mm or 5 mm, and the end of the center electrode with respect to the end of the insulator along the axis The sample of the spark plug which changed protrusion length PL variously was produced. Then, when the tip of the sample is heated under the condition that the tip of the center electrode becomes 900 ° C. when the protrusion length PL is 1.0 mm, the temperature of the tip of the insulator is analyzed by FEM (finite element method) did. FIG. 15 is a graph showing the relationship between the protrusion length PL and the temperature of the tip of the insulator. In FIG. 15, the results of the sample in which the firing position distance is 3 mm are indicated by circles, and the results of the sample in which the firing position distance is 5 mm are indicated by triangles. In each sample, the screw diameter of the screw was M14.

As shown in FIG. 15, it was confirmed that the temperature at the tip of the insulator rapidly increases in the sample in which the projection length PL is larger than 1.8 mm, and the preignition resistance is relatively poor.

On the other hand, it was revealed that in the sample in which the projection length PL was 1.8 mm or less, the temperature rise of the insulator was suppressed and the preignition resistance was excellent. This is considered to be attributable to the fact that the amount of heat received by the central electrode is reduced by setting the projection length PL to 1.8 mm or less, and thus the decrease in heat transfer performance of the insulator is suppressed.

From the above test results, it is preferable to set the projection length PL to 1.8 mm or less from the viewpoint of further improving the pre-ignition resistance.

Next, after setting B / A to 0.472 or 0.570, samples of spark plugs were prepared with various changes in the diameter difference DS between the outer diameter of the center electrode (main body) and the inner diameter of the insulator. . Then, the stress generated in the insulator when the tip of each sample was heated under the condition that the tip of the center electrode becomes 1000 ° C. (that is, under the condition that the center electrode is overheated significantly) was analyzed by FEM. FIG. 16 is a graph showing the relationship between the diameter difference DS and the stress generated in the insulator. In FIG. 16, the result of the sample in which B / A is 0.472 is indicated by circles, and the result of the sample in which B / A is 0.570 is indicated by squares. In each sample, the screw diameter of the screw portion was M14, and the outer peripheral shape of the insulator was the same.

As shown in FIG. 16, in the sample having the diameter difference DS of 0.06 mm or more, no stress is generated in the insulator even when the center electrode is heated to a very high temperature, that is, the center electrode and the insulator It has become clear that there is no contact.

From the above test results, it can be said that it is preferable to set the diameter difference DS to 0.06 mm or more in order to more reliably prevent breakage of the insulator due to thermal expansion of the center electrode.

In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other applications and modifications not illustrated below are naturally possible.

(A) In the above embodiment, the spark discharge gap 33 is formed between the noble metal tip 31 and the tip of the ground electrode 27. However, as shown in FIG. 17A, the noble metal tip 31 is not provided. The spark discharge gap 33 may be formed between the tip of the center electrode 5 and the ground electrode 27. Further, as shown in FIG. 17B, the noble metal tip 31 is provided on the center electrode 5, and the noble metal tip 32 is provided on the ground electrode 27, and the spark discharge gap 33 is formed between both the

noble metal tips

31 and 32. It is also good.

Furthermore, as shown in FIG. 18A, the noble metal tip 32 may be provided at the tip of the ground electrode 27. In this case, the growth inhibition of the flame by the ground electrode 27 is suppressed, and the flame spreadability can be improved. Alternatively, as shown in FIG. 18B, the noble metal tip 32 may be joined to the ground electrode 27 through a pedestal 35 having a linear expansion coefficient between the noble metal tip 32 and the ground electrode 27. . When the pedestal 35 is provided, the pedestal 35 can absorb the difference in thermal expansion between the ground electrode 27 and the noble metal tip 32, so that the bonding strength of the noble metal tip 32 can be improved. In addition, the tip of the ground electrode 27 may be configured to narrow in width toward the tip of the ground electrode 27. In this case, the flame spreadability can be improved.

Further, as shown in FIG. 19 (a), the center electrode 5 (the noble metal tip 31) and the insulator 2 are disposed to protrude further to the end side in the direction of the axis CL1 and from both the end face and side of the ground electrode 27. Even if the noble metal tip 42 is provided so as to protrude and spark discharge is performed between the noble metal tip 42 and the center electrode 5 (precious metal tip 31) substantially along the direction orthogonal to the axis line CL1. Good. Further, as shown in FIG. 19 (b), the center electrode 5 (the noble metal tip 31) and the insulator 2 are disposed to protrude further to the end side in the direction of the axis CL1 and from both the end surface and side of the ground electrode 27. A spark discharge may be performed substantially along the axis CL1 between the noble metal tip 42 provided to protrude and the center electrode 5 (the noble metal tip 31). According to the present invention, since the pre-ignition resistance can be improved, the center electrode 5 and the insulator 2 can be further protruded toward the tip end side in the direction of the axis line CL1 as described above, and the center electrode 5 can be protruded. Can improve the ignitability. Further, as shown in FIG. 19B, a chamfered portion 63 may be provided between the side surfaces of the ground electrode 27. In the case where the chamfered portion 63 is provided, the air-fuel mixture easily flows into the spark discharge gap 33 in the form of being wound around the ground electrode 27, and the ignition performance can be further improved.

When the center electrode 5 is protruded to the end side in the direction of the axis CL1, it may be necessary to further project the ground electrode 27 to the end side in the direction of the axis CL1. However, when the ground electrode 27 is disposed in a protruding manner, the ground electrode 27 is further heated, and the wear resistance of the noble metal tip 42 bonded to the ground electrode 27 may be reduced. Therefore, when the ground electrode 27 is disposed so as to protrude toward the front end side in the direction of the axis CL1, an inner layer made of a metal material having excellent thermal conductivity may be provided inside the ground electrode 27. In this case, the heat of the noble metal tip 42 can be efficiently conducted to the metal shell 3 through the inner layer, and the decrease in the wear resistance of the noble metal tip 42 can be effectively suppressed.

(B) Although not particularly mentioned in the above embodiment, as shown in FIG. 20A, a tapered portion 61 may be provided between the front end surface of the metal shell 3 and the inner peripheral surface. Further, as shown in FIG. 20 (b), instead of the tapered portion 61, a curved surface 62 convex toward the axis CL1 may be provided between the front end surface of the metal shell 3 and the inner peripheral surface. . In this case, the outer diameter A of the metal shell 3 is relatively small, 8.7 mm or less, and an abnormal discharge (so-called lateral discharge) along the surface of the insulator 2 between the tip of the metal shell 3 and the center electrode 5 Even in the configuration in which the generation of sparks is more concerned, the generation of abnormal discharge can be prevented more reliably. When the tapered portion 61 and the curved surface portion 62 are provided, "the inner diameter A of the metal shell 3" is a virtual surface V1 obtained by extending the inner peripheral surface of the metal shell 3 to the tip end side in the axis line CL1 direction The inside diameter of the circle formed by the virtual surface V2 obtained by extending the end surface of the metal fitting 3 to the axis CL1 side is said.

(C) In the above embodiment, although the ground electrode 27 is joined to the end portion 26 of the metal shell 3, a part of the metal shell (or a tip metal welded in advance to the metal shell) The present invention is also applicable to the case where the ground electrode is formed by scraping a part of (a) (for example, JP-A-2006-236906).

(D) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (modified 12-corner) shape [ISO 22977: 2005 (E)] or the like.

1 ... spark plug 2 ... insulation insulator (insulator)
DESCRIPTION OF SYMBOLS 3 ... Main metal fitting 5 ... Center electrode 5F ... Collar part 13 ... Leg length part 14 ... Step part 15 ... Screw part 16 ... Seat part 21 ... Annular protrusion 27 ... Grounding electrode CL1 ... Axis line

Claims

An axially extending rod-shaped center electrode,
An insulator provided on an outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A spark plug including a ground electrode extending from a front end portion of the metal shell;
The metal shell has an annular projection projecting toward the axis on the inner peripheral portion of the metal shell,
The insulator is
A step which is directly or indirectly locked to the annular projection;
And a long leg extending from the tip of the step toward the tip,
The inner diameter of the metal shell at the end position of the metal shell is A (mm), and the outer diameter of the insulator is B (mm),
The inner diameter of the metal shell is C (mm) and the outer diameter of the insulator is D (mm) at a position 4 mm from the front end of the metal shell along the axis.
Assuming that the outer diameter of the long leg portion is Y (mm) at a position on the rear end side exceeding 4 mm from the front end of the metal shell along the axis, the following formulas (1) to (4) are satisfied. Spark plug characterized by.
0.472 ≦ B / A ≦ 0.570 (1)
0.472 ≦ D / C ≦ 0.660 (2)
B <Y (3)
A ≦ 8.7 (4)
B / A ≦ 0.540
The spark plug according to claim 1, characterized in that:
When the distance from the end of the metal shell along the axis to the end of the center electrode is E (mm),
2.0 ≦ E ≦ 5.0
The spark plug according to claim 1 or 2, characterized in that
In the section including the axis,
An outline of a portion of the leg length facing the annular projection extends along the axis,
When the shortest distance between the leg long portion and the annular projection along the direction orthogonal to the axis is F (mm),
F ≦ 0.5
The spark plug according to any one of claims 1 to 3, wherein
The metal shell is
A screw for screwing into a mounting hole of the combustion device;
And a seat portion provided on the rear end side of the screw portion and formed larger in diameter than the screw diameter of the screw portion,
The spark plug according to any one of claims 1 to 4, wherein a distance from a tip end of the metal shell along the axis to the seat portion is 17.5 mm or more.
The spark plug according to any one of claims 1 to 5, wherein a protrusion length of the tip of the center electrode with respect to the tip of the insulator along the axis is 1.8 mm or less.
The center electrode bulges radially outward on the rear end side of the center electrode, and has a collar portion engaged with the inner circumferential surface of the insulator.
The diameter difference between the outer diameter of the center electrode and the inner diameter of the insulator is set to 0.06 mm or more on the tip end side in the axial direction with respect to the tip end of the flange portion. The spark plug as described in 1 or 2.