JP4676912B2 - Spark plug for internal combustion engine - Google Patents

Description

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

  A spark plug for an internal combustion engine such as an automobile engine includes, for example, a center electrode, an insulator provided outside the center electrode, a cylindrical metal shell provided outside the insulator, and a base end portion of the metal shell. And a ground electrode joined to the front end portion. The ground electrode has a substantially rectangular cross section and is arranged so that the inner side surface of the tip portion faces the tip surface of the center electrode, thereby forming a spark discharge gap between the tip portion of the center electrode and the tip portion of the ground electrode. Is done.

  A threaded portion (not shown) is formed on the outer peripheral surface of the metal shell. The spark plug is attached by being screwed to the cylinder head of the engine at the thread portion. By the way, when the air-fuel mixture directly contacts the back surface of the ground electrode in the attached state of the spark plug, the ground electrode may hinder the inflow of the air-fuel mixture into the spark discharge gap. As a result, it is difficult for the air-fuel mixture to reach the spark discharge gap, and the ignitability may be reduced.

On the other hand, there is a technique in which the width of the portion (base) on the metal shell side of the ground electrode is made relatively large and the tip side is made relatively narrow and narrow (see, for example, Patent Document 1). By making the tip side relatively narrow in this way, even when the air-fuel mixture directly contacts the back surface of the ground electrode, the inflow inhibition of the air-fuel mixture into the spark discharge gap can be suppressed to some extent. Further, in the technique described in Patent Document 1, since the width on the base side, and thus the cross-sectional area, is large, the bonding strength to the metal shell can be increased, and the so-called heat dissipation is large due to the large cross-sectional area. Can be improved. As a result, the durability is improved to some extent.
Special table 2004-521473 gazette

  However, in the technique described in the above-mentioned patent document, the position of the most base side among the narrow portions is located on the base end side with respect to the front end surface of the insulator, and there is a limit in improving heat dissipation. It is also true. On the other hand, if the base section (length) with a large width is increased in the dark clouds, the section (length) of the narrow section has to be shortened, and the inflow of the air-fuel mixture into the spark discharge gap is inhibited. Inviting and lowering the ignitability. Inhibiting the inflow of the air-fuel mixture also leads to the inhibition of the flame spread (combustion space), which also impairs the ignitability.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to suppress the inflow of the air-fuel mixture, thereby preventing deterioration in ignitability and improving the durability. To provide a plug.

  Hereinafter, each configuration suitable for solving the above-described problems will be described in terms of items. In addition, the effect etc. peculiar to the structure which respond | corresponds as needed are added.

Configuration 1. The spark plug of this configuration includes a rod-shaped center electrode extending in the axial direction, a substantially cylindrical insulator provided on the outer periphery of the center electrode, and a cylindrical metal shell provided on the outer periphery of the insulator; A base end is joined to the front end surface of the metal shell, and the front end is disposed so as to face the front end surface of the center electrode; and a ground electrode.
A spark plug for an internal combustion engine having a spark discharge gap between a front end surface of the center electrode and a front end portion of the ground electrode,
The ground electrode is
A base portion joined to a front end surface of the metal shell,
It has a substantially constant width narrower than that of the base in a direction perpendicular to the axial direction when viewed in the direction in which the center electrode and the ground electrode overlap with each other, located on the tip side of the base. A narrow portion having a convex curved surface on the back surface opposite to the center electrode side,
While the width of the narrow part is 1.0 mm or more and 2.0 mm or less, the cross-sectional area of the base part is 3.0 mm ² or more,
The most proximal portion of the narrow portion is located between the distal end surface of the insulator and the distal end surface of the central electrode in the axial direction.

  For example, a noble metal tip may be provided on at least one of the ground electrode and the center electrode. When a noble metal tip is provided on the center electrode, a spark discharge gap is formed between the opposing noble metal tip and the ground electrode body, and when a noble metal tip is provided on the ground electrode, When a spark discharge gap is formed between the noble metal tip and the center electrode main body, and noble metal tips are provided on both, a spark discharge gap is formed between the noble metal tips facing each other. Further, when no precious metal tip is provided, a spark discharge gap is formed between the front end surface of the center electrode and the inner surface of the ground electrode.

  Further, the term “width” refers to a width in a direction perpendicular to the axial direction when viewed in the direction in which the center electrode and the ground electrode overlap.

  In addition, it is good also as providing the connection part (for example, taper part) which connects both between a base part and a narrow part.

  Further, the narrow portion of the ground electrode does not necessarily have a circular cross section, and may have a convex curved surface on the back surface opposite to the center electrode side. This is because, at least if the back surface is rounded, the air-fuel mixture moves inside the ground electrode, and the air-fuel mixture easily reaches the spark discharge gap.

According to the above configuration 1, the side of the ground electrode joined to the front end surface of the metal shell is a base portion having a cross-sectional area of 3.0 mm ² or more and a substantially constant width larger than that of the narrow portion. Yes. For this reason, the heat transfer to the metal shell is smoothly performed toward the base portion side, and the ground electrode is easily cooled. Therefore, so-called “heat pulling” is improved, and it is possible to suppress problems due to an increase in the ground electrode temperature during high-speed operation, that is, deterioration in durability such as oxidation resistance and spark wear resistance. On the other hand, when the cross-sectional area of the base is less than 3.0 mm ² , sufficient heat dissipation may not be obtained, and durability such as oxidation resistance and spark wear resistance may be deteriorated. .

  The narrow portion has a width of 2.0 mm or less and a convex curved surface on the back surface opposite to the center electrode side. For this reason, even when the air-fuel mixture is in a positional relationship such that it directly contacts the back surface of the ground electrode, the air-fuel mixture tends to enter the inside of the ground electrode, and the air-fuel mixture easily reaches the spark discharge gap. As a result, a reduction in ignitability can be prevented. On the other hand, when the width of the narrow portion exceeds 2.0 mm, it is difficult to obtain the effect of having a convex curved surface on the back surface, and there is a concern that the inflow of the air-fuel mixture may be inhibited. However, the width of the narrow portion needs to be 1.0 mm or more. When the width of the narrow portion is less than 1.0 mm, there is a possibility that sufficient heat dissipation may not be achieved even if the base portion exists.

In addition, in Configuration 1, the most proximal portion of the narrow portion is located between the distal end surface of the insulator and the distal end surface of the center electrode in the axial direction. That is, the heat dissipation is improved by making the base section relatively large compared to the prior art in which the base section had to be made relatively small. In Configuration 1, the width of the narrow portion is 2.0 mm or less, and the narrow portion has a convex curved surface on the back surface opposite to the center electrode side, as described above. Even if a relatively large number of base sections are set, the ignitability is not lowered. That is, in the configuration 1, the narrow portion has a convex curved surface on the back surface opposite to the center electrode side, and the width is 1.0 mm or more and 2.0 mm or less, This is because the cross-sectional area of the base is set to 3.0 mm ² or more and the most proximal portion of the narrow portion is located between the front end surface of the insulator and the front end surface of the center electrode. Thus, it is possible to prevent the deterioration of ignitability and improve the durability.

Configuration 2. The spark plug of this configuration includes a rod-shaped center electrode extending in the axial direction, a substantially cylindrical insulator provided on the outer periphery of the center electrode, and a cylindrical metal shell provided on the outer periphery of the insulator; A base end is joined to the front end surface of the metal shell, and the front end is disposed so as to face the front end surface of the center electrode; and a ground electrode.
A spark plug for an internal combustion engine having a spark discharge gap between a front end surface of the center electrode and a front end portion of the ground electrode,
The ground electrode is formed by twisting a metal rod having a substantially oval cross section, a substantially oval cross section, or a substantially rectangular cross section,
When viewed in the direction in which the center electrode and the ground electrode overlap, the width in the direction perpendicular to the axial direction is
In the base joined to the front end surface of the metal shell, it is larger than the thickness,
The tip portion facing the tip portion of the center electrode is smaller than the thickness.

  According to the structure 2, in the base part joined to the front end surface of the metal shell among the ground electrodes, since the width is larger than the thickness, the bonding strength to the metal shell end surface where the area that can be joined is limited is increased. Can do. As a result, durability is improved.

  On the other hand, of the ground electrodes, the width of the tip portion facing the tip portion of the center electrode is smaller than the thickness. For this reason, even when the air-fuel mixture directly contacts the back surface of the ground electrode, the inflow of the air-fuel mixture is not easily inhibited, and the air-fuel mixture easily reaches the spark discharge gap. As a result, a reduction in ignitability can be prevented.

  Further, in the configuration 2, the base portion and the distal end portion are formed by twisting a metal rod-like body having a substantially oval cross section, a substantially oval cross section, or a substantially rectangular cross section. For this reason, in order to make the ground electrode partially thin or thick, it is not necessary to perform comparatively complicated processing such as cutting, extrusion, and swaging. That is, since the above-described characteristics can be obtained by performing a relatively simple twisting process, the effect of reducing the number of man-hours at the time of manufacture can be achieved.

Configuration 3. The spark plug of this configuration is the above configuration 2, wherein the ground electrode is twisted approximately 90 degrees at the twisted portion and bent toward the center at the bent portion,
The twisted portion is located on the base side with respect to the bent portion.

  According to the configuration 3, since the twisted portion does not exist in the bent portion, the twist and the bend can be made independent with respect to the design and the actual processing. As a result, manufacturing complexity can be suppressed, and manufacturing errors can be reduced.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the spark plug 100 of this embodiment includes a metal shell 1, an insulator 2, a center electrode 3, and a ground electrode 4. Although not particularly designated, the rear end side of the insulator 2 is provided with a connection terminal or the like electrically connected to the center electrode 3 via a resistor or a glass seal body. The metal shell 1 has a cylindrical shape, and an insulator 2 is held inside the metal shell 1 via talc, packing, or the like. The tip of the insulator 2 protrudes from the metal shell 1. The center electrode 3 is provided inside the insulator 2 with the noble metal tip 31 provided at the tip protruding. Furthermore, the ground electrode 4 is welded to the distal end surface of the metal shell 1 and is bent toward the center at the bent portion 5 at the middle position in the longitudinal direction. The ground electrode 4 is disposed such that the inner surface of the tip portion faces the tip surface of the center electrode 3. A noble metal tip 32 facing the noble metal tip 31 is provided on the inner surface of the ground electrode 4. A gap between the noble metal tip 31 and the noble metal tip 32 is a spark discharge gap 33.

  The insulator 2 is made of a ceramic sintered body made of alumina, for example, and has a hole 6 for arranging the center electrode 3 along its own axial direction. The metal shell 1 is formed in a cylindrical shape from a metal such as low carbon steel, and constitutes a housing of the spark plug 100, and the spark plug 100 is attached to an outer cylinder of the engine cylinder head (not shown). A threaded portion 7 is formed.

  The main body of the ground electrode 4 has a two-layer structure including an outer layer 4A and an inner layer 4B. The outer layer 4A is made of a nickel alloy or the like. On the other hand, the inner layer 4B is made of a metal having a better thermal conductivity than a nickel alloy (for example, a metal material mainly composed of copper or high-purity nickel having a higher thermal conductivity than the nickel alloy). In the present embodiment, in addition to the presence of the base 41 described later, the heat drawability (heat dissipation) is also improved by the presence of the inner layer 4B. In the present embodiment, the main body of the center electrode 3 also has a two-layer structure of an outer layer and an inner layer.

  The noble metal tip 31 on the center electrode 3 side is composed of a noble metal alloy containing, for example, iridium as a main component and containing 10% by mass of platinum, 3% by mass of rhodium, and 1% by mass of nickel. Further, the noble metal tip 32 on the side of the ground electrode 4 is made of a noble metal alloy containing, for example, platinum as a main component and containing 20% by mass of iridium and 5% by mass of rhodium. However, these material configurations are merely examples, and are not limited at all. Each noble metal tip 31, 32 is fixed to the metal shell 3 or the ground electrode 4 by a laser welding, an electron beam welding, a resistance welding, or the like, with a predetermined shape (for example, a cylindrical shape) along the outer edge portion of each joint surface. It is formed by.

  In this embodiment, both the electrodes 3 and 4 are provided with the noble metal tips 31 and 32, but the noble metal tip may be provided only on one of the ground electrode 4 and the center electrode 3. When the noble metal tip 31 is provided only on the center electrode 3, a spark discharge gap is formed between the noble metal tip 31 and the ground electrode 4 facing each other, and the noble metal tip 32 is provided only on the ground electrode 4. If so, a spark discharge gap is formed between the noble metal tip 32 and the center electrode 3 facing each other. On the other hand, no precious metal tip may be provided in any case. In this case, a spark discharge gap is formed between the front end surface of the center electrode 3 and the inner surface of the ground electrode 4.

As shown in FIGS. 1, 2, and 3, in the present embodiment, the ground electrode 4 is joined to the distal end surface of the metal shell 1 and has a base 41 having a certain width, and is positioned closer to the distal end than the base 41. A narrow circular portion 42 having a circular cross section, and a tapered portion 43 which is located between the base portion 41 and the narrow portion 42 and whose cross sectional shape gradually changes along the longitudinal direction. However, the “width” in the present embodiment refers to a width in a direction orthogonal to the axial direction (vertical direction in FIG. 1) when viewed in the direction in which the center electrode 3 and the ground electrode 4 overlap. The base 41 has a rectangular cross section with a width L1 of 2.7 mm and a thickness T1 of 1.3 mm, and the cross sectional area in the cross section is about 3.5 mm ² . The narrow portion 42 has a round bar shape with a diameter D of 1.3 mm, and has the bent portion 5 in the middle thereof. The base 41 is not necessarily limited to the above values, and the base 41 has a cross-sectional area of 3 mm ² or more, and the narrow portion 42 has a width (diameter D) of 1.0 mm or more and 2.0 mm or less. That's fine.

  Further, in the present embodiment, the portion γ of the narrow portion 42 closest to the base 41 is set so as to be positioned between the tip surface α of the insulator 2 and the tip surface β of the center electrode 3 in the axial direction. Has been. The tip surface β of the center electrode 3 here refers to the tip surface of the noble metal tip 31 when the noble metal tip 31 is provided on the center electrode 3, and when the noble metal tip is not provided, the center electrode 3. 3 Refers to the front end surface of the main body.

  Here, a method for manufacturing the spark plug 100 configured as described above will be briefly described. First, the metal shell 1 is processed in advance. That is, a metal material (for example, an iron-based material such as S15C or S25C or a stainless steel material) formed in a cylindrical shape is formed through holes by cold forging to produce a rough shape. Thereafter, the outer shape is trimmed by cutting to obtain a metal shell intermediate.

  Subsequently, the intermediate body of the ground electrode is resistance-welded to the tip portion of the metal shell intermediate body. The ground electrode intermediate body to be welded here is a straight rod before bending, and the portions corresponding to the narrow portion 42 and the tapered portion 43 on the tip side are somewhat larger than the final product. It has a cross-sectional area. More specifically, the ground electrode intermediate in the present embodiment has the same cross-sectional shape as the base 41 in the entire length. The ground electrode intermediate is obtained, for example, as follows. That is, the cup material which makes the core-sheath structure by enclosing the copper core which comprises the inner layer 4B in the nickel alloy cup which comprises the outer layer 4A is produced. Then, by subjecting the cup material to extrusion molding using a die or the like, a ground electrode intermediate body is obtained which is somewhat reduced in diameter and whose cross-sectional shape is the cross-sectional shape of the base portion 41.

  Since the so-called “sag” occurs in the resistance welding, after the “sag” is removed, the ground electrode intermediate is subjected to a swaging process. Thereby, the front-end | tip part of a ground electrode intermediate body is rounded and diameter-reduced, and the narrow part 41 mentioned above is formed. Since the ground electrode intermediate is already welded to the end face of the metal shell intermediate, swaging is performed with the metal shell intermediate held in the swaging process. In other words, since a sufficient length is secured for holding, stable swaging can be performed and workability can be improved.

  After the swaging process, the threaded portion 7 is formed by rolling at a predetermined portion of the metal shell intermediate. Thereby, the metal shell 1 to which the ground electrode 4 is welded is obtained. The metal shell 1 to which the ground electrode 4 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  Furthermore, the above-mentioned noble metal tip 32 is joined to the tip of the ground electrode 4 by resistance welding, laser welding or the like. In addition, in order to make welding more reliable, plating removal of a welding site is performed prior to the welding, or masking is performed on a planned welding site during a plating process. Further, the tip may be welded after assembling described later.

  On the other hand, the insulator 2 is molded separately from the metal shell 1. For example, a raw material powder containing alumina as a main component and containing a binder or the like is used to prepare a green granulated material for molding, and rubber press molding is used to obtain a cylindrical molded body. The obtained molded body is ground and shaped. Then, the shaped body is put into a firing furnace and fired, whereby the insulator 2 is obtained.

  In addition to the metal shell 1 and the insulator 2, the center electrode 3 is manufactured. That is, a Ni-based alloy is forged, and a copper core is provided at the center to improve heat dissipation. And the noble metal tip 31 mentioned above is joined to the front-end | tip part by resistance welding, laser welding, etc.

  The center electrode 3 to which the noble metal tip 31 obtained as described above is joined and the terminal fitting (not shown) are sealed and fixed to the hole 6 of the insulator 2 by a glass seal (not shown). As the glass seal, one prepared by mixing borosilicate glass and metal powder is generally used. First, the center electrode 3 is inserted into the hole 6 of the insulator 2, and after the prepared sealing material is injected into the hole 6 of the insulator 2, the terminal fitting is pressed from behind. And then baked and hardened in a firing furnace. At this time, the glaze layer may be fired simultaneously on the surface of the body portion on the rear end side of the insulator 2, or the glaze layer may be formed in advance.

  Thereafter, the insulator 2 provided with the center electrode 3 and the terminal fitting, respectively, produced as described above, and the metal shell 1 provided with the ground electrode 4 are assembled. More specifically, a part of the insulator 2 is formed on the metal shell 1 from the circumferential direction by performing cold crimping or hot crimping on the rear end portion of the metal shell 1 formed relatively thin. It is held so that it is surrounded.

  Finally, the spark discharge gap 33 between the center electrode 3 (the noble metal tip 31) and the ground electrode 4 (the noble metal tip 32) is bent by bending the tip portion (the narrow portion 42) of the ground electrode 4. Processing to adjust is performed.

  Thus, the spark plug 100 having the above-described configuration is manufactured through a series of steps.

As described above, according to the present embodiment, the side of the ground electrode 4 joined to the front end surface of the metal shell 1 has a cross-sectional area of 3.0 mm ² or more, and the base 41 having a larger cross-sectional area than the narrow part 42. It has become. For this reason, in the base 41, heat dissipation is achieved. For this reason, so-called “heat pulling” is improved, and it is possible to suppress problems due to an increase in the temperature of the ground electrode during high-speed operation or the like, that is, deterioration in durability such as oxidation resistance and spark wear resistance.

  Further, the narrow portion 42 on the distal end side has a width of 2.0 mm or less and has a circular cross section. For this reason, as shown in FIG. 3, even when the air-fuel mixture directly contacts the back surface of the ground electrode 4, the air-fuel mixture wraps around the narrow portion 42 and spark discharge occurs. The air-fuel mixture easily reaches the gap. As a result, a reduction in ignitability can be prevented.

  In addition, in the present embodiment, the portion γ of the narrow portion 42 closest to the base 41 is set to be positioned between the tip surface α of the insulator 2 and the tip surface β of the center electrode 3 in the axial direction. Has been. That is, in this embodiment, the heat dissipation is improved by making the section of the base 41 relatively large.

Here, if the section of the base is increased in the dark clouds, the mixture is inhibited from flowing into the spark discharge gap. In the present embodiment, the width of the narrow portion 42 is set to 2.0 mm or less, and the narrow portion 42 has a circular cross section, and therefore, as described above, a relatively large number of base sections are set. However, the ignitability is not lowered. That is, in the present embodiment, the narrow portion 42 has a circular cross section, the width is 1.0 mm or more and 2.0 mm or less, the cross-sectional area of the base is 3.0 mm ² or more, and the width The portion γ closest to the base 41 in the narrow portion 42 is configured to be positioned between the tip surface α of the insulator 2 and the tip surface β of the center electrode 3 in the axial direction. As a result, the durability can be prevented and the durability can be improved.

  Next, in order to confirm the above-described effects, various samples were prepared by changing various conditions, and various evaluations were attempted. The experimental results are described below.

  First, ground electrode samples with different base heights were prepared for a circular cross-section at the tip corresponding to the narrow portion and a rectangular shape similar to the base. Each sample does not have a taper portion, and the height of the base portion coincides with the height of the narrowest portion on the most base side. In addition, the cross-sectional area and width of the base and the width of the narrow portion (tip portion) were constant for all samples. Then, the ignition limit air-fuel ratio (A / F) was measured after setting the spark plug including each sample so that the air-fuel mixture directly hits the back surface of the ground electrode. The result is shown in the graph of FIG. However, in the graph, the position with a height of 3 cm on the horizontal axis corresponds to the tip surface α of the insulator, and the position with a height of 5 cm on the horizontal axis corresponds to the tip surface β of the center electrode. When measuring the ignition limit air-fuel ratio, each sample (spark plug) to be evaluated in the ignition device is attached to the test chamber, and the test chamber is a mixture of air and propane. Fill with gas, discharge the spark plug, and check for ignition of the mixture. Note that a fan is installed in the test chamber, and when discharging the spark plug, the fan is operated so that an air-fuel mixture flows from the back surface of the ground electrode to the spark discharge gap. This measurement was performed 10 times each time the various mixing ratios (air / fuel ratios) were changed for each sample, and the mixing ratio at the time when the misfire occurred twice was used as the ignition limit air / fuel ratio.

  As shown in the figure, in any sample, it is understood that the ignition limit air-fuel ratio is better when the cross section of the narrow portion is circular rather than rectangular. When the cross section of the narrow portion is circular, the height of the base (the height of the narrowest portion on the most base side) is between the tip surface α of the insulator and the tip surface β of the center electrode. All of the ignition limit air-fuel ratios of a sample were 16.5. On the other hand, even if the cross-section is circular, if the height of the narrowest portion on the most base side is higher than the front end surface β of the center electrode, the ignition limit air-fuel ratio has decreased. On the other hand, when the cross section of the narrow portion is rectangular, the height of the base portion (the height of the narrowest portion on the most base side) becomes 15.5 when the tip surface α of the insulator becomes higher. When the temperature is higher than that, the ignition limit air-fuel ratio further decreases. Therefore, it has a narrow section having a circular cross section, and the height position on the most base side of the narrow section exists between the front end surface α of the insulator and the front end surface β of the center electrode. It can be said that the reduction is prevented.

  Next, ground electrode samples were prepared in which the width of the base portion was constant, the cross-sectional shape of the tip portion corresponding to the narrow portion was circular, and the width (diameter) of the narrow portion was varied. Each sample did not have a taper portion, and the height of the base and the height (section) of the narrow portion (tip portion) were constant for all samples. Then, the ignition limit air-fuel ratio (A / F) was measured after setting the spark plug including each sample so that the air-fuel mixture directly hits the back surface of the ground electrode. The results are shown in the graph of FIG. The ignition limit air-fuel ratio here was also measured by the same method as described above.

  As shown in the figure, when the width of the narrow portion (tip portion) is 0.5 mm and 1.0 mm, the ignition limit air-fuel ratio is 17.0, and the width is 1.5 mm, 2 In the case of 0.0 mm, the ignition limit air-fuel ratio was 16.5 in all cases. On the other hand, when the width is 2.5 mm, the ignition limit air-fuel ratio has decreased to 15.5. For this reason, even if the narrow portion (tip portion) has a circular cross section, if the width exceeds 2.0 mm, the degree of decrease in the ignition limit air-fuel ratio increases, that is, the ignitability decreases. It can be said that it invites.

  Next, samples of ground electrodes were produced in which the cross-sectional area of the base portion and the width (diameter) of the narrow portion (tip portion) were varied. Each sample did not have a taper portion, and the height of the base portion and the height (section) of the narrow portion (tip portion) were constant for all samples. Then, a spark plug having each sample was attached to the engine, and a high rotation and high load state where the ground electrode is said to be the highest temperature was maintained for a certain period of time (specifically, a spark plug was attached to a 4-cylinder 1600 cc engine). The engine was driven with the throttle fully opened at 5500 rpm, and the tip temperature of the ground electrode was measured). Then, it was determined whether or not the highest temperature at the tip of the ground electrode was 1000 ° C. or lower. The results are shown in Table 1. However, in the table, a circle indicates that the highest temperature at the tip of the ground electrode was 1000 ° C. or less, and a mark × indicates that the highest temperature at the tip of the ground electrode exceeded 1000 ° C. Here, it was decided that the evaluation was performed at 1000 ° C. because it is empirically known that the durability such as oxidation resistance and spark wear resistance is extremely deteriorated when the temperature exceeds 1000 ° C. . That is, in the table, it can be evaluated that the durability is hardly lowered when the mark is ◯ and the durability is easily lowered when the mark is a mark X.

表１に示すように、幅狭部の幅が１ｍｍ以上２ｍｍ以下のサンプルについては、基部の断面積が３．０ｍｍ²以上であれば、接地電極先端の最も高い温度が１０００℃以下となった。一方、基部の断面積が３．０ｍｍ²であっても、幅狭部の幅が１ｍｍ未満のサンプルについては、接地電極先端の最も高い温度が１０００℃を超えてしまった。また、基部の断面積が３．０ｍｍ²未満のサンプルは、幅狭部の幅が２ｍｍのサンプルを除いて、接地電極先端の最も高い温度が１０００℃を超えてしまった。従って、幅狭部の幅が１ｍｍ以上２ｍｍ以下であり、基部の断面積が３．０ｍｍ²以上であれば、放熱性の向上を図ることができるといえる。
［第２実施形態］
次に、本発明の第２実施形態を図面を参照しつつ説明する。但し、本実施形態において、上記第１実施形態と重複する構成については同一の符号を付す等してその説明を省略するとともに、以下には、相違点を中心として説明することとする。図６，７に示すように、本実施形態のスパークプラグ２００も、主体金具１と、絶縁体２と、中心電極３と、接地電極５１とを備えている。本実施形態では、接地電極５１の構成が、第１実施形態と大きく相違している。

As shown in Table 1, for the samples having a width of the narrow portion of 1 mm or more and 2 mm or less, the highest temperature at the tip of the ground electrode was 1000 ° C. or less if the cross-sectional area of the base was 3.0 mm ² or more. . On the other hand, even when the cross-sectional area of the base portion was 3.0 mm ² , the highest temperature at the tip of the ground electrode exceeded 1000 ° C. for the sample having a width of the narrow portion of less than 1 mm. Further, the samples having a base cross-sectional area of less than 3.0 mm ² had the highest temperature at the tip of the ground electrode exceeding 1000 ° C., except for the sample having a width of 2 mm. Therefore, if the width of the narrow part is 1 mm or more and 2 mm or less and the cross-sectional area of the base part is 3.0 mm ² or more, it can be said that the heat dissipation can be improved.
[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to the drawings. However, in the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted, and the following description will be focused on the differences. As shown in FIGS. 6 and 7, the spark plug 200 of this embodiment also includes a metal shell 1, an insulator 2, a center electrode 3, and a ground electrode 51. In the present embodiment, the configuration of the ground electrode 51 is greatly different from that of the first embodiment.

  That is, the ground electrode 51 is configured by twisting a metal rod having a rectangular cross section, and at the base 52 on the side joined to the distal end surface of the metal shell 1 with the twisted portion 50 as a boundary, The width L21 is larger than the thickness T21, and the width L22 is smaller than the thickness T22 at the tip 53 that faces the tip of the center electrode 3 in the radial direction (circumferential direction).

  In the present embodiment, the ground electrode 51 is twisted approximately 90 degrees at the twisted portion 50 and is bent toward the center by the bent portion 60. The twisted portion 50 is located closer to the base portion 52 than the bent portion 60.

  According to the second embodiment having such a configuration, the base 52 bonded to the distal end surface of the metal shell 1 in the ground electrode 51 has a width L21 larger than the thickness T21, so that the area that can be bonded is large. The joining strength with respect to the limited metal shell 1 end face can be increased. As a result, durability can be improved.

  On the other hand, the width L22 is smaller than the thickness T22 at the tip 53 of the ground electrode 4. For this reason, even when the air-fuel mixture directly contacts the back surface of the ground electrode as shown in FIG. 7, the inflow of the air-fuel mixture into the spark discharge gap 33 is hardly hindered, and the spark discharge gap The air-fuel mixture easily reaches 33. As a result, a reduction in ignitability can be prevented.

  Further, in the ground electrode 51 of the present embodiment, the base 52 and the tip 53 are formed by twisting a metal rod having a substantially rectangular cross section. For this reason, in order to make the ground electrode partially thin or thick, it is not necessary to perform comparatively complicated processing such as cutting, extrusion, and swaging. That is, since the above-described characteristics can be obtained by performing a relatively simple twisting process, the effect of reducing the number of man-hours at the time of manufacture can be achieved.

  In addition, the twisted portion 50 is located closer to the base 52 than the bent portion 60. That is, since the twisted portion 50 does not exist in the bent portion 60, the twist and the bend can be made independent with respect to the design and actual processing. As a result, manufacturing complexity can be suppressed, and manufacturing errors can be reduced.

  In addition, it is not limited to the description content of embodiment mentioned above, For example, you may implement as follows.

  (A) In the first embodiment, the case where the narrow portion 42 of the ground electrode 4 has a circular cross section is embodied, but the invention is not necessarily limited to the circular cross section. That is, it is only necessary to have a convex curved surface on the back side opposite to the center electrode 3 side, and for example, it may be a ground electrode having an elliptical cross section, or the cross section is partially cut away. A circular ground electrode may be used. In this case, if the center electrode side is a flat surface, there is an advantage that it is easy to perform the work of welding the noble metal tip, which is convenient. Of course, it may be semicircular in cross section, oval, or may have a different curvature on the back. However, the width of the narrow portion needs to be 1.0 mm or more and 2.0 mm or less.

  (B) In the first embodiment, the tapered portion 43 is provided between the base portion 41 and the narrow portion 42. However, the tapered portion is omitted, that is, the boundary between the base portion and the narrow portion. May be stepped. Moreover, the base 41 may have a constant width L1 as in the first embodiment, or may be configured to be wider toward the metallic shell 1 side.

  (C) In the first embodiment, the ground electrode 4 has a two-layer structure including the outer layer 4A and the inner layer 4B. However, the ground electrode 4 may have a single layer or a three-layer structure. . Further, the inner layer 4B may extend to (expose) the tip surface of the ground electrode 4, or the tip surface of the ground electrode 4 may be covered with the outer layer 4A.

  (D) In the first embodiment, after the ground electrode intermediate body is welded to the metal shell intermediate body, the diameter is reduced by swaging, but after the diameter is reduced by swaging or the like, There is no problem with welding.

  (E) In the second embodiment, the ground electrode 51 is configured by twisting a metal rod having a substantially rectangular cross section. On the other hand, the ground electrode may be configured by twisting a metal rod having a substantially oval cross section or a substantially oval cross section.

  (F) In the second embodiment, it is described that the twisted portion 50 is preferably located on the base 52 side with respect to the bent portion 60. In this respect, more specifically, the tip of the twisted portion 50 is substantially the tip of the center electrode 3 [for example, the portion indicated by the one-dot chain line δ in FIG. It is more desirable that it is located at the height position equivalent to the boundary portion)]] or at the base end side. This is because the air-fuel mixture easily reaches the spark discharge gap 33 when the twist is completely completed at the height position of the spark discharge gap 33.

It is a partially broken front view which shows the structure of the spark plug of 1st Embodiment. It is a side view which shows the spark plug seen from the direction orthogonal to FIG. It is a top view which shows the state which looked at the spark plug from the front end side. It is a graph which shows the result of having measured the ignition limit air-fuel ratio, after preparing the sample from which the height of a base was variously made and setting it as the positional relationship that an air-fuel mixture directly hits the back surface of a ground electrode. It is a graph which shows the result of having measured the ignition limit air-fuel ratio after preparing the sample which varied the width | variety of a narrow part, and setting it as the positional relationship that an air-fuel mixture directly contacts the back surface of a ground electrode. It is a partially broken front view which shows the structure of the spark plug of 2nd Embodiment. It is a perspective view which mainly shows the ground electrode of the spark plug of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 4,51 ... Ground electrode, 33 ... Spark discharge gap, 41 ... Base part, 42 ... Narrow part, 50 ... Twist part, 52 ... Base part, 53 ... Tip Department.

Claims (3)

A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base end is joined to the front end surface of the metal shell, and the front end is disposed so as to face the front end surface of the center electrode; and a ground electrode.
A spark plug for an internal combustion engine having a spark discharge gap between a front end surface of the center electrode and a front end portion of the ground electrode,
The ground electrode is
A base portion joined to a front end surface of the metal shell,
It has a substantially constant width narrower than that of the base in a direction perpendicular to the axial direction when viewed in the direction in which the center electrode and the ground electrode overlap with each other, located on the tip side of the base. A narrow portion having a convex curved surface on the back surface opposite to the center electrode side,
While the width of the narrow part is 1.0 mm or more and 2.0 mm or less, the cross-sectional area of the base part is 3.0 mm ² or more,
The spark plug for an internal combustion engine, wherein the most proximal portion of the narrow portion is located between the distal end surface of the insulator and the distal end surface of the central electrode in the axial direction. A rod-shaped center electrode extending in the axial direction;
A substantially cylindrical insulator provided on the outer periphery of the center electrode;
A cylindrical metal shell provided on the outer periphery of the insulator;
A base end is joined to the front end surface of the metal shell, and the front end is disposed so as to face the front end surface of the center electrode; and a ground electrode.
A spark plug for an internal combustion engine having a spark discharge gap between a front end surface of the center electrode and a front end portion of the ground electrode,
The ground electrode is formed by twisting a metal rod having a substantially oval cross section, a substantially oval cross section, or a substantially rectangular cross section,
When viewed in the direction in which the center electrode and the ground electrode overlap, the width in the direction perpendicular to the axial direction is
In the base joined to the front end surface of the metal shell, it is larger than the thickness,
The spark plug for an internal combustion engine, characterized in that a tip portion facing the tip portion of the center electrode is smaller than a thickness. The ground electrode is twisted approximately 90 degrees at the twisted portion and is bent toward the center at the bent portion,
The spark plug for an internal combustion engine according to claim 2, wherein the twisted portion is located closer to the base than the bent portion.

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