JP2000252039A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spark plug for an internal combustion engine having a long service life, excellent in ignitability, and allowing reduction of a flash reducing effect from a center electrode and ground electrode. SOLUTION: In this spark plug, a front end face 6a of a center electrode 1 is formed with a recess 7 whose cross section gradually increases toward a ground electrode 4, while the front end face 6a has a spark consumption resistant member 6. The ground electrode 4 is formed such that a maximum width W of a portion of the ground electrode 4 facing to the center electrode 1 is narrower than a maximum width (d) of the front end face 6a of the center electrode 1, while an end edge part 4b of the ground electrode 4 is disposed opposite to the spark consumption resistant member 6. Thereby, a contact area of a spark with the front end face 6a of the center electrode 1 is reduced to reduce a flash reducing effect. Because the front end face 6a of the center electrode 1 has the spark consumption resistant member 6, electrode consumption of the center electrode 1 can be sufficiently suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine of an automobile or the like, and more particularly to a spark plug for an internal combustion engine having a long life and stable ignition performance.

[0002]

2. Description of the Related Art A general spark plug for an internal combustion engine (hereinafter, simply referred to as a spark plug) used for ignition of an internal combustion engine of an automobile or the like is a cylindrical metal shell and an insulator having a central through hole. An insulator held by being fitted into the metal shell and a center electrode inserted into the center through hole and held by surrounding the insulator with the insulator are provided. Further, a ground electrode having an opposing surface so as to be substantially parallel to the front end surface of the center electrode is fixed to the front end edge of the metal shell. With such a configuration, a discharge gap is formed in a gap between the two electrodes, that is, the tip surface of the center electrode and the opposing surface of the ground electrode.

[0003] In this discharge gap, a high voltage is applied to the center electrode from an ignition coil or the like, thereby causing a spark discharge. Then, a spark discharge is generated in the air-fuel mixture sucked into the combustion chamber, and the air-fuel mixture is ignited in the discharge gap to generate a flame kernel. The flame nuclei generated in the discharge gap contact the surrounding air-fuel mixture to grow a flame, burn the air-fuel mixture, and cause an explosion in the combustion chamber.

[0004]

However, the tip surface of the center electrode, which is the electrode surface forming the discharge gap, and the opposing surface of the ground electrode are generally formed in a substantially flat shape. The flame nucleus contacts the two electrode surfaces with a relatively large area. Therefore, during the process of growing the flame, the flame nucleus generated by the spark discharge may endothermic due to the cooling effect of both electrode surfaces. As a result, an effect called a so-called quenching effect occurs, in which the generated flame nucleus cannot grow the flame and cannot burn the air-fuel mixture.

For example, Japanese Patent Publication No. Sho 59-33949 discloses a spark plug in which a concave portion is formed on the front end surface of a center electrode. As described in the above publication, in the case where the concave portion is formed on the distal end surface of the center electrode, the surface area of the substantially flat surface of the distal end surface of the central electrode is reduced by forming the concave portion. Therefore, in the process of growing the flame by the flame core, the contact area between the flame kernel and the tip of the center electrode is reduced, and the flame kernel is less likely to be extinguished by the flame from the tip of the center electrode, reducing the occurrence of ignition errors and the like. Will be done.

Meanwhile, in order to maintain the effect of reducing the quenching action, the recess formed in the center electrode is left for a long period of time while the consumption of the center electrode progresses due to the aging with the use of the spark plug. It becomes important.
For that purpose, in the case of the above-mentioned publication technology, the concave portion must be formed considerably deeply or a plurality of times from the tip end surface of the center electrode. However, the formation of the concave portion on the front end face of the center electrode itself reduces the volume that contributes to the life of the center electrode, and shortens the service life of the spark plug. Therefore, if the recess is formed deeply or over a plurality of portions, the service life is further shortened. In addition, the concave portion formed on the front end surface of the center electrode is generally formed by cutting using a cutting blade or the like. However, in order to form the concave portion deeply or in a plurality, the center electrode is cut by a considerable amount. Processing must be performed, which increases the number of processing steps, and cannot be said to be excellent in terms of manufacturing cost and manufacturing efficiency.

[0007] For example, in Japanese Patent Application Laid-Open No. Hei 3-225784, a noble metal tip is joined to the tip surface of a center electrode, and a concave portion is formed near the joining surface (tip joining surface) between the tip surface of the center electrode and the noble metal tip. A disclosed spark plug is disclosed. As in the above-mentioned publication technology, by forming a concave portion near the tip bonding surface of the center electrode to which the noble metal tip is bonded, the thermal stress at the chip bonding surface is reduced, and the noble metal chip is prevented from falling off. It is possible to extend the life of the spark plug.

However, since the noble metal tip is generally very thin, the reduction of the flame-extinguishing effect by forming a concave portion near the chip joining surface as in the above-mentioned publication technology is very small.

By the way, the spark plug is assembled and fixed to the engine block (cylinder head), and the direction of the ground electrode in the state of being assembled to the engine block varies depending on the fixing direction of the spark plug. I will. In the combustion chamber, swirl (mixed air flow) is generated during the compression stroke. Therefore, depending on the direction of the ground electrode, the discharge gap (center electrode) is shaded by the ground electrode (ground electrode fixing portion) with respect to the swirl. May occur. That is, the ground electrode hinders the swirl, and the swirl cannot effectively contact the flame nucleus generated in the discharge gap, which may hinder the growth of the flame nucleus. In particular, in recent engines employing lean-burn or high-compression combustion systems, it is easy to ignite the air-fuel mixture to enable smooth operation, so the discharge gap is shaded by the ground electrode, resulting in swirl. If they cannot effectively contact the flame nucleus, ignition will not be easy and smooth operation will not be possible.

Therefore, in the configurations of Japanese Patent Publication No. 59-33949 and Japanese Patent Laid-Open Publication No. 3-225784, the swirl is effectively brought into contact with the flame nucleus generated in the discharge gap depending on the direction of the ground electrode. That is, the flame kernel may not be able to grow. Further, when a discharge gap is formed by a ground electrode having a width equal to or larger than the diameter of the center electrode, when the combustion chamber is cold when the engine is started or when the light load is low such as idling, It is feared that the flame nuclei generated in the discharge gap are also extinguished by the ground electrode.

As described above, when the flame nucleus generated in the discharge gap undergoes a phenomenon such as a quenching effect or a swirl hindrance by the ground electrode (interference between the flame nucleus and the swirl) in the process of growing the flame, The nucleus disappears and an ignition error occurs, which causes deterioration of the ignition performance of the spark plug. Alternatively, it is conceivable that an ignition delay due to a delay in the growth of the flame nucleus occurs, causing a problem that the thermal efficiency is reduced.

An object of the present invention has been made in view of the above problems, and has a long life, a reduced quenching effect from a center electrode and a ground electrode, and excellent ignitability. It is to provide a spark plug for an internal combustion engine having high performance.

[0013]

Means for solving the problems, means and effects to solve the problem, include a cylindrical metal shell, an insulator having a center through hole, held in the metal shell, and the center through hole. A center electrode inserted into the hole and held by the insulator; and a ground electrode fixed to a leading edge of the metal shell and having a facing surface facing the leading surface of the center electrode, A spark plug for an internal combustion engine in which a discharge gap is formed by the tip end surface of the center electrode and the ground electrode, wherein the tip end surface of the center electrode has a recess whose cross-sectional area gradually increases toward the ground electrode. Is formed, and a spark erosion resistant member is provided on the front end surface, and the maximum width of the ground electrode at a portion facing the center electrode is smaller than the maximum width of the front end surface of the center electrode. And the grounding electrode Edge of a spark plug for an internal combustion engine characterized by comprising arranged at a position opposite to the spark wear resistant member.

In the spark plug for an internal combustion engine having such a configuration, a concave portion whose cross-sectional area gradually increases toward the ground electrode is formed on the tip end surface of the center electrode so as to form a discharge gap with the ground electrode. The surface area of the substantially flat surface of the center electrode can be minimized. Accordingly, the area of the flame nucleus generated in the discharge gap in contact with the front end face of the center electrode when growing the flame is reduced, and as a result, the quenching effect of the center electrode can be reduced.

Since the center electrode has a spark erosion resistant member made of a simple substance or an alloy of platinum, iridium, tungsten, rhenium or the like, which is excellent in durability against spark erosion on the tip end surface of the center electrode. Even when the discharge is performed for a long time in the discharge gap, the electrode consumption of the center electrode can be sufficiently suppressed, and the concave portion (shape of the concave portion) formed in the center electrode can be sufficiently formed even after long-term use. Can be maintained.

The recess is formed so that its cross-sectional area gradually increases toward the ground electrode, and the edge of the ground electrode is formed by the upper edge of the wear-resistant member provided on the front end surface of the center electrode. And an outer edge portion, and is disposed at a position facing an upper end portion corresponding to the outer edge portion. As a result, the electric field is easily concentrated on the upper edge formed by the concave portion in the center electrode, and is easily concentrated on the edge of the opposing surface in the ground electrode. Discharge is likely to occur. Therefore, a flame nucleus is likely to be generated in the discharge gap near a portion (surface) separated from the center of the center electrode, and the flame nucleus becomes considerably large because a concave portion is formed on the tip end surface of the center electrode. Since it comes into contact with the center electrode in the state in which it is in a state of being extinguished, the quenching action can be reduced.

Further, the spark plug according to the present invention is configured such that a maximum width of a portion of the ground electrode facing the center electrode is smaller than a maximum width of the front end surface of the center electrode. When assembling to the engine cylinder head, even if the direction of the ground electrode (the direction of the ground electrode with respect to the swirl) varies and is fixed, the discharge gap (center electrode) is fixed to the ground electrode (the ground electrode fixing part) ) Less hiding behind. Therefore, since the swirl can effectively contact the discharge gap (center electrode), the flame nucleus generated by the spark discharge easily grows easily, and a good and stable ignitability can always be obtained, and the sparseness can be obtained. It enables smooth operation of engines that use the combustion system or the high compression combustion system.

Further, in the spark plug for an internal combustion engine, the spark consumable member may be made of platinum, iridium,
Selected from at least two of rhodium and having a melting point of 16
It is preferable to use a noble metal alloy having a temperature of 00 ° C. or higher.

In the spark plug for an internal combustion engine having the above structure, the spark consumable member is formed of a noble metal alloy selected from at least two of platinum, iridium and rhodium, so that the spark consumable member is provided on the end face of the center electrode. As a result, it is possible to obtain a spark plug with higher reliability because it is possible to prevent excessive temperature rise of the spark-resistant consumable member and to suppress oxidation and volatilization. Further, the spark-resistant consumable member,
By being configured to have a melting point of 1600 ° C. or higher, the heat resistance and durability (life) of the center electrode exposed to the combustion chamber under a high heat environment can be made extremely excellent.

[0020] In the spark plug for an internal combustion engine, the tip of the spark consumable member may be substantially flat, and may be formed substantially parallel to the surface facing the ground electrode.

Since the tip of the spark consumable member is formed in a substantially flat shape, the unevenness of both exposed surfaces of the discharge gap formed by the gap is reduced. Further, it is formed substantially parallel to the surface facing the ground electrode. Therefore, since the gap length of the discharge gap is set uniformly, the discharge gap does not increase rapidly even when the electrodes are worn out, and the discharge gap does not suddenly increase. It is possible to maintain the value of the discharge voltage for a long period of time.

The discharge gap may be formed such that a portion closer to the root side of the ground electrode fixed to the leading edge of the metal shell has a wider length than a portion closer to the opposite side. .

In the spark plug for an internal combustion engine having such a configuration, in the discharge gap, a portion closer to the root side of the ground electrode fixed to the leading edge of the metal shell has a wider length than a portion closer to the opposite side. When the length of the regular discharge gap is set near the opposite side, a large space for inflow (blowing) of the air-fuel mixture can be provided in the discharge gap near the base side. Thus, the mixture can be more smoothly flowed. As a result, the growth of the flame nucleus is further promoted, and more efficient, favorable and stable ignitability can be easily obtained.

[0024]

(Embodiment 1) Embodiments of the present invention will be described below with reference to the drawings. FIG.
FIG. 1 is an overall partial cross-sectional view showing a spark plug 100 for an internal combustion engine according to a first embodiment of the present invention. The spark plug 100 for an internal combustion engine has an axial direction (vertical direction in the drawing).
, A substantially cylindrical center electrode 1 made of a nickel alloy having excellent heat resistance and corrosion resistance, an insulator (insulator) 2 surrounding the center electrode, and a carbon steel (JI) holding the insulator.
S-G3507). The center electrode 1 has a resistor (not shown) at an intermediate portion, and its head is connected to a connection terminal 5 connected to an ignition coil or the like. Further, a V-shaped concave portion (not shown in FIG. 1) to be described later is formed on the tip end surface of the center electrode 1. Further, the metal shell 3 is formed with a screw (male screw) portion 3b for assembling and fixing to the engine block (cylinder head). A ground electrode 4 is fixed to the front edge 3a of the metal shell 3 by welding, and the front end of the ground electrode 4 is
a, which is bent back into a substantially L-shape so as to have a front end surface 6a of the center electrode and an opposing surface 4a to form a predetermined discharge gap.

Next, FIGS. 2A and 2B are enlarged views at the tip of the center electrode 1 which is a main part of the spark plug 100 for an internal combustion engine of the embodiment shown in FIG. In the present embodiment, the front end surface 6a of the center electrode 1 is formed in a substantially flat shape as described later.
A is formed with a V-shaped recess 7 whose sectional area gradually increases toward the facing surface 4a of the ground electrode 4. Where V
The U-shaped concave portion 7 is formed with a groove angle of 90 degrees. By forming such a shape, the surface area of the tip end surface 6a gradually increases while the consumption of the electrode (center electrode 1) progresses. In addition, it is possible to suppress as much as possible that the consumption of the electrode occurs early due to the formation of the concave portion 7.

On the tip end surface 6a of the center electrode 1 except for the recess 5, a spark consumable member 6 is provided. The spark erosion resistant member 6 is made of a material such as platinum, iridium, rhodium, palladium, gold, silver, ruthenium, rhenium, tungsten, molybdenum, zirconium, hafnium, osmium or the like, which is excellent in durability against spark erosion, or an alloy thereof. It is composed of
In addition, as the said spark consumable member 6, especially platinum,
A noble metal alloy selected from at least two of iridium and rhodium, and a noble metal alloy having a melting point of 1600 ° C. or more is preferable. By configuring the spark consumable member 6 with such a material (that is, a noble metal alloy), a spark plug excellent in suppression of oxidation and volatilization and extremely excellent in heat resistance can be configured (this embodiment). Then, the noble metal alloy constitutes the spark consumable member 6). In addition, the spark-resistant consumable member 6 can correspond to various required shapes such as a rectangular shape, a disk shape, and a cap shape. Have. Incidentally, as the various dimensions in the present embodiment, the diameter (width) d of the tip end surface of the center electrode was 2.5 mmΦ, and the thickness e of the spark consumable member was 0.4 mm.

Next, a method for forming the concave portion 5 in the center electrode 1 will be described with reference to FIGS. 3 (a) to 3 (c). First, as shown in FIG. 3A, a disk-shaped spark consumable member 6 having the same diameter (2.5 mmΦ) as the tip of the center electrode 1 is arranged on the tip of the center electrode. Third
As shown in FIG. 2B, the joint is made on the tip end surface 1a by, for example, resistance welding. Then, as shown in FIG. 3 (c), using a cutting knife (not shown), a depth (vertical direction in the figure) of about 0.8 from the top surface 6a of the spark consumable member 6 is formed.
A V-shaped recess 7 having a width of about 1.5 mm and a width of about 1.5 mm is formed.
At this time, the concave portion 7 is formed so as to have a shape having a groove angle of 90 degrees as described above.

Next, the ground electrode of this embodiment will be described with reference to FIG. In the present embodiment, the center electrode 1
0.5m than the diameter (width) d2.5mmΦ of the tip surface 6a of
The ground electrode 4 having a width w that is narrower by m, that is, a width w of 2.0 mm is provided (the thickness of the ground electrode 4 is 1.5 mm). Note that this ground electrode 4 is
As described above, the metal shell 3 is fixed to the front edge of the metal shell 3, and the front end of the metal shell 3 is attached to the front end face 6 a of the center electrode 1 having the spark consumable member 6 and the V-shaped recess 7 formed therein. The center electrode 1 is bent back into a substantially L-shape so as to form the front end surface 6a and the opposing surface 4a to form a discharge gap. Further, the edge 4 of the facing surface 4a of the ground electrode
“b” is formed so as to be disposed at a position facing the front end surface 6a of the center electrode 1 excluding the concave portion 7. Incidentally, the ground electrode 4 is bent back into a substantially L-shape after forming the V-shaped concave portion 5 on the tip end surface 6a of the center electrode to form a discharge gap.

By the way, as described above, by forming the edge 4b of the ground electrode 4 at a position facing the front end surface 6a of the center electrode 1, an electric field is formed by the recess 5 in the center electrode 1. Since it is easy to concentrate on the upper edge portion 6b and the outer edge portion 6c, and on the other hand, the ground electrode 4 easily concentrates on the edge portion 4b of the facing surface 4a. Become. That is, the spark path can be reliably set near the outer edge 6c of the center electrode (that is, the outer edge 6c of the spark erosion-resistant member 6) as shown in FIG. As a result, a flame nucleus is likely to be generated in the vicinity thereof, and in the process of growing the flame, the V-shaped recess 7 comes into contact with only the tip portion 6b whose substantially flat portion is reduced. As a result, by arranging the ground electrode having the above-described configuration, the flame nucleus hardly receives the quenching action from the center electrode 1, and the quenching action can be reduced.

Further, in the present embodiment, since the spark consumable member has a disk shape as described above in the present embodiment, the tip surface of the spark consumable member 6 (that is, the tip surface of the center electrode). That is, 6a is arranged in a substantially flat shape, and is arranged substantially in parallel with the facing surface 4a facing the ground electrode 4. Therefore, both electrode surfaces 6
The exposed electrode surface in the discharge gap formed by the a and 4a (both surfaces) has little unevenness (variation) and the gap length of the discharge gap is uniformly distributed. Variation can be further reduced, and good and stable ignitability can be provided.

(Embodiment 2) Next, a second embodiment will be described with reference to FIG. The spark plug 200 for an internal combustion engine according to the present embodiment includes a front end surface 6 of the center electrode 1.
a (that is, the tip of the spark consumable member 6) and the opposing surface 4 a of the ground electrode 4, the discharge gap of the ground electrode 4 fixed to the tip edge 3 a of the metal shell 3. The spark plug 200 has a structure in which the discharge gap Ga near the root side is bent back so as to be formed with a wider length than the discharge gap Gb near the opposite side. At that time, the discharge gap Gb
It is important that is set to have a regular (predetermined) discharge gap length. With this configuration, the air-fuel mixture (swirl) that flows into the ground electrode without hindrance
In contrast, compared to a discharge gap in which the tip surface of the center electrode and the opposing surface of the ground electrode are generally constant and narrow, a larger space for inflow (blow-through) of the air-fuel mixture is formed. Will be done. Therefore, the inflow (blow-through) of the air-fuel mixture is performed more smoothly, and the growth of the flame kernel generated in the discharge gap is further promoted.

In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above-described embodiments, and it can be said that the present invention can be appropriately modified and applied without departing from the gist thereof. Not even. For example, in the first embodiment, an example is shown in which a disk-shaped spark consumable member is resistance-welded to the front end surface of the center electrode and then a V-shaped recess is formed (see FIG. 3). Fig. 7 (a)-
As shown in (c), at least two kinds of platinum, iridium, and rhodium are selected from the outer edge 6b of the front end surface 6a of the center electrode 1, that is, the position on the front end surface 6a where the concave portion 5 is not formed in a later step. Alternatively, a granular material 8 made of a noble metal alloy having a melting point of 1600 ° C. or more may be provided. This includes:
By irradiating a laser such as a YAG laser from above the granular material 8, the granular material 8 is melted to form a fused spark-resistant consumable member 6 'on the tip surface 6a, and a cutting knife (not shown) A method of forming a V-shaped recess 7 having a depth of about 0.8 mm and a width of about 1.5 mm from the top surface 6a of the center electrode 1 excluding the spark consumable member 6 'melted by using Can be By forming the spark consumable member 6 'by such a method, an expensive noble metal alloy is arranged on the front end face 6a of the center electrode 1, and the noble metal alloy itself is processed and cut with a cutting knife or the like. Since there is no need to apply the spark plug, it is possible to contribute to cost reduction of the spark plug.

In the spark plug for an internal combustion engine obtained from the first and second embodiments, as shown in FIG. 8, the concave portion 7 is formed at the tip end surface of the original center electrode 1 (including the spark consumable member 5). ) Is expanded outward by about 20% from the diameter (width) of the center electrode 1 (spark consumable member 6).
a and a ground electrode 4 opposed to the front end surface 6a may form a spark plug in which a discharge gap is formed.
Alternatively, the shape of the recess is not limited to the V-shape, and a spark plug formed in a U-shape or the like may be used.

Further, a member made of the same material as the spark consumable member provided on the front end surface of the center electrode is welded on the opposite surface of the ground electrode, and the heat resistance, durability,
That is, a spark plug having a structure with an improved life may be used.

[0035]

EXAMPLES The following experiments were conducted to confirm the effects of the present invention. (Example 1) V is applied to the center electrode 1 shown in the first embodiment.
And a spark consumable member 6
The spark plug 100 for an internal combustion engine having the above was manufactured with the dimensions and materials exemplified above, and the life of the spark plug 100 was evaluated. Here, in evaluating the life, a judgment (evaluation) was made by examining the change in the amount of electrode wear of the center electrode 1 of the actual spark plug 100, that is, observing the change in the increase in the discharge gap with respect to the traveling distance. Incidentally, the evaluation was performed by setting the length of the discharge gap to 1.1 mm. In evaluating the life of the spark plug 100 according to the first embodiment, a concave portion having the same shape (same dimension) as that of the first embodiment is simply provided without a spark consumable member on the tip end surface of the center electrode. A spark plug having the same was manufactured and comparatively evaluated under the same conditions (the length of the discharge gap in the spark plug to be compared was also set to 1.1 mm).
The results are shown in FIG. 9A in which the horizontal axis represents the traveling distance and the vertical axis represents the increase in the discharge gap.

As apparent from FIG. 9 (a), a spark plug having only a V-shaped recess without a spark consumable member (that is, a spark plug to be compared) discharges. Large increase (change) in gap length
In contrast, in the spark plug of the first embodiment, the increase (change) in the discharge gap was almost halved. From the result, the spark plug 100 according to the first embodiment is shown.
Is provided with the concave portion 7 by having the spark consumable member 6.
It can be seen that even a spark plug having the following characteristics can maintain the service life of the spark plug for a long time and can maintain the concave portion 7 (shape of the concave portion) for a long period of time.

Further, according to the present embodiment, in the spark plug 100 for an internal combustion engine having the configuration as in the first embodiment, the increase (change) in the discharge gap is hardly observed as described above. It can be seen that the discharge voltage (required voltage) at is also kept substantially constant with little change. That is, it can be seen that the discharge voltage (required voltage) preset in the early stage of use of the spark plug can be maintained for a long time.

Example 2 In the spark plug 100 of the first embodiment, the width w (2.0
mm) is the diameter (width) d (2.5 mm) of the distal end surface 6a of the center electrode 1.
mmΦ), the direction in which each of the grounding electrodes 4 is fixed when formed to be narrower than that of
Was evaluated for the effect of ignitability (discharge gap length was 1.1 mm). In the spark plug 200 according to the second embodiment, the width w (2.0 mm) of the ground electrode 4 is set to the diameter (width) d of the front end surface of the center electrode.
(2.5 mmΦ), and the discharge gap length Ga with the center electrode near the root side of the ground electrode 4 fixed to the front edge 3 a of the metal shell 3 is 0.9 mm. The spark plug 200 having a discharge gap length Ga (regular discharge gap length) of 1.1 mm near the opposite side was also evaluated under the same conditions as described above. In these evaluations, in-line 6 cylinder 2000cc,
The DOHC four-cycle gasoline engine has the same shape without having the spark plug 100 of the first embodiment, the spark plug 200 of the second embodiment, and the spark consumable member on the front end surface of the center electrode. (The same dimension), the width w of the ground electrode and the diameter (width) d of the tip surface of the center electrode.
(The spark plug to be compared, the discharge gap length is assumed to be 1.1 mm) with the same length set in the same size, and fixed.
After assembling them so as to be in the direction of the ground electrode as shown in (d), the air-fuel ratio (A / F), which is the ignition limit, was obtained under idling conditions, and the ignitability was compared (evaluated). The results are plotted on the horizontal axis with the direction of the ground electrode (a) to (d).
FIG. 9B in which the ignition limit is set on the vertical axis.

From this result, it is found that, under a mixed gas flow (swirl) having a constant flow, the center electrode has a concave portion having the same shape without having a spark consumable member on the tip end surface, and has a ground electrode. In particular, in the case of the spark plug in which the width w of the center electrode is set to be equal in the length (diameter) d of the tip surface of the center electrode (that is, the spark plug to be compared), in particular, in FIG. In the direction of the ground electrode, a great difference was observed in the ignitability as compared with the one assembled in another direction. On the other hand, the width w of the ground electrode 4 is set to the tip surface 6a of the center electrode 1.
In the spark plug 100 according to the first embodiment formed to be smaller than the diameter (width) d of FIG.
In any of the directions shown in (a) to (d), the difference in the ignitability was slightly different. Then, the width w of the ground electrode 4 is set to the tip surface 6 of the center electrode 1.
The discharge gap length Ga between the center electrode 1 near the root side of the ground electrode 4, which is formed to be smaller than the diameter (width) d of a and is fixed to the leading edge 3 a of the metal shell 3, Discharge gap length Gb near the opposite side (regular discharge gap length)
In the second spark plug 200 formed larger,
Even when the ground electrode 4 is assembled in any of the directions shown in FIGS. 9B and 9A to 9D, there is almost no variation in the difference in ignitability, and the spark plug of the first embodiment is not changed. 1
The ignitability was better than 00.

Therefore, the spark plugs 100 and 200 according to the first and second embodiments are fixed to the engine block (cylinder head) and fixed even when the direction of the ground electrode 4 varies. It can be seen that the (center electrode) has a structure that is not hidden behind the ground electrode 4 with respect to the swirl. That is, it is understood that the flame nucleus generated in the discharge gap can effectively contact and grow with the swirl without being hindered by the ground electrode 4, and is a spark plug that easily obtains stable ignitability. . Furthermore, by providing the structure of the spark plug 200 of the second embodiment, it is possible to smoothly carry in the swirl (blow-through) regardless of the direction of the ground electrode 4 and to provide a spark plug having higher ignitability. can do.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional overall view of an internal combustion engine spark plug according to a first embodiment.

FIG. 2 is an enlarged sectional view of a main part of the spark plug for an internal combustion engine according to the first embodiment.

FIG. 3 is an explanatory diagram illustrating a method of forming a spark-resistant consumable member disposed on a front end surface of a center electrode of the spark plug for an internal combustion engine according to the first embodiment, and a method of forming a V-shaped recess. is there.

FIG. 4 is an enlarged sectional view of a main part showing a relationship between a center electrode and a ground electrode of the spark plug for an internal combustion engine according to the first embodiment.

FIG. 5 is a diagram illustrating a spark path of a spark plug for an internal combustion engine according to the first embodiment (FIG. 4).

FIG. 6 is an enlarged sectional view of a main part of a spark plug for an internal combustion engine according to a second embodiment.

FIG. 7 shows a method of forming a spark-resistant consumable member disposed on a front end surface of a center electrode of the spark plug for an internal combustion engine shown in FIG. 3 of the first embodiment, and a method of forming a V-shaped concave portion. It is explanatory drawing about another method.

FIG. 8 shows the diameter (width) of the front end face of the original center electrode via the recess.
FIG. 2 is an enlarged cross-sectional view of a main part of the spark plug for an internal combustion engine that is further expanded outward.

FIG. 9 is a graph (a) showing the relationship between the travel distance and the increase amount of the discharge gap in Experimental Example 1, and Experimental Example 2;
7B is a graph (b) showing the relationship between the influence of ignitability on the flow (swirl) of the air-fuel mixture by the direction in which each of the spark plugs (ground electrodes) is attached and fixed in FIG.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 100, 200 Spark plug for internal combustion engine 1 Center electrode 2 Insulator 3 Metal shell 4 Ground electrode 6, 6 'Spark-resistant wear-resistant member 6a Tip surface 7 Recess

Claims (4)

[Claims] 1. A cylindrical metal shell, an insulator having a center through-hole and held in the metal shell, and a center electrode inserted into the center through-hole and held by the insulator. A ground electrode fixed to a leading edge of the metallic shell and having a facing surface facing the leading surface of the center electrode, wherein a discharge gap is formed by the leading surface of the center electrode and the ground electrode. A spark plug for an internal combustion engine formed, wherein the tip end surface of the center electrode is formed with a concave portion whose cross-sectional area gradually increases toward the ground electrode, and a spark consumable member is provided on the tip end surface. The maximum width of a portion of the ground electrode facing the center electrode is formed to be smaller than the maximum width of the front end surface of the center electrode, and the edge portion of the ground electrode is Arrange it at the position facing the spark consumable member. A spark plug for an internal combustion engine characterized by being made. 2. The spark erosion resistant member is made of an alloy selected from at least two of platinum, iridium, and rhodium, and is made of a noble metal alloy having a melting point of 1600 ° C. or higher. Claim 1
A spark plug for an internal combustion engine according to claim 1. 3. The device according to claim 1, wherein a tip portion of the spark consumable member has a substantially flat shape and is formed substantially parallel to a surface facing the ground electrode. The spark plug for an internal combustion engine according to the above. 4. The discharge gap is formed such that a portion closer to a root side of the ground electrode fixed to a leading edge portion of the metal shell has a wider width than a portion closer to the opposite side. The spark plug for an internal combustion engine according to claim 1.