JP2000208234A - Spark plug and ignition system using this spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve ignitability and durability by setting a diameter of a tip part being a firing part as a thin diameter not more than a specific value in a central electrode, arranging earth electrodes so as to project to the tip side from an end surface of a main body metal fitting, and forming opposed surfaces of the earth electrodes being the firing part so as to be opposed to a side peripheral surface of a thin diameter part of the central electrode. SOLUTION: A central electrode 2 is diametrically contracted in a taper shape in a place coming out of an insulating insulator 1, and the tip part is formed as a thin diameter not more than 1.9 mm. A spark resistant consuming member 21 composed of platinum is fixed to the side periphery of this thin diameter part by laser welding. Two earth electrodes 11, 11 are arranged in mutually opposing positions, and are arranged so as to project to the tip side from an end surface of a main body metal fitting 5. In the earth electrodes 11, 11, tip parts are bent by 90 degrees, and an end surface 11A being the opposed surface is opposed to a side peripheral surface of the central electrode 2. The spark resistant consuming member 21 arranged in the central electrode 2 is slightly widely arranged so that the lower edge comes to the retreat side close to a retreat side edge position of the end surface 11A of the earth electrodes 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spark plug used as an ignition device for an internal combustion engine and an ignition system for the same.

[0002]

2. Description of the Related Art In a high-performance, high-output internal combustion engine, particularly in a two-wheeled internal combustion engine, breakage of the outer ground electrode and overheating of the ground electrode due to mechanical vibration cause problems. It is difficult to apply a protruding spark plug. In the case of small-diameter spark plugs such as M10 and M8, the cross-sectional area of the ground electrode must be reduced due to the dimensional restrictions of the metal shell, and it is difficult to protrude the ground electrode as in the parallel electrode type. For this reason, a multi-pole type spark plug in which a plurality of ground electrodes are arranged opposite to the side circumference of the center electrode has been used in such an internal combustion engine. In a multi-pole type spark plug, consumption of the center electrode becomes a major problem. Therefore, Japanese Patent Application Laid-Open No. H6-176849 proposes a structure in which a noble metal film such as platinum is provided on the side circumference of a center electrode. Japanese Patent Laid-Open Publication No. Hei 9-330783 proposes a center electrode having a large diameter at the tip to improve the ignitability.

In a standard parallel electrode spark plug, the required voltage is lower in the negative polarity, so that a negative ignition system for applying a high negative voltage to the center electrode has been generally used. For this reason, a spark plug of a negative polarity is often used even for a multipolar spark plug in which the required voltage does not change much depending on the polarity.Sometimes, a spark plug using a bipolar ignition system for cost reduction is occasionally found. Stopped.

[0004]

However, the spark plug described in Japanese Patent Application Laid-Open No. H6-176849 is a semi-surface discharge type spark plug, and is susceptible to channeling over a long period of use. was there. Further, in the spark plug described in Japanese Patent Application Laid-Open No. 9-330783, there is a problem that the ignition voltage is improved, but the effective voltage of the center electrode is increased, so that the discharge voltage is increased. In general, the smaller the diameter of the center electrode, the lower the discharge voltage and the better the ignitability. However, when the diameter of the center electrode is small, electrode wear is severe and uneven wear of the ground electrode occurs, so that there is a problem that the life of the spark plug is shortened and the spark plug cannot be put to practical use.

Accordingly, the present invention is used for a high-output, high-performance internal combustion engine, which can prevent the outer ground electrode from being broken or overheated, has excellent ignitability, is durable and has a long life. It is an object to provide a long spark plug and its ignition system.

[0006]

To achieve the above object, according to the present invention, there is provided an insulator having a center through hole, a center electrode held in the center through hole, In a spark plug including a metal shell for holding the insulator and a ground electrode electrically connected to the metal shell, the center electrode and the ground electrode are discharged with a polarity such that the center electrode side is positive. High voltage is applied, the center electrode has a small diameter of 1.9 mm or less at a tip portion serving as a firing portion, and the ground electrode is located at a tip side from an end face of the metal shell. Is provided to protrude,
It is characterized in that the opposing surface of the ground electrode serving as the ignition portion is formed so as to oppose the side peripheral surface of the small diameter portion of the center electrode.

According to an endurance experiment in which the spark plug thus formed is used in a positive polarity, that is, a method in which a positive high voltage is applied to the center electrode, the electrode consumption of the center electrode is smaller than that in the case where the center electrode is used in a negative polarity. Markedly decreased. The reason for this is
At the time of discharge, cations existing between the discharge gaps move to and collide with the negative electrode, and anions or electrons move and collide with the positive electrode. It is considered that the cations are much heavier than the anions or electrons, so that the consumption caused by the collision is due to the fact that the electrode on the negative electrode side where the cations collide increases and the temperature of the electrode tends to rise. When the center electrode is used with a negative polarity, the durability is rapidly deteriorated when the diameter is less than 2 mm. On the other hand, when the center electrode is used with a positive polarity, there is no such tendency.
m or more of the same degree as when a center electrode with a negative polarity is used,
Alternatively, a higher durability could be obtained.

When the diameter of the center electrode is 1.9 mm or less, the effect of using the positive polarity is remarkably exhibited. If the center electrode is made too thin, the balance between heat reception and heat radiation is lost and the center electrode is overheated. Therefore, the diameter of the center electrode is 0.4
mm or more, more preferably 0.6
mm to 1.8 mm is desirable.

As for the discharge voltage, a low voltage corresponding to the thin center electrode could be maintained. Since the center electrode has a small diameter, the ignitability was improved, the consumption pattern of the ground electrode was uniform, and uneven consumption was reduced. Furthermore, since the ground electrode only needs to face the side peripheral surface of the center electrode, the amount of protrusion of the ground electrode from the metal shell may be small, and breakage and overheating of the outer ground electrode can be prevented.

Here, the tip surface of the center electrode is located between the leading edge and the receding edge of the opposing surface of the ground electrode. It can be. When formed in this way, the number of sparks at the tip of the center electrode increases, and the ignitability improves accordingly. In addition, the wear of the ground electrode becomes more uniform, and uneven wear is reduced.

Here, the invention can be characterized in that the center electrode is provided with a spark consumable member at least in a part of the small diameter portion. Here, the spark-resistant consumable member refers to any precious metal material having a melting point higher than that of Inconel, which is a nickel alloy excellent in corrosion resistance and commonly used as an electrode material. More specifically, platinum (P)
t), platinum-iridium (Pt-Ir), platinum-nickel (Pt-Ni), platinum-iridium-nickel (Pt
-Ir-Ni), platinum - rhodium (Pt-Rh), iridium - rhodium (Ir-Rh), iridium - yttria (Ir-Y ₂ O ₃₎ a noble metal such as noble metal alloy, or members such as precious metal sintering body Say everything.

With such a configuration, the small diameter portion of the center electrode on which the spark is concentrated is less consumed, and the life of the spark plug is prolonged accordingly. In addition, since the tip of the center electrode is prevented from being rounded due to wear, the concentration of sparks at the tip can be maintained and the improvement of ignitability can be maintained.

Here, as in the fourth aspect of the present invention, the spark consumable member provided on the center electrode is provided from the position of the retreat side edge of the surface facing the ground electrode to the position on the retreat side. It can be characterized. When formed in this way, even if the spark from the ground electrode flows to the retreat side of the spark plug due to the strong airflow in the combustion chamber, the spark that reaches the center electrode reaches the portion where the spark-resistant consumable member is present,
Prevents wear of the center electrode.

According to the fifth aspect of the present invention, when the ground electrode is provided with a spark consumable member on at least a part of the opposing surface thereof, the center electrode is formed. The wear of the opposing surface, which is the flying surface of the ground electrode arranged on the side, is reduced, and the life of the spark plug is prolonged accordingly.

Here, as in the invention according to claim 6, there is provided an ignition system characterized in that a positive high voltage is applied to the center electrode of any one of the above spark plugs to ignite. Can be. According to experiments, when the ignition system is configured as described above, the wear of the center electrode is reduced despite its small diameter, and the durability is improved. And since the center electrode has a small diameter, the ignitability is improved.

[0016]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional view of a spark plug 20 according to the present invention. As is well known, the insulator 1 made of alumina or the like includes a corrugation portion 1A for increasing a creepage distance at an upper portion thereof, and a leg portion 1B at a lower portion exposed to a combustion chamber of an internal combustion engine. Center through hole 1
C is provided. At the lower end (tip) of the center through hole 1C,
A center electrode 2 made of a nickel alloy such as Inconel or 95 wt% nickel is held, and the center electrode 2 protrudes downward from a lower end surface of the insulator 1. Although the center electrode 2 is not actually composed of a single nickel alloy, copper (Cu) is sealed as a core at the center thereof to improve the thermal conductivity, but the drawing is complicated because the drawing becomes complicated. Not. The center electrode 2 is electrically connected to an upper terminal 4 via a glass resistor 3 provided inside the center through hole 1C. A high-voltage cable (not shown) is connected to the terminal 4 to apply a high voltage. The insulator 1 is supported by being surrounded by a metal shell 5.

The metal shell 5 is made of a low-carbon steel material, and has a hexagonal portion 5A fitted with a spark plug wrench and a screw portion 5B screwed into a cylinder head. The metal shell 5 is caulked to the insulator 1 by the caulking portion 5C,
The metal shell 5 and the insulator 1 are integrated. In order to complete the sealing by caulking, the inner peripheral step 5
The seal between the leg 1B exposed to the combustion chamber and the upper part of the insulator 1 is completed by interposing a plate-like packing member 6 between the insulator E and the insulator 1. In addition, wire-shaped sealing members 7 and 8 are interposed between the caulked portion 5C and the insulator 1, and talc (filled talc) 9 powder is filled between the sealing members 7 and 8 to elastically seal. The metal shell 5 and the insulator 1 are completely fixed. Of course, a spark plug having no talc 9 may be used. A gasket 10 is fitted at the upper end of the screw portion 5B. Two ground electrodes 11 made of a nickel alloy are joined to the lower end of the metal shell 5 by welding. The ground electrodes 11, 11 are formed such that their end faces, which face each other, face the peripheral surface of the center electrode 2.

FIG. 2 is an enlarged sectional view showing the tip of the spark plug according to the first embodiment. It is drawn upside down from FIG. 1 with the tip up. The center electrode 2 is tapered at the point where it comes out of the insulator 1 and has a narrower tip. The reason why the entire central electrode 2 is not made small in diameter and the root portion is made thicker is to improve heat drawing and prevent overheating of the tip of the central electrode 2. A spark-resistant consumable member 21 made of platinum (Pt) is fixed to the periphery of the small-diameter portion at the end of the center electrode 2 by laser welding. Two ground electrodes 11, 11
Are disposed at 180 degrees from each other, and are provided so as to protrude from the end surface of the metal shell 5 to the front end side. The ground electrode 1
The end portions 1 and 11 are bent at 90 °, and the end surface 11A which is the opposing surface thereof is opposed to the side peripheral surface of the center electrode 2. The lower end of the spark consumable member 21 provided on the small diameter portion of the center electrode 2 has an end surface 1 of the ground electrode 11.
1A is provided slightly wider so as to be on the retreat side (lower side in the drawing) from the position of the edge of the retreat side (lower side in the figure).

The details of the dimensions of each part will be described. The diameter A of the small diameter portion at the tip of the center electrode 2 is A = 0.6 (unit: mm, the same applies hereinafter), A = 1.2, A = 1.8, A =
Five types of spark plugs of 2.0 and A = 2.5 were prepared. The former three types are spark plugs according to the present invention, and the latter two types are spark plugs for comparison.
The length B of the small diameter portion of the center electrode 2 is B = 2.5, the length C of the tapered portion is C = 1.0, and the protrusion amount D of the insulator 1 from the metal shell 5 is D = 2. .5. Ground electrode 11
Has a rectangular shape, and its thickness E is E = 1.
6, the width W (not shown) is W = 2.7, and the protruding amount F of the ground electrode 11 from the metal shell 5 is F = 6.
0. That is, the position of the tip of the center electrode 2 coincides with the position of the edge on the tip side of the ground electrode 11. The air gap G between the side peripheral surface of the center electrode 2 and the edge 11A of the ground electrode 11 was set to G = 1.1. In addition, metal shell 5
The diameter of the threaded portion 5B was standard M14.

Therefore, the former three types of spark plugs according to the embodiments of the present invention satisfy the requirements of claim 1, claim 2, claim 3, and claim 4. These three types of spark plugs and the latter two types of spark plugs for comparison were subjected to an actual machine durability test in a high-speed pattern durability mode. The engine used was a 2-liter 6-cylinder in-line cylinder, and was operated at 3000 rpm to 5500 rpm corresponding to an average vehicle speed of 140 Km / Hr for 700 hours. This is equivalent to traveling about 100,000 km. The results of the actual machine durability test are shown in four graphs in FIGS. In the figure, ● indicates that the diameter A of the small diameter portion of the center electrode is A
= 0.6, ■ is the diameter A of the small diameter part,
A = 1.2 spark plug, ◆ is the diameter A of the small diameter part
Shows spark plugs with A = 1.8, respectively. On the other hand, △ indicates that the diameter A of the small diameter portion of the center electrode is A = 2.
0, spark plug, ○: diameter A of small diameter portion, A =
2.5 shows a spark plug. In other words, black symbols 記号 indicate three types of spark plugs according to the present invention, and white symbols △ indicate two types of spark plugs for comparison.

FIG. 3 is a graph showing the gap consumption when these five types of spark plugs are used with the conventional negative polarity. The horizontal axis is the endurance operation time (the unit is the time Hr), and the vertical axis is the gap consumption (the increase in the air gap G,
The unit is mm). As is apparent from the figure, in the spark plug according to the present invention indicated by the black solid symbol ● ■ ◆, the gap consumption rapidly progresses from around 400 Hr, and at 700 Hr, the thick center electrode indicated by the white symbol △ The gap between the spark plug and the spark plug shows a large gap. That is, a spark plug having a thin center electrode having a diameter A of 1.8 mm or less has a negative polarity,
Gap wear is large and not practical.

FIG. 4 is a graph showing the amount of gap consumption when these five types of spark plugs are used with opposite polarities of positive polarity. The horizontal axis and the vertical axis are the same as in FIG. In the positive polarity, the difference in gap consumption due to the center electrode diameter A is small,
All spark plugs have a similar tendency, and the gap consumption increases with the endurance operation time. And 700H
Even after elapse, the tendency is observed that the smaller the center electrode, the larger the amount of consumption, but the difference is small.
The gap consumption of 2 mm or less is maintained. That is,
Even with a spark plug using a small-diameter central electrode having a diameter A of 1.8 mm or less, the gap consumption is reduced and the durability is improved if used with a polarity opposite to the normal polarity.

FIG. 5 is a graph showing a change in discharge voltage when these five types of spark plugs are used with the conventional negative polarity. The discharge voltage was indicated by the instantaneous maximum discharge voltage at the time of idle racing in which the engine was blown with no load. The unit is KV (kilovolt). In a new state where the durable operation time is 0 Hr, the smaller the diameter A of the center electrode, the lower the discharge voltage. This is the result as before. However, the discharge voltage was reversed in the 200-hour endurance operation, and a discharge electrode having a smaller diameter A of the center electrode showed a higher discharge voltage.
In the endurance operation at 700 hours, the difference in the discharge voltage due to the diameter A of the center electrode widened, and the discharge voltage exceeded 25 KV in the case where the diameter A of the center electrode was small (■ ◆) according to the present invention.

FIG. 6 is a graph showing a change in discharge voltage when these five types of spark plugs are used with opposite polarities of positive polarity. The horizontal axis and the vertical axis are the same as in FIG. In the case of the positive polarity, the characteristic that the smaller the diameter A of the center electrode in a new state is, the lower the discharge voltage is, which is maintained even after the durable operation time has elapsed, and the reversal phenomenon of the discharge voltage as shown in FIG. I can't. The discharge voltage increases with an increase in the durable operation time, but the rate of increase is relatively slow. And
Even after 700 hours of endurance operation, the center electrode according to the present invention having a small diameter A (● ■ ◆) has a large diameter A (○ △).
It showed a lower discharge voltage. In other words, even after a long-term durable operation, if used with the opposite positive polarity, the diameter A
The spark plug according to the present invention using the center electrode having a small diameter of 1.8 mm or less was able to maintain a relatively low discharge voltage.
This means that the durability of the spark plug has been improved.

Next, of these five types of spark plugs, the diameter A of the small diameter portion of the center electrode 2 was set to the spark plug of A = 1.8, and the case of the conventional negative polarity and the case of the positive polarity of the present invention were used. In each case, the temperature of the center electrode was examined. Table 1 shows the results.
Shown in This test was carried out with a spark plug attached to a desktop chamber tester and the internal pressure increased to 6 atm. Then, each polarity was discharged at a cycle of 60 times / second and 100 times / second using an automobile ignition power source.

[0026]

[Table 1]

As is clear from Table 1, the temperature of the center electrode could be considerably reduced by making the electrode positive, as compared with the conventional negative electrode. This also becomes a factor that works favorably against the consumption of the center electrode and the increase in the discharge voltage.

Further, of these five types of spark plugs, the spark plug having the diameter A of the small diameter portion of the center electrode 2 of A = 1.8 is the same as the case of the conventional negative polarity and the case of the positive polarity of the present invention. The ignitability was compared. Table 2 shows the values of 7
4 is a table showing changes in the air-fuel ratio (A / F) serving as an ignition limit in a spark plug before and after a 00-hour durability test. The air-fuel ratio (A / F) serving as the ignition limit was represented by the air-fuel ratio (A / F) at which the misfire rate was 1%. The engine used was an in-line 6-cylinder 2 liter engine, and was measured at an idle operation at 700 rpm. At the same time, the positions of sparks between the center electrode 2 and the ground electrode 11 were also confirmed. In Table 2, the sparking rate (%) indicates the ratio in the case of sparking at the tip end of the center electrode 2 and the ground electrode 11.

[0029]

[Table 2]

When used with a positive polarity, 100% is applied at the tip side of the center electrode 2 and the ground electrode 11 because of its electrical characteristics.
It is flying. For this reason, it is understood that the ignition limit is greatly improved in the case of the positive polarity. In addition, even after the durability test, the edge of the center electrode is less worn, so that 100% of the sparks are emitted on the tip side of the center electrode 2 and the ground electrode 11. For this reason, in the case of negative polarity, the air-fuel ratio which becomes the ignition limit decreases, whereas in the case of positive polarity, the air-fuel ratio which becomes the ignition limit hardly changes.

Further, of these five types of spark plugs, the spark plug in which the diameter A of the small diameter portion of the center electrode 2 is A = 1.8 is parallel to the case where the direction of the ground electrode is perpendicular to the swirl. The ignitability at the positive polarity was compared. Table 3 shows the results. The direction A is a direction perpendicular to the swirl, and the direction B is a direction parallel to the swirl. Air-fuel ratio (A /
F) is indicated by the air-fuel ratio (A / F) at which the misfire rate becomes 1%.
The engine used was an in-line 6-cylinder 2-liter lean-burn engine, which was evaluated under engine operating conditions equivalent to 60 km / h.

[0032]

[Table 3]

By positioning the ground electrode in the direction A, that is, in the direction perpendicular to the swirl, the ignitability is further improved. This is considered to be due to the following reasons. The air-fuel mixture forms a swirl in the combustion chamber. When the sparks flying between the electrodes of the spark plug come into contact with the air-fuel mixture moving by the swirl, the air-fuel mixture ignites and spreads. At this time, if the ground electrode is positioned in parallel with the swirl, the mixture does not easily come into contact with the spark because the ground electrode blocks like a screen in the direction in which the swirl flows at the position where the spark is generated. Become. In addition, the growth of the flame nucleus generated between the gaps hits the electrode, causing heat to be drawn off by the electrode and hindering the growth of the flame nucleus. On the other hand, when the ground electrode is perpendicular to the swirl, the ground electrode does not block like a screen, so that the ignitability is improved. Also, since the direction of the swirl at the position of the spark plug is often the same direction from low to high speed, if the direction of the ground electrode is aligned vertically under one condition, good ignitability from low to high speed will be exhibited. Become.

FIG. 7 is a sectional view of a spark plug tip portion according to the second embodiment. In this embodiment, a disc-shaped spark-resistant spark made of platinum is provided not only on the entire side circumference of the small-diameter portion of the center electrode 2 but only at two portions facing the end surface 11A of the ground electrode 11 where the spark is likely to be concentrated. Tips 22 of the consumable member are fixed by laser welding. This embodiment has the advantage that the amount of expensive spark consumable members used is small.

FIG. 8 is a cross-sectional view of a tip portion of a spark plug according to a third embodiment. In this embodiment, a tip 23 of a cylindrical spark-resistant consumable member made of platinum is fixed to the tip of the reduced-diameter portion of the center electrode main body 2 made of Inconel by laser welding to form a center electrode. I have. The tip of the tip 23 is located between the leading edge and the receding edge of the end face 11A of the ground electrode 11. This embodiment can further reduce the diameter of the small-diameter portion 23 of the center electrode while suppressing the consumption of the center electrode.
There is an advantage that the discharge voltage can be further reduced. In addition, there is an advantage that the fire rate at the tip of the center electrode can be increased, and the ignitability can be improved.
This embodiment corresponds to the first, second, third and fourth aspects of the present invention.

FIG. 9 is a cross-sectional view of a tip portion of a spark plug according to a fourth embodiment. In this embodiment, a tip 2 of a spark-resistant consumable member made of platinum having a stepped cylindrical shape is provided at the tip of a center electrode body 2 made of Inconel and having a large diameter.
Numeral 4 is fixed by resistance welding to form a center electrode.
The small diameter portion of the tip 24 forms a spark portion. Chip 24
Of the ground electrode 11 is located between the front edge and the receding edge of the end face 11A of the ground electrode 11. This embodiment has an advantage in that the center electrode body 2 does not need to be reduced in diameter, so that it is easy to manufacture. This embodiment also corresponds to the invention described in claims 1, 2, 3 and 4.

FIG. 10 is a sectional view of a tip portion of a spark plug according to a fifth embodiment. In this embodiment, a tip 25 of a cylindrical spark-resistant consumable member made of platinum is fixed to the tip of the reduced-diameter portion of the center electrode main body 2 made of Inconel by laser welding to form a center electrode. I have. The tip of the tip 25 is located between the leading edge and the receding edge of the end surface of the ground electrode 11. Further, rectangular plate-shaped spark-resistant consumable members 26, 26 are fixed to the end faces of the ground electrodes 11, 11 facing each other by resistance welding. This embodiment has an advantage that the durability of the spark plug is improved because the consumption of the ground electrode 11 is greatly reduced. This embodiment corresponds to the invention described in claim 5.

FIG. 11 is a sectional view of the tip of a spark plug showing a sixth embodiment. This embodiment shows a case where the present invention is applied to a small-diameter spark plug such as M10 or M8. A tip 27 of a cylindrical consumable spark consumable member made of platinum is fixed to the distal end of the reduced diameter portion of the center electrode body 2 made of Inconel by laser welding to form a center electrode. Diameter A of tip 27
Is A = 0.8 mm, and the end face 11 of the ground electrode 11 is
The thickness E of A is E = 1.1 mm, the width W (not shown) is
W = 2.2 mm. Even if the spark plug has such a small diameter and the cross-sectional area of the outer ground electrode 11 is not sufficient, the diameter of the tip of the center electrode 2 can be reduced and the insulator 1 of the center electrode 2 can be used. Can be reduced, so that the amount of protrusion of the ground electrode 11 from the metal shell 5 can be reduced.
1 can secure sufficient strength.

FIG. 12 is a cross-sectional view of a tip portion of a spark plug according to a seventh embodiment. This embodiment shows a case where the present invention is applied to an intermittent semi-creeping discharge type spark plug. A tip 28 of a cylindrical spark-resistant consumable member made of platinum is fixed to the distal end of the reduced-diameter portion of the center electrode main body 2 made of Inconel by laser welding to form a center electrode. The two outer ground electrodes 11 ′ and 11 ′ made of Inconel
A ′ is formed so as to face the side peripheral surface of the chip 28 and the edge on the retreating side (the lower side in the drawing) is close to the end surface of the insulator 1. When formed in this manner, the insulator 1
When the surface of the insulator 1 is contaminated with carbon, the outer ground electrode 11 'is scattered from the retreating edge to the end face of the insulator 1 and the surface of the insulator 1 is spark-cleaned, so that a spark plug excellent in stain resistance is obtained. In addition, the tip 28 of the center electrode has a small diameter, is excellent in ignitability, and is durable.

FIG. 13 is a circuit diagram showing a positive polarity ignition system. The battery 31 is connected to a primary coil of an ignition coil 34, and the other end of the primary coil is grounded via an igniter 33. The igniter 33 is connected to and controlled by an engine control computer unit (ECU) 32. The secondary side of the ignition coil 34 is connected to the spark plug 20 via a high-voltage cable 35 on the negative side, which is opposite to the normal side, and the negative side is grounded. Spark plug 20
Any of the spark plugs from the first embodiment to the seventh embodiment described above is used. After the engine control computer unit (ECU) 32 sends a pulse signal to the igniter 33 at an appropriate timing to supply a current to the primary coil of the ignition coil 34 for several milliseconds,
Cut off. As a result, a positive high voltage is generated on the positive electrode side of the secondary coil of the ignition coil 34. The high voltage of the positive polarity is applied to the spark plug 20 via the high voltage cable 35.
Is applied to the center electrode 2, and the air insulation between the center electrode 2 and the ground 11 is broken to generate a spark discharge. This spark discharge causes a discharge current to flow as indicated by an arrow 101.

Since the spark discharge has a positive polarity, as described above, even if the center electrode 2 has a small diameter, the ignition system has a small amount of wear, is excellent in ignitability, and has excellent spark plug durability. The ignition system shown in FIG. 13 is an example of the invention described in claim 6.

In the embodiment described above, the ground electrode 1
Although 1 has been described as having two poles, it is apparent that only one pole may be used as the ground electrode, or a multi-pole spark plug such as three or four poles may be used.

[0043]

As described above, according to the present invention, the diameter of the front end portion of the center electrode, which is the ignition portion, is made to be a small diameter of 1.9 mm or less. Since it is formed so as to face the side peripheral surface of the small diameter portion, if this is used with the opposite polarity of positive polarity, the advantage of lowering the discharge voltage due to the small diameter of the center electrode is maintained. There is an excellent effect that electrode consumption can be reduced and the durability of the spark plug is improved. Further, since the center electrode has a small diameter, there is an effect that ignitability is improved. Further, since the amount of protrusion of the ground electrode from the metal shell may be small, there is an effect that breakage and overheating of the outer ground electrode can be prevented.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a spark plug according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing a distal end portion of the spark plug according to the first embodiment.

FIG. 3 is a graph showing the gap consumption when used with a negative polarity in an actual machine durability test.

FIG. 4 is a graph showing the gap consumption when used with a positive polarity in an actual machine durability test.

FIG. 5 is a graph showing a discharge voltage when used with a negative polarity in an actual machine durability test.

FIG. 6 is a graph showing a discharge voltage when used with a positive polarity in an actual machine durability test.

FIG. 7 is an enlarged cross-sectional view showing a tip portion of a spark plug according to a second embodiment.

FIG. 8 is a cross-sectional view showing, on an enlarged scale, a distal end portion of a spark plug according to a third embodiment.

FIG. 9 is an enlarged cross-sectional view showing a distal end portion of a spark plug according to a fourth embodiment.

FIG. 10 is an enlarged cross-sectional view showing a tip portion of a spark plug according to a fifth embodiment.

FIG. 11 is an enlarged cross-sectional view showing a tip portion of a spark plug according to a sixth embodiment.

FIG. 12 is an enlarged cross-sectional view showing a tip portion of a spark plug according to a seventh embodiment.

FIG. 13 is a circuit diagram showing an example of an ignition system according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulator 2 Center electrode 5 Metal shell 11 Ground electrode 11A End face which opposes a ground electrode 21 Spark-resistant consumable member 31 Battery 34 Ignition coil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akio Kokubu 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Inside Japan Special Ceramics Co., Ltd. (72) Inventor Kazuya Iwata 14, Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi No. 18 Japan Special Ceramics Co., Ltd. (72) Inventor Hiroshi Ohno 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Special Ceramics Co., Ltd.

Claims (6)

[Claims] An insulator having a center through hole, a center electrode held in the center through hole, a metal shell holding the insulator, and a ground electrode electrically connected to the metal shell. In the spark plug provided with, the center electrode and the ground electrode are configured such that a high voltage for discharge is applied with a polarity in which the center electrode side is positive, and the center electrode has a tip serving as a firing portion thereof. The diameter of the portion is 1.9 mm or less, and the ground electrode is provided so as to protrude from the end surface of the metal shell to the distal end side. A spark plug formed so as to face a peripheral surface. 2. The spark plug according to claim 1, wherein a front end surface of the center electrode is located between a front end edge and a retreat side edge of a facing surface of the ground electrode. 3. The spark plug according to claim 1, wherein the center electrode includes a spark consumable member at least in a part of the small diameter portion.
Or the spark plug according to 2. 4. The device according to claim 3, wherein the spark-resistant consumable member provided on the center electrode is provided from a position on a retreat side edge of a surface facing the ground electrode to a position on a retreat side. Spark plug. 5. The spark plug according to claim 1, wherein the ground electrode includes a spark consumable member on at least a part of an opposing surface thereof. 6. An ignition system, characterized in that a high positive voltage is applied to the center electrode of the spark plug according to any one of claims 1 to 5 to ignite.