JP2805781B2 - Spark plug for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a spark plug used for an internal combustion engine of an automobile or the like.

2. Description of the Related Art Conventionally, in a gasoline internal combustion engine, a method of supplying a very rich air-fuel mixture into a combustion chamber has been adopted as one means for ensuring operability at low temperatures. Therefore, a large amount of carbon is generated in the combustion chamber due to incomplete combustion. This carbon sequentially adheres to the surface of the insulator of the spark plug attached to the combustion chamber. For this reason, the spark plug tends to increase the frequency at which the high voltage supplied from the ignition coil leaks into the housing through the carbon. Therefore, the discharge in the gap becomes sporadic, and there is a problem that ignition mistakes to the air-fuel mixture in the combustion chamber increase. In particular, in a four-wheeled vehicle, since the battery ignition is used, unlike CDI ignition which improves the leakage characteristics as seen in a two-wheeled vehicle, there is a tendency that a problem occurs in the adhesion of carbon.

Therefore, in order to solve such problems, there is a spark plug for an internal combustion engine disclosed in Japanese Patent Publication No. 58-40831. This spark plug for an internal combustion engine operates normally when carbon does not adhere to the tip end side of the insulator.
A spark discharge occurs in the first gap. Also, at the time of soiling where carbon adheres to the tip surface of the insulator and the wall surface of the inner hole,
A spark is generated from the center electrode to the second gap through the wall surface of the inner hole, and the spark discharge to the second gap burns off the carbon adhered to the wall surface of the inner hole and returns to a normal spark discharge. is there.

[Problems to be Solved by the Invention] However, since the second gap of the above-described conventional spark plug for an internal combustion engine is installed on the wall side of the combustion chamber with respect to the first gap, sparks at the second gap are generated. Since the flame nucleus generated by the discharge becomes less likely to come into contact with the air-fuel mixture and the second gap is dimensionally smaller than the first gap,
Flame kernels do not grow large. Therefore, at the time of spark discharge in the second gap, there is a problem that the ignitability for the air-fuel mixture is poor.

For the purpose of solving such problems, the inventors of the present invention have previously filed Japanese Patent Application No. 63-83369 (filed on April 5, 1988).
Proposed a spark plug for an internal combustion engine.

In this spark plug for internal combustion engines, the surrounding atmosphere is ionized by capacitive discharge, and cleverly utilizes the induced discharge generated in the most ionized region of the ionized region, and is attached to the inner hole of the insulator. Burning carbon. Also, in this spark plug for an internal combustion engine, the small diameter portion of the center electrode protrudes beyond the distal end surface of the insulator from inside the inner hole of the insulator, so that the flame nucleus can grow large in the gap, The ignitability for the air-fuel mixture can also be improved.

However, in the future automobile industry, a car with a little better performance is required, and excellent parts constituting the car are required. Particularly, in the case of a spark plug for an internal combustion engine, the required quality is considered to be more severe than it is now because the performance of the internal combustion engine is directly affected. Therefore, in a future spark plug for an internal combustion engine, a spark plug for an internal combustion engine that further improves the effect of burning off carbon of the above-described spark plug for an internal combustion engine is desired.

An object of the present invention is to provide a spark plug for an internal combustion engine capable of improving the ignitability of an air-fuel mixture and dramatically improving the effect of burning off carbon adhered to an insulator.

[Means for Solving the Problems] First, a spark discharge in a spark plug includes a capacitive discharge that breaks insulation between gaps and an inductive discharge that is ionized by the capacitive discharge and continuously occurs along a region where insulation is reduced. There is. FIG. 3 shows a situation where an induced discharge occurs. In FIG. 3, a portion surrounded by oblique lines indicates an induced discharge. Fig. 3 shows that the engine speed is 15
00rpm, air-cooled 4-cycle 230cc with idling load
FIG. 4 is a model diagram in which quartz glass is embedded in a portion of the main body of the single-cylinder engine where discharge of a spark plug can be observed, and a state inside the engine is observed.

In order to achieve the above object, the inventors of the present application have conducted intensive studies and, as a result, when the diameter d of the center electrode is made extremely thinner than that of a normal electrode, the capacity discharge is performed from the front end surface of the center electrode as in the case of a normal electrode. It is found that the induced discharge occurs from the side surface of the tip region of the center electrode as shown in FIG. Therefore, the inventors of the present application have focused on the fact that carbon adhering to the insulator is surely and dramatically burned off by utilizing the induced discharge generated from the side surface of the front end region of the center electrode.

The structure is such that a cylindrical insulator having an inner hole in the axial direction, a center electrode fitted into the inner hole with its tip protruding from the inner hole and held by the insulator, A ground electrode that forms a gap between the tip and a housing that holds the ground electrode and is fixed to the outer periphery of the insulator, between the outer periphery of the center electrode and the inner wall of the inner hole. Is a spark plug for an internal combustion engine in which a cylindrical cavity opening at the tip of the insulator is formed, wherein the length of the center electrode protruding from the cylindrical cavity is 1; When the diameter of the center electrode that protrudes is d, and the inside diameter of the inner hole that forms the cylindrical space with the center electrode is D, 0.60 mm ≦ d ≦ 1.55 mm, 0.2 mm ≦ l ≦ 1.1mm, D ≧ 1.1dmm + (l / 2) mm + 0.2mm, D ≦ 0.9dmm− (l / 2) mm + 1.6mm Is obtained is characterized in that there.

Further, a tapered portion is provided at a tip of the center electrode protruding from the cylindrical cavity, and the largest diameter of the center electrode in the tapered portion may be d.

[Action] The present inventors have found the following action. The operation will be described with reference to FIGS. FIG. 4 shows a case where a capacitive discharge and an induced discharge with slight adhesion of carbon occur. FIG. 5 to FIG. 9 show the passage of discharge time and the main cleaning mechanism in the situation where carbon deposition has progressed. FIG. 10 shows a situation where one discharge is completed.

In FIGS. 4 to 10, solid arrows indicate capacitive discharges, portions surrounded by oblique lines indicate inductive discharges, waveform portions indicate pilot discharges promoting cleaning action, and portions surrounded by dots indicate ionization regions. Fig. 4 to Fig. 10 show a case in which quartz glass is buried in the body of the internal combustion engine where discharge of the spark plug can be observed, and a capacity discharge and an induction discharge in the internal combustion engine are observed.
FIG. 9 is a model diagram obtained by analyzing the result. FIG. 11 is a model diagram of a capacitive discharge and an induction discharge waveform.

Spark plugs use a very rich mixture,
Carbon adheres to the tip of the insulator and the wall surface of the inner hole.

As shown in FIG. 4, in a situation where the adhesion of carbon to the insulator is slight, when a high voltage is applied to the center electrode, a capacitive discharge occurs from the tip of the center electrode. At this time,
Induction discharge occurs in the ionized region of the surrounding atmosphere due to capacitive discharge. Here, since capacitive discharge occurs in the gap formed between the tip of the center electrode and the ground electrode, it seems that inductive discharge generally also occurs in the gap, but the ionization region due to capacitive discharge is The side surface of the center electrode also extends to a range that can be ionized. At this time, the induced discharge is generated in the gap from the side surface of the center electrode. Therefore, carbon adhering to the portion of the insulator exposed to the induced discharge generated from the side surface of the center electrode can be burned off (hereinafter referred to as side discharge).

As described above, the case where the adhesion of carbon is slight has been described. However, depending on the engine operating conditions, the generation of carbon may be more remarkable. In this case, carbon adheres almost entirely to the surface of the insulator and the inner wall of the inner hole, and the insulation resistance between the center electrode and the housing decreases.

FIG. 5 is a model diagram showing a situation in which a capacitance C and a leakage resistance R between the surface of the insulator and the housing are added in parallel due to the presence of a high resistance conductive layer due to carbon adhesion. I have.

Next, when a high voltage is applied to the center electrode, as a whole, a leakage current flows from the center electrode to the housing via the leakage resistance on the surface of the insulator, and the inner wall of the center electrode and the inner hole, the insulator, and the like. A charging current flows between the surface and the housing.

At the time when the high voltage successively rises as shown in FIG. 11, FIG. 6 shows the current for charging the capacitance between the wall surface of the inner hole of the insulator and the side surface of the small diameter portion of the center electrode, and the step of the center electrode. Starting from the edge, a leakage current flows through the leakage resistance. Thus, FIG. 6 shows that these currents ionize the interior of the cylindrical cavity.

It has been newly found that this phenomenon has the same function as that of a so-called pilot discharge occurring in a three-needle gap. Note that the attached carbon corresponds to a third electrode having a three-needle gap.

In this way, the technical idea of ionizing the cylindrical space is
It is based on the action of a third electrode in a three-needle gap, i.e., a pilot discharge that promotes ionization between the gaps. The present invention has a structure in which a sequentially-attached carbon is utilized as a third electrode, and a cylindrical space that is easily ionized is provided.

This action is performed continuously during a period in which a voltage at which a capacitive discharge that causes dielectric breakdown occurs in the gap shown in FIG. 11 is reached, and as shown in FIG. 7, the ionization region near the cylindrical space is continuously expanded. .

Then, at the moment when the voltage at which the capacitive discharge that causes dielectric breakdown occurs in the gap shown in FIG. 11 is reached, the capacitive discharge is generated in the gap from the tip of the center electrode as shown in FIG. At this time, as described above, since the ionization region due to the capacitive discharge has spread to a range in which the side surface of the center electrode can also be included in the ionization region, the side discharge immediately after the occurrence of the capacitive discharge has a gap from the side surface of the center electrode. Occurs. At this time, carbon adhering to the portion of the insulator exposed to the side discharge can be burned off.

Further, the ionized region generated in the gap by the side discharge and the ionized region generated in the cylindrical space by the pilot discharge described above are combined, and as shown in FIG. Blow out the gap from a wide area on the tip and side of the electrode. This side discharge is
It is performed continuously during the discharge duration shown in FIG. Therefore, by this side discharge, the carbon adhering to the wall surface of the inner hole forming the cylindrical space with the outer periphery of the center electrode and the tip of the insulator can be burned off.

When the discharge duration shown in FIG. 11 elapses, one discharge ends. At this time, as shown in FIG. 10, the adhering carbon is burned off on the wall surface of the inner hole exposed to the side discharge and on the tip of the insulator, and the insulator becomes a clean portion.

At the time of the next discharge, a pilot discharge occurs at the carbon portion adhering to the inner wall of the inner hole of the insulator other than the clean portion, and the discharge of the side discharge shown in FIG. 9 occurs. Carbon adhering to the wall surface of the hole and the tip of the insulator is sequentially burned off.

That is, the present invention can be carried out in a case where the carbon adhering to the insulator is burned off only by the side discharge, or in a case where the carbon is attached to the ionized region generated by the pilot discharge.

For this reason, the frequency and time at which the high voltage supplied from the ignition coil leaks through the carbon to the housing is drastically reduced, and ignition mistakes to the air-fuel mixture are significantly reduced.

Embodiment An embodiment of a spark plug for an internal combustion engine according to the present invention will be described with reference to the drawings.

FIG. 1 shows a main part of a spark plug for an internal combustion engine adopting the present invention, and FIG. 2 shows a spark plug for an internal combustion engine adopting the present invention.

 Reference numeral 1 denotes a spark plug for an internal combustion engine.

The spark plug 1 holds the cylindrical electrode 2, the center electrode 3 held by the insulator 2, the ground electrode 4 forming a gap G between the center electrode 3 and the tip end surface 31, and holds the ground electrode 4. And a metal housing 5.

The insulator 2 has an axial inner hole 23 that is open at the front end surface 21 and the rear end 22. The center electrode 3 is inserted into the inner hole 23 of the leg portion 24 of the insulator 2 which protrudes into the combustion chamber of the internal combustion engine.
Is fitted.

The center electrode 3 is fitted into the inner hole 23 with the distal end surface 31 protruding from the inner hole 23, thereby holding the leg length 24 of the insulator 2.

The portion of the center electrode 3 closer to the end than the edge 32 is an inner hole.
The small diameter portion 33 is formed to have a smaller diameter than the inner diameter of 23. The small-diameter portion 33 has a fitting portion 34 located in the inner hole 23.
And a protruding portion 35 protruding from the inner hole 23. Further, between the outer periphery of the fitting portion 34 located in the inner hole 23 of the small-diameter portion 33 and the wall surface of the inner hole 23, a cylindrical cavity 6 opening at the tip end surface 21 of the insulator 2 is formed. I have.

The ground electrode 4 is disposed so as to face the end face 31 of the center electrode 3.

The housing 5 has an end face to which the ground electrode 4 is connected, and a mounting screw portion 51 formed on the outer periphery. Further, the housing 5 is fixed to the outer periphery of the insulator 2.

Further, 71 indicates a resistor for preventing radio noise, 72 indicates a conductive glass layer, 73 indicates a terminal shaft, and 74 indicates a terminal.

Next, in FIG. 1, the length of the center electrode 3 protruding from the cylindrical space 6 is 1 and the diameter of the center electrode 3 protruding from the cylindrical space 6 is d. The inner diameter of the inner hole 23 forming the cavity 6 is represented by D, and the depth of the cylindrical cavity 6 is represented by L.
Various experiments were conducted on how the characteristics changed, and the results will be described.

 First, the side discharge will be described.

The present inventors have conducted a number of experiments and found that when the diameter of the center electrode is reduced, side discharge occurs.

It has been confirmed that when capacitive discharge occurs from the tip end surface of the center electrode, the periphery of the capacitive discharge is ionized, and induction discharge continues to occur in this ionized region. The air-fuel mixture flows in the combustion chamber of the engine. The vicinity of the center electrode itself becomes an obstacle to the flow of the air-fuel mixture, and the turbulence component of the flow becomes large. Therefore, it is presumed that side discharge occurs due to the ionization region flowing from the front end surface of the center electrode.

Therefore, the inventors of the present application have paid attention to the fact that carbon on the tip side face of the center electrode is burned off by using this side discharge.

FIG. 12 shows the diameter d of the center electrode on the horizontal axis and the frequency of occurrence of side discharge on the vertical axis. FIG. 13 is a model diagram showing a side discharge generated when the experiment of FIG. 12 was performed. The frequency of occurrence of side discharge increases sharply at 2.0mm or less, especially 1.5mm or less when the diameter (d) of the center electrode protruding from the tip of the insulator is made smaller than 2.5mm in a general spark plug. , The frequency of occurrence increases.

When the diameter (d) of the center electrode is set to around 2.5 mm, it is presumed that the ionized region is hardly caused to flow due to the turbulent component of the flow, and the occurrence of side discharge is significantly reduced. Also, the diameter (d) of the center electrode of the spark plug is
When the thickness is smaller than 0.9 mm, the frequency of occurrence of side discharge is reduced. This is because the ultrafine center electrode is apparently needle-shaped, so the potential gradient at the tip surface of the center electrode becomes very steep,
It is presumed that ionization of the tip surface of the center electrode particularly proceeds, and the frequency of occurrence of side discharge decreases. Here, if the diameter (d) of the center electrode of the spark plug is smaller than 0.5 mm, the energy of the discharge may cause a problem such as melting and damage of the center electrode. Cannot be used.

FIG. 14 shows the diameter d of the center electrode on the horizontal axis and the burned-out length F on the vertical axis. FIG. 15 shows a spark plug used in carrying out the experiment of FIG. 14, and F in the figure shows the carbon burnout length.

According to FIG. 12, the occurrence frequency of the side discharge is high (50% or more) when 0.6 mm ≦ d ≦ 1.6 mm. On the other hand, according to FIG. 14, the case where the carbon burnout length F is long (0.8 mm or more) is 0.55 mm ≦ d ≦ 1.55 mm. Therefore, as shown in FIGS. 12 and 14, the frequency of occurrence of side discharge is large and the carbon burnout length F is long when 0.60 mm ≦ d ≦ 1.55 mm.

Therefore, the present inventors have found that the occurrence of side discharge varies depending on the diameter d of the center electrode, and that the carbon burnout length also varies depending on the diameter d of the center electrode. Therefore, it is necessary to select the diameter of the center electrode within a range where the frequency of side discharge is large and the carbon burnout length F is long. That is, it is 0.60 mm ≦ d ≦ 1.55 mm from the experimental results. Furthermore, when 70% of the occurrence frequency of the side discharge, 0.80 mm ≤ d ≤ 1.4 mm, and when the carbon burnout length F is 1.2 mm, 0.8 ≤ d ≤ 1.2 mm. Can be said to be 0.8 mm ≦ d ≦ 1.2 mm.

Next, an experiment was performed on the length (l) of the center electrode.

FIG. 16 shows the length l of the center electrode on the horizontal axis and the sparking voltage between the center electrode and the ground electrode on the vertical axis. This is the result of an experiment conducted with the gap G between the ground electrode and the ground electrode fixed at 1.1 mm. FIG. 17 shows the length l of the center electrode on the horizontal axis, and the ignition limit air-fuel ratio (A / F) at idling, which is an index representing ignitability, on the vertical axis. The experiment plots the air-fuel ratio (ignition limit air-fuel ratio) at which the air-fuel ratio is reduced in a four-cycle, 1600 cc, water-cooled four-cylinder engine and idling operation to obtain stable combustion. FIG. 18 shows the dimensions of the spark plug used in carrying out the experiments of FIGS. 16 and 17.

According to FIG. 16, the spark voltage is low when the length of the center electrode is 0 mm ≦ 1. Also, from FIG. 17, it was confirmed that the influence of the ignitability was small if the end face of the center electrode protruded from the end face of the insulator.

From FIGS. 16 and 17, it is 0 mm ≦ 1 that the spark voltage is low and has little effect on the ignitability. However, when the spark plug is used, the tip surface of the center electrode gradually disappears, and the length l of the center electrode gradually decreases. The disappearance of the tip surface of the center electrode of this spark plug
It has been confirmed by experience that the maximum length is 0.2 mm during the service life. Therefore, in spark plugs, the spark voltage is low until the end of its life,
It is assumed that m ≦ l.

Further, in order to explore the length l of the center electrode, the diameter d of the center electrode, the inner diameter D of the inner hole, and the depth L of the cylindrical cavity, side discharge of the central electrode and ionization in the cylindrical cavity are performed. An experiment was conducted on the anti-fouling effect by the effective connection with the region, and will be described below.

The anti-fouling effect is based on the conditions under which carbon is likely to adhere using a 4-cycle, 1300cc, water-cooled 4-cylinder engine.
At a radiator water temperature and an engine oil temperature of −10 ° C. under an atmosphere temperature of 10 ° C., a series of patterns of starting, racing, acceleration and deceleration at low speed, and stopping were performed for 1 minute,
This is regarded as one cycle, and the result of evaluation is shown. For each evaluation, as shown in FIG. 19, the insulation resistance between the front end surface of the center electrode and the front end surface of the insulator was measured by an insulation resistance meter M.
The number of cycles up to 1 MΩ was measured. 2 above
If the insulation resistance between the points falls below 1 MΩ, engine malfunctions such as unstartable and rough idle occur. Generally a spark plug according Model W16EX-U ₁₁ to the applicant produced a typical example of the spark plug that often used in the above evaluation, being evaluated results leading to 1MΩ at 8 cycles. Therefore, it can be understood that a desired effect is not obtained unless the number of cycles exceeds eight.

FIG. 20 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 0.9 mm. FIG. 21 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 1.1 mm. FIG. 22 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 1.6 mm. FIG. 23 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 2.0 mm. FIG. 24 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 2.8 mm. FIG. 25 shows the diameter d of the center electrode on the horizontal axis and the antifouling effect on the vertical axis, when the inner diameter of the inner hole is D = 2.9 mm. 20 to 25, ○ indicates the length 1 = 0.2 mm, Δ indicates the length 1 = 0.5 mm, □ indicates the length 1 = 0.7 mm, and Δ indicates the length. The length is l = 0.9 mm, ▽ is the length is l = 1.1 mm, FIG. 26 shows the dimensions of the spark plug used in carrying out the experiments of FIGS. 20 to 25,
The depth of the cylindrical space is L = 0.5 mm.

According to Fig. 20, the antifouling effect is 40 (cycles / 1M
Ω) or more is not found. According to FIG. 21, the antifouling effect is 40 (cycles / 1 MΩ) or more because the diameter of the center electrode is d = 0.7 mm and the length is l.
= 0.2 mm only.

According to Fig. 22, the antifouling effect is 40 (cycles / 1M
Ω) or more when the diameter of the center electrode is 0.55 mm ≦ d ≦ 1.
2 mm. The antifouling effect is 40 (cycles / 1M
Ω) or more when the length is 0.2 mm ≦ l ≦ 1.1 mm. Then, in FIG. 22, when d = 0.7 mm, l ≦
All 1.1 mm spark plugs have a fouling resistance effect of 40 (cycles / 1 MΩ) or more.

According to FIG. 23, the antifouling effect is 40 (cycles / 1M
Ω) or more because the diameter of the center electrode is 0.60 mm ≦ d
≦ 1.55 mm. The antifouling effect is 40 (cycles
/ 1MΩ) or more, the length of the center electrode is 0.2mm ≦
l ≦ 1.1 mm. Then, in FIG. 23, d = 1.1 mm
At this time, all spark plugs with l ≦ 1.1 mm have a fouling resistance effect of 40 (cycle number / 1 MΩ) or more.

According to FIG. 24, the antifouling effect is 40 (cycles / 1M
Ω) or more when the diameter of the center electrode is d = 1.5 m
m and the length of the center electrode is l = 0.2 mm. According to FIG. 25, the antifouling effect is 40 (cycles / 1M
Ω) or more is not found.

From FIG. 20 to FIG. 25, it can be confirmed that the range in which the antifouling effect is good in the length of the center electrode is 0.2 mm ≦ l ≦ 1.1 mm, and the length 1 of the center electrode is It was also confirmed that it changed according to the diameter d of the center electrode.

Further, an experiment was conducted on the antifouling effect of the length l of the center electrode, the diameter d of the center electrode, the inner diameter D of the inner hole, and the depth L of the cylindrical space.

FIG. 27 shows the depth L of the cylindrical space on the horizontal axis and the stain resistance effect on the vertical axis. In FIG. 27, ○ indicates that the length of the center electrode is l = 0.2 mm, the diameter of the center electrode is d = 0.7 mm, and the inner diameter of the inner hole is D = 2.1 mm.

The diameter of the center electrode is d = 0.7 mm, and the inner diameter of the inner hole is D
= 1.1 mm. Δ indicates that the length of the center electrode is l = 0.2 mm,
The diameter of the center electrode is d = 1.5 mm and the inner diameter of the inner hole is D
= 2.8 mm.

The diameter of the center electrode is d = 1.5 mm and the inner diameter of the inner hole is D
= 2.0 mm. □ indicates that the length of the center electrode is l = 0.9 mm,
The diameter of the center electrode is d = 0.7 mm, and the inner diameter of the inner hole is D
= 1.5 mm.

The diameter of the center electrode is d = 1.5 mm and the inner diameter of the inner hole is D
= 2.4 mm.

According to Fig. 27, the antifouling effect is 40 (cycles / 1M
Ω) or more when the depth of the cylindrical space is 0.2 mm ≦ L ≦ 1.0
mm. Further, within this range, substantially constant antifouling effect can be obtained regardless of the change of the length l of the center electrode, the diameter d of the center electrode, and the inner diameter D of the inner hole. Therefore, it is presumed that the spark plug of the present invention is not affected by the depth L of the cylindrical cavity with respect to the antifouling effect. Conversely, from FIGS. 20 to 25, it is presumed that the length l of the center electrode, the diameter d of the center electrode, and the inner diameter D of the inner hole are interrelated.

FIG. 28 shows the diameter d of the center electrode on the horizontal axis and the inside diameter D of the inner hole on the vertical axis, and the length of the center electrode is l = 0.
FIG. 3 shows an example of an area where the antifouling effect of 2 mm, l = 0.7 mm, and l = 1.1 mm is 40 cycles or more.

According to FIG. 28, the anti-fouling effect due to the effective coupling of the side discharge of the center electrode and the ionization of the cylindrical space is represented by the length l of the center electrode, the diameter d of the center electrode, and the inner diameter of the inner hole. It can be confirmed that there is a good range in combination with D.

According to various experiments, the diameter of the center electrode is 0.60 mm ≦
d ≦ 1.55 mm is good. In particular, 0.80mm ≦ d ≦ 1.20mm
In this case, the probability of occurrence of side discharge is high, and the burnout length of carbon is long, so that the fouling resistance is further improved.
This is the same as the result of conducting the experiment in FIGS. 12 and 14 described above. Where d <0.60 mm and d> 1.55 mm
The reason why is not included in the favorable range is that the frequency of side discharge is low and the burnout length of carbon is short, so that the effect by the effective coupling between the side discharge and the ionized region in the cylindrical cavity is not exhibited. It is presumed.

As can be seen from various experiments and FIGS. 16 and 17, the length of the center electrode is preferably 0.2 mm ≦ l ≦ 1.1 mm. Further, as apparent from FIG. 14, particularly when 0.2 mm ≦ l ≦ 0.7 mm, side discharge can be more reliably generated from the inside of the cylindrical space, and the effect of burning off carbon can be improved.

Here, the reason why l <0.2 mm is not included in a favorable range is as follows. That is, from the experimental results of FIGS. 16 and 17, the spark voltage is high and the ignitability is not in a favorable range, and the life of the center electrode is affected. Conversely, the reason why l> 1.1 mm is not included in a favorable range is that the distance between the front end face of the center electrode and the front end face of the insulator is large from the experimental results shown in FIGS. This is because the effect of antifouling property is low.

According to various experiments, the inner diameter of the inner hole is D ≧ 1.1 dmm +
(L / 2) mm + 0.2mm and D ≦ 0.9dmm− (l / 2) mm + 1.6
The range satisfying mm is the optimum range. Where D <1.1d
The reason that mm + (l / 2) mm + 0.2mm is not included in the good range is that when the cylindrical space is narrower than the optimal size where the cleaning action can be expected, the thermal energy due to the inductive discharge will be less than the insulator and center electrode. It is supposed that the expansion action is restricted by the cooling action of, and it does not effectively act on the burning of carbon. D> 0.9d
The reason why mm− (l / 2) mm + 1.6 mm is not included in the favorable range is that even when the cylindrical cavity capable of expecting a cleaning action is provided, the inner diameter of the inner hole of the insulator becomes large, Multiple side discharges are required to burn off the carbon around or around the clean portion of the insulator where the carbon is burned off. From the experimental results, when observed with the same number of discharges,
If the inside diameter of the inner hole of the insulator becomes too large, the clean portion of the insulator becomes relatively small.

 FIG. 29 shows a modification of FIG.

In this embodiment, a tapered portion 37 is provided between the small diameter portion 33 and the large diameter portion 36 of the center electrode 3. In this example as well, a side discharge is generated from the side of the distal end of the small diameter portion 33 as in the case of FIG.

 FIG. 30 shows a modification of FIG.

In this embodiment, an intermediate portion 38 having a diameter intermediate between the small diameter portion 33 and the large diameter portion 36 of the center electrode 3 is provided. In this example as well, a side discharge is generated from the side of the distal end of the small diameter portion 33 as in the case of FIG.

 FIG. 31 shows a modification of FIG.

In this embodiment, a tapered portion 39a is provided between the small diameter portion 33 and the intermediate portion 38 of the center electrode 3, and a tapered portion 39b is provided between the intermediate portion 38 and the large diameter portion 36. . This example also
As in the case of FIG. 1, side discharge occurs from the side of the tip of the small diameter portion 33.

 FIG. 32 shows a modification of FIG.

In this embodiment, a portion 36 held by the leg portion 24 of the insulator 2 is used.
The diameter of the center electrode 3 of a is d. Further, a pocket 25 forming the cylindrical space 6 is provided between the outer periphery of the center electrode 3 and the wall surface of the inner hole 23 at the distal end portion of the insulator 2. Also in this example, a side discharge is generated from inside the pocket 25 and from the side of the tip of the center electrode 3 protruding from the pocket 25.

 FIG. 33 shows a modification of FIG.

In this embodiment, a tapered portion 31a is provided at the tip of the small diameter portion 33 of the center electrode 3. Further, in this example, the tapered portion 31a
Among them, the diameter of the large diameter portion 31b having the largest diameter is d. In this example as well, a side discharge is generated from the side of the distal end of the small diameter portion 33 as in the case of FIG.

In this embodiment, the spark plug is provided with a resistor for preventing radio noise, but the spark plug need not be provided with a resistor for preventing radio noise.

[Effect of the Invention] The spark plug for an internal combustion engine of the present invention has the following effects.

Make the center electrode diameter narrower than normal and in a specific range (0.60mm
≤ d ≤ 1.55 mm), an inductive discharge is generated from the side of the tip of the center electrode protruding from the inner hole of the insulator. This is called side discharge.

If the carbon adhering to the tip of the insulator is insignificant, the side discharge generated on the side of the tip of the center electrode contacts the insulator surface in the cylindrical space, thereby removing the carbon adhering to the insulator surface. Can be burned.

In addition, when carbon attached to the tip of the insulator is remarkable, the ionization region in the cylindrical cavity generated when the high voltage applied to the center electrode rises and the side discharge are combined, and the cylindrical cavity has a large width. Side discharges blow out from the area. The blown side discharge can burn off carbon attached to the insulator surface.

Then, the length of the center electrode protruding from the cylindrical space is limited to a specific range (0.2 mm ≦ l ≦ 1.1 mm), and the inner diameter of the inner hole that forms the cylindrical space with the center electrode is defined as Specific range ｛D
≧ 1.1mm + (l / 2) mm + 0.2mm, D ≦ 0.9mm− (l / 2) mm +
By limiting the thickness to 1.6 mm｝, the effect of resistance to fouling due to side discharge can be further improved.

As described above, the carbon burning effect can be improved,
Since the frequency and time at which the high voltage applied to the center electrode leaks through the carbon to the housing is drastically reduced, ignition errors to the air-fuel mixture can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a spark plug for an internal combustion engine according to one embodiment of the present invention, FIG. 2 is a sectional view showing a main part of the spark plug for an internal combustion engine according to one embodiment of the present invention, and FIG. Model diagram showing side discharge generated in the gap of the plug,
4 to 10 are explanatory views showing the operation of the present invention, and FIG.
The figure is a waveform diagram of the capacity discharge and the induction discharge. FIG. 12 is a graph showing the relationship between the diameter d of the center electrode protruding from the cylindrical space and the frequency of occurrence of side discharge, and FIG. 13 shows the side discharge generated when the experiment of FIG. 12 was performed. Explanatory diagram,
FIG. 14 is a graph showing the relationship between the diameter d of the center electrode protruding from the cylindrical space and the carbon burnout length F, and FIG. 15 shows a spark plug used in carrying out the experiment of FIG. In the figure, F is an explanatory diagram showing the burnout length of carbon. FIG. 16 is a graph showing the relationship between the length l of the center electrode protruding from the cylindrical cavity and the sparking voltage between the center electrode and the ground electrode. FIG. 17 is a graph showing the relationship between the center electrode protruding from the cylindrical cavity. A graph showing the relationship between the length l and the ignition limit air-fuel ratio at idle,
FIG. 18 is an explanatory diagram showing the dimensions of the spark plug used in carrying out the experiments of FIGS. 16 and 17. FIG. 19 is an explanatory view showing insulation resistance measurement for evaluating the antifouling effect, and FIG. 20 is a cylindrical shape when the inner diameter of an inner hole forming a cylindrical space with the center electrode is D = 0.9 mm. It is a graph which shows the relationship between the diameter d of the center electrode protruding from an empty space, and an antifouling effect. FIG. 21 shows the relationship between the diameter d of the center electrode projecting from the cylindrical cavity and the antifouling effect when the inner diameter of the inner hole forming the cylindrical cavity with the central electrode is D = 1.1 mm. It is a graph shown. FIG. 22 shows the relationship between the diameter d of the center electrode projecting from the cylindrical cavity and the antifouling effect when the inner diameter of the inner hole forming the cylindrical cavity with the central electrode is D = 1.6 mm. It is a graph shown. FIG. 23 shows the relationship between the diameter d of the center electrode projecting from the cylindrical cavity and the antifouling effect when the inner diameter of the inner hole forming the cylindrical cavity with the central electrode is D = 2.0 mm. It is a graph shown. FIG. 24 shows the relationship between the diameter d of the center electrode projecting from the cylindrical cavity and the antifouling effect when the inner diameter of the inner hole forming the cylindrical cavity with the central electrode is D = 2.8 mm. It is a graph shown. FIG. 25 shows the relationship between the diameter d of the central electrode protruding from the cylindrical cavity and the antifouling effect when the inner diameter of the inner hole forming the cylindrical cavity with the central electrode is D = 2.9 mm. It is a graph shown. FIG. 26 is an explanatory diagram showing the dimensions of the spark plug used in carrying out the experiments of FIGS. 20 to 25. FIG. 27 is a graph showing the relationship between the diameter d of the center electrode protruding from the cylindrical space and the antifouling effect. FIG. 28 shows that the length of the center electrode protruding from the cylindrical space is l = 0.2 mm, l = 0.7 m
m, l = 1.1 mm An example of a region having a fouling resistance effect of 40 cycles or more, in which the diameter d of the center electrode protruding from the cylindrical space and the inner diameter of the inner hole forming the cylindrical space between the center electrode and the center electrode It is a graph which shows the relationship with D. FIG. 29 is a cross-sectional view showing a main part of an internal combustion engine spark plug of another embodiment of the present invention, and FIG. 30 is a cross-sectional view showing a main part of an internal combustion engine spark plug of another embodiment of the present invention. FIG. 31 is a cross-sectional view showing a main part of an internal combustion engine spark plug of another embodiment of the present invention, and FIG. 32 is a cross-sectional view showing a main part of an internal combustion engine spark plug of another embodiment of the present invention. FIG. 33 is a sectional view showing a main part of a spark plug for an internal combustion engine according to another embodiment of the present invention. In the drawing, 1 ... a spark plug for an internal combustion engine, 2 ... a cylindrical insulator,
3 ... Center electrode, 4 ... Ground electrode, 5 ... Housing,
6 ... cylindrical hollow, 21 ... tip surface of insulator, 23 ... inner hole,
31: tip surface of the center electrode, l: length of the center electrode projecting from the cylindrical space, d: diameter of the center electrode projecting from the cylindrical space, D: cylinder between the center electrode Inner diameter of inner hole forming cylindrical cavity, L: depth of cylindrical cavity

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-126443 (JP, A) JP-A-64-27176 (JP, A) JP-A-56-67690 (JP, U) 40831 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01T 13/14 H01T 13/20

Claims (2)

(57) [Claims] 1. A cylindrical insulator having an inner hole in the axial direction, a center electrode fitted into the inner hole with a tip protruding from the inner hole and held by the insulator, and a center electrode. And a housing fixed to the outer periphery of the insulator while holding the ground electrode, between the outer periphery of the center electrode and the inner wall of the inner hole. A spark plug for an internal combustion engine, wherein a cylindrical cavity opening at the tip of the insulator is formed, wherein the length of the center electrode protruding from the cylindrical cavity is 1; Where d is the diameter of the center electrode protruding from the center, and D is the inner diameter of the inner hole that forms the cylindrical space with the center electrode, 0.60 mm ≦ d ≦ 1.55 mm, 0.2 mm ≦ l ≤1.1mm, D≥1.1dmm + (l / 2) mm + 0.2mm, D≤0.9dmm- (l / 2) mm + 1.6mm Spark plug for an internal combustion engine, characterized in that is. 2. A tapered portion is provided at a tip of the center electrode protruding from the cylindrical space, and the largest diameter of the center electrode in the tapered portion is d. Item 2. A spark plug for an internal combustion engine according to item 1.