JP2000294360A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug having resistance to 'smoldering', having a long service life, and excelling in ignitability. SOLUTION: In this spark plug, a main air gap (A) is formed between a parallel ground electrode 11 and an end surface of a center electrode 2, a semi- surface gap (B) is formed between an end surface 12C of a semi-surface ground electrode 12 and a side circumferential surface 2A of the center electrode 2, and a semi-surface insulator gap (C) is formed between the end surface 12C and a side circumferential surface 1E of an insulator 1. The difference E in level between the height of a lower end surface 1D of the insulator 1 and the height of an upper end edge 12B of the end surface 12C of the semi-surface ground electrode 12 satisfies E<=+0.7 mm, the distance B of the semi-surface gap (B) is larger than the distance A of the main air gap (A), and the distance C of the semi-surface insulator gap (C) is smaller than the distance A of the main air gap (A).

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.

[0002]

2. Description of the Related Art A conventional spark plug comprises a center electrode projecting downward from a lower end face of an insulator, and a parallel ground electrode disposed opposite to the center electrode and having one end joined to a metal shell. In general, a spark discharge is caused in the air gap between the center electrode and the parallel ground electrode to ignite the fuel mixture gas. In order to improve the ignitability in the air gap, JP-A-5-326107 and JP-A-7-130454 disclose, besides the parallel ground electrode facing the end face of the center electrode, the side of the center electrode. One in which an auxiliary ground electrode facing the peripheral surface is provided has been proposed. The purpose of these auxiliary ground electrodes is not to ignite the gap between the auxiliary ground electrode and the center electrode, but the presence of the auxiliary ground electrode improves the electric field distribution between the parallel ground electrode and the center electrode, and lowers the discharge. A voltage is applied to the gap between the parallel ground electrode and the center electrode to improve the ignitability. For this reason, these spark plugs are structurally such that the edge of the end face of the auxiliary ground electrode is not always located near the lower end face of the insulator. Further, Japanese Patent Application Laid-Open No. Hei 9-199260 proposes an arrangement in which an auxiliary ground electrode is provided near the lower end face of the insulator in addition to the parallel ground electrode facing the end face of the center electrode.

[0003]

However, Japanese Patent Application Laid-Open No. 5-326107 and Japanese Patent Application Laid-Open No. 7-13045 described above.
All of the conventional spark plugs described in Japanese Patent Application Laid-open No. 4 (1999) have a problem that they are vulnerable to so-called "smoldering". At the time of steady operation in which the internal combustion engine is rotating at a predetermined temperature at a predetermined rotation speed or more, the leg portion, which is a lower portion of the insulator of the spark plug, is appropriately burned, and the surface temperature near the lower end surface of the insulator inside the combustion chamber is reduced. It rises to about 500 ° C. For this reason, the carbon adhering to the surface of the insulator is burned and purified, and the surface of the insulator is kept clean. Therefore, "smoldering" does not occur. However, the temperature of the internal combustion engine is extremely low,
When the rotation speed is low and the load is low, the temperature of the surface of the insulator does not rise, and carbon due to combustion adheres and accumulates on the surface of the insulator, resulting in a so-called "smoldering" state. If this progresses further, the insulation between the center electrode and the ground electrode decreases, so that spark discharge becomes impossible, leading to engine stall. In addition, the conventional spark plug described in Japanese Patent Application Laid-Open No. HEI 9-199260 discloses that the distance from the parallel ground electrode or the auxiliary ground electrode to the center electrode (main air gap or semi-surface gap) and the end face of the auxiliary ground electrode are insulated. The relationship of the distance to the side peripheral surface of the insulator (semi-surface insulator gap) has not been clarified.

Further, Japanese Patent Application Laid-Open No. S59-71279 discloses a semi-creep plug in which a ground electrode is provided so as to face the side peripheral surface of the insulator. In this plug, the sparks run along the surface of the insulator, so that the carbon attached to the surface of the insulator is burned off, and the problem of "smoldering" does not occur much. However, because the sparks constantly run along the surface of the insulator, the insulator surface is damaged by the spark,
The so-called "channeling" problem arises. For this reason,
There is a problem that the life of the spark plug is short.

Therefore, the present invention is strong against "smoldering",
It is another object of the present invention to provide a spark plug having a long life and excellent ignition performance.

[0006]

Means for Solving the Problems To achieve the above object, a first aspect of the present invention is to provide an insulator having a center through-hole and a lower end face of the insulator held in the center through-hole. A center electrode configured to protrude downward, a metal shell for holding the insulator, and a parallel ground disposed such that one end is joined to the metal shell and the other end is opposed to a tip end surface of the center electrode. An electrode, wherein a main air gap (A) is formed by the parallel ground electrode and the tip end surface of the center electrode, wherein one end is joined to the metal shell and the other end is a side peripheral surface of the center electrode. Alternatively, a single or a plurality of semi-creeping ground electrodes are provided so as to face the side peripheral surface of the insulator, and the other end face of the semi-creeping ground electrode and the center electrode facing this end face are provided. Between the side A creeping gap (B) is formed, and a semi-creeping insulator gap (C) is formed between an end face of the semi-creeping ground electrode and a side peripheral face of the insulator facing this end face. The step E between the height position of the lower end surface of the insulator and the height position of the upper end edge of the end surface of the semi-creeping ground electrode is E ≦ + 0.7 (the unit is mm, and + is The upper edge of the end surface of the creepage ground electrode means a direction away from the lower end surface of the insulator), and the distance B of the semi-creep gap (B) is larger than the distance A of the main air gap (A). When the end surface of the semi-creeping ground electrode and the insulator are cut along a central axis of the insulator, a line indicating the lower end surface of the insulator extends outward, The extension and the side peripheral surface near the semi-creep gap (B) of the insulator are shown. When drawing a second extension line extending in the direction of the lower end surface and a third extension line extending downward from the line indicating the end surface of the semi-creeping ground electrode, the first and second extension lines are drawn. The distance from the intersection of the extension line 2 to the intersection of the first and third extension lines (hereinafter referred to as the distance C of the semi-surface insulator gap (C)) is greater than the distance A of the main air gap (A). It is characterized by being small. Here, the vertical positional relationship of the spark plug is described in such a manner that the front end surface of the center electrode faces downward.

When formed in this manner, the distance A of the main air gap (A) is smaller than the distance B of the semi-creeping gap (B) (A <B). Spark discharge occurs in the main air gap (A) between the parallel ground electrode. Here, the distance C of the semi-surface insulator gap (C) is smaller than the distance A of the main air gap (A) (C <A), and the height position of the lower end surface of the insulator and the semi-surface earth electrode Is less than the height of the upper end edge of the end surface of the end surface (E) is E ≦ + 0.7 (unit: mm). Therefore, when the lower end surface of the insulator becomes smolder, which is contaminated by carbon generated by combustion, the lower end surface of the insulator is located between the edge of the semi-creeping ground electrode and the side peripheral surface of the center electrode. A spark discharge occurs via the creeping surface (hereinafter, referred to as semi-creeping discharge). The spark of the semi-creeping discharge runs along the surface of the insulator after flying over the semi-creeping insulator gap (C). After repeated semi-creeping discharges, the carbon deposited on the bottom surface of the insulator is burned off and the surface of the insulator returns to a clean state, and the insulation on the surface of the insulator is restored again, eliminating "smoldering". The spark discharge returns from the semi-surface gap (B) to the main air gap (A).

Therefore, the present invention has the following effects. In the spark plug according to the present invention, a spark discharge occurs in the main air gap (A) between the parallel ground electrode and the parallel ground electrode for most of the time, and the semiconductive material is semi-conductive only when the surface of the insulator is contaminated by carbon. A semi-creeping discharge occurs in the semi-creeping gap (B) between the creeping ground electrode and the creeping ground electrode, and ignites the mixed gas in the combustion chamber. Most of the time the main air gap (A)
Since the mixed gas is ignited by the spark discharge in the above, the ignitability is excellent. In addition, since the semi-creeping discharge has a self-cleaning effect of burning off carbon deposited on the surface of the insulator, the spark plug is extremely resistant to "smoldering". Further, since the semi-creeping discharge is less frequently generated and the discharge time is completed in a very short time, the effect of "channeling" due to sparks is weakened, and almost no channeling occurs. Therefore, the life of the spark plug is sufficiently long.

Here, as in the second invention, the distance A of the main air gap (A) and the semi-creeping gap (B)
Distance B and the distance C of the semi-creep insulator gap (C)
Satisfies A ≦ (0.8 (B−C) + C) (unit is mm). When formed in this way, the spark rate in the main air gap (A) is 50% in a normal state where the spark plug is not in the state of “smoldering”.
That is all. Therefore, during normal operation, the main air gap (A)
And it is advantageous in terms of ignitability and channeling.

Here, as in the third invention, the distance B of the semi-surface crevice gap (B) is B ≦ 2.2 (unit: mm, the same applies hereinafter), and the semi-surface crevice gap (C) It can be characterized that the distance C satisfies 0.4 ≦ C ≦ (A−0.1) (A is the distance of the main air gap (A)). With such a configuration, when the surface of the insulator becomes "smoldering", a semi-surface discharge can be more reliably generated between the semi-surface ground electrode and the center electrode. If the distance B of the semi-creeping gap (B) is larger than 2.2 mm, no discharge occurs between the semi-creeping ground electrode and the center electrode, and the insulator is not placed between the center electrode and the vicinity of the insulator mounting portion of the metal shell. The probability of occurrence of so-called flashover, in which discharge occurs along the surface of the leg long portion, increases. The distance C of the semi-creep insulator gap (C) is 0.4 mm.
If it is smaller, the probability of a discharge being impossible due to the formation of a bridge between carbon and the semi-surface creeping ground electrode and the insulator is increased. On the other hand, when the distance C of the semi-creeping insulator gap (C) is larger than the distance A of the main air gap (A) of 0.1 mm, the semi-creeping gap between the semi-creeping ground electrode and the semi-creeping ground electrode can be obtained even during "smoldering" Rather than discharging at the insulator gap (C),
The probability of discharge in the main air gap (A) between the parallel electrodes increases.

Here, as in the fourth invention, the step E between the height position of the lower end surface of the insulator and the height position of the upper end edge of the end surface of the semi-creeping ground electrode is E ≦ + 0. (The unit is mm, and + means the direction in which the upper edge of the end surface of the semi-creeping ground electrode moves downward from the lower end surface of the insulator). With such a configuration, it is possible to effectively maintain the spark cleaning action of the insulator surface due to the spark of the semi-surface discharge. If the step E between the height position of the lower end surface of the insulator and the height position of the edge of the end surface of the semi-creeping ground electrode is larger than +0.5 mm, the spark of the semi-creeping discharge adheres to the lower end surface of the insulator. The effect of the spark cleaning action on the insulator surface is reduced. Note that this step E
However, when the spark plug does not have a parallel ground electrode, the discharge voltage increases in the negative direction (that is, the direction in which the upper edge of the end surface of the semi-creeping ground electrode moves upward from the lower surface of the insulator). In some cases. However, in a plug having a parallel ground electrode as in the present invention, the discharge voltage in a normal state is determined by the parallel ground electrode, so that the discharge voltage does not increase as described above. In this case, it is preferable that the cross-sectional area of the semi-surface creeping ground electrode be 3 mm2 or less. By forming in this manner, it is possible to suppress the occurrence of bridges at the time of low-temperature starting in the semi-surface insulator gap (C).

Here, as in the fifth invention, the step E
May be characterized by E ≦ −0.7 (unit: mm). With such a configuration, it is possible to more effectively maintain the spark cleaning action on the insulator surface due to the spark of the semi-surface discharge.

Here, as in the sixth invention, the protrusion amount H of the center electrode from the lower end surface of the insulator is 1.
It can be characterized that 0 ≦ H ≦ 4.0 (unit is mm, the same applies hereinafter). When formed in this manner, electrode consumption of the center electrode due to semi-surface discharge can be suppressed to a small level. In addition, it is possible to reduce the difference between the ignitability due to the spark discharge in the main air gap (A) between the parallel ground electrode and the ignitability due to the semi-surface creeping discharge of the semi-surface creeping ground electrode. It is possible to minimize the torque fluctuation of the internal combustion engine due to the change in the ignitability accompanying the change. If the protrusion amount H of the center electrode is smaller than 1.0 mm, the electrode consumption on the side of the center electrode becomes large. On the other hand, if the protruding amount H of the center electrode is larger than 4.0 mm, the ignitability due to the semi-surface creeping discharge is lower than the ignitability in the main air gap (A), and the ignitability of the two is undesirably different. In addition, the temperature of the center electrode becomes too high, and the probability of occurrence of preignition increases. In addition, in order to further reduce the divergence of the ignitability and further suppress the temperature rise of the center electrode,
It is desirable that H ≦ 2.0.

Here, as in the seventh invention, the tip diameter of the center electrode is smaller than that of the root protruding from the lower end surface of the insulator, and the tip diameter D1 of the center electrode at the tip is 0.4 ≦ D1 ≦ 1.6 (unit: mm, the same applies hereinafter), and the center electrode base diameter D2 of the root portion protruding from the lower end surface of the insulator is (D1 + 0.3) ≦ D2. It can be. When the tip diameter D1 of the center electrode is reduced as described above, the discharge voltage between the center electrode and the parallel ground electrode decreases, and the ignitability in the main air gap (A) improves. If the center electrode tip diameter D1 is smaller than 0.4 mm, even if a noble metal is used for the tip of the center electrode, the consumption by sparks increases, which is not practical. Further, when the center electrode tip diameter D1 is larger than 1.6 mm, the effect of lowering the discharge voltage becomes insignificant. In addition, the center electrode base diameter D of the root portion
If 2 is larger than the center electrode tip diameter D1, it is easy to fire at the semi-surface gap (B) during "smoldering", and easily at the main air gap (A) during normal operation. Furthermore, if the center diameter D2 of the center electrode is large to some extent, the action of heat drawing is improved, and the tip of the center electrode is prevented from being overheated. It is considered that the above-mentioned effect is obtained when the center diameter D2 of the center electrode becomes (D1 + 0.3) mm or more.

Here, as in the eighth aspect, the center electrode base diameter D2 is 2.0 ≦ D2 (unit: mm,
The same applies hereinafter). By forming the center electrode base diameter to be large in this way, overheating of the tip of the center electrode can be more effectively prevented, and
The consumption of the center electrode when a discharge occurs in the semi-creeping gap (B) can be suppressed. In addition, since the concentration of the electric field is reduced by increasing the center electrode base diameter D2, the spark generation rate to the semi-surface gap (B) in the normal state can be reduced. The material used for the center electrode is preferably a material containing nickel as a main component, and more preferably a good heat conductive alloy having a content of 85% by weight or more. By increasing the nickel content in this way, the heat removal can be further improved, and the consumption of the center electrode in the event of discharge in the semi-creeping gap (B) can be further suppressed.
In addition, when the semi-creep gap (B) is kept constant and the main air gap (A) is made wider, the discharge in the semi-creep gap (B) increases. Considering the consumption of the center electrode, it is desirable to make it thicker, but the main air gap (A)
It is thought to be related to the size of Although the relationship between the two is not clear at present, it is desirable that the center electrode base diameter D2 is set to be about twice or more the distance A of the main air gap (A).

Here, as in the ninth invention, the tip of the center electrode is made of a platinum alloy, an iridium alloy or the like having a melting point of 1 point.
It can be characterized by being made of a noble metal having a temperature of 600 ° C. or higher. When formed in this manner, the wear resistance of the center electrode against spark discharge is improved, and the life of the spark plug is prolonged. In this case, it is particularly desirable to use the above-mentioned center electrode material having a nickel content of 85% by weight or more. As a result, it is possible to secure the heat removal at the tip of the center electrode and to lower the temperature of the iridium alloy, which is often oxidized and consumed at high temperatures, which is very advantageous for the consumption of precious metals.

Here, as in the tenth aspect, the semi-surface creeping ground electrode has a straight rod shape, and a side surface of the semi-surface creeping ground electrode is joined to a lower end surface of the metal shell. It can be a feature. Since the semi-surface creeping ground electrode is located near the lower end surface of the insulator, the following problems may occur if the dimension of the insulator protruding from the lower end surface of the metal shell is small. In other words, the semi-creeping ground electrode on the lower end surface of the metal shell is joined by welding or the like, but it is necessary to bend in a substantially L-shape toward the center electrode in the immediate vicinity of the joint. For this reason, the curvature of the bent portion must be reduced, which may cause manufacturing defects such as breakage and cracking. Therefore, such a problem can be solved by forming as in the present invention.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of the spark plug according to the first embodiment. As we all know,
The insulator 1 made of alumina or the like has a corrugation 1A for increasing a creepage distance at an upper portion thereof, a leg portion 1B exposed to a combustion chamber of an internal combustion engine at a lower portion, and a central through hole 1C at an axial center thereof. ing. At the lower end of the center through hole 1C, a center electrode 2 made of a nickel alloy such as Inconel is held, and the center electrode 2 projects downward from the lower end surface of the insulator 1. The center electrode 2 is the center through hole 1
It is electrically connected to an upper terminal nut 4 via a ceramic resistor 3 provided inside C. A high voltage cable (not shown) is connected to the terminal nut 4 to apply a high voltage. The insulator 1 is supported by being surrounded by a metal shell 5. The metal shell 5 is formed of a low-carbon steel material, and includes a hexagonal portion 5A fitted with a spark plug wrench and a screw portion 5B. The metal shell 5 is caulked to the insulator 1 by the caulking portion 5C, and the metal shell 5 and the insulator 1 are integrated. In order to complete the sealing by caulking,
A plate-shaped packing member 6 and wire-shaped sealing members 7 and 8 are interposed between the metal shell 5 and the insulator 1, and the talc (talc) 9 powder is filled between the sealing members 7 and 8. I have. A gasket 10 is fitted at the upper end of the screw portion 5B.

A parallel ground electrode 11 made of a nickel alloy is joined to the lower end of the metal shell 5 by welding. The parallel ground electrode 11 is axially opposed to the front end face of the center electrode 2, and the main air gap (A) is formed between the center electrode 2 and the parallel ground electrode 11.
Is formed. Up to this point, it is the same as the conventional spark plug. In the spark plug according to this embodiment, apart from the parallel ground electrode 11, two semi-creeping ground electrodes 1 are provided.
2 and 12 are provided. The semi-surface creeping ground electrode 12 is made of a nickel alloy, one end of which is joined to the lower end of the metal shell 5 by welding, and the other end surface 12C is connected to the side peripheral surface 2A of the center electrode 2 or the side peripheral surface 1E of the leg long portion 1B. They are arranged to face each other. The two semi-creeping ground electrodes 12 are respectively disposed at positions shifted from the parallel ground electrodes 11 by 90 °.
The semi-creeping ground electrodes 12 are arranged at positions shifted by 180 °. A semi-surface creeping gap (B) is formed between the end surface 12C of each semi-surface creeping ground electrode 12 and the side peripheral surface 2A of the center electrode 12, respectively.
A semi-creep insulator gap (C) is formed between the end surface 12C of the second and the side peripheral surface 1E of the leg long portion 1B.

FIG. 2A is an enlarged partial cross-sectional view showing the vicinity of the center electrode 2, the parallel ground electrode 11, and the semi-creeping ground electrode 12 of the spark plug, and FIG. FIG. 3 is an explanatory diagram showing an electrode 12 in an enlarged manner. Center electrode 2
The distance of the main air gap (A) between the front end surface of the center electrode 2 and the parallel ground electrode 11 is A, and the semi-creep gap between the side peripheral surface 2A of the center electrode 2 and the end surface 12C of the semi-creep ground electrode 12 ( B) is the distance B, and the semi-creeping ground electrode 12 and the insulator 1
Is extended along the central axis 30 to extend a line indicating the lower end face 1D of the insulator 1 outward.
A second extension line 32 obtained by extending a line indicating the side peripheral surface 1E near the semi-creep gap (B) portion of the insulator 1 in the direction of the lower end face 1D, and an end face 12C of the semi-creep ground electrode 12 are shown. Draw a third extension line 33 obtained by extending the line downward, and from an intersection P1 of the first extension line 31 and the second extension line 32, an intersection P2 of the first extension line 31 and the third extension line 33 Assuming that the distance to the surface c is the distance C of the semi-surface insulator gap (C), there is a relationship of A <B and C <A. By setting in this way, when the insulation on the surface of the insulator 1 is normal and high, the discharge is caused in the main air gap (A) between the parallel ground electrode 11 and the insulation on the surface of the insulator 1 is reduced. "
In some cases, discharge can occur at a semi-surface gap (B) between the semi-surface ground electrode 12. Upper edge 12 of lower end surface 1D of insulator 1 and end surface 12C of semi-creeping ground electrode 12
E is the level difference from B, and the lower end face 5D of the metal shell 5 of the insulator 1
And the amount of protrusion of the center electrode 2 from the lower end face 1D of the insulator 1 is H. In the present embodiment, the protrusion F of the insulator 1 is 3.0 mm, and the original diameter D2 of the center electrode 2 is 2.0 mm. The semi-creeping ground electrode 12 has a width of 2.2 mm and a thickness of 1.3 mm, and the parallel ground electrode 11 has a width of 1.5 mm.
mm and a thickness of 2.8 mm are used. In addition, the parallel ground electrode 11 may be one having a copper core in order to reduce the temperature at the tip and to suppress spark consumption.

A step E between the height of the lower end face 1D of the insulator 1 and the height of the upper end 12B of the end face 12C of the semi-creeping ground electrode 12 has a height position of the semi-creeping ground electrode 12. As a result, as shown in FIG.
The upper edge 12B and lower edge 12A (FIG. 2 (b)) are above the lower edge 1D of the insulator 1, and only the upper edge 12B of the semi-creeping ground electrode 12 is insulated as shown in FIG. In the case where the insulator 1 is located above the lower end face 1D, FIG.
As shown in (1), the upper edge 12B of the semi-surface creeping ground electrode 12 is lower than the lower edge 1D of the insulator 1. In any case, it is preferable that one of the upper end edge 12B and the lower end edge 12A of the end surface 12C of the semi-surface creeping ground electrode 12 is located at a height near the lower end surface 1D of the insulator 1. That is, the step E is preferably small. In the semi-creeping discharge, it is considered that sparks fly from the upper end edge 12B and the lower end edge 12A of the semi-creeping ground electrode 12 where the electric field is concentrated at an acute angle.
This is because the spark flying from A is brought closer to the lower end face 1D of the insulator 1 to enhance the self-cleaning action of burning off carbon deposited on the surface of the insulator 1.

(Basis for B ≦ 2.2 (unit: mm))
FIG. 5 is a graph showing the relationship between the distance B of the semi-creeping gap (B) and the discharge voltage. In order to evaluate the relationship between the distance B of the semi-creeping gap (B) and the discharge voltage, racing was performed by fully opening the throttle from idling using an engine, and an idling → racing test was performed to observe the discharge voltage. . The spark plug used was one obtained by cutting the parallel ground electrode 11 from the welded portion of the metallic shell 5. The engine used is a 1.6-liter in-line four-cylinder engine. The semi-creep gap (B) distance B is 2.2mm
Is exceeded, the discharge voltage exceeds 25 KV, and before the discharge occurs between the semi-surface creeping ground electrode 12 and the center electrode 2, the discharge voltage from the center electrode 2 to the vicinity of the root of the leg 1 B of the insulator 1 of the metal shell 5. There is a possibility that a so-called flashover, which will cause a fire, will occur. For this reason, the distance B of the semi-creeping gap (B) needs to be 2.2 mm or less.

(A ≦ (0.8 (BC) + C), 0.4
≦ C ≦ (A−0.1), (unit: mm) FIG. 6 shows the distance A of the main air gap (A) on the vertical axis, and the distance C of the semi-surface insulator gap (C) on the horizontal axis. FIG. 7 is a graph of a 50% fire rate plotting points at which the respective fire rates in the main air gap (A) and the semi-surface creepage insulator gap (C) become 50%. The spark rate was evaluated by a desk test in which a spark plug was mounted in a chamber provided with a window through which a main air gap (A) and a semi-creepage gap (B) could be observed, and the direction of the spark was observed. In addition, the spark plug in the state of "smoldering" prepared the sample which reduced the insulation resistance value to 5-10 M (ohm) using the general-purpose engine etc. beforehand. In the figure, a straight line 101 is a semi-creeping gap (B).
In the case where the difference (BC) between the distance B of the semi-creep gap (B) and the distance C of the semi-creep gap (C) is 1.0 mm, ie, the portion of the lower end face 1D of the insulator 1
The straight line 101 ′ is the same when (B−C) is 1.2 mm,
101 "is a straight line of 50% of the fire rate measured when the spark plug is not in the state of" smoldering "when (BC) is 0.8 mm. Also, straight line 1
Reference numeral 02 denotes a straight line with a 50% fire rate when the spark plug is "smoldering". In the state of "smoldering", it is represented by the same straight line regardless of the magnitude of the distance B of the semi-creeping gap (B). Therefore, for example, when the above-mentioned (BC) is 1.0 mm, the area AA on the left side of the straight line 101 is the semi-surface creepage gap (C) even under normal conditions.
Area BB on the right side of the straight line 101
And CC are areas in which a fire occurs in the main air gap (A) under normal conditions. On the other hand, the areas AA and B on the left side of the straight line 102
B is a region where a spark occurs in the semi-surface insulator gap (C) at the time of “smoldering”, and a region CC on the right side of the straight line 102 is a region where a spark is generated at the main air gap (A) even at the time of “smoldering”. Therefore, the area which ignites in the main air gap (A) in normal operation and ignites in the semi-surface insulator gap (C) in "smoldering" is an area BB sandwiched between the two straight lines 101 and 102.

A straight line 101 is represented by C = A-0.8 (unit: mm, the same applies hereinafter), and a straight line 102 is represented by C = A-0.8
The area BB sandwiched between the straight lines 101 and 102 is expressed by the following equation (1). A−0.8 ≦ C ≦ A−0.1 (1) Further, a straight line 101 ′ obtained by linearly regressing the data when (B−C) is set to 1.2 mm is C = A− 0.96
The straight line 101 ″ obtained by linearly regressing the data when (B−C) is set to 0.8 mm is expressed by C = A−0.64. Therefore, these three types of straight lines 101, 101 ′, 1
01 ", the condition of the following formula (2) is necessary in order for the spark rate in the main air gap (A) to be 50% or more in a normal state in consideration of the semi-creep gap (B). A ≦ 0.8 (B−C) + C (2)

On the other hand, it has been found that if the distance C of the semi-surface insulator gap (C) is too small, it is vulnerable to so-called pre-delivery fouling. Predelivery fo
uling) means that when a new car is transported from the car assembly plant to the dealer, it is driven a very short distance many times, and the temperature of the spark plug does not rise, resulting in a "smoldering" state. This refers to the fouling that lowers the insulation resistance of the plug. JISD 16 to evaluate pre-delivery fouling
As specified in the Low Load Conformity Test of 2006, -1
Place the car in a low-temperature test room at 0 ° C, perform 10 cycles of operation with a predetermined operation pattern of jogging several times at low speed as one cycle, and measure the insulation resistance of the spark plug at the middle and end of each cycle A way to be taken. FIG.
Shows a test example of a pre-delivery fouling test with spark plugs having different distances C of the semi-surface insulator gap (C). In the figure, □ indicates C = 0.4 mm, ○ indicates C = 0.6 m
m and △ are insulation resistance measurement values of a two-pole semi-creeping spark plug of C = 0.8 mm. The engine is an inline 6 cylinder.
Five liters were used. At C = 0.4 mm, a carbon bridge occurred in six cycles, and the discharge became impossible, leading to engine stall.

FIG. 8 shows that the pre-delivery fouling test described above is performed several times, and the approximate probability that a carbon bridge is generated and the engine stalls and becomes N / G is determined by the distance C of the semi-surface insulator gap (C). This is shown on the axis. As is clear from the figure, when the distance C of the semi-surface insulator gap (C) becomes smaller than 0.4 mm, the probability of N / G increases rapidly. Therefore, the distance C of the semi-creep insulator gap (C) needs to satisfy the following expression (3) with the unit being mm. 0.4 ≦ C (3) From the conditions of Expressions (1) and (3), it is preferable that the distance C of the semi-creep insulator gap (C) satisfies at least the following Expression (4). 0.4 ≦ C ≦ A-0.1 (4)

(E ≦ + 0.7, preferably E ≦ + 0.
5. (Rationale for mm) Lower end face 1 of insulator 1
The step E between D and the upper edge 12B of the semi-creeping ground electrode 12 is not more than +0.7 mm, preferably not more than +0.5 mm. Here, + is the end surface 12 of the semi-surface ground electrode 12.
C means the direction in which the upper edge 12B moves downward from the lower end face 1D of the insulator 1. To test this, see FIG.
The pre-delivery soiling test was carried out for the step E having a minus (minus) dimension as shown in FIG. 4A and for the one having a plus (plus) dimension as shown in FIG. The engine used is an in-line 4-cylinder 1.8 liter.
As a result, the test results shown in the following Table 1 were obtained. In the table, ◎ indicates that the spark plug is 1 even after 12 cycles of operation.
Indicates that the insulation resistance value of 0 MΩ or more was maintained.
The spark plug shows that the insulation resistance value of 10 MΩ or more was maintained even after the operation of 0 cycle.
Although it decreased to 0 MΩ or less, it indicates that the engine could be operated for 10 cycles, and x indicates that the engine could not be started in 8 cycles.

[Table 1] In order to be able to operate for 10 cycles in this test, as apparent from Table 1 above, the step E must be +0.
7 mm or less (E ≦ + 0.7), and +0.5 m
m or less (E ≦ + 0.5). Step E is +0.7
If the step E is larger, the spark from the semi-creeping ground electrode 12 separates from the lower end face 1D of the insulator 1 and the self-cleaning action of burning off the carbon by the semi-creeping discharge. It is thought to be due to the decrease.

(The grounds for 1.0 ≦ H ≦ 4.0, unit: mm) First, the lower end face 1 of the insulator 1 of the center electrode 2
The protrusion amount H from D is preferably 1.0 mm or more (1.0 ≦ H). Projection amount H of center electrode 2
When a semi-creeping discharge occurs from the semi-creeping ground electrode 12 with a spark plug having a small diameter, the spark concentrates on the side peripheral surface 2A of the center electrode 2 near the lower end surface 1D of the insulator 1.
This neighborhood is consumed. When the protruding amount H of the center electrode 2 from the lower end face 1D of the insulator 1 is 1.0 mm or more, as shown in FIG.
It wears out like a neck. However, if the protruding amount H of the center electrode 2 from the lower end face 1D of the insulator 1 is less than 1.0 mm, the center electrode 2 gradually becomes thinner toward the end face of the center electrode 2 as shown in FIG. Wear out.

Here, the maximum value of the amount of consumption of the side peripheral surface 2A of the center electrode 2 is defined as Δd. Since the volume of the electrode consumed per spark is considered to be almost constant, FIG.
As shown in FIG. 9B, the maximum consumption amount Δd when exhausted is larger than the maximum consumption amount Δd when exhausted as shown in FIG. 9A. In order to investigate the relationship between the maximum consumption amount Δd and the protrusion amount H, spark plugs having different protrusion amounts H are prepared, and the semi-surface discharge from the semi-surface surface ground electrode 12 is performed 4 × 10 7 times (40 million times). We went and examined the spark durability. The result is shown in FIG. As is clear from FIG. 10, when the protrusion amount H is 0.5 mm, the maximum consumption amount Δd
Is 0.37 mm, the maximum consumption amount Δd is 0.33 mm when the protrusion amount H is 0.7 mm, and the maximum consumption amount Δd is 0.30 mm when the protrusion amount H is 1.0 mm. Also, the maximum consumption amount Δd was substantially constant. Therefore, in order to reduce the maximum wear amount Δd, the protrusion amount H of the center electrode 2 is 1.0 mm or more (1.
0 ≦ H) is preferred. In addition, the spark plug used for this test used the sample which cut | disconnected the parallel grounding electrode 11 by the welding surface with the metal shell 5. FIG. In this way, a spark was always fired at the semi-creep gap (B), and the amount of consumption was examined. Also,
This test was performed by a desk test in which the above-described spark plug was mounted in a chamber provided with a window through which the main air gap (A) and the semi-creeping gap (B) could be observed. The ignition device tested had a spark discharge energy of about 70 mJ.
Was used.

Next, the lower end surface 1 of the insulator 1 of the center electrode 2
The protrusion amount H from D is not more than 4.0 mm (H
≦ 4.0) is preferred. There are two reasons for this. The first reason is that the ignitability caused by the discharge in the main air gap (A) and the discharge in the semi-creeping gap (B) does not significantly differ. FIG. 11 shows the protrusion amount H of the center electrode 2 and the air-fuel ratio (A / F) serving as the ignition limit when the protrusion size of the center electrode 2 from the end face 5D of the metal shell 5 is fixed.
FIG. 6 is a graph showing the relationship between 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%. A curve 103 indicates the ignition limit air-fuel ratio due to the spark in the main air gap (A), and a curve 104 indicates the ignition limit air-fuel ratio due to the spark in the semi-surface gap (B). The engine used was an in-line 6-cylinder 2 liter engine, and was measured at an idle operation at 700 rpm. Also,
The protruding dimension (F + H) of the center electrode 2 of the spark plug from the end face 5D of the metal shell 5 was 6.0 mm, and the distance B of the semi-surface gap (B) was 1.7 mm. Since the main discharge in the main air gap (A) is essentially not affected by the protrusion amount H of the center electrode 2, the curve 103 shows a flat straight line. On the other hand, in the discharge in the semi-creeping discharge, the spark position approaches the wall surface of the combustion chamber with an increase in the protrusion amount H, so that the ignitability decreases, and the curve 104 shows a downward slope. If there is a large difference between the ignitability in the main discharge and the ignitability in the semi-creeping discharge, the torque of the engine when switching from the discharge in the main air gap (A) to the discharge in the semi-creeping gap (B) is obtained. Fluctuations occur, which is not preferable. In order to keep the difference in ignitability within an allowable range, the protrusion amount H of the center electrode 2 is preferably 4.0 mm or less (H ≦ 4.0).

The second reason is to prevent pre-ignition due to overheating of the center electrode 2. FIG. 12 shows the center electrode 2
FIG. 4 is a graph showing the relationship between the protrusion amount H and the temperature of the center electrode 2. The amount of protrusion F of the insulator 1 was 3.0 mm, and a spark plug having a heat value of No. 5 was used. Center electrode 2
When the protrusion amount H of the insulator becomes large, the heat extraction by the insulator 1 becomes poor, and the temperature of the tip of the center electrode 2 becomes high. When the protrusion amount H becomes 5.0 mm, the temperature at the tip of the center electrode 2 exceeds 850 ° C., and the possibility of preignition appears. Therefore, the protrusion amount H of the center electrode 2 is 4.0 mm.
The following is preferable (H ≦ 4.0). For the reasons described above, the protrusion amount H of the center electrode 2 from the lower end face 1D of the insulator 1 is 1.0 ≦ H ≦ 4.0 (unit is m
m) is preferred.

Next, a second embodiment of the present invention will be described with reference to the drawings. In the present embodiment, since there is no change other than the shape of the tip of the center electrode 2 as compared with the first embodiment, the description will be omitted, and only different portions will be described. FIG. 13 shows the center electrode 2 ′ of the spark plug and the parallel ground electrode 1.
1 is a partial cross-sectional view showing the vicinity of a semi-creeping ground electrode 12 in an enlarged manner. The diameter of the front end of the center electrode 2 ′ is smaller than that of the root portion protruding from the lower end surface 1 D of the insulator 1.
The tip diameter of the center electrode 2 ′ is D1, and the original diameter is D2. The tip of the reduced center electrode 2 'is formed by joining a tip 21 made of a platinum alloy by laser welding.
In the present embodiment, the protrusion amount H of the center electrode 2 'from the lower end face 1D of the insulator 1 is set to 2.0 mm, and the lower end face 1 of the insulator 1 at the start point 22 where the center electrode 2' starts reducing the diameter.
The protrusion amount J from D was 0.6 mm.

(0.4 ≦ D1 ≦ 1.6, unit is mm)
The ground diameter D1 of the center electrode 2 'is 0.4 mm or more and preferably 1.6 mm or less. If the tip diameter D1 is smaller than 0.4 mm, even if a platinum alloy or an iridium alloy is used for the tip portion of the center electrode 2 ', electrode consumption due to sparks increases, which is not practical. For the above reasons, the tip diameter D1 of the center electrode 2 'is 0.4 mm or more and 1.6 m.
m (0.4 ≦ D1 ≦ 1.6).

((D1 + 0.3) ≦ D2, (unit is m
The reason for the m)) In order to ignite at the semi-creep gap (B) at the time of "smoldering" and to stably ignite at the main air gap (A) at the normal time, the center electrode base at the root of the center electrode 2 'is required. The diameter D2 is preferably larger than the tip diameter D1. Also,
The larger the center electrode base diameter D2, the better the heat removal from the center electrode tip, and prevents the center electrode tip from overheating. For this reason,
The center electrode base diameter D2 is (center electrode tip diameter D1 + 0.3 m
m) is preferable. The upper limit of the center electrode base diameter D2 is inevitably determined by the thickness of the insulator 1 required for insulation near the lower end of the insulator 1.

(Reason for 2.0 ≦ D2, (unit: mm)) The overheating of the tip of the center electrode is more effectively prevented, and the consumption of the center electrode when a discharge occurs in the semi-creeping gap (B). In order to suppress this, it is desirable to increase the center electrode base diameter D2. In addition, since the concentration of the electric field is reduced by increasing the center electrode base diameter D2, the spark generation rate to the semi-surface gap (B) in the normal state can be reduced. In order to test this, the distance A of the main air gap (A) was 1.0 mm, the distance B of the semi-creeping discharge gap (B) was 1.5 mm, and the distance C of the semi-creeping insulator gap (C) was 0.5 mm. Using the samples in which the center electrode base diameter D2 was variously changed, the samples were mounted on the engine and evaluated by the maximum value [Delta] d of the amount of wear on the side surface of the center electrode after performing a 6000 rpm x WOT (fully open) durability test. . The engine used was an in-line 6 cylinder 2
Liters and test conditions are 6000 rpm x WOT
(Full throttle open) 400 hours. Further, a general full-transistor type ignition device having a spark discharge energy of about 70 mJ was used as the ignition device for the test. as a result,
The test results shown in Table 2 below were obtained. In the table, ◎ indicates that the maximum consumption amount Δd was less than 0.35 mm, ○ indicates that the maximum consumption amount Δd was 0.35 mm or more and 0.5 mm or less, and Δ indicates that the maximum consumption amount Δd was 0.5 mm. It indicates that it exceeds.

[Table 2] D2 dimension Maximum consumption amount Δd 1.5 △ 1.75 ○ 2.0 ◎ 2.25 ◎ 2.5 ◎ As is clear from Table 2 above, the center electrode base diameter D2 is 2.0 mm or more. (2.0 ≦ D2) is preferable. When the center electrode base diameter D2 increases, the maximum value Δd of the consumption amount of the center electrode decreases because the volume of the electrode consumed per spark is considered to be substantially constant;
This is considered to be because the concentration of the electric field is reduced by increasing the center electrode base diameter D2, so that the rate of spark generation to the semi-creeping gap (B) can be reduced.

Next, third and fourth embodiments of the present invention will be described with reference to the drawings. In the present embodiment,
Since there is no change other than the shape of the semi-surface creeping ground electrode 12 as compared with the first and second embodiments, the description will be omitted, and only different portions will be described. FIG. 14 is a partial cross-sectional view of the third embodiment in which the vicinity of the center electrode 2, the parallel ground electrode 11, the semi-surface creeping ground electrode 12 'and the lower end of the metal shell 5 of the spark plug are enlarged. The semi-creeping ground electrode 12 ′ is formed in a straight rod shape, and the side surface thereof is resistance-welded to the lower end surface 5 D of the metal shell 5. FIG. 15 is a partial sectional view of the fourth embodiment in which the vicinity of the center electrode 2, the parallel ground electrode 11, the semi-surface creeping ground electrode 12 ', and the lower end of the metal shell 5 of the spark plug are enlarged. A lower end surface 5D is formed in a wide shape by forming a swelling portion 5E swelling toward the inner diameter side at a lower end portion of the metal shell 5, and an auxiliary gap (K) is provided between the metal shell 5 and the insulator 1. Have been. Then, a straight rod-shaped semi-surface creeping ground electrode 12 ′ is formed on the lower end surface 5 </ b> D formed in the wide shape.
Are resistance welded. By forming in this manner, it is not necessary to bend the semi-surface creeping ground electrode 12 ′ in a substantially L-shape toward the center electrode 2 in the immediate vicinity of the joint of the metal shell end face, so that breakage, cracking, etc. Does not cause manufacturing defects.

(Comprehensive Test) In order to test the effect of the spark plug according to the present invention, a general spark plug (type PFR6G-11), a semi-surface spark plug (type BKR6EKUC), and first and second spark plugs according to the present invention are tested. A "smoldering" test and a "channeling" test were performed using the spark plug of the second embodiment. In the "smoldering" test, a four-cycle general-purpose engine with a single cylinder of 440 cc was used, and severe operation was performed in which idling operation was performed with the choke half open. As a result, with a general spark plug, the engine stalled due to "smoldering" in 5 minutes of operation. Semi-surface spark plugs withstand longer operation than ordinary spark plugs, but still
After a minute of driving, the engine stalled due to "smoldering". On the other hand, in the spark plugs of the first and second embodiments according to the present invention, the operation continued without any problem even after the operation for 20 minutes. The reason why the spark plug according to the present invention is better than the semi-surface spark plug is that the spark plug according to the present invention normally ignites in the main air gap (A) and thus has a good combustion state and causes "smoldering". This is probably because the amount of incomplete combustion that occurs is small.

In the "channeling" test, a pressure of 0.8 M
A continuous spark durability test was performed at 100 Hz for 100 hours with a full transistor power supply in an environment of Pa (megapascal). Normal combustion chamber pressure just before ignition is 0.4MP
Since the pressure is about a, the pressure is applied. As a result, in the semi-surface spark plug, a large channeling mark was left on the surface of the insulator, and the depth reached a maximum of 0.4 mm. On the other hand, no channeling mark was detected with the general spark plug and the spark plugs of the first and second embodiments according to the present invention.

(Other Embodiments) In each of the embodiments described above, the semi-creeping ground electrode 12 has two poles. However, the semi-creeping ground electrode may be a single pole or a multipole having three or more poles. It may be a pole. However, with a single pole, it is difficult to burn off carbon with sparks over the entire circumference of the insulator end face,
It is considered that the semi-surface creeping ground electrode preferably has two to three poles because the spark cleanliness is deteriorated. Further, the spark plug in which the diameter of the center electrode is not reduced (so-called thermo) inside the front end of the insulator has been described, but the spark plug may be reduced in diameter in one or more stages.

[0040]

As described above, according to the present invention, in addition to the parallel ground electrode for performing the main discharge, the semi-surface creeping ground electrode is provided near the lower end face of the insulator. At the time of `` smoldering '' whose surface is contaminated with carbon, it has a self-cleaning effect of burning off carbon by semi-creeping discharge from the semi-creeping ground electrode, and since the main discharge is performed by the parallel grounding electrode, it is extremely smoldering It has an excellent effect that it is strong, has high ignitability, has little "channeling", and has a long life.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a spark plug according to a first embodiment.

FIG. 2A is an enlarged partial cross-sectional view showing the vicinity of an electrode of a spark plug according to a first embodiment, and FIG. 2B is an explanatory view showing an enlarged semi-surface creeping ground electrode 12. It is.

FIG. 3 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a second embodiment.

FIG. 4 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a third embodiment.

FIG. 5 is a graph showing a relationship between a distance B of a semi-creeping gap (B) and a discharge voltage.

FIG. 6 shows the distance A of the main air gap (A) on the vertical axis and the distance C of the semi-creep insulator gap (C) on the horizontal axis, and shows the main air gap (A) and the semi-creep insulator gap (C). Rate 50 plotting the points at which the respective fire rates are 50%
It is a graph figure of%.

FIG. 7 is a graph showing a measurement example of a pre-delivery fouling test.

FIG. 8 is a graph showing a relationship between a distance C of a semi-creep insulator gap (C) and a pre-delivery fouling test N / G.

9 (a) and 9 (b) are explanatory diagrams showing the state of wear of the center electrode.

FIG. 10 is a graph showing the relationship between the protrusion amount H of the center electrode and the maximum consumption amount Δd.

FIG. 11 is a graph showing a relationship between a protrusion amount H of a center electrode and air-fuel consumption (A / F) serving as an ignition limit.

FIG. 12 is a graph showing the protrusion amount H of the center electrode and the temperature at the tip of the center electrode.

FIG. 13 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a second embodiment.

FIG. 14 is an enlarged partial cross-sectional view showing the vicinity of an electrode of a spark plug according to a third embodiment.

FIG. 15 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulator 1D Lower end surface of insulator 1E Side peripheral surface of insulator 2 Center electrode 2 'Center electrode 2A Side peripheral surface of center electrode 5 Metal shell 5D Lower surface of metal shell 11 Parallel ground electrode 12 Semi creeping ground electrode 12 '' Semi-creeping ground electrode 12A Lower edge 12B Upper edge 12C End face of semi-creeping ground electrode 30 Center axis 31 First extension line 32 Second extension line 33 Third extension line (A) Main air gap A Main Distance of air gap (B) Semi creepage gap B Semi creepage gap distance (C) Semi creepage insulator gap C Semi creepage insulator gap distance D1 Center electrode tip diameter D2 Center electrode base diameter E Step F Insulation amount of insulator H Projection amount of center electrode P1 Intersection of first and second extension lines P2 Intersection of first and third extension lines

Claims (1)

[Claims] An insulator having a center through-hole, a center electrode held in the center through-hole and protruding downward from a lower end surface of the insulator, and a metal shell holding the insulator; A parallel ground electrode, one end of which is joined to the metal shell and the other end of which is disposed so as to face the front end surface of the center electrode, and the main air gap is formed by the parallel ground electrode and the front end surface of the center electrode. In the spark plug of (A), one or a plurality of semi-conductors are arranged such that one end is joined to the metal shell and the other end is opposed to the side peripheral surface of the center electrode or the side peripheral surface of the insulator. A semi-creeping ground electrode (C), wherein a semi-creeping gap (B) is formed between an end face of the other end of the semi-creeping ground electrode and a side peripheral face of the center electrode opposed to the end face; End of the semi-creeping ground electrode A semi-creep insulator gap (C) is formed between the surface and a side peripheral surface of the insulator facing the end face, and a height position of a lower end face of the insulator;
The level difference E from the height of the upper edge of the end surface of the semi-creeping ground electrode is E ≦ + 0.7 (unit: mm, and + indicates that the upper edge of the end surface of the semi-creeping ground electrode is below the insulator. The distance B of the semi-creeping gap (B) is greater than the distance A of the main air gap (A), and the end face of the semi-creeping ground electrode and When the insulator is cut along the center axis of the insulator,
A first extension line extending outward from a line indicating the lower end surface of the insulator, and a semi-creep gap (B) of the insulator.
A second extension line extending from the line indicating the side peripheral surface near the portion toward the lower end surface, and a third extension line extending downward from the line indicating the end surface of the semi-surface creeping ground electrode. In this case, the first and third lines may be separated from the intersection of the first and second extended lines.
A distance (hereinafter, referred to as a distance C of the semi-surface insulator gap (C)) to an intersection of the extension lines of the main air gap (A) is smaller than the distance A of the main air gap (A).