JP2001160475A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug for internal combustion engine to perform aerial discharge in normal case, and on soiling, to recover from stain by eliminating carbon on the top of the insulator by creep discharge. SOLUTION: The spark plug for internal-combustion engine comprises a first grounding electrode 5 to form a first discharge gap A with the top face of a central electrode 4 and second grounding electrodes 6 and 7 to form a second discharge gap with the side face of the central electrode 4. The first discharge gap A, the shortest distance B between an insulator 3 and the second earthing electrodes 6 and 7, the axial direction distance C from the end face of a fitting 2 to the end face of the insulator 3, the axial direction distance H from the end face of the insulator 3 to the end face of the central electrode 4, and an axial direction distance F in case the end face of the above insulator and the end face of the above earthing electrodes are protruded from the side angle part of the above fitting, are set to be within the respective prescribed numerical range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine having improved self-cleaning action.

[0002]

2. Description of the Related Art Recently, interest in the environment has increased, and attention has been paid to a fuel-efficient internal combustion engine that adopts stratified combustion as a more environmentally friendly internal combustion engine.

[0003] However, when stratified combustion is caused in the combustion chamber, the rich air-fuel mixture collects in the vicinity of the spark plug, so that carbon pollution of the spark plug is easily generated. According to such carbon fouling, the insulation of the surface of the insulator holding the center electrode is deteriorated, and not a spark discharge between a regular discharge gap between the center electrode and the ground electrode. There is a problem that a spark discharge occurs in the inner part of the housing from the surface of the insulator between the insulator and the mounting bracket.

[0004] In order to solve such a problem, for example, Japanese Utility Model Publication No. 53-41629 and Japanese Patent Application Laid-Open No. 47-19236 are known as spark cleaning spark plugs.

In Japanese Utility Model Publication No. 53-41629, a plurality of ground electrodes are provided, and a first ground electrode and a center electrode are used to form a first ground electrode.
A discharge gap is formed, and a second discharge gap is formed by a second ground electrode different from the first ground electrode and the center electrode. According to this publication, a normal spark discharge is performed in the first discharge gap. However, when the insulator is contaminated with carbon as described above, the spark discharge is performed in the second discharge gap, thereby making the insulator smaller. The carbon which is contaminating is eliminated, thereby suppressing the depth of discharge and suppressing the decrease in ignitability.

Further, Japanese Patent Application Laid-Open No. 47-19236 has a first discharge gap which is a normal discharge gap and a second discharge gap which discharges when the insulator is contaminated, and the end face of the center electrode is made of an insulator. Is characterized in that the height is substantially the same as that of the end face.

By employing such a configuration, a discharge in the first discharge gap and a spark discharge in the second discharge gap can be generated at substantially the same height,
This has the effect that there is little change in ignitability in spark discharge in either gap.

[0008]

However, in Japanese Utility Model Publication No. 53-41629, the second discharge gap is provided at the end of the mounting bracket and is separated from the first discharge gap. In the case where a spark is emitted to the second discharge gap, the ignitability greatly differs, and in the case of stratified combustion, in particular, there arises a problem that poor dryness occurs.

Further, since the spark position is located on the root side of the insulator with respect to the front end face of the insulator, there is a problem that channeling easily occurs.

In Japanese Patent Application Laid-Open No. 47-19236, since the first discharge gap and the second discharge gap are the same height as the spark plug for the internal combustion engine,
The center electrode tip and the insulator tip face must be at the same height. Therefore, due to the quenching action of the insulator tip, the first
In the discharge in the discharge gap, a problem that ignitability is reduced occurs.

The present invention has been made in view of the above-mentioned problems, and usually performs aerial discharge and maintains high ignitability, and when contaminated, carbon at the tip of the insulator is dissipated by a discharge spark due to creeping discharge. By recovering the soil,
An object of the present invention is to provide a spark plug for an internal combustion engine that has significantly improved antifouling life.

[0012]

The present invention has been found to be able to solve the above-mentioned problems by adopting the following configuration in the present invention.

According to the first aspect of the present invention, a center electrode, an insulator covering the center electrode and holding the center electrode, a mounting bracket for holding the insulator, and one end of the mounting bracket are provided. A first ground electrode forming a first discharge gap by the other end of the center electrode, and one end fixed to the mounting bracket, and the other end being a side surface of the center electrode. And a second ground electrode forming a second discharge gap, wherein a tip end surface of the second ground electrode is located outside a diameter larger than a tip end outer diameter of the insulator. The discharge gap is A, the shortest distance between the insulator and the second ground electrode is B, the axial distance from the end face of the mounting bracket to the end face of the insulator is C, and the distance between the end face of the insulator and the center electrode is Axial distance to end face The H, an axial minimum distance from the end face of the mounting member to the end face of the second ground electrode L1
When 0.7 mm ≦ A ≦ 1.3 mm 0.3 mm ≦ B ≦ A−0.1 mm 1.0 mm ≦ C ≦ 4.0 mm 0.5 mm ≦ H ≦ 3.0 mm 1.0 mm ≦ L1 ≦ C + 0. The present invention provides a spark plug for an internal combustion engine having a diameter of 5 mm 2.

By employing the spark plug for an internal combustion engine having the above numerical range, it is possible to provide a spark plug for an internal combustion engine which has not only excellent self-cleaning properties but also excellent ignition performance as described later. It is.

[0015] In the present invention, the axial distance between the end face of the insulator and the corner of the end face of the second ground electrode on the side of the mounting bracket is defined as + when the end of the insulator protrudes from the end face of the insulator. Provided is a spark plug for an internal combustion engine, wherein F is -1.0 mm ≦ F ≦ + 0.5 mm.

By employing a spark plug for an internal combustion engine having such a numerical range, as described later, it is possible to provide a spark plug for an internal combustion engine which has not only excellent self-cleaning properties but also excellent ignition performance. You can do it.

Next, in the invention according to claim 3, the center electrode, an insulator covering the center electrode and holding the center electrode, a mounting bracket for holding the insulator, and one end of the mounting bracket A first ground electrode forming a first discharge gap with the other end being fixed to the metal fitting and a tip end surface of the center electrode, and one end being fixed to the mounting metal fitting, and the other end being connected to the center electrode. A second ground electrode forming a second discharge gap by the side surface, wherein a tip end surface of the second ground electrode is located outside a diameter larger than a tip end outer diameter of the insulator; 1 The discharge gap is A, the shortest distance between the insulator and the second ground electrode is B, the axial distance from the end face of the mounting bracket to the end face of the insulator is C, and the center electrode is from the end face of the insulator. Axial distance to end face of Where H is the axial distance between the end face of the insulator and the corner of the end face of the second ground electrode that is closer to the mounting bracket than the end face of the insulator, and F is the axial distance. 7 mm ≦ A ≦ 1.3 mm 0.3 mm ≦ B ≦ A−0.1 mm 1.0 mm ≦ C ≦ 4.0 mm 0.5 mm ≦ H ≦ 3.0 mm −1.0 mm ≦ F ≦ + 0.5 mm Features spark plugs for internal combustion engines.

By employing the spark plug for an internal combustion engine having the above numerical range, it is possible to provide a spark plug for an internal combustion engine which has not only excellent self-cleaning properties but also excellent ignition performance as described later. It is.

Next, in the invention according to claim 4, the center electrode comprises a base portion and a small diameter portion smaller than the diameter of the base portion, and is present in the insulator closest to the end face of the insulator. An object of the present invention is to provide a spark plug for an internal combustion engine having a starting point of the small diameter portion 0.1 mm to 0.8 mm inside an end face of the insulator.

By employing such a configuration, the discharge starting from the small diameter portion collides with the end face of the insulator, spreads around the tip of the insulator, and discharges to the second ground electrode. At this time, the discharge collides with the carbon,
The spark energy burns off the carbon at that site,
Or, it can be scattered, and has a specific function and effect that the action of cleaning carbon adhered to the insulator portion can be more easily performed.

According to a fifth aspect of the present invention, there is provided a spark plug for an internal combustion engine, wherein B + D ≧ A, where D is a radial thickness at a tip portion of the insulator.

By adopting such a positional relationship, normally, air discharge is performed, high ignitability is maintained, and, at the time of fouling, carbon at the tip of the insulator is eliminated by a discharge spark by creeping discharge. It is possible to appropriately switch the spark discharge position at the time of carbon contamination.

In the invention according to claim 6, the vicinity of the distal end of the insulator has a smaller diameter portion having a diameter smaller than that of the base of the insulator and having substantially the same diameter. And a minimum axial length E from the starting point to the end face of the second ground electrode is E ≧ B + 0.1 mm.

That is, the insulator of the second discharge gap and the second
Since the shortest distance B to the ground electrode is formed between the tip of the insulator and the second ground electrode, ignitability can be improved even in the discharge by the second discharge gap. However, in the configuration of the conventional insulator,
The spark plug has a tapered shape that becomes thicker as the insulator part approaches the base. Therefore, the shortest distance B between the insulator of the second discharge gap and the second ground electrode is formed between the root of the insulator and the second ground electrode.

Therefore, by adopting the invention of claim 6, the shortest distance between the insulator and the second ground electrode is reliably formed on the tip side of the insulator, and the spark discharge in the second discharge gap is prevented. It can be generated more on the tip side of the insulator. For this reason, the ignitability can be improved even in the discharge in the second discharge gap.

According to a seventh aspect of the present invention, there is provided a spark plug for an internal combustion engine having a noble metal member on at least one of the first ground electrode and the center electrode forming the first discharge gap.

Preferably, the noble metal member is a noble metal such as Pt or Ir or an alloy mainly containing Pt or Ir.

As described above, when the noble metal tip is provided on at least one of the center electrode and the ground electrode, the wear resistance of the electrode can be improved, and a long-life spark plug for an internal combustion engine can be provided. Can be.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings.

The spark plug according to the present embodiment is shown in FIGS. As shown in FIGS. 1 to 3, the spark plug 1 of the present embodiment has a cylindrical mounting bracket 2, and the mounting bracket 2 is a mounting screw 2 a for fixing to an engine block (not shown). It has. For example, an alumina ceramic (Al2 O
An insulator 3 composed of 3) or the like is fixed, and a center electrode 4 is fixed to a shaft hole 3a of the insulator 3. The tip 3b of the insulator 3 is provided so as to be exposed from the mounting bracket 2, and the center electrode 4 is provided so as to be exposed from the tip 3b of the insulator 3.

The distal end portion 3b of the insulator 3 is provided with a small-diameter portion 3c having a diameter smaller than that of the base portion 3b and having substantially the same diameter (see FIG. 2).

The center electrode 4 is a column made of a metal material having excellent heat transfer properties such as Cu (copper) as an inner material, and a metal material having excellent heat resistance and corrosion resistance such as a Ni (nickel) -based alloy as an outer material. As shown in FIG. 2, the tip of the center electrode 4 is provided so as to be exposed from the small-diameter portion 3 c of the insulator 3. Further, the base 4a of the center electrode 4 has a base 4a.
A first small-diameter portion 4b having a smaller diameter than that of the first noble metal member 10b forming a second small-diameter portion at the tip thereof;
Having. The starting point X, which is the boundary point between the tip of the first small diameter portion 4b and the noble metal member 10, is connected to the small diameter portion 3c of the insulator.
Is formed 0.2 mm inward from the end face of.

As shown in FIGS. 2 and 3, a first ground electrode 5 and second ground electrodes 6 and 7 are fixed to one end of the mounting bracket 2 by welding. In particular, each of the second grounding electrodes 6 and 7 has a tip end surface having a diameter larger than the outer diameter of the small-diameter portion 3c of the insulator 3 and a diameter larger by a distance B than the diameter of the small-diameter portion 3c. Are located in

The first ground electrode 5 and the second ground electrodes 6, 7 are made of a Ni-based alloy material.

The first ground electrode 5 and the noble metal member 10 are arranged to face each other so that the first discharge gap A is formed with the front end surface of the noble metal member 10 provided on the front end surface of the center electrode 4. Also, the second ground electrodes 6, 7 and the noble metal member 10 are formed such that a second discharge gap is formed via the side surface of the noble metal member 10 which is the tip of the center electrode 4 and the small diameter portion 3c of the insulator 3. They are arranged facing each other.

The noble metal member 10 formed at the tip 4b of the center electrode 4 is made of an Ir alloy material containing 10% by weight of Rh and containing Ir as a main component with the balance being Ir. In the discharge gap A of the ground electrode 5, a Pt alloy material noble metal tip 11 consisting of 10% by weight of Ni and a balance of Pt is welded and fixed by resistance welding.

Here, in the spark plug 1 for an internal combustion engine according to the present embodiment, as shown in FIG. 2, the first discharge gap A is 1.1 mm, and the front end face of the small diameter portion 3c of the insulator 3 and the second The shortest distance B to the ground electrode 6 or 7 is 0.8 mm,
The axial distance C from the end face of the mounting bracket 2 to the end face of the small-diameter portion 3c of the insulator 3 is 2.5 mm, the radial thickness D at the tip of the insulator is 1.0 mm, and the small-diameter portion 3c of the insulator is used.
The minimum length E in the axial direction from the starting point to the end face of the second ground potential electrode is 1.0 mm, and the axis from the end face of the small diameter portion 3c of the insulator 3 to the end face of the noble metal tip 10 provided on the center electrode 4 When the directional distance H is 1.5 mm, the shortest axial distance L1 from the end face of the mounting bracket 2 to the end faces of the second grounding electrodes 6 and 7 is 2.0 mm, and + is the case where it protrudes from the end face of the insulator. The axial distance F between the end face of the small diameter portion 3c of the insulator 3 and the position Y of the end face of the second grounding electrodes 6 and 7 at the corner on the side of the mounting bracket was -0.5 mm.

With respect to the spark plug for an internal combustion engine having such a shape, sufficiently satisfactory results were obtained as a result of considering the ignitability, self-cleaning properties, and the like.

In this embodiment, the center electrode 4
A first small diameter portion 4b is formed at the tip of the first small diameter portion, and a noble metal member 10 made of an Ir alloy as a second small diameter portion is provided at the further tip of the first small diameter portion 4b. In the center electrode 4, the starting point X, which is the boundary between the first small-diameter portion 4b and the second small-diameter noble metal member 10, and the starting point of the second small-diameter portion is defined as the insulator 3 Is located 0.2 mm inward from the end face of.

Further, at the tip of the insulator 3, the insulator 3 has a small diameter portion 3 c smaller in diameter than the base of the insulator 3.
It was adopted.

However, the present embodiment is not limited to such a shape.
The same effect can be obtained in a spark plug in which the noble metal member 10 is not provided. In addition, even if the insulator 3 is not provided with the small-diameter portion 3c, the function and effect of the present invention can be obtained by forming the shape of the present invention.

It should be noted that the distance from the end face of the insulator of the present invention is 0.1%.
The starting point of the small-diameter portion at the center electrode tip end that is not less than mm is the starting point of the small-diameter portion closest to the end face of the insulator. for that reason,
When a noble metal member is provided, the boundary between the first small-diameter portion 4b and the noble metal member 10 is the starting point of the small-diameter portion of the present invention as in the above embodiment. The starting point when no precious metal member is provided is the starting point X shown in FIG. 4 as the starting point of the present invention.

Further, as shown in FIG.
The operation and effect of the present invention can be obtained even if only the insulator 3 provided with the small-diameter portion 3c at the tip of the insulator 3 is adopted without providing 0.

Further, as shown in FIG. 6, a noble metal member 10 is provided, and a small-diameter portion 3c
The operation and effect of the present invention can also be obtained as a spark plug for an internal combustion engine without the above.

Further, in this embodiment, an Ir alloy containing 10% by weight of Rh is used as the noble metal member. However, the present invention is not limited to this. For example, pure Ir, Pt or Pt may be used. The same operation and effect can be obtained even if an alloy mainly composed of is used, and other noble metal members are adopted.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The grounds for a numerical range for producing a spark plug for an internal combustion engine according to the present invention will be described in detail below.

(Selection of Distance B) First, the inventors of the present invention determined the optimum value of the shortest distance B between the insulator 3 and the second ground electrodes 6 and 7. The spark plug for an internal combustion engine used in the spark plug for an internal combustion engine shown in FIG. 2 has an axial distance C from the end face of the mounting bracket 2 to the end face of the insulator 3 of 2.0 mm, and a tip end of the insulator. And the axial distance H from the end face of the insulator 3 to the end face of the center electrode 4 is 1.5 m.
m, the shortest distance L1 in the axial direction from the end face of the mounting bracket 2 to the end face of the second ground electrode 6, 7 is 1.5 mm and
The longest distance L2 in the axial direction from the end face of the first ground electrode to the end faces of the second ground electrodes 6 and 7 was kept constant at 3.0 mm. At this time, the first
The discharge gap A, the shortest distance B between the insulator 3 and the second ground electrodes 6 and 7 were sequentially changed, and the ignition state after leaving the apparatus idle for 30 minutes was measured as the forced contamination in each case.

In Table 1, x indicates rough idle after starting, that is, a case where rotation fluctuation occurs at ± 30 rpm.
X indicates a state in which a misfire stalled due to a decrease in insulation.

[0049]

[Table 1]

According to Table 1, 0.3 mm ≦ B ≦ A−0.1 m
It has been found that a good ignition state can be obtained within the range of m.

This is because when B is smaller than 0.3 mm, the growth of the flame nucleus is inhibited by the insulator 3 and the ground electrodes 6 and 7 because the flame nucleus when the insulator surface is contaminated is small. (Extinguishing action), which causes misfiring, and a sufficient ignition state cannot be stably obtained. Further, when B exceeds A-0.1 mm, when carbon adheres to the insulator surface, discharge in the second discharge gap B is unlikely to occur, and leakage occurs to the root of the insulator leg to obtain a sufficient ignition state. This is because it becomes difficult.

(Selection of distances C and H) When the axial distance C from the end face of the mounting bracket 2 to the end face of the insulator 3 is smaller than 1.0 mm, the second discharge gap B projects sufficiently from the mounting bracket 2. And the ignitability at the time of spark in the second discharge gap B deteriorates.

If the axial distance C is larger than 4.0 mm, that is, if the position of the first discharge gap A protrudes more than necessary, the heat resistance of the ground electrode 5 is deteriorated, and the oxidation and wear resistance is significantly deteriorated. Problems arise.

Further, from the end face of the insulator 3 to the center electrode 4
If the axial distance H to the end face is smaller than 0.5 mm, the ignitability at the time of spark discharge in the first discharge gap is deteriorated. This is the tip of the center electrode 4 and the insulator 3
Is too close to each other, so that the growth of the flame nuclei generated in the first discharge gap is hindered by the cooling action (extinguishing action) by the surface of the insulator 3.

On the other hand, if the axial distance H projects beyond 3.0 mm, the portion of the center electrode 4 directly exposed to the combustion gas increases, resulting in a significant decrease in the heat value of the center electrode 4. Problems arise.

As a result, it has been found that a spark plug for an internal combustion engine having a favorable range of 1.0 mm ≦ C ≦ 4.0 mm and 0.5 mm ≦ H ≦ 3.0 mm is provided.

(Selection of distance L1) Next, by changing the positions of the second ground electrodes 6 and 7, it was confirmed that there was a difference in the ignitability during the spark discharge in the second discharge gap.

Here, the spark discharge in the second discharge gap means that the noble metal member 10 and the base 4b of the center electrode 4 are connected to the second discharge gap.
This is a discharge including the end faces and corners of the ground electrodes 6 and 7.

Here, the positions of the second ground electrodes 6 and 7 are
The shortest distance L1 in the axial direction from the end face of the mounting bracket 2 to the end face of the second ground electrode was defined as L1, and the rate of occurrence of rotation fluctuation of the internal combustion engine at the time of fouling when the shortest distance L1 was changed was measured.

FIG. 7 shows the result.

The experimental conditions at this time were as follows: in the spark plug for an internal combustion engine shown in FIG. 2, the first discharge gap A was 1.1 mm, and the shortest distance B between the insulator 3 and the second ground electrodes 6 and 7 was B. Is 0.8 mm, the radial thickness D at the tip of the insulator is 1.0 mm, the axial distance from the end face of the insulator 3 to the tip end face of the center electrode 4 is 1.5 mm, and the end face of the mounting bracket 2 is 1.5 mm. The longest distance L2 in the axial direction from to the end surfaces of the second ground electrodes 6 and 7 was L1 + 1.5 mm. Further, the axial distance C from the end face of the mounting bracket 2 to the end face of the insulator 3 was changed to 1.5 mm and 2.0 mm.
At this time, the value of the shortest distance L1 was sequentially changed, and the occurrence rate of each rotation fluctuation was measured.

The rate of occurrence was evaluated by the idling instability at 650 rpm idling using a 1600 cc water-cooled automobile engine.

Here, the idle instability rate is 3
The instantaneous rotation speed was measured at intervals of 0.2 seconds per minute and determined by the following equation (900 samples).

Idle instability ratio = (standard deviation of instantaneous rotation speed / average of instantaneous rotation speed) × 100% That is, the larger the idle instability ratio, the larger the rotation fluctuation and the worse the ignitability.

From FIG. 7, it has been confirmed that, if the shortest distance L1 is set to an appropriate position, it is possible to provide a region having good ignitability and a small rotation fluctuation.

That is, good results were obtained when the optimum L1 was in the range of 1.0 mm ≦ L1 ≦ C + 0.5 mm.

It is determined that the reason is as follows.

That is, when L1 is smaller than 1.0 mm, the spark discharge position is separated from the first discharge gap A, and the ignitability greatly differs as in JP-B-53-41629. Poor performance occurs. When L1 is larger than C + 0.5 mm, C
A problem arises in that sparks float from the tip of the part, making it difficult to clean carbon adhered to the insulator.

(Selection of Distance F) Next, as described above, by changing the positions of the second ground electrodes 6 and 7, the surface discharge at the end face of the insulator 3 generated at the time of discharge in the second discharge gap is performed. Since it was confirmed that there was a difference in the ignitability of the insulator 3, the case where the end face of the insulator 3 and the position Y of the end faces of the second grounding electrodes 6, 7 on the side of the mounting bracket protruded from the end face of the insulator 3 was defined as +. The rotational fluctuation occurrence rate of the internal combustion engine at the time of fouling when the axial distance F was changed was measured.

FIG. 8 shows the result.

The experimental conditions at this time are as follows. In the spark plug for an internal combustion engine shown in FIG.
1.1 mm, the shortest distance B between the insulator 3 and the second ground electrodes 6 and 7 is 0.8 mm, the axial distance C from the end face of the mounting bracket 2 to the end face of the insulator 3 is 3.0 mm, The radial thickness D at the tip of the insulator is 1.0 mm, and the insulator 3
Is the axial distance from the end face of the center electrode 4 to the tip end face of the center electrode 4.
And the longest axial distance L2 from the end face of the mounting bracket 2 to the end faces of the second ground electrodes 6 and 7 is L1 + 1.
5 mm. At this time, the occurrence rate of each rotation fluctuation was measured while sequentially changing the value of the distance F.

The rate of occurrence was measured by the method described above.

From FIG. 8, it was confirmed that it is possible to provide a region having good ignition performance and a small rotation fluctuation if the distance F is set to an appropriate position.

That is, good results could be obtained when the optimum distance F was within the range of -1.0 mm ≦ F ≦ + 0.5 mm.

This is, in more detail, F> +0.5 mm
In the above case, since the second discharge gap B becomes substantially too large, reliable spark discharge to the second ground electrodes 6 and 7 and the like becomes difficult to be performed, and spark discharge to the back of the base of the insulator 3 is prevented. Easily occur, and the ignitability in the combustion chamber is reduced.

Further, in the case of -1.0 mm> F, the spark position in the second discharge gap B is too low, so that the positional deviation from the spark discharge in the first discharge gap A becomes large, and the ignitability increases. This is because the reduction or ignition stability is inferior.

As described above, it was confirmed that the functions and effects of the present invention were satisfied by setting the respective numerical ranges to the above ranges.

(Starting Position of Small Diameter Portion of Center Electrode) Next, it was confirmed how much the starting point of the small diameter portion X of the center electrode 4 should be inside the end face of the insulator 3.

As a result, it is preferable that the starting point of the small-diameter portion existing in the insulator closest to the end face of the insulator be 0.1 mm to 0.8 mm inside the end face of the insulator 3. I found something.

That is, 0.1 mm from the end face of the insulator 3
By setting the inner side as described above, the discharge in the second discharge gap starting as the starting point X of the small diameter portion can be made to collide with the end side surface of the insulator 3, spread around the tip of the insulator 3, and the second grounding An electrode can be discharged. At this time, the discharge collides with the carbon, and the spark energy allows the carbon adhering to the tip surface of the insulator 3 to be burned out or scattered, thereby cleaning the carbon adhering to the surface of the insulator 3. Can be made easier.

However, if it is more than 0.8 mm inside the end face of the insulator 3, the distance of the second discharge gap becomes longer, which causes a problem that the discharge itself in the second discharge gap becomes difficult to occur.

Therefore, it is preferable that the starting point of the small-diameter portion existing in the insulator closest to the end face of the insulator be 0.1 mm to 0.8 mm inside the end face of the insulator 3.

(Relationship Between First Discharge Gap and Second Discharge Gap) Next, we confirmed the relationship between the first discharge gap and the second discharge gap.

As a result, the first discharge gap A is a distance obtained by adding the shortest distance B between the insulator constituting the second discharge gap and the second ground electrode and the radial thickness D at the tip of the insulator 3. Has been found to be preferably B + D ≧ A.

With such a positional relationship, aerial discharge can be performed in the first discharge gap, and high ignitability can be maintained. Then, at the time of fouling, the spark discharge position at the time of normal and at the time of carbon fouling, in which carbon at the tip end of the insulator is extinguished by discharge spark by creeping discharge at the second discharge gap, can be appropriately switched.

(Selection of Length E) In addition, we have determined the shortest axial length from the starting point of the small diameter part having the same diameter formed near the tip of the insulator 3 to the end faces of the second ground electrodes 6 and 7. The optimum value of E was confirmed.

As a result, it was found that it is preferable that E ≧ B + 0.1 mm.

The reason will be described with reference to FIG.

As shown in FIG. 9, in the case of a conventional spark plug which becomes thicker as the insulator 3 approaches the base, the following problems occur.

That is, the shortest distance B between the insulator 3 forming the second discharge gap and the second ground electrode 6 is formed between the discharge position α of the insulator 3 and the second ground electrode. Since the discharge position α of the insulator 3 at this time is on the base side of the insulator 3, it is very difficult to ignite the inside of the combustion chamber by spark discharge in the second discharge gap.

On the other hand, by satisfying the relationship of E ≧ B + 0.1 mm, the discharge position β of the insulator 3 can be shifted to the tip side of the insulator 3 as shown in FIG. The ignitability can be improved even in the discharge caused by the gap.

[Brief description of the drawings]

FIG. 1 is a half sectional view of a spark plug for an internal combustion engine according to an embodiment of the present invention.

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

FIG. 3 is an enlarged view of a main part of the spark plug for an internal combustion engine according to the embodiment of the present invention.

FIG. 4 is an enlarged view of a main part of a spark plug according to another embodiment of the present invention.

FIG. 5 is an enlarged view of a main part of a spark plug according to another embodiment of the present invention.

FIG. 6 is an enlarged view of a main part of a spark plug according to another embodiment of the present invention.

FIG. 7 is a relationship diagram showing a relationship between a shortest distance L1 and a rotation occurrence rate.

FIG. 8 is a relationship diagram illustrating a relationship between an axial distance F and a rotation occurrence rate.

FIG. 9 is an explanatory diagram illustrating the present invention.

FIG. 10 is an explanatory diagram illustrating the present invention.

[Explanation of symbols]

1 ... spark plug, 2 ... mounting bracket, 3 ...
Insulator 4 ... Center electrode, 5 ... First ground electrode,
6,7 ... second ground electrode

[Procedure amendment]

[Submission date] June 8, 2000 (2006.8.8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

2. The spark plug for an internal combustion engine according to claim 1 , wherein B + D ≧ A, where D is a radial thickness at a tip portion of said insulator.

3. The vicinity of the tip of the insulator has a small diameter portion having a diameter smaller than that of the base of the insulator and having substantially the same diameter, and the second ground electrode from the starting point of the small diameter portion. The shortest axial length E up to the end face of the first member is E ≧ B + 0.1 mm. 3.
The spark plug for an internal combustion engine according to the above .

Wherein at least one the of the first ground electrode and the center electrode forming a first discharge gap, small of claims 1 to 3, characterized in that it has a noble metal member
2. A spark plug for an internal combustion engine according to claim 1 .

Wherein said noble metal member, noble metals Pt and Ir
5. The spark plug for an internal combustion engine according to claim 4 , wherein the spark plug is an alloy containing Pt or Ir as a main component.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013] First, in a first aspect of the invention, base and
A center electrode formed of a small diameter portion smaller than the diameter of the base , an insulator covering the center electrode and holding the center electrode, a mounting bracket for holding the insulator, and one end of the mounting bracket A first ground electrode forming a first discharge gap by the other end of the center electrode, and one end fixed to the mounting bracket, and the other end being a side surface of the center electrode. And a second ground electrode forming a second discharge gap, wherein a tip end surface of the second ground electrode is located outside a diameter larger than a tip end outer diameter of the insulator. The discharge gap is A, the shortest distance between the insulator and the second ground electrode is B, the axial distance from the end face of the mounting bracket to the end face of the insulator is C, and the distance between the end face of the insulator and the center electrode is The axial distance to the end face is H, Serial axial minimum distance from the end face of the mounting member to the end face of the second ground electrode L1, the insulating碍
Angle between the end face of the connector and the end face of the second ground electrode.
When the case where it protrudes from the end face of the insulator with the
When the axial distance is F, 0.7 mm ≦ A ≦ 1.3 mm 0.3 mm ≦ B ≦ A−0.1 mm 1.0 mm ≦ C ≦ 4.0 mm 0.5 mm ≦ H ≦ 3.0 mm 1.0 mm ≤ L1 ≤ C + 0.5 mm -1.0 mm ≤ F ≤ +0.5 mm and the insulator closest to the end face of the insulator
The starting point of the small-diameter portion of the center electrode inside the
Only 0.1 to 0.8 mm inside the end face of the insulator
And a spark plug for an internal combustion engine.

[Procedure amendment 3]

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[Correction target item name] 0014

[Correction method] Change

[Correction contents]

By employing the spark plug for an internal combustion engine having the above numerical range, it is possible to provide a spark plug for an internal combustion engine which has not only excellent self-cleaning properties but also excellent ignition performance as described later. is there. Furthermore, the insulator is located in the insulator closest to the end face of the insulator.
The starting point of the small diameter portion of the center electrode is the end of the insulator.
So that it is only 0.1-0.8 mm inside the surface
Was. By adopting such a configuration, the small diameter portion
The discharge starting as the starting point collides with the insulator end side
And progresses around the insulator tip, the second ground electrode
To discharge. At this time, the discharge collides with the carbon and the fire
The energy of the flower does not burn the carbon at that site,
Can be scattered, and the carbon attached to the insulator
Can be cleaned.

[Procedure amendment 4]

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[Procedure amendment 10]

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[Correction target item name] 0021

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[Correction contents]

According to a second aspect of the present invention, there is provided a spark plug for an internal combustion engine, wherein B + D ≧ A, where D is a radial thickness at a tip portion of the insulator.

[Procedure amendment 11]

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[Correction contents]

Further, in the invention according to claim 3, the vicinity of the tip end of the insulator has a small diameter portion having a diameter smaller than that of the base of the insulator and having substantially the same diameter. And a minimum axial length E from the starting point to the end face of the second ground electrode is E ≧ B + 0.1 mm.

[Procedure amendment 12]

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[Correction target item name] 0025

[Correction method] Change

[Correction contents]

Therefore, by adopting the invention of claim 3, the shortest distance between the insulator and the second ground electrode is reliably formed at the tip side of the insulator, and the spark discharge in the second discharge gap is prevented. It can be generated more on the tip side of the insulator. Therefore it is one that can also have a third aspect peculiar action and effect that it is possible to improve the ignitability at the discharge in the second discharge gap.

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

According to a fourth aspect of the present invention, there is provided a spark plug for an internal combustion engine having a noble metal member on at least one of the first ground electrode and the center electrode forming the first discharge gap.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Makoto Yagasu 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation (Reference) 5G059 AA02 CC03 DD04 DD19 DD21 EE04 EE19 EE21 EE23

Claims (8)

[Claims] 1. A center electrode, an insulator covering the center electrode and holding the center electrode, a mounting bracket for holding the insulator, and one end fixed to the mounting bracket and the other end A first ground electrode forming a first discharge gap by a tip end surface of the center electrode, and a second discharge gap formed by one end fixed to the mounting bracket and the other end by a side surface of the center electrode. A second ground electrode to be formed, a tip end surface of the second ground electrode is located outside a diameter larger than a tip end outer diameter of the insulator, the first discharge gap is A, the insulator is B is the shortest distance between the second ground electrode and the second ground electrode, C is the axial distance from the end face of the mounting bracket to the end face of the insulator, and H is the axial distance from the end face of the insulator to the end face of the center electrode. , The end face of the mounting bracket When the shortest axial distance to the end surface of the second ground electrode is L1, 0.7 mm ≦ A ≦ 1.3 mm 0.3 mm ≦ B ≦ A-0.1 mm 1.0 mm ≦ C ≦ 4.0 mm 0 A spark plug for an internal combustion engine, wherein: 0.5 mm ≦ H ≦ 3.0 mm 1.0 mm ≦ L1 ≦ C + 0.5 mm 2. When the distance between the end face of the insulator and the corner of the end face of the second ground electrode protruding from the end face of the insulator with respect to the end face of the insulator is +, the axial distance is F, 2. The spark plug for an internal combustion engine according to claim 1, wherein -1.0 mm≤F≤ + 0.5 mm. 3. A center electrode, an insulator covering the center electrode and holding the center electrode, a mounting bracket for holding the insulator, one end fixed to the mounting bracket and the other end. A first ground electrode forming a first discharge gap by a tip end surface of the center electrode, and a second discharge gap formed by one end fixed to the mounting bracket and the other end by a side surface of the center electrode. A second ground electrode to be formed, a tip end surface of the second ground electrode is located outside a diameter larger than a tip end outer diameter of the insulator, the first discharge gap is A, the insulator is B is the shortest distance between the second ground electrode and the second ground electrode, C is the axial distance from the end face of the mounting bracket to the end face of the insulator, and H is the axial distance from the end face of the insulator to the end face of the center electrode. The end face of the insulator and When the distance between the end of the second ground electrode and the corner on the side of the mounting bracket protruding from the end of the insulator is +, the axial distance is defined as F, and 0.7 mm ≦ A ≦ 1.3 mm. A spark plug for an internal combustion engine, wherein 3 mm ≦ B ≦ A−0.1 mm 1.0 mm ≦ C ≦ 4.0 mm 0.5 mm ≦ H ≦ 3.0 mm −1.0 mm ≦ F ≦ + 0.5 mm. 4. The center electrode includes a base portion and a small diameter portion smaller than the diameter of the base portion, and the starting point of the small diameter portion present in the insulator closest to the end face of the insulator is the insulating member. 4. The insulator according to claim 1, wherein said insulator is provided 0.1 mm to 0.8 mm inside said end face.
7. A spark plug for an internal combustion engine according to claim 1. 5. The spark plug for an internal combustion engine according to claim 1, wherein B + D ≧ A, where D is a radial thickness at a tip portion of the insulator. 6. A portion near the front end of the insulator, which has a small diameter portion having a diameter smaller than that of the base portion of the insulator and having substantially the same diameter, and from a starting point of the small diameter portion, the second ground electrode. The spark plug for an internal combustion engine according to any one of claims 1 to 5, wherein the shortest axial length E up to the end face of the internal combustion engine is E ≧ B + 0.1mm. 7. The internal combustion engine according to claim 1, wherein at least one of the first ground electrode and the center electrode forming the first discharge gap has a noble metal member. For spark plug. 8. The spark plug for an internal combustion engine according to claim 1, wherein the noble metal member is a noble metal such as Pt or Ir or an alloy containing Pt or Ir as a main component.