JPH0945457A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict generation of leak, achieve favorable startability, and prevent infiltration of combustion gas to improve dirtiness resistance of an insulator leg part by setting an inner diameter of a main body metal larger at the depth than an inner diameter at a tip, and forming an inner wall surface of the main body metal into a continuous flat surface. SOLUTION: In a spark plug for an internal combustion engine, an main body metal 4 is formed by disposing a grounding electrode 5 to face a tip of a center electrode 3 held and protruded from a tip of a leg part 2' of a tapered insulation body 2 of which diameter is reduced toward a tip. An inner diameter ϕB of the main body metal 4 at the depth is set to be larger than an inner diameter ϕA at a tip. In addition, an inner wall surface 6 of the main body metal 4 is formed as a flat surface from the depth to the tip. Infiltration of combustion gas generated in accordance with combustion of a mixture can thus be reduced to the minimum, and dartiness resistance of the leg part 2' of the insulator 2 can be improved. In addition, leak of spark from the leg part 2' of the insulator 2 to the inner wall surface 6 can be surely restricted, thereby spark discharge can be surely performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a spark plug used in an internal combustion engine, and more particularly to the structure of a metal shell that constitutes the spark plug.

[0002]

2. Description of the Related Art Conventionally, in a spark plug used in an internal combustion engine, the inner wall surface at the tip of a metal shell which constitutes the spark plug and has an insulator tapering toward the tip is In general, the metal shell has a right angle including an error with respect to the front end surface, and the inner diameter of the metal shell is generally the same at the tip and at the back.

[0003]

However, in the above-mentioned conventional one, the spark plug for an internal combustion engine is constituted, and the inside of the tip of the metal shell which holds the insulator taper toward the tip. The wall surface is at a right angle to the tip surface of the metal shell, including the error, and the inside diameter of the metal shell is the same at the tip and at the back. Because the gas volume of the space formed by the leg surface of the insulator to be held and the inner wall surface of the metal shell, that is, the space into which the combustion gas generated when the mixture gas is ignited in the combustion chamber of the internal combustion engine enters is large, Since carbon generated along with the combustion of the air-fuel mixture enters the space together with the combustion gas and adheres to the surface of the leg portion of the insulator fixed in the metal shell,
The carbon attached to the surface of the insulator leg portion lowers the insulation resistance of the plug and reduces the stain resistance.

Therefore, for the purpose of making it difficult for the combustion gas generated by the combustion of the air-fuel mixture to enter, the space formed by the leg surface of the insulator fixed in the metal shell and the inner wall surface of the metal shell. That is, in order to reduce the gas volume of the space into which the combustion gas generated when the air-fuel mixture is ignited in the combustion chamber of the internal combustion engine, it is also proposed to reduce the inner diameter of the tip of the metal shell. Since the insulator has a taper shape in which the diameter decreases toward the tip in the inner part, the insulator has a larger diameter in the inner part than the tip, so the inner wall surface of the metal shell and the insulator The distance from the leg surface of the is extremely small, the frequency of spark leakage from the leg surface of the insulator to the inner wall surface of the metal shell is likely to be high, and the startability at low temperatures is extremely reduced. There is a drawback.

Further, the space formed by the leg surface of the insulator fixed in the metal shell and the inner wall surface of the metal shell contains carbon generated when the air-fuel mixture is ignited in the combustion chamber of the internal combustion engine. In order to prevent invasion of the combustion gas, the outer peripheral edge of the metal shell holding the insulator is provided with a radially projecting peripheral edge so as to close the opening of the space as much as possible. (Actual public Sho 56
No. 25194 and Japanese Patent Laid-Open No. 52-44347), the combustion gas generated when the mixture gas is ignited in the combustion chamber of the internal combustion engine enters the space formed by the inner wall surface of the metal shell. In order to prevent this, at the tip of the metal shell, the carbon generated along with the combustion of the air-fuel mixture is generated by the projecting peripheral edge formed so as to project in the radial direction so as to close the opening of the space. Intrusion of combustion gas contained can be minimized,
In order to prevent the combustion gas from entering the space, the projecting peripheral edge provided around the opening at the tip of the metal shell will be extremely close to the insulator fixed in the metal shell.
There is a problem that the thermal load on the tip of the insulator becomes too small, the self-cleaning action of the tip of the insulator deteriorates, and drivability at low speed running becomes unstable.

[0006] Therefore, the present invention is to improve the drawbacks of the above-mentioned conventional ones, and suppresses the occurrence of leaks to ensure good startability at low temperatures, while at the same time providing an insulator fixed in the metal shell. The volume of the space formed by the leg surface and the inner wall surface of the metal shell, that is, the gas volume is minimized to prevent the invasion of combustion gas, thereby improving the stain resistance of the insulator leg. Is.

[0007]

To this end, the center electrode is held by projecting the center electrode from the tip of the leg of the insulator, which is tapered so that the diameter decreases toward the tip. In a metal shell in which a ground electrode is arranged so as to face the tip of an electrode, the inside diameter of the metal shell is larger than the inside diameter of the metal shell tip, and the inner wall surface of the metal shell is tipped from the back side. Is continuously formed on a flat surface.

In the spark plug for an internal combustion engine, the gap between the tip of the center electrode, which is held so as to project from the tip of the insulator, and the ground electrode, which is arranged so as to face the tip of the center electrode, is G Further, when the distance between the inner peripheral edge of the metal shell tip and the surface of the leg portion of the insulator fixed to the metal shell is L, the relationship L ≧ 1.2G is satisfied.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Since the present invention has the above-mentioned structure, in practice, the insulator fixed in the metal shell is tapered so that the diameter becomes smaller toward the tip, that is, the tip is formed at the inner part of the leg of the insulator. Even if the diameter is larger than that of the metal shell, the inner diameter at the back is larger than the inner diameter of the tip of the metal shell that holds this insulator, and the inner wall surface of the metal shell is continuous from the back to the tip. Since it is formed into a flat surface, the diameter of the opening at the tip of the metal shell is made small to prevent the invasion of combustion gas generated by the combustion of the air-fuel mixture, and the metal shell is fixed inside the metal shell. Even if the volume of the space formed by the leg surface of the insulator and the inner wall surface of the metal shell, that is, the gas volume is reduced, the inner wall surface is continuously flat from the tip of the insulator to its inner part. , Insulator leg surface and metal shell Since it is possible to secure an even space between the inner wall surface and the inner wall surface, it is possible to prevent the stain resistance from being deteriorated due to the entry of the combustion gas into the space, and also to prevent the deterioration of the stain resistance from the legs of the insulator to the inner wall surface of the metal shell. Can be reliably suppressed and the startability at low temperatures can be improved.

In particular, the gap between the tip of the center electrode, which is held so as to project from the tip of the insulator, and the ground electrode, which is arranged so as to face the tip of the center electrode, is G. When the distance between the peripheral edge and the surface of the leg of the insulator fixed to this metal shell is L, L <1.2G
If so, a leak is likely to occur between the surface of the leg part of the insulator and the inner wall surface of the metal shell, and the deterioration of the ignitability of the air-fuel mixture due to this leak may cause irregularity in idling or deterioration of acceleration performance. And the stain resistance to carbon adhering to the surface of the leg portion of the insulator is reduced. Therefore, by setting the relationship of L ≧ 1.2 G, the occurrence of leakage is prevented. It is possible to more reliably improve the stain resistance of the spark plug while surely suppressing it.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. (1) is a spark plug for an internal combustion engine which is an embodiment of the present invention. The spark plug (1) for an internal combustion engine holds a center electrode (3) at its tip and has a diameter directed toward the tip. A taper-shaped insulator (2) having a small size and the insulator (2) are firmly held and at a position facing the tip (tip surface) of the center electrode (3) held by the insulator (2). It is composed of a metal shell (4) provided with a ground electrode (5). In addition, (10) is a terminal electrode, and together with the center electrode (3) in the shaft hole of the insulator (2), a known conductive glass sealing material (1
It is sealed via 1).

The spark plug (1) for an internal combustion engine is formed, and is held by projecting from the tip of the leg portion (2 ') of the insulator (2) which has a taper shape whose diameter decreases toward the tip. In a metal shell (4) in which a ground electrode (5) is arranged so as to face the tip of a center electrode (3) to be formed, the inner diameter at the inner part of the metal shell (4) is deeper than the inner diameter (φA) at the tip. (ΦB) has a large diameter, and the inner wall surface (6) of the metal shell (4) is a flat surface from the back to the tip. The one shown in FIGS. 1 and 2 (a) has one ground electrode (5) with respect to the center electrode (3), but as shown in FIG. It is also possible to provide a plurality of ground electrodes (5), (5) ... Around the tip (side surface of the tip) of (3) and around the tip.

Since the spark plug (1) for an internal combustion engine according to the embodiment of the present invention has the above-mentioned structure, the metal shell (4) which constitutes the spark plug (1) for the internal combustion engine.
The insulator (2) held inside has a taper shape in which the diameter becomes smaller toward the tip, that is, the diameter of the leg (2 ') of the insulator (2) is larger than that at the tip. However, the inner diameter (φB) in the inner part (φB) of the metal shell (4) that holds the insulator (2) is larger than the inner diameter (φA) of the tip of the metal shell (4). Since a flat surface is continuously formed from the portion to the tip, the diameter of the opening (8) at the tip of the metal shell (4) is prevented in order to prevent the entry of combustion gas generated by the combustion of the air-fuel mixture. Of the space (7) formed by the surface (2) of the leg (2 ') of the insulator (2) fixed in the metal shell (4) and the inner wall surface (6) of the metal shell (4). Even if the volume, that is, the gas volume is reduced, the insulator (2) is always insulated from the tip to the inside. Since it is possible to secure an even interval between the surface of the leg portion (2 ') of 2) and the inner wall surface (6) of the metal shell (4), it is possible to reliably carry out the combustion of the air-fuel mixture. Intrusion of combustion gas into the space (7) generated as a result can minimize the pollution resistance of the legs (2 ') of the insulator (2), and the flat surface is formed. The center electrode (3) and the metal shell (4) are grounded by reliably suppressing the leakage of sparks from the legs (2 ′) of the insulator (2) to the inner wall surface (6) of the metal shell (4). Spark discharge in the spark gap G between the electrode (5) and the spark gap can be reliably performed, and the startability at low temperatures can be improved.

Further, as shown in FIG. 3, in the spark plug (1) for the internal combustion engine, the tip of the center electrode (3) which is held so as to project from the tip of the insulator (2) and the center electrode (3). The gap between the metal shell (4) disposed so as to face the tip and the ground electrode (5) is G, and the inner peripheral edge (9) of the metal shell (4) tip and the metal shell (4) When the distance between the surface of the leg (2 ′) of the insulator (2) to be held is L, and the relation L <1.2G is satisfied, the leg (2 ′) of the insulator (2). ) And the inner wall surface (6) of the metal shell (4) are apt to leak, and as a result, the legs (2 ′) of the insulator (2) are generated.
The deterioration of the ignitability of the air-fuel mixture caused by the leakage between the surface of the metal shell and the inner wall surface (6) of the metal shell (4) causes poor starting at low temperatures, irregular idling and deterioration of acceleration performance. In addition to that, since the stain resistance to carbon that adheres to the surface of the leg portion (2 ′) of the insulator (2) is reduced, the relationship of L ≧ 1.2G is established. The body (2) is firmly held in the metal shell (4) while reliably suppressing the occurrence of a leak between the surface of the leg portion (2 ') and the inner wall surface (6) of the metal shell (4). The spark discharge between the tip of the center electrode (3) held by the insulator (2) and the ground electrode (5) of the metal shell (4) is ensured, and the spark discharge is generated in the combustion gas of the spark plug (1). It is possible to reliably improve the stain resistance of the contained carbon. .

Therefore, the surface of the leg (2 ') of the insulator (2) and the inner wall surface (6) of the metal shell (4) of the spark plug (1) for an internal combustion engine according to the embodiment of the present invention are formed. In order to confirm the effect of suppressing the leakage between the two, the conventional spark plug for an internal combustion engine, that is, the surface of the leg portion (2 ′) of the insulator (2) fixed in the metal shell (4) and the metal shell. Space (7) formed by inner wall surface (6) of (4)
With a large gas volume, that is, a large gas volume, and the surface of the leg portion (2 ') of the insulator (2) fixed in the spark plug 1) for an internal combustion engine that is an embodiment of the present invention, that is, the metal shell (4). And the volume of the space (7) formed by the inner wall surface (6) of the metal shell (4), that is, the one having a small gas volume (L = 1.3 G), the spark idling of A / F After continuous operation for a certain period of time under dark conditions, the insulation resistance between the electrodes was measured.
As the leg length of the leg part (2 ′) of the metal is increased, the surface of the leg part (2 ′) of the insulator (2) fixed in the metal shell (4) as in the prior art and the metal shell (4). The volume of the space (7) formed by the inner wall surface (6), that is, the gas volume of the present invention is smaller than that of the gas volume of which the insulation volume is small, and the leg length of the insulator is increased. The same improvement in stain resistance was fully confirmed (see Figure 4).

[0016]

As described above, the inner diameter in the inner portion of the metal shell is larger than the inner diameter of the tip of the metal shell which holds the center electrode and holds the insulator whose diameter decreases toward the tip. By forming a flat surface on the inner wall surface of the metal shell that extends from the back to the tip, the legs of the insulator that are firmly held in the metal shell of the combustion gas generated by the combustion of the air-fuel mixture and the metal shell The space formed by the inner wall surface of the metal, that is, the space between the leg surface of the insulator and the inner wall surface of the metal shell, even if it is made small to prevent invasion of the gas volume and improve the stain resistance to carbon. Since it can be ensured evenly, spark leakage from the surface of the insulator leg portion to the inner wall surface of the metal shell can be reliably suppressed, and especially the tip of the center electrode that is projected and held beyond the insulator tip and the tip of this center electrode Against The gap between arranged and formed by the ground electrode to the G, and the inner peripheral edge of the further metal shell tip,
When the distance between the surface of the insulator fixed to the metal shell and the surface of the leg is L, by setting L ≧ 1.2G, it is possible to reliably suppress the leakage from the leg of the insulator and to reduce the gas volume. It has an excellent effect that it is possible to improve the anti-fouling property of the spark plug and the starting property at low temperature by reducing the above.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view of a main part of a spark plug for an internal combustion engine according to an embodiment of the present invention, (a) having one ground electrode, (b) having a plurality of ground electrodes. It is a thing.

FIG. 3 is a diagram showing a leak frequency with respect to a distance L between an inner peripheral edge of the tip of the metal shell and a surface of a leg portion of an insulator fixedly held by the metal shell.

FIG. 4 is a diagram showing an insulation resistance distribution between a spark plug for an internal combustion engine which is an embodiment of the present invention and a conventional one.

[Explanation of symbols]

 1 Spark Plug for Internal Combustion Engine 2 Insulator 2 '(Insulator) Leg 3 Center Electrode 4 Main Metal 5 Grounding Electrode 6 Inner Wall 7 Space 8 Opening 9 Inner Edge

Claims (2)

[Claims] 1. A ground electrode that holds the insulator fixed by projecting a center electrode from the tip of the leg of an insulator that is tapered toward the tip, and that is opposed to the tip of the center electrode. In the metal shell having the metal shell, the inner diameter of the metal shell is larger than the inner diameter of the tip of the metal shell, and the inner wall surface of the metal shell is continuously formed flat from the back to the tip. Spark plug for internal combustion engine. 2. The gap between the tip of the center electrode, which is held so as to project from the tip of the insulator, and the ground electrode, which is arranged so as to face the tip of the center electrode, is G, and further, the inside of the tip of the metallic shell. The spark plug for an internal combustion engine according to claim 1, having a relationship of L ≧ 1.2G, where L is a distance between a wall surface and a surface of a leg portion of an insulator fixed to the metal shell.