JPH0350394B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spark plug used in an internal combustion engine, and more particularly to a spark plug of a type in which a spark gap protrudes near the center of a combustion chamber in order to improve engine combustion. Regarding the improvement of

Conventionally, a protruding type spark plug with a protruding spark gap part has a gap 2 (commonly known as a gas volume) between it and the inner wall 1a of the mounting bracket 1, as shown in Fig. 1.
approximately 1.5 to 3 mm from the end surface 1b of the mounting bracket 1.
Providing a firing leg 3a of a porcelain insulator 3 that protrudes by mm,
A spark gap 6 is formed between the tip 4a of the center electrode 4, which is inserted through the shaft hole 3e of the firing leg and exposed from the tip surface 3b, and the opposing outer electrode 5. With this configuration, the protrusion dimension E from the end surface 1b of the mounting bracket 1 to the tip surface 4b of the center electrode 4 is 6.
By increasing the length to ~15mm, it is possible to ignite the air-fuel mixture that is easily combustible, shortening the combustion time, and to further improve ignition performance, the size of the spark gap is larger than the conventional 0.7~0.8mm. It is being considered to do so. However, it has been found that the protruding type spark plug causes the following problems because increasing the spark gap increases the required voltage, and when the electrode wears out, the spark gap widens and this tendency is further exacerbated. That is, in addition to the spark discharge at the regular spark gap 6 between the center electrode 4 and the outer electrode 5, sideways discharge occurs at other parts, resulting in a drawback that the ignition function is significantly impaired. The horizontal discharge is likely to occur at (a) the gap B between the tip side surface 3c of the firing leg 3a of the insulator 3 and the inner side surface 5a of the outer electrode 5; This tendency is especially true when the engine has a lean mixture.
Or the required voltage is higher than that of a gasoline car.
This is more likely to occur in LPG vehicles.

(b) In the gap C between the body side surface 3d of the firing leg 3a and the inner wall 1a of the end face of the mounting bracket 1, when carbon adheres to the surface of the insulator firing leg and the insulation resistance decreases, the firing leg surface is Therefore, it becomes easy for sparks to fly in the gap C.

Although these discharges other than the spark gap 6 generated in (a) and (b) contribute to ignition of the air-fuel mixture, both of them are at positions that are significantly retracted from the protruding dimension E, which is not desirable from the standpoint of ignitability. Furthermore, since the outer electrode of such a protruding type spark plug is not covered and protrudes deeper into the combustion chamber, it becomes hotter than the center electrode, which could become a hot spot and cause pre-ignition.

The present invention has been made to solve the above problem, and the gap B and C, including the gap b and the depth d between the center electrode and the shaft hole of the insulator, is the size of the spark gap A. By setting the dimension E from the end surface of the mounting bracket to the tip end surface of the ignition leg, it is possible to suppress the phenomenon of sparks flying sideways outside of the spark gap, and even if sparks jump sideways. The object of the present invention is to provide a protruding type spark plug which has satisfactory ignitability and has improved heat resistance by setting the cross-sectional area (S)/length (L) of the outer electrode by its heat conduction. It is.

The present invention will be explained in detail below with reference to embodiments of the drawings.

FIG. 2 is a sectional view of a main part of the ignition part of a protruding type spark plug showing an embodiment of the present invention, and the same parts as in the conventional FIG. 1 are designated by the same reference numerals. 1 is a mounting bracket, 3 is a porcelain insulator, and 4 is a center electrode.The tip of the center electrode 4 is exposed and inserted into the shaft hole 3e, and the insulator 3 is placed in the inner cavity of the mounting bracket 1. The firing leg 3a protrudes from the end face 1a of the mounting bracket and is sealed and fixed according to known specifications. Reference numeral 5 designates an outer electrode welded to the end surface 1b of the mounting bracket 1, and a spark plug in which a spark gap 6 is formed between the tip 5b of the inner side surface 5a of the electrode and the tip surface 4a of the center electrode 4. It is.

In the present invention, when the size of the spark gap is A, the tip side surface 3 of the ignition leg 3a including the distance b between the center electrode 4 and the shaft hole 3e and its depth d.
The distance B between c and the inner side surface 5a of the outer electrode 5 is b>
0.3mm, when d>2mm, 1.0A or more, firing leg 3
The distance C between the side surface 3d of the body part a and the inner wall 1c of the end surface of the mounting bracket 1 is 1.1A or more, and the distance C between the end surface 1c of the mounting bracket 1
The protrusion dimension D from b to the tip 3b of the firing leg 1a is set to E/3 or more with respect to the protrusion dimension E of the tip surface 4a of the center electrode 4, and the cross-sectional area of the outer electrode is set to S, and its length is set to L. When a nickel alloy having a thermal conductivity of 0.03 to 1.0 cal/cm·sec°C is used for the outer electrode, S/L is set to >0.21.

The reason for limiting to these dimensions is as follows. That is, as shown in Figures 3 and 4, the protrusion dimension E is 10 mm, D is 4 mm, b is 0.3 mm, and d is
= 2mm, spark gap A is representative of 1.1mm, and gaps B and C are changed respectively for spark gap A,
The discharge characteristics of the discharge starting voltage at which the spark jumps sideways outside the spark gap were investigated. In addition, in this experiment, the insulation resistance was increased due to carbon adhesion on the surface of the insulator firing leg.
We prepared a large number of spark plugs with a resistance of 10 MΩ or less, and tested the gaps B and C when a pressure of 4 kg/cm ² was applied to the sparking part of the plug at room temperature by attaching the plugs to a spark tester. The discharge characteristics were compared. Furthermore, X in the figure is the regular spark gap (0.8
mm), and Y is the discharge voltage when the spark gap A expands to 1.4 mm after long-term use, which is the maximum value that is generally considered to be the limit of the useful life. As a result, based on Y, which is the limit of the effective life, the gap B is 1.0 times or more the size of the spark gap A as shown in Figure 3, and C is also 1.1 times or more as shown in Figure 4. When set to , sideways discharge can be greatly reduced.

Incidentally, since the horizontal deviation of the gap B is related to the air gap length between the center electrode and the outer electrode, the gap B between the tip side surface 3c of the firing leg 3a and the inner side surface 5a of the outer electrode 5 is sufficient. Instead, it includes the gap b between the center electrode 4 and the shaft hole 3e of the insulator 3, and increasing this gap is also effective in preventing sideways flying of this part. The horizontal discharge starts from the outer electrode side and reaches the center electrode along the tip surface of the insulator. When the gap b is 0.3 mm or more, it reaches the center electrode after extending from the tip end face of the insulator by a distance d along the insulator side of the gap b. Therefore b>0.3mm,
If d>2mm, the actual discharge distance becomes longer, so B
>1.0A, C>1.1A. In fact, if b is too large, the tip of the center electrode is likely to be overheated, and as shown in FIG. 9, the heat resistance will deteriorate, so b is preferably within 0.5 mm. Furthermore, d is 2mm
The above is desirable because the actual discharge distance becomes longer like b, but if d becomes too large, the deterioration of heat resistance gradually increases as shown in FIG. 10, which is not preferable.

Also, in Figure 5, the protrusion dimension E is 10 mm, the spark gap A is 1.1 mm, the gap B is 0.9 mm or less, b = 0.3 mm,
d = 2 mm, C is A x 1.4 mm, and the protruding dimensions D are E/5 and E/3, respectively, and the gap B and the spark gap are assumed to have an equal potential, and the co-occurrence of both gap B and the above dimension B A×1.3
Prepare a spark plug that discharges only with a spark gap by changing the spark plug to mm and using one with D of E/3. For the experiment, a 4-stroke, 6-cylinder, 2000 c.c. engine was used and operated at idling (650 rpm).
We investigated the relationship between the total concentration of Co, CO ₂ and HC in exhaust gas, which correlates with air fuel efficiency, and the number of ignition errors. As a result, as shown in the figure, it was confirmed that D is preferably at least E/3 or more, which is similar to when ignition is reliably ignited with only spark gap A.

Furthermore, in Figure 6, materials with different thermal conductivities for the outer electrodes were prepared, and E = 10 mm, D = 4 mm, A = 1.0 mm,
B = A x 1.3mm, including b = 0.3mm and d = 2mm, connected to a spark plug with a configuration of C = A x 1.4mm, and the ignition timing was set at 5500 rpm x 4/4 using the same engine as above. After making changes, we compared the heat resistance due to the occurrence of pre-ignition. Note that Z is the limit line of heat resistance for use in general four-wheeled vehicles, and with the Z line as a reference, the upper part has high heat resistance, and the lower part indicates that it is not practical due to insufficient heat resistance. As a result, the T value of S/L is determined by the thermal conductivity of the outer electrode, for example.
Nickel alloy of 0.06 to 1.0 cal/cm・sec℃, e.g.
Ni−Si−Mn, Ni−Si−Mn−Cr, Ni−Si−Mn
- Materials such as Cr-Al alloy require T > 0.21,
In addition, in order to particularly improve the durability of the outer electrode, if the thermal conductivity of Inconel, which is a material with excellent oxidation resistance and corrosion resistance, is 0.03 to 0.05 cal/cm・sec℃,
T > 0.25 is desirable from the viewpoint of heat resistance. In other words, when the length of the outer electrode becomes significantly long, the T value may be appropriately selected depending on the thermal conductivity (material) of the outer electrode.

By limiting each dimension in this way, even if the plug is soiled, discharge in gaps B and C can be avoided, and even if discharge occurs in B, the ignitability will be less affected and the ignitability will be excellent. Since the S/L of the outer electrode is selected depending on the thermal conductivity, the preignition resistance can be improved.

FIG. 7 shows the ignition part of a protruding type spark plug according to another embodiment of the present invention, in which the tip 4a of the center electrode 4 is inserted into the shaft hole of the insulator 3, and the tip end face 3b of the ignition leg 3a is inserted into the shaft hole of the insulator 3. This insulator is similarly fixed within the bore of the fitting 1. An inner side surface 15 of an outer electrode 15 protruding from the end surface 1b of the mounting bracket 1 on the tip edge 4c (FIG. 7A) of the center electrode 4 or the tip side surface 4d (FIG. 7B)
a or the tip surface 15b is opposed to the spark gap 1.
6 is a spark plug formed respectively.
The dimensional conditions of the present invention described in FIG. 2 are also applied to such a spark plug, and the spark plug can be configured to advantageously prevent horizontal spark discharge and prevent pre-ignition due to the outer electrode.

FIG. 8 shows yet another embodiment of the present invention, in which the spark discharge surface forming the spark gap between the center electrode 4 and the outer electrode 5 in the protruding type spark plug of the present invention shown in FIG. precious metal chips 17 and 18 such as Pt or its alloy are bonded to the metal chips, respectively.By providing such precious metal chips, not only is maintenance free, but the spark gap is widened to the extent that wear and tear on the spark gap is reduced. This makes it possible to effectively deal with the prevention of sideways spark discharge in this expanding spark gap, and also to prevent pre-ignition caused by the outer electrode, resulting in a spark plug with excellent durability. Further, the spark plug shown in FIG. 7 can be similarly provided with a noble metal chip.

As described above, in the protruding type spark plug of the present invention, the distances B and C obtained by adding b are determined based on the size of the spark gap, and b > 0.3 mm and d > 2 mm, respectively.
When B > 1.0A, C > 1.1A, and the protrusion dimension D of the tip surface of the ignition leg is D > E/3 with respect to the protrusion dimension E to the tip surface of the center electrode, the spark The phenomenon of sideways discharge other than the gap can be effectively prevented, and a spark plug with excellent ignitability can be obtained. Furthermore, spark discharge in the gap C along the insulator surface caused by carbon contamination is prevented, and even if sparks fly in the gap B instead, deterioration in ignitability can be greatly reduced. Furthermore, since the deterioration of pre-ignition caused by the outer electrode of the protruding type spark plug can be solved by setting the S/L to a certain level or more depending on the thermal conductivity of the electrode, it can be manufactured easily and inexpensively, and has excellent durability. An excellent protruding type spark plug can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the main part of the ignition part of a conventional protruding type spark plug, Fig. 2 is a sectional view of the main part of the ignition part of the protruding type spark plug showing an embodiment of the present invention, and Figs. 3 to 6 3 and 4 are graphs showing the relationship between the sizes of gaps B and C and the horizontal discharge characteristics, and FIG. 5 is a graph showing the influence of the protrusion dimension D on ignitability. Graph shown, No. 6
The figure is a graph showing the results of heat resistance versus thermal conductivity of the outer electrode, Figures 7 and 8 are sectional views of essential parts of the ignition part of a protruding spark plug showing other embodiments of the present invention, and Figure 9 and Figure 10 shows dimensions b and d.
It is a graph showing the relationship between and heat resistance. 1...Mounting bracket, 1a...Inner wall, 1b...End face, 3...Insulator, 3a...Ignition leg, 3b...
Tip surface, 3c... Tip side surface, 3d... Body side surface,
3e...Shaft hole, 4...Center electrode, 4a...Tip, 4b...Tip surface, 5, 15...Outer electrode,
6, 16...Spark gap.

Claims (1)

[Claims] 1. A firing leg of a porcelain insulator that protrudes from the end face of the mounting bracket with a space between it and the inner wall of the mounting bracket, and a center electrode that is inserted into the shaft hole of the firing leg and exposed from the tip. and a protruding type spark plug in which a spark gap is formed between the tip of the center electrode and the outer electrode opposing the center electrode, the size of the spark gap is A, and the distance between the center electrode and the shaft hole of the insulator is The distance between the tip side surface of the firing leg including b and the outer electrode is B, the depth of the gap b is d, and the distance between the inner wall of the end surface of the mounting bracket and the side surface of the body of the firing leg is C. , when the protrusion dimension between the end surface of the mounting bracket and the tip surface of the firing leg is D, and the protrusion dimension of the tip surface of the center electrode from the end surface of the mounting bracket is E, b > 0.3 mm,
When d>2mm, set B>1.0A and C>1.1A, and set the protrusion dimension of D to D>E/3, and set the cross-sectional area of the spark discharge part of the outer electrode to S, and the mounting bracket of the electrode. When the length L from the end surface of A protruding spark plug featuring: