JPH0785947A - Spark plug - Google Patents

Abstract

PURPOSE:To provide a spark plug with less wear amount even through a long- time service, i.e., free from risk of spark gap widening and at a reasonable cost comparatively with its lifetime characteristics. CONSTITUTION:A small side-face electrode 5 is made of a noble metal or its alloy, and that end 5a of this electrode 5 on the insulator side is located within a scope 1mm or more apart toward the insulator from the side face of a center electrode 4 confronting the lower end part 3b of a ground electrode 3. Further, the other end 5b of side-face electrode 5 on the center electrode foremost side is located within a scope 0.2mm or more apart from the foremost face 4a of the center electrode, so that the spark gap is free from risk of widening, and a spark plug at a low cost for its lifetime characteristics can be offered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spur plug.

[0002]

2. Description of the Related Art In an internal combustion engine of an automobile or the like, further energy saving is required from the viewpoint of recent global problems and global resources. Therefore, reduction of fuel consumption is taken up as a global issue. As a concrete measure for the engine, high compression and reburning with a lean mixture have been studied. However, it has become clear that the discharge voltage required for discharging in the spark gap rises more than before. With this increase in discharge voltage, the electrodes of the spark plug are further consumed and the spark gap increases. As a result, the discharge voltage becomes higher and the margin until the dielectric breakdown of the ignition system is reduced. Then, it is becoming more and more apparent that discharge occurs at a place other than the spark gap. Therefore, the demand for a spark plug that uses a precious metal such as platinum or an alloy of a precious metal, which consumes significantly less electrode, as an electrode material has been further increasing.

To meet such demand, for example, Japanese Unexamined Patent Publication No.
Techniques such as 9-41734 and JP-B-62-31797 are disclosed. That is, JP-A-49-4
Japanese Patent No. 1734 is a spark plug in which, for example, a cylindrical clad material having a core material made of a nickel alloy and an outer skin made of a platinum alloy is provided at the tip of the center electrode, and the end surface of the ground electrode is opposed to the clad material. Also, Japanese Examined Japanese Patent Sho 62-3
Japanese Patent No. 1797 is a spark plug in which an annular member made of a noble metal such as platinum or iridium is fitted into a convex portion provided at the tip of the center electrode, and the end face of the ground electrode is opposed to the annular member. .

However, even in the case where the annular electrode made of a noble metal or a noble metal alloy as described above is attached, there are some cases where the electrodes are worn out severely, and there are some cases in which the durability to peel off is poor.

[0005]

In view of the above-mentioned problems, a spark plug having a higher durability, which has a small amount of wear even when used for a long period of time, does not expand the spark gap, and does not peel off. It is provided.

[0006]

To this end, as a first invention, a housing, a curved ground electrode provided on a front end surface of the housing, an insulator held by the housing, and an insulator held by the insulator are provided. And a spark gap formed by a front end surface of the ground electrode facing the side surface of the center electrode, a side surface of the center electrode facing the front end of the ground electrode. A noble metal, or a chip-shaped or a ring-shaped small side electrode made of a noble metal alloy, the insulator side end of the side electrode, from the ground electrode side end,
The diameter of the center electrode provided in the side surface electrode within 1 mm along the axis of the center electrode and within which the side surface electrode is provided is 1.4 mm or more. To have.

A second aspect of the present invention is a housing, a curved ground electrode provided on a front end surface of the housing, an insulator held by the housing, and a center electrode held by the insulator. In a spark plug having a spark gap formed such that the tip surface of the ground electrode faces the side surface of the center electrode, the side surface of the center electrode facing the tip of the ground electrode is made of a noble metal or a noble metal alloy. A side surface electrode is provided, and an end portion of the side surface electrode on the tip end surface side of the center electrode is provided in a position range separated by 0.2 mm or more from the tip end surface of the center electrode along the center electrode axial direction. It has a configuration characterized by that.

The third invention is defined by claim 1 and claim 2.
It is a combination of the configurations described in.

[0009]

According to the first aspect of the present invention, the end of the side electrode made of a noble metal or a noble metal alloy on the side of the insulator is within 1 mm from the curved lower side end of the ground electrode along the center electrode axis. Since it is provided within the position range, the amount of wear is small, and since the diameter of the center electrode provided on the side surface electrode is 1.4 mm or more, it is not broken.

According to the second aspect of the present invention, the noble metal or noble metal alloy side surface electrode is provided with the end portion of the center electrode on the tip surface side within a position range separated by 0.2 mm or more from the tip surface of the center electrode. Therefore, the oxidation of the interface between the side surface electrode and the center electrode can be significantly suppressed. According to the third invention, the end of the side electrode of the noble metal or noble metal alloy side on the side of the insulator is within 1 mm from the curved lower side end of the ground electrode to the side of the insulator along the center electrode axis. And the end portion of the noble metal or noble metal alloy side electrode on the tip end surface side of the center electrode is 0.2 mm or more away from the tip end surface of the center electrode. Therefore, the amount of consumption is small, the oxidation of the interface between the side electrode and the center electrode is significantly suppressed, and the diameter of the center electrode provided with the side electrode is 1.4 mm or more. It does not break.

[0011]

Therefore, according to the first aspect of the present invention, the spark gap does not expand so much even when used for a long period of time, and the spark plug does not expand so much. Therefore, it is possible to provide a spark plug which has a high durability and a low cost for its life. . Further, according to the second aspect of the present invention, the oxidation of the interface can be suppressed, so that the side surface electrode can be provided with a highly durable spark plug without dropping off due to oxidation.

Further, according to the third aspect of the present invention, the spark gap does not increase so much even if it is used for a long time, the durability is high, and the oxidation of the interface can be suppressed. It will be highly durable without falling off. Therefore, it is possible to provide a spark plug whose cost is very low for its life.

[0013]

【Example】

(First Embodiment) The present invention will be described with reference to the embodiment shown in FIGS. FIG. 1 is a schematic view showing a spark plug 1 which is an embodiment of the present invention. Further, FIG. 2 is an enlarged view showing the main part of FIG. In FIG. 1, the spark plug 1 holds an Inconel center electrode 4 having an outer diameter of 2.5 mm at the tip of a through hole (not shown) of an insulator 6.
Further, the stem 8 is held at the rear end of the through hole, and further, the center electrode 4, the conductive glass seal 9 held by the stem 8 and the resistor 10 are internally sealed and held, and the insulator 6 is held.
And a housing 2 in which four ground electrodes 3 having a width of 2.6 mm and a thickness of 1.4 mm are arranged so as to face the side surface 4b of the tip portion of the center electrode 4 held by the insulator 6.

Further, a cylindrical annular side surface electrode is provided on the tip end side surface 4b of the center electrode 4, which is a position facing the curved tip end 3a of the ground electrode 3 coupled to the tip of the screw portion 2b of the housing 2. The electrode 5 in which 5 is embedded and joined is a known noble metal or noble metal alloy Pt, Pt-I.
r, Pt-W, Pt-Ph, Pt-d, Pt-Ni, A
u-Pd, height 1.5 mm, outer diameter 1.4 m
It has a size of m and an inner diameter of 0.8 mm. Next, the positional relationship between the side electrode 5 and the curved tip portion 3a of the ground electrode 3 will be described. The tip side surface 4b of the center electrode 4 facing the insulator side tip 3b of the tip 3a.
From the position of the center electrode 4 toward the tip of the insulator.
The tip portion 3a is provided within 1 mm along the.

Here, the reason why the side electrodes are arranged as described above will be explained. As a result of studying the consumption level of the center electrode by making a similar product without the side electrode 5 with respect to the above-described embodiment and conducting an investigation with an actual machine such as a taxi, the consumption form is as shown in FIG. It will be as shown in a). This wear extends over a wide area of the side surface of the center electrode facing the ground electrode, and particularly, the tip portion of the center electrode is severely worn.

FIG. 4 shows the change in the cross-sectional dimension of the center electrode with respect to the traveling distance. The cross-sectional dimension of the center electrode tip is A, the cross-sectional dimension of the center electrode portion facing the insulator side of the ground electrode is B, or The consumption influence dimension from the insulator side of the ground electrode to the side surface of the center electrode is C. It can be seen that as the traveling distance increases, the wear on all the A, B, and C dimensions progresses. Generally, the usage distance called long life is 100,000 km, but it is estimated from Fig. 4 that the diameter is reduced to about 1/3 for the A dimension and about 1/2 for the B dimension.
The mm range is affected. The above is the reason for limiting the position of the side electrode. FIG. 3A shows the consumption state of the product of the present invention. It is extremely good with almost no wear. In the shape having the above-mentioned characteristics, if the width of the annular noble metal is simply reduced, the base material portion near the noble metal is consumed, and a recess is formed in the vicinity due to the difference in consumption.

On the other hand, in addition to the change in shape due to use, the center electrode gradually decreases in hardness and strength due to heat received from combustion. From both aspects of shape change and strength reduction,
There is concern that the strength of the recess will be significantly deteriorated. Although it is a spark plug that has a noble metal material for long life, the concave part near the annular noble metal progresses for a long time and may be broken if exposed to a high temperature / high vibration use environment. is there. The breakage frequency has been increasing in recent years, and the frequency of occurrence tends to increase as stress is applied to the ignition portion protruding into the combustion chamber due to valve vibration, cam vibration, combustion fluctuations, etc. at high rotation reduction.

As described above, in order to further reduce the amount of precious metal used, it is difficult to adopt the above-mentioned measure for reducing the amount of use because the possibility of breakage is further increased in the specification in which the diameter of the center electrode is also reduced. FIG. 5 shows the results of evaluation of the breakage resistance with respect to the diameter of the center electrode 4 by the product of the present invention. Evaluation is 4 cy
WOT * in 1,1600cc gasoline engine
Performed under the condition of 8000 rpm * 10H, and the ground electrode 3
A recess having a width of 1 mm is formed in the insulator direction from the side surface 4b of the central electrode facing the insulator-side end surface 3b.
The diameter of the recess was used as a standard. The recess width of 1 mm was taken into consideration in the wear range of the investigation result of FIG. In addition, the center electrode 4 has a hardness decrease due to long-term use, and is preliminarily heat-treated to Hv1.
The number of poles of the ground electrode 3 was about 30 as described above. Further, the length of protrusion of the insulator 6 from the end face of the housing 2 (dimension from the housing end face 2a to the insulator end face 6a) is 2 mm, and the spark position is 5 m.
m and 7 mm (dimension from the housing end surface 2a to the center electrode end surface 4a).

As a result, the deformation and breakage of the center electrode 4 can be avoided when the dimension of the recess is 1.4 mm or more. (Second Embodiment) Since the center electrode 4 is generally a Ni-base heat resistant alloy and the side surface electrode 5 is a noble metal or a noble metal alloy, there is a difference in thermal expansion between the two.

On the other hand, during engine operation, the temperature of the center electrode 4 rises and falls according to the load.
Since this change in the center electrode temperature is due to heat transfer from the air-fuel mixture and the combustion gas, the temperature change of the center electrode tip surface 4a, which projects most into the combustion chamber and has a large area, is the largest. Therefore, if the discharge tip is too close to the center electrode tip surface 4a, the joint surface 5c of the side surface electrode 5 is affected by the temperature change of the center electrode tip surface 4a, and the temperature change becomes large. Therefore, due to the above-mentioned difference in thermal expansion and a large temperature change, a large thermal stress is generated in the joint surface 5c, and an oxidative crack is generated in the joint surface 5c. As shown in FIG. 6, this oxidative crack significantly occurs on the joint surface 5c on the tip side of the center electrode. Due to this oxidation crack, the side surface electrode 5 may be peeled off. Therefore, when the distance between the end 5b of the side surface electrode 5 on the side of the center electrode tip surface 4a and the center electrode tip surface 4a is l, l = 0.1,
The spark plug 1 of 0.2 and 0.4 mm was subjected to engine evaluation based on two types of spark positions L = 3, 4 mm. The evaluation engine is a water-cooled 4-cycle 6-cylinder 20.
00cc is used, and the evaluation condition is a full load of 6000 rpm.
1 minute, idling 1 minute 1 cycle 100
It was H driving.

The results of the evaluation test are shown in FIG. The horizontal axis is the l dimension, and the joint surface oxidation rate on the vertical axis is D, E where the lengths of the oxidation cracks are shown in the figure, and F is the total joint surface length.

[0022]

It is shown as (D + E) / F × 100. Incidentally, FIG. 7 shows the case where L = 4 mm and L = 3 mm. First, when L = 4 mm, l is 0.
When it becomes smaller than 2 mm and becomes 0.1 mm, the oxidative crack length remarkably extends. When it is 0.2 mm or more, it is suppressed to a low value. That is, it is considered that when the thickness is 0.2 mm or more, the influence of heat from the tip surface is very small.

Next, in the case of L = 3 mm, the above L = 4.
As in the case of mm, when l is 0.2 mm or more, the oxidation crack length remains low. However, the value is smaller than that when L = 4 mm. This is because L becomes shorter,
By reducing the amount of heat transfer from the mixture and combustion gas, and improving the heat conduction to the rear of the center electrode,
It is considered that this is because the temperature of the joint surface of the discharge tip becomes lower and the thermal stress level is reduced. However, l is 0.2 m
When the length is shorter than m, the length of the oxidative crack is almost the same at L = 4 mm and L = 3 mm, which is very long. This is because if l is too short, the thermal effect on the tip surface becomes very dominant.

From the above results, within the range of l ≧ 0.2 mm, it is possible to reduce the thermal effect on the center electrode tip surface 4a and to obtain good reliability in bonding. (Third Example) As a third invention, a spark plug having a side electrode 5 having both the first and second inventions was manufactured.
In addition, the diameter of the central electrode portion provided with the side surface electrode 5 is at least 1.4.
mm.

The side surface electrode 5 is made of a noble metal or a noble metal alloy, and the end portion 5a of the side surface electrode 5 on the side of the insulator is formed.
Was provided within a position range 1 mm or more away from the side surface of the center electrode 4 facing the lower side surface end portion 3b of the ground electrode 3 toward the insulator 6 side. Moreover, the end portion 5b of the side surface electrode 5 on the side of the tip surface 4a of the center electrode is provided in a position range apart from the center electrode tip surface 4a by 0.2 mm or more along the axial direction of the center electrode 4. It was Therefore,
The side surface electrode has high durability without peeling or falling off, and has a very small consumption amount, which makes it difficult to expand the spark gap 7. Further, since the diameter of the center electrode 4 on which the side surface electrode 5 is arranged is 1.4 mm or more, the breakage resistance is excellent. Since the side surface electrode 5 is smaller than the conventional one, the spark plug is low in cost for its life.

[Brief description of drawings]

FIG. 1 is a half cross-sectional view illustrating the configuration of the product of the present invention.

FIG. 2A is a view of the product of the present invention seen from below.
(A) is a side view of the main part of the product of the present invention.

FIG. 3A is a diagram showing a typical consumption pattern of a conventional product. (A) is the figure which described the typical consumption form of the product of this invention.

FIG. 4A is a diagram showing a consumption level with respect to a traveling distance of a conventional product. (B) is a figure which shows the test piece in (a).

FIG. 5 is a diagram showing a frequency of deformation / breakage occurrence in an engine test with respect to a center electrode diameter.

FIG. 6 is a cross-sectional view showing an oxidized form of a side electrode / center electrode joint surface.

FIG. 7 is a graph showing an oxidation rate of a joint surface.

[Explanation of symbols]

 1 spark plug 2 housing 2a housing front end surface 3 ground electrode 3a ground electrode front end surface 3b ground electrode lower side surface end 4 center electrode 4a center electrode front end surface 5 side electrode 5a side electrode insulator side end 5b side electrode center electrode Tip on the tip side 5c Bonding surface 6 Insulator 7 Spark gap

Claims (3)

[Claims] 1. A housing, a curved ground electrode provided on a tip surface of the housing, an insulator held by the housing, a center electrode held by the insulator, and a tip surface of the ground electrode. A spark gap formed to face the side surface of the center electrode, and a side electrode made of a noble metal or a noble metal alloy on the side surface of the center electrode facing the tip of the ground electrode. An end portion of the side surface electrode on the insulator side is provided within a position range of 1 mm or less from the lower side surface end portion of the ground electrode along the central electrode axial direction toward the insulator side, and the side surface electrode is The diameter of the center electrode provided is 1.4 mm
The above is the spark plug characterized by the above. 2. A housing, a curved ground electrode provided on a tip surface of the housing, an insulator held by the housing, a center electrode held by the insulator, and a tip surface of the ground electrode. In a spark plug composed of a spark gap formed corresponding to the side surface of the center electrode, a side surface electrode made of a noble metal or a noble metal alloy is provided on a side surface of the center electrode facing the tip of the ground electrode. Side electrode The end of the center electrode on the tip surface side is 0.2 from the tip surface of the center electrode in the axial direction of the center electrode.
A spark plug which is provided in a position range separated by at least mm. 3. A spark plug comprising a combination of claim 1 and claim 2.