JP3699490B2 - Spark plug - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a spar plug.
[0002]
[Prior art]
In internal combustion engines such as automobiles, further energy saving has been pursued from the viewpoint of recent earth problems and earth resources. Therefore, reducing fuel consumption has been taken up as a global issue. As specific measures for the engine, high compression, reburning with a lean mixture, and the like have been studied. However, it has become clear that the discharge voltage required for discharging at the spark gap is higher than before. As the discharge voltage rises, the spark plug electrode is further consumed, and the spark gap increases. As a result, the discharge voltage becomes a higher value, and the margin to the breakdown of the ignition system is reduced. And it has come to be seen that discharge occurs in places other than the spark gap. Accordingly, there is a growing demand for spark plugs that employ noble metals such as platinum and noble metal alloys, which are extremely low in electrode consumption, as electrode materials.
[0003]
In response to such demand, for example, techniques such as JP-A-49-41734 and JP-B-62-31797 are disclosed. That is, in Japanese Patent Laid-Open No. 49-41734, for example, a cylindrical clad material provided with a core material made of nickel alloy and an outer skin made of platinum alloy is provided at the tip of the center electrode, and the end face of the ground electrode is opposed to the clad material. This is a spark plug. Japanese Examined Patent Publication No. 62-31797 discloses an annular material made of a noble metal such as platinum or iridium that is fitted to a convex portion provided at the tip of a center electrode, and the ground electrode end face is opposed to the annular material. This is a spark plug.
[0004]
However, even those provided with an annular electrode made of a noble metal or a noble metal alloy as described above can be worn out rapidly, and some of them have poor durability to peel off.
[0005]
[Problems to be solved by the invention]
In view of the above-described problems, it is an object of the present invention to provide a highly durable spark plug that consumes little amount even when used for a long time, does not expand a spark gap, and does not peel off.
[0006]
[Means for Solving the Problems]
To that 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, a center electrode held by the insulator , and the ground electrode In a spark plug composed of a spark gap formed so that a front end surface of the center electrode faces the side surface of the center electrode , a noble metal is formed only on a side surface facing the front end of the ground electrode and protruding from the insulator of the center electrode. Alternatively, a side electrode made of a noble metal alloy is provided, and the end of the side electrode on the side of the front end surface of the central electrode is in a position range that is 0.2 mm or more away from the front end surface of the central electrode along the axial direction of the central electrode. Provide provided spark plug.
[0007]
According to a second aspect of the present invention, in the first aspect of the invention, the insulator side end of the side electrode is further away from the insulator side end of the ground electrode along the central electrode axis direction. A spark plug is provided in a position range of 1 mm or less on the insulator side, and the diameter of the central electrode provided with the side electrode is 1.4 mm or more.
[0009]
[Action]
According to the first invention, the end portion of the side electrode made of a noble metal or a noble metal alloy on the side of the center electrode tip surface side is provided within a position range of 0.2 mm or more away from the tip surface of the center electrode. Oxidation at the interface between the side electrode and the center electrode can be remarkably suppressed.
[0010]
According to the second invention, the end of the side electrode made of a noble metal or a noble metal alloy on the side of the insulator is located within 1 mm from the side of the insulator side of the ground electrode along the central electrode axis. Since it is provided within the range, the amount of consumption is small, and since the diameter of the central electrode on which the side electrode is provided is 1.4 mm or more, there is no breakage.
[0011]
【The invention's effect】
Therefore, according to the first invention, since the interface oxidation can be suppressed, the side electrode can be provided with a highly durable spark plug without oxidization and dropping.
[0012]
Further, according to the second invention, since the amount of consumption is small even when used for a long time, the spark gap does not expand so much, the durability is high, and the oxidation at the interface can be suppressed. It becomes a high quality thing. Therefore, it is possible to provide a spark plug with a very low cost for its lifetime.
[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 according to an embodiment of the present invention.
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 a front end portion of a through hole (not shown) of an insulator 6 and a rear end of the through hole. Further, the insulator 6 holding and holding the central electrode 4, the conductive glass seal 9 and the resistor 10 held between the center electrode 4 and the stem 8, and the insulator 6 held by the insulator 6. It is composed of 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 tip side surface 4 b of the center electrode 4.
[0014]
Further, a cylindrical annular side electrode 5 is embedded in the distal end side surface 4b of the center electrode 4, which is a position facing the curved distal end portion 3a of the ground electrode 3 coupled to the distal end of the screw portion 2b of the housing 2. The electrodes 5 joined together are known noble metals or noble metal alloys Pt, Pt—Ir, Pt—W, Pt—Ph, Pt—d, Pt—Ni, Au—Pd, and have a height. It has a size of 1.5 mm, an outer diameter of 1.4 mm, 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 portion 3a is within 1 mm along the center electrode 4 from the position of the tip side surface 4b of the center electrode 4 facing the insulator side tip portion 3b of the tip portion 3a toward the insulator tip portion. Is provided.
[0015]
Here, the reason why the side electrodes are arranged as described above will be described. As a result of producing an analog that does not include the side electrode 5 with respect to the embodiment as described above, conducting an investigation with a real machine such as a taxi, and studying the wear level of the center electrode, the wear mode is shown in FIG. It will be as shown in a). This consumption is spread over a wide area on the side surface of the center electrode facing the ground electrode, and the tip portion of the center electrode is particularly heavily consumed.
[0016]
FIG. 4 shows the change in the cross-sectional dimension of the center electrode with respect to the travel distance, where A is the cross-sectional dimension of the front end of the center electrode, B is the cross-sectional dimension of the center electrode portion facing the insulator side of the ground electrode, or C is defined as a wear-affected dimension from the insulator side to the side surface of the center electrode. It can be seen that as the mileage increases, the consumption of A, B, and C dimensions progresses. The working distance, which is generally called long life, is 100,000 km, but it is assumed from FIG. 4 that the A dimension is reduced to 1/3 and the B dimension is reduced to about 1/2, and the C dimension is also affected by the 1 mm range. ing. The above is the reason for limiting the position of the side electrode. FIG. 3 (a) shows the consumption state of the product of the present invention. It is very good with almost no wear. In the shape having the above-described characteristics, in the specification in which the width of the annular noble metal is simply reduced, the wear of the base metal portion in the vicinity of the noble metal proceeds, and a recess is formed in the vicinity due to the wear difference.
[0017]
On the other hand, in addition to the shape change accompanying use, the hardness of the center electrode gradually decreases and the strength also decreases due to heat received from combustion. From both sides of the shape change and the strength reduction, there is a concern about the significant deterioration of the recess strength. This is a spark plug that arranges precious metal materials for long life, but the recess near the annular precious metal progresses for a long time and may break if exposed to high temperature and high vibration environment. is there. Breakage tends to increase in frequency in recent years as stress increases in the ignition part protruding into the combustion chamber due to valve vibration, cam vibration, combustion fluctuation, etc. at high rotation reduction.
[0018]
As described above, in order to further reduce the amount of noble metal used, it is difficult to adopt the above-mentioned method 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 reduced.
FIG. 5 shows the result of evaluation of the breakage resistance with respect to the diameter of the center electrode 4 by the product of the present invention. The evaluation is carried out under the condition of WOT * 8000 rpm * 10H in a 4cy1, 1600 cc gasoline engine, and a recess having a width of 1 mm from the central electrode side surface 4b facing the insulator side end surface 3b of the ground electrode 3 in the direction of the insulator. And the recess diameter was taken as a standard. For the recess width of 1 mm, the consumption range of the investigation results in FIG. 4 was taken into consideration. Further, the center electrode 4 was subjected to a heat treatment to have a Hv of around 130 in advance, and the ground electrode 3 was implemented with four poles as described above. The length of the insulator 6 protruding 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 positions are 5 mm and 7 mm (from the housing end face 2a to the center electrode end face 4a). ).
[0019]
As a result, deformation and breakage of the center electrode 4 are avoided when the concave dimension diameter is 1.4 mm or more.
(Second embodiment)
The center electrode 4 is generally a Ni-base heat-resistant alloy, and the side electrode 5 is a noble metal or a noble metal alloy, so there is a difference in thermal expansion between the two.
[0020]
On the other hand, during engine operation, the temperature of the center electrode 4 rises and falls according to the load. Since the center electrode temperature change is due to heat transfer from the air-fuel mixture and the combustion gas, the temperature change of the center electrode front end surface 4a which protrudes most into the combustion chamber and has a large area is the most severe.
Therefore, if the discharge tip is too close to the center electrode tip surface 4a, the joining surface 5c of the side 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-described difference in thermal expansion and large temperature change, a large thermal stress is generated on the bonding surface 5c, and an oxidation crack is generated on the bonding surface 5c. As shown in FIG. 6, this oxidation crack is remarkably generated on the joint surface 5c on the tip side of the center electrode. Due to this oxidation crack, the side electrode 5 may be peeled off. Therefore, the above-described spark plug 1 with l = 0.1, 0.2, and 0.4 mm, where l is the distance between the end 5b of the side electrode 5 on the side of the center electrode tip 4a and the tip 4a of the center electrode. The engine was evaluated on the basis of two types of spark positions L = 3, 4 mm. The evaluation engine was a water-cooled 4-cycle 6-cylinder 2000 cc, and the evaluation conditions were 100H operation with a full load of 6000 rpm for 1 minute and idling for 1 minute.
[0021]
The result of the evaluation test is shown in FIG. The horizontal axis takes the dimension l, and the joint surface oxidation rate on the vertical axis represents the length of the oxidation crack shown in the figure as D and E, and the total joint surface length as F.
[0022]
[Expression 1]
(D + E) / F × 100
As shown.
FIG. 7 shows a case where L = 4 mm and L = 3 mm.
First, in the case of L = 4 mm, when 1 becomes smaller than 0.2 mm and becomes 0.1 mm, the oxidation crack length is remarkably extended. If it is 0.2 mm or more, it is suppressed to a low value. That is, if the thickness is 0.2 mm or more, it is considered that the thermal influence from the tip surface is very small.
[0023]
Next, in the case of L = 3 mm, l is 0.2 mm or more as in the case of L = 4 mm, and the oxidation crack length remains low. However, the value is smaller than that in the case of L = 4 mm. This is because the heat transfer amount from the air-fuel mixture and the combustion gas is reduced by reducing L, and the heat conduction to the rear of the center electrode is improved, so that the temperature of the joint surface of the discharge tip is lowered. This is thought to be due to the reduction of the thermal stress level. However, when l becomes shorter than 0.2 mm, the oxidation crack length is almost the same regardless of whether L = 4 mm or L = 3 mm. This is because if l is too short, the thermal effect of the tip surface becomes very dominant.
[0024]
From the above results, if l ≧ 0.2 mm, the thermal effect of the center electrode tip surface 4a can be reduced, and good reliability can be obtained for bonding.
(Third embodiment)
As a third invention, a spark plug having a side electrode 5 having both the first and second inventions was produced. The diameter of the central electrode portion provided with the side electrode 5 was at least 1.4 mm.
[0025]
The side electrode 5 is made of a noble metal or a noble metal alloy, and the insulator-side end portion 5a of the side electrode 5 extends from the side surface of the central electrode 4 facing the lower side end portion 3b of the ground electrode 3 to the insulator. It was provided in a position range 1 mm or more away from the 6 side. Moreover, the end portion 5b of the side electrode 5 on the side of the tip surface 4a of the center electrode is provided in a position range that is separated 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 electrode has high durability without peeling and dropping, and the consumption amount is very small, so that the spark gap 7 is difficult to expand. In addition, since the diameter of the central electrode 4 on which the side electrode 5 is disposed is 1.4 mm or more, it has excellent breakage resistance. And since the said side electrode 5 is a small thing compared with the past, it becomes a spark plug with low cost for a lifetime.
[Brief description of the drawings]
FIG. 1 is a half cross-sectional view illustrating the configuration of a product of the present invention.
FIG. 2A is a view of the product of the present invention as viewed from below.
(A) is a side view of the principal part of the product of the present invention.
FIG. 3A is a diagram showing a typical consumption form of a conventional product.
(A) is a diagram showing a typical consumption form of the product of the present invention.
FIG. 4A is a diagram showing a consumption level with respect to a travel distance of a conventional product.
(B) is a figure which shows the test piece in (a).
FIG. 5 is a diagram showing a deformation / breakage occurrence frequency 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]
DESCRIPTION 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 side end 5c Joint surface 6 Insulator 7 Spark gap

Claims (2)

A housing, a curved ground electrode provided on the front end surface of the housing, an insulator held by the housing, a center electrode held by the insulator , and a front end surface of the ground electrode is a side surface of the center electrode In a spark plug composed of a spark gap formed opposite to
A side electrode made of a noble metal or a noble metal alloy is provided only on the side surface of the center electrode facing the tip of the ground electrode and protruding from the insulator .
The spark plug is characterized in that an end of the side electrode on the front end surface side of the center electrode is provided in a position range of 0.2 mm or more away from the front end surface of the center electrode along the center electrode axis direction . An end portion of the side electrode on the insulator side is provided within a position range within 1 mm from the insulator side surface end portion of the ground electrode along the central electrode axis direction toward the insulator side, and the side electrode The spark plug according to claim 1, wherein the diameter of the central electrode provided with is 1.4 mm or more .

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