JPH07288169A - Spark plug for internal combustion engine and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a spark plug which is less likely to misfire even when the air-fuel ratio is large, has sufficient ignitability, and has excellent durability, and a method for producing the spark plug. [Configuration] A noble metal is fitted into a groove formed around the tip of the center electrode base material, irradiated with a YAG laser beam and melt-bonded to form a noble metal alloy 12, and the tip of the center electrode base material is cut, The noble metal alloy portion is removed by cutting or polishing, and the noble metal alloy portion is arranged at the edge portion of the tip surface 13 of the center electrode 10. Further, the position of the tip surface 13 of the center electrode is equal to the position of the tip 22 of the outer electrode 20, or 0.
It is placed at a position where it is pulled down by 0 to 0.5 mm. The exposed edge of the noble metal alloy 12 forms the ignition part in a state where the edge of the noble metal alloy 12 is slightly pulled down with respect to the outer electrode 20, so that the durability is excellent, and even when the air-fuel ratio is large, there are few ignition mistakes.

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 in which a center electrode is melt-bonded with a corrosion-resistant and spark-depleting metal member made of a precious metal alloy or the like.

[0002]

2. Description of the Related Art As a conventional spark plug 1 for an internal combustion engine, a spark gap G is formed between a side surface portion 11 of a center electrode 10 and an outer electrode 20 as shown in FIGS. There is a spark plug having precious metal alloys 12 and 21 as a metal member having excellent corrosion resistance and spark consumption resistance at each ignition portion of the side surface portion 11 of the electrode 10 and the tip portion of the outer electrode 20. Such a spark plug 1 has a center electrode 10
When the precious metal alloy 12 is provided on the center electrode base material 100
A groove 102 is formed in the vicinity of the tip portion 101 of the noble metal, and the noble metal ring 10 made of a noble metal such as platinum is formed in the groove 102.
After arranging 3, the beam B of a laser beam or the like is irradiated to the noble metal ring 103 and the center electrode base material 100, and the center electrode base material 100 and the noble metal ring 103 are melt-bonded to form the noble metal alloy 12, It is integrated with the center electrode 10. (See FIGS. 1A to 1C)
When the center electrode 10 is combined with the outer electrode 20 to form the spark gap G, in order to make the noble metal alloy 12 portion which is the ignition part of the center electrode 10 face the outer electrode 20 located on the side of the center electrode 10. As shown in FIGS. 7 to 9, the position of the tip surface 13 of the center electrode 10 is set to the outer electrode 2.
It is arranged so as to protrude by about 0.2 to 0.5 mm in the axial direction of the center electrode 10 with respect to the position 0 of the tip outer end surface 22.

[0003]

In recent years, in internal combustion engines, there is a tendency to make the amount of fuel to air thinner and increase the air-fuel ratio (A / F). Regarding the ignitability due to the difference in the shape of the plug, etc., as a result of experiments and studies by the inventors of the present application, in a spark plug in which the outer electrode is located on the side of the center electrode, the tip end surface position of the center electrode is the outer electrode. Ignition is at a position that is equivalent to or slightly lower than the outer end face position of the tip of the electrode, that is, the tip end face position of the center electrode is lowered by 0.0 to 0.5 mm with respect to the outer end face of the outer electrode tip. Found that it was good.

However, as described above, in the conventional spark plug having the noble metal alloy in the center electrode, the noble metal alloy is not located at the tip end surface of the center electrode, and the center electrode base material is exposed at the tip end surface position of the center electrode. Therefore, if the tip end surface position of the center electrode is arranged at the same position as the outer end surface position of the tip of the outer electrode or at a position slightly lowered, the wear of the center electrode base material becomes faster and the operation time elapses. The required voltage tends to be high. Further, as shown in FIG. 10, when the noble metal 103 is attempted to be melt-bonded to the tip surface portion of the center electrode 100, for example, the amount of heat generated by the beam irradiation LB is imbalanced, and the temperature on the tip side of the center electrode is significantly increased. There is a problem that an appropriate spark gap cannot be formed between the center electrode and the outer electrode because the diameter of the tip edge of the center electrode becomes small and rounds because the temperature rises and melts.

According to the present invention, even when the air-fuel ratio is large, misfiring is less likely to occur, sufficient ignitability is obtained, and
An object of the present invention is to provide a spark plug for an internal combustion engine having excellent durability and a method for manufacturing the spark plug.

[0006]

The present invention provides claims 1 and 4.
In the invention, the corrosion-resistant / spark-resistant metal member is melt-bonded around the vicinity of the tip of the center electrode base material, and the tip is removed by cutting, cutting or polishing to remove the corrosion / spark-resistant property. The technical means is to arrange the metal member at the tip edge of the ignition part of the center electrode. Further, in the inventions of claims 2 and 5, fusion welding of the corrosion-resistant and spark-resistant metal member to the center electrode base material is performed by beam welding. Also,
In the invention of claims 3 and 6, the position of the tip surface of the ignition portion of the center electrode formed as described above is arranged in the centrifugal direction of the center electrode and faces the center electrode to form a spark discharge gap. It is pulled down by 0.0 to 0.5 mm in the axial direction of the center electrode with respect to the outer end surface of the tip of the outer electrode.

[0007]

According to the first and fourth aspects of the present invention, a corrosion-resistant and spark-depleting metal member is melt-bonded around the vicinity of the tip of the center electrode base material. For this reason, corrosion resistance and
The heat applied mainly to the spark-resistant metal member is also radiated to some extent on the tip end side of the center electrode base material, so that the applied heat is not accumulated at the tip end part of the center electrode base material. Therefore, the amount of heat generated in the center electrode base material is less likely to be imbalanced during melting, and the temperature of the front end side of the center electrode base material becomes extremely high and melts to reduce the diameter of the front end edge of the center electrode base material. Therefore, the corrosion-resistant and spark-depleting metal members can be melt-bonded to the center electrode base material while maintaining proper dimensional accuracy.

Thereafter, the tip portion of the center electrode base material is removed by cutting, cutting or polishing to expose the portion where the corrosion-resistant and spark-depleting metal member is joined as the tip edge of the ignition portion of the center electrode. . As a result, the corrosion-resistant and spark-depleting metal member is exposed at the edge of the tip surface of the center electrode while maintaining the dimensional accuracy. Therefore, the spark gap can be formed with appropriate dimensional accuracy between the leading edge of the center electrode and the outer electrode.

According to the second and fifth aspects of the present invention, the fusion bonding of the corrosion-resistant and spark-resistant metal member to the center electrode base material is performed by beam welding. At this time, the irradiation of the beam is performed centering on the corrosion-resistant / spark-resistant metal member, but the heat given to the center electrode base material by the beam irradiation is also conducted to the tip side of the center electrode base material. Since it is dissipated by heat, it is evenly applied to the center electrode base material. Therefore, only the tip end side of the center electrode base material is not excessively heated, and only the tip end portion does not partially melt, so that proper dimensional accuracy can be secured.

According to the third and sixth aspects of the present invention, the position of the tip surface of the firing portion of the center electrode formed as described above is set to 0.0 to the axial direction of the center electrode with respect to the outer end surface of the tip of the outer electrode. 0.
Since it is lowered by 5 mm, in the internal combustion engine, even if the fuel is thin and the air-fuel ratio is large, the ignitability is unlikely to decrease.

[0011]

According to the first and fourth aspects of the present invention, after the corrosion-resistant and spark-consumable metal member is melt-bonded around the vicinity of the tip of the center electrode base material, the tip of the center electrode base material is melted and joined. By removing by cutting, cutting or polishing
Corrosion-resistant and spark-depleting metal members can be exposed at the edge of the center electrode tip while maintaining a certain degree of dimensional accuracy. The spark gap can be formed with high accuracy. As a result, since the corrosion-resistant / spark-wear-resistant metal member is arranged at the ignition part of the center electrode, the spark plug for an internal combustion engine having the center electrode with excellent spark-wear resistance can be obtained.

According to the second and fifth aspects of the invention, the corrosion resistance and
Beam welding is used to perform fusion bonding of the spark-resistant metal member to the base material of the center electrode, which facilitates processing and improves productivity.

According to the third and sixth aspects of the invention, the position of the tip of the ignition part of the center electrode formed as described above is set to 0.0 in the axial direction of the center electrode with respect to the outer end face of the tip of the outer electrode. ~
Since it is lowered by 0.5 mm, in the internal combustion engine, even if the fuel is thin and the air-fuel ratio is large, the ignitability is unlikely to decrease.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. First, the manufacturing process of the center electrode 10 will be described with reference to FIG. As shown in FIG. 1 (a), the center electrode 10 is mainly composed of nickel with copper having good heat conductivity enclosed therein.
i, Cr, Mn, Al, nickel alloy material containing 10% or less of total amount, Ni-Cr-F containing 10% or more of Cr
The center electrode base material 100 made of an e-alloy material (for example, Inconel 600) and having a cylindrical rod shape is formed on the tip portion 10 of the center electrode base material 100 by plastic working such as rolling or pressing.
A groove 102 having a trapezoidal cross section is formed around the outer periphery of the groove 1.
In addition, the center electrode base material 100 has a diameter of 1.5 to 2.5 mm corresponding to the applied spark plug, and the groove 102 has a trapezoidal cross-section of, for example, the bottom of the groove. Length 0.3mm, groove width 0.7mm, groove depth 0.1
It is 3 mm.

Next, as shown in FIG. 1B, a platinum wire (for example, a diameter of 0.3 mm) having a length substantially equal to the outer peripheral length of the groove bottom is formed in a ring shape in the groove 102 of the center electrode base material 100. The noble metal ring 103 is inserted into the center electrode base material 100, and the noble metal ring 103 is tightened on the center electrode base material 100. Here, since the groove 102 has a trapezoidal cross-sectional shape, when the noble metal ring 103 is tightened, the groove 102 can be easily positioned in the groove 102.

Next, the center electrode base material 100 is set to (5/6) π.
While rotating at rad / sec, a pulse B of a pulse YAG laser having a pulse width of 2 mS, an energy of 7 J, and 5 pps is applied from a direction substantially perpendicular to the outer surface of the center electrode base material 100 having a width of about 1 mm including the noble metal ring 103. The number 4
Irradiate 8 pulses. By the irradiation of the pulse B of the pulse YAG laser, the pulse YAG laser melts the noble metal ring 103 and the center electrode base material 100 made of a nickel alloy material as shown in FIG. 1C, so that platinum becomes a nickel alloy material. Dispersion, diffusion alloy layer and platinum component distribution are almost constant (99.5 to 20.0 wt% range)
Noble metal alloy 12 is formed.

Next, as shown in FIG. 1D, the tip 101 side of the center electrode base material 100 to the middle of the noble metal alloy 12 is removed by cutting, cutting or polishing, and the tip surface as the center electrode 10 is removed. 13 is formed so that the noble metal alloy 12 is located on the edge portion and the side surface portion 11 of the tip surface 13 of the center electrode 10. As a result, the tip edge 1 of the tip surface 13
4 is sharply formed by cutting, cutting or polishing.

FIG. 2 shows a bipolar spark plug 1 using the center electrode 10 manufactured by the above manufacturing process. In the two-pole spark plug 1 of FIG. 2, 2 is a cylindrical metal shell, 30 is an insulator with a shaft hole 31 that is fitted and fixed in the metal shell 2, and the center electrode 10 is an insulator 30.
Is fixed in the shaft hole 31 of the insulator 30 in a protruding state from the front end surface of the insulator.

The metal shell 2 is made of low carbon steel, and the outer electrode 20 is welded to the tip surface of the metal shell 2. Further, a screw 2a for mounting on a cylinder head of an internal combustion engine via a gasket is threaded on the outer periphery of the tip of the metal shell 2. The L-shaped outer electrode 20 is formed of a nickel alloy material (for example, Inconel 600 or the like) in which copper having good thermal conductivity is encapsulated, and the discharge surfaces are arranged to face each other with the side surface 11 of the center electrode 10 therebetween. A spark gap G for medium discharge is formed.

The insulator 30 is made of a ceramic mainly composed of alumina, and the seating surface is locked to the step portion of the metal shell 2 through a packing so that the hexagonal head (not shown) of the metal shell 2 is formed.
By caulking, it is fixed in the metal shell 2 so that the tip projects from the opening 2b.

A two-pole spark plug 1 having the above structure
In the above, the position of the tip surface 13 of the center electrode 10 and the position of the outer end surface 22 of the tip of the outer electrode 20 are almost the same position, or the distance between the position of the tip surface 13 and the position of the outer end surface 22 of the tip of the outer electrode 20. L is 0.0 to 0.0 in the axial direction of the center electrode 10.
It is arranged so as to be pulled down by about 0.5 mm. As a result of the research and experiment by the present inventor, as shown in FIG.
When the relationship with the position of the outer end surface 22 of the tip of is investigated, it is found that the ignitability does not easily decrease even when the fuel is thin with respect to the air, that is, even when the air-fuel ratio is large.
This is because the above-mentioned positional relationship conditions were obtained.

The test is 4 cycles, 2000c
Using a c, 6-cylinder engine, the number of occurrences of ignition failure in idling × 3 minutes was set to a spark gap of a 2-pole spark plug of 1.0 mm, and the L dimension was changed. That is, the condition of the above positional relationship is that the air-fuel ratio A / F
In FIG. 3, the frequency of the ignition mistakes is 15.0, 15.5, and 16.0, and the relatively low range is determined based on FIG. As a result, L dimension is 0.0 ~
A satisfactory ignitability can be obtained at 0.5 mm. Further, the preferable range of the L dimension is 0.0 to
A good ignitability can be achieved with 0.4 mm.

Regarding the bipolar spark plug 1 of this embodiment, the position of the tip surface 13 of the center electrode 10 is lowered by 0.3 mm with respect to the position of the outer end surface 22 of the tip of the outer electrode 20. , The size of the spark gap G indicating the consumption state of the center electrode 10 with respect to the durability time,
Similarly, regarding the size of the spark gap in the conventional spark plug when the conventional center electrode in which the tip 101 of the center electrode base material 100 is not removed is similarly arranged,
Cycle, 2000cc, 50 with 6 cylinder engine
The results of testing under the conditions of 00 rpm × 4/4 are shown in FIG. As is clear here, in the spark plug of the present invention, the noble metal alloy 12 is disposed up to the tip surface of the ignition part of the center electrode 10, so that the degree of wear is small, but at the tip 101 of the center electrode base material 100. In the case of the conventional spark plug in which the noble metal alloy 12 is not located, the center electrode base material 10
Since 0 is consumed, the spark gap becomes large immediately and the degree of consumption is large. This is because the required voltage (discharge voltage) required for spark discharge increases according to the size of the spark gap, resulting in severe wear.

FIG. 5 shows changes in the required voltage (measured at an air pressure of a spark tester of 4 kgf / cm ² ) with respect to the endurance time in the present invention and the conventional spark plug in which the size of the spark gap G is shown in FIG. 4, respectively. Shown respectively.
As described above, in this embodiment, the tip surface 1 of the center electrode 10 is
Since the noble metal alloy 12 is arranged in 3 and the position of the tip surface 13 is lower than the position of the tip 22 of the outer electrode 20, the ignitability does not decrease, excellent ignitability is obtained, and the wear is reduced. Is small, the size of the spark gap G is hard to increase, and the required voltage does not increase. Therefore, stable ignition performance can be secured over a long period of time.

FIG. 6 shows a semi-creeping spark plug 1a as another embodiment of the present invention. 2 pole spark plug 1
The difference is that the tip surface 32 of the insulator 30 is located on the same side surface as the inner edge of the discharge surface or slightly on the combustion chamber side, and the creeping gap and the outer electrode that discharge along the tip surface 32 It is a semi-creeping spark plug in which an air gap is combined with the tip of 20, and the same effect can be obtained by adopting the configuration of the present invention. In the above embodiment, 2
Although the polar spark plug 1 and the semi-creeping spark plug 1a are shown, a multi-polar spark plug such as 3 poles or a creeping spark plug having no air gap may be used. Further, the beam for fusion bonding is not limited to the YAG laser beam,
Other electron beams may be used.

[Brief description of drawings]

FIG. 1 is a process drawing showing a manufacturing process of a center electrode in a spark plug of the present invention.

FIG. 2 is a partially enlarged view of a two-pole spark plug showing an embodiment of the present invention.

FIG. 3 is a measurement diagram showing the relationship between the position of the tip surface of the center electrode and the position of the tip of the outer electrode with respect to the frequency of ignition mistakes in the internal combustion engine, using the air-fuel ratio as a parameter.

FIG. 4 is a durability performance diagram showing the size of the spark gap with respect to the durability time in the spark plug of the present invention, together with the case of a conventional spark plug in which the tip of the center electrode base material is not removed.

FIG. 5 is a required voltage characteristic diagram showing changes in required voltage with respect to durability time in the spark plug of the present invention, together with the case of a conventional spark plug in which the tip of the center electrode base material is not removed.

FIG. 6 is a partially enlarged view of the semi-creeping spark plug showing the embodiment of the present invention.

FIG. 7 is a partial perspective view showing an example of a conventional spark plug.

FIG. 8 is a partial perspective view showing another example of the conventional spark plug.

FIG. 9 is a partial perspective view showing still another example of the conventional spark plug.

FIG. 10 is a cross-sectional view of essential parts showing an embodiment in which the tip edge of the center electrode is rounded.

[Explanation of symbols]

 1 2 pole spark plug (spark plug for internal combustion engine) 1 center electrode base material 10 center electrode 12 noble metal alloy (corrosion-resistant / spark-depleting metal member) 13 tip surface 14 tip edge 20 outer electrode 22 outer end surface

Claims (6)

[Claims] 1. A corrosion-resistant / spark-consumable metal member is melt-bonded around the vicinity of the tip of the center electrode base material, and the tip is removed by cutting, cutting or polishing to prevent corrosion-resistance.
A method for manufacturing a spark plug for an internal combustion engine, comprising disposing a spark-consumable metal member on a tip edge of an ignition part of a center electrode. 2. The method for manufacturing a spark plug for an internal combustion engine according to claim 1, wherein the welding of the corrosion-resistant and spark-depleting metal member to the center electrode base material is performed by beam welding. 3. The position of the tip end surface of the ignition part of the center electrode with respect to the outer end surface of the tip end of the outer electrode arranged in the centrifugal direction of the center electrode and facing the center electrode to form a spark discharge gap. , 0.0 to 0.5 mm in the axial direction of the center electrode
3. The method for producing a spark plug for an internal combustion engine according to claim 1, wherein the spark plug is lowered by only the amount. 4. A corrosion resistant / spark consumable metal member is melt-bonded around the vicinity of the tip of the center electrode base material, and the tip is removed by cutting, cutting or polishing to prevent corrosion.
A spark plug for an internal combustion engine, characterized in that a spark-consumable metal member is arranged at the tip edge of the ignition part of the center electrode. 5. The spark plug for an internal combustion engine according to claim 4, wherein the fusion-bonding of the corrosion-resistant and spark-depleting metal member to the center electrode base material is performed by beam welding. 6. The position of the tip end surface of the ignition part of the center electrode is positioned with respect to the outer end surface of the tip end of the outer electrode which is arranged in the centrifugal direction of the center electrode and which faces the center electrode to form a spark discharge gap. , 0.0 to 0.5 mm in the axial direction of the center electrode
6. The spark plug for an internal combustion engine according to claim 4 or 5, wherein the spark plug is lowered only by a certain amount.