JP2002260815A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug with narrow gap distance used for an engine with high discharge voltage which can further reduce the discharge voltage. SOLUTION: For the spark plug for an internal combustion engine, when g is regarded as a gap distance of a spark discharge gap G, and L as a minimum distance between the outer periphery of an ignition surface (center electrode side tip ignition surface 31A), facing to the spark discharge gap G of a center electrode side noble metal chip 31A, and the outer periphery of an ignition surface (ground electrode side tip ignition surface 32A) of the ground electrode side noble metal chip facing the center electrode side chip ignition surface 31A, it is set so as to fulfill the relation of; g<=0.6 mm, and L/g<=1.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a spark plug for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, there has been provided a spark plug aimed at reducing a discharge voltage by narrowing a gap interval. For example, in the case of a gas engine plug, the discharge voltage increases due to the characteristics of the fuel. On the other hand, by reducing the gap interval, the discharge voltage can be reduced to some extent while satisfying the required voltage.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spark plug having a narrow gap used for an engine having a high discharge voltage and capable of further reducing the discharge voltage. It is in.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a center electrode and a ground electrode opposed to each other with a spark discharge gap interposed therebetween. A noble metal tip mainly composed of a noble metal is fixed to a position facing the discharge gap, and the spark gap is formed between opposing ignition surfaces of the noble metal tip provided on the center electrode and the ground electrode. A plug, wherein an interval between the spark discharge gaps is g, and an outer peripheral edge of a spark surface (center electrode side chip firing surface) of the noble metal tip on the center electrode side facing the spark gap; When the shortest distance between the ignition surface and the outer peripheral edge of the ignition surface of the noble metal tip on the ground electrode side (the ignition electrode on the ground electrode side) is L, g
A spark plug characterized by satisfying both the relations of ≦ 0.6 mm and L / g ≦ 1.1.

In a plug using a noble metal tip for the center electrode and the ground electrode, the electric field concentrates on the outer periphery (edge) of the tip, so that the spark is more between the outer periphery than the shortest ignition surface, that is, between the edges. It becomes easier to fly. However, if the shortest distance of the outer peripheral edge is too large compared to the gap interval, a fire occurs between the ignition surfaces or between the edge and the ignition surface, and it becomes impossible to achieve a reduction in the discharge voltage based on the fire between the edges. L / g ≦ 1.
If it is set to 1, sparks are stably fired between the edges, and it is possible to stably reduce the discharge voltage. In a plug having a small gap interval that satisfies g ≦ 0.6 mm, both a reduction in the discharge voltage based on the reduction in the gap interval and a reduction in the discharge voltage caused by the discharge between the edges can be expected, which is more effective. It is.

In a spark plug having g exceeding 0.6 mm, the gap interval is wide, and discharge between edges is likely to occur regardless of the relationship between the gap interval and the distance between edges. Although the effect is hardly obtained, the discharge voltage is more greatly affected by L / g in the spark plug of g ≦ 0.6 mm.

Further, the ground electrode-side chip firing surface is formed on the tip end surface of a projection projecting from the electrode base material surface of the ground electrode, and the projection height of the projection is 0.1 mm to 0.5 mm.
mm. If the protruding height of the protruding portion is less than 0.1 mm, that is, if the distance between the ignition surface and the surface of the electrode base material is less than 0.1 mm, welding dripping when the noble metal tip is fixed to the electrode base material, etc. This may make it difficult for the outer periphery of the chip firing surface to function as an edge.
On the other hand, if it exceeds 0.5 mm, the electric field is dispersed, so that it is impossible to achieve a reduction in the discharge voltage.

In addition, if the center electrode side noble metal tip is enlarged so that the outer diameter of the center electrode side tip ignition surface becomes 1.0 mm or more, in addition to the above-mentioned size range, it is possible to improve the durability of the chip, The voltage can be satisfied, resulting in a synergistic effect.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 ((a) is a front view, (b) is a half sectional view) shows a spark plug as an example of the present invention. This spark plug 100 is used, for example, for igniting a cogeneration gas engine, and has a cylindrical metal shell 1, an insulator 2 fitted inside the metal shell 1 so that a front end portion 21 protrudes, and formed at a front end. Noble metal firing part 31 (hereinafter, the center electrode side noble metal tip 3
1 or simply a chip 31), one end of which is coupled to the center electrode 3 provided inside the insulator 2 and the metallic shell 1 by welding or the like while the other end is bent back to the side. In addition, a ground electrode 4 and the like are disposed such that the side faces the front end of the center electrode 3. The ground electrode 4 has a noble metal firing portion 32 (hereinafter referred to as a ground electrode-side noble metal tip 32,
Alternatively, the gap between the chip 31 and the opposing chip 32 is defined as a spark discharge gap G.

In the spark plug 100, the interval g of the spark discharge gap G (hereinafter, also referred to as gap interval g) is 0.1.
It is 2 mm to 0.6 mm. The total plug length L0 is 6
0-100 mm (for example, 74.5 mm), screw reach L
1 is 12.5 to 26.5 mm (for example, 19 mm), and the designation of the mounting screw portion 7 is any of M10, M12, M14, and M18 (for example, M14).

The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a hole 6 for fitting the center electrode 3 along its own axial direction. . The metal shell 1 is formed of a metal such as low-carbon steel in a cylindrical shape, constitutes a housing of the spark plug 100, and has an outer peripheral surface on which the spark plug 100 is attached to an engine block (not shown). A screw portion 7 is formed.

In the present embodiment, at least the surface layer portion of the center electrode 3 and the ground electrode 4 where the chip is fixed is formed.
It is made of a heat-resistant alloy containing i or Fe as a main component. For example, as a heat-resistant alloy containing Ni as a main component, INCO
NEL 600 or INCONEL601 (both trade names) can be used.

As shown in FIG. 2, at least one of the center electrode side noble metal tip 31 and the opposing ground electrode side noble metal tip 32, and preferably both of them can be mainly composed of Ir. The materials of the noble metals constituting the chips 31 and 32 include the following. 1: as a main component _Ir-Y 2 _{O 3} alloy Ir, a _Y 2 _{O 3} for the purpose of suppressing spark consumption of Ir may be contained in a range of 0.1 to 15 mass%. If the content of Y ₂ O ₃ is less than 0.1% by mass, the effect of suppressing the spark consumption of Ir by Y ₂ O ₃ cannot be sufficiently obtained. On the other hand, when the content of Y ₂ O ₃ exceeds 15% by mass, the thermal shock resistance of the chip decreases, and for example, when the chip is fixed to the electrode by welding or the like, problems such as cracks may occur.

2: Ir-Rh alloy Ir can be contained as a main component in the range of 1 to 50% by mass of Rh. The use of the alloy allows the Ir
Consumption of the ignition portion due to oxidation and volatilization of the components is more effectively suppressed, and a spark plug having more excellent durability is realized. The Rh content in the above alloy was 1% by mass.
If the amount is less than the above, the effect of suppressing the oxidation and volatilization of Ir by the addition of Rh becomes insufficient, and the ignition portion is easily consumed, so that the durability of the plug decreases. On the other hand, when the Rh content is 50% by mass or more, the melting point of the alloy decreases, and the durability of the plug similarly decreases.

3: Ir-Pt alloy Ir or Pt is a main component, and Ir can be contained in an amount of 2 to 98% by mass. This alloy has the advantage that the heat resistance of the ignition portion is improved by the addition of Ir, and the spark wear resistance is particularly good. However, when the Ir content is less than 2% by mass, the above effects are insufficient. When the Ir content is more than 98% by mass, the oxidation and volatilization of Ir at a high temperature tends to proceed, and the oxidation resistance of the ignition portion becomes insufficient. There is.

4: Ir-Ni alloy The main component is Ir, and Ni can be contained in an amount of 2 to 30% by mass. This alloy has an advantage that the heat resistance of the ignition portion is improved by using Ir as a main component, and the spark erosion resistance is good. In addition, the inclusion of Ni has the advantage of improving the peel resistance of the welded portion. However, when the Ni content is 2
If the content is less than 30% by mass, the peeling resistance of the welded portion may be insufficient. If the Ni content is 30% by mass or more, the melting point of the alloy may be reduced and the spark wear resistance may be insufficient.

It should be noted that a material other than one mainly composed of Ir may be used. For example, a Pt-Ni alloy, that is, Pt as a main component, and 2 to 40% by mass of Ni can be contained.
This alloy has advantages such as improved peel resistance of the welded portion. However, if the Ni content is less than 2% by mass, the above effect is insufficient. If the Ni content is more than 40% by mass, the melting point of the alloy is reduced, and the spark erosion resistance of the ignition portion becomes insufficient.

Then, the interval of the spark discharge gap G is g, and the ignition surface of the center electrode side noble metal tip 31 facing the spark discharge gap G (center electrode side chip ignition surface 31A).
When the shortest distance between the outer peripheral edge of the outer peripheral edge of the ground electrode side noble metal tip 32 and the outer peripheral edge of the ground electrode side noble metal tip 32 (ground electrode side chip firing surface 32A) facing the center electrode side chip firing surface 31A is L, g ≦ 0. .6 mm and L / g ≦ 1.1. g is 0.2m as above
m, and L / g can be 1.0 or more. If g is less than 0.2 mm, the gap interval is too small to make working difficult, and the ignitability may decrease.

FIG. 4 illustrates the definition of the outer peripheral edge position (edge position) in some examples of the noble metal tip 32 on the ground electrode side. As shown in FIG. 4A, the ground electrode-side noble metal tip 32 formed so that the cross-sectional profile in the thickness direction is square, as shown in FIG. The intersection of the tip firing surface 32A and the outline is defined as an edge position. In the present embodiment illustrates the edge position of the ground electrode tip firing surface (outer periphery position) and P _4. Further, in the cross section cut in the thickness direction, the edge position can be defined as follows in the case where the side outline 32 has a curved portion as shown in FIGS. 4B to 4D. . As shown in FIG. 4 (b), when the side surface outline 32B has a curved shape and the connection between the side surface outline 32B and the outline of the ground electrode side chip firing surface 32A is discontinuous, the curved surface shape is used. 4 and the boundary between the ground electrode side tip firing surface 32A and
In the example of (b) the boundary between the curved outline 32B and outline of the ground electrode tip firing surface 32A and the edge position P _4.

As shown in FIG. 4C, when the side outline 32B is a straight line and a radius is formed at a connection portion with the ground electrode side chip firing surface 32A, the side outline 32B Each extension line with the outline of the ground electrode side tip firing surface 32A (extension lines X and Y: FIG. 4 (c))
Considered an intersection on the edge position P _4. Further, the side outline 32B is a curved line, and a connection portion with the outline of the ground electrode side chip firing surface 32A is continuously formed.
In the case of FIG. 4D, the edge position P is determined as follows.
₄ is defined. That is, defining the electrode base metal surface 4A and parallel imaginary plane at 90% of the height H ₉₀ to the height H of the ground electrode tip firing surface 32A, and the virtual surface and the side surface 32B of the ground electrode noble metal tip 32 Is regarded as an outer peripheral edge. In the cross section as shown in FIG.
The intersection of the imaginary line L ₉₀ and the side outline 32B is an edge position P ₄ when minus electrode base material surface 4A parallel imaginary line L _{90 (line} conceptually showing a virtual surface).

Here, the definition of the edge position of the ground electrode-side chip firing surface 32A has been described, but the edge position of the center electrode-side chip firing surface 31A is also specified in a similar manner. The same applies when the center electrode side noble metal tip 31 has a side surface and a firing surface shape as shown in FIGS. 4A to 4C, and the side surface and the firing surface are continuous as shown in FIG. In the case of a shape following the following, it is defined as follows. That is, a height based on the rear edge of the tip 31 in the axial direction of the center electrode-side noble metal tip 31 (the axial direction of the spark plug) (the side facing the spark gap in the axial direction is the front side). An imaginary plane parallel to the axis direction at a height H ′ ₉₀ of 90% from the same base point of H ′ is defined, and the intersection of the imaginary plane and the side surface of the center electrode side noble metal tip 31 is defined as the outer peripheral edge. . The rear edge of the center electrode-side noble metal tip 31 here means the boundary between the electrode base material and the chip 31. If a molten portion is interposed between them, the boundary between the molten portion and the chip 31 is defined. means.

As shown in FIG. 3, the ground electrode-side chip firing surface 32A is formed on the tip end surface of the ground electrode-side noble metal tip 32 projecting from the electrode base material surface 4A of the ground electrode 4. Projection height H of electrode-side noble metal tip 32
(Hereinafter, also referred to as protrusion dimension H)
It is desirable to adjust to a range of 0.5 mm. By adjusting to such a range, the discharge voltage can be further reduced. In addition, as shown in FIGS. 3A and 3B, a circular shape in which the center electrode side noble metal tip 31 and the ground electrode side noble metal tip 32 are formed concentrically with each other is calculated by the following equation. May be regarded as the distance L between edges. When the ground electrode-side noble metal tip 32 is formed in a circular shape as shown in FIG. 3, the distance between the edges is minimized over the entire outer peripheral edge of the tip 32, so that sparks are evenly distributed and uneven wear can be suppressed.

[0023]

(Equation 1)

By using such a formula, the distance L between edges can be easily known based on the diameter a of the noble metal tip 31 on the center electrode side and the diameter b of the noble metal tip 32 on the ground electrode. Contributes to the efficient setting of In the present embodiment, the diameter of the ground electrode-side noble metal tip 32 means the diameter of the outer peripheral edge of the ground electrode-side tip firing surface 32A defined by the above method. Similarly, the diameter of the center electrode-side noble metal tip 31 means the diameter of the outer peripheral edge of the center electrode-side tip firing surface 31A.

Hereinafter, a method for manufacturing the spark plug of the present invention will be described.
Examples of the method will be described. As shown in FIG.
Alloy constituting the tip 31 (FIG. 1) on the tip surface of the electrode 3
The disc-shaped chips 31 ′ made of the composition are overlapped and further
Laser welding along the outer edge of the joint surface
Welded portion (hereinafter, also simply referred to as welded portion) W ₁Form
The chip 31 is formed by fixing the
You. The opposing chip 32 (FIG. 1)
Is placed on the ground electrode 4 at a position corresponding to
And welded along the outer edge of the joint surface in the same manner.
₂Is formed and fixed.

When the tip is made of an Ir-based metal, it has a high melting point, so that the above-mentioned joining by laser welding is desirable. Can also be used. In addition,
In the present invention, the outer diameter a of the center electrode side tip firing surface 31A can be 1.0 mm or more. In this case, the durability of the chip can be improved. When the outer diameter a is 2.0 mm or less, the welding state with the electrode base material in laser welding as described above becomes good. If a exceeds 2.0 mm, there is a possibility that the melted portion due to welding does not penetrate into the inside and peeling occurs.

These chips 31 ′ and 32 ′ (hereinafter, sometimes referred to as “150” when collectively referring to the chips 31 and 32) mix and dissolve each alloy component so as to have a predetermined composition. The molten material obtained by this is processed into a plate by, for example, cold rolling, and the plate is punched into a predetermined chip shape by hot punching, or an alloy is formed by hot rolling, hot forging, or hot rolling. After processing into a linear or rod-shaped material by drawing, it can be used by cutting it into a predetermined length in the length direction. Further, those formed into a sphere by an atomizing method or the like can also be used.

FIG. 5 shows some examples of the shape of the ground electrode noble metal side tip 32. Regarding the surface shape of the ground electrode side tip firing surface 32A, for example, FIG.
It can be a polygonal shape such as a quadrangle as shown in (a) and a hexagon as shown in (b). For example, assuming a square,
Since it can be manufactured only by cutting the precious metal ribbon formed in the shape of an elongated plate, the processing becomes easy, and since it can be manufactured without punching or the like, loss of material is small.

[0029]

[Experimental Examples] In order to confirm the effects of the present invention, the following experiments were conducted. Experiment 1: Attach a spark plug to the pressurized chamber,
The pressure in the chamber was adjusted to 0.8 MPa, and a discharge voltage measurement test was performed on a desk. The maximum value of the discharge voltage of n = 5 × 1000 shots was measured. Table 1 shows the results. In Tables 1 and 2, the units of the center electrode tip diameter, the ground electrode tip diameter, the gap interval g, and the distance L between edges are all expressed in (mm). In the subsequent experiments, the center electrode-side noble metal tip and the ground electrode-side noble metal tip have circular shapes as shown in FIG.

[0030]

[Table 1]

In samples 1 to 3, L / g was reduced by setting the tip diameter b of the ground electrode to 1.6 mm, the gap interval g to 0.4 mm, and changing the tip diameter of the center electrode. Set to stage. Sample 1
And 2 and 3, when the diameter of the center electrode is set to be larger in samples 2 and 3, L
It was confirmed that the discharge voltage can be reduced by reducing / g. In Samples 7 to 10, the center electrode tip diameter a was constant at 1.0 mm, the gap interval g was constant at 0.4 mm, and the ground electrode tip diameter b was set at a plurality of values to obtain a plurality of samples having different L / g. An experiment was performed.

Also in these cases, it was confirmed that the smaller the value of L / g, the lower the discharge voltage. Further, in samples 4 to 6, when the diameter a of the center electrode and the diameter b of the ground electrode were the same, ie, L /
For g = 1, a plurality of samples with different gap intervals were prepared and the discharge voltage was examined. Sample 2
Is also L / g = 1. In these cases, it was confirmed that the discharge voltage decreased as the gap interval g decreased.

In Table 1, comparing Samples 6 and 7 in particular, Sample 7 has a smaller center electrode and a smaller gap interval g than Sample 6, so that Sample 7 conventionally has a lower discharge voltage. It is supposed that the discharge voltage can be reduced even if the diameter of the center electrode is increased and the gap interval is increased by setting L / g low.

Samples 11 to 14 show examples where the gap interval is 0.8 mm. Comparing Samples 11 and 12, it can be seen that reducing L / g slightly reduces the discharge voltage, and comparing Samples 13 and 14 shows that the reduction in discharge voltage is not achieved even if L / g is reduced. That is, it was found that when the gap interval exceeds 0.6, it is difficult to obtain the effect of reducing the discharge voltage even if L / g is adjusted. In other words, L
It was confirmed that the discharge voltage reduction effect due to / g was a unique effect at a gap interval of 0.6 mm or less.

Experiment 2: A spark plug was attached to a three-cylinder gas engine, and city gas 13A was used as a fuel. The maximum discharge voltage value of 1000 shots data at 1000 rpm, 100% load and 10 minutes after the start was measured with an actual machine. . Table 2 shows the results.

[0036]

[Table 2]

In Samples 15 to 17, three types of plugs having different grounding electrodes and gaps and having different L / g in which the tip diameter of the center electrode was adjusted were prepared. The tip diameter and the gap interval were kept constant, and the tip diameter of the ground electrode was adjusted to prepare three types of plugs having different L / g. As in Samples 16, 17 and 20, L / g ≦ 1.
The discharge voltage is set to 20 kV for any of those set as 1.
, And it was confirmed that there was an effect of reducing the discharge voltage.

Experiment 3: Next, circular tips were used for both the center electrode and the ground electrode, and the tip diameter of the center electrode was set to 1.2.
mm, the tip diameter of the ground electrode is 1.6 mm, and the gap interval g is 0.5 mm, a plurality of spark plugs having different output dimensions within the range of 0.05 mm to 0.6 mm are provided for the ground electrode. Then, the maximum value of the discharge voltage when each of the dimensions was set was measured. Table 3 shows the experimental results.

[0039]

[Table 3]

According to the experimental results, it is confirmed that the discharge voltage increases when the protrusion dimension is less than 0.1 mm and exceeds 0.5 mm, and it is useful to adjust the discharge voltage in the range of 0.1 mm to 0.5 mm. It turned out to be.

[Brief description of the drawings]

FIG. 1 is a front view showing a spark plug according to an embodiment of the present invention, and a half sectional view thereof.

FIG. 2 is an enlarged sectional view showing a main part thereof.

FIG. 3 is a side view and a plan view showing an example of a noble metal tip shape.

FIG. 4 is an explanatory diagram showing a method for defining an edge position.

FIG. 5 is a view showing another example of a noble metal tip shape.

FIG. 6 is an explanatory view showing one example of a method for manufacturing a spark plug of the present invention.

[Explanation of symbols]

 Reference Signs List 3 center electrode 4 ground electrode 31 center electrode side noble metal tip 31A center electrode side chip firing surface 32 ground electrode side noble metal tip 32A ground electrode side chip firing surface 100 spark plug G spark discharge gap

Claims (4)

[Claims] A center electrode and a ground electrode opposed to each other with a spark discharge gap interposed therebetween, and a noble metal tip mainly composed of a noble metal is fixed to a position of each of the electrodes facing the spark discharge gap; A spark plug in which the spark gap is formed between opposing ignition surfaces of a noble metal tip provided on the center electrode and the ground electrode, wherein a distance between the spark discharge gaps is g, and The outer peripheral edge of the ignition surface facing the spark gap of the noble metal tip (hereinafter, also referred to as “center electrode side chip ignition surface”), and the ignition surface of the ground electrode side noble metal tip facing the center electrode side chip ignition surface (hereinafter, When the shortest distance from the outer peripheral edge of the “ground electrode side chip firing surface” is L, both the relations of g ≦ 0.6 mm and L / g ≦ 1.1 are satisfied. Spark plug, characterized in that. 2. The ground electrode-side chip firing surface is formed on the tip end surface of the ground electrode-side noble metal tip projecting from the electrode base material surface of the ground electrode, and the ground electrode-side noble metal tip protrudes. The spark plug according to claim 1, wherein the height is adjusted in a range of 0.1 mm to 0.5 mm. 3. The spark plug according to claim 1, wherein at least one of the noble metal tip on the center electrode side and the noble metal tip on the ground electrode side is mainly composed of Ir. 4. The spark plug according to claim 1, wherein an outer diameter of the center electrode side tip firing surface is 1.0 mm or more.