JPH11185928A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain dimensional change in a sectional area of a grounding electrode due to thermal stress in the case where a three-layer grounding electrode structure is provided, and prevent discharge gap change. SOLUTION: A grounding electrode 4 is covered with a first metal layer 41 that is a core material, a second metal layer 42, and a third metal layer in this order and is constituted, and a thermal expansion coefficient of the second metal layer 42 is greater than those of the first and third metal layers 41 and 43. A relationship between thickness T1 of the third metal layer 43 in width W direction of the grounding electrode 4 and thickness T2 of the second metal layer 42, and a relationship between thickness T3 of the third metal layer 43 in thickness H direction of the grounding electrode 4 and thickness T4 of the second metal layer are set to be T1>=T2 and T3>=T4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug used for an internal combustion engine or the like.

[0002]

2. Description of the Related Art As this kind of spark plug, one disclosed in Japanese Patent Application Laid-Open No. 4-337271 has been proposed. This is a so-called ground electrode having a three-layer structure in order to keep a discharge gap (spark discharge interval, for example, about 1 mm) between the ground electrode (outer electrode) and the center electrode at an appropriate value under use conditions. This is a spark plug having a three-layer ground electrode structure.

That is, a core material such as pure nickel is coated with copper or the like having excellent thermal conductivity, and the area around the coated copper or the like is subjected to a thermal expansion coefficient (about the same as that of the core material pure nickel or the like). (Coefficient of linear expansion) and is coated with a nickel alloy or the like which is excellent in heat resistance and corrosion resistance. When the ground electrode has such a three-layer structure, the nickel alloy in the outermost layer is excellent in heat resistance and corrosion resistance, and the second layer of copper is excellent in heat removal, thereby suppressing a change in the discharge gap. Can be.

[0004]

However, as a result of the present inventor's study on actually using the spark plug having the above-described structure in an internal combustion engine, for example, a sudden temperature change corresponding to a high or low load of the internal combustion engine has been found. It has been found that when (cold thermal shock) occurs, the thermal stress at this time causes a plastic deformation of the ground electrode, changes the discharge gap, and adversely affects the plug characteristics.

[0005] That is, even in the three-layer ground electrode structure, the copper of the second layer has a coefficient of thermal expansion that is larger than that of the innermost layer core material and the outermost layer nickel alloy (such as Inconel 600 (trade name)). Therefore, when thermal stress due to the thermal shock or the like occurs during use, the copper tends to spread the nickel alloy. Depending on the dimensional relationship between the nickel alloy and copper, the thermal stress due to copper exceeds the strength of the nickel alloy, causing a dimensional change in the cross section of the ground electrode, causing a change in the discharge gap.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide a spark plug having a three-layer ground electrode structure, in which a dimensional change of a ground electrode cross section due to thermal stress is suppressed to prevent a discharge gap change.

[0007]

In order to achieve the above object, the present inventor focused on the dimensional relationship between the layer thicknesses of the three layers of the ground electrode cross section, and conducted a thermal shock (cooling endurance) test. As the nickel alloy in the outermost layer is thinner,
It was found that the thicker the copper layer, the greater the dimensional change in the cross section of the ground electrode. Then, it was thought that if the thicknesses of the two layers were in a predetermined relationship on the thickness side and the width side of the ground electrode, a change in the cross-sectional dimension could be suppressed.

[0008] The first aspect of the present invention is based on the above findings, wherein the first metal layer (41) as the core material is sequentially formed with the second metal layer (42) and the third metal layer. A ground electrode (4) covered with (43) and having a larger coefficient of thermal expansion of the second metal layer (42) than the first and third metal layers (41, 43); In the spark plug having the structure, the ground electrode (4) has a thickness H and a width W, and the third metal layer (43) in the width W direction.
And the thickness of the second metal layer (42) are T1 and T2, respectively.
2. When the thicknesses of the third metal layer (43) and the second metal layer (42) in the thickness H direction are T3 and T4, respectively, these thicknesses T1, T2, T3, and T4 are ,
It is characterized by the following relationship, T1 ≧ T2, and T3 ≧ T4.

In the present invention, since the thicknesses T1 to T4 of the second and third metal layers (42, 43) have the above-mentioned relationship, even if thermal stress occurs, the cross section of the ground electrode (4) can be reduced. Dimensional change can be suppressed. Therefore, it is possible to provide a spark plug in which a change in discharge gap is prevented in a use environment such as a thermal shock. Furthermore, the thickness H and the width W of the ground electrode (4) can be in the relationship described in claim 2, and the respective metal layers (41-43) are made of the respective materials described in claim 3. Can be used.

[0010] The reference numerals in parentheses of the above means indicate the correspondence with the specific means described in the embodiment described later.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention. This embodiment is used, for example, as an ignition plug of an internal combustion engine. FIG. 1 is a half sectional view showing the entire configuration of the spark plug of the present embodiment. The spark plug has a cylindrical mounting bracket 1, and the mounting bracket 1 includes a mounting screw portion 1a for fixing to a not-shown engine block. An insulator 2 made of alumina ceramic (Al ₂ O ₃ ) or the like is fixed inside the mounting bracket 1, and a center electrode 3 is provided in a shaft hole 2 a of the insulator 2.
Has been fixed. The tip 2 b of the insulator 2 is provided so as to be exposed from the mounting bracket 1.

The center electrode 3 is a cylindrical body whose inner material is made of a metal material having excellent thermal conductivity such as Cu, and whose outer material is made of a metal material having excellent heat resistance and corrosion resistance such as a Ni-based alloy.
As shown in the figure, the tip 3a is the tip 2b of the insulator 2.
It is provided so that it is exposed from. The ground electrode 4 is fixed to one end of the mounting bracket 1 by welding, is bent substantially L-shaped on the way, and is separated from the distal end portion 3a of the center electrode 3 and the discharge gap 6 at the opposite portion 4a opposite to the welded portion. Are facing each other. The details such as the internal structure of the ground electrode 4 will be described later.

A noble metal tip 51 made of, for example, an Ir alloy material is fixed to the tip 3a of the center electrode 3 by welding or the like, while a noble metal tip made of, for example, an Ir alloy material is attached to the facing part 4a of the ground electrode 4. 52 is fixed by resistance welding. Here, the discharge gap 6 is a gap between the chips 51 and 52, and is, for example, about 1 mm.

Hereinafter, the ground electrode 4 which is a feature of the present invention will be described in more detail. FIG. 2 shows the ground electrode 4 in FIG.
5A is an enlarged view of FIG. 5A, showing a bent shape of the ground electrode 4, and FIG. 5B is a view of FIG. In FIG. 3, (a) corresponds to B in FIG. 2 (b).
FIG. 2B is a cross-sectional view, and FIG. 2B is a CC cross-sectional view of FIG. 2 and 3, the noble metal tip 52
Is omitted.

The ground electrode 4 is, as shown in FIG.
A column having an overall length L1 (for example, 10 mm) and a flat cross section (W is, for example, 2.8 mm, H is, for example, 1.6 mm) is formed into a substantially L-shaped shape. The thickness H and the width W of the cross section of the ground electrode 4 refer to the dimensions of the portion shown in FIG. 2B, and this is well known. Also,
The relationship between the two dimensions is 0.5 ≦ H ≦ 2 and H ≦ W ≦ 3H, which are practical ranges for the ground electrode of the plug. Hereinafter, in the dimensional relationship, the direction of the width W of the ground electrode 4 is referred to as the width direction, and the direction of the thickness H is referred to as the thickness direction.

Then, as shown in FIG. 3, a first metal layer (core material) 41, which is a bar having a flat cross section, disposed at the center of the ground electrode 4, and a cross section covering the first metal layer 41. A flat pipe-shaped second metal layer 42 and a third flat pipe-shaped third metal layer 42 covering the second metal layer 42 as the outermost layer.
And a three-layer structure with the metal layer 43 of FIG. Here, the first metal layer 41 is made of a metal (pure nickel in the present embodiment) having excellent heat resistance and relatively excellent thermal conductivity. Pure nickel (Ni) has a coefficient of thermal expansion (linear expansion coefficient) of about 1.33 (10 ⁻⁵ / deg) and a thermal conductivity of about 68 (k).
cal / m · h · deg).

The second metal layer 42 has a thickness T2 in the width direction and a thickness T4 in the thickness direction shown in FIG.
It is 2 mm to 0.4 mm, and is made of a metal having excellent thermal conductivity (in the present embodiment, copper). Note that copper (Cu) has a thermal expansion coefficient of about 1.7 (10 ⁻⁵ / deg) and a thermal conductivity of about 340 (kcal / m · h · deg). The third metal layer 43 has a thickness T1 in the width direction and a thickness T3 in the thickness direction shown in FIG. 3B of, for example, about 0.2 mm to 0.4 mm, and is excellent in heat resistance and corrosion resistance. Metal, for example, N
It is made of a nickel-based alloy containing nickel as a main component (Inconel 600 in this embodiment), such as an i-Mn-Si alloy or Inconel 600 (trade name). Inconel 60
0 has a coefficient of thermal expansion of about 1.3 (10 ^-5 / deg) and a thermal conductivity of about 25 (kcal / m · h · deg).

Here, the dimensional relationship between the thicknesses T1 to T4 depends on the use environment (for example, room temperature and about 950
In an environment where high temperatures of ℃ repeat, even if thermal stress occurs in the ground electrode 4, the cross-sectional dimensions of the ground electrode 4 (W,
In order to prevent a change in H), T1 ≧ T2,
In addition, the relationship is T3 ≧ T4. The basis for such a dimensional relationship will be described later.

The ground electrode 4 of the first metal layer 41
The front end portion (L2 in FIG. 3A) of the facing portion 4a side is
There is no second metal layer 42 and a two-layer structure directly covered with the third metal layer 43 is provided. In this embodiment,
This part has a two-layer structure because this part is particularly high in temperature due to the combustion of the internal combustion engine. If there is copper as the second metal layer 42, this copper melts and a gap is generated. This is because Incidentally, in FIG. 3A, L2 is, for example, 0.2 to 2 mm, and L3 is, for example, 1 to 2.
４4 mm.

The shapes and dimensions of the metal layers 41 to 43 in the ground electrode 4 are merely examples, and the present embodiment is not limited to these dimensions. Further, the material of each of the metal layers 41 to 43 is not limited to the above.
However, it is preferable that the first and third metal layers have substantially the same coefficient of thermal expansion (linear expansion coefficient), and the second metal layer has excellent heat dissipation.

Next, a method of manufacturing the spark plug of the present embodiment will be described. The ground electrode 4 which is a feature of the present invention will be mainly described, and the other manufacturing steps are well known and will not be described. I do. FIG. 4 and FIG. 5 are explanatory views showing the manufacturing process of the ground electrode 4. Further, each dimension value in the following steps is the same as that of each metal layer 41 described above.
Based on an example of the shape and dimensions of ４３43.

First, as shown in FIG. 4A, a nickel wire 60 made of pure nickel having a predetermined outer diameter (for example, φ2.15 mm) is used as a core material, and the nickel wire 60 is connected to a predetermined outer diameter t1 (for example, It is surrounded by a copper pipe 61 (for example, 0.4 mm in thickness) of φ3 mm. Then, the copper pipe 61 surrounding the nickel wire 60 is extruded with a die 80 to perform swaging or drawing, and the outer diameter of the copper pipe 61 is set to t1.
(For example, 3 mm), it is set to t2 (for example, 2.35 mm) smaller than this t1 (wire sticking step).

A copper pipe 61 surrounding a nickel wire 60 that has been swaged or drawn, for example, has a length of 3.0 mm.
4 mm to form a nickel-copper wire 62 shown in FIG. 4B (wire cutting step). Here, FIG.
As shown in (c), a cup 63 made of Inconel 600 (trade name) previously processed by cutting (or cold forging) may be prepared. The cup 63 has an opening 63a at one end and a bottom 63b at the other end, and the inner diameter t3 of the cylindrical cup 63c is the outer diameter t2 of the wire 62.
Slightly larger (for example, φ2.4 mm), the cup portion 6
The depth d3 of 3c is longer than the length of the wire 62, for example, 5 mm. Note that the bottom surface of the cup portion 63c has a concave shape.

The above-mentioned wire rod 62 is put into the cup portion 63c of the cup 63, and as shown in FIG.
A constant pressure press (600 kg) is performed to bring the wire 62 and the cup 63 into close contact. Thus, a composite 64 having a three-layer structure including pure nickel as the first metal layer, copper as the second metal layer, and Inconel 600 as the third metal layer is formed (composite forming step).

The outer diameter t4 of the composite 64 is the same as the outer diameter of the cup 63, for example, 3.5 mm. In addition, the first metal layer protrudes from the second metal layer due to the concave shape of the bottom of the cup portion 63c at the time of the constant-pressure pressing, and the above-described two-layer structure without the second metal layer is formed. Subsequently, the composite 64 is placed in a high-temperature furnace,
The temperature is raised to 0 ° C., and heat treatment is performed at 1000 ° C. (± 80 ° C.) for a predetermined time (for example, 3 hours) in a vacuum atmosphere (diffusion layer forming step). As a result, a diffusion layer is formed at the interface between the metal layers, and the bonding between the metal layers can be strengthened.

Thereafter, as shown in FIG. 4E, the composite 64 is put into a die 82 and pressed to caulk an opening 64a (same as the opening 63a of the cup 63) of the composite 64. Then, as shown in FIG. 5A, extrusion molding (cold forging) is performed, and the composite 64 is formed from a cylindrical body having an outer diameter t4 (for example, 3.5 mm) and a cross section having a flange 65a at an end. A rectangular (for example, 1.6 mm × 2.8 mm) prism 65 is formed (a prism forming step).

After annealing the prism 65 at 850 ° C. for 30 minutes, it is resistance-welded to the fitting 1 as shown in FIG. 5B (welding process). Then, as shown in FIG. 5C, the flange 65a is cut (a jaw cutting step). Subsequently, the center electrode 3 provided with the insulator 2 and the noble metal tip 51 (not shown) is assembled to the mounting bracket 1, and the noble metal tip 52 (not shown) is welded to the prism 65. Then, as shown in FIG. 5D, the prism 65 is deformed into an approximately L shape to form the discharge gap 6 (discharge gap forming step), and the ground electrode 4 is formed. Thus, the spark plug is completed.

The thicknesses T1 to T4 of the second and third metal layers 42 and 43 are determined when the thickness of the copper pipe 61 and the cup 63 is adjusted or extruded in each of the above manufacturing steps. The desired thicknesses T1 to T4 can be obtained by adjusting the mold type and pressure. Next, the second
The basis of the dimensional relationship between the thicknesses T1 to T4 in the third metal layer will be described. This dimensional relationship is based on the thermal shock test described below. In the thermal shock test, each dimension of the width W and the thickness H was 0.5 ≦ H ≦ 2 and H ≦ W ≦ 3H
With respect to the ground electrode 4 having the dimension range described above, samples having various thicknesses T1 to T4 were used. Each sample was subjected to 1000 cycles of thermal shock at 950 ° C. for 1 minute at room temperature for 1 minute, and dimensional changes in thickness H and width W before and after the test were examined.

As an example of the above thermal shock test, the thickness H =
The results for the ground electrode 4 having a width of 1.6 mm and a width W of 2.8 mm are shown in FIGS. FIG. 6 shows the third metal layer 4.
3 shows the relationship between the thickness T1 of the third metal layer 3 and the thickness T2 of the second metal layer 42 and the dimension increase (width dimension increase) of the width W of the ground electrode 4. The horizontal axis is T2 (mm), the vertical axis is the width dimension increase (mm), T1 = 0.2 mm (black circle in the figure),
Each case of 0.3 mm (black triangle in the figure) and 0.4 mm (black square in the figure) is shown.

In FIG. 6, for example, T1 = 0.3 mm
(In the figure, black triangle), T2 is 0.2mm ~ 0.3mm
In the range, the width dimension increase is 0, whereas when T2 is larger than 0.3 mm, the width dimension increase is 0 to 0.09.
mm. That is, from the results in FIG. 6, it can be said that the dimensional change of the width W does not occur when T1 ≧ T2, but tends to occur when T1 <T2.

FIG. 7 shows the thickness T of the third metal layer 43.
The relationship between the thickness T4 of the third and second metal layers 42 and the dimension increase (thickness dimension increase) of the thickness H of the ground electrode 4 is shown. The horizontal axis is T4 (mm), the vertical axis is the thickness dimension increase (mm), and T3 = 0.2 mm (black circle in the figure).
3mm (black triangle in the figure), 0.4mm (black square in the figure)
Each case is shown.

In FIG. 7, for example, T3 = 0.3 mm
(In the figure, black triangle), T4 is 0.2mm ~ 0.3mm
In the range, the thickness dimension increase amount is 0, while when T4 is larger than 0.3 mm, the thickness dimension increase amount is 0 to 0.0
It is about 5 mm. That is, from the result of FIG.
Does not occur when T3 ≧ T4, but tends to occur when T3 <T4.

As described above, from the results of FIGS. 6 and 7, the thickness T of the third metal layer 43 in the width direction and the thickness direction is obtained.
If T1 and T3 are thicker than the thicknesses T2 and T4 of the second metal layer 42, the third metal layer 43 is sufficient for the force of the second metal layer 42 to expand when thermal stress occurs. It is thought that we can compete. Further, in the thermal shock test, the relationship between the width dimension increase and the thickness dimension increase and the gap change (change in the discharge gap 6 before and after the thermal shock test) was examined. The results shown were obtained. FIG.
Shows the relationship between the width dimension increase (horizontal axis) and the gap change (vertical axis, unit mm), and FIG. 9 shows the thickness dimension increase (horizontal axis).
And the gap change amount (vertical axis, unit mm) is shown.

From FIG. 8 and FIG. 9, it is not always necessary that the dimension increase of the width W and the thickness H be 0 in order to make the gap change amount 0, but the dimension increase of the width W and the thickness H occurs. Is
It is presumed to be a sign of a gap change, that is, a reserve army. Therefore, the present inventor has set the thicknesses T and T of the second and third metal layers in order to prevent a change in the dimensions (W, H) of the cross section of the ground electrode 4 due to a rapid temperature change such as a thermal shock.
The dimensional relationships of 1 to T4 are T1 ≧ T2 and T3 ≧ T4. With this dimensional relationship, the gap change amount can be reliably reduced to zero.

While the embodiment has been described above,
According to the present embodiment, the dimensional relationship between the thicknesses T1 to T4 in the second and third metal layers is expressed as T1 ≧ T2 and T3 ≧
Since T4 is set, a change in the dimensions (W, H) of the cross section of the ground electrode 4 can be suppressed even when thermal stress occurs. Therefore, in a use environment such as a thermal shock, the discharge gap 6
Can be provided.

(Other Embodiment) Here, FIG.
The cross-sectional shapes of the ground electrode 4 in FIGS.
Such as shown in FIG. FIG. 10 shows that the thicknesses of the third metal layer 43 and the second metal layer 42 in the width W direction and the thickness H direction need not be constant. In that case, the thickness of each layer in the width direction and the thickness in the thickness direction assume a minimum value.

The cross-sectional shape of FIG. 10A can be produced, for example, by simultaneously applying pressure from above and below in the figure, and the cross-sectional shape of FIG. FIG.
The cross-sectional shape of (c) can be produced, for example, by simultaneously applying pressure from the top, bottom, left, and right directions in the figure.

[Brief description of the drawings]

FIG. 1 is a half sectional view showing an overall configuration of a spark plug according to an embodiment of the present invention.

FIGS. 2A and 2B are configuration diagrams showing a shape of a ground electrode in the spark plug of FIG. 1, wherein FIG. 2A shows a bent shape of the ground electrode, and FIG.

FIG. 3A is a sectional view taken along line BB of FIG. 2B;
FIG. 2B is a cross-sectional view taken along the line CC of FIG.

FIG. 4 is an explanatory diagram showing a process from a wire sticking process to a composite forming process in the manufacturing process in the embodiment.

FIG. 5 is an explanatory diagram illustrating a process from a prismatic body forming step to a discharge gap forming step in the manufacturing steps.

FIG. 6 shows a thickness T1 and a thickness T2 in the embodiment.
6 is a graph showing a relationship between the width and the amount of increase in the width W.

FIG. 7 shows a thickness T3 and a thickness T4 in the embodiment.
4 is a graph showing a relationship between the thickness H and a dimension increase amount.

FIG. 8 is a graph showing a relationship between a dimension increase amount of a width W and a gap change amount in the embodiment.

FIG. 9 shows a dimension increase amount of a thickness H in the embodiment,
9 is a graph showing a relationship with a gap change amount.

FIG. 10 is a cross-sectional view illustrating a ground electrode according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Mounting bracket, 2 ... Insulator, 3 ... Center electrode, 3a ... Center electrode tip part, 4 ... Ground electrode, 4a ... Opposing part, 6 ... Discharge gap, 41 ... First metal layer, 42 ... Second Metal layer,
43 ... third metal layer.

Claims (3)

[Claims] 1. An insulator (2) that covers a periphery of the center electrode (3) in a state where a tip (3a) of the center electrode (3) is exposed. A mounting member (1) disposed around (2) to hold the insulator (2); and a fixing member (1) fixed to the mounting member (1), and attached to the tip (3a) of the center electrode (3). A ground electrode (4) having a facing portion (4a) facing the battery via a discharge gap (6), wherein the ground electrode (4) is a first metal layer (4) as a core material.
1) having a three-layer structure of a second metal layer (42) covering the first metal layer (41), and a third metal layer (43) covering the second metal layer (42). The second metal layer (42) has a larger coefficient of thermal expansion than the first and third metal layers (41, 43), and the thickness of the ground electrode (4) is reduced. H and width are W, the thicknesses of the third metal layer (43) and the second metal layer (42) in the width W direction are T1 and T2, respectively, and the third metal layer (43) in the thickness H direction is A metal layer (43) and the second
When the thickness of the metal layer (42) is T3 and T4, respectively, these thicknesses T1, T2, T3, and T4 are in a relationship of T1 ≧ T2 and T3 ≧ T4. Spark plug. 2. A spark plug according to claim 1, wherein said width W and said thickness H are in a relationship of 0.5 mm ≦ H ≦ 2 mm and H ≦ W ≦ 3H. 3. The first metal layer (41) is made of pure nickel, the second metal layer (42) is made of copper, and the third metal layer (43) is made of a nickel-based alloy. The spark plug according to claim 1 or 2, wherein: