JP2003105467A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a parallel facing spark plug which can prevent or suppress the peeling of a noble metal chip by the selection of the material of a base metal of a parallel electrode on welding of the noble metal chip in particular. SOLUTION: The electrode base metal at least forming the surface part of the parallel electrode (ground electrode) 4 consists of an Ni alloy essentially consisting of Ni, and, in particular, for suppressing or preventing the peeling of a noble metal chip, and the electrode base metal contains, by mass, 15 to 25% Cr, 0.05 to 5% Fe, 0.05 to 5% Al, 0.01 to 0.1% C, and 0.1 to 2% Si and/or Mn.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spark plug.

[0002]

2. Description of the Related Art A spark plug used for ignition of an internal combustion engine such as an automobile engine is provided with a center electrode and a parallel electrode forming a discharge gap between its side surface and the tip surface of the center electrode. In addition, there is a so-called parallel facing type spark plug, and a spark discharge is possible in the axial direction of the center electrode in the discharge gap. In such a parallel facing type spark plug, there is a spark plug in which at least one of the center electrode and the ground electrode is welded with a noble metal tip such as Pt alloy or Ir alloy for the purpose of improving durability.

[0003]

In recent years, as the engine performance has been improved, the combustion efficiency has been improved, and the combustion gas has been changed, the electrode temperature of the spark plug has risen or is exposed to severe heat cycles. The noble metal tip welded to the base material for the purpose of improving durability may peel off. In particular, the noble metal tip is likely to be peeled off in a parallel electrode which is exposed to a high temperature environment as compared with the center electrode and in which the temperature of the cold heat changes significantly. When the noble metal tip is peeled off from the electrode base material as described above, the durability improving effect is lost, and the durability life of the spark plug may be shortened.

The object of the present invention is to prevent or suppress the peeling of the noble metal tip by selecting the material of the parallel electrode base material in the parallel facing type spark plug as described above, particularly when welding the noble metal tip. To provide a simple spark plug.

[0005]

In order to solve the above problems, a spark plug of the present invention covers a center electrode, an insulator arranged outside the center electrode, and an outside of the insulator. A tubular metal shell and a parallel electrode having one end side disposed at the tip of the metal shell and a side surface on the other end side forming a discharge gap between the end surface and the tip end surface of the center electrode are provided to face the discharge gap. A noble metal tip containing a noble metal element as a main component is arranged at a position, and the electrode base material forming at least the surface layer portion of the parallel electrode mainly contains Ni,
Cr is 15% by mass or more and 25% by mass or less, Fe is 0.05
5% by mass or more and 5% by mass or less and 0.05% by mass or more of Al
The content of C is 0.01% by mass or more and 0.1% by mass or less, and Si and / or Mn is 0.1% by mass or more and 2% by mass or less.

The parallel electrode is more exposed to the combustion environment than the center electrode, and the heat is less likely to escape. Therefore, the noble metal tip is more likely to peel off than the center electrode due to thermal oxidation or the like. Since it is relatively long, it easily breaks. Therefore, in the present invention, since the electrode base material forming at least the surface layer portion of the parallel electrode is composed of a Ni alloy having excellent high temperature strength and oxidation resistance composed of the above components, strength and corrosion resistance in a high temperature environment are high. As a result, the noble metal tip is prevented from peeling off or suppressed, and the spark plug has high durability.

The noble metal tip can be arranged on the parallel electrodes by, for example, welding. In the parallel electrode having the electrode base material containing the constituents of the present invention, the peeling of the welded noble metal tip is prevented or suppressed. To be done. In the parallel electrode, at least the surface on which the noble metal tip is provided by welding or the like, and the periphery thereof can be formed of an electrode base material containing at least the above components, and particularly at least in the vicinity of the noble metal tip. If each component is contained, peeling of the noble metal tip can be prevented or suppressed.

Next, the constituent components of the parallel electrode will be described. Cr has an effect of improving high temperature strength and high temperature corrosion resistance. If the content is less than 15% by mass, sufficient improvement in high temperature strength or corrosion resistance may not be observed, and 2
If it exceeds 5% by mass, workability in bending of the parallel electrode may be deteriorated. The Cr content is preferably 16% by mass or more and 22% by mass or less. Fe has the effect of improving high temperature strength and high temperature corrosion resistance. When the content is more than 5% by mass or less than 0.05% by mass, sufficient improvement in high temperature strength or corrosion resistance may not be observed. Fe content is preferably 0.5% by mass
It is preferable that the content is 3 mass% or less. Al has the effect of improving high temperature strength and high temperature corrosion resistance. When the content is less than 0.05% by mass, sufficient improvement in high temperature strength or corrosion resistance may not be observed, and when it exceeds 5% by mass, workability in bending of the parallel electrode may be deteriorated. . Further, when the parallel electrodes are arranged on the metal shell by welding, the weldability of the metal shell may be deteriorated. The Al content is preferably 0.3% by mass or more and 4.5% by mass or less. C has the effect of improving high temperature strength.
If the content exceeds 0.1% by mass, the workability of the parallel electrode in bending or the like may be deteriorated, and if the parallel electrode is arranged on the metal shell by welding, the weldability May also decrease. Moreover, 0.01 mass%
If it is less than 1, the improvement in high temperature strength may not be observed. C
Is preferably 0.05% by mass or more and 0.1% by mass
The following is good. Si and / or Mn improves the oxidation resistance, and if the content exceeds 2 mass%, the workability in bending of the parallel electrode may be deteriorated. The content of Si and / or Mn is preferably 0.5% by mass or more and 1
It is preferable that the content is not more than mass%.

The electrode base material may contain W in an amount of 10% by mass or more and 20% by mass or less. W is solid-solution hardened in a Ni alloy to improve high temperature strength and high temperature oxidation resistance. If it is less than 10% by mass, the effect of significantly improving the high temperature strength and high temperature oxidation resistance may not be obtained, and if it exceeds 20% by mass, the workability in bending of the parallel electrodes may be deteriorated. . The content of W is preferably 10% by mass or more and 15% by mass or less.

The electrode base material may contain Mo in an amount of 0.5% by mass or more and 5% by mass or less. Mo is W
In the same manner as described above, solid solution hardening is performed in a Ni alloy to improve high temperature strength and high temperature oxidation resistance. When it is less than 0.5% by mass, the remarkable effect of improving the high temperature strength and high temperature oxidation resistance may not be obtained, and when it exceeds 5% by mass, the workability in bending of the parallel electrodes is deteriorated. There is. The content of Mo is preferably 1% by mass or more and 3% by mass or less.

Further, the electrode base material can contain Co in an amount of 0.5% by mass or more and 5% by mass or less, and the high temperature strength can be improved by adding the Co. 0.5
If it is less than 5% by mass, the effect of notably improving the high temperature strength may not be obtained.
Since no further effect can be obtained, it is preferable to set the upper limit to 5 mass% in consideration of economy. The Co content is preferably 2% by mass or more and 5% by mass or less.

In the present specification, the terms "main component" and "comprising mainly" are used to mean inclusion in the form having the highest mass content unless otherwise specified.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A spark plug 100 as an example of the present invention shown in FIG. 1 is a so-called parallel facing type spark plug, and is a tubular metal shell 1 and its metal shell 1 with its tip protruding. The insulator 2 fitted in the inside, the center electrode 3 provided inside the insulator 2 with the tip portion protruding, and the metal shell 1 have one end side coupled and the other end side being the tip surface of the center electrode 3. The parallel electrodes 4 and the like arranged so as to face each other are provided. A discharge gap g is formed between the parallel electrode 4 and the center electrode 3.

Here, the parallel electrode 4 has a linear parallel portion 4a which is arranged substantially parallel to the tip surface 3a of the center electrode 3 as shown in FIG. 2, and the center electrode is provided on the side surface of the parallel portion 4a. A discharge gap g is formed between the end surface 3 and the tip surface 3a. In this parallel electrode 4, a noble metal tip 32 containing a noble metal element as a main component is provided at a position facing the discharge gap g.
Are joined by welding. In the case of the present embodiment, a noble metal tip 31 containing a noble metal element as a main component is similarly joined to the tip surface 3a of the center electrode 3 by welding,
The tip surface of the noble metal tip 31 is used as the tip surface 3a of the center electrode 3. By thus disposing the noble metal tip on the ignition part of the electrode, the durability of the electrode is improved.

Returning to FIG. 1, the metal shell 1 is made of carbon steel or the like, and a threaded portion 7 for mounting is formed on the outer peripheral surface of the metal shell 1. The spark plug 100 is attached to the cylinder head of, for example, a gasoline engine (internal combustion engine) by the screw portion 7. Then, in that state, the parallel electrode 4
By applying a high voltage between the center electrode 3 and the center electrode 3, a spark discharge is generated in the spark discharge gap g, which serves as an ignition source of the engine. The outer diameter of the screw portion 7 is 14 mm, for example. The center electrode 3 is made of Ni alloy such as Inconel (trademark). Furthermore, the insulator 2 is made of a ceramics sintered body such as alumina.

A through hole 6 is formed in the axial direction of the insulator 2, a terminal fitting 8 is inserted and fixed on one end side of the insulator 2, and a center electrode 3 is inserted and fixed on the other end side of the insulator. Has been done. A resistor 15 is arranged in the through hole 6 between the terminal fitting 8 and the center electrode 3. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 8 via the conductive glass seal layers 16 and 17, respectively. These conductive glass seal layers 16, 17
The resistor 15 and the resistor 15 form a conductive coupling layer. The resistor 15 may be omitted and the terminal fitting 8 and the center electrode 3 may be joined together by a single conductive glass seal layer. The terminal fitting 8 is made of low carbon steel or the like,
A Ni plating layer (not shown) for corrosion protection is formed on the surface.

In the spark plug 100, the electrode base material forming at least the surface layer portion of the parallel electrode 4 is composed of a Ni alloy containing Ni as a main component. Further, in order to prevent or suppress the peeling of the noble metal tip 32, the electrode base material contains Cr in an amount of 15% by mass or more and 25% by mass or less, Fe in an amount of 0.05% by mass or more and 5% by mass or less, and Al in an amount of 0.05% by mass or less. 5% by mass or more and 0.01% by mass of C
0.1 mass% or more and 0.1 mass% or more and 2 mass% or less of Si and / or Mn are contained.

In order to prevent further peeling of the chip in the parallel electrode 4, W is 10% by mass or more and 20% by mass or less, and / or Mo is 0.5% by mass or more and 5% by mass or less,
And / or Co can be contained in an amount of 0.5% by mass or more and 5% by mass or less. By applying the base material having such constituents as the electrode base material forming at least the surface layer portion of the parallel electrode 4, peeling of the noble metal tip 32 on the parallel electrode 4 is prevented or suppressed, and by extension, the spark plug. It becomes possible to contribute to the improvement of the durable life of 100. Further, when the tip of the parallel electrode 4 projects by 5 mm or more in the axial direction of the spark plug 100 with respect to the metal shell 1, the above effect is enhanced because it is particularly susceptible to heat.

[0019]

[Embodiment] Regarding the spark plug 100 having the above structure,
The following experiments were conducted to confirm the effects of the present invention. As the material of the electrode base material of the parallel electrode 4, alloys of various compositions containing the additive elements shown in Table 1 were adopted. This electrode base material is joined to the front end surface 1a of the metal shell 1 by resistance welding,
As the parallel electrodes 4, various spark plugs having the same form as shown in FIG. 1 were prepared (Comparative Examples 1 to 3, Examples 1 to 1).
6). This spark plug (Comparative Examples 1-3, Examples 1-
Using 6), the following tests (peeling resistance test, tensile strength test, oxidation resistance test, and breakage resistance test) were performed. In addition,
A disk-shaped member made of Pt-20 mass% Ir as the noble metal chips 31 and 32 is joined to each electrode by resistance welding.

[0020]

[Table 1]

(Peeling resistance test) First, the peeling resistance test of the noble metal tip 32 welded to the parallel electrode 4 was conducted. Specifically, 1000 ° C, 2
It was evaluated by calculating the generation rate (%) of the oxide scale after 1000 cycles of this cooling / heating cycle, with one cycle consisting of one minute heating and one minute of natural cooling. That is,
The noble metal tip is arranged in order to suppress spark consumption of the electrode material, but the peelability of the noble metal tip can be evaluated by evaluating the rate (%) of oxide scale generation at the weld surface between the electrode material and the noble metal tip. Can be evaluated. Here, the parallel electrode 4 after 1000 cycles of cooling and heating was etched on the surface cut in the axial direction including the central axis of the noble metal tip 32, and the depth of the oxide scale in the radial direction of the noble metal tip 32 was measured. did. FIG. 3 shows a schematic view of the cut surface. The oxide scale depth is determined by the crack sf generated at the interface between the base material of the parallel electrode 4 and the noble metal tip 32.
It is a value defined as the radial extension of the tip (B1 + B2). And the oxide scale occurrence rate (%) is
It is a value defined by the ratio (B1 + B2) / A of the oxide scale depth (B1 + B2) and the tip diameter A, and is a standard for measuring the degree of peeling of the noble metal tip.

(Tensile Strength Test) Using the electrode materials containing the additive elements shown in Table 1, wire rods before forming parallel electrodes were prepared. Then, they were cut appropriately and a tensile test was performed at 800 ° C. The results are shown in Table 2.

(Oxidation resistance test) The spark plugs of the comparative examples and the examples shown in Table 1 were subjected to an oxidation resistance test by heating and cooling in an electric furnace (in the air), and the oxide film thickness on the surface of the parallel electrodes 4 was measured. The number of cycles to reach 0.1 mm was confirmed.
The test consisted of heating at 1100 ° C. for 24 hours and gradual cooling to room temperature as one cycle. The results are shown in Table 2.

(Fracture resistance test) A spark resistance test engine (2000 cc, 4 cylinders, 4 cycles) was fitted with the spark plugs of the comparative examples and the examples shown in Table 1, and a breakage resistance test was conducted. The state of occurrence of cracks in the parallel electrode 4 was confirmed. The test was repeated 200 cycles, with 1 minute of operation at 7,000 rpm and 1 minute of idle. The results are shown in Table 2.

[0025]

[Table 2]

Thus, in each test, Examples 1 to 1
The spark plug of No. 6 showed relatively good results as compared with Comparative Examples 1 to 3. Specifically, in the peel resistance test, in Examples 1 to 6, the occurrence rate of oxide scale was about 30%.
The rate was below (specifically, 26% or less), which was an extremely low incidence as compared with the comparative example. In particular, in Example 6, the generation rate of oxide scale was 3%, and the sample had excellent oxidation resistance. That is, it is understood that the peel resistance of the noble metal tip is extremely high. Here, the peeling resistance of the noble metal tip after 1000 cycles of the cooling / heating cycle was observed with a metallographic microscope. The observation view is shown in FIG. Figure 4
(A) is of Example 6, and FIG. 4 (b) is of Comparative Example 1.
belongs to. In the parallel electrode 4 ′ of Comparative Example 1, the noble metal tip 32 ′ is peeled off, whereas in Example 6
It can be seen that the noble metal tip 32 is extremely difficult to peel off in the parallel electrode 4 of FIG.

Next, in the tensile strength test, the electrode base materials corresponding to Comparative Examples 1 to 3 have tensile strengths of about 120 to 160 MPa (specifically, 122.5 to 149.9 MPa), while those of Examples The electrode base material corresponding to 1 to 6 is 27
0 to 530 MPa (specifically 270.5 to 514.5 M
It can be seen that the tensile strength is about Pa), and the tensile strength is higher in the example.

In the oxidation resistance test, as a cycle in which the oxide film thickness on the surface of the parallel electrode 4 reaches 0.1 mm, in Comparative Examples 1 to 3, the cycle is as fast as 11 to 20 cycles.
Reached 1 mm. On the other hand, in Examples 1 to 6, the oxide film thickness on the surface of the parallel electrode 4 was 0.1 mm even when 30 cycles were reached.
It can be seen that the oxidation resistance is relatively high as compared with Comparative Examples 1 to 3.

In the breakage resistance test, in Comparative Examples 1 to 3, it was confirmed that the parallel electrodes 4 were broken or cracks of 0.5 mm or more were generated. On the other hand, in Examples 1 to 6, there was no breakage and no crack was generated or 0.5 mm.
The occurrence of microcracks was less than.

From the above results, in the spark plugs of Examples 1 to 6, in the parallel electrode 4, the strength is relatively improved and the breakage resistance is high as compared with the conventional one, and the noble metal tip 32 is peeled off. Is prevented or suppressed, and high oxidation resistance is provided. Therefore, the spark plugs of Examples 1 to 6 have excellent durability life.

[Brief description of drawings]

FIG. 1 is an overall vertical sectional view showing an example of a spark plug of the present invention.

FIG. 2 is an enlarged cross-sectional view of a main part of FIG.

FIG. 3 is a schematic cross-sectional view for explaining an oxide scale generation rate.

FIG. 4 is an observation view showing a result of observing a peeling property of a noble metal tip on a parallel electrode with a metallographic microscope.

[Explanation of symbols]

1 metal shell 2 insulator 3 Center electrode 4 Parallel electrode (ground electrode) 32 precious metal chips 100 spark plugs

Claims (4)

[Claims] 1. A center electrode (3), an insulator (2) arranged outside the center electrode (3), and a tubular metal shell (1) covering the outside of the insulator (2).
And one end side is disposed at the tip portion (1a) of the metal shell (1), and the side surface on the other end side is the tip surface (3) of the center electrode (3).
a) and a parallel electrode (4) forming a discharge gap (g) between them and a noble metal tip (32) containing a noble metal element as a main component is disposed at a position facing the discharge gap (g). In addition, the electrode base material forming at least the surface layer portion of the parallel electrode (4) contains Ni as a main component, Cr is 15% by mass or more and 25% by mass or less, and Fe is 0.05% by mass or more and 5% by mass or less. , Al is 0.05% by mass or more and 5% by mass or less, and C is 0.
01% by mass or more and 0.1% by mass or less, Si and / or Mn
The spark plug (100) is characterized by containing 0.1% by mass or more and 2% by mass or less. 2. The electrode base material contains W in an amount of 10 mass% or more and 20 or more.
The spark plug (100) according to claim 1, wherein the spark plug (100) contains not more than mass%. 3. The spark plug (100) according to claim 1, wherein the electrode base material contains Mo in an amount of 0.5% by mass or more and 5% by mass or less. 4. The electrode base material according to claim 1, containing Co in an amount of 0.5% by mass or more and 5% by mass or less.
Spark plug (100) according to the paragraph.