JP2019021398A - Spark plug - Google Patents

Abstract

To provide a spark plug which enables generalization of oxide included in a tip and by which tip's consumption resistance against discharge and oxidization can be ensured.SOLUTION: A spark plug comprises: a first electrode including an electrode base material with a tip joined thereto, provided that the tip includes Ir as a matrix; and a second electrode opposed to the tip through a spark gap. The tip includes at least one oxide of AlOand ZrO, and the content of the at least one oxide is 0.5-9.5 vol% to a volume of the tip.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spark plug, and more particularly to a spark plug in which a chip mainly composed of Ir is provided on an electrode.

In order to ensure wear resistance against discharge and oxidation, a spark plug is known in which a chip mainly composed of Ir is provided on an electrode. In the technique disclosed in Patent Document 1, a spark plug including a chip mainly containing Ir contains a perovskite oxide such as SrZrO ₃ in an amount of 1 to 13 vol% with respect to the volume of the chip.

JP2015-159003A

  However, in the above prior art, there is a demand for generalizing the oxide contained in the chip instead of a special perovskite oxide.

  The present invention has been made to meet the above-described demand, and an object thereof is to provide a spark plug that can ensure wear resistance while generalizing oxides contained in a chip.

In order to achieve this object, a spark plug of the present invention includes a first electrode including an electrode base material to which a chip mainly composed of Ir is bonded, and a second electrode facing the chip of the first electrode through a spark gap. An electrode. The chip contains an oxide of at least one of Al ₂ O ₃ and ZrO ₂ , and the oxide content is 0.5 to 9.5 vol% with respect to the volume of the chip.

According to the spark plug of the first aspect, since the chip contains an oxide of at least one of Al ₂ O ₃ and ZrO ₂ , the oxide contained in the chip can be generalized. Since the oxide content is 0.5 to 9.5 vol% with respect to the volume of the chip, wear resistance can be ensured.

  According to the spark plug of the second aspect, since the oxide content is 3.5 to 8.5 vol% with respect to the volume of the chip, in addition to the effect of the first aspect, the wear resistance can be further improved.

  According to the spark plug of the third aspect, since the median diameter of the oxide is 0.3 to 20 μm, in addition to the effect of the first or second aspect, the wear resistance can be further improved.

It is a half sectional view of the spark plug in one embodiment of the present invention. It is a schematic diagram of a voltage waveform and a current waveform applied between each sample and a second electrode.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a half sectional view of a spark plug 10 according to an embodiment of the present invention with an axis O as a boundary. In FIG. 1, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10. The spark plug 10 includes an insulator 11, a center electrode 13 (second electrode), and a ground electrode 18 (first electrode).

  The insulator 11 is a cylindrical member formed of alumina or the like that is excellent in mechanical properties and insulation at high temperatures, and has a shaft hole 12 that penetrates along the axis O. A center electrode 13 is disposed on the tip side of the shaft hole 12.

  The center electrode 13 is a rod-shaped member extending along the axis O, and is formed at an electrode base material 14 in which a core material mainly composed of copper or copper is covered with nickel or a nickel-based alloy, and at the tip of the electrode base material 14. And a joined chip 15. The electrode base material 14 is held by the insulator 11 and the tip is exposed from the shaft hole 12. The chip 15 is a metal member containing a noble metal such as Pt.

  The terminal fitting 16 is a rod-like member to which a high voltage cable (not shown) is connected, and is formed of a conductive metal material (for example, low carbon steel). The terminal fitting 16 is fixed to the rear end of the insulator 11 with the tip end inserted into the shaft hole 12. A metal shell 17 is fixed to the outer periphery of the insulator 11.

  The metal shell 17 is a substantially cylindrical member formed of a conductive metal material (for example, low carbon steel). A ground electrode 18 is joined to the tip of the metal shell 17. The ground electrode 18 includes a rod-shaped metal (for example, nickel-base alloy) electrode base material 19 joined to the metal shell 17 and a tip 20 joined to the tip of the electrode base material 19. The tip 20 forms a spark gap with the center electrode 13 (tip 15).

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 13 having the tip 15 bonded in advance to the tip is inserted into the shaft hole 12 of the insulator 11 and arranged so that the tip of the center electrode 13 is exposed to the outside from the shaft hole 12. After the terminal fitting 16 is inserted into the shaft hole 12 and the conduction between the terminal fitting 16 and the center electrode 13 is ensured, the metal shell 17 to which the electrode base material 19 has been joined in advance is assembled to the outer periphery of the insulator 11. After joining the tip 20 to the electrode base material 19, the electrode base material 19 is bent so that the tip 20 faces the center electrode 13, and the spark plug 10 is obtained.

The chip 20 contains a first phase made of Ir and at least one oxide of Al ₂ O ₃ (alumina) and ZrO ₂ (zirconia). In addition to the first phase and the oxide, the chip 20 can contain a second phase made of at least one metal selected from Pt, Pd, Rh, Re, Ru, and Ni, and inevitable impurities. When the chip 20 contains the second phase, the content of the first phase (Ir) with respect to the total metal component of the first phase and the second phase is 80 wt% or more.

  The oxide content is 0.5 to 9.5 vol%, preferably 3.5 to 8.5 vol%, with respect to the volume of the chip 20. This is to ensure the spark consumability of the chip 20. The oxide content (vol%) is the ratio between the area of the cross section of the chip 20 and the area of the oxide appearing in the cross section.

The oxide content is measured and calculated by the following method, for example. First, an arbitrary cross section of the chip 20 is mirror-polished, and the cross section is observed with an electron microscope. Next, the total area (S) obtained by summing the areas of all oxides present in the range of the rectangular visual field having a size of 40 μm × 60 μm is obtained. Oxide content (vol%) = S (μm ² ) / 2400 (μm ² ) × 100 is substituted for the total area S to obtain the oxide content.

  Note that the presence of oxide within the field of view can be detected by WDS analysis using EPMA. Image analysis software (for example, Analysis Five manufactured by Soft Imaging System GmbH) can be used to binarize the image in the field of view and measure the area of the oxide in the field of view. Since the oxide area varies slightly for each field of view, the average of the three fields of view is taken.

  The chip 20 is manufactured by the following method, for example. First, the first phase and oxide (second phase if necessary) raw material powders are mixed and then molded to obtain a molded body. After the molded body is fired to obtain a sintered body, the sintered body is cut as necessary to obtain the chip 20. Plastic processing such as forging, rolling, extrusion, and drawing, heat treatment, and the like can be applied to the sintered body as necessary.

  The median diameter of the oxide particles in the sintered body is 0.3 to 20 μm. By setting the median diameter of the oxide particles to 0.3 to 20 μm, it is possible to make the oxide difficult to chip due to thermal shock during discharge of the spark plug 10, and wear of the chip 20 due to the oxide deficiency is reduced. Can be suppressed. Further, since the oxide can hardly prevent the growth of the first phase during firing, the area of the grain boundary of the first phase per unit volume of the chip 20 can be prevented from becoming excessive. As a result, the consumption of the chip 20 due to the oxidation of the grain boundaries of the first phase can be suppressed.

  The median diameter is a particle diameter when the cumulative distribution of oxide particles is 50 vol%. The median diameter is measured and calculated by the following method from an electron microscope image of an arbitrary cross section of the mirror-polished tip 20.

  First, among all the oxides (particles) existing within the range of a rectangular field of view of 40 μm × 60 μm in the image obtained by an electron microscope, the parallel image when the particle image is sandwiched between two parallel lines. Measure the line spacing (Ferret diameter). The direction of the two parallel lines is always the same direction without changing each particle in order to eliminate artifacts. Since there is a slight difference in the particle size distribution for each field of view, the ferret diameters of all oxide particles appearing in the three fields of view are measured.

Next, the range from the minimum value to the maximum value of the measured ferret diameter is divided, and the number of particles (n _i ) existing in each divided particle diameter section is totalized. Next, the volume (v _i ) of a sphere whose diameter is the median value of each particle diameter interval is multiplied by the number of particles (n _i ) existing in the particle diameter interval to obtain particles existing in each particle diameter interval The total volume (V _i = v _i · n _i ) is calculated. The sum of the total volume (V _i ) of the particles existing in each particle diameter section is set to 100 vol%, and the ratio of the amount of particles existing in each particle diameter section (vol%, frequency distribution) or less than a specific particle diameter The ratio of the amount of particles (vol%, cumulative distribution) can be determined. The oxide has a particle size of 0.3 to 20 μm when the cumulative distribution is 50 vol%.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
The raw material powder prepared so that the content rate of Pt (2nd phase) might be 5 wt% with respect to the metal component which makes Ir 1st phase and Pt 2nd phase was prepared. The raw material powder and alumina powder having a median diameter of 1.0 μm were mixed at various ratios, and a molded body was obtained by press molding. The compact was fired at 1400-1600 ° C. in an Ar atmosphere while uniaxially pressing to obtain a sintered body. The sintered body was cut to obtain cylindrical samples 1 to 8 having a diameter of 1.6 mm and a length of 20 mm, each having a different content (vol%) of alumina (oxide). The median diameter of alumina (oxide) in the sample was also 1.0 μm.

  A second electrode was prepared in which a chip having a diameter of 1.6 mm and a length of 0.4 mm was joined to an electrode base material made of a nickel-based alloy. The tip of the second electrode was an alloy containing 10 wt% of Ni (second phase) with respect to the metal component having Pt as the first phase and Ni as the second phase. After the tip of the second electrode and each sample were opposed to each other with a gap of 0.8 mm, a voltage was applied between each sample and the second electrode in a nitrogen atmosphere, and the second electrode and each sample were In the meantime, discharge was repeatedly generated.

  FIG. 2 is a schematic diagram of a voltage waveform and a current waveform applied between each sample and the second electrode. In the first embodiment, the frequency of the main voltage 21 that causes discharge between each sample and the second electrode is 30 Hz, the frequency of the pulse 22 (high-frequency current) superimposed on the main voltage 21 is 2 MHz, and the main voltage 21 is applied. The waiting time W until the start of applying the pulse 22 was 100 μs, the current of the pulse 22 was 3 A, and the duration D of the pulse 22 was 500 μs. The main voltage 21 superimposed with the pulse 22 was repeatedly applied for 10 hours.

After the test, the consumption amount (mm ³ ) of each sample was measured. Samples with a consumption amount of less than 0.15 mm ³ are “particularly excellent (A)”, samples with a consumption amount of 0.15 mm ³ or more and less than 0.16 mm ³ are “excellent (B)”, and the consumption amount is 0 .16 mm ³ or more and less than 0.175 mm ³ were judged as “good (C)”, and samples with a consumption of 0.175 mm ³ or more were judged as “poor (D)”. The results are shown in Table 1. Note that the amount of consumption that is the basis for this determination is determined by estimating from the amount of consumption of the chip 20 that makes it difficult for electric discharge to occur and makes it difficult to start an internal combustion engine (not shown) or makes the operation unstable. It was.

表１に示すように、チップ（サンプル）の体積に対してアルミナ（酸化物）の含有率が０．５〜９．５ｖｏｌ％のサンプル２〜７は、判定をＣ以上にできることが確認された。サンプル８は、チップ（サンプル）の体積に対してアルミナ（酸化物）の含有率が１０．０ｖｏｌ％なので、Ｉｒ等の金属に比べて熱伝導性が低いアルミナを多く含むことになり、チップの熱引き特性（熱伝導性）が低くなり、チップの消耗量が増えたと推察される。サンプル１は、チップ（サンプル）の体積に対してアルミナ（酸化物）の含有率が０．３ｖｏｌ％なので、酸化物による消耗の抑制効果が乏しくなったと推察される。

As shown in Table 1, it was confirmed that the samples 2 to 7 having an alumina (oxide) content of 0.5 to 9.5 vol% with respect to the volume of the chip (sample) can be judged to be C or more. . Since sample 8 has a content of alumina (oxide) of 10.0 vol% with respect to the volume of the chip (sample), it contains a lot of alumina having a lower thermal conductivity than a metal such as Ir. It is presumed that the heat dissipation property (thermal conductivity) is lowered and the consumption of the chip is increased. In sample 1, the content of alumina (oxide) is 0.3 vol% with respect to the volume of the chip (sample), so it is presumed that the effect of suppressing consumption by oxide is poor.

  In particular, it was confirmed that samples 4 to 6 having an alumina (oxide) content of 3.5 to 8.5 vol% with respect to the volume of the chip (sample) can be judged as A. It is inferred that both the heat-drawing characteristics of the chip and the effect of suppressing consumption by oxides were achieved.

(Example 2)
The raw material powder prepared so that the content rate of an oxide (alumina or zirconia) might be 7 vol% with respect to the metal component which makes Ir the 1st phase was prepared. After obtaining a molded body by press molding, this molded body was fired at 1400 to 1600 ° C. in an Ar atmosphere while uniaxially pressing to obtain a sintered body. The sintered body was cut to obtain cylindrical samples 9 to 28 having a diameter of 1.6 mm and a length of 20 mm, which are different in the type and ratio (wt%) of the second phase and the type of oxide. The median diameter of the oxide in the sample was 1.0 μm.

In the same manner as in Example 1, a voltage (see FIG. 2) in which a pulse (high-frequency current) was superimposed was applied between each sample and the second electrode. After the test, the consumption amount (mm ³ ) of each sample was measured. The determination criterion was the same as that of Example 1. The results are shown in Table 2.

表２に示すように、第１相（Ｉｒ）及び第２相からなる金属成分に対し第１相（Ｉｒ）の含有率が８０ｗｔ％以上のサンプル９〜１２，１４〜１６，１８，１９，２１，２３〜２５，２７は、判定をＣ以上にできることが確認された。

As shown in Table 2, samples 9 to 12, 14 to 16, 18, 19, samples having a first phase (Ir) content of 80 wt% or more with respect to the metal component composed of the first phase (Ir) and the second phase. It was confirmed that 21, 23, 25 and 27 can make the determination C or higher.

(Example 3)
The raw material powder prepared so that the content rate of a 2nd phase might be 5 wt% with respect to the metal component which makes Ir the 1st phase and Pt the 2nd phase was prepared. The raw material powder and various alumina powders were mixed so that the alumina content was 7 vol%, and then a molded body was obtained by press molding. The compact was fired at 1400-1600 ° C. in an Ar atmosphere while uniaxially pressing to obtain a sintered body. The sintered body was cut to obtain cylindrical samples 29 to 37 having a diameter of 1.6 mm and a length of 20 mm, each having a different median diameter of alumina (oxide).

  The chip of the second electrode, which is the same as that of Example 1, and each sample were opposed to each other with an interval of 0.8 mm, and then a voltage in which a high-frequency current was superimposed in a nitrogen atmosphere between each sample and the second electrode. It was applied for 10 hours, and discharge was repeatedly generated between the second electrode and each sample. In Example 3, the frequency of the main voltage 21 (see FIG. 2) causing discharge between each sample and the second electrode is 30 Hz, the frequency of the pulse 22 (high-frequency current) superimposed on the main voltage 21 is 13 MHz, The waiting time W from the application of the voltage 21 to the start of applying the pulse 22 was 100 μs, the current of the pulse 22 was 8 A, and the duration D of the pulse 22 was 1000 μs.

After the test, the consumption amount (mm ³ ) of each sample was measured. Samples with a consumption of less than 0.12 mm ³ are “particularly excellent (A)”, samples with a consumption of 0.12 mm ³ or more and less than 0.15 mm ³ are “excellent (B)”, and the consumption is 0. .15 mm ³ or more and less than 0.16 mm ³ were determined to be “good (C)”, and samples with a consumption of 0.16 mm ³ or more were determined to be “poor (D)”. The results are shown in Table 3. The amount of consumption that is the basis for this determination is also estimated from the amount of consumption of the chip 20 that makes it difficult to start an internal combustion engine (not shown) or makes the operation unstable, as in the first embodiment. And determined.

表３に示すように、アルミナ（酸化物）のメジアン径が０．３〜２０μｍのサンプル３０〜３６は、判定をＣ以上にできることが確認された。サンプル２９は、アルミナのメジアン径が０．２μｍなので、第１相の粒界に存在する多くのアルミナの粒子が、焼成時の第１相の粒成長を妨げ、サンプルの単位体積あたりの第１相の粒界の面積が過大になったものと推察される。その結果、第１相（Ｉｒ）の粒界の酸化消耗に起因するサンプルの消耗量が増加したと考えられる。サンプル３７は、アルミナのメジアン径が５０μｍなので、放電時の熱衝撃でアルミナの粒子の一部が欠け、消耗が促進されたと推察される。

As shown in Table 3, it was confirmed that the samples 30 to 36 in which the median diameter of alumina (oxide) is 0.3 to 20 μm can be judged to be C or more. In sample 29, the median diameter of alumina is 0.2 μm, so that many alumina particles present in the grain boundaries of the first phase hinder the growth of the first phase during firing, and the first volume per unit volume of the sample It is inferred that the area of the grain boundary of the phase has become excessive. As a result, it is considered that the amount of consumption of the sample due to the oxidation consumption of the grain boundary of the first phase (Ir) increased. Since sample 37 has an alumina median diameter of 50 μm, it is presumed that a portion of the alumina particles were missing due to thermal shock during discharge, and consumption was promoted.

  In addition, it was confirmed that the samples 31 to 35 having a median diameter of alumina (oxide) of 0.5 to 5 μm can be judged to be B or more. The consumption of the sample due to the loss of alumina due to thermal shock during discharge is suppressed, and the area of the grain boundary of the first phase per unit volume of the sample is prevented from being excessive, and the first phase (Ir) It is inferred that sample consumption due to oxidation consumption from the grain boundary could be suppressed. Furthermore, since the median diameter of alumina (oxide) is as small as 0.5 to 5 μm, it is presumed that the alumina particles were melted by the heat generated during discharge and covered the surface of the sample, thereby contributing to the suppression of wear. In particular, it was confirmed that Samples 32 to 34 having a median diameter of alumina (oxide) of 0.7 to 2 μm can improve this effect and can make the determination A.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  In the embodiment, the tip 20 of the ground electrode 18 includes Ir as a main component and contains alumina or zirconia, but is not necessarily limited thereto. Of course, the tip 15 of the center electrode 13 can have the same composition as the tip 20. Of course, both chips 15 and 20 can contain alumina or zirconia with Ir as the main component. However, the present invention is not limited to this, and any one of the chips 15 and 20 may be used as long as it contains Ir as a main component and contains alumina or zirconia.

  In the embodiment, the chip 20 including alumina or zirconia (either one) is described, but the present invention is not necessarily limited thereto. Of course, the tip 20 can contain both alumina and zirconia. The ratio of alumina to zirconia can be set as appropriate. In this case, the content ratio of the oxide combining alumina and zirconia is set to 0.5 to 9.5 vol% with respect to the volume of the chip 20.

  Although the description is omitted in the embodiment, the shape of the chip 20 can be set as appropriate. Examples of the shape of the chip 20 include a columnar shape, a truncated cone shape, an elliptical column shape, and a polygonal column shape such as a triangular column and a quadrangular column.

  In the embodiment, the case where the chip 20 is bonded to the electrode base material 19 has been described, but the present invention is not necessarily limited thereto. It is naturally possible to provide an intermediate material between the chip 20 and the electrode base material 19. By interposing the intermediate material between the tip 20 and the electrode base material 19, it is possible to suppress the extinguishing action in which the electrode takes away the energy of the flame core.

  In the embodiment, the case where the electrode base material 19 joined to the metal shell 17 is bent has been described. However, it is not necessarily limited to this. Naturally, instead of using the bent electrode base material 19, it is possible to use a linear electrode base material. In this case, the front end side of the metal shell 17 is extended in the axis O direction, a linear electrode base material is joined to the metal shell 17, and the electrode base material is opposed to the center electrode 13.

  In the embodiment, the case where the ground electrode 18 is disposed so that the axis O of the center electrode 13 and the center axis of the chip 20 coincide with each other and the chip 20 faces the center electrode 13 in the direction of the axis O has been described. However, the present invention is not necessarily limited to this, and the positional relationship between the ground electrode 18 and the center electrode 13 can be set as appropriate. Other positional relationships between the ground electrode 18 and the center electrode 13 include, for example, arranging the ground electrode 18 so that the side surface of the center electrode 13 and the ground electrode 18 face each other through a spark gap. . In this case, the chip 20 is joined at a position facing the spark gap.

10 Spark plug 13 Center electrode (second electrode)
18 Ground electrode (first electrode)
19 Electrode base material 20 Tip

Claims (3)

A first electrode including an electrode base material to which a chip mainly composed of Ir is bonded;
A spark plug comprising the tip and a second electrode facing through a spark gap,
The chip contains an oxide of at least one of Al ₂ O ₃ and ZrO ₂ ,
The spark plug has a content of the oxide of 0.5 to 9.5 vol% with respect to the volume of the chip.   The spark plug according to claim 1, wherein a content of the oxide is 3.5 to 8.5 vol% with respect to a volume of the chip.   The spark plug according to claim 1, wherein the oxide has a median diameter of 0.3 to 20 μm.

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