JP6183129B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine used for an automobile engine or the like.

  A spark plug for an internal combustion engine includes a cylindrical housing, a cylindrical insulator held inside the housing, a center electrode held inside the insulator so that a tip portion projects, and the above A ground electrode connected to the front end of the housing and forming a spark discharge gap with the center electrode. The center electrode is provided with a flange that protrudes radially outward. The center electrode is supported by the flange portion coming into contact with a support portion provided on the inner peripheral surface of the insulator.

  In such a spark plug, since a high voltage is applied to the spark discharge gap, radio noise is generated from the center electrode, which may affect peripheral devices. In order to improve the performance (noise prevention) for preventing the radio noise, a resistor is disposed on the base end side of the center electrode. And in order to aim at the further improvement of noise prevention property, arrange | positioning a resistor in the position close | similar to a spark discharge gap is proposed (refer patent document 1).

Japanese Patent No. 3383920

  However, as the resistor is disposed at a position close to the spark discharge gap, a contact portion between the flange portion of the center electrode and the support portion of the insulator is formed at a position close to the spark discharge gap. If it does so, the temperature change will become large easily in the contact part vicinity, and it will be easy to apply a big thermal stress to an insulator due to the difference of the linear expansion coefficient between a center electrode and an insulator. As a result, the durability of the insulator may be reduced.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a spark plug for an internal combustion engine that can improve the durability of an insulator.

One embodiment of the present invention includes a cylindrical housing;
A cylindrical insulator held inside the housing;
A center electrode held inside the insulator so that the tip protrudes; and
A ground electrode connected to the front end of the housing and forming a spark discharge gap with the center electrode;
The center electrode is provided with a supported portion supported on the support portion provided on the inner peripheral surface of the insulator from the axial direction on the outer peripheral portion,
An annular ring member is interposed between the bearing part and the supported part,
The difference between the linear expansion coefficient and the linear expansion coefficient of the insulator of the ring member, rather smaller than the difference between the linear expansion coefficient and the linear expansion coefficient of the insulator of the center electrode,
The ring member is formed by laminating a plurality of members, and the electrode side layer provided on the surface in contact with the center electrode is harder than the insulator side layer provided on the surface in contact with the insulator. And a spark plug for an internal combustion engine.

  In the spark plug for the internal combustion engine, an annular ring member is interposed between the support portion and the supported portion. Thereby, a ring member plays the role of a shock absorbing material and can reduce the thermal stress applied to an insulator from a center electrode. That is, when the temperature of the spark plug rises, a difference in dimensional variation occurs between the support portion and the supported portion due to the difference in coefficient of linear expansion between the insulator and the center electrode. When the ring member deforms and absorbs the difference in dimensional variation, the stress acting on the support portion of the insulator can be relaxed.

  Further, the difference between the linear expansion coefficient of the ring member and the linear expansion coefficient of the insulator is smaller than the difference between the linear expansion coefficient of the center electrode and the linear expansion coefficient of the insulator. Thereby, the thermal stress applied to the insulator due to the difference in the linear expansion coefficient between the ring member and the insulator can be reduced.

  As described above, according to the present invention, it is possible to provide a spark plug for an internal combustion engine that can improve the durability of an insulator.

The partial cross section front view of the spark plug for internal combustion engines in the reference example 1. FIG. FIG. 4 is an enlarged cross-sectional view in the vicinity of a support portion in Reference Example 1. The perspective view of the ring member in the reference example 1. FIG. FIG. 3 is an enlarged cross-sectional view of the vicinity of the support portion in the first embodiment . The expanded sectional view of the bearing part vicinity in an experiment example. The partial cross-sectional front view of the spark plug for internal combustion engines in Reference Example 2 . FIG. 4 is an enlarged cross-sectional view in the vicinity of a support portion in Reference Example 2 .

In the present invention, the spark plug for the internal combustion engine can be used for an internal combustion engine such as an automobile or a cogeneration.
In the present specification, in the axial direction of the spark plug, the side inserted into the combustion chamber of the internal combustion engine will be described as the front end side, and the opposite side will be described as the base end side.

  In the spark plug for the internal combustion engine, the ring member is preferably softer than the center electrode. In this case, the role of the ring member as a cushioning material can be further improved. As a result, the thermal stress applied to the insulator can be further reduced.

( Reference Example 1)
A reference example of the spark plug for the internal combustion engine will be described with reference to FIGS.
As shown in FIG. 1, a spark plug 1 for an internal combustion engine according to the present embodiment includes a cylindrical housing 2, a cylindrical insulator 3 held inside the housing 2, and an insulator such that a tip portion protrudes. 3 and a ground electrode 5 which is connected to the tip 21 of the housing 2 and forms a spark discharge gap 11 between the center electrode 4 and the center electrode 4. As shown in FIGS. 1 and 2, the center electrode 4 is provided with a supported portion 412 supported from the axial direction on a supporting portion 31 provided on the inner peripheral surface of the insulator 3 on the outer peripheral portion.

As shown in FIG. 2, an annular ring member 6 is interposed between the support part 31 and the supported part 412.
The difference between the linear expansion coefficient of the ring member 6 and the linear expansion coefficient of the insulator 3 is smaller than the difference between the linear expansion coefficient of the center electrode 4 and the linear expansion coefficient of the insulator 3.

  The insulator 3 is provided with a shaft hole 30 through which the center electrode 4 is inserted and held in the axial direction. The shaft hole 30 has a small-diameter hole portion 30a on the distal end side thereof, and a large-diameter hole portion 30b formed with a larger diameter on the proximal end side than the small-diameter hole portion 30a. A tapered support portion 31 having a gradually decreasing diameter toward the distal end is formed at the connecting portion between the small diameter hole portion 30a and the large diameter hole portion 30b.

  As shown in FIG. 1, the center electrode 4 is inserted and held in the shaft hole 30 of the insulator 3. The center electrode 4 includes a center electrode base material 41 and a noble metal tip 42 bonded to the tip thereof. The distal end of the center electrode base material 41 is arranged closer to the distal end side than the distal end of the insulator 3. The noble metal tip 42 has a cylindrical shape, and is joined to the center electrode base material 41 by welding or the like.

  The center electrode base material 41 has a flange portion 411 at the base end portion. The flange portion 411 protrudes outward in the radial direction at the proximal end portion of the center electrode base material 41. Further, as shown in FIG. 2, the flange portion 411 is formed with a tapered surface having a diameter that gradually decreases toward the distal end side, and this portion serves as a supported portion 412. In other words, the supported portion 412 in the flange portion 411 is supported on the support portion 31 via the ring member 6, so that the center electrode 4 is held by the insulator 3.

  The ring member 6 has an annular shape as shown in FIG. Moreover, the ring member 6 is gradually reduced in diameter toward the tip side. As shown in FIG. 2, in the ring member 6, the contact surface with respect to the support portion 31 and the contact surface with respect to the supported portion 412 are substantially parallel.

  The support part 31 and the supported part 412 are pressed against each other via the ring member 6, so that the center electrode 4 is stably held inside the insulator 3. The center electrode 4 is not in pressure contact with the inner peripheral surface of the insulator 3 at portions other than the supported portion 412.

In this example, the center electrode base material 41 is made of a Ni-based alloy, the noble metal tip 42 is made of an iridium alloy, the insulator 3 is made of alumina (Al ₂ O ₃ ), and the ring member 6 is made of niobium (Nb). The difference between the linear expansion coefficient of the ring member 6 made of Nb and the linear expansion coefficient of the insulator 3 made of alumina is the difference between the linear expansion coefficient of the center electrode 4 made of Ni-based alloy and the linear expansion coefficient of the insulator 3 made of alumina. Smaller than the difference. The ring member 6 made of Nb is softer than the center electrode 4 made of a Ni-based alloy. That is, the ring member 6 made of Nb has a Vickers hardness smaller than that of the center electrode 4 made of a Ni-based alloy.

  The material of the ring member 6 is not limited to this, and may be tantalum (Ta), for example. Even in this case, the difference in linear expansion coefficient between the ring member 6 and the insulator 3 is smaller than the difference in linear expansion coefficient between the center electrode 4 and the insulator 3. Further, the ring member 6 made of Ta is softer than the center electrode 4 made of a Ni-based alloy. That is, the ring member 6 made of Ta has a Vickers hardness smaller than that of the center electrode 4 made of a Ni-based alloy.

  As shown in FIG. 1, the ground electrode 5 is bent so that one end is joined to the front end portion 21 of the housing 2 by welding or the like and the other end portion is disposed at a position facing the center electrode 4 in the axial direction. ing. Thereby, a spark discharge gap 11 is formed between the center electrode 4 and the ground electrode 5. The ground electrode 5 is made of a Ni-based alloy.

  As shown in FIG. 1 and FIG. 2, the resistor 7 is disposed on the proximal end side of the center electrode 4 through the conductive glass seal 8 in the shaft hole 30. The resistor 7 can be made of a ceramic resistor mainly composed of carbon, silicon carbide (SiC), aluminum nitride (AlN), or the like.

  Next, the function and effect of this example will be described. In the spark plug 1 for an internal combustion engine, an annular ring member 6 is interposed between the support portion 31 and the supported portion 412. Thereby, the ring member 6 plays the role of a buffer material, and the thermal stress applied to the insulator 3 from the center electrode 4 can be reduced. That is, when the temperature of the spark plug 1 rises, a difference in dimensional variation occurs between the support part 31 and the supported part 412 due to a difference in linear expansion coefficient between the insulator 3 and the center electrode 4. When the ring member 6 is deformed and absorbed by the difference in dimensional variation, the stress acting on the support portion 31 of the insulator 3 can be relaxed.

  The ring member 6 is softer than the center electrode 4. Thereby, the role as a buffer material by the ring member 6 can be further improved. As a result, the thermal stress applied to the insulator 3 can be further reduced.

  Further, the difference between the linear expansion coefficient of the ring member 6 and the linear expansion coefficient of the insulator 3 is smaller than the difference between the linear expansion coefficient of the center electrode 4 and the linear expansion coefficient of the insulator 3. Thereby, the thermal stress applied to the insulator 3 due to the difference in the linear expansion coefficient between the ring member 6 and the insulator 3 can be reduced.

  As described above, according to this example, it is possible to provide a spark plug for an internal combustion engine that can improve the durability of the insulator.

( Example 1 )
In this example, as shown in FIG. 4, the ring member 6 has a two-layer structure. That is, the ring member 6 is formed by laminating two members, and the electrode side layer 61 provided on the surface in contact with the center electrode 4 is harder than the insulator side layer 62 provided on the surface in contact with the insulator 3. It is.

The electrode side layer 61 of the ring member 6 is made of molybdenum (Mo), and the insulator side layer 62 is made of niobium (Nb). The difference between the linear expansion coefficient of the electrode side layer 61 and the insulator side layer 62 of the ring member 6 and the linear expansion coefficient of the insulator 3 made of alumina (Al ₂ O ₃ ) is the linear expansion of the center electrode 4 made of Ni-based alloy. It is smaller than the difference between the coefficient and the linear expansion coefficient of the insulator 3 made of alumina.

  In addition, the combination of the material of the electrode side layer 61 and the insulator side layer 62 is not specifically limited, The insulator side layer 62 should just be softer than the electrode side layer 61, for example, the electrode side layer 61 is molybdenum (Mo). , Tungsten (W) or Kovar alloy, and the insulator side layer 62 may be niobium (Nb), tantalum (Ta), or zirconium (Zr). Also in these cases, the difference in linear expansion coefficient between the electrode side layer 61 and the insulator side layer 62 of the ring member 6 and the insulator 3 is smaller than the difference between the linear expansion coefficients of the center electrode 4 and the insulator 3. .

Others are the same as in Reference Example 1 . Of the reference numerals used in this example or the drawings relating to this example, the same reference numerals as those used in Reference Example 1 represent the same components as in Reference Example 1 unless otherwise indicated.

In the case of this example, the durability of the ring member 6 can be improved. That is, although the thermal stress is applied to the ring member 6 due to the difference in the coefficient of linear expansion between the ring member 6 and the center electrode 4, the ring side member 6 is made harder by making the electrode side layer 61 more susceptible to thermal stress. Prevents excessive deformation. On the other hand, by making the insulator side layer 62 soft, the thermal stress applied to the insulator 3 from the center electrode 4 can be absorbed by the deformation of the insulator side layer 62.
In addition, the same effects as those of Reference Example 1 are obtained.

(Experimental example)
As shown in Table 1, this example is an example in which the durability of the insulator 3 was evaluated for the spark plugs 1 of Reference Example 1 and Example 1 . That is, the durability of the insulator 3 was evaluated with respect to a spark plug having a structure in which the ring member 6 was interposed between the support portion 31 of the insulator 3 and the supported portion 412 of the center electrode 4 and the material was variously changed. . The same evaluation was performed for a spark plug having a configuration in which the ring member 6 is not interposed. Furthermore, the thickness T (see FIG. 5) of the insulator 3 at the boundary between the large-diameter hole portion 30b of the insulator 3 and the support portion 31 was also variously changed.

Specifically, as shown in Table 1, the ring member 6 is not provided, the spark plug of Reference Example 1 is made of niobium (Nb) in the spark plug of Reference Example 1 , and the ring member 6 is replaced with tantalum in the spark plug of Reference Example 1. In the spark plug of Example 1 , the electrode side layer 61 of the ring member 6 was made of molybdenum (Mo), and the insulator side layer 62 was made of Nb. The above-mentioned four types of samples correspond to those in the order of “None”, “Nb”, “Ta”, and “Nb-Mo” in the column of “Ring member” in Table 1.
Further, for the above four types of spark plugs, the thickness T of the insulator 3 is 0.05 mm, 0.1 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.7 mm, 1.0 mm, 1.2 mm. Various changes were prepared. That is, as shown in Table 1, 32 types of spark plugs were prepared in total.

  Here, as shown in FIG. 1, the distance D from the front end surface 44 of the center electrode 4 to the flange 411 in the axial direction is fixed to 10 mm.

As in Reference Example 1 and Example 1 , the center electrode base material 41 is made of a Ni-based alloy, and the insulator 3 is made of alumina (Al ₂ O ₃ ). The linear expansion coefficient of the central electrode base material 41 made of Ni-based alloy is 16.1 × 10 ⁻⁶ / ° C., and the linear expansion coefficient of the insulator 3 made of alumina is 7 × 10 ⁻⁶ / ° C. The linear expansion coefficient of the ring member 6 made Nb, Ta, are respectively the ^{7.2 × 10 -6 /℃,7.3×10 -6 / ℃} .
The Vickers hardness of the center electrode base material 41 made of a Ni-based alloy is HV182, and the Vickers hardness of the ring member 6 made of Nb and Ta is HV96 and HV90, respectively.
Further, in the ring member 6 having a double structure of the electrode side layer 61 and the insulator side layer 62, the linear expansion coefficient of the electrode side layer 61 made of Mo is 7.1 × 10 ⁻⁶ / ° C., and the Vickers hardness is HV160. The insulator side layer 62 made of Nb has a linear expansion coefficient of 7.2 × 10 ⁻⁶ / ° C. and a Vickers hardness of HV96.

  The 32 types of spark plugs 1 were heated by a gas burner until the tip 32 on the side of the central electrode 4 of the insulator 3 reached 800 ° C. according to JIS B 8031 7.9, and then gradually cooled to room temperature. Thereafter, a penetrating flaw detection liquid was applied to the insulator 3 and it was visually observed whether or not the insulator 3 was cracked (hereinafter referred to as “insulator crack” as appropriate). The observation results are shown in Table 1. In Table 1, the case where there was no insulator cracking was marked with ◯, and the case where there was some insulator cracking.

As shown in Table 1, in the spark plug in which the ring member 6 is not provided, insulator cracks occurred when the thickness T was 0.7 mm or less. On the other hand, in the spark plug in which the ring member 6 was interposed, no insulator cracks occurred when the wall thickness T was 0.2 mm or more. From this result, it is understood that the durability of the insulator 3 is improved by interposing the ring member 6.
Further, when the ring member 6 has the Nb—Mo two-layer structure shown in Example 1 , no insulator cracking occurred even when the wall thickness T was 0.1 mm. From this, it was found that the durability of the insulator 3 can be further improved by making the ring member 6 into a double structure by combining appropriate materials as in the first embodiment .

( Reference Example 2 )
In this example, as shown in FIGS. 6 and 7, the support portion 31 is provided at the tip of the insulator 3. In this example, the tapered portion formed at the tip of the center electrode base material 41 is the supported portion 412, and is supported from the axial direction by the supporting portion 31 of the insulator 3 via the ring member 6. Yes. In this example, the collar portion (see reference numeral 411 in FIGS. 1 and 2) is not formed on the center electrode base material 41. Further, the length of the center electrode base material 41 is shorter than those shown in Reference Example 1 and Example 1, and accordingly, the resistor 7 is disposed at a position close to the spark discharge gap 11.

Others are the same as in Reference Example 1 . Of the reference numerals used in this example or the drawings relating to this example, the same reference numerals as those used in Reference Example 1 represent the same components as in Reference Example 1 unless otherwise indicated.

  In the case of this example, since the resistor 7 can be brought closer to the spark discharge gap 11 side, it is possible to improve noise prevention. On the other hand, since the support part 31 and the supported part 412 are close to the spark discharge gap 11, a problem of thermal stress in the support part 31 is likely to occur. Therefore, by interposing the ring member 6 between the support part 31 and the supported part 412, the thermal stress in the support part 31 can be reduced. That is, in this example, the effect of improving the durability of the insulator 3 by providing the ring member 6 is particularly required and expected.

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Housing 3 Insulator 31 Bearing part 4 Center electrode 412 Supported part 5 Ground electrode 6 Ring member

Claims (3)

A tubular housing (2);
A cylindrical insulator (3) held inside the housing (2);
A center electrode (4) held inside the insulator (3) such that the tip protrudes;
A ground electrode (5) connected to the tip (21) of the housing (2) and forming a spark discharge gap (11) with the center electrode (4);
The center electrode (4) is provided with a supported part (412) supported from the axial direction on a support part (31) provided on the inner peripheral surface of the insulator (3) on the outer peripheral part,
An annular ring member (6) is interposed between the support part (31) and the supported part (412),
The difference between the linear expansion coefficient of the ring member (6) and the linear expansion coefficient of the insulator (3) is the difference between the linear expansion coefficient of the center electrode (4) and the linear expansion coefficient of the insulator (3). rather smaller than,
The ring member (6) is formed by laminating a plurality of members, and the electrode side layer (61) provided on the surface in contact with the center electrode (4) is provided on the surface in contact with the insulator (3). A spark plug (1) for an internal combustion engine , which is harder than the insulator side layer (62 ).   The spark plug for an internal combustion engine according to claim 1, wherein the ring member (6) is softer than the center electrode (4). The spark plug (1) for an internal combustion engine according to claim 1 or 2, wherein the support portion (31) is provided at a tip portion of the insulator (3 ).

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