JP4435646B2 - Spark plug - Google Patents

Description

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

  Many spark plugs used for ignition of an internal combustion engine such as an automobile engine have been proposed in which a noble metal tip mainly composed of Pt, Ir or the like is welded to the tip of an electrode. This is because the ignition part of the spark plug is projected into the combustion chamber to improve the ignitability of the spark plug, and the ignition part is exposed to high temperature.

Recently, the structure of the engine head tends to be complicated, and the space around the valve to which the spark plug is attached has also decreased. Therefore, there is an increasing demand for a small spark plug in which the outer diameter of the mounting screw portion of the spark plug metal shell is 12 mm or less. In this way, when the inner diameter of the metal shell is reduced, the distance between the side surface of the central electrode protruding from the insulator and the inner surface of the metal shell is smaller than that of the conventional spark plug, and a fire is caused between the center electrode and the metal shell. There is a problem that a so-called side jump tends to occur. When such a side jump occurs, a spark discharge does not occur in the spark discharge gap, and the ignitability is affected. Therefore, various proposals have been made to prevent such side jumps.
JP 2000-243535 A

  In the spark plug of Patent Document 1, the ignition part is composed of a noble metal tip having a high melting point, so that the consumption of the ignition part does not progress so much even if the heat extraction of the center electrode due to the diameter reduction of the center electrode becomes somewhat worse. I found. Therefore, by reducing the diameter of the center electrode, a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell is ensured, thereby reducing the occurrence of side jump.

  However, in recent internal combustion engines, it has become necessary to ignite the combustion chamber at a high temperature and high pressure and with a lean fuel for the purpose of further increasing output and improving fuel consumption. However, with respect to this tendency, the spark plug disclosed in Patent Document 1 may not be able to sufficiently eliminate the lateral jump.

  An object of the present invention is to provide a spark plug that uses a noble metal tip as an ignition portion and has an outer diameter of a mounting screw portion of 12 mm or less, prevents side jumping, is small, and has excellent ignitability. is there.

The spark plug of the present invention comprises an insulator having an axial hole in the axial direction;
An electrode base material made of pure Ni or a Ni alloy containing 85 wt% or more of Ni is disposed on the front end side of the shaft hole of the insulator, and fixed to the tip of the electrode base material A center electrode composed of a precious metal tip,
A metal shell surrounding the periphery of the insulator;
One end is joined to the metal shell, the other end is opposed to the noble metal tip, and includes a ground electrode that forms a spark discharge gap between the noble metal tip,
The tip of the insulator protrudes from the tip of the metallic shell, or is located on a virtual plane including the tip of the metallic shell,
Wherein the distal end outer diameter of the metal shell M, a tip inner diameter of the front Symbol metal shell D1, the outer diameter of the center electrode in a virtual plane including the distal end of the insulator D2, virtual plane including the distal end surface of the metal shell When the outer diameter of the insulator is D3 ,
M ≦ 10.1mm
0.5mm ≦ D2 <1.4mm
D1 / D2 ≧ 3.5
2.22 ≦ D1 / D3 <3.33
D3 ≧ D2 + 0.1mm
It is.

  In the case of a spark plug having a front end outer diameter M of the metal shell of 10.1 mm or less (corresponding to a screw diameter M12), the distance between the center electrode side surface and the inner surface of the metal shell is determined according to the conventional spark plug (tip outer diameter M The spark plug is larger than 10.1 mm, and there is a possibility that lateral jump occurs between the center electrode and the metal shell. Therefore, as in the spark plug of the present invention, when the inner diameter of the front end surface of the metal shell is D1, and the outer diameter of the center electrode on the virtual plane including the front end of the insulator is D2, D1 / D2 ≧ 3.5 The structure is as follows. As a result, a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell can be secured, and the occurrence of lateral jump between the center electrode and the metal shell can be suppressed. If D1 / D2 <3.5, a sufficient distance between the side surface of the center electrode and the side surface of the metal shell cannot be secured, and there is a possibility that a side jump occurs between the center electrode and the metal shell. More preferably, D1 / D2 ≧ 5.0.

  The outer diameter M of the front end of the metal shell means the outer diameter of the front end excluding the chamfered portion formed at the corner of the front end of the metal shell. In the present invention, a mounting screw portion is formed on the outer surface of the metal shell. This is also applicable to so-called screwless plugs.

By the way, in order to adopt a structure in which D1 / D2 ≧ 3.5 in a spark plug having a tip outer diameter M of 10.1 mm or less, the outer diameter of the center electrode on a virtual plane including the tip of the insulator is used. When D2 is D2, it is desirable that 0.5 mm ≦ D2 <1.4 mm. This is because by setting D2 in this way, D1 / D2 ≧ 3.5 can be easily obtained while the outer diameter M of the front end of the metal shell is set to 10.1 mm or less.
Further, the spark plug of the present invention is an insulator on the virtual plane including the tip end surface of the metal shell, with the tip of the insulator protruding from the tip of the metal shell or positioned on the virtual plane including the tip of the metal shell. When the outer diameter of D3 is D3, 2.22 ≦ D1 / D3 <3.33 and D3 ≧ D2 + 0.1 mm. When D3 <D2 + 0.1 mm, there is a problem that the thickness of the insulator becomes thin, the withstand voltage of the insulator becomes insufficient, and dielectric breakdown is likely to occur.

  In the spark plug of Patent Document 1, as in the present invention, the ignition part is configured by a noble metal tip, and the center electrode is made thin to ensure a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell. The idea is to reduce the occurrence of jumps. However, since the spark plug of Patent Document 1 does not consider the heat sinking of the center electrode due to the diameter reduction of the center electrode when the side jump is likely to occur due to further high temperature and high pressure, the center electrode It is difficult to simply reduce the diameter. However, in the spark plug of the present invention, the center electrode is composed of an electrode base material made of pure Ni or an Ni alloy containing 85 wt% or more of Ni and a noble metal tip fixed to the tip of the electrode base material. In this way, the noble metal tip is configured at the tip of the center electrode, and further, the heat resistance of the center electrode is ensured by using pure Ni or Ni alloy containing Ni of 85 wt% or more as the electrode base material. Consumption is suppressed. Therefore, as described above, the outer diameter D2 of the center electrode on the virtual plane including the tip of the insulator can be set to 0.5 mm ≦ D2 <1.4 mm, and further, the lateral jump can be suppressed.

  Note that when the center electrode is made of an electrode base material made of an Ni alloy containing Ni of less than 85 wt%, the heat resistance of the center electrode is not sufficiently secured, and the effect of suppressing the consumption of the ignition part cannot be obtained.

Further, another spark plug of the present invention, an insulator having an axial hole in the axial direction,
A center electrode comprising an electrode base material, and a noble metal tip fixed to the tip of the electrode base material, disposed so as to protrude from the tip end of the shaft hole of the insulator;
A metal shell surrounding the periphery of the insulator;
A spark plug having one end joined to the metal shell, the other end facing the noble metal tip, and a ground electrode forming a spark discharge gap with the noble metal tip;
The electrode base material surrounds the core containing 90 wt% or more of a metal having a thermal conductivity of 90 W · mK or more of a pure metal provided therein, and has a thickness of 5 μm or more at the insulator tip. And a skin layer made of pure Ni or Ni alloy whose thermal conductivity is smaller than that of the core,
The tip of the insulator protrudes from the tip of the metallic shell, or is located on a virtual plane including the tip of the metallic shell,
Wherein the distal end outer diameter of the metal shell M, a tip inner diameter of the front Symbol metal shell D1, the outer diameter of the center electrode in a virtual plane including the distal end of the insulator D2, virtual plane including the distal end surface of the metal shell When the outer diameter of the insulator is D3 ,
M ≦ 10.1mm
0.5mm ≦ D2 <1.4mm
D1 / D2 ≧ 3.5
2.22 ≦ D1 / D3 <3.33
D3 ≧ D2 + 0.1mm
It is.

  In the case of a spark plug having a front end outer diameter M of the metal shell of 10.1 mm or less (corresponding to a screw diameter M12), the distance between the center electrode side surface and the inner surface of the metal shell is determined according to the conventional spark plug (tip outer diameter M The spark plug is larger than 10.1 mm, and there is a possibility that lateral jump occurs between the center electrode and the metal shell. Therefore, as in the spark plug of the present invention, when the inner diameter of the front end surface of the metal shell is D1, and the outer diameter of the center electrode on the virtual plane including the front end of the insulator is D2, D1 / D2 ≧ 3.5 The structure is as follows. As a result, a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell can be secured, and the occurrence of lateral jump between the center electrode and the metal shell can be suppressed. If D1 / D2 <3.5, a sufficient distance between the side surface of the center electrode and the side surface of the metal shell cannot be secured, and there is a possibility that a side jump occurs between the center electrode and the metal shell. More preferably, D1 / D2 ≧ 5.0.

By the way, in order to adopt a structure in which D1 / D2 ≧ 3.5 in a spark plug having a tip outer diameter M of 10.1 mm or less, the outer diameter of the center electrode on a virtual plane including the tip of the insulator is used. When D2 is D2, it is desirable that 0.5 mm ≦ D2 <1.4 mm. This is because by setting D2 in this way, D1 / D2 ≧ 3.5 can be easily obtained while the outer diameter M of the front end of the metal shell is set to 10.1 mm or less.
Further, the spark plug of the present invention is an insulator on the virtual plane including the tip end surface of the metal shell, with the tip of the insulator protruding from the tip of the metal shell or positioned on the virtual plane including the tip of the metal shell. When the outer diameter of D3 is D3, 2.22 ≦ D1 / D3 <3.33 and D3 ≧ D2 + 0.1 mm. When D3 <D2 + 0.1 mm, there is a problem that the thickness of the insulator becomes thin, the withstand voltage of the insulator becomes insufficient, and dielectric breakdown is likely to occur.

  In the spark plug of Patent Document 1, as in the present invention, the ignition part is constituted by a noble metal tip, and the center electrode is made thin to ensure a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell. The idea is to reduce the occurrence of jumps. However, since the spark plug of Patent Document 1 does not consider the heat pulling of the center electrode due to the diameter reduction of the center electrode when the side jump is likely to occur due to further high temperature and high pressure, the center electrode It is difficult to simply reduce the diameter. However, in the spark plug of the present invention, the center electrode surrounds the periphery of the core containing 90 wt% or more of the metal having a thermal conductivity of 90 W · mK or more of the pure metal provided therein, and the tip of the insulator An electrode base material composed of an outer skin layer made of pure Ni or Ni alloy having a thermal conductivity of 5 μm or more and a noble metal tip fixed to the tip of the electrode base material. . Thus, a noble metal tip is formed at the tip of the center electrode, and the electrode base material as an electrode base material contains 90 wt% or more of a metal having a thermal conductivity of 90 W · mK or more of a pure metal provided therein. By using a core and an outer skin layer made of pure Ni or Ni alloy having a thermal conductivity of 5 μm or more surrounding the periphery of the core and having a thickness of 5 μm or more at the insulator tip, The heat resistance of the electrode is ensured and consumption of the ignition part is suppressed. Therefore, as described above, the outer diameter D2 of the center electrode on the virtual plane including the tip of the insulator can be set to 0.5 mm ≦ D2 <1.4 mm, and further, the lateral jump can be suppressed. The thermal conductivity of pure metal is described in the science chronology (2002 edition).

  In addition, if the thickness of the outer skin layer at the tip of the insulator is less than 5 μm, the outer skin layer is too thin, and the core material having high thermal expansion breaks through the outer skin material and is exposed, and the wear resistance of the electrode base material itself Sex is reduced. Furthermore, the thickness of the outer skin layer is preferably 5 to 500 μm in the case of a Ni alloy of less than 85 wt%. When the film thickness exceeds 500 μm, heat resistance cannot be ensured and wear resistance is reduced.

  In the spark plug of the present invention, the tip of the insulator is positioned on the rear end side from the tip of the metal shell, and D1 / D4> 1.8 when the outer diameter of the tip of the insulator is D4. Good. In this way, by setting D1 / D4> 1.8, the gap formed between the outer surface of the insulator and the metal shell can be increased, and a lateral jump occurs between the center electrode and the metal shell. Further suppression can be achieved. If D1 / D4 ≦ 1.8, the gap between the outer surface of the insulator and the metal shell is too small, and the above effect cannot be obtained sufficiently. On the other hand, it is preferable that D4 ≧ D2 + 0.1 mm. When D4 <D2 + 0.1 mm, there is a problem that the thickness of the insulator becomes thin, the withstand voltage of the insulator becomes insufficient, and dielectric breakdown is likely to occur. More preferably, D1 / D4> 2.0. As shown in FIG. 3, the outer diameter D4 of the tip of the insulator is the diameter of a virtual line that intersects the virtual plane including the tip end surface of the insulator and the virtual side surface obtained by extending the side surface of the insulator to the tip side. To do.

  In the spark plug of the present invention, the noble metal tip can be composed mainly of either Ir or Pt. These metal elements can improve the wear resistance of the ignition part even in an environment where the temperature of the center electrode is likely to rise.

  In the spark plug of the present invention, the noble metal tip is mainly composed of an Ir alloy containing Ir as a main component and one or more of Pt, Rh, Ni, Ru, Pd, W, and Re added. Good. When the precious metal tip is mainly composed of Ir, since Ir has a property of being easily oxidized and volatilized in a high temperature region, if it is used as it is in the ignition part, consumption due to oxidation and volatilization becomes a problem rather than spark consumption. There are drawbacks. Therefore, the precious metal tip is mainly composed of an Ir alloy containing Ir as a main component and one or more of W, Pt, Rh, Ru, Pd, and Re added, so that the oxidation and volatilization of Ir can be performed. Can be effectively suppressed, and the wear resistance of the ignition part can be improved.

  Further, when the noble metal tip is mainly composed of an Ir alloy mainly composed of Ir and added with Rh, consumption due to oxidation / volatilization and spark consumption can be suppressed, but the side surface of the ignition part is affected. In such a case, there is a possibility that abnormal consumption occurs in the ignition part. In view of this, the Ir alloy containing Rh as a main component and the Ir alloy containing Ni as a main component is mainly composed of an Ir alloy added with Ni, thereby suppressing the consumption due to oxidation / volatilization and the consumption of sparks, while further reducing abnormal consumption. Can be suppressed.

  In addition, when the noble metal tip is composed of the above Ir alloy, the oxide, carbide, nitridation of one or more elements selected from Y, Zr, and La are used for the purpose of preventing oxidation and volatilization of Ir. 1 type, or 2 or more types of a product and a boride can be mix | blended. For example, an oxide (including a composite oxide) of one or more elements selected from Y, Zr and La can be contained within a range of 0.1 to 15% by weight. Thereby, consumption due to oxidation and volatilization of the Ir component is further effectively suppressed. When the content of the oxide is less than 0.1% by weight, the effect of preventing Ir oxidation and volatilization due to the addition of the oxide cannot be sufficiently obtained. On the other hand, when the oxide content exceeds 15% by weight, the thermal shock resistance of the tip is lowered, and for example, when the tip is fixed to the electrode by welding or the like, a problem such as cracking may occur. As the oxide, Y2O3 is preferably used, but La2O3, ZrO2 and the like can also be preferably used.

  In the spark plug of the present invention, a chamfered portion is provided on the inner surface of the tip end of the metal shell. As a result, the distance between the outer diameter of the center electrode and the inner diameter of the front end surface of the metal shell is increased, and lateral jumping can be further suppressed.

  In the spark plug of the present invention, the shortest distance in the axial direction between the core in the electrode base material and the noble metal tip is 2 mm or less. Thereby, the heat of the noble metal tip can be effectively transmitted to the core of the center electrode, and the wear resistance of the noble metal tip is improved.

(Embodiment 1)
Hereinafter, some embodiments of the present invention will be described with reference to the drawings. A spark plug 100 with a resistor as an example of the present invention shown in FIGS. 1 and 2 includes a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion protrudes, and an ignition part 31. The center electrode 3 provided inside the insulator 2 in a projecting state, the ground electrode 4 disposed so as to face the side surface of the ignition portion 31 (center electrode 3), and the like are provided. The ground electrode 4 is bent so that the front end face thereof is substantially parallel to the side surface of the ignition part 31, and the ignition part 32 is formed at a position facing the ignition part 31. A spark gap g is formed between the ignition part 31 and the ignition part 32. On the other hand, the rear end portion of the ground electrode 4 is fixed and integrated with the metal shell 1 by welding or the like.

The metal shell 1 is made of carbon steel or the like, and as shown in FIG. 1, a threaded portion 12 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface thereof. The tip outer diameter M of the threaded portion is, for example, 6.5 (M8 in the case of a screw) to 10.1 (M12 in the case of a screw). Furthermore, the metal shell has a protruding portion 1 c protruding from the inner surface in the circumferential direction, and a rear end side step portion 1 d connecting the protruding portion 1 c and the inner surface of the metal shell. A step portion 2a of the insulator 2 which will be described later with the rear-side step portion 1 d is by engaging through a packing 63 to secure the insulator 2 to the metallic shell 1.

  The center electrode 3 includes an ignition part 31 and an electrode base material 3a. The electrode base material 3a is made of pure Ni or a Ni alloy containing 85 wt% or more of Ni. Specifically, it is a 95 wt% Ni alloy. On the other hand, the electrode base material 3a of the center electrode 3 is reduced in diameter at the front end side and has a flat front end surface, on which a disk-like noble metal tip constituting the ignition portion 31 is superimposed, and the joint surface thereof The ignition part 31 is formed by forming the welded part W along the outer edge part by laser welding, electron beam welding, resistance welding or the like and fixing it. Moreover, the ignition part 32 aligns the same chip | tip with the ground electrode 4 in the position corresponding to the ignition part 31, forms the welding part W similarly along the joining surface outer edge part, and adheres this. It is formed. The ignition part 31 and the ignition part 32 are made of a metal mainly composed of Pt, Ir, and W. Specifically, Pt alloys such as Pt—Ir and Pt—Rh, Ir-5 wt% Pt, Ir-20Rh, Ir—Rh—Ni, Ir—Rh—Ni—Pt, Ir—Ru—Rh—Ni, etc. Ir alloys of The ignition unit 32 may be omitted. As used herein, the term “ignition part” refers to a part of the joined chip that is not affected by the composition variation due to welding (for example, a part that is alloyed with the material of the ground electrode or the center electrode by welding). The remaining part). In this way, a noble metal tip is formed at the tip of the center electrode, and further, the heat resistance of the center electrode is further ensured by using pure Ni or Ni alloy containing Ni of 85 wt% or more as the electrode base material. Consumption is suppressed. Therefore, the outer diameter of the center electrode can be reduced as will be described later.

  When the outer diameter of the center electrode on the virtual plane including the tip of the insulator is D2, 0.5 mm ≦ D2 <1.4 mm. This is because by setting D2 in this way, D1 / D2 ≧ 3.5 described later can be easily obtained.

  The insulator 2 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride, and has a through-hole 6 for fitting the center electrode 3 along its own axial direction. The terminal fitting 8 is inserted and fixed on one end side of the through-hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 8 and the center electrode 3 in the through hole 6. Both ends of the resistor 15 are electrically connected to the center electrode 3 and the terminal fitting 13 via conductive glass seal layers 16 and 17, respectively.

  On the other hand, when the inner diameter of the front end surface of the metal shell 1 is D1 and the outer diameter of the center electrode 3 on the virtual plane including the front end of the insulator 2 is D2, D1 / D2 ≧ 3.5. In the case of a spark plug in which the outer diameter M of the metal shell 1 is 10.1 mm or less, the distance M between the side surface of the center electrode 3 and the inner surface of the metal shell 1 is less than the conventional spark plug (the outer diameter M of the tip is 10.1 mm May be smaller than the larger spark plug), and a lateral jump may occur between the center electrode 3 and the metal shell 1. Therefore, as in the spark plug 100 of the present invention, when the inner diameter of the front end surface of the metal shell 1 is D1, and the outer diameter of the center electrode 3 on the virtual plane including the front end of the insulator 2 is D2, D1 / D2 ≧ 3 The structure is .5. As a result, a sufficient distance between the side surface of the center electrode 3 and the inner surface of the metal shell 1 can be secured, and occurrence of lateral jump between the center electrode 3 and the metal shell 1 can be suppressed.

Furthermore, when the outer diameter of the insulator on the virtual plane including the front end surface of the metal shell is D3, 2.22 ≦ D1 / D3 <3.33.

( Reference form 1 )
Next, Reference Embodiment 1 of the present invention will be described with reference to the drawings.
The spark plug 200 shown in FIG. 3 replaces the above-described form in which the tip of the insulator 2 of the spark plug 100 protrudes from the tip of the metal shell 1, and the tip of the insulator 2 is positioned on the rear end side from the tip of the metal shell 1. It is a form to do. 3, the same parts as those in FIG. 2 are denoted by the same reference numerals, and except for the positional relationship, the configuration is the same as in the first embodiment, and the positional relationship between the insulator and the metal shell is mainly described. To do.

In the spark plug 2 of Reference Embodiment 1 , the tip of the insulator 2 is located on the rear end side from the tip of the metal shell 1, and when the outer diameter of the tip of the insulator 2 is D4, D1 / D4> 1. 8. Thus, by setting D1 / D4> 1.8, the gap between the outer surface of the insulator and the metal shell can be increased, and the occurrence of lateral jump between the center electrode and the metal shell is further suppressed. be able to. When the inner diameter of the tip of the metal shell is D1 and the outer diameter of the center electrode on the virtual plane including the tip of the insulator is D2, 0.5 mm ≦ D2 <1.4 mm and D1 / D2 ≧ 3.5 Needless to say, it is.

(Embodiment 2 )
Next, Embodiment 2 of the present invention will be described with reference to the drawings.
The spark plug 300 shown in FIG. 4 has a form in which the center electrode 3 of the spark plug 100 described above is different. 4, the same parts as those in FIG. 2 are denoted by the same reference numerals, and except for the positional relationship, the configuration is the same as in the first embodiment, and the positional relationship between the insulator and the metal shell is mainly described. To do.

  The center electrode 330 includes the ignition part 31, an outer skin layer 330a, and a core 330b. The outer skin layer 330a is made of a Ni alloy, and specifically, a Ni alloy such as INCONEL600 (trademark of INCO). The outer skin layer has a thickness of 5 μm or more at the insulator tip. In addition, a disc-shaped noble metal tip constituting the ignition portion 31 is superposed on the tip of the center electrode 3, and a welded portion W is formed along the outer edge of the joining surface by laser welding, electron beam welding, resistance welding, or the like. The ignition part 31 is formed by forming and fixing this. In addition, the noble metal tip which comprises the ignition part 31 consists of the material described above.

  On the other hand, the core 3b contains 90 wt% or more of a metal having a pure metal thermal conductivity of 90 W · mK or more. Specifically, the core 3b is made of a core such as 98 wt% Cu alloy or pure Ni. As described above, a noble metal tip is formed at the tip of the center electrode, and a core containing 90 wt% or more of a metal having a thermal conductivity of 90 W · mK or more provided as an electrode base material inside the core, By using the outer peripheral layer made of a Ni alloy surrounding the periphery and having a thickness of 5 μm to 250 μm at the insulator tip, heat resistance of the center electrode is ensured, and consumption of the ignition part is suppressed.

  In the center electrode 330 as described above, the outer skin layer 330a is formed in a cup shape as in the prior art, the core 330b is inserted into the recess, and then the center electrode 330 is formed by extrusion molding or the like. Alternatively, the center electrode 330 may be formed by extruding a clad material of the core 330b and the outer skin layer 330a.

( Reference form 2 )
Next, Reference Embodiment 2 of the present invention will be described with reference to the drawings.
The spark plug 400 shown in FIG. 5 replaces the above-described configuration in which the tip of the insulator 2 of the spark plug 300 protrudes from the tip of the metal shell 1, and the tip of the insulator 2 is positioned on the rear end side from the tip of the metal shell 1. It is a form to do. 5, the same parts as those in FIG. 4 are denoted by the same reference numerals, and the configuration other than the positional relationship is the same as that of the second embodiment. The positional relationship between the insulator and the metal shell is mainly described. To do.

In the spark plug 2 of the reference form 2 , the tip of the insulator 2 is located on the rear end side from the tip of the metal shell 1, and when the outer diameter of the tip of the insulator 2 is D4, D1 / D4> 1. 8. Thus, by setting D1 / D4> 1.8, the gap between the insulator and the metal shell can be increased, and the occurrence of lateral jump between the center electrode and the metal shell can be further suppressed. Can do. When the inner diameter of the tip of the metal shell is D1 and the outer diameter of the center electrode on the virtual plane including the tip of the insulator is D2, 0.5 mm ≦ D2 <1.4 mm and D1 / D2 ≧ 3.5 Needless to say, it is.

  In addition, the center electrodes 3 and 330 can be formed so that the proximal end portion has a larger diameter than the distal end portion. Thereby, the heat dissipation of the center electrode 3 can be improved, and the wear resistance of the ignition part can be further improved. In FIG. 6, the outer peripheral surface of the electrode is formed on the tapered surface so that the proximal end portion of the center electrode 3 has a larger diameter than the distal end portion, but a stepped portion is formed on the outer peripheral surface. Thus, a large-diameter base end portion and a small-diameter distal end portion having a substantially uniform diameter may be formed. FIG. 6 uses the center electrode 3, but the same applies to the center electrode 330.

  In FIG. 6, a chamfered portion 11 is provided on the inner surface at the front end of the metal shell. By providing the chamfered portion 11, the distance between the outer diameter D <b> 2 of the center electrode 3 and the inner diameter D <b> 1 of the front end surface of the metal shell 1 is increased, and lateral jumping can be further suppressed.

In order to confirm the effect of the present invention, the following various experiments were conducted.
Various test pieces of spark plugs having the shapes shown in FIGS. 2 and 4 were prepared as follows. First, sintered alumina ceramic is used as the material of the insulator 2, Ni 85 wt% Ni alloy, Ni 85 wt% Ni alloy or Ni 95 wt% Ni alloy is used as the electrode base material of the center electrode 3, and 98 wt% Cu alloy is used as the center electrode 330. Ir-5 wt% Pt was selected as the material of the noble metal chip and the outer layer of the 95 wt% Ni alloy and the noble metal tip for forming the ignition portions 31 and 32, respectively. Each noble metal tip had a columnar shape with a height of 0.4 mm and a diameter of 0.6 mm. 2 were set to M: 8.45 mm (corresponding to M10 in terms of screws), D1: 6 mm, D3: 4.2 mm, and g: 0.9 mm. Further, as a comparative example, a spark plug was manufactured using INCONEL 600 as the material of the center electrode, and the insulator material, the noble metal tip material, and the dimensions of each part as described above. The thickness of the outer skin layer at the insulator tip is 300 μm.

  Then, a spark plug in which the dimension of D2 in FIG. 2 is set as shown in Table 1 is attached to a 6-cylinder DOHC gasoline engine with a displacement of 2000 cc, and continuously operated for 50 hours at an engine speed of 5600 rpm with the throttle fully opened. The amount of increase in gap after the end of operation was measured. The results are also shown in Table 1. A gap increase of less than 0.1 mm is marked ◎, a gap increase of 0.1 or more and less than 0.3 is marked as ◯, and ◎ or ○ is marked as acceptable, and 0.3 or more and less than 0.4. The thing of △ was made into △, and the thing of 0.4 or more was made into rejection.

  According to Table 1, with respect to the spark plugs (samples 1, 5, and 7) having a center electrode diameter of 1.5 mm, the gap increase amount was less than 0.3 mm. On the other hand, when the diameter of the center electrode is reduced (the diameter of the center electrode is 1.0 mm), the spark plug (sample 2) using the center electrode that forms the electrode base material with INCO600, the electrode base material is 80 wt%. The spark plug (sample 3) made of Ni alloy has a gap increase of 0.5 mm or more, whereas the spark plug (sample 4) or electrode base material made of 85 wt% Ni alloy is used as the electrode base material. A spark plug (sample 6) made of 95 wt% Ni alloy, and a core containing 90 wt% or more of a metal (this time Cu) having a thermal conductivity of 90 W · mK or more of a pure metal provided therein, A spark plug (sample 8) using a central electrode that surrounds the core and forms an electrode base material made of an outer layer made of a Ni alloy having a thickness of 5 μm or more at the insulator tip has a gap increase amount. And less than .3Mm, consumption of the spark portion is suppressed. That is, the center electrode is composed of an electrode base material made of a Ni alloy containing Ni of 85 wt% or more, and a noble metal tip fixed to the tip of the electrode base material, or the thermal conductivity of pure metal provided inside An electrode base material comprising a core containing 90 wt% or more of a metal having a thickness of 90 W · mK or more, and a skin layer made of a Ni alloy surrounding the periphery of the core and having a thickness of 5 μm or more at the insulator tip, By comprising the noble metal tip fixed to the tip of the electrode base material, the heat resistance of the center electrode is ensured and the consumption of the ignition part is suppressed.

  Next, various test pieces of the spark plug having the shape shown in FIGS. 2 and 4 were prepared as follows. A sintered alumina ceramic as the material of the insulator 2, a Ni alloy (samples 9 to 12) with a Ni content of 95 wt% as the electrode base material of the center electrode 3, or a core made of 98 wt% Cu as the center electrode 330, INCONEL 600 The outer layer made of (Samples 13 to 16) and Ir-5 wt% Pt were selected as the material of the noble metal tip for forming the ignition portions 31 and 32, respectively. And the dimension of each part shown in FIG. 2 was set to M: 8.45mm, D3: 4.2mm, g: 0.9mm, and it set as Table 2 below about D1 and D2.

  The above-mentioned various test products are mounted on a 6-cylinder DOHC type test gasoline engine with a displacement of 2000 cc and operated in an idling state at an engine speed of 700 rpm. When a test plug is tested, if the same waveform as the reference plug appears, it is judged as “horizontal jump”, and the horizontal jump occurs by examining how many times this waveform appears in 1000 measurements. The rate was examined. And when the occurrence rate of side jump was 0 or more and less than 10%, it was evaluated as ○, when 10% or more and less than 25%, Δ, and when 25% or more. The results are shown in Table 2.

  Samples 9 and 13 have a lateral jump of 25% or more, while samples 10, 11, 12, 14, 15, and 16 have a lateral jump of less than 25%. Furthermore, the samples 11, 12, 15, and 16 have a lateral jump of less than 10%. In other words, by setting D1 / D2 ≧ 3.5, a sufficient distance between the side surface of the center electrode and the inner surface of the metal shell can be secured, and the occurrence of lateral jump between the center electrode and the metal shell can be suppressed. Can do. And by making D1 / D2 ≧ 5.0, it is possible to suppress the occurrence of side jump more effectively.

  Next, various test pieces of the spark plug having the shape shown in FIGS. 2 and 4 were prepared as follows. An insulator and a center electrode using the same materials as in Example 2 were selected, and the dimensions of each part shown in FIG. 2 were set to M: 8.45 mm, D2: 1.0 mm, g: 0.9 mm, and D1 and D3. Was set as shown in Table 3 below.

  In the same manner as in the above test, the engine is mounted on a 6-cylinder DOHC type test gasoline engine with a displacement of 2000 cc and operated in an idling state at an engine speed of 700 rpm. When the waveform is measured and the test is performed with the test plug, if the same waveform as the reference plug appears, it is determined to be “horizontal jump”, and the horizontal jump is determined by examining how many times this waveform appears in 1000 measurements. The incidence was examined. As the electrode base material of the center electrode 3, a core made of Ni alloy (samples 17 to 20) with a Ni content of 95 wt% or 98 wt% Cu as the center electrode 330 and a skin layer made of INCONEL 600 (samples 21 to 21). 24) Used. And when the occurrence rate of side jump was 0 or more and less than 10%, it was evaluated as ○, when 10% or more and less than 25%, Δ, and when 25% or more. The results are shown in Table 3.

  In addition, the above-mentioned various test products were mounted on a 2000 cc displacement, 4-cylinder DOHC type test gasoline engine, and a smoldering stain test was performed based on the provisions of JIS D 1606 (2001). A predetermined operation pattern defined in JIS D 1606 was defined as one cycle, and the number of cycles until the insulation resistance reached 10 MΩ was investigated for each sample. The case where the number of cycles was 8 cycles or more was evaluated as ◯, the case where the number of cycles was 5 to 7 cycles, and the case where the number of cycles was less than 5 cycles as x. The results are shown in Table 3.

Samples 17 and 21 have a lateral jump of 25% or more, whereas samples 18, 19, 20, 22, 23, and 24 have a lateral jump of less than 25%. Further, the samples 19, 20, 23, and 24 have a lateral jump of less than 10% .

  On the other hand, samples 17, 18, 19, 21, 22, and 23 have a cycle number of less than 5, whereas samples 20 and 24 have a cycle number of 5 or more. That is, by setting D3 ≧ D2 + 0.1 mm, the antifouling property of the insulator is improved.

The present invention is not limited to the specific embodiments described above, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, in the spark plug 100 of the present invention, the welded portion W for welding the center electrode 3 is provided on the joint surface outer circumferential edge as shown in FIG. 2, the present invention is not limited thereto, in succession in the radial direction of the noble metal chip It may be formed. Thereby, it is possible to weld a noble metal chip to the center electrode 3 more firmly.

  In the spark plug 100 according to the present invention, one ground electrode 4 is provided. However, the present invention is not limited to this, and a plurality of ground electrodes 4 may be provided. Thereby, the ignitability of the spark plug is improved.

  Further, in the spark plug 100 of the present invention, the protruding portion from the insulator front end surface of the center electrode has a tapered surface whose diameter decreases toward the front end side, and the front end side has a small diameter shape. However, the present invention is not limited to this, and a tapered surface having a diameter that decreases from the rear end side to the front end side of the insulator front end surface may be provided.

1 is a front sectional view showing Embodiment 1 of a spark plug of the present invention. Front sectional drawing which shows the principal part of FIG. Front sectional view showing the main part of Reference Form 1 Front sectional view showing a main part of the second embodiment Front sectional view showing the main part of Reference Form 2 The principal part front sectional view which shows the Example of the spark plug using the center electrode whose base end part is thicker than the front-end | tip part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal shell 2 Insulator 3 Center electrode 4 Ground electrode 6 Through-hole 31 Ignition part (precious metal chip)
100 spark plug

Claims (7)

An insulator having an axial hole in the axial direction;
An electrode base material made of pure Ni or a Ni alloy containing 85 wt% or more of Ni is disposed on the front end side of the shaft hole of the insulator, and fixed to the tip of the electrode base material A center electrode composed of a precious metal tip,
A metal shell surrounding the periphery of the insulator;
One end is joined to the metal shell, the other end is opposed to the noble metal tip, and includes a ground electrode that forms a spark discharge gap between the noble metal tip,
The tip of the insulator protrudes from the tip of the metallic shell, or is located on a virtual plane including the tip of the metallic shell,
Wherein the distal end outer diameter of the metal shell M, a tip inner diameter of the front Symbol metal shell D1, the outer diameter of the center electrode in a virtual plane including the distal end of the insulator D2, virtual plane including the distal end surface of the metal shell When the outer diameter of the insulator is D3 ,
M ≦ 10.1mm
0.5mm ≦ D2 <1.4mm
D1 / D2 ≧ 3.5
2.22 ≦ D1 / D3 <3.33
D3 ≧ D2 + 0.1mm
Spark plug characterized by being. An insulator having an axial hole in the axial direction;
A center electrode comprising an electrode base material, and a noble metal tip fixed to the tip of the electrode base material, disposed so as to protrude from the tip end of the shaft hole of the insulator;
A metal shell surrounding the periphery of the insulator;
A spark plug having one end joined to the metal shell, the other end facing the noble metal tip, and a ground electrode forming a spark discharge gap with the noble metal tip;
The electrode base material surrounds the core containing 90 wt% or more of a metal having a thermal conductivity of 90 W · mK or more of a pure metal provided therein, and has a thickness of 5 μm or more at the insulator tip. And a skin layer made of pure Ni or Ni alloy whose thermal conductivity is smaller than that of the core,
The tip of the insulator protrudes from the tip of the metallic shell, or is located on a virtual plane including the tip of the metallic shell,
Wherein the distal end outer diameter of the metal shell M, a tip inner diameter of the front Symbol metal shell D1, the outer diameter of the center electrode in a virtual plane including the distal end of the insulator D2, virtual plane including the distal end surface of the metal shell When the outer diameter of the insulator is D3 ,
M ≦ 10.1mm
0.5mm ≦ D2 <1.4mm
D1 / D2 ≧ 3.5
2.22 ≦ D1 / D3 <3.33
D3 ≧ D2 + 0.1mm
Spark plug characterized by being. The spark plug according to any one of claims 1 and 2 ,
The spark plug according to claim 1, wherein the noble metal tip is mainly composed of Ir or Pt. The spark plug according to claim 3 , wherein
A spark plug characterized in that the noble metal tip is mainly composed of an Ir alloy containing Ir as a main component and one or more of Pt, Rh, Ni, Ru, Pd, W and Re added. The spark plug according to claim 4 , wherein
The noble metal tip is composed mainly of the Ir alloy, and one or more oxides, carbides, nitrides and borides of one or more elements selected from Y, Zr and La are blended. It is characterized by being. The spark plug according to any one of claims 1 to 5 ,
A chamfered portion is provided on the front end side of the metal shell. The spark plug according to claim 2 ,
A spark plug in which the shortest distance in the axial direction between the core in the electrode base material and the noble metal tip is 2 mm or less.