JP5291659B2 - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a capacitive discharge current, and to effectively suppress electrode wear and noise. <P>SOLUTION: A spark plug 1 working as an ignition plug, comprises a insulator 2 having a shaft hole 4 extending in an axis line CL1; a cylindrical main fitting 3 provided on the outer periphery of the insulator 2; a rod-shaped electrode 8 inserted in the shaft hole 4; and a ground electrode 27 disposed at a tip end portion of the main fitting 3, and forming a spark discharging clearance 33 between the ground electrode 27 and the tip end portion of the electrode 8. A cylindrical resistor 9 is provided between the inner peripheral surface of the insulator 2 and the outer peripheral surface of the electrode 8, in at least a part of a range from the tip end of the main fitting 3 to a part separated from a rear end of the main fitting 3 to a rear end side by 5 mm, along the axis CL1. The length along the axis line CL1 of the resistor 9 within a range from the tip end of the main fitting 3 to the rear end of the main fitting 3 is not less than 36% of the length along the axis line CL1 of the main fitting 3. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

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

  An ignition plug used in a combustion apparatus such as an internal combustion engine is, for example, inserted into an insulator having an axial hole extending in the axial direction, a center electrode inserted into the front end side of the axial hole, and a rear end side of the axial hole. A terminal electrode, a cylindrical metal shell assembled on the outside of the insulator, and a ground electrode disposed at the tip of the metal shell. In addition, a spark discharge gap is formed between the center electrode and the ground electrode, and a spark discharge is generated in the spark discharge gap, so that the mixture is ignited.

  By the way, the center electrode and the metal shell that are opposed to each other with the insulator interposed therebetween are configured to be able to store electric charges like a capacitor. Therefore, a charge is charged between the center electrode and the metal shell due to the voltage applied for spark discharge. This charge flows between both electrodes during spark discharge (that is, capacitive discharge occurs), but if the current flowing between both electrodes due to capacitive discharge (capacitive discharge current) is large, the electrodes are quickly consumed. Doing so may cause large noise. Therefore, a technique has been proposed in which a resistor is provided between the center electrode and the terminal electrode in order to suppress electrode consumption and noise (see, for example, Patent Document 1). By providing the resistor, it is possible to prevent the electric charge stored between the center electrode and the metal shell from flowing between the two electrodes due to spark discharge, and to reduce the capacity discharge current.

  In recent years, in order to meet the demand for higher output and lower fuel consumption of combustion devices, as a spark plug that spreads quickly and can be ignited more reliably even with a lean mixture with a higher ignition limit air-fuel ratio, A plasma jet ignition plug has been proposed (see, for example, Patent Document 2). The plasma jet ignition plug generally has a cylindrical space (cavity portion) formed by the inner peripheral surface of the tip end side of the shaft hole and the front end surface of the center electrode. Thus, the mixture is ignited. That is, a voltage is applied between the center electrode and the ground electrode to cause a spark discharge between the two, thereby causing a dielectric breakdown between the two. In addition, plasma is generated by transitioning the discharge state by supplying electric energy between the two. The air-fuel mixture is ignited when this plasma is ejected from the cavity.

  By the way, since a plasma jet ignition plug supplies electric energy after spark discharge, when a resistor is provided as described above, a loss of electric energy occurs due to the resistor. Therefore, there is a possibility that the intended function cannot be exhibited, for example, plasma cannot be generated.

  In view of this, a technique has been proposed in which stray capacitance reducing means is provided between the center electrode and the metal shell in order to suppress electrode consumption and noise while exhibiting the desired function (for example, Patent Document 3). reference). Specifically, by providing a low dielectric constant layer as a stray capacitance reducing means, a space between the center electrode and the metal shell is formed as a so-called multi-cylindrical capacitor, and stored between the center electrode and the metal shell. The charge is reduced. As the low dielectric constant layer, a porous body having a relatively low relative dielectric constant in which air is introduced into talc or the like has been proposed, and in order to exert a function as a capacitor, the low dielectric constant layer has an insulating property. [That is, having a very high resistance value (several hundred megaΩ)] is required.

JP 2009-245716 A JP 2006-294257 A JP 2009-283380 A

  However, when the method of Patent Document 3 is adopted, even if the charge charged between the center electrode and the metal shell can be made relatively small, there is no change in the current flowing into both electrodes at once. . Therefore, the capacity discharge current is still large, and the effect of suppressing electrode consumption and noise is poor.

  Further, in order to adjust the charge charged between the center electrode and the metal shell, it is necessary to finely adjust the relative dielectric constant of the low dielectric constant layer. Therefore, there is a risk that productivity may be reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to effectively reduce electrode consumption and noise by reducing the capacity discharge current, such as a plasma jet ignition plug. Another object of the present invention is to provide an ignition plug that can be applied to a plug in which it is difficult to provide a resistor between a center electrode and a terminal electrode.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration includes an insulator having an axial hole extending in the axial direction;
A cylindrical metal shell provided on the outer periphery of the insulator;
A rod-shaped electrode inserted through the shaft hole;
A spark plug that is disposed at the tip of the metal shell and includes a ground electrode that forms a gap with the tip of the electrode;
At least part of the range from the front end of the metallic shell to the rear end side to the rear end side of the metallic shell along the axis, up to 5 mm,
A cylindrical resistor is provided between the inner peripheral surface of the insulator and the outer peripheral surface of the electrode,
The length along the axis of the resistor in the range from the front end of the metal shell to the rear end of the metal shell is 36% or more of the length along the axis of the metal shell. And

  According to the configuration 1, a charge can be stored along the axis from the front end of the metal shell to the rear end side of the metal shell from the rear end side to 5 mm, in other words, between the electrode and the metal shell. In at least a part of the range, a cylindrical resistor is provided between the insulator and the electrode. Therefore, it is possible to more reliably prevent the stored charge from flowing into the gap between the electrode and the ground electrode by the resistor, and to reduce the capacity discharge current. Particularly, according to the configuration 1, the length along the axis of the resistor in the range from the front end of the metal shell to the rear end of the metal shell is sufficiently 36% or more of the length along the axis of the metal shell. It is considered to be big. Therefore, the capacity discharge current can be effectively reduced, and electrode consumption and noise can be extremely effectively suppressed.

  Moreover, according to the said structure 1, the fine adjustment operation | work required when the technique of the said patent document 3 is employ | adopted is unnecessary, and what is necessary is just to arrange the resistor generally used around an electrode. . Therefore, it is possible to more reliably prevent the productivity from decreasing.

  Furthermore, since the resistor is disposed around the electrode, even when electric energy is input between the center electrode and the ground electrode, the electric energy is not lost by the resistor. Therefore, the plasma jet ignition plug described above, a high-frequency ignition plug that generates plasma by supplying high-frequency current, a voltage is applied between the center electrode and the ground electrode after combustion of the air-fuel mixture, and ion current is generated. The above-described configuration 1 is suitable for an ignition plug for supplying electric energy after spark discharge, such as an ion current detection plug (for example, Japanese Patent Application Laid-Open No. 2003-286933) that detects an ion current to detect a combustion state or the like. . In addition, the technical idea of the configuration 1 can be applied to a general spark plug that ignites an air-fuel mixture by spark discharge.

  Configuration 2. The spark plug of this configuration is characterized in that, in the above configuration 1, the resistor is provided in a portion where a difference in diameter between the inner diameter of the shaft hole and the inner diameter of the metal shell is minimized.

  The smaller the distance between the electrode and the metal shell, the more charge is charged. In view of this point, according to the configuration 2, the resistor is provided corresponding to the portion where the difference in diameter between the inner diameter of the shaft hole and the metal shell is minimized, that is, the portion where a lot of electric charges are charged. Yes. Accordingly, it is possible to further reduce the capacity discharge current, and more effectively suppress electrode consumption and noise.

  Configuration 3. The spark plug of this configuration is characterized in that, in the above configuration 1 or 2, the volume resistivity of the resistor is 10 milliΩm or more.

  According to the configuration 3, since the volume resistivity of the resistor is set to 10 milliΩm or more, the capacity discharge current can be more reliably reduced. As a result, electrode consumption and noise can be more reliably suppressed.

  Configuration 4. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 to 3, the volume resistivity of the resistor is set to 10 kiloΩm or less.

  As the volume resistivity of the resistor is increased, the capacity discharge current can be reduced. However, the capacity discharge has a surface that contributes to improvement in ignitability while causing electrode consumption and the like. Therefore, if the capacity discharge current is excessively reduced, the ignitability may be reduced.

  In this regard, according to the configuration 4, the volume resistivity of the resistor is set to 10 kiloΩm or less. Therefore, it is possible to more reliably prevent the capacity discharge current from becoming excessively small, and as a result, it is possible to more reliably prevent a decrease in ignitability.

  Configuration 5. The spark plug of this configuration is characterized in that, in any of the above configurations 1 to 4, the thickness of the resistor along the direction orthogonal to the axis is 0.1 mm or more and 2.5 mm or less.

  According to the configuration 5, since the thickness of the resistor is 0.1 mm or more, the capacity discharge current can be more reliably reduced, and the effect of suppressing electrode consumption and noise can be further improved. it can.

  On the other hand, in increasing the thickness of the resistor, the thickness of the insulator must be reduced, but if the thickness of the insulator is excessively reduced, the electrode and the metal shell The electric charge stored in between increases excessively. In this regard, according to the above-described configuration 5, since the thickness of the resistor is 2.5 mm or less, the thickness of the insulator can be made relatively small, and charging is performed between the electrode and the metal shell. Charge can be reduced more reliably. As a result, electrode consumption and the like can be more effectively suppressed.

(A) is a front view of a spark plug, (b) is sectional drawing of a spark plug. It is a partial expanded sectional view which shows the internal structure of a spark plug. (A)-(c) is sectional drawing which shows the structure of a sample, (d) is sectional drawing which shows the structure of samples A and C. FIG. It is a graph which shows the relationship between a resistor ratio and a gap increase amount. It is a graph which shows the test result of the desktop spark test in the sample which changed the volume resistivity of the resistor variously. It is a graph which shows the test result of the desktop spark test in the sample which changed the thickness of the resistor variously. It is sectional drawing which shows the structure of the ignition plug in another embodiment. It is sectional drawing which shows the structure of the ignition plug in another embodiment. It is sectional drawing which shows the structure of the ignition plug in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1A is a front view of a spark plug 1 as an ignition plug, and FIG. 1B is a cross-sectional view of the spark plug 1. 1A and 1B, the direction of the axis CL1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as an insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. In addition, a tapered step portion 14 is formed at a connecting portion between the middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, a shaft hole 4 is formed through the insulator 2 along the axis CL1, and an electrode 8 is inserted and fixed in the shaft hole 4. The electrode 8 is configured by connecting the terminal electrode 6, the glass seal layer 7, and the center electrode 5 in series.

  The terminal electrode 6 is inserted into the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2 and is made of a conductive metal such as low carbon steel.

  The glass seal layer 7 has conductivity, electrically connects the front end portion of the terminal electrode 6 and the rear end portion of the center electrode 5, and fixes the terminal electrode 6 and the like to the insulator 2. .

  The center electrode 5 is formed of a Ni alloy containing nickel (Ni) as a main component, and is formed on the large diameter portion 5A inserted through the tip end side of the shaft hole 4 and the rear end side of the large diameter portion 5A. A flange portion 5B that bulges outward in the radial direction and a small diameter portion 5C that extends from the flange portion 5B to the rear end side along the axis CL1 and has a smaller diameter than the large diameter portion 5A and the flange portion 5B. A portion of the center electrode 5 excluding the tip of the large diameter portion 5 </ b> A is accommodated inside the insulator 2. Further, the flange portion 5B is locked to a tapered portion 4A formed on the tip end side of the shaft hole 4.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw for attaching the spark plug 1 to a combustion device such as an internal combustion engine or a fuel cell reformer on the outer peripheral surface thereof. A portion (male screw portion) 15 is formed. In addition, a seat portion 16 is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. Further, on the rear end side of the metal shell 3, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the spark plug 1 is attached to the combustion device is provided. A caulking portion 20 for holding the insulator 2 is provided.

  A tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the two step portions 14 and 21. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  In addition, a substantially intermediate portion of the metal shell 3 is bent back at the front end portion 26, and a ground electrode 27 whose side surface faces the front end surface of the center electrode 5 is joined. The ground electrode 27 is made of a Ni alloy, and a spark discharge gap 33 is formed between the tip of the ground electrode 27 and the tip of the center electrode 5. In the spark discharge gap 33, spark discharge is performed in a direction substantially along the axis CL1. The size GL of the spark discharge gap 33 along the axis CL1 is set to a predetermined size in view of ignitability and durability.

In addition, in the present embodiment, the outer peripheral surfaces of the flange portion 5B and the small diameter portion 5C of the center electrode 5 in at least part of the range from the front end of the metal shell 3 to 5 mm from the rear end to the rear end side of the metal shell 3 A cylindrical resistor 9 is provided between the inner peripheral surface of the insulator 2 and the insulator 2. The resistor 9 includes a conductive material (for example, carbon black) between the heated glass powder and ceramic particles, and has a predetermined resistance value. Specifically, the volume resistivity of the resistor 9 is not less than 10 milliΩm and not more than 10 kiloΩm. In addition, the volume resistivity of the resistor 9 can be measured as follows. That is, after the resistor 9 is taken out, it is formed into a rectangular parallelepiped shape having a cross-sectional area S (mm ² ) and a length L (mm), and electrodes are attached to both ends thereof. And the resistance value R ((ohm)) of the said rectangular parallelepiped resistor is measured, and cross-sectional area S, length L, and resistance value are set to the formula of volume resistivity = (R * S / L) * 10 < ^-3 >. Substitute R. Thereby, the volume resistivity (Ωm) of the resistor 9 can be measured. The volume resistivity of the resistor 9 can be adjusted by changing the ratio of glass powder or the like in the resistor 9.

  Further, as shown in FIG. 2, the resistor 9 has a portion where the difference in diameter between the inner diameter of the shaft hole 4 and the inner diameter of the metal shell 3 is minimized (in this embodiment, the inner diameter of the metal shell 3 in the direction of the axis CL1). Of the peripheral portion, the portion between the tip of the enlarged diameter portion 3A that expands toward the rear end side in the direction of the axis CL1 and the rear end of the tapered portion 4A of the shaft hole 4 corresponds).

  Further, the length XL along the axis CL1 of the resistor 9 within the range from the front end of the metal shell 3 to the rear end of the metal shell 3 is 36% or more of the length SL along the axis CL1 of the metal shell 3 ( In this embodiment, it is 90% or more). In addition, the thickness TH along the direction orthogonal to the axis CL1 of the resistor 9 (thickness along the radial direction) TH is set to 0.1 mm or more and 2.5 mm or less. In the case where the thickness along the radial direction of the resistor 9 is different along the direction of the axis CL1, the “thickness TH of the resistor 9” refers to a plurality of locations of the resistor 9 along the axis CL1 ( For example, the average value of the thickness of the resistor 9 at the most distal portion, the most rearmost portion, the middle portion of both portions, and the like.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated.

  First, the metal shell 3 is processed in advance. That is, by performing a cold forging process or the like on a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material), a through hole is formed and a rough shape is manufactured. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, a ground electrode 27 made of a Ni alloy is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained. Next, the metal shell 3 to which the ground electrode 27 is welded is subjected to zinc plating or nickel plating. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, a green body granulated material for molding is prepared using a raw material powder mainly composed of alumina and containing a binder, and a rubber molded body is used to obtain a cylindrical shaped body. And it shape | molds by giving a grinding process with respect to the obtained molded object, throws the shaped thing into a baking furnace, and bakes it. Thereby, the insulator 2 is obtained.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 and the terminal electrode 6 are manufactured. That is, the center electrode 5 is produced by forging the Ni alloy. Further, the terminal electrode 6 is manufactured by forging the alloy such as low carbon steel.

  Furthermore, a powdery resistor composition for forming the resistor 9 is prepared. More specifically, first, carbon black as a conductive material, ceramic particles, and a predetermined binder are blended and mixed with water as a medium. And the resistor composition is obtained by drying the slurry obtained by mixing and mixing and stirring glass powder to this.

  Next, the center electrode 5 and the terminal electrode 6 are fixed to the insulator 2 while providing the resistor 9 in the insulator 2. More specifically, the center electrode 5 is inserted into the shaft hole 4, and the flange portion 5 </ b> B of the center electrode 5 is locked to the tapered portion 4 </ b> A of the shaft hole 4. Next, the resistor composition is filled into the shaft hole 4 and the outer periphery of the center electrode 5 (the flange portion 5B and the small diameter portion 5C), and the filled resistor composition is compressed. The resistor composition is compressed using a cylindrical jig (not shown).

  Thereafter, the conductive glass powder prepared by generally mixing borosilicate glass and metal powder is filled into the shaft hole 4, and the filled conductive glass powder is compressed. And in the state which pressed the terminal electrode 6 into the axial hole 4 from the opposite side of the center electrode 5, it heats at the predetermined temperature (800 to 1000 degreeC in this embodiment) above a glass softening point in a baking furnace. .

  By heating, the resistor composition is sintered to become the resistor 9, and the conductive glass powder is sintered to become the glass seal layer 7, and the center electrode 5 and the terminal electrode 6 are fixed to the insulator 2. In addition, at the time of the heating in a baking furnace, it is good also as baking a glaze layer simultaneously on the surface of the rear end side trunk | drum 10 of the insulator 2, and it is good also as forming a glaze layer in advance.

  Thereafter, the insulator 2 including the resistor 9 and the metal shell 3 including the ground electrode 27 are fixed. More specifically, after inserting the insulator 2 into the metal shell 3, the opening on the rear end side of the metal shell 3 formed relatively thin is crimped radially inward to form the crimp portion 20. Fixed by.

  Finally, the ground electrode 27 is bent and the size of the spark discharge gap 33 formed between the center electrode 5 and the ground electrode 27 is adjusted, and the above-described spark plug 1 is obtained.

  As described above in detail, according to the present embodiment, the range from the front end of the metal shell 3 to 5 mm from the rear end to the rear end side of the metal shell 3 along the axis CL1. A cylindrical resistor 9 is provided between the insulator 2 and the electrode 8 in at least a part of a range where charges can be stored between the metal shell 3 and the metal shell 3. Therefore, the resistor 9 can more reliably prevent the stored charge from flowing into the space between the electrode 8 and the ground electrode 27 more reliably, thereby reducing the capacity discharge current. In particular, according to the present embodiment, the length XL along the axis CL1 of the resistor 9 is sufficiently large to be 36% or more of the length SL along the axis CL1 of the metal shell 3. Therefore, the capacity discharge current can be effectively reduced, and electrode consumption and noise can be extremely effectively suppressed.

  In addition, according to the present embodiment, a generally used resistor may be disposed around the electrode 8, so that fine adjustment work or the like is unnecessary for the resistor 9. Therefore, it is possible to more reliably prevent the productivity from decreasing.

  Furthermore, the resistor 9 is provided corresponding to a portion where the difference in diameter between the inner diameter of the shaft hole 4 and the metal shell 3 is minimized, that is, a portion where more charges are charged. Accordingly, it is possible to further reduce the capacity discharge current, and more effectively suppress electrode consumption and noise.

  In addition, since the volume resistivity of the resistor 9 is 10 milliΩm or more and 10 kiloΩm or less, the capacity discharge current can be more reliably reduced, while the ignitability is more reliably reduced. Can be prevented.

  In addition, since the thickness TH of the resistor 9 is 0.1 mm or more and 2.5 mm or less, the capacity discharge current can be reduced more reliably, and charging between the electrode 8 and the metal shell 3 can be performed. The charged charge can be reduced more reliably. As a result, electrode consumption and the like can be more effectively suppressed.

  Next, after fixing the front end position of the resistor at a position of 4 mm from the front end of the metal shell to the rear end side, as shown in FIGS. 3A, 3B, and 3C, the length IL of the resistor is obtained. Samples of the spark plugs (samples 1 to 11) with various changes, and as shown in FIG. 3 (d), outside the range from the front end of the metal shell to the rear end side of the metal shell up to 5 mm, the insulator Samples of the spark plug (samples A and C) provided with a resistor between the inner peripheral surface of the electrode and the outer peripheral surface of the electrode and samples (samples B and D) of the spark plug not provided with the resistor were prepared. Each sample was subjected to a desktop spark test. The outline of the desktop spark test is as follows. That is, after setting the frequency of the applied voltage to 60 Hz (that is, with 3600 discharges per minute being performed), a voltage was applied to the sample using a 90 mJ full-tracoil, and 0.4 MPa Each sample was discharged for 100 hours in an air atmosphere. Then, after 100 hours, the increase amount of the spark discharge gap size GL (gap increase amount) was measured. In each sample, the volume resistivity of the resistor was 1 Ωm, and the spark discharge gap size GL before the start of the test was 1.0 mm. Further, the length SL of the metal shell along the axis line CL1 was set to 42 mm or 34 mm. Further, the thickness TH of the resistor was set to 1.0 mm.

  Table 1 shows the relationship between the ratio of the resistor length IL to the metal shell length SL (resistor ratio) and the amount of increase in the gap in a sample in which the metal shell length SL is 42 mm. Table 2 shows the relationship between the resistor ratio and the gap increase in a sample in which the metal shell length SL is 34 mm. Further, FIG. 4 shows a graph showing the relationship between the resistor ratio and the gap increase amount in a sample with a length SL of 42 mm and a sample with a length SL of 34 mm. Tables 1 and 2 show the resistance of the resistor when the length of the resistor IL and the rear end of the metal shell are used as a reference and the front end side in the direction of the axis CL1 is in the-direction and the rear end side is in the + direction. The rear end position (resistor rear end position) is shown.

表１，２及び図４に示すように、サンプル１〜１１は、サンプルＡ，Ｂ，Ｃ，Ｄと比較して、ギャップ増加量が低減し、電極の消耗が抑制されることが明らかとなった。これは、火花放電に伴って、電極と主体金具との間に蓄えられた電荷が放出され、中心電極及び接地電極間に容量放電電流が流れるところ、抵抗体を配置したことで容量放電電流を低減できたためであると考えられる。特に、抵抗体割合を３６％以上としたサンプル（サンプル２〜６，８〜１１）は、ギャップ増加量が０．１０ｍｍ以下に低減し、電極の消耗抑制効果に優れることが分かった。

As shown in Tables 1 and 2 and FIG. 4, it is clear that Samples 1 to 11 have a smaller gap increase and less electrode consumption than Samples A, B, C, and D. It was. This is because the electric charge stored between the electrode and the metal shell is released along with the spark discharge, and the capacitive discharge current flows between the center electrode and the ground electrode. This is thought to be due to the reduction. In particular, it was found that the samples (samples 2 to 6, 8 to 11) having a resistor ratio of 36% or more have a gap increase amount reduced to 0.10 mm or less, and are excellent in the electrode wear suppression effect.

  Further, from the comparison between the sample 4 and the sample 5 and the comparison between the sample 9 and the sample 10, even when the resistor is arranged on the rear end side rather than the rear end of the metal shell, the consumption of the electrode is suppressed. I understood that it was planned. This is because the electric field protrudes to the rear end side in the axial direction between the metal shell and the electrode. This is presumably because the capacitive discharge current due to the discharge of the electric charge was reduced by the resistor disposed on the rear end side.

  On the other hand, when attention is paid to Samples 5 and 6 and Samples 10 and 11, in the sample in which the resistor rear end position is +5 mm and the sample in which the resistor rear end position is larger than +5 mm It was found that there was almost no difference in the wear suppression effect. In other words, it can be said that the consumption of the electrode can be suppressed by providing the resistor within a range of 5 mm from the front end of the metal shell to the rear end side from the rear end of the metal shell.

  From the above test results, from the viewpoint of effectively suppressing the consumption of the electrode, the resistor is provided in at least part of the range from the front end of the metal shell to the rear end side from the rear end of the metal shell to 5 mm, It can be said that the length along the axis of the resistor within the range from the front end of the metal shell to the rear end of the metal shell is preferably 36% or more of the length along the axis of the metal shell.

  In addition, generation | occurrence | production of noise can be suppressed by reducing a capacitive discharge current. Therefore, by adopting the above-described configuration, it can be said that there is an effect of noise suppression in addition to an effect of suppression of electrode consumption.

  Next, a spark in which a resistor is provided between a portion corresponding to the middle body portion of the insulator and the metal shell (in other words, a portion where the diameter difference between the inner diameter of the shaft hole and the inner diameter of the metal shell is minimized). A plug sample (Example sample X) and a spark plug sample (Example sample Y) in which a resistor is provided at a portion corresponding to the large diameter portion of the insulator are prepared, and the above-described desktop spark test is performed on each sample. Went. Table 3 shows the results of the test. In each sample, the metal shell length SL was 42 mm, and the resistor length IL was 15 mm. Further, the thickness TH of the resistor was set to 1.0 mm. Furthermore, the resistor ratio was 36%, and the volume resistivity of the resistor was 1 Ωm.

表３に示すように、実施例サンプルＹと比較して、実施例サンプルＸは、電極の消耗抑制効果により優れることが明らかとなった。これは、軸孔の内径と主体金具の内径との径差が小さい部分ほど、蓄えられる電荷が大きくなるため、前記径差の小さい部分に対応して抵抗体を配置したことで、容量放電電流を効果的に低減できたためであると考えられる。

As shown in Table 3, it was revealed that the example sample X is superior to the example sample Y because of the effect of suppressing electrode consumption. This is because, as the diameter difference between the inner diameter of the shaft hole and the inner diameter of the metal shell becomes smaller, the stored charge becomes larger. Therefore, by arranging the resistor corresponding to the smaller diameter difference, the capacity discharge current This is considered to be because of the effective reduction of.

  From the result of the above test, it is preferable to provide a resistor in a portion where the diameter difference between the inner diameter of the shaft hole and the inner diameter of the metal shell is relatively small from the viewpoint of more effectively suppressing electrode consumption and the like. It can be said that it is more preferable to provide a resistor in a portion where the diameter difference between the inner diameter of the shaft hole and the inner diameter of the metal shell is minimized.

  Next, spark plug samples in which the volume resistivity of the resistor was variously changed were prepared, and the above-described desktop spark test was performed on each sample. FIG. 5 shows the results of the test.

  Furthermore, an ignitability evaluation test was performed on spark plug samples in which the volume resistivity of the resistor was variously changed. The outline of the ignitability evaluation test is as follows. Specifically, each sample was mounted on a 4-cylinder DOHC engine with a displacement of 2000 cc and discharged 1000 times with an air-fuel ratio (A / F) of 19. The number of occurrences of discharge abnormality (misfire) was measured based on the discharge waveform during discharge. Here, the sample in which the discharge abnormality did not occur was evaluated as “◯” as being excellent in ignitability, and the number of occurrences of discharge abnormality during 1000 spark discharges was 1 or more and less than 10 times. Was evaluated as “△” because it was slightly inferior in ignitability. Table 4 shows the results of the ignitability evaluation test.

尚、図５及び表４では、比較対象として、抵抗体を設けなかったスパークプラグのサンプルにおける机上火花試験の結果、及び、着火性評価試験の結果を併せて示す。また、各サンプルともに、主体金具の長さＳＬを４２ｍｍとし、抵抗体の長さＩＬを４０ｍｍとし、抵抗体割合を９５％とした。加えて、抵抗体の厚さＴＨを１．０ｍｍとした。

In addition, in FIG. 5 and Table 4, the result of the desktop spark test in the sample of the spark plug which did not provide a resistor as a comparison object, and the result of the ignitability evaluation test are shown together. In each sample, the metal shell length SL was 42 mm, the resistor length IL was 40 mm, and the resistor ratio was 95%. In addition, the thickness TH of the resistor was set to 1.0 mm.

  As shown in FIG. 5, it was found that the sample in which the volume resistivity of the resistor is 10 mΩm or more has a significantly reduced gap increase, and has a very excellent electrode wear suppression effect. This is considered to be because the capacity discharge current was very effectively reduced by making the volume resistivity of the resistor sufficiently large.

  On the other hand, as shown in Table 4, it was confirmed that the sample in which the volume resistivity of the resistor was larger than 10,000 (10 k) Ωm was slightly inferior in ignitability. This is thought to be because the volume resistivity of the resistor was made very large, so that the capacity discharge current was extremely reduced, and as a result, the energy required for ignition could not be obtained. It is done.

  In view of the results of both tests, it can be said that the volume resistivity of the resistor is preferably set to 1 mΩm or more and 10 kΩm or less in order to prevent deterioration of ignitability while suppressing electrode consumption.

  Next, while making the outer shape of the insulator constant, by changing the inner diameter of the shaft hole, a plurality of samples of spark plugs with various changes in the thickness TH of the resistor along the direction orthogonal to the axis are produced. Then, the above-mentioned desktop spark test was conducted. FIG. 6 shows the results of the test. In each sample, the outer diameter of the small diameter portion of the center electrode was 1.0 mm, and the volume resistivity of the resistor was 1 kΩm.

  As shown in FIG. 6, it was found that the sample in which the resistor thickness TH is 0.1 mm or more and 2.5 mm or less can effectively reduce the gap increase. This is because the capacitive discharge current can be more reliably reduced by setting the resistor thickness TH to 0.1 mm or more, while the resistor thickness TH is set to 2.5 mm or less. This is considered to be because an excessive charge stored between the metal shell and the metal shell could be suppressed.

  From the above test results, it can be said that the thickness TH of the resistor along the direction orthogonal to the axis is preferably 0.1 mm or more and 2.5 mm or less in order to more reliably suppress electrode consumption and the like.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the resistor 9 is disposed around the center electrode 5. However, as shown in FIG. 7, when the terminal electrode 65 extends from the front end side in the axis CL <b> 1 direction, A resistor 95 may be provided around the electrode 65.

  (B) In the above embodiment, the center electrode 5 and the terminal electrode 6 are electrically connected via the glass seal layer 7, but the rear end of the center electrode 56 is connected to the terminal electrode as shown in FIG. It is good also as connecting both directly by press-fitting to the front-end | tip part of 66. In this case, since the heat of the center electrode 56 is directly conducted to the terminal electrode 66, the heat extraction of the center electrode 56 can be improved, and the durability of the center electrode 56 can be improved.

  In addition, the method of connecting both is not limited to press-fit joining, for example, it is good also as connecting both by screwing or welding. By connecting the center electrode 56 and the terminal electrode 66 by screwing or welding, the two can be electrically connected in a stable state.

  Further, since the glass seal layer 7 has a function of fixing the terminal electrode 6 to the insulator 2, when the glass seal layer 7 is not provided, in order to fix the terminal electrode 66 to the insulator 26, The shaft hole 46 may be provided with the female screw portion 4F, the terminal electrode 66 may be provided with the male screw portion 6M, and the male screw portion 6M may be screwed into the female screw portion 4F (see, for example, JP-A-57-101365). Further, the terminal electrode 66 may be fixed to the insulator 26 with an adhesive having predetermined heat resistance.

  Further, as shown in FIG. 9, a connection body 71 made of a conductive metal is provided between the center electrode 57 and the terminal electrode 67, and the electrodes 57 and 67 are electrically connected via the connection body 71. It is good. In the case where the connection body 71 is provided, the electrode 87 includes the terminal electrode 67, the connection body 71, and the center electrode 57. Therefore, a resistor 97 may be provided around the connection body 71 in the electrode 87. The connection body 71 may be fixed to the center electrode 57 and the terminal electrode 67 by press-fitting, welding, and screwing.

  In addition, it is preferable to comprise the connection body 71 with the copper and copper alloy which are excellent in thermal conductivity. By forming the connection body 71 from copper or a copper alloy, the heat extraction of the center electrode 57 can be improved, and the durability of the center electrode 57 can be further improved.

  (C) In the above embodiment, the spark plug 1 that ignites the air-fuel mixture by spark discharge is shown as the spark plug, but the spark plug to which the technical idea of the present invention can be applied is not limited to this. . Therefore, a plasma jet spark plug that ignites an air-fuel mixture by generating electric plasma immediately after the spark discharge, and a high-frequency spark plug that generates plasma by applying high-frequency power, or the center The technical idea of the present invention may be applied to an ion current detection plug that generates an ionic current between the electrode and the ground electrode and detects the ionic current to detect a combustion state or the like. In these plugs, electrical energy is input to the plugs in order to generate plasma or to generate ion current. Therefore, when a resistor that connects the center electrode 5 and the terminal electrode 6 in series is provided as before, the input electric energy is lost by the resistor, and the intended function is achieved. However, according to the present invention, loss of electrical energy can be prevented, and each plug can perform its intended function. That is, by applying the technical idea of the present invention to a plasma jet ignition plug, a high-frequency plug, or an ion current detection plug, the intended function of each plug can be exhibited while suppressing electrode consumption and noise. Can do.

  (D) In the above embodiment, the spark discharge gap 33 is formed between the center electrode 5 and the ground electrode 27. However, a noble metal tip is provided on one of the center electrode 5 and the ground electrode 27, and one electrode A spark discharge gap may be formed between the noble metal tip provided on the side and the other electrode. Further, a noble metal tip may be provided on both the center electrode 5 and the ground electrode 27, and a spark discharge gap may be formed between the two noble metal tips.

  (E) In the above embodiment, the case where the ground electrode 27 is joined to the distal end portion 26 of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell). The present invention can also be applied to the case where the ground electrode is formed so as to cut out a part of (see Japanese Patent Laid-Open No. 2006-236906, etc.).

  (F) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

1 ... Spark plug (ignition plug)
2. Insulator (insulator)
3 ... metal shell 4 ... shaft hole 8 ... electrode 9 ... resistor 27 ... ground electrode 33 ... spark discharge gap (gap)
CL1 ... axis

Claims (5)

An insulator having an axial hole extending in the axial direction;
A cylindrical metal shell provided on the outer periphery of the insulator;
A rod-shaped electrode inserted through the shaft hole;
A spark plug that is disposed at the tip of the metal shell and includes a ground electrode that forms a gap with the tip of the electrode;
At least part of the range from the front end of the metallic shell to the rear end side to the rear end side of the metallic shell along the axis, up to 5 mm,
A cylindrical resistor is provided between the inner peripheral surface of the insulator and the outer peripheral surface of the electrode,
The length along the axis of the resistor in the range from the front end of the metal shell to the rear end of the metal shell is 36% or more of the length along the axis of the metal shell. And spark plug.   The spark plug according to claim 1, wherein the resistor is provided in a portion where a difference in diameter between the inner diameter of the shaft hole and the inner diameter of the metal shell is minimized.   The spark plug according to claim 1 or 2, wherein the resistor has a volume resistivity of 10 milliΩm or more.   The spark plug according to any one of claims 1 to 3, wherein the resistor has a volume resistivity of 10 kiloΩm or less.   The spark plug according to any one of claims 1 to 4, wherein a thickness of the resistor along a direction orthogonal to the axis is set to 0.1 mm or more and 2.5 mm or less.

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