JP2022023348A - Spark plug and manufacturing method of the same - Google Patents

Abstract

To provide a spark plug that can improve the detection accuracy of an ion current and a manufacturing method of the same.SOLUTION: The spark plug includes: an insulator having a shaft hole; and a terminal fitting having a shaft portion disposed in the shaft hole and a head portion connected to the shaft portion and disposed outside the shaft hole. The head portion includes a connection portion to which an ignition coil is electrically connected. The connection portion includes an electrically conductive anti-corrosion film covering a metal member and an insulating film covering the anti-corrosion film. The insulating film is a top surface film, and at least part of the film is 2 μm or less in thickness.SELECTED DRAWING: Figure 2

Description

The present invention relates to a spark plug in which an ignition coil is electrically connected to a terminal fitting and a method for manufacturing the same.

When the terminal to which the ignition coil is connected is connected to the terminal fitting of the spark plug and a high voltage is applied to the terminal fitting, the spark plug generates a discharge between the electrodes and ignites the fuel gas. Atoms and molecules of fuel gas are ionized and ions are generated during combustion. A method of detecting an ion current flowing between the electrodes of a spark plug through a terminal and determining a combustion state is known. If the detection accuracy of the ion current is low, the accuracy of determining the combustion state will decrease. One of the causes of the decrease in the detection accuracy of the ion current is the contact resistance between the insulating film formed on the surface of the terminal fitting and the terminal (Patent Document 1). Patent Document 1 discloses a technique of providing a conductive film covering an insulating film on a terminal fitting in order to reduce the contact resistance of the terminal.

Japanese Unexamined Patent Publication No. 10-89221

However, in the above technique, if the insulating film covered with the conductive film is thick, the resistance value of the insulating film becomes large, so that the detection accuracy of the ion current is lowered.

The present invention has been made to solve this problem, and an object of the present invention is to provide a spark plug capable of improving the detection accuracy of an ion current and a method for manufacturing the same.

To achieve this object, the spark plug of the present invention has an insulator having a shaft hole, a shaft portion arranged in the shaft hole, and a head portion connected to the shaft portion and arranged outside the shaft hole. It is equipped with terminal fittings, the head includes a connection part to which the ignition coil is electrically connected, and the connection part has a conductive anticorrosion film covering a metal member and an insulating film covering the anticorrosion film. , And the insulating film is the outermost film, and at least a part thereof has a thickness of 2 μm or less.

The method for manufacturing a spark plug of the present invention provides a preparatory step for preparing a terminal fitting having an anticorrosion film formed on the head and an insulator in which glass powder is arranged inside a shaft hole, and an anticorrosion film. It is provided with a welding step of fixing the terminal fitting and the insulator by welding the glass by heating the terminal fitting and the glass powder while pushing the shaft portion of the terminal fitting into the glass powder. In the welding process, an insulating film covering the anticorrosion film is formed. After the welding step, a removing step of removing at least a part of the insulating film is provided so that the thickness of at least a part of the insulating film at the connection portion is 2 μm or less.

According to the first aspect, the head of the terminal fitting includes a connection to which the ignition coil is electrically connected. The connection portion includes a conductive anticorrosion coating that covers the metal member and an insulating coating that covers the anticorrosion coating. The insulating film is the outermost film, and at least a part of the insulating film has a thickness of 2 μm or less. As a result, the contact resistance of the terminal connected to the ignition coil is reduced, so that the detection accuracy of the ion current can be improved.

According to the second aspect, the anticorrosion coating contains one or more elements selected from the group consisting of Ni, Cr, Ag and Zn. Thereby, in addition to the effect of the first aspect, anticorrosion property can be ensured.

According to the third aspect, the anticorrosion coating has a thickness of 1 to 100 μm. In addition to the effects of the first or second aspect, it is possible to reduce the occurrence of peeling of the film while ensuring anticorrosion properties.

According to the fourth aspect, a terminal fitting having an anticorrosion coating formed on the head and an insulator in which glass powder is arranged inside the shaft hole of the insulator are prepared, and the shaft portion of the terminal fitting is made of glass. By heating the terminal fittings and the glass powder while pushing them into the powder, the terminal fittings and the insulator are fixed by welding the glass. After the insulating film covering the anticorrosion film is formed, at least a part of the insulating film has a thickness of 2 μm or less at the connection portion where the ignition coil is electrically connected. Part is removed. Since the contact resistance of the terminal connected to the ignition coil of the obtained spark plug is reduced, the detection accuracy of the ion current can be improved.

It is one side sectional view of the spark plug in 1st Embodiment. It is sectional drawing of the connection part which enlarged the part shown by II of FIG. (A) is a cross-sectional view of an insulator in a preparatory step, and (b) is a cross-sectional view of an insulator in a welding step. It is a circuit diagram of an ion current detection device. It is sectional drawing of the spark plug attached to an engine. It is sectional drawing of the connection part of the spark plug in 2nd Embodiment. It is sectional drawing of the connection part of the spark plug in 3rd Embodiment. It is sectional drawing of the spark plug in 4th Embodiment attached to an engine.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a one-sided cross-sectional view of the spark plug 10 with the axis O as a boundary in the first embodiment. In FIG. 1, the lower side of the paper surface is referred to as the front end side of the spark plug 10, and the upper side of the paper surface is referred to as the rear end side of the spark plug 10 (the same applies to FIGS. 2, 3, and 5-8). As shown in FIG. 1, the spark plug 10 includes an insulator 11 and a terminal fitting 20.

The insulator 11 is a substantially cylindrical member having a shaft hole 12 along the axis O. The insulator 11 is made of ceramics such as alumina, which has excellent mechanical properties and insulating properties at high temperatures. The insulator 11 is provided with a flange 13 projecting outward in the radial direction at a position substantially at the center in the axial direction. The center electrode 14 is arranged on the tip end side of the shaft hole 12 of the insulator 11.

The center electrode 14 is a rod-shaped metal member having conductivity. In the center electrode 14, for example, a bottomed cylindrical base material containing Ni as a main component covers a core material containing copper as a main component. It is possible to omit the core material. The center electrode 14 is fixed to the shaft hole 12 of the insulator 11 by welding the conductive glass 15.

The glass 15 contains an amorphous material and a conductive powder. As the amorphous material, for example, B ₂ O ₃ -SiO ₂ system, BaO-B ₂ O ₃ system, SiO ₂ -B ₂ O ₃ -CaO-BaO system and the like can be adopted. As the conductive powder, for example, non-metal conductive materials such as carbon particles (carbon black and the like), TiC particles and TiN particles, and metals such as Al, Mg, Ti, Zr, Cu and Zn can be adopted.

The resistor 16 contains an amorphous material, a ceramic powder, and a conductive powder. As the amorphous material, for example, B ₂ O ₃ -SiO ₂ system, BaO-B ₂ O ₃ system, SiO ₂ -B ₂ O ₃ -CaO-BaO system and the like can be adopted. As the ceramic powder, for example, TiO ₂ , ZrO ₂ , or the like can be adopted. As the conductive powder, for example, non-metal conductive materials such as carbon particles (carbon black and the like), TiC particles and TiN particles, and metals such as Al, Mg, Ti, Zr and Zn can be adopted.

The glass 17 contains an amorphous material and a conductive powder, and has conductivity. As the amorphous material, for example, B ₂ O ₃ -SiO ₂ system, BaO-B ₂ O ₃ system, SiO ₂ -B ₂ O ₃ -CaO-BaO system and the like can be adopted. As the conductive powder, for example, non-metal conductive materials such as carbon particles (carbon black and the like), TiC particles and TiN particles, and metals such as Al, Mg, Ti, Zr, Cu and Zn can be adopted. The glasses 15 and 17 are connected to the resistor 16.

The terminal fitting 20 includes a shaft portion 21 arranged in the shaft hole 12, and a head portion 22 connected to the shaft portion 21 and arranged outside the shaft hole 12. The shaft portion 21 is fixed to the shaft hole 12 of the insulator 11 by the glass 17. The terminal fitting 20 is electrically connected to the center electrode 14 via the glass 15, 17 and the resistor 16. The head 22 includes a connection portion 23. In this embodiment, the connecting portion 23 is located on the rear end surface of the head 22. The connection portion 23 is a portion electrically connected to the ignition coil 51 (see FIG. 4).

FIG. 2 is a cross-sectional view of the connecting portion 23 in which the portion shown by II in FIG. 1 is enlarged. The connecting portion 23 includes a conductive anticorrosion coating 25 covering the metal member 24 and an insulating coating 26 covering the anticorrosion coating 25. The metal member 24 is a material for the shaft portion 21 and the head portion 22, and is made of an iron-based material such as low carbon steel. The anticorrosion coating 25 is made of a material containing one or more elements selected from the group consisting of Ni, Cr, Ag and Zn. The anticorrosion coating 25 reduces corrosion and oxidation of the metal member 24.

When the anticorrosion film 25 is thin, the anticorrosion property of the metal member 24 tends to decrease, and when the anticorrosion film 25 is thick, the anticorrosion film 25 tends to be easily peeled off from the metal member 24. The thickness of the anticorrosion coating 25 at the connecting portion 23 is preferably 1 μm or more and 100 μm or less. This is to reduce the occurrence of peeling of the anticorrosion film 25 while ensuring the anticorrosion property of the metal member 24. In the connecting portion 23, it is desirable that the thickness of the anticorrosion coating 25 in every portion of the connecting portion 23 is 1 μm or more and 100 μm or less. The thickness of the anticorrosion coating 25 is determined by observing the cross section of the connecting portion 23 including the axis O with a scanning microscope (SEM).

The insulating film 26 is an outermost insulating film that covers the anticorrosion film 25. The insulating film 26 is, for example, an oxide film. The insulating film 26 in the connecting portion 23 has at least a part having a thickness of 2 μm or less. The thickness of the insulating film 26 is specified by SEM observation of the cross section of the connecting portion 23 including the axis O.

It will be described back to FIG. The main metal fitting 30 is a substantially cylindrical member made of a conductive metal material (for example, low carbon steel or the like). The main metal fitting 30 surrounds the tip end side of the insulator 11 and holds the insulator 11 inside. A male screw 31 is formed on the outer peripheral surface of the main metal fitting 30. The male screw 31 is a portion to be screwed into a screw hole of an engine (not shown). The ground electrode 32 is connected to the main metal fitting 30. The ground electrode 32 is a conductive metal member. A spark gap 33 is formed between the ground electrode 32 and the center electrode 14.

An example of a method for manufacturing the spark plug 10 will be described with reference to FIG. FIG. 3A is a cross-sectional view of the insulator 11 in the preparation step, and FIG. 3B is a cross-sectional view of the insulator 11 in the welding step.

As shown in FIG. 3A, in the preparatory step, first, the insulator 11 is inserted into a support 40 formed in a cylindrical shape with substantially the same material as the material of the insulator 11, and the insulator is formed at the end face of the support 40. Supports the flange 13 of 11. Next, the center electrode 14 is inserted into the shaft hole 12 of the insulator 11. The glass powder 41, which is the raw material of the glass 15 (see FIG. 1), is put into the shaft hole 12 and filled around the center electrode 14. The glass powder 41 contains a conductive powder. After filling the glass powder 41, the glass powder 41 in the shaft hole 12 is precompressed using a compression bar (not shown).

Next, the glass powder 42, which is the raw material of the resistor 16 (see FIG. 1), is put into the shaft hole 12 and filled on the rear end side of the glass powder 41. The glass powder 42 contains a ceramic powder and a conductive powder. After filling the glass powder 42, the glass powder 42 in the shaft hole 12 is precompressed using a compression bar (not shown).

Next, the glass powder 43, which is the raw material of the glass 17 (see FIG. 1), is put into the shaft hole 12 and filled on the rear end side of the glass powder 42. The glass powder 43 contains a conductive powder. After filling the glass powder 43, the glass powder 43 in the shaft hole 12 is precompressed using a compression bar (not shown).

Separately from this, a terminal fitting 20 having an anticorrosion coating 25 formed on at least the head portion 22 by electrolytic plating or electroless plating is prepared.

In the welding step shown in FIG. 3B, first, the insulator 11 supported by the support 40 is placed in a heating furnace (not shown), and is amorphous contained in, for example, glass powders 41, 42, 43. The insulator 11 is heated in the atmosphere to a temperature (800 to 1000 ° C.) higher than the glass transition point of the material.

Next, the shaft portion 21 of the terminal fitting 20 is inserted into the shaft hole 12 of the insulator 11, and the softened glass powders 41, 42, and 43 are compressed in the axial direction by the shaft portion 21. The glass 15, 17 and the resistor 16 are formed by hotly compressing the softened glass powders 41, 42, and 43 by the terminal fitting 20. When the terminal fitting 20 is heated in the atmosphere, an insulating film 26, which is an oxide film, is formed on the surface of the anticorrosion film 25 of the head 22. A part of the shaft portion 21 enters the glass 17, and the glass 17 is welded to the shaft portion 21 and the insulator 11. The terminal fitting 20 is fixed to the insulator 11 by the hardened glass 17.

After the insulator 11 to which the terminal fitting 20 is fixed is taken out of the heating furnace, the thickness of at least a part of the insulating film 26 at the connection portion 23 of the head 22 is reduced to 2 μm or less in the removing step. , At least a part of the insulating film 26 is removed. The means for removing the insulating film 26 include chemical means and mechanical means.

Examples of the chemical means include immersing the head 22 in an acid or applying a rust removing agent to the head 22 to clean and remove the insulating film 26. Examples of the acid in which the head 22 is immersed are oxalic acid and phosphoric acid. The rust removing agent applied to the head 22 is exemplified by Contact Revival King (registered trademark, Sanhayato Co., Ltd.). The head 22 soaked in the acid or the rust preventive may be shaken, or the head 22 soaked in the acid or the rust preventive may be rubbed.

Examples of the mechanical means include those for removing the insulating film 26 by polishing or grinding. Examples of polishing and grinding include processing in which fixed abrasive grains and free abrasive grains are rubbed against the insulating film 26, and blasting in which the abrasive is supplied to a fluid and the abrasive is made to collide with the insulating film 26.

After removing at least a part of the insulating film 26 in the connecting portion 23, the main metal fitting 30 to which the grounding electrode 32 (see FIG. 1) is connected in advance is assembled to the insulator 11, the grounding electrode 32 is bent, and the spark plug is used. Get 10. After assembling the main metal fitting 30 to the insulator 11, the insulating film 26 at the connecting portion 23 may be removed.

FIG. 4 is a circuit diagram of an ion current detection device 50 including a spark plug 10. The ion current detection device 50 includes an ignition coil 51 including a primary winding 52 and a secondary winding 53. The terminal fitting 20 (see FIG. 2) of the spark plug 10 is electrically connected to the ignition coil 51. The power transistor 54 that interrupts the primary current is connected to the primary winding 52. The center electrode 14 of the spark plug 10 is connected to the first end of the secondary winding 53. The capacitor 55 and the Zener diode 56 are connected in parallel to the second end of the secondary winding 53. The resistor 57 and the diode 58 are connected to the capacitor 55 in parallel. The voltage generated in the resistor 57 is detected at the output terminal 59.

When the power transistor 54 is turned off and the primary current of the primary winding 52 is cut off at the ignition timing of the engine (not shown), a high voltage for ignition is generated in the secondary winding 53, and the center electrode of the spark plug 10 is used. A discharge is generated in the spark gap 33 between the 14 and the ground electrode 32. This ignites the fuel gas. The discharge current at this time charges the capacitor 55. When the atoms and molecules of the fuel gas are ionized and ions are generated during combustion, an ion current flows between the center electrode 14 and the ground electrode 32 of the spark plug 10 due to the voltage of the capacitor 55. Combustion of fuel gas can be detected by detecting the voltage of the output terminal 59 due to the generation of ion current.

FIG. 5 is a cross-sectional view of a spark plug 10 attached to an engine (not shown). In FIG. 5, the main metal fitting 30 is not shown. A plug cap 60 is attached to the spark plug 10. The plug cap 60 is a member for electrically connecting the ignition coil 51 (see FIG. 4) to the head portion 22 of the terminal fitting 20.

The plug cap 60 includes an inner cylinder 61 extending in the axial direction, an outer cylinder 62 connected to the tip side of the inner cylinder 61 in the axial direction, a metal cylinder 63 arranged inside the inner cylinder 61, and the tip of the metal cylinder 63. It has a terminal 64 connected to the side. The inner cylinder 61 is a member made of synthetic resin having electrical insulation. The outer cylinder 62 is a rubber member having electrical insulation. The insulator 11 of the spark plug 10 is fitted in the outer cylinder 62. The plug cap 60 is fixed to the spark plug 10 by the friction generated between the outer cylinder 62 and the insulator 11.

The metal cylinder 63 is a conductive metal member. The ignition coil 51 (see FIG. 4) is electrically connected to the metal cylinder 63. The terminal 64 includes a metal compression coil spring. The terminal 64 is arranged between the rear end surface of the head 22 and the metal cylinder 63, and applies an axial force (restoring force of the spring) to the rear end surface (connection portion 23) of the head 22. The state in which the terminal 64 is in contact with the connection portion 23 is either line contact, surface contact, or point contact.

In the manufacturing process of the spark plug 10, the shaft portion 21 of the terminal fitting 20 is fixed to the shaft hole 12 of the insulator 11 by the glass 17 in the welding process. Of the insulating film 26 formed on the head portion 22 of the terminal fitting 20 in the welding step, at least the insulating film 26 in the connecting portion 23 is removed in the removing step. In the removing step, the thickness of at least a part of the insulating film 26 at the connecting portion 23 is processed to be 2 μm or less. In the manufacturing process after the removal step, when the head 22 is not heated to a temperature higher than the temperature heated in the welding step, the thickness of at least a part of the insulating film 26 in the connecting portion 23 is kept at 2 μm or less. Is done.

When the plug cap 60 is fixed to the spark plug 10 and the terminal 64 hits the connection portion 23, the portion where the thickness of the insulating film 26 of the connection portion 23 is 2 μm or less is electrically destroyed when the ion current is detected. The contact resistance of the terminal 64 is reduced. As a result, the detection accuracy of the voltage of the output terminal 59 due to the generation of the ion current is improved. Since the accuracy of detecting the ion current by the ion current detecting device 50 can be improved, the accuracy of determining the combustion state can be improved.

The connecting portion 23 may have a portion where the thickness of the insulating film 26 is 2 μm or less in a part of the connecting portion 23. This is because a current flows in a portion of the connection portion 23 where the thickness of the insulating film 26 is 2 μm or less, the insulating film 26 in that portion is electrically destroyed, and the contact resistance of the terminal 64 is reduced.

FIG. 6 is a cross-sectional view of the spark plug connection portion 27 in the second embodiment. FIG. 6 is an enlarged partial cross-sectional view of the portion shown by II in FIG. 1, as in FIG. 2. The connecting portion 27 is provided in the spark plug 10 instead of the connecting portion 23 in the first embodiment.

The connecting portion 27 includes a conductive anticorrosion coating 25 covering the metal member 24 and an insulating coating 26 covering the anticorrosion coating 25. The insulating film 26 in the connecting portion 27 has a portion having a thickness of 0 μm (that is, a thickness of 2 μm or less). In this case, when the terminal 64 hits the connection portion 27, the terminal 64 comes into contact with the anticorrosion coating 25, so that the contact resistance of the terminal 64 is reduced. As a result, the accuracy of detecting the voltage of the output terminal 59 due to the generation of the ion current is improved, and the accuracy of detecting the ion current by the ion current detecting device 50 can be improved.

FIG. 7 is a cross-sectional view of the spark plug connection portion 28 according to the third embodiment. FIG. 7 is an enlarged partial cross-sectional view of the portion shown by II in FIG. 1, as in FIG. 2. The connecting portion 28 is provided in the spark plug 10 instead of the connecting portion 23 in the first embodiment.

The connecting portion 28 includes a conductive anticorrosion coating 25 that covers the metal member 24. The insulating film 26 (see FIG. 2) does not exist in the connecting portion 28. The insulating film at the connecting portion 28 has a thickness of 0 μm (that is, a thickness of 2 μm or less). When the terminal 64 hits the connection portion 28, the terminal 64 comes into contact with the anticorrosion coating 25, so that the contact resistance of the terminal 64 is reduced. As a result, the accuracy of detecting the voltage of the output terminal 59 due to the generation of the ion current is improved, and the accuracy of detecting the ion current by the ion current detecting device 50 can be improved.

The fourth embodiment will be described with reference to FIG. In the first to third embodiments, the case where the connection portions 23, 27, and 28 are provided on the rear end surface of the head portion 22 of the terminal fitting 20 of the spark plug 10 has been described. On the other hand, in the fourth embodiment, the spark plug provided with the connecting portion 29 on the side surface of the head 22 will be described. The connecting portion 29 is provided in the spark plug 10 instead of the connecting portion 23 in the first embodiment. The same parts as those described in the first embodiment are designated by the same reference numerals, and the following description will be omitted.

FIG. 8 is a cross-sectional view of a spark plug attached to an engine (not shown). In FIG. 8, the main metal fitting 30 is not shown. A plug cap 70 is attached to the insulator 11. The plug cap 70 is a member for electrically connecting the ignition coil 51 (see FIG. 4) to the head 22.

The plug cap 70 includes an inner cylinder 71 extending in the axial direction, an outer cylinder 72 connected to the tip side of the inner cylinder 71 in the axial direction, a metal cylinder 73 arranged inside the outer cylinder 72, and the inside of the metal cylinder 73. It has a terminal 74 connected to. The inner cylinder 71 is a member made of synthetic resin having electrical insulation. The outer cylinder 72 is a rubber member having electrical insulation. The spark plug insulator 11 is fitted in the outer cylinder 72. The plug cap 70 is fixed to the spark plug by the friction generated between the outer cylinder 72 and the insulator 11.

The metal cylinder 73 is a conductive metal member. The ignition coil 51 (see FIG. 4) is electrically connected to the metal cylinder 73. The terminal 74 is made of a metal ring spring. The terminal 74 is arranged between the side surface of the head 22 and the metal cylinder 73. The terminal 74 applies a radial force (restoring force of the spring) to the side surface of the head 22. The side surface of the head portion 22 of the terminal fitting 20 is a connection portion 29 to which the ignition coil 51 is electrically connected.

The connecting portion 29 includes a conductive anticorrosion coating 25 covering the metal member 24 (see FIG. 2) and an insulating coating 26 covering the anticorrosion coating 25. Similar to the first to third embodiments (see FIGS. 2, 6 and 7), the insulating film 26 in the connecting portion 29 has at least a portion having a thickness of 2 μm or less. As a result, the same effects as those of the first to third embodiments can be obtained.

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

Using the terminal fitting 20 having the anticorrosion coating 25 formed on the head 22, the softened glass powders 41, 42, and 43 are hot-compressed in the heating furnace to heat the glass 15, 17 and the resistor. 16 was formed, and the terminal fitting 20 was welded to the glass 17. At this time, an insulating film 26, which is an oxide film, was formed on the surface of the anticorrosion film 25 of the head 22 heated in the atmosphere.

The head 22 was immersed in an oxalic acid solution to remove at least a part of the insulating film 26. By immersing the head 22 in the oxalic acid solution at different times, the thickness of the insulating film 26 formed on the head 22 was made different. The main metal fitting 30 to which the ground electrode 32 was connected was assembled to the insulator 11, and the ground electrode 32 was bent to produce a spark plug in which an insulating film 26 having various thicknesses was formed on the head 22.

The manufactured spark plug is attached to the engine in which the pressure sensor that detects the pressure in the combustion chamber is arranged, and the contact probe (terminal) electrically connected to the ignition coil 51 of the ion current detection device 50 is attached to the head of the spark plug. It was brought into point contact with 22. The contact probe was pressed against the head 22 with a force that did not mechanically destroy the insulating film 26. The part where the contact probe is pressed is the connection part.

The ion current detection device 50 is operated, and a single high voltage for ignition generated in the secondary winding 53 causes a discharge between the center electrode 14 of the spark plug 10 and the ground electrode 32, which is detected by the pressure sensor. The pressure in the combustion chamber and the voltage at the output terminal 59 were detected. When the fuel gas burns, an ion current is generated between the center electrode 14 and the ground electrode 32, and the pressure in the combustion chamber becomes high. Therefore, the voltage is detected at the output terminal 59 and the pressure detected by the pressure sensor becomes high. .. When the voltage detected by the pressure sensor becomes high, the case where the voltage is detected in the output terminal 59 is judged as "normal", and the case where the pressure sensor detects the pressure but the voltage is not detected in the output terminal 59 is "normal". It was judged to be "abnormal".

After removing the spark plug determined to be normal or abnormal from the engine, SEM image processing of the cross section including the axis O of the connection part to which the contact probe is pressed is performed, and the thickness of the insulating film 26 at the connection part ( The minimum value at the connection part) was measured. The number of spark plugs judged to be "normal" was examined for each of the 10 spark plugs having a thickness of 0 μm to 5 μm, which was obtained by rounding off the first decimal place of the measured value of the thickness of the insulating film 26.

表１は絶縁性皮膜の厚さ（μｍ）と「正常」と判定した数との関係を示す一覧表である。表１に示すように、絶縁性皮膜の厚さが２μｍ以下のときは、３０個全てのスパークプラグが正常と判定された。絶縁性皮膜の厚さが２μｍよりも厚いと、異常と判定されるスパークプラグが現れた。この実施例によれば、絶縁性皮膜の少なくとも一部の厚さが２μｍ以下であるとイオン電流の検知精度を向上できることが明らかになった。

Table 1 is a list showing the relationship between the thickness (μm) of the insulating film and the number determined to be “normal”. As shown in Table 1, when the thickness of the insulating film was 2 μm or less, all 30 spark plugs were judged to be normal. When the thickness of the insulating film was thicker than 2 μm, a spark plug judged to be abnormal appeared. According to this example, it was clarified that the detection accuracy of the ion current can be improved when the thickness of at least a part of the insulating film is 2 μm or less.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It is easy to guess. For example, the shape of the head 22 of the terminal fitting 20 is an example and can be set as appropriate.

In the embodiment, the case where the terminal fitting 20 is fixed to the insulator 11 by welding the glass 17 and then the insulating film 26 of the head 22 is removed has been described, but the present invention is not limited to this. For example, the heating temperature of the head 22 is lowered so that the insulating film 26 cannot be formed on the head 22 of the terminal fitting 20 or the thickness of the insulating film 26 formed on the head 22 becomes thin (glass). The temperature of the heating furnace when welding 17 can be lowered).

In the embodiment, the case where the resistor 16 is arranged in the shaft hole 12 of the insulator 11 has been described, but the present invention is not limited to this. Of course, it is possible to omit the resistor 16. When the resistor 16 is omitted, the glass 15 is omitted, and the center electrode 14 is welded to the shaft hole 12 by the glass 17 that welds the shaft portion 21 to the shaft hole 12.

The ion current detection device 50 (see FIG. 4) is an example. Of course, it is possible to adopt other ion current detection devices. Examples of other ion current detection devices include those disclosed in Japanese Patent Application Laid-Open No. 4-191465.

The plug caps 60 and 70 (see FIGS. 5 and 8) are examples. A plug cap having a terminal in contact with the head 22 is appropriately adopted.

10 Spark plug 11 Insulator 12 Shaft hole 17 Glass 20 Terminal metal fittings 21 Shaft part 22 Head 23, 27, 28, 29 Connection part 24 Metal member 25 Anticorrosion film 26 Insulation film 43 Glass powder 51 Ignition coil

Claims (4)

Insulators with shaft holes and
A terminal fitting having a shaft portion arranged in the shaft hole and a head portion connected to the shaft portion and arranged outside the shaft hole is provided.
The head comprises a connection to which the ignition coil is electrically connected.
The connection portion is a spark plug including a conductive anticorrosion film covering a metal member and an insulating film covering the anticorrosion film.
The insulating film is the outermost film, and at least a part of the spark plug has a thickness of 2 μm or less. The spark plug according to claim 1, wherein the anticorrosion coating contains one or more elements selected from the group consisting of Ni, Cr, Ag and Zn. The spark plug according to claim 1 or 2, wherein the anticorrosion film has a thickness of 1 to 100 μm. Insulators with shaft holes and
A terminal fitting having a shaft portion arranged in the shaft hole and a head portion connected to the shaft portion and arranged outside the shaft hole is provided.
The head comprises a connection to which the ignition coil is electrically connected.
The connection portion is a method for manufacturing a spark plug including a conductive anticorrosion film covering a metal member and an insulating film covering the anticorrosion film.
A preparatory step for preparing the terminal fitting having the anticorrosion film formed on the head and the insulator in which the glass powder is arranged inside the shaft hole.
By heating the terminal fitting and the glass powder while pushing the shaft portion of the terminal fitting provided with the anticorrosion film into the glass powder, the terminal fitting and the insulator are fixed by welding the glass. With a welding process,
In the welding step, an insulating film covering the anticorrosion film is formed.
A method for manufacturing a spark plug, comprising a removing step of removing at least a part of the insulating film so that the thickness of at least a part of the insulating film at the connection portion becomes 2 μm or less after the welding step.

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