JP2015115302A - Spark plug and ignition system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug capable of reducing a possibility to generate flashover while preventing a strength of a main component from being reduced.SOLUTION: The spark plug includes: an insulator including a shaft hole in an axial direction; a center electrode disposed in the shaft hole; a bearing surface directly or indirectly in contact with an engine head of an internal combustion engine if mounted in the internal combustion engine; a main component which includes a main component front end portion positioned closer to a front end than the bearing surface and a main component rear end portion positioned closer to a rear end than the bearing surface, and surrounds an outer peripheral part of the insulator; and a grounding electrode mounted in the main component front end portion. The main component front end portion is formed from a metal, and the main component rear end portion includes a resin part formed from an insulative resin.

Description

  The present invention relates to a spark plug technology.

  2. Description of the Related Art Conventionally, in order to reduce the weight of a spark plug, a technique is known in which a cylindrical fixture disposed outside a cylindrical insulator is formed of carbon fiber reinforced plastic (for example, Patent Document 1).

JP-A-60-230387

  Here, when the spark plug is attached to and detached from the engine head, an external force is applied to the cylindrical fixture by a tool. Here, as in Patent Document 1, when the entire cylindrical fixture is made of plastic, the strength of the cylindrical fixture is reduced, so that the possibility of breakage when the spark plug is attached / detached is increased. On the other hand, when the entire tubular fitting of the spark plug is made of metal, the strength can be improved as compared with the case of forming it by plastic, but flashover may occur. When a flashover occurs, a short circuit occurs between the center electrode and the ground electrode, resulting in problems such as no spark discharge occurring between the spark plug electrodes. The flashover is a phenomenon in which current flows between the terminal fitting (terminal) and the cylindrical fixture along the surface of the insulator.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms or application examples.

(1) According to one aspect of the present invention, an insulator having an axial hole along the axial direction, a center electrode disposed in the axial hole, and an engine head of the internal combustion engine when attached to the internal combustion engine A seat surface that is in direct or indirect contact with, a main component front end portion located on the front end side with respect to the seat surface, and a main component rear end portion located on the rear end side with respect to the seat surface; There is provided a spark plug including a main part surrounding an outer peripheral part and a ground electrode attached to the front end part of the main part. The spark plug is characterized in that the front end portion of the main component is made of metal, and the rear end portion of the main component has a resin portion formed of an insulating resin. According to the spark plug of this aspect, the main component front end portion is formed of metal and the main component rear end portion has the resin portion formed of an insulating resin, thereby suppressing a decrease in strength of the main component. The possibility of flashover can be reduced.

(2) In the spark plug according to the above aspect, the rear end portion of the main component may be configured by the resin portion at the rear end. According to the spark plug of this embodiment, since the rear end of the main component rear end is formed of the resin portion, the possibility of occurrence of flashover can be further reduced.

(3) The spark plug according to the above aspect, wherein the rear end portion of the main component has a tool engaging portion for engaging with a tool, and is formed by at least the resin portion of the tool engaging portion. The tool resin portion may have a bigat softening temperature of 125 ° C. or higher. According to the spark plug of this embodiment, it is possible to suppress a decrease in the strength of the main component, and thus it is possible to reduce the possibility that the main component is damaged.

(4) In the spark plug according to the above aspect, the tool resin portion may have substantially the same outer shape in a cross section perpendicular to the axial direction along the axial direction. According to this form of the spark plug, even when an external force is applied to the main component by a tool or the like, the stress concentration (maximum stress value) can be reduced.

(5) The spark plug according to the above aspect, wherein the main component rear end portion has a metal portion formed of metal, and the first portion located at the rear end of the resin portion of the insulator; The shortest distance through the outer surface of the resin part with the metal part may be 5 mm or more, and the withstand voltage of the resin part may be 10 kV / mm or more. According to this form of the spark plug, the possibility of the occurrence of flashover can be further reduced, and the possibility that the resin portion 54 is broken (insulation breakdown) can be reduced.

(6) In the spark plug according to the above aspect, the center electrode includes a first electrode located on a front end side and a second electrode located on a rear end side, and the first electrode is disposed in the shaft hole. A resistor disposed between the electrode and the second electrode may be further included, and a resistance value between the rear end of the second electrode and the front end of the first electrode may be 1 kΩ or less. According to the spark plug of this embodiment, since the resistance value is 1 kΩ, the voltage rise time between the first electrode and the ground electrode can be shortened. On the other hand, although the voltage rise time is shortened, the flashover is likely to occur. However, the occurrence of the flashover can be suppressed by having the resin part formed of the insulating resin at the rear end part of the main component.

(7) Moreover, according to the other form of this invention, an ignition system can be provided. The ignition system according to this aspect includes a spark plug according to the above aspect, a voltage application unit that applies a voltage to the center electrode after a spark discharge between the center electrode and the ground electrode, and ions that flow by application of the voltage. A current detection unit for detecting current. According to the spark plug of this embodiment, the main component rear end portion has the resin portion, so that it is possible to reduce the occurrence of noise that occurs when detecting the ionic current. Thereby, the detection accuracy of the ion current using the current detector can be improved.

  The present invention can be realized in various forms, for example, a spark plug, an ignition system including a spark plug, a spark plug manufacturing method, an ignition system control method, a spark plug, or an ignition system. It can implement | achieve in the form of the vehicle etc. which were equipped with.

It is a fragmentary sectional view of the spark plug as an embodiment of the present invention. It is a figure for demonstrating the manufacturing process of the spark plug of this embodiment. It is a fragmentary sectional view of the spark plug as a comparative example used for the evaluation test. It is a figure which shows the result of flashover evaluation and 1st intensity | strength evaluation. It is a figure which shows the result of 2nd intensity | strength evaluation. It is a figure which shows the result of the 1st evaluation test of the shortest distance Dt. It is a figure which shows the result of the 2nd evaluation test of the shortest distance Dt. It is a figure which shows the comprehensive evaluation result of the shortest distance Dt. It is a figure which shows the result of the evaluation test of resistance value. It is a circuit diagram of an ignition system having an ion current detection function. It is a figure which shows the ion current waveform which appears in an output terminal after completion | finish of spark discharge. It is a figure which shows the ion current waveform at the time of misfire. It is a figure which shows the result of the noise evaluation test of an ignition system.

A. Spark plug configuration and manufacturing method:
FIG. 1 is a partial cross-sectional view of a spark plug 90 as an embodiment of the present invention. Here, for convenience of explanation, the upper side in the figure of the spark plug 90 is the rear end side BS, and the lower side in the figure is the front end side FS. The spark plug 90 surrounds an insulator 10 as an insulator having an axial hole 12 extending along the direction of the axis CL, a center electrode 20 at least partially disposed in the axial hole 12, and an outer periphery of the insulator 10. A main component 50 and a ground electrode 30 attached to the end face of the main component 50 are provided. Here, the main component 50 is a member corresponding to a “cylindrical fixture” used in a conventional art and a “conventional metal fitting” used in a general conventional spark plug.

  The center electrode 20 is a first electrode 21 that is located on the front end side and forms a spark gap with the ground electrode 30, and a terminal fitting that is located on the rear end side of the first electrode 21 and connected to an external circuit. A second electrode 22. Both the first electrode 21 and the second electrode 22 are held in the shaft hole 12. Further, both the first electrode 21 and the second electrode 22 extend along the axis line CL direction. In the shaft hole 12, a resistor 60 is disposed between the first electrode 21 and the second electrode 22 (gap). The resistor 60 is formed of a composition including, for example, glass particles as a main component, ceramic particles other than glass, and a conductive material (for example, silver, copper, copper, etc.). By filling the gap between the first electrode 21 and the second electrode 22 with the resistor 60, the electrodes 21 and 22 are electrically connected. Here, the resistance value between the front end of the first electrode 21 and the rear end of the second electrode (that is, the resistance value of the resistor 60) is preferably 1 kΩ or less, and more preferably 500Ω or less. And more preferably 100Ω or less. The resistance value is measured using a tester.

  The insulator 10 is held by the main component 50. The insulator 10 is formed by firing a ceramic material such as alumina. In the insulator 10, a center body portion 19 having an outer diameter larger than that of the other portion is formed at the center in the axis CL direction of the spark plug 90. A rear end side barrel portion 18 that insulates between the second electrode 22 and the main component 50 is formed on the rear end side BS with respect to the central barrel portion 19. An uneven corrugation 14 is formed on the rear end side outer periphery of the rear end side body portion 18. In addition, an unevenness (streak-like groove) 15 is formed on the front end side outer periphery of the rear end side body portion 18 to improve adhesion to a resin portion 54 described later. A front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 is formed on the front end side FS with respect to the central body portion 19, and a front end side body portion is further provided on the front end side FS of the front end side body portion 17. A distal end portion 13 having an outer diameter smaller than 17 and having a smaller outer diameter toward the distal end FS is formed.

  The ground electrode 30 is bent such that the base end is attached to the main component 50 and the tip is opposed to the first electrode 21. A spark gap for generating a spark is formed between the tip 23 of the first electrode 21 and the ground electrode 30. The tip portion 23 is a portion exposed from the insulator 10 to the tip side FS. For example, when a high voltage of 20,000 to 30,000 volts is applied to the second electrode 22, a spark is generated in a spark gap formed between the first electrode 21 and the ground electrode 30. Here, the part which consists of the front-end | tip part 23 among the spark plugs 90 and the protrusion 11 which protrudes from the main components 50 to the front end side FS among the insulators 10 is also called the ignition part 29.

  The main component 50 is a cylindrical component that holds the insulator 10 by surrounding a portion extending from a part of the rear end side body portion 18 to the front end portion 13 of the insulator 10. The main component 50 includes a metal portion 55 formed of metal and a resin portion 54 formed of insulating resin. The main component 50 includes a tool engaging portion 56, a seal portion 57, and a mounting screw portion 58 in order from the rear end side BS to the front end side FS. A tool (not shown) for attaching the spark plug 90 to the engine head EH is engaged with the tool engaging portion 56 of the main component 50. The tool engaging portion 56 has substantially the same outer shape along the axis CL direction in a cross section (orthogonal cross section) orthogonal to the axis CL direction. In the present embodiment, the tool engaging portion 56 has a hexagonal outer shape in the orthogonal cross section, and the outer shape is substantially the same in any orthogonal cross section. Thus, by making the outer shape in the orthogonal cross section of the tool engaging portion 56 formed by the resin portion 54 substantially the same, even when an external force is applied to the tool engaging portion 56 by a tool or the like, stress concentration ( Maximum stress value) can be reduced. Thereby, possibility that the tool engaging part 56 will be damaged can be reduced.

  The mounting screw portion 58 of the main component 50 has a thread that is screwed into the mounting screw hole 80 of the engine head EH. The seal part 57 of the main component 50 is formed in a hook shape at the base of the mounting screw part 58. An annular gasket 62 formed by bending a plate is fitted between the seal portion 57 and the engine head EH.

  The front end side FS end surface of the seal portion 57 forms a seat surface 51 that directly or indirectly contacts the engine head EH of the internal combustion engine when attached to the internal combustion engine. In the present embodiment, the seat surface 51 indirectly contacts the engine head EH via the gasket 62. Further, in the outer periphery of the portion formed by the metal portion 55 described later in the seal portion 57, an unevenness (streak-like groove) 55p for improving adhesion to the resin portion 54 described later is formed. .

  The main component 50 includes a metal portion 55 formed of a metal such as low carbon steel and a resin portion 54 formed of an insulating resin mainly composed of polyethylene (PE). In the present embodiment, the resin portion 54 is formed of a resin in which PE and glass fiber (GF) are mixed. The resin part 54 and the metal part 55 are connected, and the resin part 54 is disposed on the rear end side BS with respect to the metal part 55.

  In the main component 50, the front end side FS from the seat surface 51 is referred to as a main component front end portion 52, and the rear end side BS from the seat surface 51 is also referred to as a main component rear end portion 53. The main component front end portion 52 is formed of a metal portion 55. The main component rear end portion 53 is formed by a metal portion 55 and a resin portion 54. Specifically, the tool engaging portion 56 forming the main component rear end portion 53 is formed of the resin portion 54. Of the main component rear end portion 53, the seal portion 57 is formed of a metal portion 55 and a resin portion 54. That is, the rearmost end 59 of the main component rear end portion 53 (the rearmost end 59 of the main component 50) is constituted by the resin portion 54. In the present embodiment, since the tool engaging portion 56 is constituted by the resin portion 54, the tool engaging portion 56 is also referred to as a tool resin portion 56.

  The tool engaging portion 56 formed by the resin portion 54 preferably has a bigat softening temperature of 125 ° C. or higher. The bigat softening temperature is calculated based on JIS K7206 (the method for testing the bigat softening temperature of thermoplastics). Here, when the part located in the rear end 59 (rear end 59) of the resin part 54 in the insulator 10 is the first part 10f, the outer surface of the resin part 54 between the first part 10f and the metal part 55 is It is preferable that the shortest distance Dt to pass is 5 mm or more. Moreover, it is preferable that the withstand voltage of the resin part 54 is 10 kV / mm or more. The reason why the shortest distance Dt and the withstand voltage are preferable will be described later. The withstand voltage of the resin portion 54 can be calculated by a known method. Specifically, a test piece having a diameter of 40 mm and a thickness of 5 mm is created using the same material as that of the resin portion 54, and the test piece is sandwiched between electrodes described in JIS C2110. Then, the test piece and the electrode are immersed in insulating oil, a voltage is applied at a boosting rate of 1 kV / 1 second, and the voltage value when dielectric breakdown occurs is divided by the thickness of the test piece. Thereby, the withstand voltage of the test piece is calculated, and the calculated withstand voltage is set as the withstand voltage of the resin portion 54 created using the same material as the test piece.

  FIG. 2 is a view for explaining a manufacturing process of the spark plug 90 of the present embodiment. First, a member preparation process is performed (step S10). The member preparation step is a step of preparing the insulator 10, the first electrode 21, and the second electrode 22. Next, a member assembly process is performed (step S12). In the member assembling step, the first electrode 21 is disposed in the shaft hole 12 of the insulator 10, the resistor 60 is disposed in the shaft hole 12, and then the second electrode 22 is disposed in the shaft hole 12. Later, the assembly 60 is created by heating and compressing the resistor 60. Thereby, each member 10, 21, 22, 60 is united. Next, the metal part 55 of the main component 50 is prepared (metal part preparation step: step S14). The ground electrode 30 before being bent is joined to the metal portion 55. In addition, you may perform a metal part preparation process before step S10 or step S12. Next, the prepared metal part 55 is arranged at a predetermined position of the assembly 100 created in step S12, and then the resin part 54 is created by molding (resin part forming step: step S16). Thereby, the main component 50 including the metal part 55 and the resin part 54 is formed. Next, the ground electrode 30 is bent to form a spark gap (spark gap forming step: step S18). Thereby, the spark plug 90 can be created.

  FIG. 3 is a partial cross-sectional view of a spark plug 90t as a comparative example used in an evaluation test described later. The spark plug 90t is a conventional spark plug, and the main component 50t is formed only of metal. Further, the spark plug 90t is provided with a thin caulking portion 59t on the rear end side of the tool engaging portion 56t of the main part 50t. Further, a thin compression deformation portion 99t is provided between the seal portion 57t and the tool engagement portion 56t, similarly to the caulking portion 59t. Between the inner peripheral surface of the main part 50t from the tool engaging portion 56t to the crimping portion 59t and the outer peripheral surface of the rear end side body portion 18 of the insulator 10, an annular first wire packing 84 and an annular A second wire packing 86 is interposed. A talc (talc) 82 is filled between the first wire packing 84 and the second wire packing 86. Since the other configuration is the same as that of the spark plug 90 (FIG. 1) of the present embodiment, the same configuration is denoted by the same reference numeral and description thereof is omitted.

B. Flashover evaluation test and first strength evaluation:
FIG. 4 is a diagram showing the results of the flashover evaluation and the first intensity evaluation. Sample No. which is a spark plug. 1-No. 3 was used to perform a flashover evaluation test and a first strength evaluation. Sample No. 1 is a spark plug 90t shown in FIG. 2 is a spark plug 90 (FIG. 1) of the present embodiment. Reference numeral 3 denotes a spark plug in which the main components 50 of the spark plug 90 are all formed of an insulating resin (the same material as the resin portion 54 of the present embodiment).

Sample No. 1-No. Reference numeral 3 denotes an M14HEX16 general type plug based on the JIS B 8031 standard, and details are as follows.
-Diameter of mounting screw part 58: 14 mm
・ HEX of tool engaging portion 56, 56t (distance between opposite sides of hexagonal portion): 16 mm
Screw reach (length of mounting screw portion 58 in the axis CL direction): 19 mm
Sample No. 1-No. 3, a corrugation 14 (FIGS. 1 and 3) is formed. In addition, the sample No. of this embodiment. 2 resin part 54 (FIG. 1) was formed using a resin material in which PE was 70% by weight and glass fiber was 30% by weight.

<Flash over evaluation method>
(I) A flashover occurs when a high voltage is applied between the first electrode 21 and the ground electrode 30 when a cable (not shown) is connected to the second electrode 22 without covering the rubber member (coil boot). The voltage (flashover voltage) was measured. Further, the portion of the first electrode 21 facing the tip portion 13 of the ground electrode 30 and the tip portion 13 of the ground electrode 30 is immersed in insulating oil, and the ground electrode 30 is deformed so as to be separated from the tip portion 13 of the first electrode 21 ( That is, the ground electrode 30 is raised) or the ground electrode 30 is removed to prevent the occurrence of spark discharge.
(Ii) The evaluation of a sample in which flashover does not occur even at a maximum voltage of 35 kV or more that may occur in a market engine is “◯”. In addition, the evaluation of the sample in which flashover occurred at a maximum voltage of less than 35 kV was “x”.

<First strength evaluation method>
(I) Sample No. 1-No. When a sample is fastened to a predetermined aluminum jig (bush) using a predetermined plug wrench with a predetermined plug wrench, and the tool engaging portions 56 and 56t are broken. The tightening torque was measured.
(Ii) Evaluation of a sample having a tightening torque of 60 N · m or more, which is a JIS standard of the M14HEX general-purpose plug, was evaluated as “◯”.
In addition, samples having both “flash” evaluation and strength evaluation of “◯” were evaluated as overall evaluation “◯”.

  As shown in FIG. 4, the spark plug 90 (sample No. 2) of the present embodiment has a comprehensive evaluation of “◯”, can reduce the possibility of flashover, and can suppress the strength reduction of the main component 50. It was.

C. Second strength evaluation:
FIG. 5 is a diagram illustrating a result of the second strength evaluation. In the second strength evaluation, sample No. 2, samples having different bigat softening temperatures of the resin portion 54 (FIG. 1) were used. The resin part 54 having a different bigat softening temperature was created by changing the composition of the resin part 54. Specifically, the bigat softening temperature was raised by increasing the ratio of the glass fiber having a composition (ratio of PE and glass fiber) in the resin portion 54. The samples used for the second strength evaluation have bigat softening temperatures of 80 ° C, 100 ° C, 125 ° C, 150 ° C, and 200 ° C.

<Second strength evaluation method>
(I) For samples having different bigat softening temperatures, the temperature (engagement portion temperature) of the resin portion 54 (specifically, the tool engagement portion 56) is changed, and the tool engagement portion 56 is used using a predetermined plug wrench. The sample was clamped with respect to a predetermined aluminum jig (bush) and removed. The tightening torque is 40 N · m.
(Ii) The evaluation of the sample having an engagement portion temperature of 150 ° C. or higher when the tool engagement portion 56 is broken is “◎”, and the evaluation of the sample of less than 150 ° C. is “◯”.

  As shown in FIG. 2, the evaluation of the sample having the bigat softening temperature of the tool engaging portion 56 of 125 ° C. or higher was “◎”, and the decrease in the strength of the tool engaging portion 56 could be further suppressed. Thereby, when the bigat softening temperature of the tool engaging part 56 shall be 125 degreeC or more, possibility that the main component 50 will be damaged can be reduced.

D. Evaluation test of shortest distance Dt:
FIG. 6 is a diagram illustrating a result of the first evaluation test of the shortest distance Dt (FIG. 1) passing through the outer surface of the resin portion 54 between the first portion 10 f and the metal portion 55. FIG. 7 is a diagram illustrating a result of the second evaluation test for the shortest distance Dt. Sample No. which is a spark plug. 1b, No. 1 2ba, No. 2 2bb, No. 2 First and second evaluation tests of the shortest distance Dt (FIG. 1) were performed using 2bc. Sample No. 1b is a spark plug 90t shown in FIG. 2ba, No. 2 2bb, No. 2 Reference numeral 2bc denotes a spark plug 90 (FIG. 1) of the present embodiment. Each sample is a spark plug as an M12HEX14 long reach based on JIS B 8031 standard, and details are as follows.
-Diameter of mounting screw part 58: 12 mm
・ HEX of tool engaging portions 56 and 56t (distance between opposite sides of hexagonal portion): 14 mm
Screw reach (length of mounting screw portion 58 in the axis CL direction): 26.5 mm
Sample No. 1b, No. 1 2ba, No. 2 2bb, No. 2 Corrugation 14 (FIG. 1, FIG. 3) is formed in 2bc.

  Sample No. The withstand voltage of the 2ba resin part 54 at room temperature (20 ° C.) is 5 kV / mm. The withstand voltage of the resin portion 54 of 2 bb at room temperature is 10 kV / mm. The withstand voltage of the 2bc resin portion 54 at room temperature is 15 kV / mm. The withstand voltage was adjusted by changing the composition of the resin portion 54 (grade indicating the type of PE, density of the resin portion 54). Sample No. 2ba, No. 2 2bb, No. 2 2bc has a bigat softening temperature of 125 ° C.

  Sample No. 2ba, No. 2 2bb, No. 2 For each of 2bc, the shortest distance Dt (FIG. 1) was changed within a range of 2 to 20 mm, and an evaluation test of the shortest distance Dt described below was performed.

<First Evaluation Test Method of Shortest Distance Dt>
(I) A flashover occurs when a high voltage is applied between the first electrode 21 and the ground electrode 30 when a cable (not shown) is connected to the second electrode 22 without covering the rubber member (coil boot). The voltage (flashover voltage) was measured. The portion of the first electrode 21 facing the tip portion 13 of the ground electrode 30 is immersed in insulating oil, and the ground electrode 30 is deformed so as to be separated from the tip portion 13 of the first electrode 21. (In other words, the ground electrode 30 is raised) or the ground electrode 30 is removed to prevent the occurrence of spark discharge.
(Ii) Samples in which flashover does not occur even at a maximum voltage of 35 kV or higher that may occur in a market engine are evaluated as “◯”, and samples in which flashover does not occur even at a general coil supply voltage of 40 kV or higher. Was evaluated as “◎”.

  As shown in FIG. 6, sample No. which is a spark plug of the present embodiment. 2ba, No. 2 2bb, No. 2 In 2bc, the evaluation was “◯” or more in any of the shortest distances Dt of 2 to 20 mm, and the possibility of occurrence of flashover could be reduced. Sample No. 2ba, No. 2 2bb, No. 2 For each of 2bc, the evaluation of the sample having the shortest distance Dt of 5 mm or more was “◎”, and the possibility of flashover could be further reduced.

<Second Evaluation Test Method of Shortest Distance Dt>
(I) A cable (not shown) is connected to the second electrode 22 without covering the rubber member (coil boot), and a voltage (predetermined) that is 1 kV lower than the voltage (flashover voltage) at which flashover occurs in the first evaluation test. Voltage) was applied between the first electrode 21 and the ground electrode 30. Further, a predetermined voltage was applied 500 times or 2000 times (that is, ON / OFF of voltage application was repeated), and it was confirmed whether or not the resin portion 54 was broken (penetrated). That is, after the voltage is applied 500 times, if the resin portion 54 is not broken, the remaining 1500 times (total of 2000 times) is applied and then the resin portion 54 is broken. It was confirmed whether or not. In addition, the part facing the front-end | tip part 13 of the 1st electrode 21 and the front-end | tip part 13 of the ground electrode 30 is immersed in insulating oil, and the ground electrode 30 is changed so that it may leave | separate from the front-end | tip part 13 of the 1st electrode 21 ( That is, the ground electrode 30 is raised) or the ground electrode 30 is removed to prevent the occurrence of spark discharge.
(Ii) In the first evaluation test, when the penetration portion (dielectric breakdown location) occurs in the resin portion 54, the evaluation is “x”, and when the penetration portion occurs in the resin portion 54 by applying the voltage 500 times, the evaluation is performed. Is “△”, and the evaluation is “◯” when the penetration portion is generated in the resin portion 54 by 2000 times of voltage application, and the penetration portion is not generated in the resin portion 54 even after 2000 times of voltage application Was evaluated as “◎”.

  As shown in FIG. 7, sample No. with a withstand voltage of 10 kV / mm. For 2bb, the evaluation was “◯” or “◎” regardless of whether the shortest distance Dt was 2 to 20 mm. Sample No. with a withstand voltage of 15 kV / mm was used. The evaluation of “2bc” was “◎” regardless of whether the shortest distance Dt was 2 to 20 mm.

FIG. 8 is a diagram showing a comprehensive evaluation result of the shortest distance Dt. The overall evaluation was determined as follows.
Overall evaluation “△”: the evaluation of FIG. 6 is “◯”, and the evaluation of FIG. 7 is “△”.
Overall evaluation “◯”: the evaluation of FIG. 6 is “○” or “◎”, and the evaluation of FIG.
Overall evaluation “◎”: The evaluation in FIG. 6 is “◯”, and the evaluation in FIG. 7 is “◎”.
・ Comprehensive evaluation “☆”: Both the evaluation in FIG. 6 and the evaluation in FIG. 7 are “◎”.

  As shown in FIG. 8, the withstand voltage of the resin part 54 is 10 kV / mm or more (sample No. 2bb, 2bc), the sample whose shortest distance Dt is 5 mm or more has a comprehensive evaluation of “☆”, and flashover is The possibility of occurrence could be further reduced, and the possibility of the resin portion 54 being broken could be reduced.

E. Resistance evaluation test:
FIG. 9 is a diagram showing the results of resistance value evaluation tests. The samples used for the resistance value evaluation test are the spark plug 90 of this embodiment and the spark plug 90t shown in FIG. The spark plugs 90 and 90t are M14HEX16 general type plugs based on the JIS B 8031 standard, and details are as follows.
-Diameter of mounting screw part 58: 14 mm
・ HEX of tool engaging portion 56, 56t (distance between opposite sides of hexagonal portion): 16 mm
Screw reach (length of mounting screw portion 58 in the axis CL direction): 19 mm
Corrugation 14 (FIGS. 1 and 3) is formed in the spark plugs 90 and 90t.

  The shortest distance Dt of the spark plug 90 used for the resistance value evaluation test is 5 mm. Further, samples having different resistance values of the resistor 60 (resistance values between the rear end of the second electrode 22 and the front end of the first electrode 21) were prepared for the spark plugs 90 and 90t. The resistance values are 100Ω, 500Ω, 1000Ω, 3000Ω, 5000Ω, 10000Ω, and 15000Ω. The resistance value was changed by changing the composition of the resistor 60 (the ratio of glass, ceramics other than glass, and conductive material).

ここで、Ｖａは、スパークプラグ９０ｔのフラッシュオーバー電圧であり、Ｖｂは、スパークプラグ９０のフラッシュオーバー電圧である。なお、向上率の算出に用いるスパークプラグ９０，９０ｔの抵抗体６０の抵抗値は同一である。 <Evaluation method of resistance value>
(I) For the spark plugs 90, 90t in which a cable (not shown) is connected to the second electrode 22 without covering the rubber member (coil boot) and the resistance value of the resistor 60 is changed, the first electrode 21 and the ground electrode The voltage at which flashover occurs when a high voltage is applied between the two (flashover voltage) was measured. When measuring the flashover voltage, the portion facing the tip 13 of the first electrode 21 and the tip 13 of the ground electrode 30 is immersed in insulating oil to prevent the occurrence of spark discharge.
(Ii) The improvement rate was calculated using the following formula (1).

Here, Va is the flashover voltage of the spark plug 90t, and Vb is the flashover voltage of the spark plug 90. In addition, the resistance value of the resistor 60 of the spark plugs 90 and 90t used for calculation of the improvement rate is the same.

  As shown in FIG. 9, the spark plug 90 having a resistance value of 1000Ω or less has an improvement rate of 15% or more. This means that if the resistance value is 1000Ω or less (that is, 1 kΩ or less), the flashover improvement rate by using the resin part 54 made of an insulating resin as the main component rear end portion 53 is increased. . In other words, it can be said that the effect of using the resin part 54 formed of an insulating resin as the main component rear end part 53 is high. This is because the step-up speed at which the voltage rises becomes faster as the resistance value is smaller, and flashover is more likely to occur as the resistance value is smaller. Therefore, the rear end portion 53 of the main component is formed of an insulating resin. This is considered to be due to the fact that the flashover is effectively prevented from occurring, that is, the flashover voltage can be increased. Further, as shown in FIG. 9, the improvement rate is further increased when the resistance value is 500Ω or less, and the improvement rate is highest when the resistance value is 100Ω.

F. An ignition system using a spark plug 90;
FIG. 10 is a circuit diagram 150 (ignition system 150) of an ignition system having an ion current detection function. FIG. 11 is a diagram showing an ion current waveform appearing at the output terminal 136 after the spark discharge is completed. An ignition system 150 shown in FIG. 10 constitutes a circuit similar to the ignition system disclosed in, for example, Japanese Patent Laid-Open No. 2000-68031.

  As shown in FIG. 10, the battery 131 is connected to the primary coil of the ignition coil 134. The engine control computer unit (ECU) 132 sends a pulse signal to the igniter 133 at an appropriate timing, energizes the primary coil of the ignition coil 134 for several milliseconds, and then shuts off. As a result, a negative high voltage is generated at one end of the secondary coil of the ignition coil 134. The secondary side of the ignition coil 134 is connected to the spark plug 90 by a high voltage cable 135. The other end of the secondary coil of the ignition coil 134 is connected to a Zener diode ZD having a rated number of hundreds of volts, and is grounded via a backflow preventing diode D1. A capacitor C1 is connected in parallel to the Zener diode ZD, and one end of the capacitor C1 is connected in series to the two resistors R1 and R2 and grounded. An output terminal 136 is provided between the two resistors R1 and R2 connected in series, and is used as a terminal for detecting an ionic current as a voltage signal. The output terminal 136 is connected to a computer (not shown) and is used for engine control by analyzing ion current. In the above configuration, the Zener diode ZD and the capacitor C1 constitute a voltage application unit that applies a voltage to the first electrode 21 (FIG. 1) immediately after the end of the spark discharge. The two resistors R1 and R2 connected in series constitute a current detection unit that detects an ionic current flowing between the first electrode 21 and the ground electrode 30 (FIG. 1) by the voltage from the voltage application unit.

  When the igniter 133 cuts off the power supply to the ignition coil 134, a negative high voltage (tens of KV to several tens of KV) is applied. Due to this high voltage, the spark gap between the first electrode 21 and the ground electrode 30 breaks down, and the spark discharge continues for several milliseconds at a substantially constant spark discharge voltage. During this time, a discharge current indicated by an arrow 101 flows and the capacitor C1 is charged with a positive voltage. When the spark discharge is completed, the voltage of the first electrode 21 converges after showing a slight vibration waveform due to the slight energy remaining in the ignition coil 134. After the spark discharge is completed, the voltage of the capacitor C1 (for example, 200 to 300 V) is applied to the first electrode 21 (FIG. 1), and an ion current waveform as shown in FIG. That is, when the ion current waveform shown in FIG. 11 appears, it indicates that the engine is normally burned by the spark plug 90.

  FIG. 12 is a diagram showing an ion current waveform at the time of misfire. As shown in FIG. 12, when the engine is not burning normally (when misfiring), a waveform having an ion current smaller than that of FIG. 11 appears as shown in FIG.

  Here, in the ignition system 150 shown in FIG. 10, when a conventional spark plug 90t (FIG. 3) in which the main component 50 is made of metal is used, corona discharge occurs in the vicinity of the rearmost end of the tool engaging portion 56t. As a result, a noise wave due to corona discharge may occur in the ion current waveform. However, by forming the tool engaging portion 56 with resin, generation of noise waves due to corona discharge can be reduced. The noise evaluation test method and the results will be described below.

FIG. 13 is a diagram illustrating a result of a noise evaluation test of the ignition system 150. Sample No. 1c is a sample using the spark plug 90t (FIG. 3) of the comparative example in the ignition system 150. 2 c is a sample using the spark plug 90 (FIG. 1) of the present embodiment in the ignition system 150. Sample No. 1c, No. 1 The spark plugs 90 and 90t used in 2c are M12HEX14 long reach based on JIS B 8031 standard, and the details are as follows.
-Diameter of mounting screw part 58: 12 mm
・ HEX of tool engaging portions 56 and 56t (distance between opposite sides of hexagonal portion): 14 mm
Screw reach (length of mounting screw portion 58 in the axis CL direction): 26.5 mm
-Length of the ignition part 29 (FIG. 1) in the direction of the axis CL: 3.0 mm
-Length of protrusion 11 (FIG. 1) in the direction of the axis CL: 1.5 mm
-Length of the tip 23 (FIG. 1) in the direction of the axis CL: 1.5 mm
・ Spark gap: 1.1mm
The shortest distance Dt (FIG. 1) of the spark plug 90 is 5 mm.

<Noise evaluation test method>
(I) An in-line 4-cylinder, 1.5-liter PFI (Port Fuel Injection) engine is idling at a rotational speed of 650 rpm and ions are applied for 1000 cycles (voltage application to the first electrode 21 is 1000 times) under no-load conditions. The current is sample No. 1c, No. 1 Detection was performed using the ignition system 150 of 2c. Of 1000 cycles, 10% (100 cycles) were intentionally misfired and 90% (900 cycles) were burned.
(Ii) The average value S of the integrated values Sa for each cycle of the ion current waveform (FIG. 11) in the combustion state 900 cycles was calculated. Moreover, the average value N of the integral value Na for every cycle of the ion current waveform (FIG. 12) of misfire state 100 cycles was calculated. A value obtained by dividing the average value S by the average value N (S / N ratio) is taken as the vertical axis of FIG.

  As shown in FIG. 13, the ignition system 150 using the spark plug 90 of the present embodiment has a lower S / N ratio than the ignition system 150 using the spark plug 90t of the comparative example. That is, since the rear end portion 53 (FIG. 1) of the main component has the resin portion 54, the detection accuracy of the ion current using the current detection portion (two resistors R1 and R2 in FIG. 10) can be improved.

G. Variation:
G-1. First modification:
Although all the tool engaging portions 56 of the spark plug 90 of the present embodiment are configured by the resin portion 54, at least a part of the tool engaging portion 56 may be formed by the resin portion 54. Further, the tool engaging portion 56 is preferably constituted by the resin portion 54 from the rear end 59 to the front end side FS up to a predetermined distance. Since at least a part of the tool engaging portion 56 is formed by the resin portion 54, the possibility of flashover is reduced while suppressing a decrease in the strength of the main component, as in the spark plug 90 of the present embodiment. it can. Note that the spark plug 90 has a high probability that a flashover will occur between the second electrode 22 and the rearmost end 59 of the main component 50 closest to the second electrode 22 among the main components 50, so that at least the rearmost end. More preferably, 59 is formed by the resin portion 54.

  Further, a part of the main component rear end portion 53 (FIG. 1) in the axis CL direction may be formed by the resin portion 54 from the inner surface to the outer surface. Even in this case, even when a flashover occurs, the resin portion 54 can insulate the first electrode 21 and the ground electrode 30, so that the possibility that both the electrodes 21 and 30 are short-circuited can be reduced.

G-2. Second modification:
In the above embodiment, the outer shape of the tool engaging portion 56 in the orthogonal cross section is substantially the same, but is not limited thereto. For example, a part of the tool engaging portion 56 may have a small outer shape.
Moreover, in the said embodiment, although the external shape in the orthogonal cross section of the tool engaging part 56 was hexagonal shape, the shape of the tool engaging part 56 is not limited to this. For example, it is good also as Bi-HEX (deformation | decoration 12 angle | corner) shape [ISO22977: 2005 (E)].

G-3. Third modification:
In the above embodiment, the spark plug 90 has the gasket 51 (FIG. 1), but the gasket 51 may not be provided. When the spark plug 90 does not have the gasket 51, the seat surface 51 of the seal portion 57 directly contacts the engine head EH.
Moreover, although the spark plug 90 of the said embodiment had the corrugation 14 (FIG. 1), it does not need to have the corrugation 14. FIG.
Moreover, in the said embodiment, although the spark plug 90 had the resistor 60 (FIG. 1) between the 1st electrode 21 and the 2nd electrode 22 in the axial hole 12, in addition to the resistor 60, an axis line A sealing material may be disposed so as to sandwich the resistor 60 in the CL direction. The sealing material is formed from a material containing, for example, metal powder such as copper or iron and glass powder. In this case, the assembly body 100 is created by disposing the sealing material in the shaft hole 12 together with the resistor 60 and compressing and compressing it (step S12 in FIG. 2).

  The present invention is not limited to the above-described embodiments and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments and the modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 10 ... Insulator 10f ... 1st part 11 ... Protrusion part 12 ... Shaft hole 13 ... Tip part 14 ... Corrugation 17 ... Front end side trunk | drum 18 ... Rear end side trunk | drum 19 ... Central trunk | drum 20 ... Center electrode 21 ... 1st Electrode 22 ... second electrode 23 ... tip portion 29 ... ignition portion 30 ... ground electrode 50, 50t ... main part 51 ... seat surface 52 ... main part front end 53 ... main part rear end 54 ... resin part 55 ... metal part 56 ... Tool engaging part (tool resin part)
56t ... Tool engaging portion 57, 57t ... Seal portion 58 ... Mounting screw portion 59 ... Left end 59t ... Clamping portion 60 ... Resistor 62 ... Gasket 80 ... Mounting screw hole 84 ... First wire packing 86 ... Second Wire packing 90, 90t ... Spark plug 99t ... Compression deformation part 100 ... Assembly body 131 ... Battery 133 ... Igniter 134 ... Ignition coil 135 ... High voltage cable 136 ... Output terminal 150 ... Ignition system CL ... Axis D1 ... Diode C1 ... Capacitor R1 ... Resistance ZD ... Zener diode EH ... Engine head BS ... Rear end side FS ... Front end side Sa ... Integration value Na ... Integration value Dt ... Shortest distance

Claims (7)

An insulator having an axial hole along the axial direction;
A central electrode disposed in the shaft hole;
When mounted on an internal combustion engine, the seat face directly or indirectly in contact with the engine head of the internal combustion engine, the main component tip located on the tip side of the seat face, and the rear end side of the seat face A main part having a main part rear end and surrounding an outer peripheral part of the insulator;
A spark plug provided with a ground electrode attached to the tip of the main component,
The main component tip is formed of metal,
The spark plug according to claim 1, wherein the rear end portion of the main component has a resin portion formed of an insulating resin. The spark plug according to claim 1,
The spark plug is characterized in that the rear end portion of the main component is formed of the resin portion at the rear end. The spark plug according to claim 1 or 2, wherein
The main component rear end portion has a tool engaging portion for engaging with a tool,
The spark plug characterized in that the tool resin portion formed by at least the resin portion of the tool engaging portion has a bigat softening temperature of 125 ° C. or higher. The spark plug according to claim 3, wherein
The spark plug is characterized in that the tool resin portion has substantially the same outer shape in a cross section perpendicular to the axial direction along the axial direction. The spark plug according to any one of claims 1 to 4, wherein
The main component rear end portion has a metal portion made of metal,
The shortest distance passing through the outer surface of the resin part between the first part located at the rear end of the resin part of the insulator and the metal part is 5 mm or more,
A spark plug, wherein a withstand voltage of the resin portion is 10 kV / mm or more. The spark plug according to any one of claims 1 to 5, wherein
The center electrode has a first electrode located on the front end side and a second electrode located on the rear end side,
In the shaft hole, further comprising a resistor disposed between the first electrode and the second electrode,
A spark plug, wherein a resistance value between a rear end of the second electrode and a front end of the first electrode is 1 kΩ or less. An ignition system,
A spark plug according to any one of claims 1 to 6,
A voltage application unit for applying a voltage to the center electrode after a spark discharge between the center electrode and the ground electrode;
An ignition system comprising: a current detection unit configured to detect an ionic current that flows when the voltage is applied.

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