JP5971806B2 - Plasma jet ignition plug and manufacturing method thereof - Google Patents

Description

  The present invention relates to a plasma jet ignition plug that ignites an air-fuel mixture or the like by generating plasma and a method for manufacturing the same.

  Conventionally, in a combustion apparatus such as an internal combustion engine, an ignition plug that ignites an air-fuel mixture or the like by spark discharge is used. 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, Plasma jet spark plugs have been proposed.

  In general, a plasma jet ignition plug has a cylindrical insulator having a shaft hole, a center electrode inserted into the shaft hole in a state where the tip surface is submerged than the tip surface of the insulator, and an outer periphery of the insulator. The metal shell is disposed, and an annular ground electrode joined to the tip of the metal shell. The plasma jet ignition plug has a space (cavity portion) formed by the tip surface of the center electrode and the inner peripheral surface of the shaft hole, and the cavity portion has a through hole formed in the ground electrode. It is designed to communicate with the outside via this.

  In addition, in such a plasma jet ignition plug, the air-fuel mixture or the like is ignited as follows. First, a voltage is applied between the center electrode and the ground electrode to cause a spark discharge between the two electrodes. Then, a high energy current is passed between both electrodes to change the discharge state, thereby generating plasma inside the cavity portion. Then, by igniting the generated plasma from the opening of the cavity portion, the air-fuel mixture or the like is ignited.

  Further, from the viewpoint of further improving the ignitability, the plasma jet ignition plug is configured such that the tip of the plasma jet ignition plug protrudes from the inner wall surface of the combustion chamber when the plasma jet ignition plug is attached to an internal combustion engine or the like. A method is conceivable in which the squirting is generated at the center side of the combustion chamber (see, for example, Patent Document 1). When this method is adopted, a cylindrical cylindrical portion is provided at the distal end portion of the metal shell, and the distal end portion of the insulator, that is, the cavity portion is disposed inside the cylindrical portion. The ground electrode is joined to the tip of the cylindrical portion.

JP 2008-177142 A

  By the way, as for the general spark plug, the front-end | tip part of an insulator protrudes rather than the front-end | tip part of a metal shell. Therefore, the tip of the insulator is cooled by direct contact with fresh air flowing into the combustion chamber, and overheating of the tip of the insulator is sufficiently suppressed.

  However, in the plasma jet ignition plug, the tip of the insulator is disposed inside the metal shell, so that fresh air hardly comes into contact with the tip of the insulator. Therefore, the tip of the insulator is likely to be overheated, and there is a risk that early ignition (so-called pre-ignition) using the tip of the insulator as a heat source may occur. In particular, as described above, when the front end portion of the plasma jet ignition plug protrudes from the inner wall surface of the combustion chamber, the amount of heat received by the front end portion (cylindrical portion) of the metal shell and the ground electrode increases. For this reason, the tip of the insulator is also more easily heated, and there is a greater concern about the occurrence of pre-ignition.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a front end of an insulator in a plasma jet ignition plug in which a front end portion projects from an inner wall surface of a combustion chamber when attached to an internal combustion engine or the like. It is to suppress the overheating in the part very effectively and more reliably prevent the occurrence of pre-ignition.

  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 plasma jet ignition plug of this configuration includes a cylindrical insulator having an axial hole extending in the axial direction,
A cylindrical metal shell provided on the outer periphery of the insulator, having a mounting screw for mounting to an internal combustion engine, and having a cylindrical portion on the tip end side in the axial direction of the mounting screw;
A rod-shaped center electrode inserted into the shaft hole so that the tip is located on the rear end side of the tip of the insulator;
A ground electrode provided at the tip of the cylindrical portion;
A cavity portion formed by an inner peripheral surface of the shaft hole and a front end side surface of the center electrode, and opening toward the front end side;
A plasma jet ignition plug provided in the ground electrode, wherein at least a part of the plasma electrode ignition plug includes a through-hole located inside a virtual plane formed by extending an opening of the cavity portion toward the tip end in the axial direction;
The ground electrode is spaced apart from the tip of the insulator;
The cylindrical portion penetrates from the outer periphery to the inner periphery, and has openings that are provided intermittently along the circumferential direction.
The opening area of the opening is S (mm ² ), the length in the axial direction from the mounting screw to the tip surface of the ground electrode is P (mm), and the tip side of the center electrode of the insulator When the maximum thickness along the direction perpendicular to the axis of the part located on the tip side in the axial direction from the surface is T (mm),
S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)}
And P> 1
A plasma jet ignition plug characterized by satisfying

  Note that ln represents a natural logarithm.

  In a general internal combustion engine, the distance from the tip of the female screw portion (end portion on the combustion chamber side) to which the mounting screw of the plasma jet ignition plug is screwed to the inner wall surface of the combustion chamber is about 1 mm. Here, according to Configuration 1, the length P from the mounting screw to the tip surface of the ground electrode is set to be greater than 1 mm. Therefore, when the plasma jet ignition plug having the above configuration 1 is attached to the internal combustion engine, the tip of the plasma jet ignition plug protrudes from the inner wall surface of the combustion chamber. Therefore, there is a greater concern about the overheating of the tip of the insulator and the occurrence of preignition associated therewith.

  In this regard, according to the above-described configuration 1, the ground electrode is configured to be separated from the tip portion of the insulator. Therefore, the amount of heat conducted from the ground electrode to the tip of the insulator can be effectively reduced.

Furthermore, according to the configuration 1, the cylindrical portion disposed in the combustion chamber is provided with a plurality of openings intermittently along the circumferential direction, and the opening area of the opening is defined as S (mm ² ). In this case, S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)} is satisfied. That is, the opening area S corresponds to the amount of fresh air flowing into the metal shell (cylindrical portion), and thus the cooling effect of the insulator tip. By satisfying the above equation, the opening of the insulator tip is received. The cooling effect is greater than the amount of heat (corresponding to the maximum thickness T or length P). As a result, overheating at the tip of the insulator can be effectively suppressed, and in combination with the fact that the ground electrode is separated from the tip of the insulator, overheating of the insulator tip is extremely effective. Can be suppressed. As a result, the occurrence of pre-ignition can be prevented more reliably.

  The relationship between the maximum thickness T and length P and the amount of heat received at the tip of the insulator is as follows. That is, a portion of the insulator that is located on the tip end side in the axial direction from the tip end surface of the center electrode is a portion in which the inner peripheral surface is largely separated from the center electrode. Therefore, the heat is not easily drawn by the center electrode and is a part where overheating is more concerned. The greater the maximum thickness T of this part, the greater the amount of heat received at the tip of the insulator. Further, the protruding amount of the tip surface of the ground electrode with respect to the inner wall surface of the combustion chamber is substantially equal to a value (P-1) obtained by subtracting 1 mm from the length P, and the larger the value of the length P, the more the tip of the insulator. The amount of heat received increases. In the said structure 1, after considering these points, favorable pre-ignition resistance is implement | achieved by prescribing | regulating the opening area S by said Formula.

  Configuration 2. The plasma jet ignition plug of this configuration is characterized in that, in the above configuration 1, the shortest distance between the ground electrode and the tip of the insulator is 0.10 mm or more and 1 mm or less.

  According to Configuration 2, the shortest distance between the ground electrode and the tip of the insulator is 0.10 mm or more. Therefore, the heat of the ground electrode is less likely to be transmitted to the tip portion of the insulator, and overheating of the tip portion of the insulator can be prevented more reliably. As a result, the pre-ignition resistance can be further improved.

  Moreover, according to the said structure 2, since the said shortest distance is 1 mm or less, the voltage (discharge voltage) required in order to produce a spark discharge between a center electrode and a ground electrode can be made small enough. . Therefore, it is possible to more reliably prevent the center electrode, the ground electrode, and the insulator from being consumed due to the spark discharge, and to improve the durability.

Configuration 3. The method of manufacturing a plasma jet ignition plug of this configuration is the method of manufacturing a plasma jet ignition plug according to the above configuration 1 or 2, wherein the metal shell and the ground electrode are configured by separate members.
Including a bonding step of bonding the ground electrode to the tip of the cylindrical portion;
In the joining step, the ground electrode is joined to the tip end portion of the cylindrical portion with a predetermined jig sandwiched between the insulator and the ground electrode.

  According to the configuration 3, the shortest distance between the insulator and the ground electrode can be more reliably and more easily set to an expected value.

  In addition, since the opening portion is provided in the cylindrical portion, by passing the opening portion, the jig can be easily disposed between the insulator and the ground electrode, and the jig is provided with the insulator and It can be easily removed from between the ground electrodes. That is, when the plasma jet ignition plug is used, the opening that contributes to the cooling of the insulator tip can be used as a passage for the jig during the manufacture of the plasma jet ignition plug, and between the insulator and the ground electrode. In addition, the desired gap can be used more reliably and more easily.

It is a partially broken expanded front view which shows the structure of an ignition system. It is a partially broken front view which shows the structure of a spark plug. It is a perspective schematic diagram for demonstrating the formation position of a through-hole. It is an expansion perspective view which shows the opening part etc. which were provided in the cylindrical part. It is the JJ sectional view taken on the line of FIG. It is an expanded sectional view which shows the structure of the front-end | tip part of a spark plug. It is an expanded sectional view which shows the jig | tool etc. which are used in a joining process. It is a graph which shows the result of the pre-ignition-proof evaluation test in the sample which changed length P and opening area S variously after setting maximum thickness T to 4 mm. It is a graph which shows the result of the pre-ignition resistance evaluation test in the sample which changed length P and opening area S variously after setting the maximum thickness T to 1.5 mm. It is a graph which shows the result of the pre-ignition-proof evaluation test in the sample which changed the maximum thickness T and the opening area S after setting length P to 4 mm. It is a graph which shows the result of the pre-ignition-proof evaluation test in the sample which changed the maximum thickness T and the opening area S after setting length P to 6 mm. It is an expanded sectional view showing composition of an opening in another embodiment. It is an expanded sectional view showing composition of an opening in another embodiment.

  Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a partially broken front view showing an ignition system 101 including a plasma jet ignition plug (hereinafter simply referred to as “ignition plug”) 1 and an internal combustion engine EN to which the ignition plug 1 is attached. .

  The internal combustion engine EN has a mounting hole PH through which the spark plug 1 is inserted, and a female screw portion FS is formed in a portion of the internal combustion engine EN where the mounting hole PH is formed. The spark plug 1 is attached to the internal combustion engine EN by a mounting screw 15 described later being screwed into the female screw portion FS. Note that the spark plug 1 attached to the internal combustion engine EN has a tip portion (a lower portion in FIG. 1) disposed in the combustion chamber ER of the internal combustion engine EN. Further, in order to improve the ignitability, the tip of the spark plug 1 is configured to protrude relatively larger toward the center of the combustion chamber ER than the inner wall surface RW forming the combustion chamber ER.

  Next, the configuration of the spark plug 1 will be described in detail. As shown in FIG. 2, the spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like. In FIG. 2, 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.

  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. On the side, a leg length part 13 formed with a smaller diameter than this is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and the leg long portion 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the 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. A rod-like center electrode 5 is inserted on the tip end side of the shaft hole 4. The center electrode 5 includes an inner layer 5A made of a metal having excellent thermal conductivity (for example, copper, copper alloy, pure nickel (Ni), etc.), and an alloy mainly composed of Ni (for example, Inconel (trade name) 600, 601 etc.]. Furthermore, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and the tip thereof is located on the rear end side of the tip of the insulator 2. Moreover, the front-end | tip part of the center electrode 5 is made into the taper shape which tapers toward the front-end | tip side in the axis line CL1 direction.

  A terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Furthermore, between the center electrode 5 of the shaft hole 4 and the terminal electrode 6, a columnar glass seal portion 9 including a conductive metal and glass is disposed. The center electrode 5 and the terminal electrode 6 are electrically connected to each other by the glass seal portion 9 and are fixed to the insulator 2.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a mounting screw (male thread) 15 for mounting the spark plug 1 to the internal combustion engine is formed on the outer peripheral surface thereof. Yes. A hook-shaped seat 16 is formed on the rear end side of the mounting screw 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 at the rear end of the mounting screw 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 metal shell 3 is attached to the combustion device is provided. 1 is provided with a caulking portion 20 for holding the insulator 2.

  In addition, a cylindrical cylindrical portion 21 is formed on the metal shell 3 on the tip end side of the mounting screw 15 in the axis CL1 direction. When the ignition plug 1 is attached to the internal combustion engine EN, most of the cylindrical portion 21 protrudes toward the center of the combustion chamber ER from the inner wall surface RW (see FIG. 1). Further, a ground electrode 27 described later is provided at the tip of the cylindrical portion 21 disposed in the combustion chamber ER.

  A tapered step portion 22 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 step 14 of the metal shell 3 is locked to the step 22 of the metal shell 3. It is fixed by caulking the rear end side opening portion radially inward, that is, by forming the caulking portion 20. An annular plate packing 23 is interposed between the step portions 14 and 22. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas that enters the gap between the leg long portion 13 of the insulator 2 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 24 and 25 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 24. , 25 is filled with powder of talc (talc) 26. That is, the metal shell 3 holds the insulator 2 via the plate packing 23, the ring members 24 and 25, and the talc 26.

  In addition, the tip of the metal shell 3 is formed of an alloy containing Ni as a main component and is joined to a disk-shaped ground electrode 27 (that is, the metal shell 3 and the ground electrode 27 are separated from each other). Member). The ground electrode 27 is joined by welding its outer peripheral portion to the cylindrical portion 21 while being engaged with the tip portion of the cylindrical portion 21. The ground electrode 27 is joined to the metal shell 3 in a state of being slightly separated from the distal end surface of the insulator 2.

  Furthermore, a cavity 31 is formed at the tip of the insulator 2 by the inner peripheral surface of the shaft hole 4 and the tip side surface of the center electrode 5 and is a space that opens toward the tip. In the present embodiment, a voltage is applied between the center electrode 5 and the ground electrode 27, and a large current is applied between the electrodes 5 and 27 in a short time in a state where a spark discharge is generated between the electrodes 5 and 27. As a result, plasma is generated in the cavity portion 31. In the present embodiment, the cavity portion 31 has an inner diameter (1.0 mm or more and 3.0 mm or less in this embodiment) that is constant along the direction of the axis CL1, but the inner diameter of the cavity portion 31 is not necessarily the same. It is not necessary to make it constant along the direction of the axis CL1. Therefore, for example, the cavity portion 31 is tapered toward the distal end side or is tapered toward the distal end side, and the inner peripheral surface of the shaft hole 4 forming the cavity portion 31 is slightly (with respect to the axis CL1). (For example, about ± 5 °) may be inclined.

  The ground electrode 27 has a through hole 28 that penetrates the ground electrode 27 in the thickness direction. At least a part of the through hole 28 is formed in the opening of the cavity portion 31 (the tip of the shaft hole 4 as shown in FIG. ) On the inner side of the virtual plane VC extending to the front end side in the direction of the axis CL1. That is, at least a part of the through hole 28 is formed on the opening of the cavity portion 31, and the cavity portion 31 communicates with the outside through the through hole 28. And the plasma produced | generated in the cavity part 31 is ejected through the through-hole 28 to the exterior.

Furthermore, in this embodiment, as shown in FIGS. 4 and 5, the cylindrical portion 21 penetrates from the outer periphery to the inner periphery and is provided intermittently along the circumferential direction (in this embodiment, at equal intervals). 4) of openings 33. Each opening 33 has a rectangular shape in a cross section perpendicular to the radial direction of the metal shell 3, and the opening region gradually expands from the inner peripheral side to the outer peripheral side along the radial direction of the metal shell 3. It is configured. The opening area S of each opening 33 (mm ² : when the opening area changes along the radial direction as in this embodiment, the opening area S is the minimum value of the opening area. In the present embodiment, the opening area in the inner periphery of the metallic shell 3) is configured to satisfy the following configuration. That is, as shown in FIG. 6, the length in the direction of the axis CL1 from the mounting screw 15 to the tip surface of the ground electrode 27 is P (mm), and the axis CL1 of the insulator 2 from the tip side surface of the center electrode 5 is larger. S ≧ {4 (mm) × ln (P−1)} + {4 (mm), where T (mm) is the maximum thickness along the direction orthogonal to the axis CL1 of the portion located on the front side of the direction Xln (T)} is satisfied. Note that ln represents a natural logarithm.

  In this embodiment, P> 1 is satisfied. In a general internal combustion engine EN, the distance from the internal thread portion FS to the inner wall surface RW is about 1 mm. Therefore, in the present embodiment, by configuring so as to satisfy P> 1, as shown in FIG. 1, in the state where the ignition plug 1 is attached to the internal combustion engine EN, the tip surface of the ground electrode 27 is more than the inner wall surface RW. Projecting toward the center of the combustion chamber ER. P-1 indicates the amount of protrusion of the ground electrode 27 with respect to the inner wall surface RW along the axis CL1. In order to improve the ignitability more reliably, the length P is preferably set to a predetermined value or more (for example, 3 mm or more), and the length P is set to prevent overheating of the ground electrode 27 and the metal shell 3 more reliably. P is preferably set to a predetermined value or less (for example, 6 mm or less). Further, in order to suppress the occurrence of discharge penetrating the insulator 2, the maximum thickness T is preferably set to a predetermined value or more (for example, 1.5 mm or more). The upper limit of the maximum thickness T is set according to the inner diameter of the metal shell 3 and the outer diameter of the center electrode 5.

  Furthermore, in this embodiment, as shown in FIG. 6, the shortest distance L between the ground electrode 27 and the tip of the insulator 2 is configured to be 0.10 mm or more and 1 mm or less.

  Moreover, in this embodiment, in the joining process which joins the ground electrode 27 to the front-end | tip part of the cylindrical part 21, between the insulator 2 and the ground electrode 27, as shown in FIG. The ground electrode 27 is joined to the distal end portion of the cylindrical portion 21 by resistance welding or laser welding in a state where the following flat jig JG is sandwiched. As a result, a gap is more reliably formed between the tip of the insulator 2 and the ground electrode 27, and the shortest distance L is set to 0.10 mm or more and 1 mm or less. The jig JG is inserted into the cylindrical portion 21 through the opening 33 before the ground electrode 27 is joined, and is disposed between the ground electrode 27 and the tip of the insulator 2. Further, the jig JG is pulled out of the cylindrical portion 21 through the opening 33 after joining the ground electrode 27, and is removed from between the ground electrode 27 and the tip of the insulator 2.

  As described above in detail, according to the present embodiment, the ground electrode 27 is configured to be separated from the distal end portion of the insulator 2. Accordingly, the amount of heat conducted from the ground electrode 27 to the tip of the insulator 2 can be effectively reduced.

Furthermore, in this embodiment, the cylindrical part 21 arrange | positioned in the combustion chamber ER is provided with the some opening part 33 intermittently along the circumferential direction, and the opening area of each opening part 33 is S ( mm ² ), S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)} is satisfied. That is, the opening area S corresponds to the amount of fresh air flowing into the inside of the metal shell (cylindrical portion) and thus the cooling effect of the tip of the insulator 2, and by satisfying the above formula, the tip of the insulator 2 is satisfied. The cooling effect exceeds the amount of heat received (corresponding to the maximum thickness T and length P). Thereby, overheating at the front end portion of the insulator 2 can be effectively suppressed, and the overheating of the front end portion of the insulator 2 is coupled with the fact that the ground electrode 27 is separated from the front end portion of the insulator 2. Can be suppressed extremely effectively. As a result, the occurrence of pre-ignition can be prevented more reliably.

  The shortest distance L between the ground electrode 27 and the tip of the insulator 2 is 0.10 mm or more. Therefore, the heat of the ground electrode 27 is less likely to be transmitted to the tip portion of the insulator 2, and overheating of the tip portion of the insulator 2 can be further reliably prevented. As a result, the pre-ignition resistance can be further improved.

  On the other hand, since the shortest distance L is set to 1 mm or less, the voltage necessary for generating a spark discharge between the center electrode 5 and the ground electrode 27 can be sufficiently reduced. Accordingly, it is possible to more reliably prevent the center electrode 5, the ground electrode 27, and the insulator 2 from being consumed due to the spark discharge, thereby improving the durability.

  Furthermore, since the ground electrode 27 is joined to the tip of the cylindrical portion 21 with the jig JG sandwiched between the insulator 2 and the ground electrode 27, the shortest distance L can be more reliably and more reliably. The expected value can be easily obtained.

  In addition, since the cylindrical portion 21 is provided with the opening 33, the jig JG can be easily disposed between the insulator 2 and the ground electrode 27 by passing through the opening 33, and The jig JG can be easily removed from between the insulator 2 and the ground electrode 27. That is, when the spark plug 1 is used, the opening 33 that contributes to cooling the tip of the insulator 2 can be used as a passage for the jig JG when the spark plug 1 is manufactured. It can be used to form a desired gap between the electrodes 27 more reliably and more easily.

Next, in order to confirm the effect achieved by the above-described embodiment, the length P (mm) from the mounting screw to the tip surface of the ground electrode and the position on the tip side of the insulator on the tip side of the center electrode are positioned. Samples of spark plugs with various changes in the maximum wall thickness T (mm) and the opening area S (mm ² ) of the opening were prepared, and a pre-ignition resistance evaluation test was performed on each sample. The outline of the pre-ignition resistance evaluation test is as follows. That is, the sample was mounted on a 1.6 L, 4-cylinder DOHC engine, and the engine was operated for 2 minutes in a fully open state (5500 rpm) with the ignition angle as a predetermined initial value. Thereafter, it was confirmed whether or not pre-ignition occurred during engine operation. When pre-ignition occurred, the ignition angle at that time was specified as the pre-ignition occurrence angle. On the other hand, if preignition does not occur, advance the ignition angle by 1 degree, operate the engine again in the fully open state for 2 minutes, and then check whether preignition has occurred. Was repeated until pre-ignition occurred, and the pre-ignition occurrence angle was specified. Here, it can be said that the sample in which the pre-ignition occurrence angle is 32 degrees or more has good pre-ignition resistance. In each sample, two openings facing each other with the axis line CL1 sandwiched between the cylindrical portions were provided, and the shortest distance L was set to 0.1 mm.

  8 to 11 show the results of the above test. 8 to 11, samples with a pre-ignition generation angle of 32 degrees or more are indicated by circles, and samples with a pre-ignition generation angle of less than 32 degrees are indicated by crosses. FIG. 8 shows the test results of samples in which the maximum thickness T is set to 4 mm and the length P and the opening area S are variously changed. FIG. 9 shows the maximum thickness T set to 1.5 mm. Then, the test result of the sample which changed length P and opening area S variously is shown. Further, FIG. 10 shows the test results of samples in which the maximum thickness T and the opening area S are variously changed with the length P being 4 mm, and FIG. 11 is the maximum with the length P being 6 mm. The test result of the sample which changed variously the thickness T and opening area S is shown. 8 to 11 show approximate curves obtained from test results of samples having good pre-ignition resistance, and formulas of the approximate curves. It can be said that the approximate curve shows a boundary between a sample having good pre-ignition resistance and other samples.

  When the maximum thickness T is 4 mm, ln (T) is about 1.3863 mm and 4 (mm) × ln (T) is about 5.5542. When the maximum thickness T is 1.5 mm, ln (T) is about 0.4055 mm and 4 (mm) × ln (T) is about 1.6219. Further, when the length P is 4 mm, ln (P-1) is about 1.0986 mm and 4 (mm) × ln (P-1) is about 4.3944. In addition, when the length P is 6 mm, ln (P-1) is about 1.6094 mm, and 4 (mm) × ln (P-1) is about 6.4378.

  As shown in FIG. 8, the sample having the maximum wall thickness T of 4 mm has an opening area S of 4 (mm) × ln (P−1) +5.5542 [= 4 (mm) × ln (4)] or more. As shown in FIG. 9, the sample having the maximum wall thickness T of 1.5 mm has an opening area S of 4 (mm) × ln (P −1) +1.6219 [= 4 (mm) × ln (1.5)] It was revealed that the pre-ignition resistance was more reliably improved when the value was equal to or greater than −1) +1.6219 [= 4 (mm) × ln (1.5)].

  Furthermore, as shown in FIG. 10, the sample with a length P of 4 mm has an opening area S of 4 (mm) × ln (T) +4.3499 [= 4 (mm) × ln (3)] or more. 11, the pre-ignition resistance is more reliably improved. As shown in FIG. 11, the sample with the length P of 6 mm has an opening area S of 4 (mm) × ln (T) +6.4378 [ = 4 (mm) × ln (5)] or more, it was found that the pre-ignition resistance is more reliably improved.

  That is, from the above test results, pre-ignition can be effectively suppressed by satisfying S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)}. It became clear. This is because the length P and the maximum thickness T correspond to the amount of heat received at the tip of the insulator, and the opening area is the amount of fresh air flowing into the metal shell, that is, at the insulator tip. It is considered that the tip of the insulator is sufficiently cooled by the fresh air that has flowed into the metal shell by satisfying the above formula, corresponding to the size of the cooling effect.

  From the results of the above test, from the viewpoint of effectively suppressing the occurrence of pre-ignition, the cylindrical portion is provided with a plurality of openings intermittently along the circumferential direction, and the opening area S of the openings is S ≧ It can be said that it is preferable to configure so as to satisfy the expression {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)}.

  Next, samples of spark plugs satisfying S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)} and having different minimum distances L are prepared. About each sample, the above-mentioned preignition-proof evaluation test was done. In this test, a sample having an ignition angle of 34 degrees or more was evaluated as “◎” because it had excellent pre-ignition resistance. On the other hand, a sample having an ignition angle of less than 34 degrees was evaluated as “Δ”.

Table 1 shows the results of the above test. As a sample, the length P is 2 mm, the maximum thickness T is 1.5 mm, the opening area S is 2 mm ² , the length P is 11 mm, and the maximum thickness T is 4.0 mm. What prepared the opening area as 15 mm < ² > was prepared. In addition, each sample was provided with two openings facing each other with the axis CL1 interposed therebetween.

  As shown in Table 1, it was found that the sample having the shortest distance L of 0.10 mm or more has very excellent pre-ignition resistance. This is presumably because the amount of heat conducted from the ground electrode to the insulator was sufficiently reduced.

  From the results of the above test, it can be said that the shortest distance L is more preferably 0.10 mm or more from the viewpoint of more effectively suppressing the occurrence of pre-ignition.

  If the shortest distance L is excessively large, the voltage required to cause a spark discharge between the center electrode and the ground electrode increases excessively, which may lead to a decrease in ignitability and durability. There is. Therefore, it can be said that the shortest distance L is preferably set to 1 mm or less in order to more reliably prevent deterioration of ignitability and durability.

  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) The number of the openings 33 in the above embodiment is an example, and the number is not particularly limited as long as the number is two or more. Therefore, as shown in FIG. 12, two openings 34 may be provided intermittently along the circumferential direction, and as shown in FIG. 13, the openings 35 are intermittently provided along the circumferential direction. One may be provided.

  Moreover, in the said embodiment, although the opening part 33 is provided at equal intervals, it is not necessary to necessarily provide an opening part at equal intervals. However, from the viewpoint of ensuring that fresh air flows through the opening 33 into the metal shell 3 more reliably, the opening is preferably provided at the next position. That is, in a cross section orthogonal to the axis CL1 and passing through one opening, a first imaginary line connecting the axis CL1 and the center along the circumferential direction of the one opening is drawn and the first imaginary line passes through the axis CL. A second virtual line perpendicular to the line is drawn. At this time, it is preferable to form an opening different from the first opening on the other side when the first opening is on the one side with respect to the second virtual line.

  (B) In the above embodiment, the opening 33 has a rectangular shape, but the shape of the opening is not particularly limited. Therefore, for example, the opening may be circular.

  (C) In the above embodiment, the tip of the center electrode 5 is tapered, but the shape of the tip of the center electrode 5 is not particularly limited.

  (D) Although not specifically described in the above embodiment, in order to improve durability, a metal (for example, platinum) having excellent wear resistance is provided at a portion of the center electrode 5 or the ground electrode 27 that can be a starting point of spark discharge. A chip made of an alloy, an iridium alloy, or the like may be provided.

  (E) 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)].

  DESCRIPTION OF SYMBOLS 1 ... Spark plug (plasma jet spark plug), 2 ... Insulator (insulator), 3 ... Main metal fitting, 4 ... Shaft hole, 5 ... Center electrode, 15 ... Mounting screw, 21 ... Cylindrical part, 27 ... Ground electrode, 28 ... Through hole, 31 ... Cavity part, 33 ... Opening part, CL1 ... Axis, JG ... Jig.

Claims (3)

A cylindrical insulator having an axial hole extending in the axial direction;
A cylindrical metal shell provided on the outer periphery of the insulator, having a mounting screw for mounting to an internal combustion engine, and having a cylindrical portion on the tip end side in the axial direction of the mounting screw;
A rod-shaped center electrode inserted into the shaft hole so that the tip is located on the rear end side of the tip of the insulator;
A ground electrode provided at the tip of the cylindrical portion;
A cavity portion formed by an inner peripheral surface of the shaft hole and a front end side surface of the center electrode, and opening toward the front end side;
A plasma jet ignition plug provided in the ground electrode, wherein at least a part of the plasma electrode ignition plug includes a through-hole located inside a virtual plane formed by extending an opening of the cavity portion toward the tip end in the axial direction;
The ground electrode is spaced apart from the tip of the insulator;
The cylindrical portion penetrates from the outer periphery to the inner periphery, and has openings that are provided intermittently along the circumferential direction.
The opening area of the opening is S (mm ² ), the length in the axial direction from the mounting screw to the tip surface of the ground electrode is P (mm), and the tip side of the center electrode of the insulator When the maximum thickness along the direction perpendicular to the axis of the part located on the tip side in the axial direction from the surface is T (mm),
S ≧ {4 (mm) × ln (P−1)} + {4 (mm) × ln (T)}
And P> 1
A plasma jet ignition plug characterized by satisfying   The plasma jet ignition plug according to claim 1, wherein the shortest distance between the ground electrode and the tip of the insulator is 0.10 mm or more and 1 mm or less. The method of manufacturing a plasma jet ignition plug according to claim 1 or 2, wherein the metal shell and the ground electrode are configured by separate members.
Including a bonding step of bonding the ground electrode to the tip of the cylindrical portion;
In the joining step, the ground electrode is joined to the tip portion of the cylindrical portion with a predetermined jig sandwiched between the insulator and the ground electrode. Production method.

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