JP2014175177A - Spark plug for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve withstand voltage of a spark plug.SOLUTION: A spark plug 1 for an internal combustion engine comprises: a columnar center electrode 100 having a discharging part 150; a cylindrical insulator 300 for holding the center electrode 100 on an inner peripheral side; a cylindrical housing 400 for holding the insulator 300 on an inner peripheral side; and a ground electrode 200 extending from the housing 400 and opposed to the discharging part 150. Spark is discharged in a spark discharging gap P between the discharging part 150 and the ground electrode 200. The center electrode 100 has: a columnar axial core part 110 made of a conductive material and provided with the discharging part 150; a cylindrical protection part 130 made of a conductive material, covering the axial core part 110 from an outer peripheral side, and covered by the insulator 300 from the outer peripheral side; and a cylindrical insulation part 120 made of an insulation material and provided between the axial core part 110 and the protection part 300.

Description

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

  2. Description of the Related Art Conventionally, a spark plug that generates a spark discharge for igniting the fuel in order to burn the fuel in a combustion chamber of an internal combustion engine is known. In general, a spark plug is extended from a columnar center electrode having a discharge portion, a cylindrical insulator that holds the center electrode on the inner peripheral side, a cylindrical housing that holds the insulator on the inner peripheral side, and a housing. And a ground electrode arranged to face the discharge part. Such a spark plug ignites the fuel in the combustion chamber by generating a spark discharge in a spark discharge gap between the discharge portion and the ground electrode in response to a voltage applied to the spark plug from the outside.

  As such a spark plug, Patent Document 1 discloses that an axial core portion made of a conductive material and an oxidation or corrosion of the axial core portion in order to minimize the voltage loss until reaching the discharge portion in the center electrode. The thing which comprised the center electrode from the protection part to suppress is disclosed.

JP-A-5-144545

  In recent years, a supercharged intake engine has been developed as an internal combustion engine to improve fuel efficiency, and the in-cylinder pressure at the time of ignition tends to be higher than that of a conventional engine. In this case, there is a concern that the discharge voltage at the spark plug is higher than before and the voltage applied to the center electrode of the spark plug exceeds the withstand voltage value of the insulator, causing a dielectric breakdown in the insulator. Therefore, the spark plug is required to have a withstand voltage that can withstand a high voltage without causing dielectric breakdown.

  In addition, when a high voltage is applied to the center electrode in the spark plug disclosed in Patent Document 1, the high voltage drops extremely after discharge, and thus the fluctuation of the current value flowing through the center electrode increases. Due to such fluctuation, a skin effect that increases the current density on the surface of the conductor is generated by causing the current to flow through the center electrode so as to include many high-frequency components in which the amplitude of the current value greatly fluctuates in a short time. At this time, in the spark plug disclosed in Patent Document 1, the current including the high-frequency component flows intensively on the outer peripheral surface of the protective portion that is in direct contact with the shaft core portion of the center electrode. The electrons are activated. As a result, the temperature of the outer peripheral surface of the protection part in contact with the insulator rises, and electrons collide from the protection part side toward the insulator, so that the impact ionization of electrons in the insulator is accelerated. This may reduce the withstand voltage of the spark plug.

  The present invention has been made in view of these problems, and an object thereof is to improve the withstand voltage of the spark plug.

  The present invention comprises a columnar center electrode (100) having a discharge part (150), a cylindrical insulator (300) that holds the center electrode on the inner peripheral side, and a conductive material, and the insulator is disposed on the inner peripheral side. And a spark discharge gap (G) between the discharge portion and the ground electrode, and a cylindrical housing (400) that is held on the ground portion, and a ground electrode (200) that extends from the housing and is disposed to face the discharge portion. ), A spark plug (1) for an internal combustion engine that performs a spark discharge, wherein the center electrode is made of a conductive material, and is insulated from the columnar shaft core portion (110) provided with the discharge portion on the outer peripheral side of the shaft core portion. It has a cylindrical protective part (130) covered from the outer peripheral side by an insulator and a cylindrical insulating part (120) made of an insulating material and provided between the shaft core part and the protective part. .

  In the present invention, the center electrode has a cylindrical insulating portion made of an insulating material between a columnar axial core portion made of a conductive material and a cylindrical protective portion on the outer peripheral side. The part and the protection part can be electrically insulated by the insulating part. As a result, since a high voltage is applied to the shaft center portion from the outside and a current containing a large amount of high frequency components flows not on the outer peripheral surface of the protective portion of the center electrode but on the outer peripheral surface of the shaft core portion, The temperature rise of the outer peripheral surface of the protection part covered from the outer peripheral side can be suppressed. Therefore, it is possible to suppress the phenomenon that the impact ionization of electrons in the insulator is accelerated and the withstand voltage of the spark plug is lowered due to the collision of electrons from the center electrode side toward the insulator. .

  In addition, according to the present invention, between the housing that holds the insulator on the inner peripheral side and the shaft core portion of the central electrode held on the inner peripheral side of the insulator, the outer peripheral side of the shaft center portion of the central electrode Since the insulating portion is provided in addition to the insulator, the electric resistance can be increased. Furthermore, since the applied voltage is divided and reduced by the insulating portion and the insulator, the electric field strength in each of the insulating portion and the insulator is relaxed. Therefore, the dielectric breakdown of the insulator can also be suppressed by such an increase in electric resistance and relaxation of the electric field strength.

  According to the dielectric breakdown suppression action of the present invention described above, the withstand voltage of the spark plug can be improved.

  In addition, the code | symbol in the parenthesis described in the claim and the means for solving a problem shows the correspondence with the specific means as described in embodiment mentioned later as one aspect of this invention. However, it does not limit the technical scope of the present invention.

The whole sectional view showing the spark plug in one embodiment. Sectional drawing which shows the center electrode in one Embodiment. Explanatory drawing of the ceramic coating process in one Embodiment. Explanatory drawing of the drawing process in one Embodiment. The characteristic view which shows the relationship between the electric current at the time of the electric current containing a high frequency component producing by the discharge which arises in a spark plug, and time. Explanatory drawing which showed a mode that an electron collided with an insulator. The characteristic view which shows a mode that an electric current value changes with a temperature rise at the time of applying a voltage to the resistance which has the same resistance value. The expanded sectional view which expands and shows VIII in FIG. Sectional drawing which shows the center electrode in the modification 1. FIG. Sectional drawing which shows the center electrode in the modification 2. FIG.

  In the following embodiments, the combustion chamber side of the internal combustion engine is the front end, and the opposite side of the combustion chamber side is the base end.

  As shown in FIG. 1, a spark plug 1 according to an embodiment of the present invention is applied to an internal combustion engine mounted on, for example, an automobile, a two-wheeled vehicle, a cogeneration, a gas pressure pump, and the like, and is placed in a combustion chamber of the internal combustion engine. To generate a spark discharge to burn the fuel. The spark plug 1 includes a housing 400, an insulator 300, a ground electrode 200, a center electrode 100, a glass seal 500, a terminal 600, a resistor 700, and the like.

  The housing 400 is made of a conductive material such as a metal such as carbon steel and has a cylindrical shape. A male screw portion 410 is formed on the outer periphery of the housing 400 so as to be screwed into a female screw portion formed in a cylinder head (not shown) of the internal combustion engine. When the male screw part 410 is screwed into the female screw part, the spark plug 1 is attached to the internal combustion engine.

  The ground electrode 200 is made of a conductive material such as a metal such as a nickel alloy, has a rectangular cross section, and protrudes from the front end of the housing 400 into the combustion chamber. The ground electrode 200 is disposed so as to face the discharge unit 150 that is bent and provided at the tip of the center electrode 100. A discharge unit 210 is provided at a position facing the discharge unit 150 in the ground electrode 200.

  The insulator 300 is made of an insulating material such as ceramic such as alumina and has a cylindrical shape. The insulator 300 has a function of insulating each element of the internal combustion engine and the center electrode 100 so that a voltage applied to the spark plug 1 is applied to the center electrode 100. The insulator 300 is coaxially fitted and held on the inner peripheral side of the housing 400, and protrudes on both sides in the axial direction from the housing 400. A stepped portion 310 formed in a bellows shape is formed at a portion protruding from the housing 400 on the base end side of the insulator 300. The step portion 310 can exhibit a good insulating effect by increasing the insulation distance while reducing the axial dimension of the insulator 300. The insulator 300 has a cylindrical hole-like internal space, and the center electrode 100, the glass seal 500, the terminal 600, and the like are held in the internal space.

  The terminal 600 is made of a conductive material such as a metal such as a steel material, and transmits a voltage applied from the outside to the center electrode 100. The terminal 600 includes a columnar stem portion 620 covered with the insulator 300 from the outer peripheral side, and a terminal portion 610 exposed from the insulator 300. The terminal unit 610 is connected to an external booster such as an ignition coil, and transmits a voltage applied from the booster to the stem unit 620.

  The glass seal 500 which is a conductive member is made of a sintered body such as glass and metal such as copper, and is held in the internal space of the insulator 300. The glass seal 500 is disposed between the stem portion 620 and the center electrode 100. The glass seal 500 seals between the insulator 300 and joins the stem portion 620 and the center electrode 100. The glass seal 500 electrically connects the stem portion 620 and the center electrode 100 by such bonding. Furthermore, by welding with the insulator 300, the internal space of the insulator 300 is sealed to ensure the airtightness of the internal space.

  The resistance portion 700 has a cylindrical shape and is provided so as to be covered with the glass seal 500, and is held in the internal space of the insulator 300. The resistance unit 700 is provided between the terminal 600 and the center electrode 100, thereby reducing radio wave noise by reducing the discharge current of the spark plug 1 immediately before the center electrode 100.

  As a whole, the cylindrical center electrode 100 is covered with the insulator 300 and is held on the inner peripheral side of the insulator 300. As shown in FIG. 2, the center electrode 100 includes an axial core part 110, an insulating part 120, and a protection part 130.

  The shaft core part 110 has an intermediate part 140 and a core body part 160 in order from the discharge part 150 at the front end toward the base end side. The core main body 160 is made of a conductive material such as a metal such as a copper alloy, and is substantially formed in a cylindrical shape. The core main body 160 constitutes the most part of the shaft core 110 that is coaxially disposed on the inner peripheral side of the insulator 300. The core main body 160 is in contact with the proximal end surface of the glass seal 500. As a result, a high voltage is applied to the core body 110 from the glass seal 500.

  The discharge part 150 is made of a conductive material such as noble metal such as iridium, tungsten, or platinum, or nickel, and has a cylindrical shape with a smaller diameter than the core body part 160. The discharge part 150 is provided so as to face the discharge part 210 of the ground electrode 200 at the tip of the shaft core part 110. A spark discharge gap G having a predetermined interval is formed between the discharge part 150 and the discharge part 210. When a high voltage is applied to the discharge unit 150, a potential difference is generated between the discharge unit 150 and the discharge unit 210. As a result, when a potential difference that breaks the insulation of the spark discharge gap G occurs between the discharge parts 150 and 210, a spark discharge occurs in the gap G, and the fuel in the combustion chamber is ignited.

  The intermediate portion 140 is made of a conductive material having good bonding properties to the discharge portion 150 and the core body portion 160, for example, a metal such as a nickel alloy, and is adjacent to the proximal end side of the distal discharge portion 150 in the axial core portion 110. . The intermediate part 140 has a columnar column part 141 and a truncated cone (tapered) truncated cone part 142 arranged coaxially between the discharge part 150 and the core body part 160. The column part 141 has a substantially same diameter as the core body part 160 and extends straight in the axial direction, and is joined to the distal end surface of the core body part 160. The truncated cone part 142 extends in the axial direction so as to gradually reduce and change from substantially the same diameter as the column part 141 to substantially the same diameter as the discharge part 150, and is joined to the base end face of the discharge part 150. The intermediate portion 140 is thus joined to the discharge portion 150 and the core main body portion 160, thereby electrically connecting the elements 150 and 160 to enable voltage application to the discharge portion 150.

  The protection part 130 is made of a conductive material having lower conductivity than the shaft core part 110 and having good heat resistance and oxidation resistance, such as a metal such as nickel or cobalt, and has a cylindrical shape. The protection part 130 is disposed on the coaxial circumference on the outer peripheral side of the shaft core part 110, and is covered with the insulator 300 from the outer peripheral side. Thereby, the outer peripheral surface 132 of the protection part 130 constitutes the outer peripheral surface of the center electrode 110 held by the insulator 300. The protection unit 130 prevents the shaft core 110 from being oxidized or corroded by heat generated by the combustion of fuel in the combustion chamber, an atmosphere in the combustion chamber whose temperature has increased, or the like.

  The insulating part 120 is made of an insulating material such as ceramic such as alumina and has a cylindrical shape. The insulating portion 120 is provided on the coaxial circumference between the shaft core portion 110 and the protection portion 130, so that the core main body portion 160 and the columnar portion of the outer peripheral surface 112 of the shaft core portion 110, particularly in this embodiment, are provided. The outer peripheral surface of 142 is covered. Thereby, the truncated cone part 142 of the axial core part 110 protrudes together with the discharge part 150 at the tip of the axial core part 110 on the ground electrode 200 side of the insulating part 120 in the axial direction. That is, the discharge portion 150 is formed at the tip of the shaft core portion 110 that protrudes beyond the insulating portion 120.

  The insulating part 120 has a flange 121 on the base end side of the body part 122. The flange 121 is provided at a location that covers the proximal end of the axial core 110 opposite to the discharge portion 150 at the tip. The flange portion 121 has a larger diameter than the body portion 122 by protruding in a flange shape from the body portion 122 toward the outer peripheral side. By the flange 121 contacting the base end surface of the protection part 130 in the axial direction, the body part 122 excluding the flange 121 in the insulating part 120 is covered by the protection part 130 from the outer peripheral side. At the same time, the protection part 130 is isolated from the glass seal 500 by the flange 121 because the flange 121 comes into contact with the proximal end surface of the glass seal 500 in the axial direction. Furthermore, in the axial direction, the insulating part 120 protrudes closer to the ground electrode 200 than the protective part 130. Thereby, the protection part 130 further covers the entire part of the insulating part 120 that covers at least the core body part 160.

(Production method)
Next, a method for manufacturing the center electrode 100 used in this embodiment will be described.

  The insulating part 120 is formed by performing a coating process by plasma spraying on the core material 11 in which the intermediate part 140 is welded to the metal bar material used as the shaft core part 110. Specifically, first, the truncated cone part 142 of the core material 11 to which the discharge part 150 is joined is covered with the masking material 22.

  Next, the surface of the core material 11 is polished by shot blasting while rotating the core material 11. After that, as shown in FIG. 3, the core material 11 is rotated, and after undercoating for improving adhesion, a powder body 23 of an insulating material such as dissolved alumina is jetted by the plasma gas 21. Plasma spraying is performed. In this plasma spraying, first, a plasma gas 21 is generated by applying a voltage to the plasma gas injection device 20. And while injecting the plasma gas 21 from the injection port of the plasma gas injection apparatus 20, the powder body 23 is sent to the plasma gas 21 from the powder port formed around the injection port. At the same time, it is injected into the core material 11. The plasma gas 21 injected into the rotating core material 11 forms the insulating layer 122 on the outer peripheral surface of the core material 11. Plasma spraying is terminated when the thickness of the insulating layer 122 to be formed reaches a desired thickness. Here, at the end portion of the core material 11, the large-diameter portion that becomes the flange portion 121 is formed by increasing the thickness of the insulating layer 122.

  After the insulating layer 122 having a desired thickness is formed on the core material 11, the masking material 22 is removed and the outer peripheral surface of the insulating layer 122 is finish-polished. As described above, the base material 12 in which the insulating portion 120 is formed on the outer peripheral surface of the core material 11 is completed by the coating process by plasma spraying.

  The protection part 130 is formed by squeezing the base material 12. Specifically, first, the base material 12 is inserted into the cylindrical material 13 to be the protection unit 130 as a preparation process for the drawing process. Here, the cylindrical member 13 is inserted so as not to cover the large diameter portion of the substrate 12. Next, the base material 12 covered with the cylindrical material 13 as shown in FIG. 4 is press-fitted into the press-fitting hole 31 of the mold member 30 by a linear drive device or the like (not shown). The press-fitting hole 31 is formed with a diameter smaller than the total diameter of the base material 12 and the cylindrical material 13 covering the base material 12. Therefore, by carrying out a squeezing process in which the base material 12 covered with the cylindrical material 13 is press-fitted into the press-fitting hole 31, the cylindrical material 13 is squeezed and plastically deformed, and a protective portion 130 having a desired thickness is formed on the outer periphery of the base material 12. Is formed.

  Through these steps, the center electrode 100 in which the insulating portion 120 is provided between the shaft core portion 110 and the protective portion 130 is completed.

(principle)
Next, the principle of improving the withstand voltage of the spark plug 1 according to the present embodiment will be described.

  As shown in FIG. 5, the spark discharge generated in the spark discharge gap G is classified into two types. Specifically, one of them is a so-called capacitive discharge S1 in which a dielectric breakdown occurs between the spark discharge gaps G due to an initial high voltage, and a large current flows in an extremely short time. Another one is that the air-fuel mixture between the spark discharge gaps G is ionized by the capacitive discharge S1, and the current easily flows through the spark discharge gap G, so that the voltage is lower than the voltage at the capacitive discharge S1. This is so-called induction discharge S2 in which discharge is performed by voltage. During the transition from the capacitive discharge S1 to the induction discharge S2, the current value varies greatly in a short time. Therefore, the current flowing through the center electrode 100 includes a high-frequency component in which the amplitude of the current value varies greatly within a short time. Here, in general, when a current flows through a cylindrical conductor, in the case of a direct current, a uniform current density is obtained in a circular cross section of the conductor. On the other hand, in the case of an alternating current, as the frequency of the alternating current increases, a phenomenon called a skin effect occurs in which the current density is larger on the conductor surface than in the conductor.

  Therefore, assuming a comparative example in which the shaft core part 110 and the protection part 130 are in direct contact as in the prior art, the outer surface 132 of the protection part 130 on the outer peripheral surface 132 of the central electrode 100 through which a current containing a high-frequency component flows flows. An effect will occur. Due to the skin effect, when a current flows on the outer peripheral surface 132 of the protection unit 130, that is, the outer peripheral surface of the center electrode 100, the cross-sectional area through which the current flows substantially decreases as the electrode 100 as a whole. The value increases. Since the increase in resistance value causes local heat generation due to Joule heat, the electrons 40 that have obtained thermal energy as shown in FIG. 6 are connected to the outer peripheral surface 132 of the protection unit 130 that is the outer peripheral surface of the center electrode 100. It is discharged to the insulator 300 that has come into contact with it and comes to collide actively. As a result, a phenomenon called collision ionization occurs in which electrons 40 collide with particles (for example, ceramic particles) constituting the insulator 300 and new electrons are emitted from the particles. In this manner, in the insulator 300, the collision of electrons in the radial direction is repeated, and when the electrons reach the housing 400, the insulation breakdown of the insulator 300 between the center electrode 100 and the housing 400 occurs. There is a concern that current will flow.

  Also, as shown in FIG. 7, the current does not flow in accordance with the proportional relationship of Ohm's law as the voltage increases. This is because, when a high voltage is applied, a Schottky effect in which the energy emitted by the electrons is reduced occurs, so that electrons are easily emitted and a large amount of current flows. Further, the Schottky effect is more likely to occur in the case of B at a higher temperature than in the case of A at a lower temperature. Therefore, in the case of the comparative example as described above, as the temperature rises, the current flows over the outer peripheral surface 132 of the protection unit 130 beyond the leakage current, which is a small amount of current flowing through the insulator 300, thereby insulating the insulator 300. There are further concerns that make destruction easier.

  On the other hand, in the center electrode 100 of the present embodiment with respect to these concerns, as shown in FIG. 8, an insulating portion is provided between the shaft core portion 110 and the protective portion 130 on the outer peripheral side of the shaft core portion 110. Since 120 is provided, the insulating part 120 insulates the shaft core part 110 and the protection part 130, and suppresses a current from flowing through the protection part 130. As a result, the current is likely to flow through the shaft core portion 110 that is the shortest path between the discharge portion 150 and the glass seal 500, and the skin effect described above is not the outer peripheral surface 132 of the protection portion 130 in the center electrode 100. This occurs at the outer peripheral surface 112 of the shaft core portion 110. Therefore, on the outer peripheral surface 132 of the protection part 130 which is in contact with the insulator 300, it is possible to suppress an increase in temperature due to a current flowing due to the skin effect. According to this, both the phenomenon in which the electrons 40 actively collide with the insulator 300 and the phenomenon in which more current than that caused by the leakage current flows are made difficult to occur, and the dielectric breakdown of the insulator 300 is suppressed. Can do.

  In addition to the above, in this embodiment, in order to suppress the dielectric breakdown of the insulator 300, it is considered to reduce the electric field strength between the shaft core portion 110 and the housing 400. Here, in general, the electric field strength is determined by the charge density in each of the shaft core portion 110 and the housing 400, the distance between these elements 110 and 400, and the like. However, in the present embodiment, by focusing on the relaxation of the electric field strength by changing the dielectric constant of the insulating material, the two insulating portions 120 and the insulator 300 are interposed between the shaft core portion 110 and the housing 400. Insulating material is provided. As a result, the voltage applied between the elements 110 and 400 is divided and reduced by the insulating portion 120 and the insulator 300, so that the polarization generated in each insulating material between the elements 110 and 400 is relaxed. As a result, the force acting on the electrons 40 between the elements 110 and 400 is reduced because the electric field strength in each of the insulating portion 120 and the insulator 300 is relaxed. It can suppress that dielectric breakdown arises by receiving.

  Moreover, in this embodiment, the insulating portion 120 is provided together with the insulator 300 as an insulating material between the shaft core portion 110 and the housing 400, so that the electrical resistance between the elements 110 and 400 is increased. By such an increase in electrical resistance, the function of suppressing the dielectric breakdown of the insulator 300 is enhanced.

(effect)
Hereinafter, the effect of this embodiment will be described.

  In the above-described embodiment, the center electrode 100 has a cylindrical shape made of an insulating material between a columnar shaft core portion 110 made of a conductive material and a cylindrical protective portion 130 made of a conductive material on the outer peripheral side. Since the insulating portion 120 is provided, the elements 110 and 130 can be electrically insulated by the insulating portion 120. As a result, since a high voltage is applied from the outside and a current containing a large amount of high-frequency components flows not on the outer peripheral surface of the protection portion 130 but on the outer peripheral surface of the shaft core portion 110 in the center electrode 100, the cylindrical insulator 300 causes the current to flow. The temperature rise of the outer peripheral surface of the protection part 130 covered from the outer peripheral side can be suppressed. Therefore, the phenomenon in which the insulator 300 causes dielectric breakdown at a voltage value lower than the set voltage value due to the collision of the electrons 40 from the central electrode 100 side toward the insulator 300 can be suppressed.

  At the same time, between the cylindrical housing 400 that holds the insulator 300 on the inner peripheral side and the shaft portion 110 of the center electrode 100 that is held on the inner peripheral side of the insulator 300, Since the insulating part 120 on the outer peripheral side of the core part 110 is provided in addition to the insulator 300, the electric resistance can be increased. Furthermore, since the applied voltage is divided and reduced by the insulating part 120 and the insulator 300, the electric field strength in each of the elements 120 and 300 is relaxed. Therefore, the dielectric breakdown of the insulator 300 can be suppressed also by such an increase in electrical resistance and relaxation of the electric field strength.

  According to the dielectric breakdown suppression action of the present embodiment described above, the withstand voltage of the spark plug 1 can be improved.

  Further, in the present embodiment, the protection part 130 is made of a conductive material having lower conductivity than the shaft core part 110. According to this, the current flowing due to the voltage applied to the spark plug 1 is more likely to flow through the shaft core part 110 than the protection part 130. Therefore, the current including the high frequency component generated by the high voltage flows not on the outer peripheral surface of the protective portion 130 but on the outer peripheral surface of the shaft core portion 110, so that the dielectric breakdown of the insulator 300 due to the temperature rise on the outer peripheral surface is suppressed. can do. Therefore, it is possible to contribute to improvement of the withstand voltage of the spark plug 1.

  Further, since the insulating part 120 and the protection part 130 are provided on the circumference coaxial with the shaft core part 110, the electric field distribution is in the circumferential direction on the outer peripheral side of the central electrode 100 composed of the elements 120, 130, 110. It becomes uniform. According to this, in the insulator 300 that holds the center electrode 100 from the outer peripheral side, it is possible to suppress a situation in which dielectric breakdown is likely to occur due to an increase in electric field strength due to local concentration of charge. be able to. Therefore, it is possible to contribute to improvement of the withstand voltage of the spark plug 1.

  In the present embodiment, a potential difference is generated between the elements 110 and 130 due to the improvement in insulation between the shaft core part 110 and the protection part 130. Therefore, when a voltage is applied to the discharge part 150 in the shaft core part 110, there is a concern that a discharge may occur between the discharge part 150 and the protection part 130 instead of discharging at the spark discharge gap G between the discharge parts 150 and 210. The However, the insulating portion 120 of the present embodiment covers the shaft core portion 110 in the vicinity of the discharge portion 150 by covering the intermediate portion 140 adjacent to the proximal end side of the distal discharge portion 150 with the shaft core portion 110 from the outer peripheral side. Thus, it is possible to reliably insulate the protection portion 130 on the outer peripheral side of the insulation portion 120. At the same time, the insulating part 120 of the present embodiment protrudes further toward the ground electrode 200 than the protective part 130, so that the discharge part 150 at the tip of the axial center part 110 protrudes further toward the ground electrode 200 than the insulating part 120. Therefore, it is possible to reliably insulate the protection unit 130. According to these, since the phenomenon (lateral jump) that discharges from the shaft core part 110 to the protection part 130 and causes insulation failure can be suppressed, the withstand voltage is improved without impairing the reliability of the spark plug 1. It becomes possible.

  In addition, since the flange 121 having a large diameter in the insulating part 120 isolates the protective part 130 and the glass seal 500 at a place covering the base end opposite to the discharge part 130 at the tip in the axial center part 110, The applied voltage transmitted from the glass seal 500 to the center electrode 100 is not easily transmitted to the protection unit 130. Thereby, the current generated by the applied voltage is likely to flow through the shaft core portion 110, but is difficult to flow through the protection portion 130. Therefore, it is possible to suppress a situation in which the current flows through the protection unit 130 and the insulator 300 breaks down. Therefore, it is possible to contribute to an improvement in the withstand voltage of the spark plug 1.

(Other embodiments)
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can be applied to various embodiment.

  For example, as illustrated in FIG. 9, in the first modification, the protection unit 130 may not protrude from the insulating unit 120 toward the ground electrode 200. Further, as shown in FIG. 10, in the second modification, the flange 121 may not be formed. Furthermore, in the modification 3, the insulation part 120 does not need to be formed in coaxial circle shape.

  Furthermore, in Modification 4, the method of forming the insulating portion 120 on the core material 11 may be a method of fitting and inserting the core material 11 into a cylindrical insulating material. Or in the modification 5, the method of forming the insulation part 120 in the core material 11 inserts the core material 11 in the cylindrical insulation material which heat-shrinks, and also shrink | contracts an insulating material by heating, and it is set as the insulation part 120. It may be a method.

  In addition, in the modification 6, the insulating part 120 may cover all of the intermediate part 140 other than the part where the discharge part 150 is joined.

  DESCRIPTION OF SYMBOLS 1 Spark plug, 100 center electrode, 110 axial center part, 112 core outer peripheral surface, 120 insulation part, 121 collar part, 130 protection part, 140 intermediate part, 141 pillar part, 142 truncated cone part, 150 discharge part, 160 core main body Part, 200 ground electrode, 210 discharge part, 300 insulator, 400 housing, 500 glass seal, 600 terminal, 700 resistor, G spark discharge gap

Claims (6)

A columnar center electrode (100) having a discharge part (150), a cylindrical insulator (300) for holding the center electrode on the inner peripheral side, and a conductive material, and holding the insulator on the inner peripheral side A cylindrical housing (400) that extends, and a ground electrode (200) that extends from the housing and is disposed so as to face the discharge portion, and a spark between the discharge portion and the ground electrode. A spark plug (1) for an internal combustion engine that sparks in a discharge gap (G),
The center electrode is made of a conductive material, and a columnar shaft core portion (110) provided with the discharge portion;
A cylindrical protective part (130) made of a conductive material and covered from the outer peripheral side by the insulator on the outer peripheral side of the shaft core part, and made of an insulating material and provided between the shaft core part and the protective part A spark plug for an internal combustion engine comprising a cylindrical insulating portion (120).   The spark plug for an internal combustion engine according to claim 1, wherein the protection part is made of a conductive material having lower conductivity than the shaft core part.   The spark plug for an internal combustion engine according to claim 1, wherein the insulating portion and the protection portion are provided on a circumference coaxial with the shaft core portion. The shaft core portion has a middle portion adjacent to the discharge portion on the base end side with respect to the discharge portion at the tip,
The spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein the insulating portion covers the intermediate portion from an outer peripheral side. The insulating part protrudes to the ground electrode side than the protective part,
5. The shaft core portion further protrudes toward the ground electrode than the insulating portion, and the discharge portion is formed at the protruding tip. 6. Spark plug for internal combustion engines. A transmission member (500) made of a conductive material and transmitting a voltage applied to the spark plug to the center electrode;
The insulating portion is formed with a flange portion (121) having a large diameter at a location covering the proximal end opposite to the discharge portion at the tip in the shaft core portion,
The spark plug for an internal combustion engine according to any one of claims 1 to 5, wherein the protection portion is isolated from the conductive member by the flange portion.

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