JP4562030B2 - Spark plug - Google Patents

Description

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

As a spark plug used for ignition of an internal combustion engine such as an automobile engine, an insulator having an axial hole in the axial direction, a center electrode disposed on a tip end side of the axial hole of the insulator, and the periphery of the insulator A metal shell that surrounds the metal shell, one end coupled to the metal shell, the other end connected to the front end surface of the center electrode, one end coupled to the metal shell, and the other end to the center electrode side There is known a spark plug including a second ground electrode facing a peripheral surface or a side peripheral surface of the insulator. The spark plug ignites the fuel mixed gas by causing a spark discharge in a discharge gap formed by the center electrode and the first ground electrode. On the other hand, when carbon or the like adheres to the tip end surface of the insulator and becomes a so-called “smoldering” state, the surface of the insulator is covered with a creeping gap formed by the second ground electrode and the side peripheral surface of the center electrode. Since the spark discharge occurs in a crawl shape, the fouling substance is constantly burned out, and the fouling resistance can be achieved. (For example, see Patent Document 1)
JP 2001-237045 A

  Recently, there has been an increasing demand for higher performance of engines, and spark plugs are also required to have further improved ignitability. In order to improve the ignitability, the following method is effective for a spark plug in which only the first ground electrode is disposed (no second ground electrode is provided). That is, in the noble metal tip bonded to the inner surface of the other end of the first ground electrode body, the axial distance (hereinafter also referred to as the protrusion amount) between the facing surface facing the center electrode and the inner surface can be increased. It is valid. This is because a flame nucleus formed between the discharge gap formed by the center electrode and the first ground electrode tends to grow by swirl or the like. However, if the protruding amount of the noble metal tip is small, the distance between the discharge gap and the first ground electrode body is short, so that in the process of the growth of the flame nucleus, the flame nucleus contacts the first ground electrode body at an early stage and grows. (Hereinafter also referred to as an anti-inflammatory effect). Therefore, many structures that promote the growth of the flame kernel by increasing the protruding amount of the noble metal tip as much as possible are employed.

  Therefore, the inventors joined a spark plug of Patent Document 1 with a noble metal tip having a large protrusion amount to the first ground electrode body, and studied further improvement in ignitability. However, the spark plug of Patent Document 1 has a structure in which a flame nucleus contacts the second ground electrode when the flame nucleus grows even when the second ground electrode is arranged. May hinder growth. Furthermore, even in the first ground electrode main body in which the protruding amount of the noble metal tip is increased, there is a possibility that the growth of the flame nucleus may be hindered when the flame nucleus grows further than the above state. As a result, there is a problem that sufficient ignitability cannot be secured.

  An object of the present invention is to prevent a second ground electrode or a first ground electrode body from coming into contact with a flame core as much as possible in a spark plug including a first ground electrode and a second ground electrode, and to ensure sufficient ignitability. Is to provide a spark plug.

Therefore, as a result of intensive studies by the present inventors, the spark plug of the present invention comprises an insulator having an axial hole in the axial direction, a center electrode disposed on the tip side of the axial hole of the insulator, and the insulator A metal shell surrounding the periphery of the metal plate, a first ground electrode body having one end bonded to the metal shell, an inner surface of the other end of the first ground electrode body, and a discharge gap between the front end surface of the center electrode and the discharge gap A first ground electrode having a noble metal tip opposed to each other, and a second ground electrode having one end coupled to the metal shell and the other end facing the side peripheral surface of the center electrode or the side peripheral surface of the insulator And comprising
A distance t in the axial direction between the facing surface of the noble metal tip facing the tip surface of the center electrode and the inner surface of the first ground electrode body is 0.3 mm or more;
An imaginary line s1 passing through the center of the second ground electrode and including the axis, passing through an intermediate point of the discharge gap on the axis, and in contact with the first ground electrode body; and the discharge gap And the virtual line s2 that is in contact with the second ground electrode and the angle between the virtual line s1 and the virtual line s2 is θ,
θ ≧ 55 °
It is characterized by being.

  The spark plug of the present invention is configured such that the axial distance t between the facing surface of the noble metal tip and the inner surface of the first ground electrode body facing the center electrode is 0.3 mm or more. Thus, when the amount of protrusion of the noble metal tip from the first ground electrode main body becomes large, the flame nucleus formed in the discharge gap formed by the center electrode and the noble metal tip grows with a swirl or the like. The possibility that the nuclei come into contact with the first ground electrode body is reduced, and the ignitability is improved by promoting the growth of the flame nuclei. When the distance t in the axial direction between the facing surface of the noble metal tip and the inner surface of the first ground electrode body is less than 0.3 mm, it is possible to effectively prevent the flame kernel from contacting the first ground electrode body as described above. It is difficult to obtain the effect. On the other hand, the axial distance t between the facing surface of the noble metal tip and the inner surface of the ground electrode body is preferably 1.5 mm or less. When the distance t in the axial direction between the facing surface of the noble metal tip and the inner surface of the ground electrode body exceeds 1.5 mm, the heat capacity of the noble metal tip increases and the durability of the noble metal tip may deteriorate. The “inner surface” in the present invention refers to the surface of the first ground electrode body that faces the center electrode.

  By the way, even with the spark plug in which the protruding amount of the noble metal tip is increased as described above, depending on the arrangement of the second ground electrode, when the flame nucleus grows, the flame nucleus comes into contact with the second ground electrode, so that the flame extinguishing action occurs. There is a risk of hindering the growth of the flame kernel. Further, even in the first ground electrode main body in which the protruding amount of the noble metal tip is increased, there is a possibility that the growth of the flame nucleus may be hindered when the flame nucleus grows further than the above state. Therefore, there has been a problem that the ignitability of the spark plug cannot be secured sufficiently.

  Therefore, the spark plug of the present invention passes through the center of gravity of the second ground electrode and passes through the midpoint of the discharge gap on the axis in a virtual cross section including the axis, and is in virtual contact with the first ground electrode body. Θ ≧ 55 when a virtual line s2 passing through the intermediate point of the line s1 and the discharge gap and in contact with the second ground electrode is defined, and an angle between the virtual line s1 and the virtual line s2 is θ. It is configured to be °. As described above, by expanding the distance between the first ground electrode body and the second ground electrode, when the flame nucleus generated near the middle point of the discharge gap grows, the second ground electrode and the first ground electrode body The contact of the flame kernel can be reduced, and the flame kernel can be efficiently grown. Therefore, the ignitability of the spark plug can be sufficiently improved. When θ is less than 55 °, it is difficult to obtain the effect of efficiently growing the flame kernel as described above. On the other hand, it is preferable that θ is 90 ° or less. If θ exceeds 90 °, problems such as overheating of the first ground electrode body and a fuel bridge may occur. In addition, the “clipping angle” in the present invention refers to an angle between the imaginary line s1 and the imaginary line s2 that does not sandwich the axis (acute angle θ1 in FIG. 2) as illustrated in FIG.

  In the spark plug of the present invention, it is preferable that the angle θ between the imaginary line s1 and the imaginary line s2 is θ ≧ 60 °. Thereby, it can further reduce that a flame nucleus contacts a 2nd ground electrode and a 1st ground electrode main body, and a flame nucleus can be grown efficiently. Therefore, the ignitability of the spark plug can be further improved sufficiently.

  In the spark plug of the present invention, it is preferable that the first ground electrode body forms a chamfered portion including at least the imaginary line s1 and the contact in the outer peripheral edge of the inner surface of the center electrode. Thereby, the space | interval of a 1st ground electrode main body and a 2nd ground electrode can be expanded further, and a flame nucleus contacts a 1st ground electrode main body when the flame nucleus which generate | occur | produced near the intermediate point of the discharge gap grows. Can be reduced, and the flame kernel can be efficiently grown.

  In the spark plug of the present invention, it is preferable that the other end portion of the first ground electrode main body is tapered toward the other end including the virtual line s1 and the contact. Thereby, the space | interval of a 1st ground electrode main body and a 2nd ground electrode can be expanded further, and a flame nucleus contacts a 1st ground electrode main body when the flame nucleus which generate | occur | produced near the intermediate point of the discharge gap grows. Can be reduced, and the flame kernel can be efficiently grown. The “taper” in the present invention may be a taper that gradually decreases toward the other end, or may be a step.

  The spark plug of the present invention has an imaginary line s3 in contact with the noble metal tip passing through the intermediate point of the discharge gap on the axis in the above-described imaginary cross section, and the angle between the imaginary line s3 and the imaginary line s2 is When θ, θ ≧ 55 ° (more preferably, θ ≧ 60 °) is preferably satisfied. By widening the distance between the noble metal tip and the second ground electrode, it is possible to reduce the contact of the flame core with the noble metal tip when the flame nucleus generated near the midpoint of the discharge gap grows. Nuclei can be grown efficiently. Therefore, the ignitability of the spark plug can be sufficiently improved.

  The spark plug of the present invention preferably has a columnar shape in which the diameter φB of the noble metal tip is 0.3 mm or greater and 1.0 mm or less. Thus, when the diameter φB of the noble metal tip is 1.0 mm or less, the discharge voltage is reduced and the ignitability is further improved. On the other hand, when the diameter φB of the noble metal tip is 0.3 mm or more, durability of the noble metal tip can be obtained.

  Hereinafter, some embodiments of the present invention will be described with reference to the drawings. 1 and FIG. 2, a spark plug 100 with a resistor according to the first embodiment of the present invention includes a cylindrical metal shell 1, an insulator 2 fitted into the metal shell 1 so that a tip portion protrudes, and a tip side. The first noble metal tip 31 bonded to the center electrode 3 provided inside the insulator 2 with the first noble metal tip 31 protruding, and the first noble metal tip 31 (center electrode 3) disposed opposite to the front end surface. One ground electrode 4, a center electrode 3, and two second ground electrodes 5 disposed so as to face the insulator 2 are provided. The second ground electrodes 5 are respectively disposed at positions shifted by 90 ° from the first ground electrode 4, and the second ground electrodes 5 are disposed at positions shifted by 180 °. The other end of the first ground electrode 4 is bent so as to face the tip surface of the first noble metal tip 31 in a substantially parallel manner, and a second noble metal tip 41 is formed at a position facing the first noble metal tip 31. ing. A discharge gap g1 is formed between the first noble metal tip 31 and the second noble metal tip 41. Further, the second ground electrode 5 has a creeping gap g2 between the other end surface and the side peripheral surface of the center electrode. In this creepage gap, the spark discharge includes a creeping discharge over the surface of the insulator and an air discharge flying in the air. In this embodiment, the discharge gap g1 is the discharge gap of the present invention.

  The metal shell 1 is made of carbon steel or the like, and as shown in FIG. 1, a threaded portion 12 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface thereof. The insulator 2 is made of a ceramic sintered body such as alumina or aluminum nitride, and has a through hole 6 for fitting the center electrode 3 along its own axial direction. A terminal fitting 13 is inserted and fixed on one end side of the through hole 6, and the center electrode 3 is inserted and fixed on the other end side. A resistor 15 is disposed between the terminal fitting 13 and the center electrode 3 in the through hole 6. Conductive glass sealing layers 16 and 17 are provided at both ends of the resistor 15, and are electrically connected to the center electrode 3 and the terminal fitting 13 through the conductive glass sealing layers 16 and 17, respectively. .

  The center electrode 3 has an electrode base material 3a formed on the surface and a metal core 3b inserted therein. The electrode base material 3a of the center electrode 3 is a Ni alloy such as INCONEL600 (registered trademark of INCO). On the other hand, the metal core 3b is made of an alloy mainly composed of Cu, Ag, or the like. The metal core 3b has a higher thermal conductivity than the electrode base material 3a. The electrode base material 3a of the center electrode 3 is reduced in diameter on the tip side and has a flat tip surface. A disc-shaped noble metal tip is superimposed on the tip surface, and laser welding is performed along the outer edge of the joint surface. The first noble metal tip 31 is formed by forming a welded portion by electron beam welding, resistance welding or the like and fixing it. The first noble metal tip 31 is made of a metal mainly composed of Pt, Ir, and W. Specific examples include Pt alloys such as Pt-20 wt% Ir and Pr-20 wt% Rh, and Ir alloys such as Ir-5 wt% Pt and Ir-20 wt% Rh.

  The first ground electrode 4 includes a first ground electrode body 4 a and a second noble metal tip 41. Among them, the first ground electrode body 4a has one end 42 (not shown) fixed and integrated with the front end surface of the metal shell 1 by welding or the like. On the other hand, a second noble metal tip 41 is provided at the other end 43 of the first ground electrode body 4a. The second noble metal tip 41 is formed by providing a cylindrical noble metal tip at a predetermined position of the first ground electrode body 4a and fixing it by laser welding, electron beam welding, resistance welding or the like. . The second noble metal tip 41 is made of a metal containing Pt, Ir, and W as main components. Specific examples include Pt alloys such as Pt-20 wt% Ni and Pr-20 wt% Rh, and Ir alloys such as Ir-5 wt% Pt and Ir-20 wt% Rh. The facing surface 41a of the second noble metal tip 41 faces the center electrode tip surface (specifically, the tip surface 31a of the first noble metal tip 31). The first ground electrode body 4a is made of a Ni alloy such as INCONEL600.

  In the second noble metal tip 41 of the first embodiment, the diameter B of the facing surface 41a is 0.7 mm, and the protruding amount t from the first ground electrode body 4a is 0.8 mm. Thus, when the protrusion amount t of the second noble metal tip 41 from the first ground electrode body 4a is 0.3 mm or more, the discharge gap g1 formed by the first noble metal tip 31 and the second noble metal tip 41. When the flame nuclei formed in the meantime grow by swirl or the like, the possibility of the flame nuclei coming into contact with the first ground electrode body 4a at an early stage is reduced, and the ignitability is improved by promoting the growth of the flame nuclei. To do.

  Further, since the diameter φB of the second noble metal tip 41 of the first embodiment is 0.3 mm or greater and 1.0 mm or less, the discharge voltage can be reduced, the ignitability is improved, and the second noble metal tip is improved. A durability of 41 can be obtained.

  One end 52 of the second ground electrode 5 is fixed and integrated with the front end surface of the metal shell 1 by welding or the like. On the other hand, the other end 53 of the second ground electrode 5 faces the side peripheral surface of the center electrode and the side peripheral surface of the insulator 2. The second ground electrode 5 is made of a Ni alloy containing 90 wt% or more of Ni.

  Then, it passes through an intermediate point (h in FIG. 2) of the first discharge gap g1 on the axis O, passes through a virtual line s1 in contact with the first ground electrode body 4a, and an intermediate point h of the first discharge gap g1, When the imaginary line s2 is in contact with the ground electrode 5, the included angle θ1 between the imaginary line s1 and the imaginary line s2 in the first embodiment is θ1 = 65 °. As described above, the angle θ between the virtual line s1 and the virtual line s2 is θ ≧ 55 ° (more preferably θ ≧ 60 °), so that the first ground electrode body 4a and the second ground electrode 5 are formed. Can be widened. Thereby, when a flame nucleus generated near the intermediate point h of the first discharge gap g1 grows, it is possible to reduce the contact of the flame nucleus with the second ground electrode 5 and the first ground electrode body 4a. Flame nuclei can be grown efficiently. Therefore, the ignitability of the spark plug 100 can be sufficiently improved. Further, when an imaginary line s3 that passes through the intermediate point h of the first discharge gap g1 and is in contact with the second noble metal tip 41 is formed, an angle θ1 ′ between the imaginary line s1 and the imaginary line s3 is θ1 ′ = 76. It is °. Thus, by setting θ1 ′ to 55 ° or more, the noble metal tip 41 has a structure that is unlikely to hinder the growth of the flame kernel.

  Such a spark plug 100 is manufactured as follows. However, the manufacturing method of the main part of the spark plug 100 will be mainly described, and the description of the known part will be omitted or simplified.

  First, the insulator 2 is formed by using alumina as a main raw material and firing it into a predetermined shape at a high temperature. Moreover, the metal shell 1 is formed by using a steel material and plastic processing into a predetermined shape. At this time, the threaded portion 12 is formed on the outer peripheral surface of the distal end portion of the metal shell 1. Next, a rod-shaped center electrode 3 made of a Ni heat-resistant alloy, a first ground electrode body 4a, and a second ground electrode 5 are formed. Note that when the center electrode 3 is formed, the metal core 3b is inserted. Then, the first ground electrode body 4 a and the second ground electrode 5 are electrically resistance-welded to the front end surface of the metal shell 1. Thereafter, the second ground electrode 5 is bent in the axial direction by a known method. On the other hand, the center electrode 3 is reduced in diameter at the tip, and a noble metal tip is fixed to the tip surface by electric resistance welding, laser welding or the like to form the first noble metal tip 31.

  Then, the center electrode 3 is inserted into the shaft hole 6 of the insulator 2 so that the tip side protrudes from the insulator 2, and then the conductive seal layer 16, the resistor 15, and the conductive seal layer 17 are sequentially arranged on the rear end side. Further, the terminal fitting 13 is inserted on the rear end side of the insulator 2 so that the rear end side of the terminal fitting 13 protrudes from the rear end of the insulator 2 and fixed using a known method. . Then, the insulator 2 to which the center electrode 3, the terminal fitting 13 and the like are fixed is connected to the metal shell 1 to which the first ground electrode body 4a and the second ground electrode 5 are fixed, and the second ground electrode 5 is connected to the second ground electrode 5. Assembling is performed by a known method while adjusting the discharge gap g2. Then, a second noble metal tip 41 is formed by fixing a noble metal tip to the other end portion 43 of the first ground electrode body 4a by electric resistance welding, laser welding or the like. The first ground electrode 4 (first ground electrode body) is arranged so that the facing surface 41a of the second noble metal tip 41 faces the tip surface 31a of the first noble metal tip 31 of the center electrode 3 via the first discharge gap g1. 4a) is bent to complete the spark plug 100 for the internal combustion engine as shown in FIG.

Next, Embodiment 2 of the present invention will be described with reference to the drawings.
The spark plug 200 shown in FIGS. 3 and 4 is different in the first ground electrode 4 of the spark plug 100 described above. 3 and 4, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the configuration is the same as that of the first embodiment except for the shape of the first ground electrode 4. Explained.

  In the spark plug 200 of the second embodiment, the first ground electrode body 4a is formed of a Ni alloy such as INCONEL600. The first ground electrode body 4a has one end 42 (not shown) fixed and integrated with the front end surface of the metal shell 1 by welding or the like. On the other hand, the other end 43 of the first ground electrode body 4a faces the center electrode tip surface 3a (specifically, the tip surface 31a of the first noble metal tip 31). A chamfered portion 45 is provided on the outer peripheral edge of the inner side surface of the other end portion 43. The chamfered portion 45 of the second embodiment may be a C chamfer as shown in FIG. 3 or an R chamfer as shown in FIG. Furthermore, what is necessary is just the shape which cut off the corner | angular part of the outer periphery of an inner surface. In the present invention, the size of the chamfered portion 45 is C 0.5 mm in FIG. 3 and R 0.5 mm in FIG. Accordingly, when the virtual line s1 in contact with the first ground electrode body 4a in FIGS. 3 and 4 and the virtual line s2 in contact with the second ground electrode 5 through the intermediate point h of the first discharge gap g1 are obtained, The included angles θ2 and θ3 between the line s1 and the virtual line s2 are θ2 = 70 ° and θ3 = 67 °. Thus, by forming the chamfered portion 45 at least on the outer peripheral edge of the inner side surface in the first ground electrode body 4a, the distance between the first ground electrode body 4a and the second ground electrode 5 can be further increased, and the discharge When flame nuclei generated near the intermediate point h of the gap g1 grow, it is possible to reduce the contact of the flame nuclei with the first ground electrode body 4a, and the flame nuclei can be efficiently grown. 3 and 4, when the virtual line s3 is in contact with the second noble metal tip 41 through the intermediate point h of the first discharge gap g1, the angle θ2 between the virtual line s1 and the virtual line s3 'And θ3' are θ2 '= 71 ° and θ3' = 73 °, respectively. As described above, by setting θ2 ′ and θ3 ′ to 55 ° or more, the noble metal tip 41 has a structure that does not easily interfere with the growth of the flame kernel.

Next, Embodiment 3 of the present invention will be described with reference to the drawings.
The spark plug 300 shown in FIG. 5 has a configuration in which the first ground electrode 4 of the spark plug 100 described above is different. 5, the same parts as those in FIG. 2 are denoted by the same reference numerals, and the configuration is the same as that of the first embodiment except for the shape of the first ground electrode 4. The first ground electrode 4 will be mainly described. .

  In the spark plug 300 of the third embodiment, the first ground electrode body 4a is formed of a Ni alloy such as INCONEL600. The first ground electrode body 4a has one end 42 (not shown) fixed and integrated with the front end surface of the metal shell 1 by welding or the like. On the other hand, the other end 43 of the first ground electrode body 4a faces the center electrode tip surface 3a (specifically, the tip surface 31a of the first noble metal tip 31). The other end 43 of the first ground electrode body 4a is tapered toward the other end surface 43a (in the present embodiment, tapered). Accordingly, when the virtual line s1 that is in contact with the first ground electrode body 4a in FIG. 5 and the virtual line s2 that is in contact with the second ground electrode 5 through the intermediate point h of the first discharge gap g1, The included angle θ4 with the virtual line s2 is θ4 = 70 °. That is, the distance between the first ground electrode body 4a and the second ground electrode 5 can be further widened, and when the flame nucleus generated near the intermediate point h of the first discharge gap g1 grows, the first ground electrode body It can reduce that a flame kernel contacts 4a, and can make a flame kernel grow efficiently. Further, in FIG. 5, when an imaginary line s3 that passes through the intermediate point h of the first discharge gap g1 and is in contact with the second noble metal tip 41, an angle θ4 ′ between the imaginary line s1 and the imaginary line s3 is In each case, θ4 ′ = 70 °. Thus, by setting θ4 ′ to 55 ° or more, the noble metal tip 41 has a structure that is unlikely to hinder the growth of the flame kernel.

In order to confirm the effect of the present invention, the following various experiments were conducted.
Various test pieces of spark plugs having the shapes shown in FIGS. 1 and 2 were prepared as follows. First, sintered alumina ceramic is used as the material of the insulator 2, INCONEL 600 as the electrode body 3 a of the center electrode 3, copper core as the core material 3 b, INCONEL 600 as the first ground electrode body 4 a, and heat-resistant Ni alloy as the second ground electrode 5 ( 90 wt% Ni alloy), Ir-20 wt% Rh as the material of the first noble metal tip 31, and Pt-20 wt% Ni as the material of the second noble metal tip 41, respectively. The first noble metal tip 31 has a cylindrical shape with a diameter of φ0.55 mm, and the second noble metal tip 41 has a cylindrical shape with a height t of 0.8 mm and a diameter of φ0.6 mm. Furthermore, the width of the first ground electrode body 4a was 2.5 mm and the height was 1.4 mm, and the width of the second ground electrode 5 was 2.2 mm and the height was 1.2 mm. Furthermore, the distance of the discharge gap g1 is 1.1 mm.

  Then, the spark plug 100 in which the angle θ1 (θ in the table) in FIG. 2 is set to 46, 52, 55, 60, 65, 70, 72 (unit: °) is a 2000 cc displacement, 6 cylinder DOHC gasoline. Attached to the engine, an ignitability test was performed in an operating state equivalent to 60 km / h (engine speed 2000 rpm). In this test, discharge was performed between the discharge voltage gaps 1000 times under the above engine conditions, and the A / F value when 10 misfires occurred was measured as the ignition limit. The results are shown in Table 1.

  According to Table 1, when the angle of θ1 is 46 °, A / F is 22.4, when the angle of θ1 is 52 °, A / F is 22.5, and when the angle of θ is 55 °, A / F If F is 23.2 and the angle of θ1 is 60 °, A / F is 23.4, the angle of θ1 is 65 °, A / F is 23.4 and the angle of θ1 is 70 °, then A When / F was 23.5 and the angle θ1 was 72 °, A / F was 23.5. Thus, by setting θ1 to 55 ° or more, A / F is 23.2, and the ignitability is drastically improved. Furthermore, by setting θ to 60 °, the A / F becomes 23.4, and the ignitability is further improved.

  The present invention is not limited to the specific embodiments described above, and various modifications can be made within the scope of the present invention depending on the purpose and application. For example, in the spark plug 100 of the present invention, the metal core 3 b is inserted only into the center electrode 3, but the present invention is not limited thereto, and the metal core is inserted into either the first ground electrode body 4 a or the second ground electrode 5. May be. And the material of the metal core in this case is formed from simple substance or alloy, such as Cu and Ag.

  Further, the spark plug 100 of the present invention has two second ground electrodes 5, but is not limited thereto, and may be one. Moreover, the number may be three or more. Further, the spark plug 100 of the present invention has a shape in which only the tip portion of the center electrode 3 protrudes from the insulator 2, but the base portion of the center electrode 3 protrudes from the insulator 2 as shown in FIG. It may be. Thereby, since the distance between the first discharge gap g1 and the second ground electrode 5 is increased, the distance between the first ground electrode body 4a and the second ground electrode 5 can be further increased, and the ignitability is further improved.

1 is a front sectional view showing a spark plug 100 of the present invention. Front sectional drawing which shows the principal part of FIG. Front sectional drawing which shows the principal part of Embodiment 2 of this invention. Front sectional drawing which shows the principal part of another Example of FIG. The front sectional view and top view showing the important section of Embodiment 3 of the present invention. FIG. 6 is a front sectional view showing another example of the first embodiment.

Explanation of symbols

1 metal shell 2 insulator 3 center electrode 4 first ground electrode 5 second ground electrode 6 through hole 31 first noble metal tip 41 second noble metal tip 100, 200, 300 spark plug

Claims (5)

An insulator having an axial hole in the axial direction;
A center electrode disposed on the tip side of the shaft hole of the insulator;
A metal shell surrounding the periphery of the insulator;
A first ground electrode main body having one end bonded to the metal shell, a noble metal tip bonded to the inner surface of the other end of the first ground electrode main body and facing the front end surface of the center electrode across a discharge gap; A first ground electrode having
A second ground electrode having one end coupled to the metal shell and the other end facing the side peripheral surface of the center electrode or the side peripheral surface of the insulator;
A distance t in the axial direction between the facing surface of the noble metal tip facing the tip surface of the center electrode and the inner surface of the first ground electrode body is 0.3 mm or more;
An imaginary line s1 passing through the center of gravity of the second ground electrode and passing through an intermediate point of the discharge gap on the axis in a virtual cross section including the axis; and the virtual line s1 in contact with the first ground electrode body; When passing through an intermediate point and making it a virtual line s2 that is in contact with the second ground electrode, and the angle between the virtual line s1 and the virtual line s2 is θ,
θ ≧ 55 °
Spark plug characterized by being. The spark plug according to claim 1, wherein
The angle θ of the included angle between the virtual line s1 and the virtual line s2 is
θ ≧ 60 °
Spark plug characterized by being. The spark plug according to claim 1 or 2,
The spark plug according to claim 1, wherein the first ground electrode body forms a chamfered portion including at least the imaginary line s1 and a contact in the outer peripheral edge of the inner side surface. In the spark plug according to any one of claims 1 to 3,
The other end portion of the first ground electrode main body is tapered toward the other end including the virtual line s1 and the contact point. In the spark plug according to any one of claims 1 to 4,
  The spark plug, wherein the noble metal tip has a cylindrical shape having a diameter φB of 0.3 mm or more and 1.0 mm or less.