JP2005209562A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug which increases flexibility in designing engine heads with improving and stabilizing ignition performance and preventing screw parts from being large. <P>SOLUTION: Distance F is given as the distance between a midpoint A between a pair of a center electrode 3 and a ground electrode 5 of the spark plug 100 equipped with a plurality of spark discharging spaces and the axis center C of the whole spark plug 100, intersection 3A is given as the point where the center axis B of the center electrode 3 intersects with the end face of the center electrode 3, and distance E is given as the distance between the intersection 3A and the axis center C. In this case, bending profile of the ground electrode 5 is adjusted so that it may become distance F> distance E. A spark discharge space is formed between the center electrode 3 side end face of the ground electrode 5 welded to an end of an screw part 2A and the ground electrode 5 side side face of the end of the center electrode 3. In this way, distances between a plurality of positions where spark discharges occur are enlarged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spark plug for an internal combustion engine, and more particularly, to a spark plug including a plurality of center electrodes and a plurality of ground electrodes corresponding thereto.

  Conventionally, since a spark plug for ignition of an internal combustion engine is usually provided with only one pair of a center electrode and a ground electrode constituting a spark discharge gap, one spark per cylinder is used in one ignition process of the internal combustion engine. There was a spark discharge only at the location. For this reason, in an atmosphere in which a rich mixture and a thin portion exist like a direct injection engine, spark discharge is performed at the timing when the rich mixture reaches the vicinity of the spark discharge gap and the spark discharge gap. When there is a deviation in timing, there is a possibility that ignition may fail with only one spark discharge. In order to provide a plurality of spark discharge gaps in one cylinder, it is conceivable to provide a plurality of spark plugs. However, it is necessary to provide a plurality of plug holes in the engine head. In some cases, there is a limitation in providing a plurality of plug holes depending on the arrangement.

  Therefore, as shown in FIG. 13, two insulators 202 and 203 are held by the metal shell 201 of the spark plug 200, and the center electrodes 204 and 205 and the power connection terminals 209 and 210 are respectively attached to the insulators 202 and 203. Two independent electrical paths are provided, and ground electrodes 206 and 207 are provided at the tip of the threaded portion 208 of the metallic shell 201 so as to be opposed to the tip surfaces of the center electrodes 204 and 205, respectively. A spark plug has been proposed (see, for example, Patent Document 1).

As shown in FIG. 14, one insulator 302 is held by the metal shell 301 of the spark plug 300, and is extended in parallel to the axial direction of the spark plug 300 at the tip of the threaded portion 308 of the metal shell 301. Two grounding electrodes 309 and 310 are provided, and two through holes 305 and 306 are opened in the insulator 302 in parallel to the axial direction, and the center electrodes 303 and 304 are inserted into the through holes 305 and 306, respectively. There are proposed ones in which the tip portions 303A and 304B of the center electrodes 303 and 304 are projected from the tip of the insulator 302 and bent so as to face the ground electrodes 309 and 310, respectively (for example, , See Patent Document 2). These conventional spark plugs 200 and 300 have a feature that a single spark discharge can be performed at a plurality of locations. Accordingly, only one plug hole is provided per cylinder for the internal combustion engine.
West German Patent Application Publication No. DE34221023A1 Japanese Utility Model Publication No. 60-60895

  By the way, in order to ensure the freedom of attachment of the spark plug to the internal combustion engine and to improve the ignitability and stable combustibility, the interval between the plurality of center electrodes is suppressed while suppressing the increase in the outer diameter of the spark plug. Must be made as wide as possible to widen the intervals between the occurrence positions of the plurality of spark discharges. However, in the spark plug 200 described in Patent Document 1, when the interval between the two center electrodes 204 and 205 is increased, the screw of the metal shell 201 is compared with the spark plug in which only one pair of the center electrode and the ground electrode is provided. There has been a problem that the outer diameter of the portion 208 is significantly increased, and the degree of freedom of attachment to the internal combustion engine is reduced. Further, in the spark plug 300 described in Patent Document 2, the interval between the spark discharge generation positions can be increased while suppressing an increase in the outer diameter of the threaded portion. However, since a plurality of through holes 305 and 306 are formed in the insulator 302, the insulator 302 in the outer portion of the center electrodes 303 and 304 is compared with a spark plug in which only a pair of center electrodes and ground electrodes are provided. The wall thickness is thin. For this reason, there is a problem that the insulator 302 is broken when the center electrodes 303 and 304 are bent. Further, since the through holes 305 and 306 of the insulator 302 are easier to manufacture in the case of a cylinder than a quadrangular column, the center electrodes 303 and 304 inserted therein are inevitably in a columnar shape. If the cylindrical center electrodes 303 and 304 are bent in the direction of the ground electrodes 309 and 310, respectively, the difference in compression and tension between the inside and outside of the bent portion is larger than that of the plate-like one. There was a problem that the electrodes 303 and 304 were broken.

  The present invention has been made to solve the above problems, and is a spark plug having a plurality of spark discharge gaps, which improves the ignition performance and stabilizes the combustion of the internal combustion engine. An object of the present invention is to provide a spark plug capable of improving the degree of freedom in designing an engine head without increasing the size.

  In order to solve the above-described problem, the spark plug according to the first aspect of the present invention includes an insulator in which a plurality of center electrodes are provided, a metal shell that holds the insulator, and a tip of the metal shell. A spark plug having one end joined and the other end bent in the direction of the center electrode, and comprising a plurality of ground electrodes corresponding to each of the center electrodes, wherein at least one center of the plurality of center electrodes The distance between the intermediate point of the spark discharge gap formed between the electrode and the ground electrode paired with the central electrode and the central axis of the whole spark plug is the center axis of the one central electrode and the central electrode It is characterized by being larger than the distance between the intersection with the tip surface of the center electrode and the center axis of the whole spark plug.

  Further, in the spark plug of the invention according to claim 2, in addition to the structure of the invention according to claim 1, the outer diameter of the tip of the attachment portion of the metal shell to the internal combustion engine is 15.5 mm or less. It is characterized by that.

  The spark plug of the invention described in claim 3 is characterized in that, in addition to the configuration of the invention described in claim 1 or 2, a noble metal is provided in at least one of the center electrode and the ground electrode. .

  According to a spark plug of the invention described in claim 4, in addition to the configuration of the invention described in any of claims 1 to 3, a discharge portion is formed from a pair of the center electrode and the ground electrode. The spark discharge position of the discharge part is asymmetric with respect to the spark discharge position of other discharge parts with respect to the central axis of the entire spark plug.

  In the spark plug of the invention according to claim 1, the spark discharge gap intermediate point formed between at least one center electrode of the plurality of center electrodes and the ground electrode paired with the center electrode, and the spark The distance between the central axis of the entire plug is greater than the distance between the intersection of the central axis of the one central electrode and the tip surface of the central electrode and the central axis of the entire spark plug. For this reason, in a multi-ignition spark plug having a plurality of spark discharge gaps with a single spark plug, the location of occurrence of spark discharge can be located radially outward with respect to the central axis of the spark plug, The distance between the spark discharge occurrence positions can be increased. Therefore, the ignition performance can be improved and the combustion of the internal combustion engine can be stabilized. Here, the spark plug of the multi-ignition type is more specifically, a plurality of center electrodes each having a ground electrode corresponding to each center electrode, and a plurality of center electrodes penetrating the insulator in an electrically insulated state. A spark plug is formed with a spark discharge gap between the pair of and a ground electrode, and a spark discharge voltage is individually applied to each spark discharge gap. Moreover, it is preferable that all of the plurality of center electrodes and each ground electrode paired therewith have the above-described positional relationship.

  Further, the present invention is particularly effective for a multi-ignition spark plug in which the outer diameter of the front end portion of the metal fitting according to claim 2 attached to the internal combustion engine is 15.5 mm or less. It is possible to increase the ignition performance by separating the distance between the occurrence positions of the.

  In addition to the effect of the invention described in claim 1 or 2, the spark plug of the invention described in claim 3 includes a noble metal in at least one of the center electrode and the ground electrode. The corrosion resistance of the formed portion is improved, and the durability of the spark plug can be improved.

  Further, in the spark plug of the invention according to claim 4, in addition to the effect of the invention according to any one of claims 1 to 3, the spark discharge position of one discharge part is relative to the central axis of the whole spark plug. Therefore, it is asymmetrical with the spark discharge positions of the other discharge portions, so that the distance between the spark discharge generation positions can be increased to improve the ignition performance.

  Hereinafter, a spark plug 100 for an internal combustion engine according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of a spark plug 100 according to a first embodiment of the present invention. In the spark plug 100 shown in FIG. 1, the lower side of the drawing is a front end portion, and the upper side of the drawing is a rear end portion. As shown in FIG. 1, a multi-ignition spark plug 100 having a plurality of spark discharge gaps is roughly provided with an insulator 1 constituting an insulator and a substantially central portion in the longitudinal direction of the insulator 1. 1 is a metal shell 2 that holds 1; two central electrodes 3 and 4 that are held in parallel in the axial direction in the insulator 1; and a screw that is a mounting portion of the metal shell 2 to an internal combustion engine (not shown). One end is joined to the tip of the part 2A by welding and the other end is bent in the direction of the center electrode 3, and similarly, one end is welded to the tip of the screw part 2A of the metal shell 2 The ground electrode 6 is joined and the other end is bent in the direction of the center electrode 4. Hereinafter, the combination of the center electrode 3 and the ground electrode 5 and the center electrode 4 and the ground electrode 6 is referred to as a spark discharge portion. In the spark plug 100 of the present embodiment, the outer diameter D of the tip portion of the threaded portion 2A of the metal shell 2 is 14 mm as an example, but if the outer diameter D is 15.5 mm or less, the present invention The effect of can be produced effectively.

  Next, the insulator 1 constituting the insulator of the spark plug 100 will be described. As is well known, the insulator 1 is formed by firing alumina or the like, and a corrugation (not shown) for increasing the creeping distance is formed at the rear end portion (upper portion in FIG. 1). In addition, leg end portions 1A and 1B that are exposed to the combustion chamber of the internal combustion engine are provided at the tip of the insulator 1 (the lower portion in FIG. 1). These long leg portions 1A and 1B are extended in parallel at symmetrical positions with the axial center of the insulator 1 interposed therebetween. That is, the insulator 1 is divided into two forks in the threaded portion 2A of the metal shell 2, and the distal ends thereof are exposed from the distal end portions of the threaded portion 2A.

  Further, a center electrode 3 is provided at the center of the leg of the leg 1A of the insulator 1, and similarly, a center electrode 4 is provided at the center of the leg of the leg 1B of the insulator 1. Examples of the material of the center electrodes 3 and 4 include 6 to 20% by mass of iron such as Inconel (trade name) 600 or 601, 14 to 25% by mass of chromium, 3% or less of other impurities, and aluminum 1 to 2 if desired. It has at least a surface layer portion of an electrode base material made of a nickel-based alloy or the like containing at least 58% by mass of nickel. The tip portions of the center electrodes 3 and 4 protrude from the tip surfaces of the leg long portions 1A and 1B of the insulator 1, respectively.

  Further, the center electrode 3 is electrically connected to an upper terminal fitting 7 in FIG. 1 via a ceramic resistor 9 connected to the rear end thereof, and a high voltage cable (not shown) is connected to the terminal fitting 7 with a plug cap (not shown). A high voltage is applied via a connection (not shown). Similarly, the center electrode 4 is electrically connected to an upper terminal fitting 8 in FIG. 1 via a ceramic resistor (not shown), and a high voltage cable (not shown) is connected to the terminal fitting 8 with a plug cap (not shown). And a high voltage is applied.

  Next, the metal shell 2 will be described. As shown in FIG. 1, the metal shell 2 is a metal bracket for holding the insulator 1 and fixing the spark plug 100 to an internal combustion engine (not shown). Accordingly, the insulator 1 is surrounded by the metal shell 2 and is held by the holding portion 2D and the caulking portion 2B. The metal shell 2 is made of a low carbon steel material, and a hexagonal portion 2C that is a tool engaging portion into which a spark plug wrench (not shown) is fitted, and a screw portion 2A that is screwed into an upper portion of a cylinder of an internal combustion engine not shown. And. As an example of the standard of the screw portion 2A, M14S or the like is used. The metal shell 2 is caulked to the insulator 1 by the caulking portion 2B, and the metal shell 2 and the insulator 1 are integrated. In order to complete sealing by caulking, a pair of ring-shaped seal members 12 and 13 are interposed between the metal shell 2 and the insulator 1, and between the seal member 12 and the seal member 13. Talc (talc) powder 14 is filled. Further, a gasket 20 is inserted into the rear end (the upper portion in FIG. 1) of the screw portion 2 </ b> A, that is, the seat surface of the metal shell 2.

  Further, at the tip of the threaded portion 2A, there are ground electrodes 5 and 6 that face the center electrodes 3 and 4 and have a substantially rectangular cross section perpendicular to the longitudinal direction of the threaded portion 2A, and have a bent rectangular bar-like outer shape. They are joined by welding. Details of the structure of the ground electrodes 5 and 6 will be described later. The ground electrode 5 is opposed to the side surface of the tip of the center electrode 3 to form a spark discharge gap G1, and the ground electrode 6 is opposed to the side of the tip of the center electrode 4 to be spark discharge gap. G2 is formed.

  Next, with reference to FIG.1 and FIG.2, the arrangement | positioning relationship and the effect | action of the center electrode 3 and the ground electrode 5 are demonstrated. FIG. 2 is an enlarged view of the vicinity of the spark discharge portion of the spark plug 100. As shown in FIGS. 1 and 2, an intermediate point A between the minimum gap between the pair of center electrodes 3 and the ground electrode 5 constituting the spark discharge gap G1 of the spark plug 100 of the present embodiment, and the entire spark plug 100. The shortest distance from the axis C is defined as a distance F. A point where the center axis B of the center electrode 3 intersects the tip surface of the center electrode 3 is an intersection point 3A, and a shortest distance between the intersection point 3A and the axis C is a distance E. In this case, the bent shape of the ground electrode 5 is adjusted so that distance F> distance E. For example, as shown in FIG. 1, the spark discharge gap G <b> 1 includes a tip surface on the side of the center electrode 3 of the ground electrode 5 welded to the tip of the screw portion 2 </ b> A of the metal shell 2 and a grounding of the tip of the center electrode 3. It is formed between the side surface on the electrode 5 side. Note that the positional relationship between the pair of center electrodes 4 and the ground electrode 6 constituting the spark discharge gap G2 of the spark plug 100 is the same as described above.

  In one spark plug 100, by arranging the center electrodes 3 and 4 and the ground electrodes 5 and 6 as described above, the spark discharge gap is not on the axial center of the center electrodes 3 and 4, but the center electrodes 3 and 3 are disposed. 4 is formed on the outer peripheral side in the radial direction of the threaded portion 2A at the tip end portion, so that an increase in the outer diameter of the spark plug can be suppressed and the distance between the locations where a plurality of spark discharges are generated can be increased. And the internal combustion engine can be stably combusted.

  In addition, this invention is not restricted to said embodiment, Various deformation | transformation are possible. Hereinafter, with reference to FIG. 3, the modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 3 is an enlarged view showing a first modification of the spark discharge part of the spark plug 100. In the first modification, as shown in FIG. 3, the point where distance F> distance E is the same as in the first embodiment, except that a pair of center electrode 3 and ground electrode 5 are different. The pair of center electrode 4 and ground electrode 6 is asymmetric. That is, the shape of the pair of center electrode 3 and ground electrode 5 is the same as that of the first embodiment, but the center electrode 4 protrudes longer from the leg length portion 1B of the insulator 1 than the center electrode 3. A noble metal band (Pt as an example) for preventing corrosion is wound around the tip. The ground electrode 6 also extends from the tip of the threaded portion 2 </ b> A of the metal shell 2 in accordance with the length of the center electrode 4. By adopting such a shape, the distance between the locations where a plurality of spark discharges are generated can be made longer than that of the first embodiment, the ignition performance can be improved, and the internal combustion engine can stably burn. it can.

  Next, with reference to FIG. 4, the 2nd modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 4 is an enlarged view showing a second modification of the spark discharge part of the spark plug 100. In the second modification, the ground electrodes 5 and 6 extend in parallel to the axial direction of the spark plug 100 from the tip of the threaded portion 2A of the metal shell 2. In addition, electrode plates 3B and 4B made of a noble metal (Pt as an example) or Ni alloy are welded to the distal ends of the center electrodes 3 and 4. These electrode plates 3B and 4B project to the ground electrodes 5 and 6 side, respectively, between the radial outer peripheral side of the screw portion 2A of the electrode plate 3B and the ground electrode 5, and in the radial direction of the screw portion 2A of the electrode plate 4B. Spark discharge is performed between the outer peripheral side and the ground electrode 6. Also in this case, the distance between the intermediate point A of the gap between the electrode plate 3B and the ground electrode 5 and the entire axis C of the spark plug 100 is the distance F, and the center axis B of the center electrode 3 is the center. A point intersecting the tip surface of the electrode 3 is defined as an intersection 3A, a distance between the intersection 3A and the axis C is defined as a distance E, and the size of the electrode plate 3B is adjusted so that distance F> distance E. The same applies to the electrode plate 4B. By comprising in this way, the corrosion resistance of the center electrodes 3 and 4 can be improved, and the distance between the locations where a plurality of spark discharges are generated can be made longer than that of the first embodiment, and the ignition performance is improved. In addition, the internal combustion engine can perform stable combustion.

  Next, with reference to FIG. 5, the 3rd modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 5 is an enlarged view showing a third modification of the spark discharge part of the spark plug 100. In the third modification, the center axis B of the center electrode 3 penetrating the leg long portion 1A is inclined in the direction of the entire axis C of the spark plug 100. The same applies to the center electrode 4. Therefore, the center electrode 3 and the center electrode 4 are in a state in which they face each other in the radial direction of the screw portion 2A. Also in this case, the distance between the intermediate point A of the gap between the pair of center electrodes 3 and the ground electrode 5 constituting the spark discharge gap of the spark plug 100 and the entire axis C of the spark plug 100 is a distance F. A point where the center axis B of the center electrode 3 intersects the tip surface of the center electrode 3 is defined as an intersection point 3A, and a distance between the intersection point 3A and the axis C is defined as a distance E. At this time, the bent shape of the ground electrode 5 is adjusted so that the distance F> the distance E. The positional relationship between the pair of center electrodes 4 and the ground electrode 6 is the same as described above.

  In one spark plug 100, by arranging the center electrodes 3 and 4 and the ground electrodes 5 and 6 as described above, the spark discharge gap is not on the axial center of the center electrodes 3 and 4, but the center electrodes 3 and 3 are disposed. 4 is formed on the outer peripheral side in the radial direction of the threaded portion 2A at the tip end portion, it is possible to increase the distance between the locations where a plurality of spark discharges occur, improve the ignition performance, and stably burn the internal combustion engine. it can.

  Next, with reference to FIG. 6, the 4th modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 6 is an enlarged view showing a fourth modification of the spark discharge part of the spark plug 100. The fourth modification has the same general configuration as the spark discharge portion of the spark plug 100 of the first embodiment shown in FIG. 2 except that the center electrodes 3 and 4 and the ground electrodes 5 and 6 are the same. Is provided with a noble metal (Pt as an example) chip. Specifically, the noble metal tip 3C is welded to the tip of the center electrode 3 penetrating the leg length 1A, and the noble metal tip 4C is welded to the tip of the center electrode 4 penetrating the leg length 1B. Has been. Further, a noble metal tip 5A is welded to the outside (the lower side in FIG. 6) of the ground electrode 5, and a noble metal tip 6A is welded to the outside of the tip of the ground electrode 6. Here, the distance between the midpoint A of the gap between the tip 3C of the pair of center electrodes 3 and the tip 5A of the ground electrode 5 constituting the spark discharge gap of the spark plug 100 and the entire axial center C of the spark plug 100. Is a distance F, a point where the center axis B of the center electrode 3 intersects the tip surface of the tip 3C of the center electrode 3 is an intersection point 3A, and a distance between the intersection point 3A and the axis C is a distance E. At this time, the bent shape of the ground electrode 5 is adjusted so that the distance F> the distance E. The positional relationship between the pair of center electrodes 4 and the ground electrode 6 is the same as described above.

  With the above-described structure, in one spark plug 100, the corrosion resistance of the center electrodes 3 and 4 and the ground electrodes 5 and 6 is improved, and the distance between the locations where a plurality of spark discharges are generated is increased. Thus, the ignition performance is improved, and the internal combustion engine can stably burn.

  Next, with reference to FIG. 7, the 5th modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 7 is an enlarged view showing a fifth modification of the spark discharge part of the spark plug 100. The fifth modified example has the same general configuration as the spark discharge part of the spark plug 100 of the fourth modified example shown in FIG. 6, except that the noble metal (Pt as an example) of the ground electrodes 5 and 6 is different. The welding position of the tip is the tip of the ground electrodes 5 and 6 and the inside facing the center electrodes 3 and 4 respectively. Specifically, the noble metal tip 3C is welded to the tip of the center electrode 3 penetrating the leg length 1A, and the noble metal tip 4C is welded to the tip of the center electrode 4 penetrating the leg length 1B. Has been. Further, a noble metal tip 5B is welded to the inside of the tip of the ground electrode 5 (opposite side to the center electrode 3), and similarly, the noble metal tip 5B is welded to the inside of the tip of the ground electrode 6 (opposite side to the center electrode 4). The tip 6B is welded. Here, the distance between the midpoint A of the gap between the tip 3C of the pair of center electrodes 3 and the tip 5B of the ground electrode 5 constituting the spark discharge gap of the spark plug 100 and the entire axial center C of the spark plug 100. Is a distance F, a point where the central axis B of the center electrode 3 intersects the tip surface of the center electrode 3 is an intersection 3A, and a distance between the intersection 3A and the axis C is a distance E. At this time, the bent shape of the ground electrode 5 is adjusted so that the distance F> the distance E. The positional relationship between the pair of center electrodes 4 and the ground electrode 6 is also adjusted in the same manner as described above.

  With the above structure, in one spark plug 100, the corrosion resistance and durability of the center electrodes 3 and 4 and the ground electrodes 5 and 6 are improved, and the distance between the locations where a plurality of spark discharges are generated. Can be released, the ignition performance is improved, and the internal combustion engine can stably burn.

  Next, with reference to FIG.8 and FIG.9, the 6th modification of the spark discharge part of the spark plug 100 is demonstrated. FIG. 8 is an enlarged view showing a sixth modification of the spark discharge part of the spark plug 100, and FIG. 9 is a bottom view of the spark discharge part of the spark plug 100. This sixth modification includes three sets of a center electrode and a ground electrode. Specifically, the leg length portion of the insulator 1 is divided into three leg portions 1A, 1B, and 1C. The center electrode 3 is provided through the leg length portion 1A, and the center electrode 4 extends through the leg length portion 1B. The center electrode 10 is penetrated by the leg long part 1C. In addition, a ground electrode 5 facing the center electrode 3, a ground electrode 6 facing the center electrode 4, and a ground electrode 11 facing the center electrode 10 are provided at the tip of the threaded portion 2 </ b> A of the metal shell 2. The ground electrodes 5, 6, and 11 are bent in the directions of the center electrodes 3, 4, and 10, respectively. Note that the arrangement angle of the center electrodes 3, 4, 10 and the arrangement angle of the ground electrodes 5, 6, 11 are, for example, every 120 degrees with respect to the entire axis of the spark plug 100.

  Here, the distance between the intermediate point A of the gap between the pair of center electrodes 3 constituting the spark discharge gap and the ground electrode 5 and the entire axial center C of the spark plug 100 is a distance F, and the center electrode 3 A point at which the central axis B intersects the tip surface of the center electrode 3 is defined as an intersection 3A, and a distance between the intersection 3A and the axis C is defined as a distance E. In this case, the bent shape of the ground electrode 5 is adjusted so that distance F> distance E. The positional relationship between the pair of center electrodes 4 and the ground electrode 6 and the positional relationship between the pair of center electrodes 10 and the ground electrode 11 are the same as described above.

  In one spark plug 100, by arranging the center electrodes 3, 4, 10 and the ground electrodes 5, 6, 11 as described above, even if there are three places where spark discharge occurs, Since the generation location is not on the axial center of the center electrodes 3, 4, 10, but on the outer peripheral side in the radial direction of the screw portion 2 A at the tip of the center electrodes 3, 4, 10, The distance between them can be increased, the ignition performance is improved, and the internal combustion engine can stably burn.

  Next, a modification of the insulator 1 will be described with reference to FIGS. 10 and 11. 10 and 11 are front views of modified examples of the insulator 1. In the present invention, the insulator 1 is not limited to an integral structure, and like the spark plug 101 shown in FIG. 10, the insulators 1, 1 and the leg length portions 1 </ b> A, 1 </ b> B are formed in separate structures, respectively. It can also be applied to a case in which two insulators 1 and 1 are held. Further, according to the present invention, like the spark plug 102 shown in FIG. 11, the insulator 1 and its leg length 1A are integrated, and two through holes are formed in the insulator 1 and its leg length 1A. The present invention can also be applied to a structure in which a plurality of center electrodes 3 and 4 are inserted.

  Next, the distance F / distance E of the spark plug 100 and the misfire rate of the engine equipped with the spark plug 100 will be described with reference to the graph shown in FIG. FIG. 12 is a graph showing the value of distance F / distance E (hereinafter referred to as “F / E”) of the spark plug 100 and the misfire rate (%) of the engine to which the spark plug 100 is attached.

  As shown in FIG. 12, when the F / E value of the spark plug 100 is 0.25, the misfire rate is 20%, and when the F / E value is 0.5, the misfire rate is 10%. When the F / E value is 0.75, the misfire rate is 5%. When the F / E value is 1, the misfire rate is 1%. When the F / E value is 1.25. The misfire rate is 0.5%, the misfire rate when the F / E value is 1.25 is 0.3%, and the misfire rate when the F / E value is 1.75 is 0%. It is. Therefore, the value of F / E exceeds 1, that is, as shown in FIGS. 1 and 2, the pair of center electrode 3 and ground electrode 5 that constitute the spark discharge gap G1 of the spark plug 100 of the present embodiment, The distance F between the intermediate point A of the gap and the entire axis C of the spark plug 100 is defined as an intersection 3A where the center axis B of the center electrode 3 intersects the tip surface of the center electrode 3, and the intersection 3A It can be seen that when the distance E from the axis C is larger than the misfire rate, the misfire rate is improved rapidly.

  As described above, in the multi-ignition spark plug 100 having a plurality of spark discharge gaps, the distance F is set to be longer than the distance E, and the spark discharge is generated on the radially outer side with respect to the center axis of the spark plug. The distance between the occurrence positions of the respective spark discharges can be increased. Therefore, the ignition performance can be improved and the combustion of the internal combustion engine can be stabilized. Also, a plurality of distances between the locations where a plurality of spark discharges are generated can be provided while suppressing an increase in the outer diameter of the thread portion 2A of the metal shell 2. Further, since the center electrodes 3 and 4 are not bent, it is possible to prevent breakage of the insulator and breakage of the center electrodes 3 and 4 in the assembly process. Further, if a noble metal such as Pt or Ni alloy is used for the center electrodes 3 and 4 and the ground electrodes 5 and 6, not only the ignition performance is improved but also the durability can be improved.

  In addition, this invention is not restricted to said embodiment, Various deformation | transformation are possible. In the above embodiment, the center electrode and the ground electrode are described as having two sets and three sets. However, in the present invention, the number of the center electrode and the ground electrode is not limited to two sets and three sets. Further, the distance F may be larger than the distance E in some or all of the plurality of spark discharge portions.

  The present invention is not limited to spark plugs for automobile engines, but can be applied to various types of spark plugs for internal combustion engines that ignite by spark discharge.

It is a fragmentary sectional view of the spark plug 100 of the 1st Embodiment of this invention. 3 is an enlarged view of the vicinity of a spark discharge portion of a spark plug 100. FIG. FIG. 6 is an enlarged view showing a first modification of the spark discharge part of the spark plug 100. FIG. 6 is an enlarged view showing a second modification of the spark discharge part of the spark plug 100. It is an enlarged view which shows the 3rd modification of the spark discharge part of the spark plug 100. FIG. It is an enlarged view which shows the 4th modification of the spark discharge part of the spark plug 100. FIG. FIG. 10 is an enlarged view showing a fifth modification of the spark discharge part of the spark plug 100. It is an enlarged view which shows the 6th modification of the spark discharge part of the spark plug 100. FIG. It is a bottom view showing the 6th modification of a spark discharge part of spark plug 100. It is a front view of the modification of the insulator 1. It is a front view of the modification of the insulator 1. It is a graph which shows the value of the distance F / distance E of the spark plug 100, and the misfire rate of the engine with which the spark plug 100 was mounted | worn. It is a front view of the spark plug 200 of a prior art. It is a front view of the spark plug 300 of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulator 1A, 1B, 1C Leg long part 2 Metal shell 2A Screw part 3, 4, 10 Center electrode 5, 6, 11 Ground electrode 7, 8 Terminal metal fitting 9 Ceramic resistance 100 Spark plug A Intermediate point B Center axis C Axis center D Outer diameter E Distance F Distance G1 Spark discharge gap G2 Spark discharge gap

Claims (4)

An insulator having a plurality of center electrodes provided therethrough, a metal shell for holding the insulator, one end joined to the tip of the metal shell, and the other end bent toward the center electrode. A spark plug comprising an electrode and a plurality of corresponding ground electrodes,
A distance between an intermediate point of a spark discharge gap formed between at least one center electrode of the plurality of center electrodes and a ground electrode paired with the center electrode, and a center axis of the entire spark plug But,
A spark plug characterized by being larger than the distance between the intersection of the central axis of the one central electrode and the tip surface of the central electrode and the central axis of the entire spark plug.   2. The spark plug according to claim 1, wherein an outer diameter of a distal end portion of a mounting portion of the metal shell to the internal combustion engine is 15.5 mm or less.   The spark plug according to claim 1, wherein a noble metal is provided in at least one of the center electrode and the ground electrode. A discharge part is composed of a pair of the center electrode and the ground electrode,
4. The spark plug according to claim 1, wherein a spark discharge position of one discharge portion is asymmetric with a spark discharge position of another discharge portion with respect to a central axis of the entire spark plug. 5. .

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