JP2016004730A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of suppressing the generation of problems when smoking occurs in a spark plug.SOLUTION: A spark plug 100 is equipped with a center electrode 10, an insulation body 20, a main body fitting 40, and a ground electrode 13. The insulation body 20 holds the center electrode 10 in a shaft hole 21. The main body fitting 40 holds the center electrode 10 through the insulation body 20 while a tip end portion 11 of the center electrode 10 is exposed to the outside. The ground electrode 13 is fixed to an opening end portion 42 of the main body fitting 40. At a tip end extending portion 22 of the insulation body 20, a projecting portion 50 locally projecting out in a direction intersecting orthogonally to an axial direction. An apex 51 of the projecting portion 50 is disposed outside the main body fitting 40. A rear end side inclined surface 53 of the projecting portion 50 is superimposed with an opening end portion 42 of the main body fitting 40, when viewed in a direction vertical to a center axis CX.

Description

  The present invention relates to a spark plug.

  The spark plug ignites the fuel gas by generating a spark discharge in the combustion chamber of the internal combustion engine. The spark plug usually includes a center electrode, a ground electrode, an insulator, and a metal shell. Each of the insulator and the metal shell has a cylindrical shape. The insulator holds the center electrode in the through hole, and the metal shell holds the insulator in the through hole. The tip of the center electrode extends outward from the opening end of the metal shell. The ground electrode is attached to the open end of the metal shell. A predetermined gap (hereinafter also referred to as “spark discharge gap”) for generating spark discharge is provided between the tip of the center electrode and the tip of the ground electrode.

  By the way, in the spark plug, carbon generated by incomplete combustion of the fuel gas may adhere to the surface of the tip portion in the vicinity of the spark discharge gap, so-called “sagging” may occur. If carbon accumulates on the surface of the front end portion of the insulator, the carbon functions as a conductive path, and the occurrence of spark discharge may be hindered. For example, the following Patent Documents 1 and 2 have been proposed as techniques for suppressing the occurrence of defects due to spark plugs.

Japanese Patent No. 4187654 Japanese Utility Model Publication No. 60-153492

  The spark plug of Patent Document 1 has a protrusion provided on the side surface of the insulator (FIG. 1B) and an additional electrode (FIG. 5A) disposed in proximity to the side surface of the insulator. In the spark plug of Patent Document 1, when a crack is generated, a spark discharge is generated between the protrusion or the additional electrode and the metal shell, and the deposited carbon is burned out and disappears.

  However, in the spark plug of FIG. 1B of Patent Document 1, since the apex of the protrusion is at the position of the opening end surface of the metal shell, when spark discharge occurs between the protrusion and the metal shell, There is a high possibility of misfire due to the extinguishing action. Moreover, there is a high possibility that the growth of the flame is hindered by the metal shell and the ignitability is lowered.

  In the spark plug of FIG. 5A of Patent Document 1, an electric field concentrates around the additional electrode, a conductive path that penetrates the insulator is formed, and a so-called spark penetration occurs that destroys the insulator. There is a possibility. Thus, in the spark plug, there is still room for improvement with respect to a technique for suppressing the occurrence of a problem when the spark is generated.

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

[1] According to one aspect of the present invention, a spark plug is provided. The spark plug may include a center electrode, an insulator, a metal shell, and a ground electrode. The center electrode may extend in the axial direction. The insulator may have a cylindrical shape, and the center electrode may be accommodated in a state where a tip portion of the center electrode extends to the outside. The metal shell may contain the insulator, and may have an open end where the tip of the center electrode and the tip of the insulator extend. The ground electrode may have a tip portion disposed with a predetermined gap with respect to the tip portion of the center electrode, and may be at least electrically connected to the open end portion of the metal shell. The insulator locally protrudes in a direction extending in the axial direction at a distal end extending portion extending in the axial direction on the distal end side, and a vertex that is a part farthest from a central axis of the insulator is the main body You may have at least 1 convex part arrange | positioned outside a metal fitting. The convex portion may have a rear end side inclined surface that is an inclined surface facing the rear end side in the axial direction. When viewed in a direction perpendicular to the central axis, the inclined surface on the rear end side and the opening end may overlap each other. According to the spark plug of this embodiment, since the apex of the convex portion is located outside the metal shell, a reduction in ignitability when a sag occurs is suppressed. Moreover, since the rear end side inclined surface is located at the opening end portion of the metallic shell, the occurrence of spark penetration is suppressed.

[2] In the spark plug of the above aspect, the shortest distance X between the ground electrode and the tip extension portion may be larger than the shortest distance G between the tip portion of the center electrode and the ground electrode. According to this form of the spark plug, it is possible to suppress the occurrence of a spark discharge at a position other than the gap between the tip portions of the center electrode and the ground electrode other than when the ringing occurs.

[3] In the spark plug of the above aspect, the ground electrode has a base end portion extending along the axial direction from the opening end portion of the metal shell, and the base end portion and the tip extension portion And the shortest distance Db between the apex and the opening end of the metal shell may satisfy the relationship Da> Db. According to the spark plug of this embodiment, it is possible to suppress the occurrence of spark discharge at a site other than between the convex portion and the metal shell when the sag is generated.

[4] In the spark plug of the above aspect, the ground electrode has a base end portion extending along an axial direction from an opening end portion of the metal shell, and the base end portion is formed of the metal shell. A rear end portion fixed to the opening end portion, and a thickness Ta of the rear end portion in the radial direction of the metal shell is smaller than a thickness Tb of the opening end portion of the metal shell; The fixed position of the rear end portion of the ground electrode at the opening end portion is the shortest distance Da between the base end portion and the extending portion, and the apex and the opening end portion of the metal shell. The shortest distance Db between them may be adjusted so as to satisfy the relationship of Da> Db. According to this form of the spark plug, the adjustment of the shortest distance Da between the base end portion of the ground electrode and the distal end extending portion of the insulator is facilitated.

[5] In the spark plug of the above aspect, the thickness of the insulator is the largest in the axial distance Dc between the apex of the convex portion and the opening end of the metal shell, and on the inclined surface on the rear end side. The distance Dd in the axial direction between the rear end portion of the slope, which is a smaller portion, and the apex may satisfy the relationship Dd> Dc. According to the spark plug of this embodiment, since the apex of the convex portion is located outside the metal shell, a reduction in ignitability when a sag occurs is suppressed.

[6] In the spark plug of the above aspect, the distance Dc and the distance Dd may satisfy a relationship of Dc> 1/2 · Dd. According to this form of the spark plug, spark discharge is likely to occur between the apex of the convex portion and the metal shell when bending occurs.

  A plurality of constituent elements of each aspect of the present invention described above are not indispensable, and some or all of the effects described in the present specification are to be solved to solve part or all of the above-described problems. In order to achieve the above, it is possible to appropriately change, delete, replace with another new component, and partially delete the limited contents of some of the plurality of components. In order to solve part or all of the above-described problems or to achieve part or all of the effects described in this specification, technical features included in one embodiment of the present invention described above. A part or all of the technical features included in the other aspects of the present invention described above may be combined to form an independent form of the present invention.

  The present invention can be realized in various forms other than the spark plug. For example, it can be realized in the form of an internal combustion engine including a spark plug, an ignition device, an insulator used for the spark plug, or the like.

Schematic which shows the structure of a spark plug. Schematic for demonstrating the structure of the protrusion part of an insulator. Schematic for demonstrating the parameter relevant to the structure of a projection part. Schematic for demonstrating vertex offset distance and slope length. Explanatory drawing which shows the evaluation result of the ignitability by the spark discharge between a projection part and a main metal fitting. Schematic which shows the structure of the spark plug as 2nd Embodiment. Schematic which shows the structure of the spark plug as 3rd Embodiment.

A. First embodiment:
FIG. 1 is a schematic view showing a configuration of a spark plug 100 as a first embodiment of the present invention. In FIG. 1, the center axis CX of the spark plug 100 is shown by a one-dot chain line. In FIG. 1, the left side of the drawing with respect to the center axis CX of the spark plug 100 is illustrated by a schematic cross section showing the internal configuration. In FIG. 1, a direction parallel to the center axis CX of the spark plug 100 (hereinafter also referred to as “axial direction”) is indicated by an arrow PD. An arrow PD indicates a direction from the rear end side (upper side of the drawing) to the front end side (lower side of the drawing) of the spark plug 100. The center axis CX of the spark plug 100 and the arrow PD indicating the axial direction are similarly shown in the drawings referred to in the following description. The center axis CX of the spark plug 100 is also the center axis of the center electrode 10, the insulator 20, and the metal shell 40 that constitute the spark plug 100.

  The spark plug 100 is attached to an internal combustion engine and used for ignition of fuel gas in the combustion chamber. When attached to the internal combustion engine, the front end side of the spark plug 100 is disposed in the combustion chamber of the internal combustion engine, and the rear end side is disposed outside the combustion chamber. The spark plug 100 includes a center electrode 10, a ground electrode 13, an insulator 20, a terminal electrode 30, and a metal shell 40.

  The center electrode 10 and the ground electrode 13 are electrodes for generating a spark discharge. The center electrode 10 is held by the metal shell 40 via the insulator 20 with the tip 11 of the center electrode 10 exposed to the outside on the center axis CX. The center electrode 10 is electrically connected to an external power source (not shown) via a terminal electrode 30 disposed on the rear end side.

  The ground electrode 13 is attached to the metal shell 40 and is electrically connected to the metal shell 40. The ground electrode 13 has a proximal end portion 13a, a distal end portion 13b, and a tip portion 13c. The base end portion 13a is a portion that extends substantially straight from the opening end portion 42 on the distal end side of the metal shell 40 toward the distal end side along the axial direction. The distal end portion 13 b is a portion that is bent from the proximal end portion 13 a and extends toward the distal end portion 11 of the center electrode 10. The tip portion 13c is a portion protruding in the direction of the tip portion 11 of the center electrode 10 at the tip portion 13b. The chip part 13c may be omitted.

  A predetermined gap SG for generating spark discharge is provided between the tip portion 13 c of the ground electrode 13 and the tip portion 11 of the center electrode 10. Hereinafter, the gap SG is also referred to as “spark discharge gap SG”. In the spark plug 100 of the present embodiment, normally, spark discharge occurs in the spark discharge gap SG during ignition. When the tip portion 13c is omitted, spark discharge occurs with the gap between the tip portion 11 of the center electrode 10 and the tip portion 13b of the ground electrode 13 facing the tip portion 11 as a spark discharge gap SG. To do.

  The insulator 20 has a cylindrical shape and has a shaft hole 21 penetrating the center thereof. The insulator 20 is made of, for example, a ceramic sintered body such as alumina or aluminum nitride. The insulator 20 has a tip extension portion 22 on the tip side. The tip extending portion 22 is a portion extending at a position separated from the inner wall surface of the metal shell 40. In the present embodiment, the distal end extending portion 22 has a tapered shape in which the diameter of the portion other than the protruding portion 50 becomes smaller toward the distal end side.

  The center electrode 10 is accommodated and held in the shaft hole 21 of the tip extension portion 22, and the tip portion 11 of the center electrode 10 extends from the open end 23 of the tip extension portion 22 in the insulator 20. A protruding portion 50 corresponding to a protruding portion that locally protrudes is provided on a side surface of the tip extending portion 22. The protrusion 50 is formed by rotating and polishing the base material of the insulator 20 with a grindstone. Details of the protrusion 50 will be described later.

  The insulator 20 has a rear end extending portion 25 on the rear end side. The rear end extending portion 25 extends in the axial direction, and extends from the opening end portion 48 on the rear end side of the metal shell 40. A shaft-like terminal electrode 30 is inserted into the shaft hole 21 of the rear end extending portion 25 from the opening end portion 26. The rear end portion 31 of the terminal electrode 30 is exposed to the outside so that it can be connected to an external power source (not shown).

  The center electrode 10 and the terminal electrode 30 are electrically connected through a resistor 35 sandwiched between first and second glass seal materials 36 and 37 in the shaft hole 21 of the insulator 20. This suppresses the generation of radio noise when spark discharge occurs.

  The metal shell 40 is a substantially cylindrical metal member having a cylindrical hole 41 penetrating the center. The metal shell 40 is made of, for example, carbon steel. In the cylindrical hole 41 of the metal shell 40, the center electrode 10 and the center electrode 10 and the tip end portion 22 of the insulator 20 extend from the opening end 42 on the tip end side. The insulator 20 is held. Further, the base end portion 13a of the ground electrode 13 is fixed to the opening end portion 42 on the front end side of the metal shell 40 by welding.

  A threaded portion 43 that is screwed into a thread groove of a mounting hole (not shown) of the internal combustion engine is provided on the outer peripheral surface on the front end side of the metal shell 40. On the rear end side of the screw portion 43, a tool engaging portion 45 is provided to which a tool is engaged when the spark plug 100 is attached to the internal combustion engine. On the rear end side of the tool engaging portion 45, a caulking portion 47 for caulking and fixing the rear end extending portion 25 of the insulator 20 is provided. The caulking portion 47 is formed by caulking the opening end portion 48 on the rear end side of the metal shell 40 inward.

  As described above, the protrusion 50 is provided on the side surface of the tip extension portion 22 of the insulator 20. Even if the spark plug 100 according to the present embodiment has the protrusions 50, carbon is deposited on the surface of the extended end portion 22 of the insulator 20, so-called warpage occurs. The occurrence of defects due to the sag is suppressed. Specifically, it is as follows.

  FIG. 2 is a schematic diagram for explaining the configuration of the protrusion 50 of the insulator 20. In the upper part of FIG. 2, the distal end portion of the spark plug 100 is illustrated with the distal end side being the upper side of the paper and the rear side being the lower side of the paper. In the upper part of FIG. 2, for convenience, the metal shell 40 and the ground electrode 13 are illustrated by a schematic cross section. In the lower part of FIG. 2, the center electrode 10 and the insulator 20 when viewed along the axial direction are illustrated so as to correspond to the upper part. In the lower part of FIG. 2, the contour lines of the ground electrode 13 and the metal shell 40 are shown by two-dot chain lines for convenience.

  In the present embodiment, the protruding portion 50 protrudes in the direction perpendicular to the central axis CX at the distal end extending portion 22 of the insulator 20. The protrusion 50 has a substantially annular shape centered on the central axis CX when viewed along the axial direction. The protrusion 50 has a substantially triangular cross-sectional shape at an arbitrary cut surface passing through the central axis CX, and has a vertex 51, a tip-side inclined surface 52, and a rear-end-side inclined surface 53 (see FIG. 2 top). The vertex 51 is a portion that is the farthest from the central axis CX in the protrusion 50. In the present embodiment, the vertex 51 is a corner between the front end side inclined surface 52 and the rear end side inclined surface 53. The apex 51 is located on the tip side from the opening end 42 of the metal shell 40.

  The front end side inclined surface 52 is an inclined surface facing the front end side, and the rear end side inclined surface 53 is an inclined surface facing the rear end side. In the rear end side inclined surface 53, the shortest distance between the surface and the central axis CX is reduced toward the rear end side. Hereinafter, the portion where the thickness of the insulator 20 is the smallest in the rear end side inclined surface 53 is also referred to as “the lower end of the rear end side inclined surface 53”. The lower end of the rear end side inclined surface 53 corresponds to the rear end portion of the slope. The lower end of the rear end side inclined surface 53 is located on the rear end side with respect to the opening end portion 42 of the metal shell 40.

  Here, when carbon is deposited on the surface of the extended end portion 22, the current of the center electrode 10 flows to the protruding portion 50 through the carbon, and between the apex 51 of the protruding portion 50 and the metal shell 40. Spark discharge occurs (dashed arrow LP). By this spark discharge, the fuel gas in the combustion chamber is ignited, and the carbon adhering to the tip extending portion 22 is burned out and disappears. As described above, the protrusion 50 functions as a sub-electrode that generates a spark discharge when the ringing occurs.

  In the protrusion 50 of this embodiment, as described above, the apex 51 of the protrusion 50 is located on the tip side of the opening end 42 of the metal shell 40 and is located outside the metal shell 40. As a result, a spark discharge can be generated at a spaced position outside the metal shell 40, so that it is suppressed that the flame core generated by the spark discharge is affected by the flame extinguishing action in which the metal shell 40 takes heat away. . In addition, the growth of the flame kernel is inhibited from being hindered by the metal shell 40.

  In the protrusion 50 of the present embodiment, the lower end of the rear end side inclined surface 53 is located on the rear end side with respect to the opening end 42 of the metal shell 40, and when viewed in a direction perpendicular to the central axis CX, The rear end side inclined surface 53 and the opening end portion 42 of the metal shell 40 overlap each other. Therefore, the thickness of the insulator 20 in the direction perpendicular to the central axis CX (the radial direction of the metallic shell 40) is large at a position facing the inner peripheral edge of the opening end portion 42 of the metallic shell 40.

  An electric field concentrates at the corner of the inner peripheral edge of the opening end 42 of the metal shell 40 when the central electrode 10 is energized to generate a spark discharge. In the extended end portion 22 of the insulator 20, the thickness at the position facing the portion where the electric field concentrates is increased by the protrusion 50. Therefore, the occurrence of spark penetration through which the current from the center electrode 10 flows through the insulator 20 to the opening end 42 of the metal shell 40 due to the electric field concentration at the opening end 42 of the metal shell 40 is suppressed. The destruction of the insulator 20 due to is suppressed.

  In the spark plug 100 of the present embodiment, the shortest distance Da between the distal end extending portion 22 of the insulator 20 and the proximal end portion 13a of the ground electrode 13 is the apex 51 of the protrusion 50 and the proximal end portion 13a of the ground electrode 13. Is the distance between The spark plug 100 of the present embodiment is configured such that the shortest distance Da is larger than the shortest distance Db between the apex 51 of the protrusion 50 and the open end 42 of the metal shell 40 (Da>). Db). This suppresses the occurrence of spark discharge in a narrow region between the tip extension portion 22 and the base end portion 13a of the ground electrode 13 where there is little flame growth space when the burn is occurring. Yes.

  Here, the thickness Ta of the base end portion 13a of the ground electrode 13 in the direction perpendicular to the central axis CX is smaller than the thickness Tb of the opening end portion 42 of the metal shell 40 in the direction perpendicular to the central axis CX. Therefore, the welding position MP corresponding to the fixing position of the rear end portion of the base end portion 13 a of the ground electrode 13 at the opening end portion 42 of the metal shell 40 can be adjusted in the thickness direction of the opening end portion 42 of the metal shell 40. In the spark plug 100 of this embodiment, the shortest distance Da is adjusted to be larger than the shortest distance Db by adjusting the welding position MP of the ground electrode 13 at the opening end 42 of the metal shell 40. ing.

  The shortest distance Da corresponds to the shortest distance X between the ground electrode 13 and the extended end portion 22 of the insulator 20 (X = Da). In the spark plug 100 of the present embodiment, the shortest distance X is configured to be larger than the shortest distance G between the tip portion 11 of the center electrode 10 and the tip portion 13b (tip portion 13c) of the ground electrode 13. (X> G). Accordingly, it is possible to suppress the occurrence of spark discharge between the apex 51 of the protrusion 50 and the ground electrode 13 when no warpage has occurred. In the present embodiment, the shortest distance G is the shortest distance between the center electrode 10 and the tip portion 13 c of the ground electrode 13. When the tip portion 13 c is omitted, the shortest distance G is the shortest distance between the center electrode 10 and the tip portion 13 b of the ground electrode 13.

  The shortest distance Db corresponds to the shortest distance Y between a portion having the same potential as that of the ground electrode 13 and a portion extending to the outside of the metal shell 40 in the tip extending portion 22 (Y = Db). In the spark plug 100 of the present embodiment, the shortest distance Y is configured to be larger than the shortest distance G between the tip portion 11 of the center electrode 10 and the end portion of the ground electrode 13 (Y>). G). Therefore, the occurrence of spark discharge between the apex 51 of the protrusion 50 and the metal shell 40 is suppressed when no warpage occurs.

  A more preferable configuration of the protrusion 50 will be described with reference to FIGS. FIG. 3 is almost the same as the upper diagram of FIG. 2 except that the notation of parameters relating to the protrusion 50 is different. Hereinafter, the distance from the lower end of the inclined surface on the rear end side of the protrusion 50 to the apex 51 in the protrusion direction of the protrusion 50 (direction perpendicular to the central axis CX) is referred to as “the height H of the protrusion 50”. Further, the distance in the axial direction between the apex 51 of the protrusion 50 and the open end 42 of the metal shell 40 is referred to as “vertex offset distance Dc”, and the apex 51 of the protrusion 50 and the lower end of the rear end side inclined surface 53. The distance in the axial direction is called “slope length Dd”.

  FIG. 4 is a schematic diagram showing a change in the configuration of the protrusion 50 when the vertex offset distance Dc or the slope length Dd is changed. 4A to 4C show schematic views of the vicinity of the protrusion 50 in the spark plug 100, respectively. In the columns (A) to (C) of FIG. 4, the ground electrode 13 is not shown for convenience.

  The protrusion 50 in the column (B) in FIG. 4 has a configuration in which the vertex offset distance Dc is larger than the protrusion 50 in the column (A) in FIG. When the vertex offset distance Dc is increased, the position of the vertex 51 is separated from the opening end 42 of the metal shell 40 toward the distal end side in the axial direction.

  The protrusion 50 in the column (C) of FIG. 4 has a configuration in which the slope length Dd is larger than the protrusion 50 in the column (A) of FIG. When the slope length Dd increases while the height H of the protrusion 50 remains constant, the inclination angle θ of the rear end side inclined surface 53 decreases. The “inclination angle θ of the rear end side inclined surface 53” is an angle on the front end side among the angles between the axial direction and the rear end side inclined surface 53.

  FIG. 5 is an explanatory view showing an evaluation result of ignitability by spark discharge between the protrusion 50 and the metal shell 40. Each sample S1-S11 is a test body of the spark plug 100, and has substantially the same configuration except that the vertex offset distance Dc and the slope length Dd are different.

  In this evaluation experiment, carbon was attached in advance to the surface of the insulator 20 of each of the samples S1 to S11 so that the projecting portion 50 would ignite. Moreover, each sample S1-S11 was attached to the combustion chamber, the ignition with respect to the mixture of propane and air (air-fuel excess ratio (lambda) = 1.5) was repeated 10 times, and the number of misfires was counted. The state of ignition of the air-fuel mixture was observed by the Schlieren method.

  In all the samples S9 to S11, the vertex offset distance Dc was 0, and the vertex 51 of the protrusion 50 was at the position of the opening end 42 of the metal shell 40 in the axial direction. In samples S9 to S11, the number of misfires was 5 or more. On the other hand, the samples S1 to S8 in which the vertex offset distance Dc is greater than 0 all had the number of misfires of 4 or less. Thus, the ignitability at the time of flying from the protrusion 50 was enhanced by positioning the apex 51 of the protrusion 50 outside the metal shell 40.

  In the samples S1 to S4, the vertex offset distance Dc is all 1, and the slope length Dd is in the range of 1.5 to 4 and becomes smaller as the sample number is smaller. In samples S1 to S4, sample S1 showed the highest ignitability. In samples S5 to S8, the vertex offset distance Dc is 1.5, and the slope length Dd is 2 to 5 and the smaller the sample number, the smaller. In samples S5 to S8, sample S5 showed the highest ignitability.

  As described above, when the vertex offset distance Dc is the same, the smaller the slope length Dd, the lower the number of misfires and the higher the ignitability. From the results of the samples S1 to S8, when the vertex offset distance Dc is the same, it is desirable that the rear end-side inclined surface 53 has a small slope length Dd (large inclination angle θ) and a steep slope. Recognize. This is presumed to be because when the inclination angle θ of the rear end side inclined surface 53 is small, there is a high possibility that the rear end side inclined surface 53 does not ignite, and the rear end side inclined surface 53 flares. Is done.

  When samples S2 and S5 having the same slope length Dd were compared, sample S5 having a larger vertex offset distance Dc showed higher ignitability. From this result, it is understood that when the inclination angle θ of the rear end side inclined surface 53 is the same, it is desirable that the vertex offset distance Dc is larger. This is presumably because the position where the spark is generated can be separated from the metal shell 40 as the vertex offset distance Dc is larger, and the flame kernel becomes easier to grow. Thus, the ignitability can be improved by increasing the vertex offset distance Dc.

Here, in samples S1 and S5 having high ignitability among samples S1 to S8, the vertex offset distance Dc and the slope length Dd satisfy the relationship of the following inequality (A). On the other hand, in the other samples S2 to S4 and S6 to S8, the vertex offset distance Dc and the slope length Dd do not satisfy the relationship of the following inequality (A). Thus, the ignitability was improved when the vertex offset distance Dc and the slope length Dd satisfy the relationship of the following inequality (A). Therefore, in the spark plug 100 of the present embodiment, it is desirable that the protrusion 50 is adjusted so that the vertex offset distance Dc and the slope length Dd satisfy the relationship of the following inequality (A).
Dc> 1/2 · Dd (A)

  As described above, according to the spark plug 100 of the present embodiment, even when the swell occurs, a decrease in ignitability due to the sag is suppressed by the spark discharge at the protrusion 50. In addition, damage to the insulator 20 due to spark penetration is suppressed by the rear end side inclined surface 53 of the protrusion 50. In addition, since the carbon that is the cause of the beat is removed by the spark discharge at the protrusion 50, the state of the beat of the spark plug 100 is improved, and the occurrence of problems due to the beat is suppressed.

B. Second embodiment:
FIG. 6 is a schematic view showing a configuration of a spark plug 100A as a second embodiment of the present invention. FIG. 6 is a view similar to FIG. 2 referred to in the first embodiment, in which the top end portion of the spark plug 100A is illustrated in the upper stage, and the center electrode 10 when viewed along the axial direction in the lower stage and An insulator 20A is shown. The spark plug 100A of the second embodiment has substantially the same configuration as the spark plug 100 of the first embodiment, except that the configuration of the protrusion 50A is different.

  The protrusion 50A included in the insulator 20A of the second embodiment corresponds to a configuration in which the electrode facing surface 54 is provided on the protrusion 50 of the first embodiment. The electrode facing surface 54 is a plane that faces and is parallel to the surface 13 s on the central axis CX side of the base end portion 13 a of the ground electrode 13. The electrode facing surface 54 is formed at a position close to the outer peripheral contour line of the tip extending portion 22 when viewed along the axial direction. The electrode facing surface 54 is formed by polishing and scraping a part of the protrusion 50 of the first embodiment. When the protrusion 50 </ b> A of the second embodiment is viewed along the axial direction, the outer peripheral contour formed by the vertex 51 forms an arc shape that is open with respect to the ground electrode 13.

  Even in the spark plug 100 </ b> A of the second embodiment, spark discharge can be generated between the apex 51 of the protrusion 50 </ b> A and the opening end 42 of the metal shell 40 when the sag occurs. Therefore, it is possible to suppress a decrease in ignitability due to the occurrence of the rotting and to remove the carbon that is the cause of the rotting. In addition, since the rear end side inclined surface 53 is located at a position facing the opening end portion 42 of the metal shell 40, the occurrence of spark penetration in the insulator 20A is suppressed.

  Here, in the spark plug 100A of the second embodiment, the shortest distance Da between the proximal end portion 13a of the ground electrode 13 and the distal end extending portion 22 of the insulator 20A is a protrusion between the proximal end portion 13a of the ground electrode 13 and the protrusion. This is the shortest distance between the electrode facing surface 54 of the portion 50A. The spark plug 100A of the second embodiment is configured such that the shortest distance Da is larger than the shortest distance Db between the apex 51 of the protrusion 50A and the open end 42 of the metal shell 40 (Da > Db). This suppresses the occurrence of a spark discharge in a narrow region between the base end portion 13a of the ground electrode 13 and the electrode facing surface 54 when the warpage occurs.

  Further, the shortest distance Da corresponds to the shortest distance X between the ground electrode 13 and the tip extending portion 22 of the insulator 20A (X = Da). The spark plug 100 according to the second embodiment is configured such that the shortest distance X is larger than the shortest distance G between the tip 11 of the center electrode 10 and the end of the ground electrode 13 (X> G). . Accordingly, it is possible to suppress the occurrence of a spark discharge between the ground electrode 13 and the tip extending portion 22 when no warpage has occurred. In the spark plug 100A of the second embodiment, since the electrode facing surface 54 is provided on the protrusion 50A, the shortest distance Da (shortest distance X) can be set larger than the shortest distances Db and G. Easy.

  The spark plug 100 of the second embodiment is configured such that the shortest distance Db is larger than the shortest distance G. The shortest distance Db corresponds to the shortest distance Y described in the first embodiment. As with the spark plug 100 of the first embodiment, this configuration suppresses the occurrence of spark discharge between the distal end extending portion 22 and the metal shell 40 when no warpage has occurred.

  As described above, even the spark plug 100A of the second embodiment can achieve the same effects as those of the first embodiment. Further, in the spark plug 100A of the second embodiment, the protrusion 50A has the electrode facing surface 54, so that the gap between the base end portion 13a of the ground electrode 13 and the distal end extending portion 22 of the insulator 20B. It is easy to secure the shortest distance X. In the spark plug 100A of the second embodiment, the ignitability can be ensured by configuring the protrusion 50A so that the relationship of the inequality (A) described in the first embodiment is satisfied.

C. Third embodiment:
FIG. 7 is a schematic view showing a configuration of a spark plug 100B as a third embodiment of the present invention. FIG. 7 is a view similar to FIG. 6 referred to in the second embodiment. In the lower part of FIG. 7, an arrow DD indicating the extending direction of the tip portion 13 b of the ground electrode 13 is illustrated. The “extending direction of the distal end portion 13b of the ground electrode 13” is a direction in which the distal end portion 13b extends when viewed along the axial direction, and is a direction from the proximal end portion 13a of the ground electrode 13 toward the tip portion 13c. It is.

  The spark plug 100B of the third embodiment is substantially the same as the spark plug 100A (FIG. 6) of the second embodiment, except that the configuration of the protrusion 50B is different. The protrusion 50B of the insulator 20B of the third embodiment has a substantially triangular cross-sectional shape that locally protrudes in a direction perpendicular to the central axis CX, and is configured in a substantially bowl shape (substantially bowl shape). Has been.

  The protrusion 50B has an annular shape when viewed along the axial direction, and its center CP is offset from the center axis CX of the spark plug 100B in the extending direction of the tip 13b of the ground electrode 13. In position. In the protrusion 50B of the third embodiment, the virtual straight line VL that connects the central axis CX and the center CP of the protrusion 50B and the protrusion out of the corners between the front-end-side inclined surface 52 and the rear-end-side inclined surface 53. The portion corresponding to the intersection with the outer peripheral contour line of 50B is the vertex 51.

  In the spark plug 100B of the third embodiment, the shortest distance Da between the protrusion 50B and the base end portion 13a of the ground electrode 13 is larger than the shortest distance Db between the vertex 51 of the protrusion 50B and the metal shell 40. (Da> Db). Further, the two shortest distances Da and Db (corresponding to the shortest distances X and Y, respectively) are both greater than the shortest distance G between the tip portion 11 of the center electrode 10 and the tip portion 13c of the ground electrode 13. (X, Y> G).

  In the spark plug 100A according to the third embodiment, the apex 51 of the protrusion 50A is at a position spaced apart from the base end 13a of the ground electrode 13 on the opposite side across the central axis CX. The ignitability when it is on is further enhanced. Moreover, since the vertex 51 of the protrusion 50B is a single point, the location where spark discharge occurs is limited, and more stable ignitability can be obtained. In addition, the spark plug 100B of the third embodiment can provide the same effects as the spark plug 100 of the first embodiment and the spark plug 100A of the second embodiment. In the spark plug 100B of the second embodiment, the ignitability can be ensured by configuring the protrusion 50B so that the relationship of the inequality (A) described in the first embodiment is satisfied.

D. Variation:
D1. Modification 1:
In each of the above embodiments, the insulators 20, 20A, 20B are provided with one protrusion 50, 50A, 50B as a protrusion. On the other hand, the insulators 20, 20A, 20B may be further provided with one or more convex portions on the tip side from the protrusions 50, 50A, 50B. Even if it is such a structure, the effect similar to said each embodiment can be acquired.

D2. Modification 2:
In each of the embodiments described above, the protrusions 50, 50A, and 50B as the protrusions protrude in the direction perpendicular to the central axis CX of the spark plugs 100, 100A, and 100B. On the other hand, the protrusions of the insulators 20, 20A, 20B do not have to protrude in a direction perpendicular to the central axis CX. The convex part should just protrude in the direction which crosses the central axis CX, and may protrude in the direction inclined to the front end side in the axial direction or the direction inclined to the rear end side.

D3. Modification 3:
In each of the embodiments described above, the protrusions 50, 50A, and 50B as the protrusions are configured in a substantially bowl shape. On the other hand, the protrusions of the insulators 20, 20A, 20B may be configured in a shape other than a substantially bowl shape. The convex portion may have a columnar shape or a hemispherical shape. The convex part should just have the shape which protruded locally.

D4. Modification 4:
In the spark plugs 100, 100A, 100B of the above-described embodiments, the shortest distance X between the ground electrode 13 and the extended end portion 22 of the insulators 20, 20A, 20B is such that the distal end portion 11 of the center electrode 10 and the ground electrode 13 It is comprised so that it may become larger than the shortest distance G between these edge parts (X> G). On the other hand, the spark plugs 100, 100A, 100B of the embodiments may be configured such that the shortest distance X is equal to or less than the shortest distance G (X ≦ G).

D5. Modification 5:
In each of the above embodiments, the shortest distance Da between the proximal end portion 13a of the ground electrode 13 and the distal end extending portion 22 of the insulators 20, 20A, 20B, the apex 51 of the protruding portions 50, 50A, and the metal shell 40 The shortest distance Db between the opening end portion 42 satisfies the relationship Da> Db. On the other hand, the shortest distance Da and the shortest distance Db may not satisfy the relationship of Da> Db, and may have a relationship of Da ≦ Db.

D6. Modification 6:
In each of the embodiments described above, the shortest distance Da between the base end portion 13a of the ground electrode 13 and the distal end extending portion 22 of the insulators 20, 20A, 20B is equal to the ground electrode 13 at the open end portion 42 of the metal shell 40. It is adjusted by the welding position MP. On the other hand, the shortest distance Da between the base end portion 13a of the ground electrode 13 and the distal end extending portion 22 of the insulators 20, 20A, 20B is adjusted by the welding position MP at the open end portion 42 of the metal shell 40. It is not necessary. The shortest distance Da between the base end portion 13a of the ground electrode 13 and the tip extension portion 22 of the insulators 20, 20A, 20B may be adjusted by, for example, the thickness of the base end portion 13a of the ground electrode 13, You may adjust with the opening diameter in the opening edge part 42 of the metal shell 40. FIG.

D7. Modification 7:
In the protrusions 50, 50A, and 50B of the above-described embodiments, the surface of the rear end side inclined surface 53 is configured by a flat surface. On the other hand, the surface of the rear end side inclined surface 53 may not be a flat surface. The surface of the rear end side inclined surface 53 may be configured by a curved surface, or irregularities may be formed. The rear end side inclined surface 53 may be formed by combining inclined surfaces having a plurality of inclination angles.

D8. Modification 8:
The protrusions 50, 50A, 50B of the above embodiments are formed integrally with the insulators 20, 20A, 20B. On the other hand, the protrusions 50, 50 </ b> A, 50 </ b> B may be formed as separate bodies by joining an insulating member different from the insulators 20, 20 </ b> A, 20 </ b> B to the tip extension portion 22.

D9. Modification 9:
The protrusion 50B of the third embodiment does not have the electrode facing surface 54 like the protrusion 50A of the second embodiment. On the other hand, the protruding portion 50B of the third embodiment may be provided with the electrode facing surface 54 similarly to the protruding portion 50A of the first embodiment. With this configuration, the occurrence of spark discharge between the ground electrode 13 and the protrusion 50B is further suppressed.

B10. Modification 10:
The distal end extending portions 22 of the insulators 20, 20 </ b> A, and 20 </ b> B of the above embodiments have a substantially tapered shape that decreases in diameter toward the distal end side. On the other hand, the tip extension part 22 of the insulators 20, 20A, 20B may have other shapes. For example, the front end extending portion 22 may be configured in a shape in which the front end side is formed in a substantially tapered shape and the rear end side is extended with substantially the same diameter. Or the front-end | tip extension part 22 may be comprised by the shape which the rear end side is comprised in the taper shape, and is extended | stretched with the substantially same shape in the front end side. Moreover, the front-end | tip extension part 22 may be the structure by which the taper-shaped site | part is pinched | interposed into the site | part extended with substantially the same diameter formed in the front end side and the rear end side. The protrusions 50, 50 </ b> A, 50 </ b> B may be formed in a portion that extends with the same diameter of the tip extending portion 22.

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

DESCRIPTION OF SYMBOLS 10 ... Center electrode 11 ... Tip part 13 ... Ground electrode 13a ... Base end part 13b ... Tip part 13c ... Tip part 13s ... Surface 20, 20A, 20B ... Insulator 21 ... Shaft hole 22 ... End extension part 23 ... Opening edge part 25 ... rear end extending part 26 ... opening end part 30 ... terminal electrode 31 ... rear end part 35 ... resistors 36 and 37 ... glass sealing material 40 ... metal shell 41 ... cylindrical hole 42 ... opening end part 43 ... threaded part 45 ... Tool engaging portion 47 ... caulking portion 48 ... opening end portions 50, 50A, 50B ... projection portion 51 ... apex 52 ... tip end side inclined surface 53 ... rear end side inclined surface 54 ... electrode facing surfaces 100, 100A, 100B ... sparks Plug CX ... Center axis MP ... Welding position SG ... Spark discharge gap

Claims (6)

A central electrode extending in the axial direction;
A cylindrical insulator that houses the center electrode in a state in which the tip of the center electrode extends to the outside;
A metal shell containing the insulator, and having an open end extending from the tip of the center electrode and the tip of the insulator;
A ground electrode having a tip portion disposed with a predetermined gap with respect to the tip portion of the center electrode, and being at least electrically connected to the opening end portion of the metal shell;
With
The insulator locally protrudes in a direction extending in the axial direction at a distal end extending portion extending in the axial direction on the distal end side, and a vertex that is a part farthest from a central axis of the insulator is the main body Having at least one convex portion arranged outside the metal fitting,
The convex portion has a rear end side inclined surface that is an inclined surface facing the rear end side in the axial direction,
The spark plug, wherein the rear end side inclined surface and the opening end portion overlap each other when viewed in a direction perpendicular to the central axis. The spark plug according to claim 1, wherein
A spark plug in which a shortest distance X between the ground electrode and the tip extension portion is larger than a shortest distance G between the tip portion of the center electrode and the ground electrode. The spark plug according to claim 1 or 2,
The ground electrode has a base end extending along the axial direction from the opening end of the metal shell,
The shortest distance Da between the base end portion and the distal end extending portion and the shortest distance Db between the apex and the opening end portion of the metal shell satisfy a relationship of Da> Db. plug. The spark plug according to any one of claims 1 to 3,
The ground electrode has a base end extending along the axial direction from the opening end of the metal shell,
The base end portion has a rear end portion fixed to the opening end portion of the metal shell,
The thickness Ta of the rear end portion in the radial direction of the metal shell is smaller than the thickness Tb of the opening end portion of the metal shell,
The fixing position of the rear end portion of the ground electrode at the opening end portion of the metal shell is the shortest distance Da between the base end portion and the tip extending portion, the apex, and the opening end portion of the metal shell. The spark plug is adjusted so that the shortest distance Db between the two and the second electrode satisfies a relationship of Da> Db. The spark plug according to any one of claims 1 to 4, wherein
A distance Dc in the axial direction between the apex of the convex portion and the opening end of the metal shell, and a rear end of the slope which is a portion where the thickness of the insulator is smallest on the rear end inclined surface A spark plug satisfying a relationship of Dc <Dd with a distance Dd in the axial direction from the apex. The spark plug according to claim 5, wherein
The spark plug, wherein the distance Dc and the distance Dd satisfy a relationship of Dc> 1/2 · Dd.

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