JP4699918B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine that performs ignition by spark discharge.

  Conventionally, spark plugs for ignition are used in internal combustion engines. In this spark plug, generally, a ground electrode is welded to the tip of the metal shell that holds the insulator in which the center electrode is inserted, and the other end of the ground electrode is connected to the tip of the center electrode. A main spark discharge gap is formed so as to face the front end surface of the portion. Then, a spark discharge is performed between the center electrode and the ground electrode, and a flame nucleus is formed by igniting the air-fuel mixture exposed between the two electrodes.

  Such an attachment of the spark plug to the internal combustion engine is performed by screwing a male screw portion formed on the outer peripheral surface of the metal shell into a female screw portion of the mounting hole of the engine head. Depending on the mounting direction, a ground electrode may be disposed upstream of the flow of the air-fuel mixture toward the spark discharge gap in the combustion chamber, and the air-fuel mixture becomes difficult to reach the spark discharge gap, so the ignitability is reduced. There is a fear. Therefore, if the ground electrode is formed in a columnar shape and the resistance to the flow of the air-fuel mixture is reduced, the air-fuel mixture can easily go around the ground electrode, and deterioration of ignitability can be suppressed (for example, Patent Document 1 and Patent Document 2). reference.).

Furthermore, in Patent Document 1, since the ground electrode is formed in a cylindrical shape, the surface is curved even when it comes into contact with the ground electrode when a flame nucleus (fire type) formed by ignition in the spark discharge gap grows. Therefore, the energy loss is small and the ignitability is hardly lowered.
JP 52-48742 A Japanese Patent Laid-Open No. 11-121142

  However, in Patent Document 1, the ground electrode is disposed on the center side of the combustion chamber as viewed from the spark discharge gap, and it is necessary to bypass the ground electrode in order for the flame nucleus to grow and spread toward the center of the combustion chamber. Therefore, there is a problem that it takes time for the combustion to spread throughout the combustion chamber. Further, in Patent Document 2, although the ground electrode is not disposed on the center side of the combustion chamber as viewed from the spark discharge gap, the spark discharge is performed on the side of the center electrode. There was a problem that it took a long time for the flame to spread out and reach the center of the combustion chamber away from the center of the chamber. Further, since the spark discharge is performed at a position close to the insulator, there is a problem that it is easy to receive a flame extinguishing action.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug that can improve ignitability.

In order to achieve the above object, a spark plug according to a first aspect of the present invention includes a columnar center electrode having a first axis as its center axis, and an axial hole extending in the first axis direction, and the center An insulator that holds the electrode in the shaft hole, a metal shell that surrounds and holds the periphery of the insulator in the radial direction, and a cylindrical shape having a second axis as its central axis, and one end portion of the metal shell Joined to the front end surface, the other end is bent toward the inner peripheral side of the metal shell, the other end is located at least on the front end side of the front end surface of the center electrode, and the front end of the center electrode The second axis that bends together with the ground electrode is in a twisted positional relationship with the first axis at the other end of the ground electrode. have a portion along the first virtual line, and, prior to When the tip of the center electrode, the first axis, and the other end of the ground electrode are projected onto a first virtual plane orthogonal to the first virtual line, the first virtual plane is projected on the first virtual plane. A second imaginary line passing through the position of the first imaginary line and passing through a position of a point on the contour of the tip of the center electrode closest to the position of the first imaginary line, and the first axis The angle θ formed with the projection line is in a relationship of 25 ° ≦ θ ≦ 60 ° .

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the spark plug according to the second aspect includes the tip of the center electrode and the ground electrode on a second imaginary plane orthogonal to the first axis. When the other end portion is projected, the contour line of the tip end portion of the center electrode and the contour line of the other end portion of the ground electrode are point-contacted or separated from each other on the second virtual plane. It is characterized by being.

According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the spark plug of the invention is further provided with the tip of the center electrode and the other end of the ground electrode on the second virtual plane. When projecting the first imaginary line and the first imaginary line, the contour line of the end face on the other end side of the ground electrode closest to the position of the first axis on the second imaginary plane is the first imaginary line. It is characterized in that it is located between two third imaginary lines that are parallel to the direction perpendicular to the projection line of the imaginary line and circumscribe the outline of the tip of the center electrode.

  Since the ground electrode is bent to form a spark discharge gap between the other end and the tip of the center electrode, the second axis that is the center axis of the ground electrode is also bent. In the spark plug according to the first aspect of the present invention, the second axis is a portion along the first imaginary line that is twisted with the first axis that is the center axis of the center electrode at the other end of the ground electrode. Have. If the positional relationship between the tip of the center electrode and the other end of the ground electrode is configured in this way, the other end of the ground electrode is placed at a position shifted from the center of the combustion chamber as viewed from the spark discharge gap. Can be made. For this reason, when the flame nucleus formed in the spark discharge gap grows, the other end of the ground electrode does not become an obstacle in the direction toward the center of the combustion chamber, and quickly spreads throughout the combustion chamber. This can improve the ignitability of the spark plug.

Further, since the other end portion of the ground electrode is located on the tip side of the tip surface of the center electrode, the spark discharge gap is also formed on the tip side of the tip surface of the center electrode. Thereby, the flame kernel formed in the spark discharge gap is not easily subjected to the flame extinguishing action by the spark plug constituent member such as an insulator, and the ignitability of the spark plug can be improved.
In addition, on the outline of the tip of the center electrode projected onto the first virtual plane orthogonal to the first virtual line, the first pass through the point closest to the position of the first virtual line and the position of the first virtual line. If the angle θ formed by the two imaginary lines and the projection line of the first axis is set to 25 ° or more and 60 ° or less, the discharge direction in the spark discharge gap can be surely set to a direction non-parallel to the first axis. it can. Thereby, it can be set as the structure which the other end part of a ground electrode is not arrange | positioned reliably in the front end side of the 1st axial direction used as the center side of a combustion chamber seen from the spark discharge gap, and it forms in a spark discharge gap. The flame nuclei thus burned can quickly spread throughout the combustion chamber.
When θ is less than 25 °, the arrangement position of the other end portion of the ground electrode viewed from the spark discharge gap is closer to the center side of the combustion chamber, which may hinder the growth of the flame kernel toward that direction. On the other hand, when θ is larger than 60 °, the spark discharge gap approaches the one end of the ground electrode, the tip of the center electrode, the insulator, and the like, so that it is easy to receive a flame extinguishing action from those parts and members, and the ignitability is improved. Difficult to do.

As described above, the other end portion of the ground electrode is located on the tip side of the tip surface of the center electrode, and further to the second virtual plane orthogonal to the first axis of the center electrode as in the invention according to claim 2. If the contour line of the projected tip of the center electrode and the contour line of the other end of the ground electrode are in point contact with each other or separated from each other, it is ensured that the ground electrode is positioned at the center of the combustion chamber as viewed from the spark discharge gap. It can be set as the structure by which the other end part is not arrange | positioned.

In the invention according to claim 2, it is described that “the contour line of the front end portion of the center electrode and the contour line of the other end portion of the ground electrode are in point contact with or separated from each other on the second virtual plane”. However, for example, a columnar first virtual extension body in which the outer periphery of the tip of the center electrode is virtually extended in the first axis direction, and the second axis at the other end of the ground electrode becomes the first virtual line. In the part along, the columnar second virtual stretched body in which the outer periphery of the other end portion in the part is virtually stretched in the first imaginary line direction is in a twisted positional relationship, and the outer peripheral surfaces of both are mutually Examples of point contact or separation are exemplified. Of course, the present invention is not limited to this.

Further, as in the invention according to claim 3 , the contour line of the end surface on the other end side of the ground electrode projected onto the second imaginary plane is orthogonal to the first imaginary line and circumscribes the contour line of the tip portion of the center electrode. If it is positioned between two third imaginary lines, the flame extinguishing action by the other end of the ground electrode can be reduced to improve the ignitability, and the occurrence of spark discharge can be dispersed to improve the durability. .

  When the contour line of the end surface on the other end side of the ground electrode is outside the virtual line on the side close to one end portion of the ground electrode among the two third virtual lines, the spark discharge occurrence position in the spark discharge gap is It becomes easy to concentrate on one point where the size of the discharge gap is the smallest. Then, the position is concentrated and consumed by the spark discharge, and the size of the spark discharge gap may increase, leading to a decrease in durability. On the other hand, when the contour line of the end surface on the other end side of the ground electrode is outside the virtual line on the side farther from one end portion of the ground electrode among the two third virtual lines, the other end of the ground electrode is between the two straight lines. Since the volume of the ground electrode facing the spark discharge gap is increased, the flame extinguishing action is likely to occur, and the ignitability may be reduced.

  Hereinafter, an embodiment of a spark plug embodying the present invention will be described with reference to the drawings. First, with reference to FIG. 1, the structure of the spark plug 100 as an example of the spark plug of this Embodiment is demonstrated. FIG. 1 is a partial cross-sectional view of a spark plug 100. In FIG. 1, the axis O direction of the spark plug 100 will be described as the vertical direction in the drawing, the lower side will be described as the front end side, and the upper side will be described as the rear end side.

  As shown in FIG. 1, the spark plug 100 generally includes an insulator 10, a metal shell 50 that holds the insulator 10, a center electrode 20 that is held in the insulator 10, and a front end surface of the metal shell 50. 57 is provided at the rear end portion of the insulator 10 and the cylindrical ground electrode 30 having the axis P bent so that the proximal end portion 32 is welded to the distal end portion 31 of the central electrode 20. The terminal fitting 40 is formed.

  First, the insulator 10 of the spark plug 100 will be described. As is well known, the insulator 10 is a cylindrical insulating member that is formed by firing alumina or the like and has an axial hole 12 extending in the direction of the axis O of the center electrode 20 held inside. A flange portion 19 having the largest outer diameter is formed substantially at the center in the direction of the axis O, and a rear end side body portion 18 is formed on the rear end side. Further, a front end side body portion 17 having an outer diameter smaller than that of the rear end side body portion 18 on the front end side from the flange portion 19, and a further outer diameter than the front end side body portion 17 on the front end side of the front end side body portion 17. A small leg length 13 is formed. The long leg portion 13 is reduced in diameter toward the distal end side, and is exposed to the combustion chamber when the spark plug 100 is assembled to an internal combustion engine (not shown). The axis O corresponds to the “first axis” in the present invention.

  Next, the center electrode 20 is formed of a Ni-based alloy such as Inconel (trade name) 600 or 601, and has a metal core 23 made of copper or the like having excellent thermal conductivity. The center electrode 20 has a columnar shape extending along the axis O serving as the center axis of the center electrode 20, and the insulator 10 having the extension direction of the shaft hole 12 in the direction of the axis O is disposed on the distal end side in the shaft hole 12. Is retained. The distal end side of the center electrode 20 protrudes from the distal end surface of the insulator 10, and the protruding portion is formed to taper toward the distal end side. A columnar noble metal tip 25 is welded to the tip of the protruding portion, and a small-diameter tip 22 is formed integrally with the center electrode 20 body. In the present embodiment, the noble metal tip 25 integrated with the center electrode 20 is also referred to as “center electrode”.

  The center electrode 20 is electrically connected to the terminal fitting 40 on the rear end side via the seal body 4 and the ceramic resistor 3 provided in the shaft hole 12. A high voltage cable (not shown) is connected to the terminal fitting 40 via a plug cap (not shown) so that a high voltage is applied.

  Next, the metal shell 50 will be described. The metal shell 50 is a cylindrical metal fitting for fixing the spark plug 100 to an engine head of an internal combustion engine (not shown), and is held so as to surround the insulator 10. At this time, the distal end portion of the long leg portion 13 of the insulator 10 protrudes forward (lower side in the figure) from the distal end surface 57 of the metal shell 50. The metal shell 50 is made of an iron-based material, and includes a tool engaging portion 51 to which a spark plug wrench (not shown) is fitted, and a screw portion 52 to be screwed into an engine head provided on an internal combustion engine (not shown). I have.

  Further, a caulking portion 53 is provided on the rear end side of the metal fitting 50 from the tool engaging portion 51. Annular ring members 6, 7 are interposed between the metal shell 50 from the tool engaging portion 51 to the caulking portion 53 and the rear end side body portion 18 of the insulator 10, and both ring members Between 6 and 7, talc (talc) 9 powder is filled. Then, by crimping the crimping portion 53, the insulator 10 is pressed toward the distal end side in the metal shell 50 through the ring members 6, 7 and the talc 9. As a result, the stepped portion between the leg long portion 13 and the distal end side body portion 17 is supported by the stepped portion formed on the inner peripheral surface of the screw portion 52 of the metal shell 50 via the packing 80. Thus, the metal shell 50 and the insulator 10 are integrated. Airtightness between the metal shell 50 and the insulator 10 is maintained by the packing 80, and the outflow of combustion gas is prevented. Further, a flange 54 is formed between the tool engaging portion 51 and the screw portion 52, and the gasket 5 is inserted into the vicinity of the rear end side of the screw portion 52, that is, the seat surface 55 of the flange 54. ing.

  Next, the ground electrode 30 will be described with reference to FIGS. FIG. 2 is an enlarged front view of the tip portion of the spark plug 100. FIG. 3 is an enlarged right side view of the tip portion of the spark plug 100. FIG. 4 is an enlarged bottom view of the tip portion of the spark plug 100. In FIG. 4, the upper side in the figure is the front side of the spark plug 100.

  As shown in FIGS. 2 to 4, the ground electrode 30 is made of a metal having high corrosion resistance. As an example, a Ni-based alloy such as Inconel (trade name) 600 or 601 is used. The ground electrode 30 has a substantially circular cross section in the longitudinal direction and is formed in a columnar shape with the axis P as the central axis. One end (base end portion 32) of the ground electrode 30 is the distal end surface of the metal shell 50. 57 is joined by welding. At this time, as shown in FIG. 2 and FIG. 3, positioning is performed such that the direction of the axis P at the base end portion 32 is parallel to the direction of the axis O. On the other hand, the other end portion (tip portion 31) of the ground electrode 30 is bent in a substantially L shape toward the inner peripheral side of the metal shell 50 so as to face the tip portion 22 of the center electrode 20. The axis P is also bent along with the bent ground electrode 30. At this time, as shown in FIGS. 3 and 4, the axis P has a portion along the imaginary line C in the tip portion 31 of the ground electrode 30 that does not intersect the axis O and is in a twisted relationship with each other. Yes. The tip portion 31 of the ground electrode 30 is bent so as to satisfy the positional relationship with the tip portion 22 of the center electrode 20. In particular, in the spark plug 100 of the present embodiment, the ground electrode 30 has a configuration in which the axis P is along the imaginary line C in the entire tip 31 (the bent portion of the ground electrode 30 is not on the tip 31). The tip portion 31 is configured to extend straight along the axis P). The axis P corresponds to the “second axis” in the present invention, and the virtual line C corresponds to the “first virtual line” in the present invention.

More specifically, as shown in FIG. 2, the position of the tip 31 of the ground electrode 30 is the tip surface 21 of the tip 22 of the center electrode 20 in the direction of the axis O (the tip of the noble metal tip 25 in this embodiment). The ground electrode 30 is bent so as to be on the tip side (lower side in the drawing) from the surface 21). Further, as shown in FIG. 4, the tip 22 of the center electrode 20 and the tip 31 of the ground electrode 30 are planes perpendicular to the axis O (the “ second virtual plane” in the present invention. As an example, FIG. When the image is projected onto the virtual plane, the respective contour lines are point-contacted or separated (separated in this embodiment) from each other. That is, the imaginary line I extending the tip 22 of the center electrode 20 shown in FIG. 3 and the imaginary line J extending the tip 31 of the ground electrode 30 shown in FIG. Is configured to be in point contact or separated.

  In the spark plug 100 of the present embodiment configured as described above, flame nuclei generated in the spark discharge gap G formed between the tip 31 of the ground electrode 30 and the tip 22 of the center electrode 20 grow. Based on the result of an evaluation test to be described later, the positional relationship between the tip 22 of the center electrode 20 and the tip 31 of the ground electrode 30 is determined so that ignitability can be improved without impeding its growth in the process of spreading in the combustion chamber. It prescribes.

First, in the present embodiment, in the right side view of the spark plug 100 shown in FIG. 3, that is, in a plane orthogonal to the imaginary line C, the distal end portion 22 of the center electrode 20 that passes through the position of the imaginary line C and is projected onto the plane. The angle θ between the imaginary line D passing through the point E closest to the position of the imaginary line C and the axis O at a point on the contour line is defined to have a relationship of 25 ° or more and 60 ° or less. . By defining in this way, the discharge direction of the spark discharge gap G is surely an oblique direction with respect to the direction of the axis O. That is, the arrangement position of the tip 31 of the ground electrode 30 viewed from the spark discharge gap G is shifted from the center side of the combustion chamber (usually the tip side in the direction of the axis O of the spark plug 100 and the lower side in FIG. 3). It is difficult to prevent the growth of the flame kernel toward the center of the combustion chamber. In the present embodiment, the direction of the imaginary line C is made coincident with the direction in which the spark plug 100 is viewed from the side, and in this case, the paper surface of FIG. It corresponds to “ one virtual plane”. However, the direction of the imaginary line C is merely an example, and the direction in which the spark plug 100 is viewed from the side does not necessarily coincide with the direction of the imaginary line C. That is, the virtual line C only needs to satisfy the positional relationship between the axis O and the twist. The virtual line D corresponds to the “second virtual line” in the present invention.

Further, in the present embodiment, in the bottom view of the spark plug 100 shown in FIG. 4, that is, in the plane orthogonal to the axis O (corresponding to an example of the second imaginary plane), the contour line of the tip end surface 35 of the ground electrode 30 is It is defined to be located between two virtual lines (virtual lines A and B) that are orthogonal to the virtual line C and circumscribe the outline of the tip 22 of the center electrode 20. Note that a side closer to the base end portion 32 of the ground electrode 30 is a virtual line A and a far side is a virtual line B. When the contour line of the tip end face 35 is outside the virtual line B, a part of the tip 31 is disposed between the virtual lines A and B, and the tip 31 facing the spark discharge gap G is disposed. Since the volume becomes large, there is a possibility that the ignitability may be lowered due to the extinguishing action by the tip 31 when the flame nucleus formed in the spark discharge gap G grows. On the other hand, when the contour line of the tip end surface 35 is outside the virtual line A, the spark discharge occurrence position in the spark discharge gap G is one point where the size of the spark discharge gap G is the smallest (for example, the ground electrode 30). Of the front end side end surface 35 and the outer peripheral surface). Then, the position of the ground electrode is concentrated and consumed due to the spark discharge, and there is a possibility that the durability is lowered such that the size (gap) of the spark discharge gap G is increased and the discharge voltage is increased. Each of the virtual lines A and B corresponds to two “third virtual lines” in the present invention.

  In the spark plug 100 of the present embodiment, the tip end surface 35 of the ground electrode 30 is configured by a plane orthogonal to the axis P, and in this case, the position of the tip end surface 35 in the bottom view of FIG. By adjusting and arranging between the virtual lines A and B, the contour line of the end surface 35 on the front end side of the ground electrode 30 can be arranged between the virtual lines A and B.

  Thus, in order to confirm the effect of this invention obtained by prescribing | regulating the positional relationship of the front-end | tip part 22 of the center electrode 20, and the front-end | tip part 31 of the ground electrode 30, each evaluation test shown below was conducted.

[Example 1]
First, an evaluation test was performed in order to confirm the effect of having the axis P at the tip 31 of the ground electrode 30 along the imaginary line C in a positional relationship of twist with the axis O of the center electrode 20. In this evaluation test, the virtual line C is positioned so that the projection line of the virtual line C projected on the plane orthogonal to the axis O is shifted by 1.3 mm from the position of the axis O, and the virtual line C is positioned at the tip of the ground electrode at the virtual line C. A spark plug sample 1 (with an offset) in which the tip of the ground electrode is positioned so that the axis P is along, and the tip of the ground electrode so that the axis O and the axis P at the tip of the ground electrode intersect. Sample 2 (no offset) was prepared, and the ignition limit air-fuel ratio was measured for each. The center electrode of each sample uses a tip having an outer diameter of Φ0.6, the ground electrode uses a tip having an outer diameter of Φ1.7, and both samples 1 and 2 have a spark discharge gap. The arrangement position of each tip was adjusted so that G was 1.1 mm. Further, the positional deviation of the front end face of the ground electrode is −0.3 mm from the position of the axis O (described later with reference to FIG. 4, the position of the end face 35 on the front end side of the ground electrode 30 is the position of the axis O. Further, the position is shifted by 0.3 mm to the imaginary line A side, and in this embodiment, the center electrode is Φ0.6, which coincides with the imaginary line A). Each sample was actually assembled into a 4-cylinder 2000 cc engine, this engine was driven at 2000 rpm, and the spark-discharge was performed 1000 times, and the fuel / air mixture ratio was ignited when 10 misfires occurred (1%). The critical air-fuel ratio was confirmed. The result of this evaluation test is shown in the graph of FIG.

  As shown in FIG. 5, the ignition limit air-fuel ratio was 22.3 in sample 1 where offset was performed, and the ignition limit air-fuel ratio was 21.5 in sample 2. In sample 2 where no offset was performed, the tip of the ground electrode viewed from the spark discharge gap G is arranged closer to the center of the combustion chamber than in sample 1 where offset was performed. The flame nucleus formed in the spark discharge gap G of the sample 2 is more susceptible to the extinguishing action by the ground electrode than the sample 1 when growing, and the combustion is in a direction avoiding the tip of the ground electrode, that is, the spark discharge. The gap G extends in a direction perpendicular to the center of the combustion chamber. On the other hand, in the sample 1 in which the offset is performed, the arrangement position of the tip of the ground electrode as viewed from the spark discharge gap G is shifted from the center of the combustion chamber. It is difficult to prevent the growth of the flame kernel toward From the result of this evaluation test, it is possible to improve the ignitability by performing offset so that the axis O of the center electrode and the virtual line C along the axis P at the tip of the ground electrode are in a twisted positional relationship. I understood.

[Example 2]
Next, when the tip 31 of the ground electrode 30 is offset, the position of the virtual line C passes through the plane orthogonal to the virtual line C so that the positional relationship with the tip 22 of the center electrode 20 is suitable. Further, an evaluation is made on the range of the angle θ formed by the virtual line D passing through the point E closest to the position of the virtual line C and the axis O at the point on the contour line of the tip 22 of the center electrode 20 projected onto the plane. went. In this evaluation test, the outer diameter of the tip of the center electrode is Φ0.6, the outer diameter of the tip of the ground electrode is Φ1.7, the size of the spark discharge gap G is 1.1 mm, and the axis described in FIG. Sample group 3 of 14 types of spark plugs produced by shifting the angle θ formed between O and the imaginary line D by 5 ° in the range of 10 ° to 75 °, and similarly, the outer diameter and spark of the tip of the ground electrode The ignition limit air-fuel ratio was measured under the same test conditions as in Example 1 for 14 types of sample groups 4 produced by changing the size of the discharge gap G to Φ1.1 and 0.8 mm, respectively. For each sample, those with an ignition limit air-fuel ratio of 21.8 or more were evaluated as “◯” because the ignitability was good, and those with less than 21.8 were considered as “ignitability could not be improved” “×”. The results of this evaluation test are shown in Table 1.

  As shown in Table 1, both the sample groups 3 and 4 have an ignition limit air-fuel ratio of 21.8 or more when the angle θ between the axis O and the virtual line D is in the range of 25 ° to 60 °, and the ignitability is good. there were. In each sample group, the ignition limit air-fuel ratio is less than 21.8 when the angle θ between the axis O and the imaginary line D is in the range of 10 ° to 20 ° and in the range of 65 ° to 75 °. It has been found that the ignitability cannot be sufficiently improved even if the axis O of the above and the virtual line C along the axis P at the tip of the ground electrode satisfy the twisted positional relationship.

  When the angle θ formed by the axis O and the imaginary line D is less than 25 °, the arrangement position of the tip of the ground electrode viewed from the spark discharge gap G is closer to the center of the combustion chamber. There is a risk that the growth of nuclei may be hindered. On the other hand, when the angle θ formed by the axis O and the imaginary line D is larger than 60 °, the spark discharge gap G approaches the proximal end portion of the ground electrode, the distal end portion of the center electrode, the insulator, and the like. It has been found that it becomes difficult to improve the ignitability because it is easy to receive a flame extinguishing action from the member.

[Example 3]
Next, on the plane orthogonal to the axis O, the relationship between the position of the contour line of the distal end surface 35 of the ground electrode 30 and the position of the contour line of the distal end of the center electrode 20 is evaluated with good or poor ignitability. It was. In this evaluation test, as a spark plug sample, as in the present embodiment, the end surface on the tip side of the ground electrode is composed of a plane orthogonal to the axis P, and the entire tip extends straight along the axis P ( That is, a configuration in which the axis P is along the imaginary line C in the entire tip is used. Then, a sample in which the arrangement position of the distal end side end surface is shifted along the virtual line C is produced, and the position of the contour line of the distal end side end surface projected on the plane orthogonal to the axis O and the contour line of the distal end portion of the center electrode 20 Classified by relationship. If it demonstrates with reference to FIG. 4, when the perpendicular drawn from the position of the axis line O on the virtual line C and the position of the outline of the front end side end surface of the ground electrode coincide, the deviation of the front end side end surface is 0 mm. The case where the position of the end surface on the tip side is on the imaginary line B side along the imaginary line C is defined as positive (+), and the case where it is on the imaginary line A side is defined as negative (−). In addition, in this evaluation test, samples 5 to 9 of five spark plugs in which the displacement of the position of the end face of the ground electrode is −0.6 mm, −0.3 mm, 0 mm, 0.3 mm, and 0.6 mm. The ignition limit air-fuel ratio of each sample was measured under the same test conditions as in Example 1. Each sample was configured so that the outer diameter of the tip of the center electrode was Φ0.6, the outer diameter of the tip of the ground electrode was Φ1.7, and the size of the spark discharge gap G was 1.1 mm. . The result of this evaluation test is shown in the graph of FIG.

  As shown in FIG. 6, in samples 5 and 6, the ignition limit air-fuel ratio was 22.3. Further, the ignition limit air-fuel ratios of Samples 7, 8, and 9 were 22.0, 21.9, and 21.5, respectively. As a result of this evaluation test, as the displacement of the position of the end surface on the tip side of the ground electrode becomes larger on the negative side, the arrangement position of the tip portion of the ground electrode as viewed from the spark discharge gap G is greatly displaced from the center side of the combustion chamber It has been found that the ignitability is improved because is reduced more.

[Example 4]
Furthermore, the same samples 5 to 9 as in Example 3 were used, and the relationship between the position of the contour line of the front end side end surface 35 of the ground electrode 30 and the position of the contour line of the front end portion of the center electrode 20 had good or bad durability. Evaluation was performed. In this evaluation test, each sample was actually assembled into a 6-cylinder 2000 cc engine, and the engine was operated for 700 hours according to a pattern simulating an actual running state. Then, the size of the spark discharge gap G was measured every 100 hours, and the amount (length) of the gap (gap) increased from 1.1 mm before the test was examined. It should be noted that the state of the spark plug when the simulated driving test for 680 hours is performed in accordance with the test conditions corresponds to the state of the spark plug when the actual vehicle travels about 100,000 km. In the determination, in this embodiment, the increase amount of the gap after 680 hours is used as a reference. The result of this evaluation test is shown in the graph of FIG.

  As shown in FIG. 7, it was found that the gap increase amount increased with the passage of time for all the samples, and the gap increase amount was increased as the position of the end surface on the tip side of the ground electrode was larger on the negative side. As the position of the end surface on the front side of the ground electrode increases to the positive side, the position on the surface of the ground electrode whose distance from the center electrode approximates the shortest distance spreads over a wider area. The occurrence position is easily dispersed. Then, since it becomes difficult for the consumption due to the spark discharge to concentrate on one point, the increase amount of the gap with respect to the number of times of the spark discharge is reduced, and the durability is improved. On the other hand, if the position of the end face of the ground electrode increases to the negative side, the consumption due to spark discharge tends to concentrate at the position where the distance to the center electrode is the shortest distance, and the gap is likely to increase. Durability decreases.

  In the case of sample 5, the gap increase after 600 hours and 700 hours are 0.33 mm and 0.35 mm, respectively, and the gap increase after 680 hours is expected to exceed 0.3 mm. In sample 6, the gap increments after 600 hours and 700 hours are 0.27 mm and 0.29 mm, respectively. In sample 7, the gap increments after 600 hours and 700 hours are 0.23 mm and 0.23 mm, respectively. It was 0.26 mm. From this, it is predicted that in both samples 6 and 7, the gap increase after 680 hours exceeds 0.2 mm and is 0.3 mm or less. In sample 8, the gap increments after 600 hours and 700 hours are 0.18 mm and 0.20 mm, respectively, and in sample 9, the gap increments after 600 hours and 700 hours are 0.17 mm, respectively. It was 0.19 mm. From this, it is predicted that the amount of increase in gap after 680 hours is 0.2 mm or less in both samples 8 and 9.

  And in order to obtain | require the position of the front end side end surface of an optimal ground electrode, evaluation based on the result of the said Example 3 and Example 4 was performed. First, from the results of Example 3, a sample having an ignition limit air-fuel ratio of 22.1 or higher was evaluated as “◎” as being excellent in ignitability. Moreover, the sample which was 21.8 or more and less than 22.1 was evaluated as “◯” because the ignitability was good. And the sample which was less than 21.8 was evaluated as "x" because it was difficult to improve ignitability.

  Next, from the results of Example 4, a sample that can be considered that the amount of increase in gap after the 680 hour evaluation test exceeds 0.3 mm was evaluated as “x” because there was a problem in durability. Moreover, the sample which can be considered that the increase amount of the gap after the evaluation test of 680 hours exceeded 0.2 mm and became 0.3 mm or less was evaluated as “◯” because the durability was good. And the sample which can be considered that the increase of the gap after the evaluation test of 680 hours was 0.2 mm or less was evaluated as “◎” as being excellent in durability. Table 2 shows the results of the above evaluation.

  As apparent from Table 2, the samples 6 to 8 were not evaluated as “x” in any of ignitability and durability. That is, if the displacement of the position of the end surface on the front end side of the ground electrode is −0.3 mm or more and 0.3 mm or less, the flame kernel formed by the spark discharge gap G will burn and spread well toward the center side of the combustion chamber. It was found that electrode consumption due to spark discharge can be suppressed. As described above, in the present embodiment, the front end side end surface 35 of the ground electrode 30 is constituted by a plane orthogonal to the axis P. Accordingly, as described above, it is preferable that the displacement of the position of the front end side end surface of the ground electrode is −0.3 mm or more and 0.3 mm or less. In the plane orthogonal to the axis O, the front end side end surface This corresponds to evaluating that the contour line is preferably located between two virtual lines A and B that are orthogonal to the virtual line C and circumscribe the center electrode.

  Needless to say, the present invention can be modified in various ways. For example, in the present embodiment, one ground electrode 30 is provided, but two ground electrodes 230 are provided as in the spark plug 200 shown in FIGS. 8 and 9, and the tip part 231 and the tip part of the center electrode 20 are provided. 22 may be in the same positional relationship as in the present embodiment. In this case, it is desirable that the arrangement positions of the ground electrodes 230 be equal as shown in FIG.

  The present invention can be applied to a spark plug for an internal combustion engine.

1 is a partial cross-sectional view of a spark plug 100. FIG. FIG. 2 is an enlarged front view of a tip portion of a spark plug 100. FIG. 3 is an enlarged right side view of the tip portion of the spark plug 100. FIG. 4 is an enlarged bottom view of the tip portion of the spark plug 100. It is a graph which shows the result of the evaluation test for confirming the effect which made the axis line O of the center electrode, and the virtual line C along the axis line P in the front-end | tip part of a ground electrode mutually make the positional relationship of a twist. It is a graph which shows the result of having evaluated ignitability about the relationship between the position of the outline of the front end side end surface of a ground electrode, and the position of the outline of the front-end | tip part of a center electrode. It is a graph which shows the result of having evaluated durability about the relationship between the position of the outline of the front end side end surface of a ground electrode, and the position of the outline of the front-end | tip part of a center electrode. It is the right view which expanded the front-end | tip part of the spark plug 200 as a modification. It is the bottom view to which the front-end | tip part of the spark plug 200 as a modification was expanded.

DESCRIPTION OF SYMBOLS 10 Insulator 12 Shaft hole 20 Center electrode 21 Front end surface 22 Front end portion 30 Ground electrode 31 Front end portion 32 Base end portion 35 Front end side end surface 50 Metal shell 57 Front end surface 100 Spark plug

Claims (3)

A columnar center electrode having the first axis as its center axis;
An insulator having an axial hole extending in the first axial direction and holding the central electrode in the axial hole;
A metal shell that surrounds and holds the periphery of the insulator in the radial direction;
It has a cylindrical shape with the second axis as its central axis, one end is joined to the front end surface of the metal shell, the other end is bent toward the inner peripheral side of the metal shell, and the other end is A grounding electrode that is positioned at least on the tip side of the tip surface of the center electrode and that forms a spark discharge gap with the tip of the center electrode;
It said second axis for bending together with the ground electrode, at the other end of the ground electrode, have a portion along a first imaginary line in a skewed positional relationship between the first axis, and,
When the tip of the center electrode, the first axis, and the other end of the ground electrode are projected onto a first virtual plane orthogonal to the first virtual line, the first virtual plane is projected. Above,
A second imaginary line passing through the position of the first imaginary line and passing through the position of a point on the contour of the tip of the center electrode closest to the position of the first imaginary line, and projection of the first axis The angle θ made with the line is
25 ° ≦ θ ≦ 60 °
A spark plug characterized by the relationship . When the tip of the center electrode and the other end of the ground electrode are projected onto a second virtual plane orthogonal to the first axis, the tip of the center electrode is projected on the second virtual plane. 2. The spark plug according to claim 1, wherein a contour line of a portion and a contour line of the other end portion of the ground electrode are in point contact with or separated from each other. The second virtual plane, and the distal end portion of the center electrode, and the other end of the ground electrode, when viewed by projecting said first imaginary line, on the second virtual plane,
The contour line of the end surface on the other end side of the ground electrode closest to the position of the first axis is parallel to the direction orthogonal to the projection line of the first imaginary line and circumscribes the contour line of the tip portion of the center electrode. The spark plug according to claim 1 , wherein the spark plug is located between two third imaginary lines.

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