JP5980247B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug.

  As a spark plug, there is known a spark plug including a ground electrode in which an electrode tip is joined to a base material surface extending from a base end portion to a tip end portion of an electrode base material in order to improve ignitability and durability ( For example, see Patent Document 1). The electrode tip of such a spark plug is made of a material that is more resistant to spark discharge and oxidation than the electrode base material. For example, the material of the electrode tip is a noble metal (for example, platinum, iridium, ruthenium, rhodium, etc.) or an alloy containing the noble metal as a main component.

JP-A-2005-123166

  In the spark plug of Patent Document 1, the thermal energy of the flame kernel is taken away by the ground electrode due to the contact between the flame kernel and the ground electrode on the base end side from the electrode tip. There was a problem that the spread of the flame kernel was likely to be hindered. Therefore, there has been a demand for improving the ignitability of the spark plug by guiding the starting point of the flame kernel toward the tip of the ground electrode.

The present invention has been made to solve the above-described problems, and can be realized as the following forms. A first aspect of the present invention is a spark plug comprising a center electrode, an electrode tip that forms a gap between the center electrode, and a ground electrode having an electrode base material to which the electrode tip is joined. The electrode tip protrudes toward the center electrode from a base material surface extending from a front end portion to a base end portion of the electrode base material, and around the electrode tip of the electrode base material, the electrode base A fusing part containing a material component and an electrode tip component is formed, and passes through the axis of the electrode tip in parallel to the longitudinal direction of the electrode base material from the tip portion toward the base end portion. A boundary line between the electrode tip and the melted portion viewed from a direction orthogonal to the plane is an intersection A between the boundary line and the virtual surface on the tip end side, and the base line between the boundary line and the virtual surface is As you go to the intersection B on the end side, The electrode base material is chamfered by at least one of an inclined surface and a curved surface between the base material surface and the front end surface of the front end portion, away from the front end surface of the electrode tip facing the center electrode. Provided as a spark plug.

(1) According to one aspect of the present invention, a center electrode; and a ground electrode having an electrode tip that forms a gap between the center electrode and an electrode base material to which the electrode tip is joined are provided. A spark plug is provided. In this spark plug, the electrode tip protrudes toward the center electrode from a base material surface extending from a distal end portion to a base end portion of the electrode base material; around the electrode tip in the electrode base material, A melted portion containing an electrode base material component and an electrode tip component is formed; the axial center of the electrode tip is parallel to the longitudinal direction of the electrode base material from the tip portion toward the base end portion. The boundary line between the electrode tip and the melted portion viewed from the direction orthogonal to the passing virtual plane is the intersection between the boundary line and the virtual plane on the tip end side from the boundary A and the virtual plane. As it goes to the intersection B on the base end side, it moves away from the tip surface of the electrode tip facing the center electrode. According to this embodiment, the work function of the melting portion is lower than that of the electrode tip due to the component of the electrode base material, and the distal end side of the melting portion is closer to the distal end surface than the proximal end portion side of the melting portion. For this reason, a spark discharge that tends to fly to the lower work function is more likely to occur on the distal end side of the electrode tip than on the proximal end side of the electrode tip. Therefore, the starting point of the flame kernel can be guided to the tip side of the ground electrode. As a result, the ignitability of the spark plug can be improved.

(2) In the spark plug described above, an angle S formed by a virtual line AB passing through the intersection A and the intersection B and the tip surface may satisfy 3 ° ≦ S ≦ 20 °. According to this embodiment, it is possible to sufficiently ensure the ignitability and sufficiently ensure the peeling resistance against the peeling of the electrode tip.

(3) In the spark plug described above, a length La from the tip surface to the intersection A may satisfy 0.25 mm ≦ La ≦ 0.60 mm. According to this embodiment, sufficient ignitability can be secured, and sufficient wear resistance against wear of the electrode tip due to spark discharge can be secured.

(4) In the above-described spark plug, the relationship between the tip outer diameter OD1 of the center electrode and the outer diameter OD2 of the electrode tip may satisfy 0.0 mm <(OD2-OD1) ≦ 0.6 mm. According to this form, ignitability can be improved effectively.

(5) In the spark plug described above, the electrode base material may have a chamfered portion formed of at least one of an inclined surface and a curved surface on the tip side from the electrode tip. According to this embodiment, the spread of the flame kernel can be promoted while the contact between the flame kernel and the ground electrode is delayed by the chamfered portion on the tip side from the electrode tip. As a result, the ignitability of the spark plug can be further improved.

  The present invention can be realized in various forms other than the spark plug. For example, it may be realized in the form of a spark plug ground electrode, a spark plug manufacturing method, a spark plug manufacturing apparatus, a computer program for controlling the manufacturing apparatus, a non-temporary recording medium storing the computer program, and the like. it can.

It is explanatory drawing which shows the partial cross section of a spark plug. It is explanatory drawing which shows the front end side of a spark plug. It is the elements on larger scale which expanded further the front end side of the ground electrode seen from the + X-axis direction. It is explanatory drawing which shows a mode that an electrode tip is joined to an electrode base material. It is explanatory drawing which shows the ground electrode of a 1st modification. It is explanatory drawing which shows the ground electrode of a 2nd modification. It is a table | surface which shows the result of having evaluated the ignition property and peeling resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignition property and peeling resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignition property and peeling resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignition property and peeling resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignition property and peeling resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignition property and wear resistance of the spark plug. It is a table | surface which shows the result of having evaluated the ignitability of the spark plug.

A. First embodiment A-1. Configuration of Spark Plug FIG. 1 is an explanatory view showing a partial cross section of a spark plug 10. FIG. 1 illustrates the external shape of the spark plug 10 on the left side of the drawing with respect to the axis CA, which is the axis of the spark plug 10, and the cross-sectional shape of the spark plug 10 on the right side of the drawing with respect to the axis CA. ing. In the description of the present embodiment, the lower side of the spark plug 10 in FIG. 1 is referred to as “front end side”, and the upper side of FIG. 1 is referred to as “rear end side”.

  The spark plug 10 includes a center electrode 100, an insulator 200, a metal shell 300, and a ground electrode 400. In the present embodiment, the axis CA of the spark plug 10 is also the axis of each member of the center electrode 100, the insulator 200, and the metal shell 300.

  The spark plug 10 has a gap SG formed between the center electrode 100 and the ground electrode 400 on the tip side. The gap SG of the spark plug 10 is also called a spark gap. The spark plug 10 is configured to be attachable to the internal combustion engine 90 in a state where the tip end side where the gap SG is formed protrudes from the inner wall 910 of the combustion chamber 920. When a high voltage (for example, 10,000 to 30,000 volts) is applied to the center electrode 100 with the spark plug 10 attached to the internal combustion engine 90, a spark discharge is generated in the gap SG. The spark discharge generated in the gap SG realizes ignition of the air-fuel mixture in the combustion chamber 920.

  FIG. 1 shows XYZ axes orthogonal to each other. The XYZ axes in FIG. 1 correspond to the XYZ axes in other figures described later.

  Of the XYZ axes in FIG. 1, the X axis is an axis orthogonal to the Y axis and the Z axis. Among the X-axis directions along the X-axis, the + X-axis direction is a direction from the back of the sheet of FIG. 1 toward the front of the sheet, and the −X-axis direction is a direction opposite to the + X-axis direction.

  Of the XYZ axes in FIG. 1, the Y axis is an axis orthogonal to the X axis and the Z axis. Among the Y-axis directions along the Y-axis, the + Y-axis direction is a direction from the right side to the left side in FIG. 1, and the −Y-axis direction is a direction opposite to the + Y-axis direction.

  Of the XYZ axes in FIG. 1, the Z axis is an axis along the axis CA. Of the Z-axis direction (axial direction) along the Z-axis, the + Z-axis direction is a direction from the rear end side to the front-end side of the spark plug 10, and the −Z-axis direction is a direction opposite to the + Z-axis direction. .

  The center electrode 100 of the spark plug 10 is an electrode having conductivity. The center electrode 100 has a rod shape extending about the axis CA. In the present embodiment, the center electrode 100 is made of a nickel alloy containing nickel (Ni) as a main component (for example, Inconel 600 (“INCONEL” is a registered trademark)). The outer surface of the center electrode 100 is electrically insulated from the outside by an insulator 200. The distal end side of the center electrode 100 protrudes from the distal end side of the insulator 200. The rear end side of the center electrode 100 is electrically connected to the rear end side of the insulator 200. In the present embodiment, the rear end side of the center electrode 100 is electrically connected to the rear end side of the insulator 200 via the terminal fitting 190.

  The insulator 200 of the spark plug 10 is an insulator having electrical insulation. The insulator 200 has a cylindrical shape extending about the axis CA. In this embodiment, the insulator 200 is produced by firing an insulating ceramic material (for example, alumina). The insulator 200 has a shaft hole 290 that is a through hole extending about the axis CA. In the shaft hole 290 of the insulator 200, the center electrode 100 is held on the axis CA in a state where the center electrode 100 protrudes from the distal end side of the insulator 200.

  The metal shell 300 of the spark plug 10 is a metal body having conductivity. The metal shell 300 has a cylindrical shape extending about the axis CA. In the present embodiment, the metal shell 300 is a member obtained by applying nickel plating to a low carbon steel formed into a cylindrical shape. In other embodiments, the metallic shell 300 may be a member that has been galvanized or a member that has not been plated (no plating). The metal shell 300 is fixed to the outer surface of the insulator 200 by caulking while being electrically insulated from the center electrode 100. An end face 310 is formed on the front end side of the metal shell 300. From the center of the end surface 310, the insulator 200 together with the center electrode 100 protrudes in the + Z-axis direction. A ground electrode 400 is joined to the end face 310.

  The ground electrode 400 of the spark plug 10 is an electrode having conductivity. The ground electrode 400 includes an electrode base material 410 and an electrode tip 450. The electrode base material 410 has a shape bent from the end surface 310 of the metal shell 300 in the + Z-axis direction and then bent toward the axis CA. The rear end side of the electrode base material 410 is joined to the metal shell 300. An electrode tip 450 is joined to the tip side of the electrode base material 410. The electrode tip 450 forms a gap SG between the electrode tip 450 and the center electrode 100.

  In the present embodiment, the material of the electrode base material 410 is a nickel alloy containing nickel (Ni) as a main component, like the center electrode 100. In the present embodiment, the material of the electrode tip 450 is an alloy containing platinum (Pt) as a main component. In another embodiment, the material of the electrode tip 450 may be any material that is more durable than the electrode base material 410 and may be a pure noble metal (for example, platinum (Pt), iridium (Ir), ruthenium (Ru), Rhodium (Rh) or the like, or other alloys mainly composed of these noble metals. Since platinum (Pt) has better oxidation resistance than iridium (Ir), the main component of the electrode tip 450 is preferably platinum (Pt).

A-2. Detailed Configuration of Ground Electrode FIG. 2 is an explanatory view showing the tip side of the spark plug 10. FIG. 2A in the upper stage in FIG. 2 is a partially enlarged view of the center electrode 100 and the ground electrode 400 as seen from the + X-axis direction. 2B in FIG. 2 is a partially enlarged view of the tip side of the ground electrode 400 as viewed from the −Z axis direction. FIG. 3 is a partially enlarged view in which the tip side of the ground electrode 400 is further enlarged as viewed from the + X-axis direction.

  The center electrode 100 has a cylindrical shape. The center electrode 100 has a tip surface 101 and a side surface 107. The distal end surface 101 and the side surface 107 constitute an end portion on the distal end side of the center electrode 100. The tip surface 101 of the center electrode 100 is a surface that is parallel to the X axis and the Y axis and faces the + Z axis direction. The side surface 107 of the center electrode 100 is a surface parallel to the Z axis formed around the axis CA. In the present embodiment, the front end surface 101 among the portions of the center electrode 100 forms a gap SG between the ground electrode 400 and the electrode tip 450.

  The electrode base material 410 of the ground electrode 400 has base material surfaces 411, 412, 413, 414, 415, 416. The base material surface 411 is formed from the rear end side to the front end side of the electrode base material 410, is curved in the middle from the rear end side to the front end side, and is a surface facing the −Z-axis direction on the front end side of the ground electrode 400 It is. In the present embodiment, the base material surface 411 is parallel to the X axis and Z axis and faces the + Y axis direction on the rear end side, and is parallel to the X axis direction and Y axis direction and faces the −Z axis direction on the front end side. . In the present embodiment, the angle formed by the base material surface 411 and the base material surface 413 is substantially a right angle.

  The base material surface 412 is a surface formed from the rear end side to the front end side of the electrode base material 410 and facing the + Z-axis direction on the front end side of the ground electrode 400. The base material surface 413 is a surface that constitutes the tip of the ground electrode 400 and faces the + Y-axis direction. The base material surface 414 constitutes the base end portion of the ground electrode 400 and is a surface facing the −Z axis direction. The base material surface 415 is a surface that is formed from the rear end side to the front end side of the electrode base material 410 and faces the −X axis direction. The base material surface 416 is a surface that is formed from the rear end side to the front end side of the electrode base material 410 and faces the + X-axis direction. An electrode tip 450 is provided on the tip side of the base material surface 411 extending from the base material surface 413 of the electrode base material 410 to the base material surface 414 in the portion of the electrode base material 410.

  The electrode tip 450 of the ground electrode 400 is a columnar protrusion protruding from the base material surface 411 of the electrode base material 410 toward the −Z axis direction. In the present embodiment, the axis CAc of the electrode tip 450 is on the axis CA and is parallel to the Z axis. The electrode tip 450 has a tip surface 451 and a side surface 453. The distal end surface 451 is a distal end surface that is parallel to the X axis and the Y axis and faces the −Z axis direction. The tip surface 451 forms a gap SG between the tip surface 451 and the tip surface 101 of the center electrode 100. The side surface 453 is a side surface that is formed around the axis CAc and is parallel to the Z axis. The electrode tip 450 is joined to the electrode base material 410 around the side surface 453 on the + Z-axis direction side.

  FIG. 4 is an explanatory view showing a state in which the electrode tip 450 is joined to the electrode base material 410. In the present embodiment, the electrode tip 450 before being bonded to the electrode base material 410 has a protruding portion 459 that protrudes outward from the side surface 453 at the end opposite to the tip surface 451. The electrode tip 450 is bonded to the electrode base material 410 after the electrode tip 450 is disposed on the electrode base material 410 with the protruding portion 459 of the electrode tip 450 facing the base material surface 411 of the electrode base material 410. This is done by laser welding the boundary between the material 410 and the electrode tip 450.

  In laser welding in which the electrode tip 450 is joined to the electrode base material 410, the incident direction LD in which the laser is incident is a direction inclined with respect to the base material surface 411 of the electrode base material 410 and the side surface 453 of the electrode tip 450, This is the direction toward the overhanging portion 459 of the electrode tip 450. In laser welding in which the electrode tip 450 is joined to the electrode base material 410, the moving direction LM for moving the laser is a direction that goes around the periphery of the electrode tip 450.

  Around the electrode tip 450 in the electrode base material 410, a melting part 430 is formed by laser welding for joining the electrode tip 450 to the electrode base material 410. In FIG. 2, the melting part 430 is hatched. The melting part 430 is a part (so-called weld bead) in which the metal derived from the electrode base material 410 and the electrode tip 450 once melted by laser welding is solidified. The melting part 430 contains the component of the electrode base material 410 and the component of the electrode tip 450. Melting part 430 contains a noble metal component derived from electrode tip 450. In this embodiment, the overhang | projection part 459 of the electrode base material 410 has lose | disappeared completely by laser welding. In another embodiment, at least a part of the overhang portion 459 may be left on the electrode tip 450 after being laser welded to the electrode base material 410. In another embodiment, the ground electrode 400 may be manufactured using the electrode tip 450 in which the overhanging portion 459 is not formed.

  2B passes through the axis CAc of the electrode tip 450 in parallel to the longitudinal direction of the electrode base material 410 from the base material surface 413 toward the base material surface 414. The virtual surface VP shown in FIG. The X-axis direction is a direction orthogonal to the virtual plane VP. As shown in FIGS. 2A and 3, the boundary line 435 between the electrode tip 450 and the melting portion 430 is viewed from the X-axis direction on the base material surface 413 side of the boundary line 435 and the virtual surface VP. It moves away from the intersection A toward the intersection B on the base material surface 414 side between the boundary line 435 and the virtual plane VP. In the present embodiment, the boundary line 435 viewed from the X-axis direction is a curve that connects the intersection A and the intersection B while winding. In another embodiment, the boundary line 435 viewed from the X-axis direction may be a curve protruding in the −Z-axis direction, a curve protruding in the + Z-axis direction, or a straight line. May be.

  From the viewpoint of sufficiently securing the peeling resistance against peeling of the electrode tip 450, the angle S formed by the virtual line AB passing through the intersection A and the intersection B and the tip surface 451 preferably satisfies 3 ° ≦ S ≦ 20 °. . The evaluation of the angle S will be described later.

The angle S is expressed by the following relational expression.
tanS = (Lb−La) / OD2
La: Length from the tip surface 451 to the intersection point A Lb: Length from the tip surface 451 to the intersection point B OD2: Outer diameter of the electrode tip 450

  From the viewpoint of sufficiently ensuring the wear resistance of the electrode tip 450 due to spark discharge, the length La preferably satisfies 0.25 mm ≦ La ≦ 0.60 mm. The evaluation of the length La will be described later. The length Lb is shorter than the protruding length Ls that the electrode tip 450 protrudes from the base material surface 411.

  FIG. 5 is an explanatory diagram showing the ground electrode 401 of the first modification. The ground electrode 401 of the first modification is the same as the ground electrode 400 described above except that the electrode base material 410 having the chamfered portion 417c is provided. The chamfered portion 417 c is formed between the base material surface 411 and the base material surface 413 on the base material surface 413 side from the electrode chip 450. The chamfered portion 417 c is configured by an inclined surface that is inclined with respect to the base material surface 411 and the base material surface 413. A part of the chamfered portion 417c may be a curved surface.

  FIG. 6 is an explanatory view showing a ground electrode 402 of a second modification. The ground electrode 402 of the second modified example is the same as the ground electrode 400 described above except that the electrode base material 410 having the chamfered portion 417r is provided. The chamfered portion 417r is formed between the base material surface 411 and the base material surface 413 on the base material surface 413 side of the electrode chip 450. The chamfered portion 417r is configured by a curved surface protruding outward. A part of the chamfered portion 417r may be a flat surface.

A-3. Evaluation Test FIGS. 7 to 11 are tables showing the results of evaluating the ignitability and peel resistance of the spark plug 10. In the evaluation tests of FIGS. 7 to 11, the tester prepared a plurality of spark plugs 10 having different dimensions as the samples for the center electrode 100 and the ground electrode 400, and evaluated the ignitability and peel resistance of each sample.

These samples differ in at least one of the following various dimensions.
-Tip electrode outer diameter OD1 of the center electrode 100
・ Outer diameter OD2 of electrode tip 450
・ Projection length Ls of electrode tip
-Distance La from tip surface 451 to intersection A
-Gap distance Lsg from tip surface 101 to tip surface 451
The angle S formed by the imaginary line AB and the tip surface 451

The specifications common to each sample are as follows.
-Material of electrode base material 410: Inconel 601
-Material of the electrode tip 450: an alloy containing platinum (Pt) as a main component and containing 20% by mass of iridium (Ir)

  The tester performed a spark test on each sample in order to evaluate the ignitability. In the spark test, the tester generates a negative discharge at a frequency of 100 Hz by energizing a sample installed in a test chamber (atmosphere: nitrogen, pressure: 1.2 MPa) of the spark test apparatus, and uses a high-speed camera to spark. The discharge was photographed. Thereafter, the tester analyzes an image obtained by photographing the spark discharge, thereby causing a spark discharge that has struck to the + Y-axis direction side (the tip portion side of the electrode base material 410) in the electrode tip 450 and the -Y-axis in the electrode tip 450. The spark discharge that struck on the direction side (the base end side of the electrode base material 410) was measured, and the spark ratio that was the ratio of the spark discharge on the tip end side and the spark discharge on the base end side was calculated. Specifically, the tester counts the spark discharges on the distal end side and the proximal end side from the start of the test until the spark discharge is confirmed 10 times on the distal end side based on an image obtained by photographing the spark discharge. The flying ratio was calculated from the counted number.

  According to the spark test of FIGS. 7 to 11, the ratio of the spark discharge on the tip side is increased by making the angle S larger than 0 ° so that the boundary line 435 moves away from the tip surface 451 as it goes from the intersection A to the intersection B. It turns out that becomes large. As the ratio of the spark discharge on the front end side increases, the starting point of the flame kernel can be guided to the front end side of the ground electrode 400, so that the ignitability of the spark plug 10 is improved. As a result, the work function of the melted part 430 is lower than that of the electrode tip 450 due to the components of the electrode base material 410, and further, the tip side of the melted part 430 is closer to the front end surface 451 than the base end side of the melted part 430 It is considered that this is because a spark discharge that tends to fly to a lower function side is more likely to be generated on the distal end side of the electrode tip 450 than on the proximal end side of the electrode tip 450.

In order to evaluate the peel resistance, the tester performed a thermal cycle test in which the following procedures 1 and 2 were repeated 1000 times for each sample.
(Procedure 1) The electrode tip 450 bonded to the electrode base material 410 is heated with a burner for 2 minutes so that the temperature of the electrode tip 450 becomes 1000 ° C.
(Procedure 2) Slowly cool the electrode tip 450 for 1 minute.

The tester confirmed the presence or absence of a crack (crack) in the fusion | melting part 430, after finishing a thermal cycle test. The tester evaluated the peel resistance of each sample based on the following evaluation criteria.
◎ (Excellent): No crack ○ (Normal): Cracked × (Inferior): Peeling of electrode tip 450

  According to the thermal cycle test of FIGS. 7-11, when angle S exceeds 20 degrees, it turns out that peeling resistance falls. This result is considered to be because when the angle S is too large, the size of the melting portion 430 cannot be sufficiently secured on the −Y axis direction side from the electrode tip 450. Therefore, it is preferable that the angle S satisfies 3 ° ≦ S ≦ 20 ° from the viewpoint of sufficiently ensuring the ignitability and the peel resistance.

  FIG. 12 is a table showing the results of evaluating the ignitability and wear resistance of the spark plug 10. In the evaluation test of FIG. 12, the tester prepared a plurality of spark plugs 10 having at least one of the distance La and the angle S as samples, and evaluated the ignitability and wear resistance of each sample. In the sample in the evaluation test of FIG. 12, each material of the electrode base material 410 and the electrode tip 450 is the same as that of the sample in the evaluation test of FIGS.

  In order to evaluate the ignitability, the tester performed a spark test on each sample in the same manner as the evaluation tests in FIGS. According to the spark test of FIG. 12, by increasing the distance La from the front end surface 451 to the intersection A, the ratio of spark discharge on the front end side increases, and as a result, the ignitability of the spark plug 10 is improved. I understand.

In order to evaluate the wear resistance, the tester performed a durability test for generating a spark discharge for 200 hours under the same conditions as the spark test. The tester evaluated the peel resistance of each sample based on the following evaluation criteria.
A (excellent): the increase amount of the gap distance Lsg is less than 0.2 mm ○ (ordinary): the increase amount of the gap distance Lsg is 0.2 mm or more and less than 0.3 mm x (poor): the increase amount of the gap distance Lsg is 0. 3mm or more

  According to the durability test of FIG. 12, it can be seen that when the distance La is less than 0.25 mm, the wear resistance decreases. This result is considered to be because, when the distance La is too short, the melted portion 430 is easily affected by consumption due to spark discharge. According to another evaluation test by the tester, when the distance La exceeds 0.60 mm, the ratio of the spark discharge on the tip side cannot be sufficiently secured. Therefore, it is preferable that the distance La satisfies 0.25 mm ≦ La ≦ 0.60 mm from the viewpoint of sufficiently ensuring the ignitability and wear resistance.

  FIG. 13 is a table showing the results of evaluating the ignitability of the spark plug 10. In the evaluation test of FIG. 13, the tester prepared a plurality of spark plugs 10 having different outer diameters OD2 of the electrode tips 450 as samples, and evaluated the ignitability of each sample. In the sample in the evaluation test of FIG. 13, each material of the electrode base material 410 and the electrode tip 450 is the same as the sample in the evaluation test of FIGS. 7 to 11.

  In order to evaluate the ignitability, the tester performed a spark test on each sample in the same manner as the evaluation tests in FIGS. In the evaluation test of FIG. 13, the tester performs the spark discharge on the distal end side and the proximal end side from the start of the test until the spark discharge is confirmed 30 times on the distal end side based on the image obtained by photographing the spark discharge. Counting was performed, and the ratio of fire was calculated from the counted number. According to the spark test of FIG. 13, the larger the outer diameter OD2 of the electrode tip 450 relative to the outer diameter OD1 of the center electrode 100, the greater the proportion of spark discharge on the tip side, and as a result, the spark plug 10 It can be seen that the ignitability of is improved. Therefore, from the viewpoint of effectively improving the ignitability, the relationship between the tip outer diameter OD1 and the outer diameter OD2 preferably satisfies 0.0 mm <(OD2-OD1) ≦ 0.6 mm.

A-4. Effects According to the embodiment described above, the boundary line 435 moves away from the tip surface 451 as it goes from the intersection A on the + Y axis direction side to the intersection B on the −Y axis direction side. As a result, a spark discharge that tends to ignite toward the lower work function is more likely to occur on the −Y axis direction side of the electrode tip 450 than on the + Y axis direction side of the electrode tip 450. Therefore, the starting point of the flame kernel can be guided to the + Y axis direction side of the ground electrode 400. As a result, the ignitability of the spark plug 10 can be improved.

  Further, when the angle S formed by the virtual line AB with the tip surface 451 satisfies 3 ° ≦ S ≦ 20 °, the ignitability can be sufficiently ensured, and the peel resistance against the peeling of the electrode tip 450 can be sufficiently secured.

  In addition, when the length La from the tip surface 451 to the intersection point A satisfies 0.25 mm ≦ La ≦ 0.60 mm, sufficient ignitability can be ensured and sufficient wear resistance against wear of the electrode tip 450 due to spark discharge can be secured. Can be secured. Further, when the relationship between the outer diameter OD1 of the tip of the center electrode 100 and the outer diameter OD2 of the electrode tip 450 satisfies 0.0 mm <(OD2-OD1) ≦ 0.6 mm, the ignitability can be effectively improved. .

  Further, when the electrode base material 410 has chamfered portions 417c and 417r formed by at least one of an inclined surface and a curved surface on the + Y axis direction side from the electrode tip 450, the flame on the + Y axis direction side from the electrode tip 450. While the contact between the nucleus and the ground electrode 400 is delayed by the chamfered portions 417c and 417r, the spread of the flame nucleus can be promoted. As a result, the ignitability of the spark plug 10 can be further improved.

B. Other Embodiments 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-described 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 ... Spark plug 90 ... Internal combustion engine 100 ... Center electrode 101 ... Tip surface 107 ... Side surface 190 ... Terminal metal fitting 200 ... Insulator 290 ... Shaft hole 300 ... Main metal fitting 310 ... End face 400, 401, 402 ... Ground electrode 410 ... Electrode mother Material 411, 412, 413, 414, 415, 416 ... Base material surface 417c, 417r ... Chamfered part 430 ... Melting part 435 ... Boundary line 450 ... Electrode tip 451 ... Tip face 453 ... Side face 459 ... Overhang part 910 ... Inner wall 920 ... combustion chamber

Claims (5)

A center electrode;
A spark plug comprising: an electrode tip that forms a gap with the center electrode; and a ground electrode having an electrode base material to which the electrode tip is joined,
The electrode tip protrudes toward the center electrode from the base material surface that spreads from the distal end portion to the base end portion of the electrode base material,
Around the electrode tip in the electrode base material, a melting portion containing the component of the electrode base material and the component of the electrode tip is formed,
A boundary line between the electrode tip and the melted portion as viewed from a direction orthogonal to a virtual plane passing through the axis of the electrode tip parallel to the longitudinal direction of the electrode base material from the distal end toward the base end The electrode tip that faces the central electrode from the intersection A on the distal end side of the boundary line and the virtual plane toward the intersection B on the proximal end side of the boundary line and the virtual plane rent farther away from the tip surface,
The electrode base material is a spark plug having a chamfered portion formed by at least one of an inclined surface and a curved surface between the base material surface and a front end surface of the front end portion .   2. The spark plug according to claim 1, wherein an angle S formed by an imaginary line AB passing through the intersection A and the intersection B and the tip surface satisfies 3 ° ≦ S ≦ 20 °.   3. The spark plug according to claim 1, wherein a length La from the tip surface to the intersection point A satisfies 0.25 mm ≦ La ≦ 0.60 mm.   4. The relationship between the tip outer diameter OD <b> 1 of the center electrode and the outer diameter OD <b> 2 of the electrode tip satisfies 0.0 mm <(OD <b> 2 − OD <b> 1) ≦ 0.6 mm. Spark plug as described in.   Of the width of the melted portion in the radial direction centered on the axis when viewing the melted portion in a direction perpendicular to the base material surface, the width at the portion closest to the tip surface of the electrode base material The spark plug according to any one of claims 1 to 4, wherein the spark plug is smaller than a width of a portion located on the base end side from the axis.

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