JP2015138726A - spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug capable of achieving both of wear resistance and peeling resistance of a grounding electrode forming a melting part on the periphery of an electrode chip in an electrode base material.SOLUTION: The spark plug includes: a center electrode; and the grounding electrode including the electrode chip forming a gap from the center electrode and the electrode base material to which the electrode chip is joined. The electrode chip is projected from a base material surface to the center electrode, and the melting part containing a component of the electrode base material and a component of the electrode chip is formed on the periphery of the electrode chip. When it is defined that a section formed from the tip portion side from an axis of the electrode chip is a first section and a section formed from the base end portion side from the axis is a second section in a cross section of the grounding electrode cut by a virtual surface passing the axis of the electrode chip in parallel with a longitudinal direction of the electrode base material directed from the tip portion to the base end portion, length from the tip surface of the electrode chip opposed to the center electrode up to the first section is shorter than the length from the tip surface up to the second section, and the first section contains a nobel metal component more than the second section.

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 an electrode base material in order to increase the durability of the ground electrode (see, for example, 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. In the spark plug of Patent Document 1, a melted portion is formed around the electrode tip in the electrode base material by welding when joining the electrode tip to the electrode base material.

  The melted portion of the ground electrode is an alloy containing a component of the electrode base material and a component of the electrode tip, and is easily consumed by spark discharge as compared with the electrode tip. Therefore, from the viewpoint of improving the wear resistance against wear due to spark discharge, it is desirable to make the melting portion small.

  On the other hand, in order to prevent the electrode tip from peeling from the electrode base material, it is necessary to sufficiently ensure the strength of the melted portion. Therefore, from the viewpoint of improving the peeling resistance against peeling of the electrode tip, it is desired to enlarge the melted part.

JP 2006-128076 A

  In the spark plug of Patent Document 1, sufficient studies have not been made to achieve both wear resistance and peeling resistance in a ground electrode in which a melted portion is formed around an electrode tip in an electrode base material.

  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 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. In the cross section of the ground electrode cut along the imaginary plane that passes through, the portion formed from the distal end side of the melt center of the melt portion is defined as a first portion, and is formed from the base end side from the shaft center. A length from the front end surface of the electrode tip facing the center electrode to the first portion is shorter than a length from the front end surface to the second portion; Part is precious metal Minute containing more than said second portion. According to this aspect, the first part that is easily affected by thermal stress due to combustion heat improves the resistance to peeling of the electrode tip by securing a size larger than that of the second part, and the precious metal component is added to the first part. By containing more than 2 parts, the wear resistance with respect to the consumption by a spark discharge can be improved. Further, in the second portion, it is possible to improve wear resistance against wear due to spark discharge by moving away from the tip surface of the electrode tip as compared with the first portion. For these reasons, it is possible to achieve both wear resistance and peel resistance of the ground electrode. As a result, the life of the spark plug can be extended.

(2) In the above-described spark plug, the first portion and the second portion may each contain 10 to 80% by mass of a noble metal component. According to this embodiment, it is possible to avoid an insufficient strength of the melted part. Therefore, it is possible to sufficiently ensure the peel resistance of the ground electrode.

(3) In the spark plug described above, the first portion may contain a noble metal component in an amount of 20 to 30% by mass more than the second portion. According to this form, generation | occurrence | production of the crack (crack) resulting from a thermal stress can be disperse | distributed to a 1st part and a 2nd part. Accordingly, it is possible to prevent the electrode tip from being inclined due to the cracks being biased toward one of the first portion and the second portion. As a result, the life of the spark plug can be further extended.

(4) In the above spark plug, the outer diameter of the electrode tip may be 0.7 to 1.5 mm. According to this embodiment, it is possible to prevent an increase in cracks in the second portion due to the second portion becoming susceptible to thermal stress as the electrode tip is reduced in diameter, and to melt as the electrode tip is increased in diameter. Insufficient strength of the part can be prevented. Therefore, it is possible to sufficiently ensure the peel resistance of the ground electrode.

(5) In the spark plug described above, the main component of the electrode tip may be platinum (Pt). According to this embodiment, the oxidation resistance of the electrode tip can be sufficiently ensured.

  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 explanatory drawing which shows the cross section which cut | disconnected the front end side of the ground electrode. It is explanatory drawing which shows a mode that an electrode tip is joined to an electrode base material. It is a table | surface which shows the result of having evaluated the durability of a 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 other embodiments, 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 an explanatory view showing a cross section of the tip end side of the ground electrode 400. The cross section of FIG. 3 is a partial cross section of the ground electrode 400 viewed from the arrow F3-F3 in FIG.

  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 a surface that is formed from the rear end side to the front end side of the electrode base material 410 and faces the −Z-axis direction on the front end side of the ground electrode 400. 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 distal end side of the base material surface 411 extending from the distal end portion (base material surface 413) to the base end portion (base material surface 414) of the electrode base material 410. It has been.

  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 parallel to the Z axis. The electrode tip 450 has tip surfaces 451 and 453. The tip surface 451 is a tip 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 101 of the center electrode 100. The chip 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 + Z-axis direction side on the tip surface 453.

  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 joined to the electrode base material 410 has an overhanging portion 459 that projects outward from the tip 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 tip surface 453 of the electrode tip 450. This is the direction toward the protruding 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.

  Melting portion 430 has an exposed surface 431 and a boundary surface 433. The exposed surface 431 of the fusion part 430 is a surface that is formed at a site where a laser is incident during laser welding and is exposed from the electrode base material 410 and the electrode tip 450. The exposed surface 431 is formed from the contact A with the chip surface 453 to the contact B with the base material surface 411. The boundary surface 433 of the melting part 430 is a surface that defines the boundary between the electrode base material 410 and the electrode tip 450.

  The cross section of the ground electrode 400 shown in FIG. 3 is an imaginary plane passing through the axis CAc of the electrode chip 450 in parallel with the longitudinal direction (Y-axis direction) of the electrode base material 410 from the base material surface 413 toward the base material surface 414. It is the cross section which cut | disconnected the ground electrode 400 by VP. In the cross-sectional shape of the melted part 430 shown in FIG. 3, the melted part 430 includes a first portion 430 </ b> A formed from the + Y-axis direction side (base material surface 413 side) from the axial center CAc of the electrode chip 450 and the electrode chip 450. And a second portion 430B formed from the −Y-axis direction side (base material surface 414 side) from the axis CAc. The first portion 430A contains more noble metal component than the second portion 430B. 3, the length La from the chip surface 451 to the first portion 430A is shorter than the length Lb from the chip surface 451 to the second portion 430B. As a result, both the wear resistance and the peel resistance of the ground electrode 400 can be achieved. Evaluation regarding the length La and the length Lb will be described later.

  From the viewpoint of sufficiently ensuring the peel resistance of the ground electrode 400, the first portion 430A and the second portion 430B preferably each contain 10 to 80% by mass of a noble metal component. In other words, the content ratio CRa of the noble metal component in the first portion 430A is preferably 10 to 80% by mass, and the content ratio CRb of the noble metal component in the second portion 430B is preferably 10 to 80% by mass. In the present embodiment, the content rate CRa and the content rate CRb are 10 to 80% by mass, respectively. In other embodiment, content rate CRa may be more than 80 mass%, and content rate CRb may be less than 10 mass%. Evaluation on the content ratio CRa and the content ratio CRb will be described later.

  From the viewpoint of preventing the inclination of the electrode tip 450 caused by the cracks being developed to be biased to one of the first part 430A and the second part 430B, the first part 430A has a precious metal component 20 to 20% higher than the second part 430B. It is preferable to contain 30% by mass. In other words, the content difference (CRa-CRb) is preferably 20 to 30% by mass. In this embodiment, the difference in content (CRa-CRb) is 20 to 30% by mass. In another embodiment, the content difference (CRa−CRb) may be 10% by mass or more and less than 20% by mass, or may be more than 30% by mass and 80% by mass or less. Evaluation regarding the difference in content (CRa-CRb) will be described later.

  From the viewpoint of sufficiently ensuring the peel resistance of the ground electrode 400, the outer diameter ODc of the electrode tip 450 is preferably 0.7 to 1.5 mm. Evaluation regarding the outer diameter ODc of the electrode tip 450 will be described later.

A-3. Evaluation Test FIG. 5 is a table showing the results of evaluating the durability of the spark plug 10. In the evaluation test of FIG. 5, the tester evaluated a plurality of spark plugs 10 having different aspects of the melting part 430 and at least one of the outer diameters ODc of the electrode tips 450 as samples 1 to 17. When the tester joins the electrode tip 450 to the electrode base material 410 by laser welding, the tester prepared samples having different aspects of the melting portion 430 by setting a combination of laser output, processing speed, and irradiation position.

The specifications of the electrode base material 410 in each sample are as follows.
・ Material: Inconel 601
-Cross-sectional dimension on the tip side (length in the X-axis direction): 2.7 mm (millimeters)
-Cross-sectional dimension on the tip side (length in the Z-axis direction): 1.3 mm

The specifications of the electrode tip 450 in each sample are as follows.
-Material: Alloy containing platinum (Pt) as a main component and containing 20% by mass of iridium (Ir)-Shape: cylinder-Outer diameter ODc: 0.6-1.6 mm
-Length in the axial center CAc direction before welding: 1.1 mm
-Protrusion from the base metal surface 411 after welding: 0.9 mm

  The tester observed the cross section which cut | disconnected the ground electrode 400 of each sample with the virtual surface VP using the electron beam microanalyzer (EPMA: Electron Probe MicroAnalyser). The tester measured the lengths La and Lb and the content ratios CRa and CRb by analyzing the image of the EPMA image.

  In the measurement of the content ratios CRa and CRb, as a first step, the tester virtually uses the wavelength dispersive X-ray spectrometer (WDS) included in the EPMA to virtually connect the ground electrode 400 of each sample. A qualitative analysis was performed on the melted part 430 in the cross section cut by the plane VP. By this qualitative analysis, the tester specified the elements included in the cross section of the fusion zone 430, and specified the element having the maximum mass percentage concentration as the main component element among these elements.

  As a second step, the tester determined EPMA measurement conditions in order to improve the analysis accuracy. This measurement condition is a condition under which a measurement count number of 10,000 counts or more can be obtained with a beam current amount that does not cause counting down due to a large amount of X-ray incidence when detecting the main component element specified in the first stage.

Specific measurement conditions are as follows.
・ Acceleration voltage: 20 kV (kilovolts)
Probe current: 2.5 × 10 ⁻⁸ A (ampere)
-Beam irradiation diameter: 50 to 200 μm
・ Main peak capture time: 10 seconds ・ Background capture time: 5 seconds each on the high angle side and low angle side

The tester set the observation region in the first portion 430A of the melting part 430 by the following procedures 1 to 6.
Procedure 1: Identify contact A and contact B in the first part 430A.
Procedure 2: Specify midpoint C of line segment AB connecting contact A and contact B.
Procedure 3: Specify the end point D farthest from the midpoint C in the first portion 430A.
Procedure 4: The intersection point E where the line segment CD connecting the middle point C and the end point D intersects the exposed surface 431 is specified.
Step 5: Specify three points F1, F2, and F3 that divide the line segment DE connecting the end point D and the intersection point E into four equal parts.
Procedure 6: Circles CL1, CL2, and CL3 centering on points F1, F2, and F3, respectively, having a length obtained by dividing the line segment DE into four equal parts are set as observation regions.
The tester also set the observation region in the second portion 430B of the melting part 430 in the same manner as the first portion 430A.

  As a third stage, the tester performed a quantitative analysis on each element specified in the first stage under the measurement conditions determined in the second stage. Specifically, the tester compares the count rate (CPS: Count Per Second) of each element obtained from the net X-ray intensity with a comparative sample in which the aluminum content is analyzed in advance (STIMEX standard). Quantitative calculation was performed by the ZAF correction method (Z (Atomic number) effect-Absorption effect-Fluorescence excitation correction method) using the coefficient rate obtained from the sample under the same conditions. In this quantitative calculation, the tester normalized (normalized) so that the total content was 100%.

  The tester calculates the content ratio CRa of the noble metal component in the first portion 430A based on the average value obtained by averaging the measurement values obtained by the quantitative analysis for the observation regions of the circles CL1, CL2, and CL3 in the first portion 430A of the melting portion 430. Calculated. The tester calculates the content ratio CRb of the noble metal component in the second portion 430B based on the average value obtained by averaging the measurement values by the quantitative analysis for each observation region of the circles CL1, CL2, and CL3 in the second portion 430B of the melting portion 430. Calculated.

The tester conducted an endurance test on the samples prepared for each of the samples 1 to 17 separately from the sample used for the observation of the cross section. In this endurance test, the tester attaches each sample to the internal combustion engine (displacement 2.0 liters, 4 cylinders), repeats the following operation states 1 and 2, and the endurance time until an abnormality occurs in the electrode tip 450 Was measured.
Operation state 1: The internal combustion engine is operated for 1 minute at 5000 rpm (rotation per minute) with the throttle fully opened.
Operating state 2: The internal combustion engine is operated for 1 minute in the idling state.

  The tester judged the inclination and peeling of the electrode tip 450 as an abnormality of the electrode tip 450. The inclination of the electrode tip 450 is a state in which the tip surface 451 of the electrode tip 450 is inclined with respect to the base material surface 411 of the electrode base material 410 when a part of the electrode tip 450 is peeled from the electrode base material 410. The electrode tip 450 is peeled from the electrode tip 450 completely peeled from the electrode base material 410.

The tester evaluated the durability of each sample according to the following evaluation criteria for each of the samples 1 to 17 according to the average of the durability time until an abnormality occurred in the electrode tip 450.
☆ (Evaluation level 5): Over 400 hours ◎ (Evaluation level 4): Over 300 hours 400 hours or less ○ (Evaluation level 3): Over 200 hours 300 hours or less △ (Evaluation level 2): Over 100 hours 200 hours or less × (Evaluation level 1): 100 hours or less

From the comparison between Samples 4-7, 10-16 and Samples 1-3, 8, 9, 17, the length La is made shorter than the length Lb, and the content CRa is made higher than the content CRb. It can be seen that a long endurance time can be realized. This result is considered to be caused by the following action.
In the first part 430A that is easily affected by thermal stress due to combustion heat, by securing a size larger than that of the second part 430B, the resistance to peeling of the electrode tip 450 is improved, and the noble metal component is added to the second part 430A. Containing more than 430B improved wear resistance against wear due to spark discharge.
The second portion 430B has improved wear resistance against wear due to spark discharge by moving away from the tip surface 451 of the electrode tip 450 as compared to the first portion 430A.

  Compared with Samples 6, 7, 10-12, and 14-16 and Samples 4, 5, and 13, the content CRa and the content CRb are 10 to 80% by mass, thereby realizing a longer durability time. I understand that I can do it. This result is considered to result from a decrease in the mechanical strength of the melted portion 430 when the content of the noble metal component is less than 10% by mass or more than 80% by mass.

  From the comparison between the sample 6 and the sample 7 and the comparison between the sample 15 and the sample 16, it is understood that a longer durability time can be realized by setting the difference in content (CRa-CRb) to 20 to 30% by mass. . As a result, when the difference in content (CRa-CRb) is less than 20% by mass, cracks are biased toward the first portion 430A, and the difference in content (CRa-CRb) is 30% by mass. In the case of exceeding, it is considered that the inclination of the electrode tip 450 is likely to occur due to the cracks being biased toward the second portion 430 </ b> B.

  From the comparison between the samples 6, 11, 15 and the samples 10, 12, it can be seen that a longer durability time can be realized by setting the outer diameter ODc of the electrode tip 450 to 0.7 to 1.5 mm. As a result, when the outer diameter ODc is less than 0.7 mm, the second portion 430B is easily subjected to thermal stress, and cracks in the second portion 430B increase. If it exceeds 0.5 mm, it is considered that the mechanical strength of the fusion zone 430 is insufficient.

A-4. Effects According to the embodiment described above, the length La from the chip surface 451 to the first portion 430A is shorter than the length Lb from the chip surface 451 to the second portion 430B, and the first portion 430A has a noble metal component. More than the second part 430B. As a result, both the wear resistance and the peel resistance of the ground electrode 400 can be achieved. As a result, the life of the spark plug 10 can be extended.

  Moreover, since the 1st part 430A and the 2nd part 430B contain 10-80 mass% of noble metal components, respectively, the intensity | strength lack of the fusion | melting part 430 can be avoided. Therefore, the peel resistance of the ground electrode 400 can be sufficiently ensured.

  Further, since the first portion 430A contains a noble metal component in an amount of 20 to 30% by mass more than the second portion 430B, the generation of cracks due to thermal stress is dispersed in the first portion 430A and the second portion 430B. Can do. Accordingly, it is possible to prevent the inclination of the electrode tip 450 caused by the cracks being developed to be biased to one of the first portion 430A and the second portion 430B. As a result, the life of the spark plug 10 can be further extended.

  Further, since the outer diameter ODc of the electrode tip 450 is 0.7 to 1.5 mm, the second portion 430B caused by the second portion 430B being easily subjected to thermal stress as the electrode tip 450 is reduced in diameter. In addition, it is possible to prevent an increase in cracks at the same time, and to prevent insufficient strength of the melted portion 430 accompanying the increase in the diameter of the electrode tip 450. Therefore, the peel resistance of the ground electrode 400 can be sufficiently ensured.

  Moreover, since the main component of the electrode tip 450 is platinum (Pt), the oxidation resistance of the electrode tip 450 can be sufficiently ensured.

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.

  Regarding the content rate CRa of the noble metal component in the first portion 430A and the content rate CRb of the noble metal component in the second portion 430B, the content rate CRa intends an average value in the entire first portion 430A, and the content rate CRb is The average value in the entire area of the two portions 430B is intended. Therefore, the method for obtaining the content ratios CRa and CRb is not limited to the method based on the observation regions of the circles CL1, CL2, and CL3, and a value corresponding to the average value in the entire portions of the first portion 430A and the second portion 430B is obtained. Any technique can be used.

DESCRIPTION OF SYMBOLS 10 ... Spark plug 90 ... Internal combustion engine 100 ... Center electrode 101 ... Front end surface 107 ... Side surface 190 ... Terminal metal fitting 200 ... Insulator 290 ... Shaft hole 300 ... Main metal fitting 310 ... End surface 400 ... Ground electrode 410 ... Electrode base material 411,412 , 413, 414, 415, 416 ... base material surface 430 ... melting part 430A ... first part 430B ... second part 431 ... exposed surface 433 ... boundary surface 450 ... electrode tip 451 ... tip surface (tip surface)
453 ... Chip surface 459 ... Overhang 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,
In the cross section of the ground electrode cut along 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 shaft of the melting portion The tip of the electrode tip that faces the center electrode when the portion formed from the tip side of the center is the first portion and the portion formed from the base end side of the axis is the second portion The length from the surface to the first portion is shorter than the length from the tip surface to the second portion,
The spark plug according to claim 1, wherein the first portion contains more noble metal component than the second portion.   The spark plug according to claim 1, wherein the first portion and the second portion each contain 10 to 80% by mass of a noble metal component.   The spark plug according to claim 1, wherein the first portion contains a noble metal component in an amount of 20 to 30% by mass more than the second portion.   The spark plug according to any one of claims 1 to 3, wherein an outer diameter of the electrode tip is 0.7 to 1.5 mm.   The spark plug according to any one of claims 1 to 4, wherein a main component of the electrode tip is platinum (Pt).

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