WO2018123539A1

WO2018123539A1 - Ignition plug and method for manufacturing ignition plug

Info

Publication number: WO2018123539A1
Application number: PCT/JP2017/044369
Authority: WO
Inventors: 柴田　正道
Original assignee: 株式会社デンソー
Priority date: 2016-12-27
Filing date: 2017-12-11
Publication date: 2018-07-05

Abstract

This ignition plug is provided with: a main metal fitting (11); a ground electrode (13) having one end which is affixed to the main metal fitting, and also having the other end, a part of which forms a sloped section (13A) tilted toward the center axis of the main metal fitting; a ground electrode tip (13B) joined to the sloped section; and a center electrode (14) having one end exposed from the main metal fitting. The ignition plug has: a base (14A) which is elliptic column shaped, is disposed so that the minor diameter direction faces the ground electrode tip, and has an end surface which is a sloped surface (14C) sloped in the minor diameter direction relative to the center axis; and a center electrode tip (14B) which is laser welded to the sloped surface. The ground electrode tip and the center electrode tip face each other.

Description

Spark plug and method of manufacturing spark plug

Cross-reference of related applications

This application is based on Japanese Application No. 2016-253130 filed on Dec. 27, 2016 and Japanese Application No. 2017-183792 filed on Sep. 25, 2017. Is used.

This disclosure relates to a spark plug.

An internal combustion engine such as a gasoline engine is provided with an ignition plug, and is present in the combustion chamber of the internal combustion engine by generating a discharge spark between a center electrode and a ground electrode facing each other provided in the ignition plug. It is configured to ignite the air-fuel mixture. Regarding this spark plug, there is a spark plug described in Patent Document 1, for example. In this spark plug, the center line of the center electrode is in a position eccentric from the center line of the spark plug, and is parallel to the center line of the spark plug. The center axis of the center electrode tip attached to the tip of the center electrode is inclined with respect to the center electrode center line, and the center of the ground electrode tip attached to the inside of the tip of the ground electrode (corresponding to the side electrode) The axis is inclined with respect to the center line of the spark plug. The center electrode tip and the ground electrode tip are opposed to each other across the center line of the spark plug, and the respective center axes coincide with each other.

JP 2005-339981 A

In the spark plug described in the cited document 1, the center electrode tip protrudes from the annular insulator tip surface in a cylindrical shape by a predetermined amount, and a taper portion having a gradually smaller diameter is formed. . A cylindrical center electrode side tip is attached to the tip of the taper portion on the small diameter side. At this time, the tapered portion formed at the tip of the center electrode has a substantially conical shape. By the way, since the tip end portion of the center electrode of a generally ignited spark plug has a cylindrical shape, it is difficult to say that the center electrode in which a substantially conical tapered portion is formed at the tip portion has a general shape. . For this reason, compared with the manufacturing cost of a column-shaped center electrode, there exists a possibility that the manufacturing cost of the center electrode in which a substantially cone-shaped taper part is formed in a front-end | tip part may become high. For this reason, in order to suppress an increase in the manufacturing cost of the center electrode, it is desirable that the tip portion of the center electrode is cylindrical. However, when the tip of the center electrode is cylindrical, even if the tip of the center electrode is attached to the tip of the center electrode, the tip of the center electrode and the tip of the ground electrode inclined with respect to the center line of the spark plug They do not face each other.

As a countermeasure, it is conceivable to place a pedestal with a cylindrical part processed between the center electrode and the center electrode tip. Specifically, a pedestal is formed at the end of the center electrode exposed from the metal shell. An inclined surface inclined so as to face the end surface of the ground electrode side chip is formed on the end surface of the pedestal, and it is conceivable to attach the center electrode side chip to the inclined surface.

At this time, if the pedestal is cylindrical, the inclined surface formed on the pedestal is assumed to be elliptical. When the cylindrical center electrode side tip is laser-welded to the elliptical inclined surface, the molten state in the melting portion of the central electrode side tip and the pedestal is changed between the major axis side and the minor axis side of the elliptical inclined surface. Will be different. Specifically, the melted portion on the longer diameter side in the elliptical inclined surface contains a larger amount of metal constituting the pedestal than the melted portion on the shorter diameter side in the elliptically inclined surface. In this case, there is a possibility that a difference in thermal expansion coefficient occurs between the melted portion on the long diameter side and the melted portion on the short diameter side on the elliptical inclined surface. That is, the magnitude of the internal force (thermal stress) generated by the temperature change in the melted portion that joins the center electrode side tip and the inclined surface of the pedestal is less than the melted portion on the long diameter side of the elliptically inclined surface, There may be a difference between the melted portion on the diameter side (the thermal stress generated by a temperature change in the melted portion joining the center electrode side tip and the inclined surface of the pedestal may be uneven). There is. For this reason, when the above-mentioned ignition plug in which the center electrode tip is laser-welded to the end face of the cylindrical pedestal formed at the end of the center electrode exposed from the metal shell is mounted in the internal combustion engine, Each time the combustible air-fuel mixture is burned, thermal stress is generated non-uniformly at the melted portion that joins the center electrode tip and the inclined portion of the pedestal. Therefore, the joint strength of the melted portion where particularly strong thermal stress is generated decreases every time the combustible air-fuel mixture burns in the internal combustion engine. As a result, the center electrode tip is peeled off from the tapered portion of the center electrode. there's a possibility that.

The present disclosure has been made in order to solve the above-described problem. The main purpose of the present disclosure is that the center axis of the ground electrode side tip and the center axis of the center electrode side tip are inclined with respect to the center axis of the metal shell. In addition, in the configuration in which the pedestal is interposed between the center electrode tip and the center electrode, the center electrode tip is separated from the pedestal due to a temperature change caused by repeated combustion of the air-fuel mixture in the internal combustion engine. An object of the present invention is to provide a spark plug capable of suppressing this.

A first disclosure is a spark plug mounted on an internal combustion engine, in which a cylindrical metal shell and one end side are fixed to the metal shell, and a part of the other end side approaches a central axis of the metal shell. A ground electrode forming an inclined portion, a ground electrode-side chip joined to the inclined portion of the ground electrode, and housed in the metal shell, with one end exposed from the metal shell and extending. A center electrode and an elliptical columnar shape, the minor axis direction is arranged to face the ground electrode side chip, and is formed at the end of the center electrode exposed from the metal shell of the center electrode, and the end surface is the end surface A pedestal forming an inclined surface inclined in a minor axis direction with respect to a central axis, and a cylindrical center electrode side tip laser welded to the inclined surface of the pedestal, the ground electrode side tip, The end of the center electrode side tip Each other are opposed to each other.

The ground electrode of the present spark plug is formed with an inclined portion in which one end side is fixed to the metal shell and a part on the other end side is inclined so as to approach the central axis of the metal shell. And the ground electrode side chip | tip is joined to the inclination part. On the other hand, an inclined surface inclined with respect to the central axis of the metal shell is formed on the end surface of the pedestal formed at the end of the center electrode exposed from the metal shell. Are laser welded. The end surfaces of the ground electrode side chip and the center electrode side chip face each other. That is, it can be said that the center axis of the ground electrode side tip and the center axis of the center electrode side tip are inclined with respect to the center axis of the metal shell.

In the above spark plug, if the pedestal on which the center electrode tip is laser welded is cylindrical, the inclined surface formed on the pedestal is assumed to be elliptical. When the cylindrical center electrode side tip is laser-welded to the elliptical inclined surface of the pedestal, the molten state in the melting portion of the central electrode side tip and the pedestal is formed on the major axis side and the minor axis side of the elliptical inclined surface. Will be different. Specifically, the melted portion on the longer diameter side in the elliptical inclined surface contains a larger amount of metal constituting the pedestal than the melted portion on the shorter diameter side in the elliptically inclined surface. Thereby, there is a possibility that a difference in thermal expansion coefficient occurs between the melted part on the long diameter side and the melted part on the short diameter side in the elliptical inclined surface. In other words, the magnitude of the thermal stress generated by the temperature change in the melted part that joins the center electrode side tip and the inclined surface of the pedestal is that the melted part on the major axis side and the melted part on the minor axis side on the elliptical surface. The part is different. For this reason, when the above ignition plug having the center electrode side tip attached to the inclined surface formed on the end surface of the pedestal formed at the end portion of the center electrode exposed from the metal shell is mounted on the internal combustion engine, Each time the combustible air-fuel mixture is burned in the engine, thermal stress is generated non-uniformly at the melted portion that joins the center electrode tip and the inclined surface of the pedestal. Accordingly, the joint strength of the melted portion where particularly strong thermal stress is generated decreases every time the combustible air-fuel mixture burns in the internal combustion engine, and as a result, the inclination in which the center electrode side tip is formed on the pedestal. There is a possibility of peeling from the surface.

As a countermeasure, the pedestal provided in the spark plug has an elliptical columnar shape and is arranged so that the minor axis direction faces the tip of the ground electrode side tip, and the end surface on the side where the center electrode side tip is laser welded has a center axis line. In contrast, an inclined surface that is inclined in the minor axis direction is formed. As a result, the inclined surface formed on the pedestal can be made close to a perfect circle, and when the pedestal and the center electrode side tip are laser welded, the molten state between the center electrode side tip and the center electrode can be made uniform. Can be planned. As a result, when this spark plug is mounted on an internal combustion engine, the combustible air-fuel mixture is combusted in the internal combustion engine, so that the thermal stress generated in the melted portion that joins the center electrode tip and the inclined surface of the pedestal. Since uniformity can be achieved, it is possible to prevent the center electrode side tip from being peeled off from the pedestal.

A second disclosure is a spark plug mounted on an internal combustion engine, in which a cylindrical metal shell and one end side are fixed to the metal shell, and a part of the other end side approaches a central axis of the metal shell. A ground electrode forming an inclined portion, a ground electrode-side chip joined to the inclined portion of the ground electrode, and housed in the metal shell, with one end exposed from the metal shell and extending. A center electrode, a columnar shape, a pedestal formed at an end of the center electrode exposed from the metal shell, and an elliptical columnar shape, with a minor axis direction facing the ground electrode side chip The end surface forms an inclined surface inclined in the minor axis direction with respect to its own axis, and the inclined surface is laser welded to the pedestal, and a center electrode side tip, and the ground electrode side tip, End faces of the center electrode tip are It is opposed to the stomach.

According to the above configuration, the pedestal has a cylindrical shape and is formed at the end of the center electrode exposed from the metal shell. The center electrode side tip has an elliptical columnar shape and is arranged so that the minor axis direction faces the ground electrode side chip, and the end surface forms an inclined surface inclined in the minor axis direction with respect to its own axis. The inclined surface is laser welded to the pedestal. As a result, the inclined surface formed on the center electrode side tip can be made close to a perfect circle, and when the pedestal and the center electrode side tip are laser welded, the molten state of the center electrode side tip and the center electrode can be reduced. Uniformity can be achieved.

Here, in the first disclosure, it is necessary to perform laser welding along the inclined surface of the base inclined with respect to the central axis of the metal shell. On the other hand, according to the said structure, the inclined surface is formed in the center electrode side chip | tip, and it is not necessary to form an inclined surface in a base. For this reason, laser welding can be performed along the surface of the pedestal perpendicular to the central axis as in the conventional case, and laser welding can be easily performed.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing
FIG. 1 is a half sectional view of a spark plug according to the present embodiment, 2 is an enlarged view of a main part of α in FIG. FIG. 3 is a diagram showing a bonding state between the inclined surface formed on the columnar pedestal according to the comparative example and the center electrode side chip from a plurality of viewpoints, FIG. 4 is a schematic diagram illustrating a melting state of a melting portion between an inclined surface formed on a columnar pedestal according to a comparative example and a center electrode side tip, FIG. 5 is a diagram showing a bonding state between the inclined surface formed on the elliptical columnar pedestal according to the present embodiment and the center electrode side chip from a plurality of viewpoints. FIG. 6 is a schematic view showing a bending strength test of the center electrode tip. FIG. 7 is a diagram showing the results of a bending strength test of the center electrode side tip, FIG. 8 is a schematic diagram showing the major axis and minor axis of the pedestal and the inclination angle of the pedestal, FIG. 9 is a perspective view showing a modified example of the spark plug, FIG. 10 is an enlarged view of a main part of the modified example of FIG. FIG. 11 is a view showing a joining state of the columnar pedestal and the inclined surface formed on the center electrode side chip according to the modified example of FIG. 9 from a plurality of viewpoints. FIG. 12 is a perspective view showing a method of manufacturing the center electrode side chip, FIG. 13 is an enlarged view of a main part showing another modification of the spark plug.

FIG. 1 is a half sectional view of a spark plug 1 attached to the internal combustion engine 10. The spark plug 1 is provided with a substantially cylindrical metal shell 11 made of metal.

The outer peripheral edge of the metal shell 11 has a hexagonal outer periphery for engaging a plug wrench used when the metal shell 11 is attached to the wall of the cylinder head 10A forming the combustion chamber 10B of the internal combustion engine 10. A tool engaging portion 113 is provided. A threaded portion (male threaded portion) 116 for attaching the spark plug 1 to the wall portion of the cylinder head 10A is formed on the metal shell 11 on the combustion chamber 10B side (referred to as the tip side) with respect to the tool engaging portion 113. .

An insulator 12 is inserted into the metal shell 11. The insulator 12 is supported by a support portion 117 whose inner diameter formed at the inner peripheral edge of the metal shell 11 becomes smaller toward the tip side. Further, the insulator 12 is fixed by a caulking portion 114 formed at an end portion (rear end portion) of the tool engagement portion 113 opposite to the combustion chamber 10B side (rear end side). Has been.

A substantially cylindrical center electrode 14 is held on the inner periphery of the insulator 12. Further, a ground electrode 13 is provided that protrudes toward the front end side of the metal shell 11 and is disposed so as to face the front end side of the center electrode 14 so as to have a predetermined discharge gap.

FIG. 2 shows an enlarged cross-sectional view of the main part of the center electrode 14 and the ground electrode 13. Here, the main part refers to a region indicated by α in FIG.

One end side of the ground electrode 13 is fixed to the metal shell 11, and a part including the other end is inclined so as to approach the center axis AX1 of the metal shell 11 (in other words, the center axis of the center electrode 14). 13A is formed. And the ground electrode side chip | tip 13B is joined to the surface (surface in which the center electrode 14 exists in the inclination part 13A) inside the inclination part 13A.

On the other hand, the center electrode 14 held in the inner periphery of the insulator 12 has its tip exposed from the insulator 12 (in other words, the tip of the center electrode 14 is exposed from the metal shell 11). You may). A pedestal 14A is formed at the tip of the center electrode 14 exposed from the insulator 12, and an inclined surface 14C (see FIG. 5) is inclined on the end surface of the pedestal 14A with respect to the central axis AX1 of the metal shell 11. ) Is formed. A cylindrical center electrode side tip 14B is laser welded to the inclined surface 14C. The ground electrode side chip 13B and the center electrode side chip 14B face each other. That is, it can be said that the center axis AX2 of the ground electrode side tip 13B and the center axis AX3 of the center electrode side tip 14B are inclined with respect to the center axis AX1 of the metal shell 11. In the present embodiment, the center axis AX2 of the ground electrode side chip 13B and the center axis AX3 of the center electrode side chip 14B are arranged on the same axis.

The pedestal 14A is made of a Ni alloy, and the ground electrode side tip 13B and the center electrode side tip 14B are made of a noble metal such as an Ir alloy.

In the spark plug 1, if the pedestal 14 A is cylindrical as in the comparative example described in FIG. 3, the inclined surface 14 C formed on the pedestal 14 A is assumed to be elliptical. When the cylindrical center electrode side tip 14B is laser-welded to the elliptical inclined surface 14C of the pedestal 14A, as shown in FIG. 4, on the major axis side and the minor axis side of the elliptical inclined surface 14C, The width of the outer portion of the center electrode side tip 14B and the base 14A is different from that of the melted portion, and therefore the melted state of the melted portion is different. Specifically, the longer diameter side melted portion in the elliptical inclined surface 14C contains a larger amount of Ni alloy constituting the base 14A than the shorter diameter side melted portion in the elliptical inclined surface 14C. Become. On the contrary, the melted portion on the short diameter side of the elliptical inclined surface 14C contains a larger amount of noble metal constituting the center electrode side tip 14B than the melted portion on the long diameter side of the elliptically inclined surface 14C. Become. Thereby, there is a possibility that a difference in the thermal expansion coefficient occurs between the melted portion on the long diameter side and the melted portion on the short diameter side in the elliptical inclined surface 14C. That is, the magnitude of the thermal stress generated by the temperature change in the melted portion joining the center electrode side tip 14B and the inclined surface 14C of the pedestal 14A is such that the melted portion on the long diameter side and the short diameter on the elliptical surface There is a possibility that it differs depending on the melted part on the side.

For this reason, when the above-described ignition plug 1 in which the center electrode side tip 14B is laser-welded to the inclined surface 14C formed on the end surface on the front end side of the cylindrical base 14A is mounted on the internal combustion engine 10, the internal combustion engine 10 Each time the combustible air-fuel mixture is combusted, thermal stress is unevenly generated in the melted portion that joins the center electrode side tip 14B and the inclined surface 14C of the base 14A. Therefore, the joint strength of the portion where particularly strong thermal stress is generated in the melted portion decreases every time the combustible air-fuel mixture burns in the internal combustion engine 10, and as a result, the center electrode tip 14B is formed on the base 14A. There is a possibility of peeling from the inclined surface 14C.

As a countermeasure against this, in the present embodiment shown in FIG. 5, the base 14A provided in the spark plug 1 is in the shape of an elliptic cylinder, and is arranged so that the minor axis direction faces the ground electrode side chip 13B, and the center electrode side chip 14B. An inclined surface 14 C that is inclined in the minor axis direction with respect to the central axis AX 1 of the metal shell 11 is formed on the end surface on the side where laser welding is performed. Thereby, since the inclined surface 14C formed on the pedestal 14A can be made close to a perfect circle, when the pedestal 14A and the center electrode side tip 14B are laser-welded, the pedestal 14A and the center electrode side tip 14B The width of the outer portion can be made uniform from the melting portion. As a result, it is possible to make the molten state uniform in the molten portion between the base 14A and the center electrode tip 14B. Therefore, when the spark plug 1 is mounted on the internal combustion engine 10, the combustible air-fuel mixture is combusted in the internal combustion engine 10, so that the center electrode side tip 14B and the inclined surface 14C of the base 14A are joined. Therefore, it is possible to suppress the separation of the center electrode side chip 14B from the base 14A. 3 and 5 illustrate a state before the center electrode side tip 14B is laser-welded to the inclined surface 14C of the pedestal 14A.

By the way, when a vehicle is inspected by a dealer, a length (gap length) between the electrodes of the spark plug 1 may be checked by passing a rod having a predetermined diameter between the electrodes of the spark plug 1. . At this time, when the rod comes into contact with the center electrode side tip 14B, a bending moment is generated in the center electrode side tip 14B, and there is a possibility of peeling from the base 14A.

Even when a bending moment is generated in the center electrode side tip 14B due to the contact of the rod with the center electrode side tip 14B, the center electrode side tip 14B leads to a configuration capable of withstanding the bending strength. Conducted the tests described below.

By the time the vehicle is inspected including the step of examining the length between the electrodes of the spark plug 1, the spark plug 1 is repeatedly in a high temperature environment by burning the combustible mixture in the internal combustion engine 10. It is assumed that thermal stress has already occurred several times in the melted part joining the center electrode tip 14B and the inclined surface 14C of the pedestal 14A. That is, it is assumed that the step of examining the length between the electrodes is performed on the spark plug 1 in which thermal stress has already occurred several times in the melted portion. Considering this, before performing the bending strength test described later, first, the center electrode side tip is placed in an environment equivalent to the environment where the spark plug 1 is exposed by the combustion of the combustible air-fuel mixture several times in the internal combustion engine 10. 14B was exposed to laser-welded pedestal 14A. Specifically, the pedestal 14A in which the center electrode side tip 14B is laser-welded to the inclined surface 14C is exposed to a low temperature environment (for example, 150 ° C.) for a predetermined time (for example, 6 minutes), and then in a high temperature environment (for example, 950 ° C.). Was repeated a predetermined number of times (for example, 200 cycles).

After performing the above process, as shown in FIG. 6, the center electrode side chip 14B is peeled off by pressing the center electrode side chip 14B from the direction perpendicular to the center axis AX3 of the center electrode side chip 14B. The bending strength was measured. The result is shown in FIG. As shown in the plan view of FIG. 8, the length of the major axis of the pedestal 14A is defined as the major axis a, and the minor axis of the pedestal 14A is defined as the minor axis b.

If the pedestal 14A is cylindrical, the lengths of the major axis a and the minor axis b are equal, so the value obtained by dividing the minor axis b by the major axis a is 1. On the other hand, when the pedestal 14A has an elliptical column shape, the major axis a and the minor axis b have different lengths, and the value obtained by dividing the minor axis b by the major axis a is a value away from 1. In addition, the larger the difference between the major axis a and the minor axis b, the farther the shape of the pedestal 14A is from the cylinder. Therefore, by calculating the value obtained by dividing the minor axis b by the major axis a, the pedestal 14A is calculated. The elliptical cylinder that is formed serves as a guideline for determining how far away from the cylinder. Accordingly, the vertical axis in FIG. 7 is a value obtained by dividing the minor axis b by the major axis a, and this value is called the ellipticity. On the other hand, the horizontal axis of FIG. 7 is the inclination angle θ of the pedestal 14A. As shown in FIG. 8, the inclination angle θ is an inclined surface formed on the pedestal 14A with respect to a plane perpendicular to the central axis AX4 of the pedestal 14A. It indicates an inclination angle of 14C. In the present embodiment, the center axis AX4 of the pedestal 14A is disposed on the same axis as the center axis AX1 of the metal shell 11, so that the center axis AX1 of the metal shell 11 is aligned with the center axis AX1 of the metal shell 11, as shown in FIG. In other words, the inclination angle of the inclined surface 14 C formed on the pedestal 14 A with respect to the vertical surface.

In this test, it is assumed that the force applied to the center electrode side chip 14B by contact of the rod with the center electrode side chip 14B is 30 N at the maximum, and the center electrode side chip 14B is sufficient if it can withstand a force of 50 N or more. It was judged to have a good bending strength. For this reason, the graph shown in FIG. 7 is a cross if the bending strength when the center electrode side chip 14B peels off is lower than 50N, and the bending strength when the center electrode side chip 14B peels off is higher than 50N and higher than 100N. If the bending strength when the center electrode side chip 14B is peeled off is higher than 100N, it is indicated by a double circle.

At this time, as the inclination angle θ of the pedestal 14A increases, the ellipticity of the pedestal 14A is reduced (by moving the shape of the pedestal 14A away from the columnar shape), whereby the bending strength when the center electrode side chip 14B is peeled off is increased. I was able to keep it high. Further, it has been found that there are a plurality of ellipticities having a bending strength of 50 N or more when the center electrode side tip 14B is peeled off when the inclination angle θ of the base 14A is a predetermined value. Therefore, the formula (1) can be obtained by approximating the minimum value and the maximum value of the ellipticity with a bending strength of 50 N or more when the center electrode tip 14B is peeled off. That is, it was found that by forming the pedestal 14A so as to satisfy the obtained expression (1), the center electrode side tip 14B laser welded to the inclined surface 14C can have high bending strength. More specifically, the quotient obtained by dividing the minor axis b by the major axis a (the ellipticity of the pedestal 14A) is larger than the product of 0.9 and the cosine value of the inclination angle θ, and the cosine of the inclination angle θ. By forming the pedestal 14A so as to be smaller than the quotient obtained by dividing the value by 0.9, the center electrode side tip 14B laser-welded to the inclined surface 14C can have a high bending strength. I understood.

0.9 × cos θ ≦ b / a ≦ cos θ / 0.9 (1)
From the test results shown in FIG. 7, when the center electrode tip 14B is laser welded to the cylindrical pedestal 14A (ellipticity = 1), the inclination angle θ of the inclined surface 14C of the pedestal 14A is 15 ° or less. It was found that the center electrode side tip 14B can have a high bending strength of 100 N or more. In other words, when the inclination angle θ of the inclined surface 14C of the cylindrical pedestal 14A is larger than 15 °, it was found that the center electrode side tip 14B cannot have a high bending strength of 100 N or more. . Therefore, when the inclination angle θ of the inclined surface 14C of the pedestal 14A is set to 20 ° or more, by adopting the elliptical columnar pedestal 14A, the center electrode side tip 14B is more than when the cylindrical pedestal 14A is adopted. Can have a high bending strength.

On the other hand, when the inclination angle θ of the inclined surface 14C of the pedestal 14A is 55 ° or more, the pedestal is subjected to a laser welding process to be described later in which laser welding is performed with the center electrode side tip 14B in contact with the inclined surface 14C of the pedestal 14A. The tip portion of 14A cannot withstand the force applied when the center electrode side tip 14B is pressed, and may break.

Based on the above, the inclination angle θ of the inclined surface 14C of the pedestal 14A with respect to the plane perpendicular to the central axis AX4 of the elliptical columnar pedestal 14A is set to 20 ° to 50 °. Thereby, it becomes possible to give the center electrode side tip 14B a higher bending strength than when the cylindrical pedestal 14A is adopted, and the small diameter side portion of the inclined surface 14C is broken during the laser welding process. It became clear that it became possible to suppress.

Therefore, the elliptical columnar pedestal 14A according to the present embodiment is inclined such that the end surface on the distal end side is inclined in the minor axis direction with respect to the central axis AX1 of the metal shell 11 so that the inclination angle θ is 20 ° or more and 50 ° or less. The surface 14C is formed and formed so as to satisfy the expression (1). The pedestal 14A thus formed is arranged so that the minor axis direction faces the ground electrode side chip 13B.

The spark plug 1 can be manufactured by performing the first to fourth steps described below. Note that the major axis a and the minor axis b of the pedestal 14A and the inclination angle θ of the inclined surface 14C of the pedestal 14A are determined before performing the first step.

The first step is to perform cold forging in which a certain force is applied to a plate material made of an Ni alloy at room temperature using a jig or the like, and the predetermined major axis a and minor axis b are This is a step of forming an elliptical columnar pedestal 14A at one end of a substantially cylindrical center electrode having a length.

The second step is a step of cutting one end of the base 14A formed in the first step to form an inclined surface 14C having an inclination angle θ that is inclined in the minor axis direction with respect to the central axis AX1 of the metal shell 11. is there.

The third step is a step of welding using a laser in a state where the end surface of the center electrode tip 14B is in contact with the inclined surface 14C of the base 14A formed in the second step. At this time, the center point of the end surface of the center electrode side chip 14B is brought into contact with the center point of the inclined surface 14C of the base 14A. Thereby, the width | variety of an outer side part can be approached uniformly rather than the fusion | melting part of the center electrode side chip | tip 14B and the base 14A.

The fourth step is a step in which the center electrode 14 is accommodated in the insulator 12 so that the pedestal 14A is exposed. At this time, the center electrode 14 is arranged so that the minor axis direction of the pedestal 14A faces the ground electrode side chip 13B, the center axis AX2 of the ground electrode side chip 13B, and the center axis AX3 of the center electrode side chip 14B. And the height of the metal shell 11 in the direction of the central axis AX1 is adjusted so that they are arranged on the same axis.

The above embodiment can be implemented with the following modifications. In addition, about the part same as the said embodiment, description is abbreviate | omitted by attaching | subjecting the same code | symbol.

In the above embodiment, the inclined surface 14C formed on the pedestal 14A is true by forming the inclined surface 14C inclined in the minor axis direction with respect to the central axis AX1 of the metal shell 11 on the end surface of the pedestal 14A. It was formed to approach a circle. About this, you may form so that the shape of 14 C of inclined surfaces formed in the base 14A may become a perfect circle. In this case, when laser welding is performed on the pedestal 14A and the center electrode side tip 14B, the width of the outer portion of the pedestal 14A and the center electrode side tip 14B can be equalized.

In the above embodiment, the inclination angle θ of the pedestal 14A is formed so as to be 20 ° or more and 50 ° or less. However, even if the inclination angle θ of the pedestal 14A is lower than 20 °, it is set higher than 50 °. Also good.

In the above embodiment, the pedestal 14A is formed so as to satisfy the relationship described in the expression (1). Instead of the expression (1), the following expression (2), expression (3), expression (4), or expression (5) may be used. Regardless of the formula, the pedestal 14A satisfying the relationship of the formula can satisfy the relationship described in the formula (1).

0.9 × cos θ ≦ b / a ≦ 1.1 × cos θ (2)
cos θ / 1.1 ≦ b / a ≦ cos θ / 0.9 (3)
cos θ / 1.1 ≦ b / a ≦ 1.1 × cos θ (4)
0.9 ≦ b / (a × cos θ) ≦ 1.1 (5)
In the above embodiment, the base 14A is formed so as to satisfy the relationship described in the expression (1). Regarding this, it is not always necessary to satisfy the relationship described in the equation (1). That is, the pedestal 14A is formed in an elliptical columnar shape, the center electrode 14 is disposed so that the minor axis direction of the pedestal 14A faces the ground electrode side chip 13B, and the minor axis with respect to the central axis AX1 of the metal shell 11 If the inclined surface 14C inclined in the direction is formed on the end surface of the pedestal 14A, the inclination angle θ of the pedestal 14A and the relationship between the major axis a and the minor axis b of the pedestal 14A are limited to those satisfying the relationship of the expression (1). I can't.

In the above embodiment, the inclined portion 13A formed on the ground electrode 13 is inclined so that a part including the other end opposite to the one end fixed to the metal shell 11 approaches the center axis AX1 of the metal shell 11. Was formed. In this regard, the inclined portion 13 A formed on the ground electrode 13 may be formed to be inclined so that a part of the other end side not including the other end approaches the central axis AX 1 of the metal shell 11. At this time, the shape of the other end of the ground electrode 13 is not limited. For example, the ground electrode 13 may be formed so as to be parallel to the central axis AX1 of the metallic shell 11 or with respect to the central axis AX1 of the metallic shell 11. And may be formed to be vertical.

In the above embodiment, the center axis AX2 of the ground electrode side chip 13B and the center axis AX3 of the center electrode side chip 14B are arranged on the same axis. In this regard, if the ground electrode side chip 13B and the center electrode side chip 14B are opposed to each other, the center axis AX2 of the ground electrode side chip 13B and the center axis AX3 of the center electrode side chip 14B are the same. It does not need to be arranged on the axis.

In the manufacturing process of the spark plug 1 according to the above embodiment, a resistance welding process may be added after the second process and before the third process. Specifically, in a state in which the end surface of the center electrode side chip 14B is in contact with the inclined surface 14C of the pedestal 14A formed in the second step, a predetermined size is provided between the pedestal 14A and the center electrode side chip 14B. Resistance welding is carried out by passing a current of. As a result, the portion where the inclined surface 14C of the pedestal 14A is in contact with the center electrode side tip 14B generates heat when energized due to contact resistance, and the center electrode side tip 14B is joined to the inclined surface 14C. By performing the third step in this state, it is possible to prevent the center electrode side tip 14B from being displaced with respect to the pedestal 14A during welding by laser.

In the above embodiment, the pedestal 14A is formed with the inclined surface 14C whose end surface is inclined in the minor axis direction with respect to the central axis AX1. On the other hand, as shown in FIGS. 9 to 11, it has an elliptical column shape and is arranged so that the minor axis direction faces the ground electrode side chip 13B, and the end surface is in the minor axis direction with respect to its own axis AX5. An inclined surface 214C that is inclined may be formed in the center electrode side chip 214B. In this case, the pedestal 214 A has a cylindrical shape and is formed at the end of the center electrode 14 exposed from the metal shell 11. The inclined surface 214C of the center electrode tip 214B is laser welded to the surface 215 of the base 214A. In addition, an elliptical columnar member is formed by hot-drawing a cylindrical chip material through a drawing-type elliptical hole. Then, as shown in FIG. 12, the elliptical columnar member 214B having the inclined surface 214C can be formed by obliquely cutting the elliptical columnar member with a wire saw or the like.

According to the above configuration, the inclined surface 214C formed on the center electrode side chip 214B can be made close to a perfect circle, and when the base 214A and the center electrode side chip 214B are laser welded, the center electrode side chip 214B And the center electrode 14 can be made uniform in the molten state. Further, an inclined surface 214C is formed on the center electrode side chip 214B, and it is not necessary to form an inclined surface on the pedestal 214A. For this reason, laser welding can be performed along the surface 215 (that is, the inclined surface 214C) of the pedestal 214A perpendicular to the central axis AX1 as in the conventional case, and laser welding can be easily performed. Further, by setting the angle θ between the surface 215 of the pedestal 214A and the axis AX5 of the center electrode side chip 214B to 20 ° or more and 50 ° or less as in the above embodiment, the same effects as in the above embodiment can be obtained. Can do.

In the above configuration, the inclined surface 214C that is inclined in the minor axis direction with respect to its own axis AX5 is formed on the end surface of the center electrode side chip 214B so that the inclined surface 214C approaches a perfect circle. Was forming. In this regard, the inclined surface 214C formed on the center electrode side chip 214B may be formed in a perfect circle (circle). In this case, when the pedestal 214A and the center electrode side chip 214B are laser welded, the width of the outer portion of the pedestal 214A with respect to the melted portion with the center electrode side chip 214B can be made uniform.

The shape of the ground electrode side chip 13B is not limited to a columnar shape but may be a prismatic shape. As shown in FIG. 13, the shape of the ground electrode side chip 13 B may be a disk shape or a square plate shape (plate shape). The diameter of the ground electrode side chip 13B is the same as the diameter of the center electrode side chip 14B, the same as the long diameter a of the center electrode side chip 214B, the same as the short diameter b of the center electrode side chip 214B, and larger than those diameters. Or, it can be set arbitrarily such as small.

The end surface has an inclined surface 14C inclined in the minor axis direction with respect to the central axis AX1 and is formed in an elliptical column shape, and is arranged so that the minor axis direction faces the ground electrode side chip 13B. It is also possible to form the inclined surface 214C inclined in the minor axis direction with respect to its own axis AX5 in the center electrode side chip 214B. Even with this configuration, when the pedestal 14A and the center electrode tip 214B are laser welded, the molten state of the center electrode tip 214B and the center electrode 14 can be made uniform. Furthermore, the angle θ of the axis AX5 of the center electrode side chip 214B with respect to the plane perpendicular to the center axis AX1 can be increased without changing the pedestal 14A and the center electrode side chip 214B from a cylindrical shape to an elliptical column shape.

Although the present disclosure has been described based on the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more or less, are within the scope and spirit of the present disclosure.

Claims

A spark plug (1) mounted on an internal combustion engine (10),
A cylindrical metal shell (11);
One end side is fixed to the metal shell, and a ground electrode (13) that forms an inclined portion (13A) that is inclined so that a part of the other end side approaches the central axis of the metal shell,
A ground electrode side tip (13B) joined to the inclined portion of the ground electrode;
A central electrode (14) housed in the metal shell and having one end exposed and extending from the metal shell;
It is in the shape of an ellipse, and is arranged so that the minor axis direction faces the tip of the ground electrode side tip, is formed at the end of the center electrode exposed from the metal shell, and the end surface is in the minor axis direction with respect to the central axis A pedestal (14A) forming an inclined surface (14C) inclined to
A cylindrical center electrode side tip (14B) laser welded to the inclined surface of the pedestal;
With
The spark plug in which the end faces of the ground electrode side tip and the center electrode side tip are opposed to each other.
The elliptic columnar pedestal is defined by defining the length of the major axis as a, the length of the minor axis as b, and the inclination angle of the inclined surface with respect to a plane perpendicular to the central axis of the pedestal as θ.
0.9 × cos θ ≦ b / a ≦ cos θ / 0.9
The spark plug according to claim 1, wherein:
The elliptical columnar pedestal is defined by defining an inclination angle of the inclined surface with respect to a plane perpendicular to the central axis of the pedestal as θ
20 ° ≦ θ ≦ 50 °
The spark plug according to claim 1 or 2, wherein:
The spark plug according to any one of claims 1 to 3, wherein the shape of the inclined surface is a circle.
The spark plug according to any one of claims 1 to 4, wherein, on the inclined surface, a width of an outer portion is uniform from a melted portion where the center electrode tip is laser welded.
A method for manufacturing a spark plug according to any one of claims 1 to 5,
A first step of forming the elliptical columnar pedestal at one end of the center electrode by cold forging;
A second step of cutting one end of the pedestal formed in the first step to form the inclined surface inclined in the minor axis direction with respect to the central axis;
A third step of performing welding by laser in a state where the end surface of the center electrode side tip is in contact with the inclined surface formed by the second step;
When,
A fourth step of accommodating the central electrode in the metallic shell such that the pedestal is exposed;
A method of manufacturing a spark plug comprising:
After the completion of the second step, before the third step is performed, the pedestal and the pedestal are in contact with the inclined surface formed by the second step and the end surface of the center electrode side tip. The spark plug manufacturing method according to claim 6, further comprising a resistance welding step of performing resistance welding with the center electrode side tip.
A spark plug (1) mounted on an internal combustion engine (10),
A cylindrical metal shell (11);
One end side is fixed to the metal shell, and a ground electrode (13) that forms an inclined portion (13A) that is inclined so that a part of the other end side approaches the central axis of the metal shell,
A ground electrode side tip (13B) joined to the inclined portion of the ground electrode;
A central electrode (14) housed in the metal shell and having one end exposed and extending from the metal shell;
A pedestal (214A) that is cylindrical and formed at the end of the central electrode exposed from the metal shell;
It is in the shape of an elliptical column, arranged so that the minor axis direction faces the ground electrode side tip, and the end surface forms an inclined surface (214C) inclined in the minor axis direction with respect to its own axis, A center electrode tip (214B) whose surface is laser welded to the pedestal;
With
The spark plug in which the end faces of the ground electrode side tip and the center electrode side tip are opposed to each other.
The spark plug according to claim 8, wherein the shape of the inclined surface is a circle.
The spark plug according to claim 8 or 9, wherein, in the pedestal, the width of the outer portion is uniform from the melted portion where the center electrode side tip is laser welded.
The spark plug according to any one of claims 8 to 10, wherein the inclined surface is perpendicular to the central axis.