JP2016081633A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure enough welding strength between a ground electrode and a main metal fitting.SOLUTION: A spark plug comprises a ground electrode which is joint to a tip end of a main metal fitting, and includes a rod-like base end and a bent part arranged at a tip end side of the base end and bent toward the center electrode side, in which the base end includes an outside layer and an inside layer having a thermal conductivity higher than that of the outside layer. The base end of the ground electrode includes an outer layer and an inner layer having a thermal conductivity higher than that of the outer layer. The sectional center of the inside layer of the ground electrode is biased from the sectional center of the base end toward the width direction of the base end.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a spark plug.

  In general, a spark plug has a center electrode and a ground electrode on the tip side. The center electrode protrudes from the tip of the insulator while being held in the shaft hole of the insulator. On the other hand, the ground electrode is welded to the tip of the metal shell by resistance welding or the like.

  As a kind of spark plug, there is a type in which a heat transfer portion formed of a material having high thermal conductivity (for example, Cu) is provided in the ground electrode in order to improve the heat extraction performance of the ground electrode (Patent Literature). 1, 2). Since the heat transfer section has high thermal conductivity, the heat extraction performance of the ground electrode is improved, and the heat generated by the spark discharge at the tip of the ground electrode can be efficiently released to the metal shell. Therefore, as the occupation ratio of the heat transfer portion in the ground electrode increases, heat can be efficiently released to the metal shell.

JP 2011-181523 A Japanese Patent Laid-Open No. 11-185928

  However, since the heat transfer part is made of a material having high thermal conductivity, it is not welded to the metal shell, and the outer layer outside the heat transfer part is welded to the metal shell. Accordingly, the welding strength between the ground electrode and the metal shell is lower than that of a ground electrode having no heat transfer portion. On the other hand, since the spark plug is used in an environment where a rapid temperature change (cold thermal shock) occurs, a large thermal stress is generated in the ground electrode. For this reason, in the ground electrode which has a heat-transfer part inside, the weld strength of a ground electrode and a metal fitting becomes inadequate, and there existed a subject that it might be damaged by stress, such as thermal stress. This problem is particularly likely to occur as the occupation ratio of the heat transfer portion in the ground electrode increases.

  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, the ground electrode is joined to the distal end of the metal shell, provided at the distal end side of the rod-like base end portion and the base end portion, and bent toward the center electrode side. There is provided a spark plug having a ground electrode having a bent portion, the base end portion having an outer layer portion, and an inner layer portion having a higher thermal conductivity than the outer layer portion disposed inside the outer layer portion. The The spark plug has a cross section of the base end perpendicular to the axial direction of the spark plug, a thickness along the radial direction of the metal shell, and a width along a direction perpendicular to the radial direction, The cross-sectional center of the inner layer portion is eccentric from the cross-sectional center of the base end portion in the width direction of the base end portion.
According to this spark plug, since the cross-sectional center of the inner layer part is eccentric from the cross-sectional center of the base end part in the width direction of the base end part, there is a sufficient margin for the displacement of the welding position of the base end part to the metal shell. The welding strength of the ground electrode can be increased while ensuring.

(2) In the spark plug, the amount of eccentricity at the center of the cross section of the inner layer portion may be 2% or more of the width of the base end portion.
According to this spark plug, it is possible to sufficiently increase the welding strength of the ground electrode while ensuring a sufficient margin regarding the displacement of the welding position of the base end portion to the metal shell.

(3) In the spark plug, the amount of eccentricity of the cross-sectional center of the inner layer portion may be 10% or less of the width of the base end portion.
According to this spark plug, the welding strength of the ground electrode can be sufficiently increased without excessively decentering the inner layer portion.

  Note that the present invention can be realized in various modes. For example, it is realizable with forms, such as a manufacturing method of a spark plug.

The front view which shows the spark plug as one Embodiment. Explanatory drawing which shows the cross section of the metal shell and the ground electrode in the front-end | tip part of a spark plug. The schematic diagram which shows the 3-3 cross section of the base end part of a ground electrode. Explanatory drawing which shows the relationship between the eccentric amount of an inner layer part, and welding strength. Explanatory drawing which shows the relationship between the eccentric amount of an inner layer part, and welding strength.

  FIG. 1 is a front view showing a spark plug 100 as an embodiment of the present invention. In FIG. 1, the lower side where the ignition part of the spark plug 100 exists is defined as the front end side of the spark plug 100, and the upper side is defined as the rear end side. The spark plug 100 includes an insulator 10, a center electrode 20, a ground electrode 30, a terminal fitting 40, and a metal shell 50. The insulator 10 has an axial hole extending along the axis O. The axis O is also referred to as “center axis”. The center electrode 20 is a rod-shaped electrode extending along the axis O, and is held in a state of being inserted into the shaft hole of the insulator 10. The ground electrode 30 is an electrode having one end fixed to the tip 52 of the metal shell 50 and the other end facing the center electrode 20. The terminal fitting 40 is a terminal for receiving power supply, and is electrically connected to the center electrode 20. The metal shell 50 is a cylindrical member that covers the periphery of the insulator 10, and fixes the insulator 10 inside. A screw portion 54 is formed on the outer periphery of the metal shell 50. The screw part 54 is a part where a screw thread is formed, and is screwed into a screw hole of the engine head when the spark plug 100 is attached to the engine head.

  FIG. 2 shows a cross section of the metal shell 50 and the ground electrode 30 at the tip of the spark plug 100. The ground electrode 30 has a rod-like base end portion 30a joined to the tip end 52 of the metal shell 50, a bent portion 30b provided on the tip end side of the base end portion 30a and bent toward the center electrode 20 side, and a bent portion 30b. And a tip portion 30c provided on the tip side. The ground electrode 30 has an outer layer portion 30out and an inner layer portion 30in disposed inside the outer layer portion 30out. The inner layer portion 30in is formed of a metal material having a higher thermal conductivity than the outer layer portion 30out. The outer layer portion 30out is formed of, for example, a nickel-based alloy (Inconel 600, Inconel 601 or the like). The inner layer portion 30in is formed of, for example, copper (Cu) or nickel (Ni). The inner layer portion 30 in has a function as a heat transfer portion for releasing heat generated at the tip portion 30 c of the ground electrode 30 to the metal shell 50. For this reason, the inner layer portion 30in starts from the interface between the base end portion 30a and the metal shell 50, and extends to the vicinity of the position where the distal end portion 30c intersects the axis O.

3A is a schematic diagram illustrating an example of a 3-3 cross section (a cross section perpendicular to the direction of the axis O) at the base end portion 30a of the ground electrode 30 of FIG. Here, the cross section at a position of 1 mm from the contact surface between the base end portion 30a of the ground electrode 30 and the metal shell 50 to the front end side is a 3-3 cross section. The inner layer portion 30in is entirely included in the outer layer portion 30out. The meanings of the various codes shown in FIG. 3A are as follows. In addition, the cross-sectional center as used in this application means the geometric gravity center of a cross-sectional shape, and this is computed by tracing the cross-sectional image of a 3-3 cross section by CAD.
(1) Tout, Wout: thickness and width of the outer layer portion 30out (2) Tin, Win: thickness and width of the inner layer portion 30in (3) Cout: cross-sectional center of the outer layer portion 30out (geometric center of gravity of the cross-sectional shape)
(4) Cin: center of cross section of inner layer portion 30in (geometric center of gravity of cross section)
(5) δC: Eccentricity of the cross-sectional center Cin of the inner layer part 30in with reference to the cross-sectional center Cout of the outer layer part 30out (6) X, Y: width direction and thickness direction of the base end part 30a

  The thickness direction Y of the base end portion 30a is the radial direction of the metal shell 50 (the direction from the axis O toward the outside), and the width direction X of the base end portion 30a is a direction perpendicular thereto. Further, the thickness Tout and the width Wout of the outer layer portion 30out are the same as the thickness and width of the base end portion 30a.

  As can be understood from FIG. 3A, the cross-sectional center Cin of the inner layer portion 30in and the cross-sectional center Cout of the outer layer portion 30out are substantially the same in the thickness direction Y of the base end portion 30a, but the width direction X It is shifted to. In other words, the inner layer portion 30in is eccentric from the outer layer portion 30out. As described above, since the inner layer portion 30in is formed of a member having high thermal conductivity such as Cu, it is not welded to the metal shell 50, but only the outer layer portion 30out is welded to the metal shell 50. As shown in FIG. 3A, when the inner layer portion 30in is decentered from the outer layer portion 30out to the right side, a large-area joining portion where the outer layer portion 30out is welded to the metal shell 50 is formed on the left side of the base end portion 30a. The As will be described later, when the welding strength is calculated in the state where the inner layer portion 30in is eccentric as described above, the large-area joint portion generated by the eccentricity increases the welding strength between the base end portion 30a and the metal shell 50. confirmed.

  Note that the cross-sectional shape of the inner layer portion 30in is preferably similar to the cross-sectional shape of the proximal end portion 30a. By adopting such a cross-sectional shape, it is possible to reduce the possibility of stress concentration due to thermal shock (rapid temperature change) at the interface between the inner layer portion 30in and the outer layer portion 30out, so that the strength of the ground electrode 30 can be increased. It is.

  Note that it is also conceivable to select the thickness direction Y instead of the width direction X of the base end portion 30a as the direction in which the inner layer portion 30in is eccentric. However, regarding the thickness direction Y of the base end portion 30a, the positioning margin during welding is small. The reason is that the thickness direction Y of the base end portion 30a corresponds to the radial direction of the metallic shell 50, and the radial thickness of the metallic shell 50 and the thickness Tout of the proximal end portion 30a are set to substantially the same size. Because. That is, when the welding position of the ground electrode 30 is shifted in the thickness direction Y, the joint portion between the ground electrode 30 and the metal shell 50 is shifted in the radial direction of the metal shell 50, so that the welding strength is excessively small. There is a possibility. On the other hand, since the distal end 52 of the metal shell 50 continues in an annular shape in the width direction X of the base end portion 30a (the width direction of the ground electrode 30), the welding position is slightly shifted with respect to the width direction X of the base end portion 30a. Even so, the effect on welding strength is relatively small. In consideration of these points, the inventor of the present application selects not the thickness direction Y of the base end part 30a but the width direction X of the base end part 30a as the direction in which the inner layer part 30in is decentered. That is, by decentering the inner layer part 30in in the width direction X of the base end part 30a, the welding strength of the ground electrode 30 is ensured while ensuring a sufficient margin for the displacement of the welding position of the base end part 30a to the metal shell 50. Can be increased. However, the inner layer portion 30in may be slightly decentered not only in the width direction X of the base end portion 30a but also in the thickness direction Y of the base end portion 30a.

  FIG. 3B is a schematic diagram illustrating another example of a 3-3 cross section (a cross section perpendicular to the direction of the axis O) at the base end portion 30a of the ground electrode 30 of FIG. In this example, the inner layer part 30in has a two-layer structure of a heat transfer part 30ht and a core part 30co formed further inside the heat transfer part 30ht. Accordingly, the entire cross section of the base end portion 30a has a three-layer structure. The heat transfer part 30ht is formed of a metal member having a high thermal conductivity such as Cu. The core part 30co is formed of a metal member (for example, Ni) having an intermediate thermal conductivity between the outer layer part 30out and the heat transfer part 30ht. The reference numerals used in FIG. 3B are used in the same definition as in FIG. In FIG. 3B, the cross-sectional center Cin of the inner layer part 30in is the center of the area obtained by summing the heat transfer part 30ht and the core part 30co. In addition, when the inner layer part 30in includes the heat transfer part 30ht and the core part 30co, it is preferable that the cross-sectional centers of both coincide with each other, but the cross-sectional centers of both may be slightly shifted.

  The ground electrode 30 having a multilayer structure as shown in FIGS. 2 and 3 can be manufactured according to a manufacturing method described in, for example, Japanese Patent Application Laid-Open No. 2011-181523.

FIG. 4 is an explanatory diagram showing the relationship between the amount of eccentricity δC of the inner layer portion 30in and the welding strength for a plurality of samples S01 to S08. Here, the two-layer structure shown in FIG. 3A is adopted as the cross-sectional shape of the base end portion 30a of the ground electrode 30, and the sample dimensions are as follows.
(1) Outer layer portion 30out thickness Tout = 1.1 mm, width Wout = 2.2 mm
(2) Inner layer 30in thickness Tin = 0.5mm, width Win = 1.6mm
(3) The entire length of the ground electrode 30 was 8 mm, and the length of the inner layer portion 30 in was 5 mm.

  In addition, as the shape of the ground electrode 30, a linear member without the bent portion 30b was assumed. Further, it is assumed that only the outer layer portion 30out is welded at the interface between the ground electrode 30 and the metal shell 50, and the cross-sectional shape after welding is also in accordance with FIG. The welding strength is the tensile strength when the ground electrode 30 is pulled along the direction of the axis O (FIG. 1) at a speed of 1 mm / min. The welded portion of the ground electrode 30 and the metal shell 50 is joined by the finite element method. This is a value calculated by analysis.

  The graph in FIG. 4A shows the relationship between the eccentricity δC [%] of each sample S01 to S08 in FIG. 4B and the welding strength. The eccentric amount δC [%] is a value obtained by dividing the absolute value (Cin−Cout) of the eccentric amount by the width Wout of the base end portion 30a (see FIG. 3A). As can be understood from this graph, by decentering the inner layer portion 30in, the welding strength increases as compared with the case where there is no decentering. The reason for this is presumed to be that the large-area joint portion generated by the eccentricity increases the welding strength between the base end portion 30a and the metal shell 50. Further, if the amount of eccentricity δC of the inner layer portion 30 in is 2% or more, the welding strength can be sufficiently increased.

FIG. 5 is an explanatory diagram showing the relationship between the eccentricity δC of the inner layer portion 30in and the welding strength for a plurality of samples S11 to S18 having dimensions different from those in FIG. Here, the two-layer structure shown in FIG. 3A is adopted as the cross-sectional shape of the base end portion 30a of the ground electrode 30, and the sample dimensions are as follows.
(1) Outer layer portion 30out thickness Tout = 1.3 mm, width Wout = 2.7 mm
(2) Inner layer portion 30in thickness Tin = 0.5mm, width Win = 1.9mm
(3) The entire length of the ground electrode 30 was 8 mm, and the length of the inner layer portion 30 in was 5 mm.

  It can be understood that the graph of FIG. 5A has the same tendency as the graph of FIG. That is, by decentering the inner layer portion 30in, the welding strength is increased as compared with the case where there is no decentering. Further, if the amount of eccentricity δC of the inner layer portion 30 in is 2% or more, the welding strength can be sufficiently increased.

  4A and 5A, the eccentricity δC of the inner layer portion 30in may exceed 10%. However, if the eccentricity δC exceeds 10%, the welding strength is increased. The rate of increase is somewhat lower. On the other hand, if the amount of eccentricity δC exceeds 10%, the thickness of the portion where the thickness of the outer layer portion 30out becomes thinner due to the eccentricity (the right end portion in FIG. 3A) further decreases, so that the inner layer portion There is a possibility that 30 inches are exposed to the outside. In this sense, it is preferable that the amount of eccentricity δC of the inner layer portion 30 in be 10% or less.

Modification Examples The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

・ Modification 1:
As the spark plug, spark plugs having various configurations other than those shown in FIG. 1 can be applied to the present invention. In particular, various modifications can be made to the specific shapes of the terminal fitting and the insulator.

Modification 2
In the embodiment described above, the cross-sectional shape of the base end portion 30a of the ground electrode 30 is rectangular, but it may be a substantially rectangular shape with rounded corners. Moreover, you may employ | adopt other cross-sectional shapes other than a rectangle or a substantially rectangular shape.

DESCRIPTION OF SYMBOLS 10 ... Insulator 20 ... Center electrode 30 ... Ground electrode 30a ... Base end part 30b ... Bending part 30c ... Tip part 30co ... Core part 30ht ... Heat-transfer part 30in ... Inner layer part 30out ... Outer layer part 40 ... Terminal metal fitting 50 ... Main metal fitting 52 ... Tip 54 ... Screw part 100 ... Spark plug

Claims (3)

A ground electrode joined to the distal end of the metal shell, comprising a ground electrode having a rod-like base end portion and a bent portion provided on the distal end side of the base end portion and bent toward the center electrode side, A spark plug having a base end portion having an outer layer portion and an inner layer portion having a higher thermal conductivity than the outer layer portion disposed inside the outer layer portion,
The cross section of the base end portion perpendicular to the axial direction of the spark plug has a thickness along the radial direction of the metal shell and a width along the direction perpendicular to the radial direction, and a cross section of the inner layer portion The spark plug is characterized in that a center is decentered in a width direction of the base end portion from a cross-sectional center of the base end portion. The spark plug according to claim 1, wherein
The spark plug according to claim 1, wherein an eccentric amount of a cross-sectional center of the inner layer portion is 2% or more of a width of the base end portion. The spark plug according to claim 2,
The spark plug characterized in that the amount of eccentricity at the cross-sectional center of the inner layer portion is 10% or less of the width of the base end portion.

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