JP6043564B2 - Method for manufacturing spark plug for internal combustion engine - Google Patents

Description

The present invention relates to a process for the production of ignition plug for an internal combustion engine.

Conventionally, ignition plugs that generate arc discharge by applying a high voltage between a center electrode and a ground electrode have been widely used for ignition of internal combustion engines.
In recent years, by improving the durability and improving the flying property and the ignitability, a noble metal tip having high heat resistance is fused and fixed to at least one of the center electrode and the ground electrode.

  For example, in Patent Document 1, in an ignition plug for an internal combustion engine having a noble metal tip at the tip of an electrode, the content of Cr in the noble metal tip is 7 wt% or more and 30 wt% or less, and the remaining main component is Ir. Thus, an ignition plug for an internal combustion engine in which the oxidation resistance consumption performance of the welded portion is improved is disclosed.

  On the other hand, Patent Document 2 discloses a method of melting and fixing a noble metal tip to the tip of such a center electrode by laser welding.

However, the welded part of the noble metal tip as in Patent Document 1 is excellent in oxidation resistance, but is inferior in spark consumption.
For this reason, the discharge arc is pulled by the air flow generated in the combustion chamber, such as in a low-load operation, and the discharge is started from the welded portion of the noble metal tip. There is.

Further, as disclosed in Patent Document 2, when the noble metal tip is welded to the substantially cylindrical pedestal portion provided at the tip of the center electrode by laser welding, scattering of laser light occurs on the outer peripheral ridge line of the pedestal portion, In order to prevent the irradiated energy from being absorbed and to be in an insufficiently melted state, the convex part that swells toward the outer diameter side remains in the welded part, and conversely, in order to prevent the corner part from remaining in the welded part, When excessive energy is irradiated, there is a possibility that the welded portion may have an ogre that is greatly depressed toward the center.
If the pedestal is not sufficiently melted and there is a convex part that swells in the outer diameter direction in the welded part, electric field concentration occurs there, and electric discharge is likely to start from that part, which is more fireproof than precious metal tips. There is a risk of spark consumption at a weld with low flower wear.
In addition, when the weld part is aggravated by excessive energy irradiation, a local swell of the weld beat occurs at the edge of the weld part, electric field concentration occurs in that part, and a spark is induced in the weld part. There is a risk of spark consumption. Furthermore, since the aegle portion becomes thin, the reliability in terms of strength also decreases.

  Therefore, in view of such a situation, the present invention provides a manufacturing method in which a convex portion and an egle are hardly generated in a welded portion in the manufacture of a spark plug for an internal combustion engine provided with a noble metal tip at the tip, and discharge at the welded portion It is an object of the present invention to provide a spark plug for an internal combustion engine that is difficult to cause, and has high durability and reliability.

In the invention of claim 1, a substantially columnar center electrode (1), a substantially cylindrical insulator (2) having a through hole (22) for holding the center electrode (1) on the inside, and the front edge insulator ( 2) a substantially cylindrical housing (3) for holding the inner side, and a noble metal tip (10) disposed at the tip of the center electrode (1) and extending to the housing (3), A method for manufacturing a spark plug for an internal combustion engine comprising a tip (10) and a ground electrode (32) facing each other with a predetermined discharge gap, at least in a substantially cylindrical shape at the tip of the center electrode (1) A protruding pedestal portion (11) is provided, and a laser beam (LSR) is irradiated to a boundary portion between the pedestal portion (11) and the noble metal tip (10) to form a welded portion (110), thereby forming the noble metal tip. (10) A noble metal chip for fixing the tip of the center electrode (1). Comprising a welding process, in the noble metal tip welding process, the noble metal tip (10) and the tip side boundary face boundary surfaces of the welded portion (110) and (P _1), the weld (110) above the pedestal Boundary with the central electrode exposed portion inclined surface (12) exposed from the tip of the insulating insulator (2) on the tip side of the portion (11) or the center electrode (1) and reduced in diameter toward the tip side The distal end boundary surface (P1) and the proximal end side so that the surface is the proximal end boundary surface (P ₂ ) and all or a part of the outer peripheral side surface of the pedestal portion (11) is reduced in diameter toward the distal end. along a straight line connecting the boundary surface (P _2), or so as not to protrude outside the straight, pedestal inclined surface (T ₂₎ is provided, the laser beam to the pedestal portion inclined surface (T ₂₎ To form the welded part (110).

In the invention of claim 2, the elevation angle (θ ₂ ) between the pedestal inclined surface (T ₂ ) and the plane perpendicular to the central axis of the center electrode (1) is 55 ° or more and 70 ° or less.

  In the invention of claim 3, the beam diameter of the laser beam at the position where the welded portion (110) is formed is 50 μm or more and 1000 μm or less.

In the invention of claim 4, the front end side boundary surface (P ₁ ) is 0.3 mm or less in the axial direction from the contact boundary surface between the pedestal portion (11) and the noble metal tip (10) toward the front end side. The base end side boundary surface (P ₂ ) is 0.15 mm or more in the axial direction from the contact boundary surface between the pedestal portion (11) and the noble metal tip (10) toward the base end side. It exists in the range of 0.45 mm or less.

According to the method of manufacturing an ignition plug for an internal combustion engine of the present invention, the noble metal tip welded portion forms a concave curved surface that is smoothly recessed inward, and the discharge starting from the welded portion does not occur. In addition, it is possible to generate a discharge between the tip of the noble metal tip and the ground electrode, to suppress the spark consumption of the electrode, and to realize a highly durable and reliable ignition plug for an internal combustion engine.
Further, in the ignition plug for an internal combustion engine in which the noble metal tip welded portion is formed in a concave curved surface smoothly recessed inward by the manufacturing method of the present invention, the center electrode shoulder portion exposed from the insulator and the noble metal tip It has been found that by defining the distance to the tip within a certain range, the electric field strength at the center electrode shoulder can be suppressed and the occurrence of spark discharge starting from the tip tip weld can be suppressed.
Furthermore, the effect of suppressing electric field concentration can be further ensured by defining the inclination angle of the center electrode shoulder within a certain range.

The side view which shows the principal part of the manufacturing method of the ignition plug for internal combustion engines in the 1st Embodiment of this invention. FIG. 1B is a top view of FIG. 1A. The side view which shows the outline | summary of the welding part obtained by the manufacturing method of FIG. 1A. The drawing substitute photograph which shows the principal part of the spark plug tip obtained by the manufacturing method in the 1st Embodiment of this invention. The side view which shows the manufacturing method of the conventional ignition plug for fuel engines shown as the comparative example 1, and its problem. The drawing substitute photograph which shows the principal part of the spark plug tip obtained by the manufacturing method of the comparative example 1. The side view which shows the manufacturing method of the other conventional ignition plug for fuel engines shown as the comparative example 2, and its problem. The drawing substitute photograph which shows the principal part of the spark plug tip obtained by the manufacturing method of Comparative Example 2. The schematic diagram which shows the effect with respect to the discharge of the internal combustion engine ignition plug obtained by the manufacturing method of the internal combustion engine ignition plug in the 1st Embodiment of this invention. The schematic diagram which shows the effect with respect to the discharge of the internal combustion engine ignition plug obtained by the conventional manufacturing method shown as the comparative example 1. FIG. The side view which shows the modification of the manufacturing method of the ignition plug for internal combustion engines in the 1st Embodiment of this invention. The side view which shows the other modification of the manufacturing method of the ignition plug for internal combustion engines in the 1st Embodiment of this invention. The side view which shows the other modification of the manufacturing method of the ignition plug for internal combustion engines in the 1st Embodiment of this invention. The side view which shows the manufacturing method of the ignition plug for internal combustion engines in the 2nd Embodiment of this invention. The side view which shows the modification of the manufacturing method of the ignition plug for internal combustion engines in the 2nd Embodiment of this invention. The side view which shows the manufacturing method of the ignition plug for internal combustion engines which cannot demonstrate the effect of this invention shown as the comparative example 3. The side view which shows the modification of the manufacturing method of the ignition plug for fuel engines of the comparative example 3. FIG. The center electrode is exposed from the above insulator and shows the conditions of the test conducted to confirm the effect when changing the cone apex angle of the inclined surface of the center electrode exposed portion whose diameter decreases toward the tip. FIG. Similarly, the side view when the angle is 120 °. Similarly, the side view when the angle is 135 °. The side view which shows the preferable modification of FIG. 8B. The characteristic view which shows the test result of FIGS. 10A-10C with respect to a lateral jump occurrence probability. The characteristic view which shows the test result of FIG. 10A-10C with respect to the electric field strength of a center electrode shoulder part. A side view showing the conditions of a test conducted to confirm the effect when the distance from the tip of the insulator to the center electrode shoulder where the diameter of the center electrode is reduced is changed, and the distance is 0.5 mm . Similarly, the side view when the distance is 0.35 mm. Similarly, the side view when the distance is 0.05 mm. The characteristic view which shows the test result of FIG. 1 is a partial cross-sectional view showing an overall outline of an ignition plug for an internal combustion engine of the present invention.

  As shown in FIG. 12, an ignition plug 6 for an internal combustion engine according to the present invention includes a substantially columnar center electrode 1, a substantially cylindrical insulator 2 having a through hole 22 that holds the center electrode 1 inside, A substantially cylindrical housing 3 that holds the edge insulator 2 inside, and a ground electrode that extends from the housing 3 and is opposed to the center electrode 1 provided with a noble metal tip 10 at the tip thereof with a predetermined discharge gap. 32.

The center electrode 1 includes a noble metal tip 10 including a noble metal such as Ir or Cr and having high heat resistance, and a center electrode tip formed in a long axis shape using a metal material having good electrical conductivity such as copper, Ni, or iron. Part 13 and a center electrode terminal part 14 for conducting electrical connection between the center electrode tip part 13 and the outside.
In the portion where the center electrode tip 13 is exposed from the tip 20 of the insulator 2, a center electrode exposed portion inclined surface 12 whose diameter is reduced by a predetermined angle (θ ₁ ) toward the tip is formed.

  The noble metal tip 10 is welded and fixed by laser welding according to the manufacturing method described later, which is a main part of the present invention, and the surface of the welded portion 110 has a substantially truncated cone-shaped inclined plane whose diameter decreases toward the tip, or A substantially frustoconical inclined curved surface 111 is formed which is recessed toward the inner side while decreasing in diameter toward the tip.

The insulator 2 is formed in a substantially cylindrical shape using a known high heat-resistant ceramic material such as alumina, and the center electrode 1 is inserted and held in a through hole 21 provided in the center.
The insulator tip 20 is exposed from the tip of the housing 3 so as to face a combustion chamber (not shown).

The housing 3 is formed in a substantially cylindrical shape from a heat-resistant metal material such as Ni, Fe, carbon steel, and stainless steel. The insulator 2 is accommodated and held inside, and is fixed to an internal combustion engine (not shown) by a screw portion 35.
A ground electrode 32 extending in a substantially L shape is provided on the front end side of the housing 3, and a ground electrode-side noble metal tip 30 is fixed to the surface of the ground electrode 32 facing the center electrode 1 via a weld 31.

With reference to FIG. 1A, FIG. 1B, FIG. 1C, and FIG. 1D, the noble metal tip welding process which is the principal part of the manufacturing method of the ignition plug for internal combustion engines in the 1st Embodiment of this invention is demonstrated.
As shown in FIG. 1A, at the tip of the center electrode 1, the center electrode tip 13 exposed from the insulator tip 20 is reduced in diameter so as to become smaller in diameter toward the tip, and has a substantially truncated cone shape. A central electrode exposed portion inclined surface 12 is formed.

The elevation angle θ ₁ formed by the inclined surface 12 of the central electrode exposed portion and the plane perpendicular to the central axis of the central electrode 1 is formed to be 30 ° or more.
The distance (L ₄ ) from the surface of the insulator tip 20 to the center electrode shoulder C ₁ located at the boundary between the center electrode tip 13 and the center electrode exposed portion inclined surface 12 is set to 0.2 mm or less. Has been.

On the distal end side of the central electrode inclined surface 12, a pedestal portion 11 that protrudes in a substantially columnar shape (φD11 × L2) toward the distal end side is formed.
A noble metal tip 10 formed in a substantially cylindrical shape (φD10 × L1) is disposed on the distal end side of the pedestal portion 11, and is fixed by temporary fixing means such as resistance welding as necessary.
Furthermore, the distance (L-L4) from the center electrode shoulder C1 to the tip of the noble metal tip 10 is set to 1.35 mm or more.

All of the outer peripheral side surface of the pedestal portion 11, or in part, is provided with pedestal inclined surfaces T ₂ as reduced in diameter toward the distal end.
Elevation theta ₂ with respect to the central axis perpendicular to the plane of the center electrode 1 of the pedestal inclined surfaces T ₂ are, the boundary surface between the noble metal tip 10 and the welded portion 110 and the distal end side boundary surface P _1, the welding portion 110 and the base portion 11 or, the boundary surface between the center electrode exposed portion inclined surface 12 and the base end side boundary plane P _2, the tip side boundary surface P as all or part of the outer peripheral side is reduced in diameter toward the distal end of the pedestal 11 along a straight line connecting the ₁ and the base end side boundary surface P _2, or is formed such that the angle does not protrude outside the straight line.

Incidentally, the pedestal inclined surfaces T ₂ are, in advance may be provided by tapering in forming the pedestal 11, after temporarily fixed by resistance welding the noble metal tip 10, fit the required weld region AR _WLD Alternatively, it may be formed by trimming.
The welding range AR _WLD is determined by the beam diameter of the laser beam LSR at the position where the weld 110 is formed, and can be adjusted as appropriate within a range of 50 μm or more and 1000 μm or less.
Further, for example, when the laser beam LSR is irradiated so that the welding range AR _WLD becomes 0.6 mm, the front end side boundary surface P ₁ is directed from the contact boundary surface between the seat portion 11 and the noble metal tip 10 toward the front end side. The base end side boundary surface P ₂ can be changed as appropriate within the range of 0.3 mm or less in the axial direction, and the base end side boundary surface P ₂ is 0 in the axial direction from the contact boundary surface between the base portion 11 and the noble metal tip 10 toward the base end side. It can be appropriately changed within a range of 15 mm to 0.45 mm.

Figure 1A, as shown in FIG. 1B, by applying a laser beam to the pedestal inclined surfaces T _2, and absorbed portion melted laser energy between the pedestal 11 and the noble metal tip 10 while forming an alloy phase welding A portion 110 is formed.
More specifically, the laser light LSR, as shown in FIG. 1A, with respect to the axial cross-section, the base portion inclined partitioned by a straight line connecting the tip side boundary surface P1 and the base end side boundary surface P ₂ includes normal direction vector component perpendicular to the plane T _2, as shown in FIG. 1B, for the radial plane, a straight line connecting the focal point FP of the laser light LSR, the central axis of the center electrode 10 On the other hand, irradiation is performed toward the welding area AR _WLD from a direction including a vector component in a direction inclined by a predetermined angle θω in the circumferential direction.
The weld 110 is formed so as to surround the outer periphery of the noble metal tip 10 by irradiating the laser beam LSR a plurality of times while rotating the center electrode 1 or a laser welding machine (not shown) in the circumferential direction. The welded part 110 is formed.
Easy to absorb energy in a substantially planar base portion inclined surface T ₂ because the laser beam is irradiated, as shown in FIG. 1C, the surface of the welded portion 110 has a substantially frustoconical gradient whose diameter decreases toward the distal end A substantially frustoconical inclined curved surface 111 that is recessed toward the inside while being reduced in diameter toward the flat surface or the distal end is formed, and the end-side boundary surface P ₁ and the proximal-side boundary surface P _{2 are formed.} It does not protrude outside the straight line connecting
FIG. 1D is a drawing-substituting photograph showing a state of a welded portion in an example of the present invention.
Since the surface of the welded portion 110 is smoothly curved, electric field concentration at the welded portion 110 is difficult to occur, and as a result, the welded portion 110 is suppressed from becoming a starting point of discharge, and spark consumption is suppressed. Can do.

Here, with reference to FIG. 2A and FIG. 2B, the problem in the manufacturing method of the conventional ignition plug for internal combustion engines shown as the comparative example 1 is demonstrated.
In Comparative Example 1, the same reference numerals are used for the components corresponding to the components of the present invention, and the symbol z is attached as the branch number. Therefore, detailed description is omitted, and the differences from the present invention are mainly described. explain. Also on the left side of the center line in FIG. 2A. A side view before laser light irradiation is shown, and on the right side, a side view after laser light irradiation is shown (in the following description, it is also illustrated in a similar manner as appropriate).
Furthermore, the numerical values displayed in parentheses in the figure indicate the size of the sample actually used as a sample in millimeters.
That the inclined surfaces T ₂ on the side surface of the pedestal portion 11z is not formed is significantly different from the present invention.
For this reason, when 5 mJ laser light is irradiated to the base part 11z, it will hit the ridgeline of the front end side outer periphery edge of the base part 11z.
As a result, as shown on the right side of FIG. 2A, a protruding portion 111z in which the surface of the welded portion 110z is partially expanded is formed. This is presumably because the laser beam LSR causes diffraction and scattering at the edge of the outer peripheral edge on the front end side of the pedestal portion 11z, making it difficult to absorb sufficient energy for melting the pedestal portion 11z.
FIG. 2B is a drawing-substituting photograph showing the actual state of the welded portion of Comparative Example 1.
In Comparative Example 1, since the convex portion 111z is formed on the surface of the welded portion 110z, the electric field is easily concentrated here, and discharge starting from the welded portion 110z occurs, resulting in spark consumption.

Further, Comparative Example 2 will be described with reference to FIGS. 3A and 3B. In Comparative Example 2, a symbol y is attached as a branch number.
In Comparative Example 2, the height L2y of the pedestal portion is half that of Comparative Example 1 (0) so that the pedestal portion 11y is sufficiently melted and no convex portion is formed on the welded portion 110z when the laser beam LSR is irradiated. .15 mm), and the irradiation energy was 10 mJ.
In Comparative Example 2, as shown on the right side of FIG. 3A, the surface of the welded portion 110y forms a concave curved surface 111y that is recessed inward, which causes excessive melting of the pedestal portion 110y, A dimple that is greatly depressed toward the edge is generated, and a local swell of the welding beat occurs at the weld edge 112y.
For this reason, electric field concentration occurs in the swelled portion, and a spark may be induced in the welded portion 110y, resulting in spark consumption. Furthermore, since the aegle portion becomes thin, the reliability in terms of strength also decreases.

The effect of the present invention will be described with reference to FIGS. 4A and 4B.
When the ignition plug 4 formed by the method for manufacturing the ignition plug for the internal combustion engine in the first embodiment is mounted on the cylinder head 50 of the internal combustion engine 5 (not shown) and a low load operation is performed, as shown in FIG. 4A. The discharge arc ARK is elongated for a long time by the in-cylinder airflow TMB flowing through the combustion chamber 500, but provided on the tip of the noble metal tip 10 provided at the tip of the center electrode 1 and the surface of the ground electrode 32 facing the center electrode 1. A discharge occurs between the tip of the ground electrode-side noble metal tip 30 and the surface of the welded portion 110 does not fly.
On the other hand, when the ignition plug 4z formed by the manufacturing method of Comparative Example 1 is attached to the cylinder head 50z of the internal combustion engine 5z (not shown) and the low load operation is performed, as shown in FIG. Since discharge occurs between the convex portion 111z remaining on the surface of the welded portion 110z of the noble metal tip 10z and the tip of the ground electrode side noble metal tip 30z provided on the surface facing the center electrode 1z of the ground electrode 32z, This results in spark consumption of the welded part 110z.

Next, with reference to FIGS. 5A, 5B, and 5C, some modified examples in the first embodiment of the present invention and results of studying optimum conditions will be described.
In this example, the size of the noble metal tip 10 (φD ₁₀ = 0.6 mm, L ₁ = 0.6 mm), the elevation angle (θ ₁ = 40 °) of the central electrode exposed portion inclined surface T ₁ , the insulator 20 The distance (L = 1.55 mm) from the surface of the noble metal tip 10 was used, and the elevation angle (θ ₂ ) of the base part inclined surface T ₂ provided on the side surface of the base part 11 was changed to form a welded part.
As shown on the right side of FIGS. 5A, 5B, and 5C, the elevation angle (θ ₂ ) of the pedestal portion inclined surface T ₂ is within the range of 55 ° to 70 °, and in any case, as in the above embodiment, the welded portion. The surface of 110 is smoothly curved, forming a substantially truncated cone-shaped inclined curved surface 111 that is recessed toward the inner side while reducing the diameter toward the distal end, and forms an end-side boundary surface P ₁ and a proximal end It is not as protrude outside the straight line connecting the side boundary surface P _2.

When the elevation angle (θ ₂ ) of the pedestal portion inclined surface T ₂ is provided at a large angle exceeding 70 °, the center of the laser beam LSR having the highest energy density is irradiated on the surface of the metal chip 10, and thus the local angle Or the diffusion of energy at the outer peripheral edge on the front end side of the pedestal portion 11 may occur and the convex portion may remain.
When the elevation angle (θ ₂ ) of the pedestal portion inclined surface T ₂ is provided at a small angle below 55 °, the center of the laser beam LSR having the highest energy density is irradiated on the surface on the base end side of the pedestal portion 11. There is a possibility that local egress occurs or energy transmitted to the surface of the noble metal 10 becomes small, and an alloy layer with the pedestal portion 11 is not sufficiently formed.

With reference to FIG. 6A and FIG. 6B, the manufacturing method of the ignition plug for internal combustion engines in the 2nd Embodiment of this invention is demonstrated. In this figure, the state after welding is omitted in order to make it easier to understand the current difference from the above embodiment.
The above embodiment has been described an example of forming the pedestal inclined surfaces T ₂ on a part of the outer peripheral surface of the pedestal portion 11, but in this embodiment, the pedestal portion 11a and the center electrode exposed portion inclined surface 12 boundaries as the base end side boundary surface P _2, all of the outer peripheral surface of the base portion 11a is different is that provided pedestal inclined surfaces T ₂ which is inclined so reduced in diameter toward the distal end side.

Also in the present embodiment, as in the above embodiment, the elevation angle (θ ₂ ) of the pedestal inclined surface T ₂ is smoothly curved in the range of 55 ° to 70 °, and the surface of the welded portion 110a is curved toward the tip. A substantially frustoconical inclined curved surface 111 is formed so as to be convex toward the inside while having a diameter, and protrudes outside the straight line connecting the end-side boundary surface P ₁ and the base-side boundary surface P _2. There is nothing.
Further, in the present embodiment, the tip side boundary surface P ₁ is, various modifications can be made within the scope in the axial direction below 0.3mm from the contact boundary surface toward the distal end side of the seat portion 11a noble metal tip 10a, group the end-side boundary surface _{P 2,} can be appropriately changed in a range from the contact boundary surface of 0.15mm or 0.45mm or less in the axial direction toward the base end side of the base portion 11a and the noble metal tip 10a.

With reference to FIG. 7A and FIG. 7B, the manufacturing method of the ignition plug for internal combustion engines in the comparative example 3 which cannot exhibit the effect of this invention, and its modification are demonstrated.
As shown in FIGS. 7A and 7B as Comparative Example 3, the pedestal portion 11b does not protrude from a straight line connecting the distal end side boundary surface P1 and the proximal end side boundary surface P2 by adjusting the height L ₂ b of the pedestal portion 11b. Even if an inclined surface is not provided by forming in a range, an approximately frustoconical inclined curved surface 111 that is concaved toward the inside while being reduced in diameter toward the tip is formed, and the end boundary surface forming a weld so that no such protrude outside the straight line connecting the P ₁ and the base end side boundary surface P ₂ is considered possible.
However, as shown in FIG. 7A, the pedestal portion 11b is not sufficiently melted at the edge portion of the pedestal portion 11b due to the scattering of the laser light LSR, and the same corners as in Comparative Example 1 remain, or FIG. As shown, since the center of the laser beam LSR is irradiated to the side surface closer to the base end side than the front end side edge portion of the pedestal portion 11b, there is a possibility that local egress similar to that in the comparative example 2 may occur.

Referring to FIGS. 8A, 8B, 8C and FIGS. 9A and 9B, the noble metal tip 10 is welded and fixed by laser welding to a pedestal portion 11 which is manufactured using the manufacturing method of the present invention and provided at the tip of the center electrode 1. In the internal combustion engine ignition plug 4, the welded portion 110 formed between the center electrode pedestal 11 and the noble metal tip 10 has a substantially frustoconical inclined plane whose diameter decreases toward the tip, or the tip. Several modified examples of the ignition plug for an internal combustion engine including the substantially truncated cone-shaped inclined curved surface 111 that is recessed toward the inside while decreasing in diameter will be described.
In the above embodiment, an example of a case where the elevation angle theta ₁ of the center electrode exposed portion inclined surface 12 was set to 40 °, Fig. 8A, 8B, as shown in 8C, elevation of the center electrode exposed portion inclined surface 12 When θ ₁ is changed from 40 ° to 22.5 °, the occurrence probability P (%) of lateral flight to the welded portion 110 and the center electrode electric field strength E (V / mm) are investigated, and the results are shown respectively. Shown in FIGS. 9A and 9B.

As shown in FIG. 9A, when the cone apex angle of the central electrode exposed portion inclined surface 12 is 120 ° or less, that is, when the elevation angle θ _{1 of the} central electrode exposed portion inclined surface 12 is 30 ° or more, no lateral jump occurred. However, when the angle was smaller than 30 °, side jumping was observed.
Furthermore, as shown in FIG. 9B, when the cone apex angle of the central electrode exposed portion inclined surface 12 exceeds 120 °, that is, the elevation angle θ _{1 of the} central electrode exposed portion inclined surface 12 is an angle smaller than 30 °, the field strength of the center electrode shoulder C ₁ positioned at the boundary between the center electrode tip 13 and the center electrode exposed portion inclined surface 12 is increased has been found.
The smaller the elevation angle θ _{1 of the} central electrode exposed portion inclined surface 12 is, the higher the electric field strength of the central electrode shoulder C _{1 is} , and the electric discharge is pulled to generate the electric discharge starting from the surface of the welded portion 110. This is probably because of this.
Therefore, the central electrode exposed portion inclined surface elevation angle θ ₁ formed by the inclined surface 12 where the center electrode 1 is exposed from the insulator 20 and whose diameter decreases toward the tip and the plane perpendicular to the central axis of the central electrode ₁ is 30. It can be seen that it is desirable to set the cone apex angle of the central electrode exposed portion inclined surface 12 to 120 ° or less, that is, at least 120 °.

As shown in FIGS. 8B and 8C, when the cone apex angle of the central electrode exposed portion inclined surface 12 is set to 120 ° or more, the second shoulder C ₂ is formed in the weld 110, and the electric field concentration is formed here. May occur, and a spark may be generated from the welded portion 110 as a starting point.
Therefore, as shown in FIG. 8D, when the elevation angle theta ₁ of the center electrode exposed portion inclined surface 12 and 30 ° is, the pedestal inclined surface T2, in the same manner as in Example 3, the base portion 11 and the center electrode exposed It is desirable to form from the boundary with the part inclined surface 12.
By forming the pedestal inclined surface T2 in this way, the surface of the welded portion 110 does not form the second shoulder C2, as shown on the right side of FIG. Since the surface smoothly connected to the inclined surface 12 of the central electrode exposed portion is formed, it is difficult to generate sparks starting from the surface of the welded portion 110.

Furthermore, referring to FIGS. 10A, 10B, 10C, and FIG. 11, in the ignition plug for the internal combustion engine formed by the manufacturing method of the present invention, the center electrode shoulder C ₁ where the diameter of the center electrode 1 is reduced from the surface of the insulator 20. effect will be described with respect to a change in the distance L ₄ to.
In the above embodiment, an example has been described in which the center electrode 1 from the surface of the insulator 20 has a 0.05mm distance _{L 4} to the center electrode shoulder _{C 1} reduced in diameter, is shown in FIG. 10A, 10B, 10C Thus, when this distance is changed from 0.5 to 0.05, the spark occurrence probability P (%) starting from the surface of the weld 110 is measured, and the result is shown in FIG.
In addition, it turned out that the generation | occurrence | production of the spark starting from the surface of the discharge part 110 occurred easily in the above-mentioned test, and the cone apex angle of the center electrode exposure part inclined surface 12 was set to 135 degrees, and this test was done. .
In any sample, the surface of the welded portion 110 is formed with a substantially truncated cone-shaped inclined curved surface 111 that is recessed toward the inside while being reduced in diameter toward the tip.

As a result, as shown in FIG. 11, from the surface of the insulator 20, the distance to the center electrode shoulder C ₁ is more than 0.2 mm, impetigo in the discharge portion 110 surface found to be likely to occur did.
Therefore, the center electrode exposed portion inclined surface elevation angle θ ₁ formed by the inclined surface 12 exposed from the insulator 20 and having a diameter that decreases toward the tip and a plane perpendicular to the central axis of the central electrode _1. Has been found to be 30 ° or more, that is, the cone apex angle of the central electrode exposed portion inclined surface 12 is preferably 120 ° or less.

DESCRIPTION OF SYMBOLS 1 Center electrode 10 Precious metal tip 11 Base part 110 Welding part 111 Substantially frustoconical shape inclined curved surface 12 Center electrode exposure part inclined surface 13 Center electrode front-end | tip part 2 Insulator 20 Insulator front-end | tip part 21 Through-hole 3 Housing 30 Ground electrode side noble metal Tip 31 Ground side welding portion 32 Ground electrode 4 Spark plug for internal combustion engine 5 Internal combustion engine 50 Cylinder head 500 Combustion chamber LSR Laser beam P ₁ Front end side boundary surface P ₂ Base end side boundary surface T ₂ Pedestal portion inclined surface θ ₁ Center electrode Exposed part inclined surface elevation angle θ ₂ Pedestal part inclined surface elevation angle C ₁ Center electrode shoulder

JP 2011-18612 A Japanese Patent Laid-Open No. 11-3765

Claims (4)

A substantially columnar center electrode (1), a substantially cylindrical insulator (2) having a through hole (22) for holding the center electrode (1) on the inside, and the insulator (2) on the inside. A noble metal tip (10) is disposed at the tip of the substantially cylindrical housing (3) and the center electrode (1), and is extended to the housing (3) so that the noble metal tip (10) and a predetermined A method of manufacturing a spark plug for an internal combustion engine comprising a grounding electrode (32) opposed to each other by providing a discharge gap,
At least a pedestal portion (11) protruding in a substantially columnar shape is provided at the tip of the center electrode (1), and laser light (LSR) is applied to the boundary between the pedestal portion (11) and the noble metal tip (10). Irradiating to form a welded part (110) and fixing the noble metal tip (10) to the tip of the center electrode (1),
In the noble metal tip welding process,
The noble metal tip (10) and the tip side boundary face boundary surfaces of the welded portion (110) and _{(P 1),} the weld (110) and the pedestal (11), or said center electrode (1) The boundary surface with the central electrode exposed portion inclined surface (12) that is exposed from the distal end of the insulating insulator (2) on the distal end side and is reduced in diameter toward the distal end side is defined as a proximal end boundary surface (P ₂ ).
Along a straight line connecting the distal end side boundary surface (P ₁ ) and the proximal end side boundary surface (P ₂ ) such that all or a part of the outer peripheral side surface of the pedestal portion (11) is reduced in diameter toward the distal end. Alternatively, a pedestal sloped surface (T ₂ ) is provided so as not to protrude outside the straight line, and the welded part (110) is formed by irradiating the pedestal sloped surface (T ₂ ) with laser light. A method of manufacturing a spark plug for an internal combustion engine. 2. The ignition for an internal combustion engine according to claim 1, wherein an elevation angle (θ ₂ ) between the pedestal inclined surface (T ₂ ) and a plane perpendicular to the central axis of the center electrode (1) is 55 ° or more and 70 ° or less. Plug manufacturing method.   The method for manufacturing an ignition plug for an internal combustion engine according to claim 1 or 2, wherein a beam diameter of the laser beam at a position where the welded portion (110) is formed is 50 µm or more and 1000 µm or less. The tip side boundary surface (P ₁ ) is in a range of 0.3 mm or less in the axial direction from the contact boundary surface between the pedestal portion (11) and the noble metal tip (10) toward the tip side,
The base end side boundary surface (P ₂ ) is 0.15 mm or more and 0.45 mm or less in the axial direction from the contact boundary surface between the pedestal portion (11) and the noble metal tip (10) toward the base end side. 4. A method for manufacturing a spark plug for an internal combustion engine according to claim 1, wherein the spark plug is in the range.