JP2007134318A - Spark plug and manufacturing method of spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug which has better ignitability and a flame growing property without spoiling longevity of the spark plug provided with an ultra fine precious metal chip, and provide an effective manufacturing method of the above sparkplug. <P>SOLUTION: An external chip 43 of precious metal alloy is welded on a side face facing a central electrode 10 with a ground electrode 40 in an extension direction. At a time of welding, a curvature radius of a welded face shall be larger than a curvature radius of unwelded face with the external chip 43. With this structure, welding of the external chip 43 with the ground electrode 40 can be possible without spoiling a welding strength of the external chip 43. Furthermore, the manufacturing method of the above includes a welding process in which a laser welding is conducted in a changed manner according to an irradiating angle, an irradiating position and an irradiating output of the laser beam LB which is irradiated on the contact face of the external chip 43 positioned and fixed temporarily with the ground electrode 40 at a time of the laser welding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug that is used by being attached to an internal combustion engine, and particularly relates to a spark plug that achieves excellent flame growth.

  A spark plug is used as an ignition device for engine combustion by exposing a center electrode and a ground electrode to a combustion chamber of an internal combustion engine and performing a spark discharge with a spark discharge gap between both electrodes. Conventionally, spark wear resistance and high-temperature oxidation resistance (hereinafter referred to as spark wear resistance and resistance) are applied to the tip of one or both of the electrodes, which are the starting point of spark discharge, in order to realize a long life of the spark plug. A chip made of a noble metal alloy (hereinafter also simply referred to as a noble metal chip) excellent in high temperature oxidation property and also called durability is joined (for example, see Patent Document 1). By using a noble metal tip with excellent durability in this way, the diameter of the noble metal tip that is the starting point of the spark discharge can be reduced, so that not only a longer life but also an ignition by making the tip extremely fine. It is also possible to realize a configuration that does not hinder the spread of the flame that is the air-fuel mixture (hereinafter also simply referred to as flame growth) (see, for example, Patent Document 2).

  By the way, as a means for improving the flame growth property, various contrivances have been made before using an extremely fine noble metal tip. This is because the spark plug is used by attaching the male screw formed on the metal shell to the female screw formed on the internal combustion engine, but it is very difficult to attach in consideration of the direction of the ground electrode at the time of attachment. . For this reason, when the air-fuel mixture goes from the spark plug to the location where spark discharge occurs, and when the air-fuel mixture ignites and the flame grows, the presence of the ground electrode inhibits the movement of the air-fuel mixture and the growth of the flame. This is because there is a problem that the combustion efficiency is lowered.

In order to solve such a problem, for example, there is a configuration in which the cross-sectional shape of the ground electrode described in Patent Document 3 is circular (hereinafter also simply referred to as a round ground electrode). With this configuration, it is possible to prevent the air-flow of the air-fuel mixture from being obstructed by the ground electrode and causing the air flow to peel off from the ground electrode, or the growth flame to contact the ground electrode, so that heat is drawn. This is because it is possible to avoid the deterioration of the flame growth.
JP-A-8-339880 JP 2002-313524 A Japanese Patent Laid-Open No. 11-121142

  Now, in order to improve the life and improve the ignition performance, an ultra-fine noble metal tip is provided, and in order to achieve better flame growth, a configuration in which an ultra-fine noble metal tip is joined to the round ground electrode is examined. However, it is not easy to strengthen the bonding between the columnar noble metal tip having flat surfaces at the upper and lower ends and the round ground electrode having an arcuate surface. For example, when considering joining by resistance welding, only the part near the center of the bottom surface of the columnar tip (the end face on the side to be joined to the ground electrode) is in contact with the ground electrode. Does not flow, and welding is performed in a so-called “floating state” in which only the portion near the center of the noble metal tip is joined. On the other hand, when considering laser welding, only the part near the center of the noble metal tip is in contact with the side surface of the round ground electrode having a predetermined radius of curvature with respect to the bottom surface of the noble metal tip, which is a flat surface, and separated from the center. Since the part is also separated from the side surface of the round ground electrode, even if the laser is irradiated, the melt between the round ground electrode and the noble metal tip is weak, and it is difficult to achieve strong bonding.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a spark plug in which a noble metal tip is firmly bonded to a round ground electrode and to provide a manufacturing method thereof.

In order to solve the above problems, a spark plug of the first configuration of the present invention is:
A rod-shaped center electrode extending in the axial direction;
A cylindrical insulator that includes a shaft hole and holds the center electrode in the shaft hole in a state where the tip of the center electrode protrudes from the tip surface of the shaft hole;
A metal shell for holding the insulator;
One end is joined to the front end surface of the metal shell, extends from one end to the other end, and has a circular cross-sectional shape, and
A columnar noble metal tip bonded to the side of the ground electrode where the center electrode is desired;
A spark plug comprising:
When the ground electrode is viewed from the other end side in its extending direction,
The outline of the ground electrode is
The noble metal tip is divided between two intersecting points intersecting two straight lines parallel to the column axis of the noble metal tip passing through the portion closest to the ground electrode, and a section having a small distance between the two intersections is defined as section A, When the section excluding the section A is defined as the section B,
The curvature radius RA of the section A and the curvature radius RB of the section B satisfy the relationship of RA ≧ RB.

  As in the above configuration, the radius of curvature RA of the portion (corresponding to the section A) where the noble metal tip is joined among the side surfaces of the round ground electrode is equivalent to the portion (corresponding to the section B) where the noble metal tip is not joined. The following effects can be expected by setting the radius of curvature RB or more. That is, when the noble metal tip is pressed, the contact area of the central portion where the bottom surface of the noble metal tip comes into contact with the side surface of the round ground electrode increases. As a result, for example, when resistance welding is performed, the portion that melts at the initial stage of resistance welding becomes larger than before, so that the weldability is improved and the problem of joining in a “floating state” can be reduced. It becomes possible. Moreover, since the distance which the side surface of a round ground electrode and the bottom face of a noble metal tip separate can be reduced also when performing laser welding, more stable joining is attained. Of course, it is more preferable that RA> RB except RA = RB.

By the way, the risk of falling off the noble metal tip can be considered as follows.
Unlike a ground electrode having a substantially rectangular cross section, a round ground electrode does not have an edge portion where an electric field tends to concentrate. Therefore, there are few portions where the electric field gradient is steep around the round ground electrode. Originally, a spark discharge is performed between the tip of the center electrode and the noble metal tip joined to the round ground electrode, but since there is no edge like the substantially rectangular ground electrode, the spark discharge seems to wrap around the round ground electrode. Sometimes, it is performed on the substantially opposite side of the center electrode. Further, since the melted portion of the noble metal tip and the base material of the round ground electrode has a low work function, discharge is likely to occur, and this portion may be performed. In particular, when the latter spark discharge is repeatedly performed, the portion where the noble metal tip is fixed is consumed and reduced, which may reduce the bonding strength. Then, the heat generated by the combustion of the engine will not be sufficiently drawn from the noble metal tip, and as a result, the noble metal tip may be peeled off from the ground electrode due to the vibration of the engine and even fall off into the combustion chamber. Absent.

Therefore, in order to avoid such a risk, it is desirable to employ the following configuration which is the third configuration of the present invention. that is,
A spark discharge gap G formed by a tip of the center electrode and a noble metal tip bonded to the ground electrode;
A gap H between the tip of the center electrode and a portion of the ground electrode closest to the center electrode is
0.5mm ≦ H-G ≦ 1.0mm
To satisfy the relationship.

  By providing the above configuration, it is possible to reduce the probability that a spark discharge is performed at a portion on the opposite side of the center electrode and that the spark discharge is performed on a melted portion between the round ground electrode and the noble metal tip. . In order to obtain this effect more remarkably, it is desirable that the amount of protrusion to the center electrode with respect to the joint surface of the noble metal tip with the round ground electrode is 0.5 mm or more and 1.0 mm or less.

In addition, as a method of manufacturing a spark plug having the above configuration,
A spark plug manufacturing method in which a columnar noble metal tip is bonded to one side surface of a columnar ground electrode,
A resistance welding step of temporarily fixing the noble metal tip to one side surface of the ground electrode by resistance welding;
A step of fixing by laser welding from the entire circumference to the joint surface between the noble metal tip and the ground electrode after the temporary fixing;
It is good to manufacture so that it may have. By manufacturing in this way, it becomes possible to stably fix the noble metal tip having a flat bottom surface to a very unstable portion such as the side surface of the round ground electrode.

As another manufacturing method,
A method of manufacturing a spark plug in which a columnar noble metal tip is laser welded to one side of a columnar ground electrode,
Means for positioning the noble metal tip relative to one side of the ground electrode;
Means for performing welding by changing the irradiation angle or irradiation position of the laser according to the positioning state of the noble metal tip;
You may manufacture so that it may have. Further, even if the irradiation angle or irradiation position of the laser is fixed, welding may be performed by changing the output according to the positioning state.

  The means for positioning the noble metal tip with respect to the round ground electrode may be temporarily fixed by the above resistance welding, or a positioning jig may be used. It is sufficient that the positional deviation does not occur.

The “positioning state” will be described in detail.
FIG. 4 shows the positioning with respect to the round ground electrode 40. FIG. 4A is a straight line view for welding from the other end side (the front side of the drawing) of the round ground electrode 40, and FIG. 4B is an enlarged view of a portion surrounded by a circle C in FIG. And it is a figure shown exaggerated for description. In addition, in FIG.4 (b), the state in which temporary fixing by resistance welding was performed as an example is shown.

  As shown in FIG. 4B, in the state in which the temporary fixing is performed by resistance welding, the portion M near the center of the noble metal tip 43 is in contact with the round ground electrode 40, but the portion N excluding the portion near the center M (Hereinafter also referred to as the outer peripheral portion N) is separated from the round ground electrode 40 by a distance L and is in a “floating state” (note that there is a slight amount of welding sag W). The state where the center portion M of the noble metal tip 43 is in contact with the round ground electrode 40 and the outer peripheral portion N is not in contact is an example of the “positioning state”.

Now, the manufacturing method will be described in such a positioning state.
FIG. 4C shows a process of welding the noble metal tip 43 to the round ground electrode 40 as a view seen from a direction perpendicular to the extending direction. Since the noble metal tip 43 is temporarily fixed by resistance welding in the positioning state of (b), the bottom surface 432 of the noble metal tip 43 is in a state of being slightly sunk with respect to the surface 401 of the round ground electrode 40. Laser welding is performed by irradiating the laser beam LB in this state. In FIG. 4C, the laser beam LB is irradiated from a location where the noble metal tip 43 and the round ground electrode 40 are joined by temporary fixing. The irradiation angle of the laser beam LB at this time is θ1 with respect to the column axis O ′ of the noble metal tip 43.

  The laser beam LB is sequentially performed in the circumferential direction of the noble metal tip 43 from the position joined by temporary fixing, and the state shown in (d) is obtained when the state advances about 90 ° from the state (c). In this state (d), if the irradiation angle of the laser beam LB remains θ1, the noble metal tip 43 is in a “floating state”, so that the laser beam LB contacts the noble metal tip 43 and the round ground electrode 40. The interface is not irradiated. Therefore, sufficient welding strength cannot be obtained. Therefore, as shown in (d), it is possible to irradiate the contact interface by setting the irradiation angle of the laser beam LB to θ2, and the noble metal tip 43 is firmly bonded to the round ground electrode 40. Is possible. The output of the laser beam LB during this laser welding is E1 for both θ1 and θ2.

  Note that the irradiation angles θ1 and θ2 of the laser beam LB are not switched suddenly, but change at any time according to the irradiation position (rotation angle) of the laser beam LB to the noble metal tip 43. The conceptual diagram is shown in (e). In (e), the horizontal axis indicates the circumferential position where the laser beam LB of the noble metal tip 43 is irradiated by the rotation angle, and the vertical axis indicates the irradiation angle θ of the laser beam LB with respect to the column axis O ′ of the noble metal tip 43. is there. The irradiation angle θ does not necessarily have a sinusoidal waveform as shown in (e). For example, if the positioning state is detected by a CCD camera or the like prior to the irradiation of the laser beam LB and feedback control is performed to the irradiation angle θ based on the detected state, the irradiation angle θ draws a waveform in which the sine waveform is distorted. Of course, since the feedback control is performed, the joining state can be a more accurate state.

  Another manufacturing method of the present invention replaces the concept of changing the irradiation angle θ with the irradiation output of the laser beam LB. That is, the irradiation angle is set to θ1 as shown in (c), and the irradiation output of the laser beam LB at this time is set to E1. In the state (f) in which the irradiation position of the laser beam LB advances about 90 ° in the circumferential direction of the noble metal tip 43, the irradiation output is set to E2 which is larger than E1 so that the surface can be melted to the surface of the round ground electrode 40. It is. By making the irradiation output as large as E2, not only the noble metal tip 43 but also the round ground electrode 40 can be melted, so that the noble metal tip 43 can be welded without changing the irradiation angle θ. It becomes possible. A conceptual diagram of this change in irradiation output is shown in (g). (G) shows the circumferential position where the laser beam LB of the noble metal tip 43 is irradiated on the horizontal axis in the same manner as (e), and the irradiation output of the laser beam LB on the vertical axis.

  In the above description, an example of manufacturing by changing the irradiation angle or the irradiation output is shown. However, the position where the laser beam is irradiated may be changed while the irradiation angle is constant, and the irradiation angle may be changed. While changing, the position irradiated with the laser beam may be changed to perform welding. Further, the means for welding the noble metal tip and the round ground electrode is not necessarily limited to any one method, and can be carried out in combination.

  Furthermore, when irradiating a laser beam while changing the irradiation angle, irradiation position, or irradiation output as described above, the bonding state of the noble metal tip obtained by the resistance welding process for positioning the noble metal tip is acquired and the state is obtained. By performing laser welding while variously changing the angle, position, output, etc. of laser beam irradiation according to the above, it becomes possible to realize a more accurate joining state.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an overall view of a spark plug 100 of the present invention. The spark plug 100 is generally configured by combining a center electrode 10, a terminal electrode 20, an insulator 30, a ground electrode 40 and a metal shell 50. Hereinafter, each member will be described. In FIG. 1, the lower side of the drawing will be described as the front end side, and the upper side will be described as the rear end side.

  The center electrode 10 is formed in a substantially rod-like shape having a base 11 made of a Ni-based alloy such as Inconel 600 (registered trademark) and having a flange 11 at the rear end. A Cu alloy constitutes the core 12 for the purpose of improving thermal conductivity at the center of the base material made of Ni-based alloy. Further, the inner tip 13 made of a noble metal alloy containing Pt, Ir or the like and having excellent durability is joined to the tip of the center electrode 10. In this embodiment, this joining is performed by so-called laser welding in which a laser beam is irradiated and pressed.

  On the other hand, the ground electrode 40 provided in the metal shell 50 is made of a Ni-based alloy as a base material, is formed in a rod shape, and is joined to the tip of the metal shell 50. The ground electrode 40 is bent at a substantially right angle so as to form a spark discharge gap G with the inner chip 13 having one side surface joined to the center electrode 10 on one side. An outer tip 43 made of a noble metal alloy is joined to one side surface of the ground electrode 40 in the same manner as the center electrode 10 for the purpose of improving ignitability, flame growth and durability. The outer tip 43 corresponds to the “noble metal tip” of the present invention. The detailed configuration of the ground electrode 40, which is the main point of the present invention, will be described later.

  The metal shell 50 is formed into a substantially cylindrical shape by subjecting an iron-based metal member such as S15C or S25C or a metal member such as stainless steel to plastic processing, and its rough shape is formed after finishing such as cutting. A threaded portion 51 for attaching the spark plug 100 to an internal combustion engine (not shown) is rolled on the distal end side of the outer peripheral surface of the metal shell 50. On the rear end side of the threaded portion 51, a flange portion 52 having a seat surface for hermetically sealing the combustion chamber via the gasket 4 when formed on the internal combustion engine is formed. On the rear end side of 52, a tool engaging portion 53 having a hexagonal cross section, for example, is formed to which a tool such as a plug wrench engages when attached to the internal combustion engine. Between the tool engaging portion 53 and the flange portion 52 of the metal shell, it is formed thin so as to be buckled when the insulator 30 is assembled (FIG. 1 shows the shape after buckling). ing). In the present embodiment, the opposite side dimension of the tool engaging portion 53 is configured as HEX14.

  The rear end side of the tool engaging portion 53 is formed in a thin cylindrical shape so that a caulking lid 60 serving as the rearmost end portion of the metal shell 50 is formed when the spark plug 100 is completed. The inner hole 57 of the metal shell 50 is formed with a small-diameter hole 54 at a position in the direction of the axis O where the threaded portion 51 is formed, and a shelf 55 protruding radially inward is formed at the distal end side of the small-diameter hole 54. Is formed. On the rear end side connected to the small-diameter hole 54, a large-diameter hole 56 is formed up to the rear end at a position in the direction of the axis O where the flange portion 52 is formed. The ground electrode 40 is joined to the tip of the metal shell 50 formed in this way. This joining is performed by resistance welding, and after removing the welding sag, the metal shell 50 is plated with zinc or the like together with the ground electrode 40.

  The insulator 30 is manufactured by mixing an insulating ceramic powder such as alumina or aluminum nitride with a binder, etc., forming a rough shape by a press, grinding and shaping with a grindstone, and firing. The insulator 30 has a substantially cylindrical shape, and has a shaft hole 31 formed therein, and a flange-shaped middle body portion 32 protruding outward in the radial direction is formed at a substantially center of the outer surface in the axis O direction. A front end side body portion 34 having a stepped portion 33 facing the front end is formed on the front end side of the middle body portion 32. On the other hand, a rear end side barrel portion 35 having substantially the same outer diameter is formed on the rear end side of the middle barrel portion 32. Note that the tip end side of the stepped portion 33 formed on the tip end side body portion 34 constitutes a leg length portion 36 that is exposed to the combustion gas when the spark plug 100 is completed. In the shaft hole 31, a support step portion 37 that supports the flange portion 11 of the center electrode 10 is formed on the rear end side of the leg long portion 36, and the inner end of the shaft hole 31 has a rear end on the tip side of the support step portion 37. It is thinner than the side.

  The assembly of the insulator 30, the center electrode 10, and the terminal electrode 20 will be described. The center electrode 10 is inserted into the shaft hole 31 of the insulator 30 so that the tip thereof is downward. A glass sealing material prepared by mixing and metal powder and a resistance material prepared by changing the mixing ratio of these raw material powders are filled. The terminal electrode 20 is inserted from the rear end of the insulator 30 so that the leg portion 21 of the terminal electrode 20 formed in a shaft shape is embedded in the filled glass sealing material. With the terminal electrode 20 inserted, the insulator 30 is put into a heating furnace, heated to a predetermined temperature, and pressed to position the terminal electrode 20 at a predetermined position. Thereafter, the insulator 30 is removed from the heating furnace, whereby the glass sealing material and the resistance material are cured, so that the glass seals 5 and 5 and the resistor 6 are formed, respectively. It is fixed in an electrically conductive state. This process is generally called a glass sealing process. In addition, you may perform simultaneously the glaze of the glaze layer formed in the outer surface of a rear-end side trunk | drum at the time of this glass sealing process.

  Each member is configured as described above, and the metal shell 50 including the insulator 30 including the center electrode 10 and the terminal electrode 20 and the ground electrode 40 includes the plate packing 7, the wire packing 8, 8. The caulking lid 60 is formed by a known caulking process using talc (talc) 9 or the like, and the spark plug 100 is completed.

Now, the configuration of the ground electrode 40, which is the main point of the present invention, will be described in detail.
As shown in FIG. 2A, the ground electrode 40 has a substantially perfect circular cylindrical shape, and the outer tip 43 also has a substantially perfect circular cylindrical shape. As shown in the enlarged view of FIG. 2B, a portion of the ground electrode 40 where the outer tip 43 is joined and its periphery are a section A having a slightly larger curvature radius than the width of the outer chip 43 and a section A. The curvature radius of the section B is substantially the same as the radius of the ground electrode 40. Note that (b) exaggerates the outline of the ground electrode 40 for explanation. Moreover, the state after joining of the ground electrode 40 and the outer chip | tip 43 is shown using the broken line.

The sections A and B of the present invention will be described with reference to FIG.
The two straight lines (indicated by alternate long and short dash lines) parallel to the column axis O ′ of the outer chip 43 that divides the section A and the section B may be arbitrarily separated as long as they pass through the portion of the outer chip 43 closest to the ground electrode 40. However, in this description, the dividing line is made to coincide with the outer peripheral edge of the outer chip 43. When the curvature radii RA and RB of the section A and the section B divided in this way are compared, RA> RB. For this reason, since the joint surface of the ground electrode 40 to the outer chip 43 can be made substantially flat, a stronger joint strength can be obtained.

  The spark discharge gap G formed by the inner tip 13 and the outer tip 43 of the spark plug 100 manufactured in this way is 1.1 mm, and the tip of the inner tip 13 and the portion of the ground electrode 40 closest to the center electrode 10 The gap H is 1.9 mm, and H−G = 0.8 mm. With this configuration, it is possible to reduce the proportion of spark discharge generated at the ground electrode 40, and to realize a spark plug that does not cause problems such as dropping of the outer tip 43.

The gap H is determined from the following consideration.
The gap G is fixed to 1.1 mm, and the gap H between the tip of the inner tip 13 joined to the center electrode 10 and the portion of the ground electrode 40 closest to the center electrode 10 is variously changed, and HG is shown in Table 1. Each of the spark plugs 100 is created so as to have the relationship shown in FIG.

  The created spark plug 100 is subjected to a desktop spark discharge test for generating 100 spark discharges under an atmospheric pressure condition of 0.4 MPa. At that time, the ground electrode 40 is not the outer chip 43 joined to the ground electrode 40. The number of discharges to the melted part for joining the base material and the outer tip 43 is counted, and the generation ratio is shown as the flying ratio.

  On the other hand, for the spark plug 100 prepared so that HG has the relationship shown in the following Table 2 in the same manner as described above, a corresponding simulation test was conducted after running 160,000 km in an actual vehicle, and the amount of increase in the gap was examined. . The engine used is a 2000cc, 4-cylinder engine.

  From Table 2 above, if HG is 0.5 mm or more, the result that the fire rate becomes 0% is obtained, so that 0.5 mm is set as the lower limit for HG. On the other hand, paying attention to the consumption amount of the noble metal tip 43, if HG exceeds 1 mm, specifically, the gap increase amount exceeds 0.2 mm when 1.2 mm. In general, a spark plug having a high durability specification is required to have a gap increase amount of 0.2 mm or less when traveling 100,000 km, and therefore H-G is set to have an upper limit of 1.0 mm.

Next, the welding process of the outer tip 43 to the ground electrode 40 will be described in detail.
FIG. 3A shows a spark plug before the noble metal tip to be joined as the outer tip 43 is assembled by assembling the insulator 30 having the center electrode 10 and the terminal electrode 20 and the metal shell 50 to which the ground electrode 40 is joined. The assembly 101 is shown. As shown in FIG. 3B, the outer tip 43 positioned with respect to the inner surface 401 facing the center electrode 10 of the ground electrode 40 is a bottom surface opposite to the facing surface 431 on the center electrode 10 side by the welding electrode 90. Resistance welding is performed in a state where 432 is pressed against the inner surface 401 of the ground electrode 40, and temporary fixing is performed (resistance welding process). During the resistance welding process, the outer tip 43 is held by the welding electrode 90 except for the bottom surface 432 and the surrounding bottom portion, and the outer tip 43 is pressed toward the inner surface 401 so that the outer tip 43 is welded. The part exposed from the electrode 90 swells like a bowl (FIGS. 3C and 3D).

  Next, as shown in FIG. 3E, the irradiation of the laser beam LB is performed on the buttocks that swell at the irradiation angle θ1 with respect to the column axis O ′ of the outer tip 43 with the extending direction of the ground electrode 40 as the start position 0 °. Is done. In a state where the irradiation position of the laser beam LB has advanced by 90 °, the irradiation angle with respect to the column axis O ′ becomes θ2 as shown in FIG. 3F, and a state of 180 ° further advanced by 90 ° (FIG. 3G). Then, the irradiation angle θ1 is reached again. This is shown conceptually in FIG. 4 (e). In the process of laser welding progressing from 180 ° to 270 ° and 360 °, the irradiation angle θ is similarly changed to perform welding.

  At this time, the irradiation output of the laser beam LB may be changed depending on the irradiation rotation angle, and FIG. 4G shows a concept of changing the output at that time with respect to the irradiation position. Further, when performing this laser welding, a holder (not shown) that holds the spark plug assembly 101 is rotated (in order to clarify the explanation in FIGS. 3 (e) to 3 (g)). The holder is not only rotated about the column axis O ′ of the outer tip 43, but also the column axis O ′ is moved horizontally so that the position of the laser beam is changed. The locus drawn by the irradiated portion may be an ellipse, or the irradiation angle with respect to the laser beam may be changed by tilting the column axis O ′. Of course, it goes without saying that the laser beam irradiation jig (not shown) may be movable. Further, the irradiation angle, output, and position of the laser beam may be varied without causing the bottom surface 432 of the outer chip 43 to bulge out like a bowl.

  The spark plug 100 manufactured as described above is realized as a noble metal tip firmly bonded to the round ground electrode and excellent in wear resistance and flame growth.

  As an embodiment of the present invention, the relationship between the radius of curvature RA of the section A and the radius of curvature RB of the section B is described as an example where RA> RB. However, as described in the claims, RA = RB The contour line of the ground electrode 40 that is related may draw a substantially perfect circle.

1 is an overall view of a spark plug 100 of the present invention, and is a partial cross-sectional view thereof. It is explanatory drawing (a) which looked at the ground electrode 40 from the other end side of the extending | stretching direction, and is shown with the outer side chip | tip 43 joined, and its enlarged view (b). FIG. 10 is an explanatory diagram of a process of joining the outer tip 43 to the ground electrode 40. It is a figure explaining the positioning state at the time of joining the outside chip 43 to the ground electrode 40, and the process of joining.

Explanation of symbols

40 Ground electrode 43 Outer (noble metal) chip 50 Metal shell 100 Spark plug

Claims (6)

A rod-shaped center electrode extending in the axial direction;
A cylindrical insulator that includes a shaft hole and holds the center electrode in the shaft hole in a state where the tip of the center electrode protrudes from the tip surface of the shaft hole;
A metal shell for holding the insulator;
One end is joined to the front end surface of the metal shell, extends from one end to the other end, and has a circular cross-sectional shape, and
A columnar noble metal tip joined to the inner surface of the ground electrode where the center electrode is desired;
A spark plug comprising:
When the ground electrode is viewed from the other end side in its extending direction,
The outline of the ground electrode is
Passing through the portion of the outer peripheral surface of the noble metal tip that is closest to the ground electrode and delimited by two straight lines parallel to the column axis of the noble metal tip;
Among the divided inner surfaces, the section between the two straight lines is defined as section A, and the section excluding the section A is defined as section B.
A spark plug characterized in that a radius of curvature RA of an inner surface of the section A and a radius of curvature RB of an inner surface of the section B satisfy a relationship of RA ≧ RB. A spark discharge gap G formed by a tip of the center electrode and a noble metal tip bonded to the ground electrode;
A gap H between the tip of the center electrode and a portion of the ground electrode closest to the center electrode is
0.5mm ≦ H-G ≦ 1.0mm
The spark plug according to claim 1, wherein: A spark plug manufacturing method in which a columnar noble metal tip is bonded to one side surface of a columnar ground electrode,
A resistance welding step of temporarily fixing the noble metal tip to one side surface of the ground electrode by resistance welding;
A step of fixing by laser welding from the entire circumference to the joint surface between the noble metal tip and the ground electrode after the temporary fixing;
A method for manufacturing a spark plug, comprising: A method of manufacturing a spark plug in which a columnar noble metal tip is laser welded to one side of a columnar ground electrode,
Means for positioning the noble metal tip relative to one side of the ground electrode;
Means for performing welding by changing the irradiation angle or irradiation position of the laser according to the positioning state of the noble metal tip;
The method of manufacturing a spark plug according to claim 3, comprising: A method of manufacturing a spark plug in which a columnar noble metal tip is laser welded to one side of a columnar ground electrode,
Means for positioning the noble metal tip relative to one side of the ground electrode;
Means for performing welding by changing the irradiation output of the laser according to the positioning state of the noble metal tip;
The method of manufacturing a spark plug according to claim 3, comprising: A method of manufacturing a spark plug in which a columnar noble metal tip is laser welded to one side of a columnar ground electrode,
A state acquisition step of acquiring a joining state of the noble metal tip by the resistance welding step;
A step of performing laser welding while changing at least one of the irradiation angle of the laser, the irradiation position, or the irradiation output based on the bonding state of the noble metal tip obtained by the state acquisition means;
The method of manufacturing a spark plug according to claim 3, wherein:

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