JP3534497B2 - Spark plug manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a spark plug in which an assembly having a center electrode held in a cylindrical insulator is fixed in a cylindrical metal shell, and more particularly, a tip of the center electrode. A creeping discharge gap along the tip of the insulator and an air discharge gap between the tip of the insulator and the electrode of the metal shell. The present invention relates to a method for manufacturing a spark plug.

[0002]

2. Description of the Related Art Conventionally, an insulator having an axial shaft hole therein, and a center electrode which is fitted into the shaft hole with its tip portion protruding from the shaft hole and held in the insulator, In a spark plug for an internal combustion engine equipped with a cylindrical metal shell fitted to the outer periphery of the ceramic insulator and fixing the ceramic insulator by crimping, a creeping discharge gap between the tip of the center electrode and the electrode of the metal shell. There is known a spark plug (so-called semi-creeping discharge type spark plug) in which an air discharge gap is formed. It should be noted that the gap obtained by adding the air discharge gap to the creeping discharge gap is a spark discharge gap (spark gap) for blowing an ignition spark to the air-fuel mixture in the combustion chamber of the internal combustion engine.

The metal shell of such a spark plug is
It was manufactured by the following first to eighth manufacturing steps. In the first manufacturing process, after cold forging a metal material to obtain a cold forged product (cold former product) 101 having a large hole 111 inside, the outer peripheral surface of the cold forged product 101 has an outer diameter. A predetermined external shape is obtained by cutting [FIG. 12]
(A)].

Next, in the second manufacturing process, the cold forged product 1
01 is drilled (pierced) through a φ4.0 mm drill (not shown) to form a large hole 111 and a small hole 11.
A machined product 102 having No. 3 is obtained [FIG. 12 (b)].
Next, in the third manufacturing process,
A large hole 111, a medium hole 112 and a small hole 113 are prepared by drilling (reaming) with a 5.8 mm drill (not shown).
A machined product 103 having is obtained [FIG. 12 (c)].

Next, in the fourth manufacturing process, the cut product 1
The hole 112 of 03 is reamed with a drill 121 of φ6.5 mm to obtain a machined product 104 in which the hole 114 is finished so that the inner diameter is φ6.5 ± 0.05 mm (FIG. 13 (d)). ]. Next, in the fifth manufacturing process, the small hole 113 of the machined product 104 is cut into the boring bit 12 of φ4.3 mm.
Reamed by 2 and the inner diameter is φ4.3 ± 0.05mm
A machined product 105 is obtained in which the small holes 115 are finished so that [Fig. 13 (e)].

Next, in the sixth manufacturing process, the cut product 1
The small hole 115 of No. 05 is subjected to deburring (chamfering of the tip thread) [FIG. 13 (f)]. Next, in the seventh manufacturing step, a machined product 106 is obtained in which the electrode surface 116 is finished by the taper drill 123 so that the inner diameter of the small hole 115 of the machined product 105 is tapered [FIG. 14 (g)]. . Next, in the eighth manufacturing process, the outer periphery of the circular tubular portion 117 of the machined product 106 is subjected to the rolling processing to attach the screw portion 1 to the internal combustion engine.
A metal shell (rolled product) 107 having 18 is obtained [FIG. 14 (h)].

After that, the metal shell 107 is plated, and the center electrode and the center rod are fitted in the shaft hole with the tip of the center electrode protruding from the shaft hole of the insulator, and the insulator and the center electrode are inserted. And the central shaft. Next, by fitting the insulator into the metal shell 107 to assemble the insulator, the center electrode, the center pole and the metal shell,
A spark plug that forms a creeping discharge gap and an air discharge gap between the tip of the center electrode and the electrode portion of the metal shell 107 is manufactured.

[0008]

However, in the conventional spark plug manufacturing method, the roundness and cylindricity of the metal shell are poor, and the actual gap variation is ± 0.
It was about 25 mm, and the pass rate was about 50% to 60% when the reference value was ± 0.1 mm. The reason for this is that small holes (φ
This is because the shaft center is easily eccentric because the drill of the drilling machine is replaced in 4.3) and the intermediate hole (φ6.5). In addition, when the electrode portion of the metal shell is formed and then rolled, the electrode portion is contracted toward the inner diameter side, is distorted, etc., and the eccentricity of the small hole and the inner hole is further increased.

As a result, the deviation between the axis of the insulator and the axis of the central hole of the metal shell, and the deviation of the axis of the center electrode from the axis of the small hole of the metal shell are further increased, thereby causing air discharge. It becomes difficult to satisfy the gap tolerance of the gap or the spark gap, and the pass rate at the standard value ± 0.1 mm decreases.
Furthermore, when assembling the insulator to the metal shell, there is a problem that the productivity of the spark plug is lowered due to the occurrence of defective products such as the insulator being twisted and cracked due to the distortion of the electrode part of the metal shell. Has occurred.

An object of the invention described in claim 1 is to provide a method for manufacturing a spark plug capable of satisfying the gap tolerances of the spark gap and the air discharge gap and improving the productivity. .

The object of the invention described in claim 2 is to improve the productivity by reducing the deviation of the tips of the metal shell and the insulator, and further improving the accuracy of the spark gap and the air discharge gap. It is to provide a manufacturing method of a spark plug.

An object of the present invention is to reduce the gas volume between the metal shell and the insulator to prevent the unburned gas from entering the gas volume, thereby suppressing smoldering stains. It is an object of the present invention to provide a method for manufacturing a spark plug that is capable of

[0013]

According to a first aspect of the present invention, there is provided a cylindrical insulator having an axial axial hole, and a tip end portion of which is held in the insulating insulator in a state of protruding from the axial hole. And a tubular metal shell for fixing the assembled body holding the central electrode inside the insulator,
A creeping discharge gap along the tip of the insulator between the tip of the center electrode and the electrode of the metal shell, and an air gap between the tip of the insulator and the electrode of the metal shell It is a method of manufacturing a spark plug in which a discharge gap is formed. This spark plug manufacturing method includes a thread rolling process of rolling the outer periphery of a metal material to form a rolled product having a mounting screw portion for an internal combustion engine, and a cutting process of the inside of the rolled product. a through prepared hole forming a cutting workpiece having a through hole axially, said cutting workpiece
Finishing step of cutting the inner surface to form the electrode part
And a gap forming step of fitting the assembly into the through hole to hold the assembly in the metal shell to obtain the creeping discharge gap and the air discharge gap. And

According to a second aspect of the present invention, in addition to the method for manufacturing a spark plug according to the first aspect, the insulator has a circular tubular leg portion on a tip side and a tip side of the circular tubular leg portion. Has a tip having an inner diameter smaller than that of the circular tubular leg. Further, the through hole has a small hole into which the tip portion of the insulator is fitted, and a middle hole having an inner diameter larger than that of the small hole and into which the cylindrical leg portion of the insulator is fitted. The method further comprises a step drill finishing step of simultaneously finishing the inner surface of the small hole and the inner surface of the middle hole with a step drill. Claim 3
In addition to the method for manufacturing a spark plug according to a second aspect of the invention, there is provided a small hole finishing step of finishing the inner surface shape of the small hole along the shape of the tip end portion of the insulator.

[0015]

According to the invention of claim 1, before the through pilot hole step of forming the through hole in the axial direction of the machined product, the mounting screw portion is formed on the outer periphery of the rolled product. Since the screw rolling process is performed, when the spark plug is manufactured by assembling the assembly including the insulator in the metal shell in the gap forming process, the variation of the spark gap and the air discharge gap from the standard value The amount becomes smaller.

As a result, the gap tolerances of the spark gap and the air discharge gap can be satisfied, so that the passing rate within the gap tolerance after manufacturing the spark plug is improved, so that the production of the spark plug is improved. It is possible to improve the property.

According to the second aspect of the invention, since the small hole and the middle hole of the metal shell can be easily centered by performing the step drill finishing step, the tip misalignment between the metal shell and the insulator is almost eliminated. It can be lost. This allows
Since the accuracy of the spark gap and the air discharge gap can be further improved, the productivity of the spark plug can be further improved.

According to the third aspect of the present invention, since the inner surface shape of the small hole of the metal shell can be formed so as to follow the shape of the tip of the insulator, the gas volume between the metal shell and the insulator becomes small. Therefore, it becomes difficult for the unburned gas to invade into the gas volume, so that smoldering stain can be suppressed.

[0019]

Next, a method for manufacturing a spark plug according to the present invention will be described based on the embodiment shown in the drawings.

[Structure of First Embodiment] FIGS. 1 to 7 show a first embodiment of the present invention. FIG. 1 is a view showing an ignition part of a spark plug of the present invention, and FIG. It is a figure showing the whole spark plug structure of the present invention.

The spark plug 1 is a spark plug for an internal combustion engine which causes ignition and explosion in a mixture of an internal combustion engine (gasoline engine), and as shown in FIG. 2, a cylindrical insulator 2 and this insulator. 2, a center electrode 3 held by the center electrode 2, a center shaft 4 arranged on the same axis as the center electrode 3, a high voltage terminal 5 to which a high voltage is applied from an ignition device (not shown), a metal shell 6 constituting an outer shell, etc. Is equipped with. It should be noted that the spark plug 1 has the tip of the center electrode 3 as shown in FIG. 1 when the assembly body 8 in which the center electrode 3 and the like are assembled to the insulator 2 is fitted into the through hole 7 of the metal shell 6. A creeping discharge gap E and an air discharge gap A along the tip of the insulator 2 are formed between the side surface and the electrode portion 9 of the metal shell 6.

The creeping discharge gap E is formed between the tip side surface of the center electrode 3 and the outer peripheral surface of the insulator 2. The air discharge gap A is formed between the outer peripheral surface of the insulator 2 and the electrode portion 9 of the metal shell 6. Then, between the tip side surface of the center electrode 3 and the electrode portion 9 of the metal shell 6, the sum of the creeping discharge gap E and the air discharge gap A is obtained, and an ignition spark is generated in the mixture gas in the combustion chamber of the internal combustion engine. A spark discharge gap (spark gap) S for flying is formed.

Next, the structure of the spark plug insulator 2 will be described with reference to FIGS. Insulator 2
Is the center electrode 3, the center shaft 4, the high voltage terminal 5, and the metal shell 6.
A high-purity alumina (aluminum oxide) porcelain, which has a high insulation resistance even at high temperatures and is excellent in mechanical strength and thermal conductivity, is used to form an insulator that electrically insulates and.

An annular body portion (maximum diameter portion) 10 is formed on the outer periphery of the insulator 2 so as to project like a collar on the outer periphery thereof. The ring-shaped body 10 is fixed to the metal shell 6 by caulking or the like via the ring 11 and the filling powder 12. Further, a tubular leg portion 13 fitted in the metal shell 6 and having its axial center regulated is formed on the tip side of the annular body portion 10. An outer peripheral stepped portion (locked portion) 14 that is locked to the inner peripheral surface of the metal shell 6 via a packing is formed on the tip side of the circular tubular leg portion 13. Further, a tapered taper portion (tip portion) 15 is formed on the tip side of the outer peripheral step portion 14.

Inside the insulator 2, an axial shaft hole 16 is formed which is open at the front end surface and the rear end surface. In the shaft hole 16, the center electrode 3 and the center shaft 4 are
Are fixed and fixed by a filling powder 18 such as talc. Further, the high voltage terminal 5 is fixed to the rear end side with an adhesive 19 such as alumina cement. An inner peripheral stepped portion (locking portion) 17 that locks the center electrode 3 is formed on the inner circumference of the insulator 2.

Next, the structure of the spark plug center electrode 3 will be described with reference to FIGS. 1 and 2. Center electrode 3
Is a nickel-chromium-iron alloy or nickel-manganese-
A composite center electrode in which a core material such as copper having excellent thermal conductivity is enclosed in an electrode base material made of a heat-resistant conductive metal such as a silicon alloy.

The center electrode 3 is fitted into the shaft hole 16 with its tip portion protruding from the shaft hole 16 and is then inserted into the insulator 2.
It has a rod-shaped portion 21 held by the rod, a collar-shaped portion 22 provided on the rear end side of the rod-shaped portion 21, and the like. This collar-shaped part 2
2 has a larger outer diameter than the rod-shaped portion 21 and constitutes a locked portion that is locked to the inner peripheral stepped portion 17 of the insulator 2.

Next, the structure of the spark plug metal shell 6 will be described with reference to FIGS. 1, 2 and 4. The metal shell 6 is a housing of the spark plug 1, which plays a role of supporting the insulator 2 and mounting it on the internal combustion engine.
The metal shell 6 is formed into a substantially cylindrical shape as shown in FIG. 4 by cold forging a metal material such as low carbon steel (S10C, S17C) that is easy to cut, and then performing outer diameter cutting and inner diameter cutting. It is molded.

The metal shell 6 is fitted on the outer periphery of the insulator 2 and supports the insulator 2 by caulking the caulking portion 23 at the rear end portion to the inner peripheral side. A large-diameter cylinder portion (body portion) 25 that forms a sealing surface with a cylinder head (not shown) of an internal combustion engine (gasoline engine) via a gasket 24 is formed in a substantially central portion of the metal shell 6.

A hexagonal bolt-shaped hexagonal portion 26 having an outer diameter larger than that of the large diameter tubular portion 25 is formed on the outer periphery of the metal shell 6 on the rear end side of the large diameter tubular portion 25. Hexagonal part 26
Is for applying a tool such as a wrench for tightening,
For example, the width across flats is 13.0 mm. Further, between the large-diameter tubular portion 25 and the hexagonal portion 26, a thin-walled portion 27 having a substantially cylindrical shape is formed.
Is formed, and the thin portion 27 is made thinner than other portions by cutting.

A small-diameter cylindrical portion 28 having an outer diameter smaller than that of the large-diameter cylindrical portion 25 is formed on the tip side of the large-diameter cylindrical portion 25. A mounting screw portion 29 having an outer diameter smaller than that of the large diameter tubular portion 25 is formed on the outer periphery of the small diameter tubular portion 28. The attachment screw portion 29 is for attaching the spark plug 1 to the cylinder head of the internal combustion engine by tightening.

An annular recess 30 into which the gasket 24 is mounted is formed on the large-diameter tubular portion 25 side of the small-diameter tubular portion 28 with respect to the mounting screw portion 29. An annular recess 31 is formed on the tip side of the small-diameter tubular portion 28 with respect to the mounting screw portion 29. Further, inside the small-diameter cylindrical portion 28, an inner peripheral stepped portion (locking portion) 32 that locks the outer peripheral stepped portion 14 of the insulator 2 via packing is formed.

Inside the metallic shell 6, that is, inside the large-diameter tubular portion 25, the hexagonal portion 26, the thin portion 27, and the small-diameter tubular portion 28, there is an axial direction (longitudinal direction of the metallic shell 6).
A through hole 7 is formed so as to pass through. The through hole 7 is a large hole 33 provided on the rear end side of the metal shell 6 and the large hole 33.
The inner hole 34 has an inner diameter smaller than that, the small hole 35 having an inner diameter smaller than the inner hole 34, and the like.

The electrode portion 9 is integrally formed at the most distal end of the small diameter tubular portion 28 of the metal shell 6 and is exposed to the atmosphere in the combustion chamber of the internal combustion engine. A tapered inclined surface (electrode surface) 36 having a tapered inner diameter is formed on the inner peripheral surface of the electrode portion 9 by cutting. The tip of the inclined surface 36 is chamfered. As shown in FIG. 1, the inclined surface 36 of the electrode portion 9 forms a spark gap S between the tip end side surface of the center electrode 3 and an outer surface of the tapered portion 15 of the insulator 2. The middle discharge gap A is formed.

[Manufacturing Method of First Embodiment] Next, a manufacturing method of the spark plug 1 of this embodiment will be briefly described with reference to FIGS. 1 to 7. Here, FIGS.
6 (d), (e) and FIGS. 7 (f) to (h) are diagrams showing respective manufacturing steps of the metal shell 6 of the spark plug 1.

1) First manufacturing process of metal shell 6 First, a cold forged product (cold homer product) 41 is obtained by subjecting a metal material such as low carbon steel to a known cold forging process (cold forging process). Process). And the cold forged product 41
As shown in FIG.
As shown in (a), the large diameter tubular portion 25, the hexagonal portion 26, the thin portion 27, and the small diameter barrel portion 37 having an outer diameter smaller than that of the large diameter tubular portion 25 are formed. In addition, the large-diameter tubular portion 25 of the small-diameter body portion 37
Annular recesses 30 and 31 are formed on the side and the tip side. Further, a large hole 33 is formed inside the cold forged product 41 (outer diameter cutting step).

2) Second manufacturing process of metal shell 6 Next, the cold forged product 41 is sandwiched between a flat die type thread rolling machine or a round die type thread rolling machine to perform a thread rolling process. That is, a thread is formed on the outer circumference of the small diameter body portion 37 of the cold forged product 41 to form the mounting screw portion 29 on the outer circumference of the small diameter body portion 37. By rolling such a screw,
A rolled product 42 as shown in FIG. 5B is obtained (screw rolling process).

3) Third manufacturing process of metal shell 6 Next, the rolled product 42 is fastened to the chuck of the drilling machine, and a φ5.0 mm drill is attached to one end of the spindle of the drilling machine. At this time, attach the drill so that its center line coincides with the center line of rotation of the spindle. Then, by making the drill perform a rotary cutting motion, a prepared hole 38 of a middle hole is formed on the tip side of the large hole 33. By such an inner diameter cutting process, a machined product 43 as shown in FIG. 5C is obtained (prepared hole processing step). This step may be omitted.

4) Fourth manufacturing process for metal shell 6 Next, the machined product 43 is fastened to the chuck of the drilling machine described above, and a φ3.9 mm drill is attached to one end of the spindle of the drilling machine. At this time, as in the third manufacturing process, the center line of the drill is attached so as to coincide with the center line of rotation of the spindle. Then, by making the drill perform a rotary cutting motion, a small hole prepared hole 39 is formed on the tip side of the prepared hole 38. By such an inner diameter cutting process, a machined product 44 as shown in FIG. 6D is obtained (through prepared hole processing step).

5) Fifth manufacturing process of metal shell 6 Next, the machined product 44 is attached to the table of the boring machine, and the boring tool B is attached to the boring bar of the boring machine. Then, the boring tool B is caused to perform a rotary cutting motion, so that the inner surface of the prepared hole 39 of the machined product 43 is cut and unfolded (reamer processing), and the opening shape at the tip portion is a perfect circle. Prepared hole 4 with an inner diameter of φ4.2 ± 0.05 mm 4
Form 0. With such a bite finish,
A machined product 45 as shown in (e) is obtained (bite finishing step). This step may be omitted.

6) Sixth manufacturing process of metal shell 6 Next, the machined product 45 is fastened to the chuck of the drilling machine, and the step drill Df of φ4.3 mm and φ6.4 mm is attached to one end of the spindle of the drilling machine. At this time, as in the fourth manufacturing process, the center line of the step drill Df is attached so as to coincide with the center line of rotation of the spindle.

Then, the stepped drill Df is caused to perform a rotary cutting motion, whereby the inner surface of the pilot hole 38 and the pilot hole 39 or 40 of the machined product 45 is simultaneously shaved and reamed (reamer machining). A small diameter cylindrical portion 28 is obtained by forming a middle hole 34 and a small hole 35 that have the same axis. By such simultaneous finishing of the stepped drill medium hole and small hole, a machined product 46 as shown in FIG. 7F is obtained (stepped drill simultaneous finishing step). The inner diameter of the middle hole 34 of the machined product 46 is, for example, φ6.4 ± 0.05 mm, and the inner diameter of the small hole 35 is, for example, φ4.3 ± 0.05 mm.

7) Seventh manufacturing process of metal shell 6 Next, as shown in FIG. 7G, the small hole 35 of the machined product 46 is deburred (tip chamfering). This step may not be performed.

8) Eighth manufacturing process of metal shell 6 Next, the machined product 46 is fastened to the chuck of the drilling machine and the taper drill Dh is attached to one end of the spindle of the drilling machine. At this time, as in the fourth manufacturing step, the center line of the tapered drill Dh is attached so as to coincide with the center line of rotation of the spindle. Then, the tapered drill Dh is caused to perform a rotary cutting motion, whereby the small hole 3 of the machined product 46 is formed.
The inner surface of 5 is shaved into a taper shape and unrolled (reamer processing) to form the electrode portion 9 at the tip. By such taper finishing, the metal shell 6 as shown in FIG. 7H is obtained (taper finishing step).

9) Ninth manufacturing process of the metal shell 6 Next, the metal shell 6 is pickled. That is, the metal shell 6
Of the metal shell 6 to remove the rust, oxides, cutting chips generated by outer diameter cutting and inner diameter cutting, and then wash with water, and then the inner surface (inner peripheral surface) and outer surface (outer peripheral surface) of the metal shell 6. ) Is plated with nickel. As a result, the metal shell 6 shown in FIG. 4 is manufactured.

10) Assembling Step of Assembling Body First, the center electrode 3 and the center rod 4 are joined by using a joining means such as welding, and the center electrode 3 and the center rod 3 are inserted into the shaft hole 16 from the rear end surface of the insulator 2. The joint body with 4 is inserted until the collar-shaped portion 22 comes into contact with the inner peripheral stepped portion 17 of the insulator 2 (center electrode inserting step). At this time, the center electrode 3 is fitted into the shaft hole 16 with its tip portion protruding from the shaft hole 16.

Next, the filling powder 18 is inserted from the rear end surface of the insulator 2 into the shaft hole 16 to fill the gap between the inner surface of the insulator 2 and the outer surface of the inner shaft 4 with the insulating powder 18. The high voltage terminal 5 is screwed into the shaft hole 16 from the rear end surface of the insulator 2 to the rear end side of the insulator 2 (high voltage terminal assembling step). Therefore, the assembly 8 (see FIG. 2) is obtained in which the center electrode 3, the central shaft 4 and the filling powder 18 are housed in the insulator 2 and the high voltage terminal 5 is screwed into the rear end side of the insulator 2.

11) Gap forming step (final step) Next, the assembly 8 is fitted into the through hole 7 of the metal shell 6.
That is, the circular tubular leg portion 13 of the insulator 2 is fitted into the small-diameter tubular portion 28 (middle hole 34) of the metal shell 6, and the outer peripheral step portion 1
By inserting the assembly body 8 into the through hole 7 of the metal shell 6 so that the contact member 4 contacts the inner peripheral step portion 32 of the metal shell 6 via the packing, the axial center position of the insulator 2 is regulated (positioning). The axial center of the small-diameter tubular portion 28 (the central hole 34) of the metallic shell 6 and the axial center of the cylindrical leg portion 13 of the insulator 2 are aligned.

Next, after inserting the ring 11 and the filling powder 12 between the annular body portion 10 of the insulator 2 and the hexagonal portion 26 of the metal shell 6, the caulking portion 23 of the metal shell 6 is caulked. The assembly body 8 is fixed in the through hole 7 of the metal shell 6 to manufacture the spark plug 1 shown in FIG.

Therefore, as shown in FIG. 1, a creeping discharge gap E within the gap tolerance range is formed between the tip side surface of the center electrode 3 and the outer surface of the insulator 2, and the insulator 2
An air discharge gap A within the gap tolerance range is formed between the outer surface of the tapered portion 15 and the inclined surface 36 of the electrode portion 9 of the metal shell 6.

[Effects of First Embodiment] As described above, the spark plug 1 has the through hole 7 in the axial direction of the machined product 43.
Before the through pilot hole step of forming the (prepared hole 39) and the taper finishing step of finishing the inclined surface 36 of the electrode portion 9 of the metal shell 6, a mounting screw is attached to the outer periphery of the small diameter body portion 37 of the cold forged product 41. Since the screw rolling process for rolling the portion 29 is performed, there is no unevenness in the contraction margin of the electrode portion 9 toward the inner diameter side, distortion, etc., and the eccentricity of the middle hole 34 and the small hole 35 is extremely small. Therefore, when the spark plug 1 is manufactured by mounting the assembly body 8 in the metal shell 6 in the gap forming step,
The variation amount of the spark gap S and the air discharge gap A from the reference value becomes small.

That is, by performing the thread rolling process before the through pilot hole process and the taper finishing process, it is possible to prevent unevenness in the shrinkage margin of the metal shell 6 toward the inner diameter side, distortion, etc. By improving the circularity and cylindricity, it is possible to almost eliminate the deviation between the axis of the metal shell 6 and the axis of the insulator 2. As a result, the forming ability of the spark gap S and the air discharge gap A is significantly improved, so that the gap tolerance of the spark gap S and the air discharge gap A can be satisfied, and the accuracy can be improved. . As a result, the productivity of the spark plug 1 can be improved by improving the pass rate within the tolerance after manufacturing the spark plug 1.

Further, by performing a step drill finishing step of simultaneously finishing the middle hole 34 and the small hole 35 by using the step drill Df, the middle hole 34 and the small hole 35 of the metal shell 6 are carried out.
Since the centering of the insulator is easy, the cylindrical leg portion 13 of the insulator 2 is
Since there is almost no axial misalignment between the small-diameter tubular portion 28 (medium hole 34) of the metallic shell 6 and the tapered portion 15 of the insulator 2.
There is almost no axial misalignment between the metal shell 6 and the electrode portion 9 of the metal shell 6, that is, a misalignment between the metal shell 6 and the insulator 2.
As a result, the gap tolerances of the spark gap S and the air discharge gap A can be satisfied, so that the spark gap S and the air discharge gap A can be satisfied.
The accuracy of can be further improved. As a result, the passing rate within the tolerance after the spark plug 1 is manufactured can be further improved, so that the productivity of the spark plug 1 can be further improved.

Furthermore, since the inner surface shape of the small hole of the metal shell 6 can be formed so as to follow the shape of the tip of the insulator 2, the gas volume between the metal shell 6 and the insulator 2 becomes small, so that the internal combustion engine Since it is difficult for the unburned gas to enter the gas volume during operation, it is possible to suppress smoldering stains. Thereby, misfire of the spark plug 1 can be suppressed, and the durable life of the spark plug 1 can be improved.

[Second Embodiment] FIG. 8 shows a second embodiment of the present invention and is a view showing the ignition portion of the spark plug 1. In this embodiment, the metal shell 6 is more than in the first embodiment.
The inclined surface 36 of the electrode part 9 and the taper part 15 of the insulator 2
The space between the outer surface and the outer surface is narrow. The manufacturing method of the present invention may be used for such a spark plug 1.

[Third Embodiment] FIG. 9 shows a third embodiment of the present invention and is a view showing an ignition portion of the spark plug 1. In this embodiment, chamfering of the tip of the inclined surface 36 of the electrode portion 9 of the metal shell 6 is eliminated. Further, the outer peripheral surface of the electrode portion 9 of the metal shell 6 is tapered. The manufacturing method of the present invention may be used for such a spark plug 1.

[Fourth Embodiment] FIG. 10 shows a fourth embodiment of the present invention and is a view showing an ignition part of the spark plug 1. In this embodiment, an annular portion 51 whose outer surface extends in the axial direction is formed at the tip of the insulator 2, and the inner surface of the electrode portion 9 of the metal shell 6 is formed along the annular portion 51. The manufacturing method of the present invention may be used for such a spark plug 1.

[Fifth Embodiment] FIG. 11 shows a fifth embodiment of the present invention and is a view showing an ignition portion of the spark plug 1. In this embodiment, a protruding plug is used in which the tip end portion of the insulator 2 is protruded beyond the tip end surface of the metal shell 6 to improve heat resistance. In addition, the electrode portion 9 of the metal shell 6
The outer peripheral surface of has a tapered shape. The manufacturing method of the present invention may be used for such a spark plug 1. The creeping discharge gap E of the spark plug 1 of this embodiment includes the gap E1 between the tip side surface of the center electrode 3 and the outer peripheral surface of the insulator 2, the tip surface of the insulator 2 and the metal shell 6.
And a gap E2 between the outer peripheral surface of the insulator 2 and a position corresponding to the front end surface of the insulator.

[Modification] In this embodiment, the manufacturing method of the present invention is applied to the spark plug 1 including the metal shell 6 in which the outer diameter of the hexagonal portion 26 is larger than that of the large-diameter tubular portion 25. The manufacturing method may be applied to a spark plug provided with a metal shell whose hexagonal portion has an outer diameter smaller than that of the large-diameter tubular portion.

[Brief description of drawings]

FIG. 1 is a sectional view showing an ignition part of a spark plug of the present invention (first embodiment).

FIG. 2 is a half sectional view showing the overall structure of the spark plug of the present invention (first embodiment).

FIG. 3 is a side view showing an insulator for a spark plug of the present invention (first embodiment).

FIG. 4 is a half sectional view showing a metal shell for a spark plug of the present invention (first embodiment).

5 (a) to 5 (c) are process drawings showing a method for manufacturing a metal shell for a spark plug according to the present invention (first embodiment).

6 (d) and 6 (e) are process drawings showing a method for manufacturing a metal shell for a spark plug according to the present invention (first embodiment).

7 (f) to (h) are process drawings showing a method for manufacturing a metal shell for a spark plug according to the present invention (first embodiment).

FIG. 8 is a cross-sectional view showing the ignition part of the spark plug of the present invention (second embodiment).

FIG. 9 is a cross-sectional view showing the ignition part of the spark plug of the present invention (third embodiment).

FIG. 10 is a cross-sectional view showing the ignition part of the spark plug of the present invention (fourth embodiment).

FIG. 11 is a sectional view showing an ignition part of the spark plug of the present invention (fifth embodiment).

12A to 12C are process diagrams showing a conventional method for manufacturing a metal shell for a spark plug (prior art).

13 (d) to (f) are process drawings showing a conventional method for manufacturing a metal shell for a spark plug (prior art).

14 (g) and (h) are process drawings showing a conventional method for manufacturing a metal shell for a spark plug (prior art).

[Explanation of symbols]

1 spark plug 2 Insulator (insulator) 3 Center electrode 4 center axis 5 high voltage terminals 6 metal shell 7 through holes 8 assembly 9 Electrode part 16 shaft holes 29 Mounting thread 34 Medium hole 35 small holes 36 Inclined surface (electrode surface) 42 Rolled products 43 cut products 44 cut products 45 cut products 46 Cut products A air discharge gap Df Step drill E Creeping discharge gap S spark gap

Front page continued (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01T 21/02 B23P 13/00 H01T 13/20

Claims (3)

(57) [Claims] 1. A cylindrical insulator having an axial hole in the axial direction,
A center electrode held in the insulator with the tip portion protruding from the shaft hole; and a tubular metal shell for fixing an assembly holding the center electrode in the insulator inside. Comprising: between the tip portion of the center electrode and the electrode portion of the metal shell, a creeping discharge gap along the tip portion of the insulator, and between the tip portion of the insulator and the electrode portion of the metal shell. In a manufacturing method for manufacturing a spark plug formed by forming an air discharge gap, (a) thread rolling in which the outer periphery of a metal material is rolled to form a rolled product having a mounting screw portion for an internal combustion engine. And (b) a through pilot hole step of cutting the inside of the rolled product to form a machined product having an axial through hole, and (c) cutting the inner surface of the machined product. The electrode part
And ( d ) a gap formation in which the assembled body is fitted into the through hole to hold the assembled body in the metal shell to obtain the creeping discharge gap and the air discharge gap. A method of manufacturing a spark plug, comprising: 2. The method of manufacturing a spark plug according to claim 1, wherein the insulator is a circular tubular leg portion on a tip side and smaller than the circular tubular leg portion on a tip side of the circular tubular leg portion. An end portion having an inner diameter, the through hole is a small hole into which the tip portion of the insulator is fitted, and an inner hole having a larger inner diameter than the small hole and into which the circular tubular leg portion of the insulator is fitted. And a step drill finishing step of simultaneously finishing the inner surface of the small hole and the inner surface of the middle hole with a step drill. 3. The spark plug manufacturing method according to claim 2, further comprising a small hole finishing step of finishing an inner surface shape of the small hole along a shape of a tip end portion of the insulator. Method.