JP2006185795A - Mold body for insulator of spark plug, manufacturing method of spark plug and spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a straight mold body for an insulator for a spark plug having an axial line formed into a straight line, and also to provide a park plug having excellent durability without impairing ignitability. <P>SOLUTION: This mold body 1 for an insulator includes: a large-diameter tube part 3 formed into a flange-like shape projecting in a direction perpendicular to the axial direction and having an axial length of 6-12 mm; a first small-diameter tube part 2 formed in a diameter smaller than that of the large-diameter tube part 3 on the side of one end of the large-diameter tube part 3 and having its outside diameter not larger than 10.8 mm; and a second small-diameter tube part 4 formed in a diameter smaller than that of the large-diameter tube part 3 on the side of the other end of the large-diameter tube part 3 and having its axial length not smaller than 30 mm. This mold body 1 for an insulator is formed into an insulator 11 of a spark plug 30 by baking a plurality of the mold bodies by erecting and aligning them in a sheath 20. The mold body 1 for an insulator is so formed that the large-diameter tube parts 3 of the plurality of the mold bodies 1 for insulators are brought into contact with one another when they are erected and aligned by setting the first small-diameter tube parts 2 lower than the second small-diameter tube parts 4 while tilting the sheath 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a molded body for an insulator of a spark plug, a method for manufacturing a spark plug, and a spark plug.

  Conventionally, a spark plug 90 shown in FIG. 6 is known. The spark plug 90 includes a cylindrical metal shell 91. An insulator 81 is fixed in the metal shell 91, extending in the axial direction of the metal shell 91, with both ends projecting from both ends of the metal shell 91. A shaft hole 85 is provided in the axial direction of the insulator 81. Further, the center electrode 92 extends in the axial direction of the metal shell 91, the front end side of the center electrode 92 is disposed at the front end of the insulator 81 so as to form a discharge portion, and the rear end of the center electrode 92 is the insulator 81. It is fixed inside. Further, the terminal 93 extends in the axial direction of the metal shell 91, the tip of the terminal 93 is electrically connected to the center electrode 92 in the insulator 81, and the rear end of the terminal 93 is connected to the rear end of the insulator 81. It protrudes. In a normal spark plug, one end of the parallel ground electrode 94 is fixed to the metal shell 91, and a discharge gap is formed between the other end of the parallel ground electrode 94 and the discharge portion of the center electrode 92. A spark plug is also known in which the metal shell itself forms a discharge gap with the discharge portion of the center electrode.

  The insulator 81 of the spark plug 90 is obtained, for example, by firing a molded body for an insulator disclosed in FIG. As shown in FIG. 7, the molded body 71 for insulator includes a large-diameter cylindrical portion 73 that forms a flange shape projecting in a direction perpendicular to the axial direction, and a large-diameter cylindrical portion 73 on one end side of the large-diameter cylindrical portion 73. It has a first small-diameter cylindrical portion 72 formed to have a small diameter, and a second small-diameter cylindrical portion 74 formed to have a smaller diameter than the large-diameter cylindrical portion 73 on the other end side of the large-diameter cylindrical portion 73.

  In the first step, after the molded body for insulator 71 is molded, in the second step, the plurality of molded bodies for insulator 71 are fired in an upright and aligned state in the sheath, thereby obtaining an insulator 81. It is done. In the insulator 81, the diamond portion 83 fixed in the metal shell 91 of the spark plug 90 is configured by the large diameter cylindrical portion 73, and the main body portion 82 from which the terminal 93 of the spark plug 90 protrudes from one end is defined as the first small diameter cylinder. The second small diameter cylindrical portion 74 constitutes a shaft portion 84 that is configured by the portion 72 and the center electrode 92 of the spark plug 90 forms a discharge portion on the other end side. Thereafter, the spark plug 90 is obtained by assembling the metal shell 91, the insulator 81, the center electrode 92, the terminal 93, and the parallel ground electrode 94.

  The spark plug 90 is used with the threaded portion of the metal shell 91 screwed into the cylinder head of the engine and the terminal 93 energized to the battery. As a result, the spark plug 90 performs spark discharge in the discharge gap in the combustion chamber of the engine and ignites the air-fuel mixture.

Japanese Patent Laid-Open No. 2000-100500

  However, it has been clarified that in the above-described conventional molded body for an insulator, the axis of the insulator does not become a straight line but may be bent. In a spark plug using such an insulator, for example, in a case having a ground electrode, eccentricity occurs between the metal shell and the insulator, and the center electrode and the metal shell discharge through the insulator, so-called side fire. Is likely to occur. If this side fire occurs frequently, the spark discharge in the discharge gap becomes weak, causing not only a problem in ignitability, but also the so-called channeling in which the surface of the insulator is cut into a groove shape, and the durability is lowered. It will be.

  In particular, in recent years, spark plugs with a small diameter have been required due to problems such as securing a space above the cylinder head of the engine. In addition, a spark plug having a long threaded portion of the metal shell is also required in order to sufficiently dissipate heat (dissipate heat) in the discharge part. In response to such a demand, even when trying to produce a small-diameter and long-sized insulator, such a molded body for an insulator is difficult to stand by in particular in the firing process, and falls or tilts, As a result, the axis was not straight and was often fired as a bent insulator. As a cause of this, it is conceivable that the axial dimension of the large-diameter cylindrical portion of the molded body for insulator forming the diamond portion of the insulator of the spark plug was short and could not be supported sufficiently.

  The present invention has been made in view of the above-described conventional situation, and is to solve the problem by providing a molded body for an insulator of a spark plug capable of obtaining a straight insulator having a straight axis. As an issue.

  Moreover, this invention makes it the 2nd problem which should be solved to provide the spark plug which can suppress the generation | occurrence | production of side-fire and can exhibit the outstanding durability, without impairing ignitability.

  The present inventors have intensively studied to solve the above problems. And it discovered that the said subject could be solved by paying attention to the shape etc. of the molded object for insulators of a spark plug, and came to complete this invention.

  That is, the molded article for an insulator of a spark plug according to the present invention has a flange shape protruding in a direction perpendicular to the axial direction, and has a large-diameter cylindrical portion having an axial length of 6 to 12 mm, and the large-diameter cylinder. A first small-diameter cylindrical portion having an outer diameter of 10.8 mm or less and a smaller diameter than the large-diameter cylindrical portion on the other end side of the large-diameter cylindrical portion. A second small-diameter cylindrical portion having an axial length of 30 mm or more,

The large-diameter cylindrical portion constitutes a diamond portion fixed in the metal shell of the spark plug by firing a plurality of standing and aligned in the sheath, and the terminal of the spark plug protrudes from one end The first small-diameter cylindrical portion is configured as a main body portion, and the second small-diameter cylindrical portion is configured as a shaft portion in which the center electrode of the spark plug forms a discharge portion on the other end side. In a molded body for an insulator of a spark plug to be
When the first small-diameter cylindrical portion is raised and aligned with respect to the second small-diameter cylindrical portion while the sheath is inclined, the large-diameter cylindrical portions of the plurality of molded bodies for insulator come into contact with each other. It is shaped as follows.

  When the first small-diameter cylindrical portion is stood and aligned with the second small-diameter cylindrical portion while the sheath is inclined, the large-diameter cylindrical portions abut against each other. It is shaped as follows. Thereby, the molded bodies for insulators support each other with the large-diameter cylindrical portion, and it is possible to prevent tilting or overturning before firing and during firing.

  According to the test results of the inventors, the molded body for insulator according to the present invention has an axial length of the large-diameter cylindrical portion of 6 to 12 mm and an outer diameter of the first small-diameter cylindrical portion of 10.8 mm or less. In particular, the effect is particularly great when the axial length of the second small diameter portion is 30 mm or more. This is because the above-mentioned problem is particularly remarkable in an insulator having a small diameter and a long length.

  Therefore, according to the molded article for an insulator of a spark plug of the present invention, a straight insulator having an axis that is a straight line can be obtained.

  In addition, since the molded body for insulator of the present invention is molded so that the large-diameter cylindrical portions are in contact with each other, it can be prevented from entering into the large-diameter cylindrical portion of the adjacent molded body for insulator. it can. For this reason, it is hard to produce a crack in the diamond part by a large diameter cylinder part, and an insulator can be manufactured with a high yield.

  It is preferable that the molded body for insulator of the present invention is aligned in the sheath so that there are six around one. Thereby, the molded object for insulators can be supported from all directions among the directions parallel to the end surface of a 1st small diameter cylinder part. For this reason, especially the effect which prevents that the molded object for insulators inclines or falls before baking and during baking becomes large.

  According to the test results of the inventors, the molded body for insulator of the present invention has an outer diameter of the main body portion of 9.0 mm or less, and the axial direction from the edge of the other end of the diamond portion to the end face of the shaft portion This is particularly effective when the insulator is 25 mm or more in length and the length of the diamond portion in the axial direction is 5 to 10 mm. This is because the above-mentioned problem is particularly remarkable in an insulator having a small diameter and a long length.

The spark plug manufacturing method of the present invention has a flange shape projecting in a direction perpendicular to the axial direction, and has a large-diameter cylindrical portion having an axial length of 6 to 12 mm, and one end side of the large-diameter cylindrical portion. The first small-diameter cylindrical portion having a smaller diameter than the large-diameter cylindrical portion, and having an outer diameter of 10.8 mm or less, and the other end of the large-diameter cylindrical portion is smaller in diameter than the large-diameter cylindrical portion, A first step of forming a molded body for an insulator of a spark plug having a second small diameter cylindrical portion having an axial length of 30 mm or more;
A plurality of the molded bodies for insulator are fired in an upright and aligned state in a sheath to form the large diameter cylindrical portion, the diamond portion fixed in the metal shell of the spark plug, and the first small diameter A main body portion that includes a cylindrical portion, and a terminal of the spark plug that protrudes from one end; and a shaft portion that includes the second small-diameter cylindrical portion and the center electrode of the spark plug forms a discharge portion on the other end side. In the manufacturing method of a spark plug comprising the second step of obtaining an insulator of the spark plug,
In the first step, when the first small-diameter cylindrical portion is raised and aligned with respect to the second small-diameter cylindrical portion while tilting the sheath in the second step, a plurality of the molded bodies for insulator are formed. Each of the molded bodies for an insulator is formed such that the large-diameter cylindrical portions are in contact with each other.

  In the manufacturing method of the present invention, first, in a first step, a molded body for an insulator of a spark plug is molded. Then, in the second step, the plurality of molded bodies for insulator are fired in an upright and aligned state in the sheath, thereby obtaining an insulator for a spark plug.

  The manufacturing method according to the present invention includes a plurality of methods for raising and aligning the first small-diameter cylindrical portion of the molded article for insulator as a lower side with respect to the second small-diameter cylindrical portion while tilting the sheath in the first step. The molded body for insulator is molded so that the large-diameter cylindrical portions of the individual molded bodies for insulator are in contact with each other. For this reason, since a straight insulator whose axis is a straight line can be obtained, it is possible to manufacture a spark plug that suppresses the occurrence of side fire and can exhibit excellent durability without impairing ignitability.

The spark plug of the present invention includes a cylindrical metal shell, a cylindrical insulator fixed in the metal shell so as to extend in the axial direction of the metal shell, and having a shaft hole, and the metal shell. Extending at the front end side of the insulator so as to form a discharge portion, the rear end is fixed in the insulator, and extends in the axial direction of the metal shell, A terminal having a tip electrically connected to the central electrode in the insulator and a rear end projecting from the rear end of the insulator, the other end of the ground electrode having one end fixed to the metal shell being the discharge In the spark plug in which the discharge gap is formed with the discharge portion or the metal shell itself forms the discharge gap with the discharge portion,
The insulator is a product obtained by firing the molded body for insulator.

  Since the spark plug of the present invention is a straight one in which the axis of the insulator is a straight line, the occurrence of side fire is suppressed, and excellent durability can be exhibited without impairing ignitability.

  Hereinafter, the present invention will be described with reference to test products 1 to 18 with reference to the drawings.

As the first step, first, a slurry containing raw material powder such as Al ₂ O ₃ powder and SiO ₂ powder, flux (subcomponent), binder and the like and water is prepared. The slurry is granulated by a spray drying method, and the molded body 1 for an insulator of test products 1 to 18 is molded by a rubber press method using the obtained granulated powder.

  As shown in FIG. 1 (A), each molded body 1 for an insulator is formed with a large-diameter cylindrical portion 3 having a flange shape and a diameter smaller than that of the large-diameter cylindrical portion 3 on one end side of the large-diameter cylindrical portion 3. It has the 1st small diameter cylinder part 2, and the 2nd small diameter cylinder part 4 formed in the other end side of the large diameter cylinder part 3 in the diameter smaller than the large diameter cylinder part 3. FIG. Further, a shaft hole 5 is formed by a press pin in the axial direction of the molded body 1 for insulator.

  These molded bodies for insulator 1 have a smaller diameter as the outer peripheral surface of the second small-diameter cylindrical portion 4 is directed to the other end side. Next, the outer shape of the molded body 1 for insulator is adjusted through a grinding process. At this time, corrugation is provided on the outer peripheral surface on the one end side of the first small-diameter cylindrical portion 2, but there is a case where the corrugation is not provided particularly when a small-sized insulator is manufactured.

  In the molded body 1 for an insulator thus formed, for example, for the test product 1, the outer diameter Φ0 of the first small-diameter cylindrical portion 2 is 10.8 mm, and the edge on the other end side of the large-diameter cylindrical portion 3 To the end face of the second small-diameter cylindrical portion 4 is 27.6 mm in the axial direction L0, and the axial length D0 of the large-diameter cylindrical portion 3 is 6.0 mm. Table 1 shows the dimensions of the molded body 1 for an insulator of these test products 1-18.

  As a 2nd process, each molded object 1 for insulators is baked. At this time, as shown in FIGS. 2A, 2 </ b> B, and FIG. 3, a plurality of the molded bodies 1 for insulators are erected and aligned in the sheath 20. 2A and 2B are side views of a partial cross section viewed from the horizontal direction, and FIG. 3 is a plan view viewed from above. 2A and 2B show a state in which the molded body for insulator 1 is in the process of being aligned with the bottom surface of the sheath 20 that is inclined with respect to the horizontal plane. Here, normally, each insulator molded body 1 is aligned with the bottom surface in the sheath 20 as shown in FIG. Since the molded body 1 for an insulator is molded so that the large-diameter cylindrical portions 3 are in contact with each other, it is possible to prevent the insulating molded body 1 from entering the large-diameter cylindrical portion 3 of the adjacent molded body 1 for an insulator. In addition, since the large-diameter cylindrical portions 3 can be aligned at the base point when they are arranged, each of the insulator molded bodies 1 as shown in FIG. 2 (B) is prevented from being perpendicular to the bottom surface in the sheath 20 and has a large diameter. It is possible to avoid occurrence of chipping in the cylindrical portion 3 and bending as an insulator. FIG. 3 is a plan view of the insulator molded body 1 aligned in the sheath 20. In this state, the insulator molded body 1 is fired at a firing temperature of 1560 ° C. for about 1 hour.

  At this time, each molded body 1 for insulator is such that there are six molded bodies 1 for insulator around one molded body 1 for insulator, and the end surface of the first small-diameter cylindrical portion 2 is downward, Aligned within the sheath 20.

  Here, since each molded body 1 for insulator has a large-diameter cylindrical portion that is sufficiently longer than 6 mm as compared with the conventional case, the end surface of the first small-diameter cylindrical portion 2 is formed while the sheath 20 is inclined. When standing and aligning as the lower side, the large-diameter cylindrical portions 3 come into contact with each other by line contact.

  Thus, the insulator 11 shown in FIG. 1B is obtained. The diamond portion 13 of the insulator 11 is constituted by the large-diameter cylindrical portion 3 of the molded body 1 for insulator, and the main body portion 12 of the insulator 11 is constituted by the first small-diameter cylindrical portion 2 of the molded body 1 for insulator. The shaft portion 14 of the body 11 is constituted by the second small diameter cylindrical portion 4. A shaft hole 15 is provided in the axial direction of the insulator 11.

  For example, the insulator 11 of the test article 1 has an outer diameter Φ1 of the main body portion 12 of 9.0 mm, and an axial length L1 from the edge on the other end side of the diamond portion 13 to the end face of the shaft portion 14 is 23 mm. The length D1 in the axial direction of the diamond portion 13 is 5.0 mm. Table 2 shows the dimensions of the insulators 11 of these test products 1 to 18.

  For the insulators 11 of the test products 1 to 18, the runout amount H1 was obtained. Hereinafter, how to determine the amount of run-out H1 and evaluation will be described.

(1) How to Find In FIG. 4 showing the insulator 11, the shaft portion 14 will be described by dividing it into a cylindrical body portion 14a and a leg length portion 14b including a tapered surface. First, an intermediate position of the body portion 14a indicated by an arrow is held by a plurality of rollers (not shown). In addition, the measurement part 40 of the dial gauge (PCN-7A manufactured by Peacock) is brought into contact with the tip of the leg length part 14b, and the dial gauge instruction at that position is set to zero. And the insulator 11 is rotated by rotating a roller. At this time, if the insulator 11 is bent, the distal end portion of the leg length portion 14b moves, and accordingly, the dial gauge instruction swings. The minimum amount and maximum value of the dial gauge instruction are read and the difference is obtained to determine the amount of forward swing H1.

(2) Evaluation “O” was given when the runout amount H1 was 0.1 mm or less. Moreover, when the runout amount H1 was larger than 0.1 mm, it was determined as x. The results are shown in Table 3.

  From Table 3, it can be seen that the insulators 11 of the test products 1, 4, 5, 7, 10, 11, 13, 16 to 18 are straight ones whose axis is a straight line. This is because these molded bodies for insulator 11 support each other with the large-diameter cylindrical portion 3 and prevent tilting or overturning before and during firing. In particular, since it is aligned in the sheath 20 so that there are six insulator molded bodies 1 around one insulator molded body 1, any of the directions parallel to the end face of the first small-diameter cylindrical portion 2 can be used. It seems that they supported each other from the direction.

  Therefore, it can be seen that according to these spark plug insulator molded bodies 1, it is possible to manufacture a straight insulator 11 whose axis is a straight line.

  Moreover, since these molded bodies 1 for insulators are molded so that the large-diameter cylindrical portions 3 are in contact with each other, they are prevented from entering the large-diameter cylindrical portions 3 of the adjacent molded bodies 1 for insulators. I was able to. For this reason, the diamond part 13 by the large diameter cylindrical part 3 is hard to be chipped, and the insulator 11 can be manufactured with a high yield.

  In Table 3, the insulation of test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16 having an outer diameter Φ1 of 9.0 mm or less and a length L1 of 25 mm or more. If the body 11 is seen, when the length D1 is 3.5 mm, the amount of forward swing H1 is all x (test products 3, 6, 8, 14). In other words, for insulators of test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16 having an outer diameter Φ0 of 10.8 mm or less and a length L0 of 30 mm or more. Looking at the molded body 1, when the length D0 is 4.2 mm, the runout amount H1 is all x (test products 3, 6, 8, and 14).

  On the other hand, in the insulator 11 of the test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, the runout amount H1 when the length D1 is 5 to 10 mm is , Except for the test products 9, 12, and 15. In other words, in the molded article for insulator 1 of the test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, the runout when the length D0 is 6 to 12 mm The amount H1 is ◯ except for the test products 9, 12, and 15.

  Thus, if the insulator 11 has an outer diameter Φ1 of 9.0 mm or less, a length L1 of 25 mm or more, and a length D1 of 5 to 10 mm, in other words, the outer diameter Φ0 is 10.8 mm or less and the length L0. Is 30 mm or more and the length D0 is 6 to 12 mm, it can be seen that a straight insulator 11 having a high yield and a straight axis can be produced. The forward deflection amount H1 of the insulator 11 can be obtained even after glazing described later.

  Next, the metal shell 31, the center electrode 32, the terminal 33, and the parallel ground electrode 34 were assembled | attached to the insulator 11 of the test products 1-18, and the spark plug 30 shown in FIG. 5 was obtained. Note that glaze is applied to each insulator 11 before the spark plug 30 is assembled. The composition of the glaze and the location of the glaze are the same as those conventionally known.

  The spark plug 30 includes a cylindrical metal shell 31. The insulator 11 is fixed in the metal shell 31 so as to extend in the axial direction of the metal shell 31 and project both ends from both ends of the metal shell 31. A central electrode 32 extends in the axial direction of the metal shell 31, the distal end side of the central electrode 32 is disposed at the distal end of the insulator 11 so as to form a discharge portion, and the rear end of the central electrode 32 is disposed at the insulator 11. It is fixed inside. Further, the terminal 33 extends in the axial direction of the metal shell 31, the tip of the terminal 33 is electrically connected to the center electrode 32 in the insulator 11, and the rear end protrudes from the rear end of the insulator 11. Yes. One end of the parallel ground electrode 34 is fixed to the metal shell 31, and a discharge gap is formed between the other end of the parallel ground electrode 34 and the discharge portion of the center electrode 32.

  The eccentricity H2 was calculated | required about each spark plug 30 assembled | attached using the insulator 11 of the test products 1-18. Hereinafter, how to calculate and evaluate the eccentricity H2 will be described.

(1) How to Obtain After the insulator 11 and the metal shell 31 are assembled, an image is taken from the front end side of the spark plug 30. At this time, the parallel ground electrode 34 is cut or bent to the outside of the metal shell 31 so as not to hinder image shooting. For this photographing, for example, a CNC image measurement system NEXIV manufactured by Nikon Corporation can be used.

  The captured image is processed by a personal computer or the like, and the center point of the inner circle of the metallic shell 31 and the center point of the outer circle of the tip surface of the insulator 11 are coordinated. And the eccentric amount H2 is calculated | required by calculating the distance between the two points. Note that the captured image may be subjected to analysis, image quality correction, and the like as appropriate.

(2) Evaluation The eccentricity H2 was also evaluated as ◯ when it was 0.1 mm or less. Moreover, it determined with x when eccentricity H2 was larger than 0.1 mm. The results are shown in Table 4.

  From Table 4, if the insulators 11 of the test products 1, 2, 4 to 7, 9 to 13, and 15 to 18 are used, the occurrence of side fire is suppressed, and the excellent durability is obtained without impairing the ignitability. It turns out that the spark plug which can be demonstrated can be manufactured.

  And in Table 4, the insulation of the test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16 having an outer diameter Φ1 of 9.0 mm or less and a length L1 of 25 mm or more. When the body 11 is viewed, a situation occurs in which the eccentricity H2 becomes x when the length D1 is 3.5 mm (test products 3, 8, and 14). In other words, for insulators of test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16 having an outer diameter Φ0 of 10.8 mm or less and a length L0 of 30 mm or more. If the molded object 1 is seen, when the length D0 is 4.2 mm, the eccentricity H2 will become x (test product 3, 8, 14).

  On the other hand, when the length D1 is 5 to 10 mm in the insulators 11 of the test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, the amount of eccentricity H2 is all (circle) (test goods 4, 6, 7, 9, 10, 12, 13, 15, 16). In other words, when the length D0 is 6 to 12 mm in the molded body for insulator 1 of the test products 3, 4, 6, 7, 8, 9, 10, 12, 13, 14, 15, 16, The eccentricity H2 is all ◯ (test products 4, 6, 7, 9, 10, 12, 13, 15, 16).

  Accordingly, it can be seen that an excellent spark plug 30 can be manufactured if the insulator 11 has an outer diameter Φ1 of 9.0 mm or less, a length L1 of 25 mm or more, and a length D1 of 5 to 10 mm. In other words, it can be seen that an excellent spark plug 30 can be manufactured if the molded body 11 for an insulator has an outer diameter Φ0 of 10.8 mm or less, a length L0 of 30 mm or more, and a length D0 of 6 to 12 mm.

  In the above, the present invention has been described with reference to the test products 1 to 18. However, the present invention is not limited to the test products 1 to 18, and can be appropriately modified and applied without departing from the spirit of the present invention. Needless to say.

  The present invention is applicable to an engine that achieves high output.

In connection with Test Examples 1 to 18, FIG. (A) is a cross-sectional view of a molded body for an insulator, and FIG. (B) is a cross-sectional view of the insulator. It is a side view of the partial cross section of the molded object for insulators which concerns on Test Examples 1-18 and was arranged in the sheath. It is a top view of the molded object for insulators which concerns on Test Examples 1-18 and was arranged in the sheath. It is a front view of the molded object for insulators concerning Test Examples 1-18 for testing the amount of runout. It is sectional drawing of a spark plug in connection with Test Examples 1-18. It is sectional drawing of the conventional spark plug. It is sectional drawing of the conventional molded object for insulators.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Molded body for insulators 2 ... 1st small diameter cylinder part 3 ... Large diameter cylinder part 4 ... 2nd small diameter cylinder part 11 ... Insulator 12 ... Main body part 13 ... Diamond part 14 ... Shaft part 15 ... Shaft hole 20 ... Saya 30 ... Spark plug 31 ... Metal shell 32 ... Center electrode 33 ... Terminal 34 ... Parallel ground electrode

Claims (5)

It has a flange shape that protrudes in a direction perpendicular to the axial direction, and has a large-diameter cylindrical portion having an axial length of 6 to 12 mm and a smaller diameter than the large-diameter cylindrical portion on one end side of the large-diameter cylindrical portion. A first small-diameter cylindrical portion having an outer diameter of 10.8 mm or less and a smaller diameter than the large-diameter cylindrical portion at the other end of the large-diameter cylindrical portion, and an axial length of 30 mm or more. 2 having a small diameter cylindrical portion,
The large-diameter cylindrical portion constitutes a diamond portion fixed in the metal shell of the spark plug by firing a plurality of standing and aligned in the sheath, and the terminal of the spark plug protrudes from one end The first small-diameter cylindrical portion is configured as a main body portion, and the second small-diameter cylindrical portion is configured as a shaft portion in which the center electrode of the spark plug forms a discharge portion on the other end side. In a molded body for an insulator of a spark plug to be
When the first small-diameter cylindrical portion is raised and aligned with respect to the second small-diameter cylindrical portion while the sheath is inclined, the large-diameter cylindrical portions of the plurality of molded bodies for insulator come into contact with each other. A molded body for an insulator of a spark plug, which is molded as described above.   2. The molded body for an insulator of a spark plug according to claim 1, wherein the molded body for an insulator is aligned in the sheath so that there are six around one.   The outer diameter of the main body portion is 9.0 mm or less, the axial length from the edge on the other end side to the end surface of the shaft portion in the diamond portion is 25 mm or more, and the axial length of the diamond portion The molded body for an insulator of a spark plug according to claim 1 or 2, wherein the insulator is 5 to 10 mm. It has a flange shape that protrudes in a direction perpendicular to the axial direction, and has a large-diameter cylindrical portion having an axial length of 6 to 12 mm and a smaller diameter than the large-diameter cylindrical portion on one end side of the large-diameter cylindrical portion. A first small-diameter cylindrical portion having an outer diameter of 10.8 mm or less and a smaller diameter than the large-diameter cylindrical portion at the other end of the large-diameter cylindrical portion, and an axial length of 30 mm or more. A first step of forming a molded body for an insulator of a spark plug having two small diameter cylindrical portions;
A plurality of the molded bodies for insulator are fired in an upright and aligned state in a sheath to form the large diameter cylindrical portion, the diamond portion fixed in the metal shell of the spark plug, and the first small diameter A main body portion that includes a cylindrical portion, and a terminal of the spark plug that protrudes from one end; and a shaft portion that includes the second small-diameter cylindrical portion and the center electrode of the spark plug forms a discharge portion on the other end side. In the manufacturing method of a spark plug comprising the second step of obtaining an insulator of the spark plug,
In the first step, when the first small-diameter cylindrical portion is raised and aligned with respect to the second small-diameter cylindrical portion while tilting the sheath in the second step, a plurality of the molded bodies for insulator are formed. A method for manufacturing a spark plug, comprising molding each of the molded bodies for an insulator so that the large-diameter cylindrical portions are in contact with each other. A cylindrical metal shell, a cylindrical insulator fixed in the metal shell so as to extend in the axial direction of the metal shell, and having an axial hole, and extending in the axial direction of the metal shell, The center electrode is disposed at the tip of the insulator so that the side forms a discharge portion, the rear end is fixed in the insulator, and extends in the axial direction of the metal shell, and the tip is the center electrode in the insulator And a terminal for projecting the rear end from the rear end of the insulator, and the other end of the ground electrode having one end fixed to the metal shell forms the discharge gap between the discharge portion and the discharge portion. In the spark plug that is formed or the metal shell itself forms a discharge gap with the discharge part,
4. The spark plug according to claim 1, wherein the insulator is obtained by firing the insulator molded body according to any one of claims 1 to 3.

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