JP2868685B2 - Split type insulator for spark plug - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug split insulator mounted on an internal combustion engine of a vehicle.

[0002]

2. Description of the Related Art Conventionally, with the increase in speed, output, and fuel efficiency of an internal combustion engine, a high value-added spark plug has been developed by dividing an insulator into two parts and using different ceramic materials. Has been made. In such a spark plug, after two insulating ceramics are arranged in the metal shell in the axial direction, the end faces of the two insulating ceramics are firmly fitted to each other by caulking the rear end side of the metal shell. By doing so, the split insulator was supported by the metal shell.

[0003]

However, in the conventional split-type insulator, the strength of the two divided insulating ceramics is different due to the difference in the material of the ceramics. When the low-strength insulating ceramics and the high-strength insulating ceramics are firmly abutted when assembling the low-strength ceramics, stress concentrates on the convex surface of the contact surface of the low-strength insulating ceramics. As a result, cracks may be generated in the insulating ceramics on the low strength side. As described above, if a crack is generated in the insulating ceramic on the low strength side, electricity leaks from the cracked portion, so that no spark discharge occurs at the regular spark discharge gap, and the internal combustion engine misfires or stops. There was a possibility that such a problem would occur.

[0004] The present invention relates to a split type insulator for a spark plug capable of preventing the occurrence of cracks in the low-strength insulating ceramics of the two insulating ceramics and preventing the misfire or stoppage of the internal combustion engine. For the purpose of providing.

[0005]

According to a first aspect of the present invention, there is provided a split-type insulator for a spark plug supported in a cylindrical metal shell with two insulating ceramics having different strengths abutting each other. For the low-strength insulating ceramics of the two insulating ceramics, a technical means in which a contact surface that contacts the high-strength insulating ceramics of the two insulating ceramics is employed.

The contact surface of the low-strength insulating ceramic preferably has a surface roughness of 2.0 μmRz or less. Further, the low-strength insulating ceramic is provided on a spark discharge gap side where a spark discharge occurs, and the high-strength insulating ceramic is provided on a rear end side of the low-strength insulating ceramic. May be. The low-strength insulating ceramic is preferably formed of a material mainly containing aluminum nitride, and the high-strength insulating ceramic is preferably formed of a material mainly containing aluminum oxide. .

[0007]

According to the first aspect of the present invention, the contact surface of the low-strength insulating ceramics formed of a material having lower strength than the high-strength insulating ceramics is smoothed. The amount of protrusion of the surface convex portion of the contact surface of the conductive ceramic becomes very small. With this, when assembling the cylindrical metal shell and the split-type insulator, even if the low-strength insulating ceramic and the high-strength insulating ceramic are firmly abutted, the low-strength insulating ceramic can be used. Since the stress is dispersed over the entire contact surface, no crack occurs in the insulating ceramic on the low strength side.

[0008]

【Example】

[Structure of Embodiment] A split type insulator for a spark plug according to the present invention will be described with reference to an embodiment shown in FIGS. FIG. 1 is a diagram showing a spark plug attached to a gasoline engine mounted on an automobile. The spark plug 1 of this automobile gasoline engine includes a rod-shaped center electrode 2 having a flange portion, a substantially L-shaped ground electrode 3 forming a spark discharge gap G between the center electrode 2 and a front end face of the center electrode 2. It includes a cylindrical metal shell 4 for holding the ground electrode 3, a cylindrical split insulator 5 supported by the metal shell 4, and the like.

The center electrode 2 is held in the split insulator 5 so as to protrude from the end face of the split insulator 5. The ground electrode 3 is joined to the distal end surface of the metal shell 4 by means such as welding. The metal shell 4 forms an outer shell of the spark plug 1 and plays a role of attachment to a gasoline engine. A screw portion 6 for attachment to a cylinder head (not shown) of a gasoline engine is formed at a front end side of the metal shell 4, and a tool such as a tightening wrench is engaged with a rear end side of the metal shell 4. A hexagonal portion 7 is formed for the purpose.

The split-type insulator 5 is composed of ceramics A supported at the front end of the metal shell 4 and ceramics B supported at the rear end of the metal shell 4. The materials of the ceramics A include MgO, AlN, AlON, Si, as shown in Examples 1 to 6 in Table 1 described later.
₃ N _4, SiAlON, thermal shock resistance excellent insulative ceramic material such as Al ₂ O ₃ is used. The ceramics A is provided on the spark portion 8 (spark discharge portion) side of the spark plug 1 and has a leg portion 9 exposed to the atmosphere in the combustion chamber of the gasoline engine, and the front end side of the center electrode 2 is fitted therein. It has an inner hole 10.

[0011] The rear end of the ceramics A is shown in FIG.
As shown in FIG. 3, a cylindrical portion 12 is formed to form a concave portion 11 into which ceramics B is fitted. The inner periphery of the recess 11 is inclined so that the cross-sectional area gradually increases toward the rear end surface. The contact surface 13 which is the rear end surface of the ceramics A,
1a or the annular end face 12a of the cylindrical portion 12 is
Strong contact with ceramics B during caulking. Also,
The step part 14 formed on the outer periphery of the cylindrical part 12 is
Are locked via a packing 16 to an annular ridge 15 formed on the inner periphery of the rim.

The material of the ceramic B is shown in Table 1 below.
As shown in Examples 1 to 6, Al ₂ O ₃ , S
An insulating ceramic material having excellent mechanical strength such as i ₃ N ₄ is used. The ceramic B has a corrugated portion 17 on the outer periphery of the rear end portion, and a rear end side of the flange portion of the center electrode 2, the center shaft 19 of the high voltage terminal 18, and the resistor 20 for preventing radio noise are conductive in the inner hole 22. Heat sealing is performed by the conductive glass layer 21.

As shown in FIG. 2, the cylindrical portion 23 formed at the tip of the ceramic B has a convex portion 24 fitted into the concave portion 11 of the ceramic A. The outer periphery of the convex portion 24 is inclined so that the cross-sectional area gradually increases toward the distal end surface. The contact surface 25, which is the tip surface of the ceramic B,
Is joined to the contact surface 13 of the ceramics A. Rings 28 and 29 and ceramic filling powder 30 are interposed between the large diameter portion 26 of the ceramic B and the caulking portion 27 of the metal shell 4.

Next, a method of assembling the metal shell 4 and the split-type insulator 5 of this embodiment will be briefly described with reference to Example 2 in Table 1 described later. First, when the molding material of ceramics A is relatively expensive AlN having excellent thermal shock resistance and the molding material of ceramics B is relatively inexpensive Al ₂ O ₃ having excellent mechanical strength, the following table is used. As shown in FIG. 1, the flexural strength of ceramics A is 24
The flexural strength of ceramics B is 31 at 5MPa (experimental value)
Since it is 3 MPa (experimental value), it can be seen that the strength of ceramics A is lower than that of ceramics B.

For this reason, at least the annular end surface 12a, which is the contact surface 13 of the ceramic A on the low strength side, is smoothed by a grinder so that the surface roughness is equal to or less than a set value (= 2.0 μmRz) (see Table 1). In Example 2, the surface roughness was 1.6.
0 μm Rz). In addition, a center electrode 2 having a tip protruding from the inner hole 22 is disposed in the inner hole 22 of the ceramic B on the high strength side, and the resistor 20 and the center shaft 19 are sealed by the conductive glass layer 21, and the A ceramic B on the strength side is formed.

In the cylindrical metal shell 4 to which the ground electrode 3 is welded to the front end surface, the step 14 of the cylindrical portion 12 of the ceramic A on the low strength side is packed with the annular ridge 15 of the metal shell 4 by a packing 16. In order to fit with the low-strength ceramic A, a high-strength ceramic B integrally sealing the center electrode 2 and the like is provided, and an inner hole 10 of the low-strength ceramic A is provided. The distal end of the center electrode 2 is inserted therein and arranged so as to protrude from the distal end surface, and the concave portion 11 of the ceramic A on the low strength side and the convex portion 24 of the ceramic B on the high strength side are fitted and divided. The mold insulator 5 is formed.

The caulking portion 27 of the metal shell 4 is caulked by pressing using a caulking jig, so that the annular protruding portion 15 and the caulking portion 27 of the metal shell 4 are sandwiched via the ceramic filling powder 30. A large pressing force is applied between the stepped portion 14 of the cylindrical portion 12 of the low-strength ceramic A and the large-diameter portion 26 of the high-strength ceramic B. Thereby, the contact surface 1 of the ceramic A on the low strength side
3 (especially the annular end face 12a) and the ceramic B on the high strength side
And the contact surface 25 (particularly, the annular end surface 23a) is firmly abutted.

As described above, the surface roughness of the contact surface 13 of the ceramic A on the low strength side is equal to the set value (= 2.0 μm).
mRz). As a result, the amount of protrusion of the surface protrusions protruding from the contact surface 13 of the ceramic A on the low strength side toward the contact surface 25 of the ceramic B on the high strength side becomes extremely small, and the stress is reduced.
3, the ceramics A on the low-strength side does not crack.

[Comparison between Example and Comparative Example] Next, Table 1 is used to describe the relationship between the polished surface roughness of the annular end face 12a in contact with the ceramics A and the annular end face 23a in contact with the ceramics B and the state of occurrence of cracks. Will be explained. Here, Table 1 shows the occurrence of cracks while variously changing the material and strength of the ceramics A and B and the surface roughness of the annular end face after polishing.

[0020]

[Table 1]

In Table 1, the term "strength" refers to the values of Examples 1 to
Ceramics A using the material of Example 7, Comparative Examples 1 to 7
This is the bending strength obtained by examining each of the split-type insulators obtained by molding the ceramic and ceramic B by performing a JIS three-point bending test. The surface roughness is determined by a ten-point average roughness defined in the JIS standard for surface roughness.

Furthermore, the crack generation condition is determined by the load applied to the annular end face where ceramics A and ceramics B come into contact when the metal shell 4 of the spark plug 1 and the split insulator 5 are assembled (at the time of caulking). Was set by an autograph, and the load was investigated as shown in FIG. In FIG. 3, reference numeral 100 denotes a receiving stand, and 101 denotes a guide cylinder. In this investigation, 50 divided insulators each formed by molding ceramics A and B with the materials described in Examples 1 to 7 and the materials described in Comparative Examples 1 to 7 were experimentally manufactured. .

Table 1 shows each split type insulator.
If no cracks were found in 0 pieces, mark ○. If 50 pieces of each split-type insulator were cracked, only 1 to 24 pieces were marked as △. 50 pieces of each split-type insulator. 25 in
Those in which cracks occurred in as many as 50 pieces were marked X. In addition,
The load applied to the autograph was set at 2 ton from the load at the time of caulking the metal shell 4.

From Table 1, Examples 1 to 3, and Example 6 are shown.
And, as in Example 7, the annular end face 12a of the ceramic A on the low strength side of the ceramics A and B is polished by a polishing machine to reduce the surface roughness of the annular end face 12a to 2.02.
It can be confirmed that cracks did not occur in those having a μmRz or less. Similarly, as in Example 4 and Example 5, the annular end surface 23a of the ceramic B on the lower strength side of the ceramics A and B is polished by a polishing machine to reduce the surface roughness of the annular end surface 23a to 1. It can be confirmed that cracks did not occur in the alloys of 98 μm Rz or less.

Conversely, as in Comparative Examples 1 to 7, ceramics A and B having a low-strength annular end surface having a surface roughness of 2.37 μmRz or more have low-strength ceramics A and B. It can be confirmed that cracks occur in B and that the ceramics A and B on the low-strength side whose surface roughness of the annular end faces is 4.23 μmRz or more have cracks in a considerable number of 50 prototypes. As a result, in the case of Comparative Examples 1 to 7, there is a sufficient possibility that sparks will not be generated in the spark discharge gap due to the leakage of electricity from the cracked portion and the gasoline engine will be misfired or stopped. Can be confirmed.

[Effects of Embodiment] As described above, Embodiment 1
In the seventh to seventh embodiments, since the cause of the crack is that stress is concentrated on the surface convex portion of the contact surface of the ceramics on the low strength side of the two ceramics A and B during the caulking assembly, the low strength side Is polished by a polishing machine to smooth the surface roughness of the contact surface so as to be equal to or less than a set value (= 2.0 μmRz). Accordingly, when the metal shell 4 and the split insulator 5 are assembled (when caulked), even if a large pressing force is applied to the contact surfaces 13 and 25 of the two ceramics A and B, the two ceramics A and B There is no crack in the ceramics on the low strength side.

For this reason, when a high voltage is applied to the center electrode 2 via the high voltage terminal 18, no electricity leaks from the middle of the split type insulator 5, and the tip surface of the center electrode 2 is always connected to the ground electrode. The spark discharge occurs in the regular spark discharge gap G formed between the discharge end face 3 and the discharge end face.
Therefore, misfire or stoppage of the gasoline engine can be prevented, so that the ignitability of the compressed air-fuel mixture sucked into the combustion chamber of the gasoline engine can be drastically improved.

[Modification] In this embodiment, the present invention is applied to the split-type insulator 5 of the ordinary spark plug 1, but the present invention is applied to the split-type insulator of the surface discharge type spark plug and the semi-surface discharge type spark plug. The invention may be applied. In this embodiment, caulking using the ceramic filler powder 30 is used as a method of assembling the metal shell 4 and the split-type insulator 5, but the metal shell is used as a method of assembling the metal shell 4 and the split-type insulator 5. A large current is applied to a part of the outer periphery of the metal member 4 to melt it while pressurizing, and then the split type insulator 5 is tightened by the annular ridge 15 and the caulking portion 27 of the metal member 4 by shrinkage force due to cooling. Heat caulking in which the split insulator 5 is assembled may be used.

In this embodiment, the concave portion 11 is provided on the rear end side of the ceramic A, and the convex portion 24 is provided on the distal end side of the ceramic B. A convex portion may be provided on the rear end side, and a concave portion may be provided on the front end side of ceramics B, and ceramics A and B may be integrally fitted by concave and convex fitting. Also, ceramics A,
The contact surfaces 13 and 25 of B may be simple annular end surfaces.

Further, the ceramics A and B may be fitted with concaves and convexes to form contact surfaces only on the annular end faces 12a and 23a. Conversely, the annular end faces 12a and 23a are non-contact surfaces, and 11a and outer peripheral surface 24a of convex portion 24
Only the contact surface may be used. Alternatively, an adhesive or the like may be used for joining the ceramics A and B, assembled into the metal shell 4 before the adhesive or the like is solidified, and then the adhesive or the like may be heated and solidified.

[0031]

According to the first aspect of the present invention, since the contact surface of the low-strength insulating ceramics is smoothed, the low-strength insulating ceramics can be combined with the low-strength insulating ceramics when assembling the metal shell and the split-type insulator. Even when the insulating ceramics on the strength side are strongly butted against each other, it is possible to prevent cracks from being generated on the insulating ceramics on the low strength side. As a result, it is possible to prevent the leakage of electricity in the insulating ceramics on the low-strength side, so that a spark discharge is reliably generated in the spark discharge gap. Can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a spark plug according to one embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of a spark plug according to one embodiment of the present invention.

FIG. 3 is an explanatory diagram of an experimental apparatus using an autograph.

[Explanation of symbols]

 Reference Signs List A ceramics B ceramics G spark discharge gap 1 spark plug 2 center electrode 3 ground electrode 4 metallic shell 5 split insulator 11 concave portion 11a inner peripheral surface 12 cylindrical portion 12a annular end surface 13 contact surface 23 cylindrical portion 23a annular end surface 24 convex portion 24a Outer surface 25 Contact surface

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Tanabe 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi Inside Japan Special Ceramics Co., Ltd. (56) References JP-A-2-309584 (JP, A) JP-A Heihei JP-A-2-306565 (JP, A) JP-A-2-183990 (JP, A) JP-A-2-107580 (JP, A) JP-A-60-96550 (JP, A) JP-A-62-170880 (JP, A A) JP-A-5-301780 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01T 13/38 H01T 13/20 H01T 13/36 C04B 37/00

Claims (4)

(57) [Claims] 1. A split-type insulator for a spark plug supported in a cylindrical metal shell with two insulating ceramics having different strengths abutting each other, wherein a low strength of the two insulating ceramics is provided. A split insulator for a spark plug, characterized in that the insulating ceramic on the side has a smooth contact surface in contact with the insulating ceramic on the high strength side of the two insulating ceramics. 2. The spark plug split insulator according to claim 1, wherein the contact surface of the low-strength insulating ceramics has a surface roughness of 2.0 μmRz or less. For split type insulator. 3. The split-type insulator for a spark plug according to claim 2, wherein the low-strength insulating ceramic is provided on a spark discharge gap side where a spark discharge occurs, and the high-strength insulating material is provided on the high-strength side. A split insulator for a spark plug, wherein the ceramic is provided on a rear end side of the low-strength insulating ceramic. 4. The split-type insulator for a spark plug according to claim 3, wherein the low-strength insulating ceramic is formed of a material containing aluminum nitride as a main component, and the high-strength insulating ceramic is formed. Is a split type insulator for a spark plug characterized by being formed of a material containing aluminum oxide as a main component.