JPH02112189A - Spark plug of internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain excellent thermal shock resistance and cheap manufacturing coast by a method wherein a corrugation part insulator and a long stem part insulator are engaged through a recessed part and a projection part respective while interposing a material of glass matte or ceramic matter having an intermittent thermal expansion coefficient between nitriding silicon matter ceramic and alumina matter ceramic on an engaging face. CONSTITUTION:A long stem part insulator 1 of a spark plug A is alumina. A corrugation part insulator 2 is nitriding silicon. Further, an interior part 22 of a recessed part 21 of this insulator 2 directly comes in contact with the tip face 12 of a projection part 11 of the insulator 1 while the tip face 23 of the recessed part 21 directly comes in contact with the flange face 13 of the recessed part 11. Cylinder glass 3 is high melting point glass having an intermittent thermal expansion coefficient between nitriding silicon and alumina. This cylinder glass 3 is externally engaged with the projection part 11 so that it may completely cover the projection part outer side 14 while coming in close contact with the recessed part internal side 24.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spark plug for a high-output engine, and particularly to a spark plug for an internal combustion engine suitable for use in an automobile racing engine or a rotary engine.

[Prior Art] The insulators (alumina, etc.) of spark plugs used in high-output engines, such as rotary engines, develop cracks on the surface due to thermal shock from intense heating and cooling, and the cracks grow due to this thermal history. If it reaches a certain length, it may crack and fall off, damaging the engine.

For this reason, spark plugs using silicon nitride as an insulator, which has excellent thermal shock resistance, have been proposed.

[Problems to be Solved by the Invention] However, conventional spark plugs have the following drawbacks.

If silicon nitride is used for the entire spark plug insulator, the cost will be significantly higher and productivity will be poor.

An object of the present invention is to provide a spark plug for an internal combustion engine that has excellent thermal shock resistance and is inexpensive to manufacture.

[Means for Solving the Problems] In order to achieve the first problem, the spark plug for an internal combustion engine of the present invention adopts the following configurations (a) to (o).

(A) A cylindrical metal shell, a cylindrical leg assembly that is fitted into the tip side of the metal shell and is made of silicon nitride ceramic, and a cylindrical leg assembly located at the rear of the leg assembly. , a spark plug for an internal combustion engine comprising a cylindrical corrugation insulator made of alumina ceramic and a center electrode fitted into each of the insulators, the corrugation insulator and the leg length assembly; are fitted into each other by a concave portion and a convex portion, and have a structure in which a vitreous material or a ceramic material having a coefficient of thermal expansion between that of the silicon nitride ceramic and the alumina ceramic is interposed on the mating surface. .

(b) It has the configuration of (a) above, and the fitting of each insulator is performed between the caulking part of the metal shell and the packing contact surface, and The material has a multi-N structure that makes the thermal expansion coefficients of silicon nitride ceramic and alumina ceramic asymptotic.

(C) It has the structure of (A) and (C) above, and (c) the silicon nitride ceramic has a structure in which a silica layer is formed on the bonding surface in an oxygen atmosphere.

(e) It has the configurations of (i) and (c) above, and the multilayer Wi structure has an inner oxynitride glass layer based on A, fl-Si-0-N, and an outer of Na2
A structure that is a ring-shaped joined body consisting of an oxide glass layer such as O, B203, S102, etc. and a middle oxide glass layer such as Na2O3, B2O3, SiO2.

(E) A configuration having the configurations (A) to (E) above, and in which the gap G between each of the insulators and the cylindrical metal shell is filled with a paste-like insulator.

[Action and effect of invention] The present invention has the following effects and the effects of the invention.

<Regarding Claim 1> The corrugation part insulator and the leg length assembly are each fitted and joined by a concave part and a convex part, and the fitting surface has a coefficient of thermal expansion between that of silicon nitride ceramic and alumina ceramic. A glassy or ceramic material is interposed to erase the

Therefore, the stress caused by thermal stress applied to the fitting surface is alleviated. In addition, silicon nitride ceramic is used for the long leg assembly (on the ignition side), which requires thermal shock resistance, and inexpensive alumina ceramic is used for the corrugation insulator, making the spark plug highly resistant to thermal shock. It has excellent properties and the manufacturing cost is low.

Alumina ceramics have a larger coefficient of thermal expansion than silicon nitride ceramics. Therefore, when this fitting portion becomes hot, compressive stress is applied from the outer corrugation portion insulator to the inner leg length assembly (see FIG. 2), thereby making the connection stronger. The reason why the insulator of the corrugation part is made into a concave part is that it has been experimentally shown that the bonding strength is better this way.
-Because it was obtained.

<Regarding Claim 2> Since each insulator is fitted between the caulking part of the one-piece metal fitting and the contact surface of the seal (middle body part), it can withstand stress from the radial direction for one minute. can.

The glassy material or the ceramic material has a multilayer structure in which the thermal expansion coefficients of the silicon nitride ceramic and the alumina ceramic are asymptotic. Therefore, these layers act as stress relaxation layers (see FIG. 3), and the stress caused by thermal stress is further alleviated.

<Regarding Claim 3> In the silicon nitride ceramic, a silica layer is formed on the bonding surface in an oxygen atmosphere. Here, the silicon nitride ceramic (leg length insulator) and alumina ceramic (corrugation part insulator) are wetted with the insulating glass material (borosilicate glass, etc.) or ceramic material (alumina cement, etc.) to be bonded. Bad sex. However, this silica layer improves wettability and increases bonding strength.

Regarding Claim 4> The multilayer structure is a ring-shaped joined body consisting of an inner oxide-based glass layer, an outer oxide-based glass layer, and a middle oxide-based glass layer.

Here, the physical properties of the inner oxynitride glass layer are similar to those of silicon nitride ceramics, the outer oxide glass layer is similar to alumina ceramics, and the middle oxide glass layer is similar to that of silicon nitride ceramics. It has intermediate characteristics between the ride-based glass layer and the outer oxide-based glass layer. Therefore, the wettability between the corrugation part insulator and the leg length part insulator can be ensured, and the bonding strength can be improved.

Regarding Claim 5> The gap between each insulator and the cylindrical metal shell is filled with a paste-like insulator. Therefore, the dielectric breakdown voltage between each insulator and the cylindrical metal shell is improved.

[Embodiment] Next, a spark plug for an internal combustion engine according to the present invention will be described based on a first embodiment (corresponding to claim 1) shown in FIGS. 1 to 3.

The spark plug A includes a cylindrical main metal fitting (not shown), a cylindrical leg insulator 1 having a protrusion 1 at the rear end, and a cylindrical corrugation insulator having a recess 21 at its tip. 2
and a center electrode (
(not shown) and an insulating cylindrical glass 3 that fits into the convex portion 11 and the concave portion 21.

The leg insulator 1 is alumina as shown in Table 1.

The corrugation insulator 2 is silicon nitride, which is also shown in Table 1. Further, the inner part 22 of the recess 21 of the insulator 2 is in direct contact with the tip surface 12 of the protrusion 11 of the insulator 1, and the tip surface 23 of the recess 21 is in direct contact with the flange surface 12 of the protrusion 11.
It is in direct contact with C.

The cylindrical glass 3 has a softening point of 705°C and a coefficient of thermal expansion of 5.
It is a high melting point glass with a temperature of 70 x 10-6/°C. This cylindrical glass 3 covers the convex portion 11 completely so as to completely cover the convex portion outer surface 14. It is fitted onto the outside of the recess and is in contact with the inner surface 24 of the recess. In this embodiment, the fitting surfaces are the outer surface 14 of the convex portion and the inner surface 24 of the recessed portion.

This spark plug A has the action and effect of sparking.

(a) Spark plug A uses silicon nitride for the long leg insulator 1 on the ignition part side, which requires thermal shock resistance, and uses inexpensive alumina for the corrugation part insulator 2, so it has good thermal shock resistance. Excellent and low manufacturing cost.

(a) When the fitting part between the corrugation part insulator 2 and the leg length insulator 1- becomes high temperature, compressive stress is applied from the outer corrugation part insulator 2 to the inner leg length insulator core, and the bond becomes stronger. becomes stronger.

(1) The cylindrical glass 3 has a coefficient of thermal expansion of 5.70×10-'/'C, which is between that of silicon nitride and alumina.

Therefore, the fitting surfaces (the outer surface 14 of the convex portion and the inner surface 2 of the recessed portion
4) Stress due to thermal stress applied to the material is alleviated.

Next, a spark plug for an internal combustion engine according to the present invention will be described based on a second embodiment (corresponding to claim 1.2) shown in FIGS. 4 and 5.

In this embodiment, each insulator 1.2 of the spark plug B is fitted between the clamping portion 41 of the metal shell 4 and the packing contact surface 42.

The cylindrical crow 3 contains Na2O, B2 as shown in Table 2.
Oxide glass layers of 0:+, 5io2 are laminated so that the coefficient of thermal expansion decreases from the outside to the inside.

31 is 7. 55X 10"/℃, 32 is 5.70x
10-6/'C133 is 455x10-6/'C (shown in Table 2).

Moreover, this three-layer structure (see FIG. 5) is formed by coating or press molding.

This spark plug B has the following functions and effects.

(1) The multilayer structure of the cylindrical glass 3 made of vitreous materials with different coefficients of thermal expansion can alleviate the thermal stress caused by the rapid heating and cooling of engine combustion scum, and suppress the occurrence of scratches due to thermal stress at the joint. I'll come.

(e) The leg length section insulator 1 and the corrugation section insulator 2 fit together between the clamping section 4 of the metal shell 4 and the packing contact surface 42, so they resist stress from the radial direction.
can also be adequately addressed.

A third embodiment of the spark plug for an internal combustion engine according to the present invention (corresponding to claim 1.2.3) will now be described with reference to FIGS. 4 and 6.

In spark plug C, silicon nitride (long leg assembly 1
) was previously left in the atmosphere at 000'C□ to 1300'C to form a silica layer I5 of 1/l-30μ on the surface, and then manufactured with the structure of the second embodiment.

(Strength) As shown in FIG. 6, this spark plug C has increased bonding strength compared to one in which the silica layer 5 is not formed at the same bonding area.

A fourth embodiment of the spark plug for an internal combustion engine according to the present invention (corresponding to claim 11.2.1) is shown in FIGS. 7 and 8.
This will be explained with figures.

This leg of the spark plug D (fitted into the convex part 11 of the insulator 1)1. The ring-shaped bonded body 5 has an inner oxynitride-based glass layer 51 based on l5i-0-N, which has a high C affinity for silicon nitride (long leg assembly), and an outer Na oxynitride-based glass layer 51. , ○, B, 03, S]07, etc., and an oxide glass layer 53 such as Na2O3, B203, S]02, etc. that is compatible with these glass layers 51 and 52. (See Figure 8).

This ring-shaped joined body 5 having a multilayer structure is obtained by forming each of the glass layers 5], 52, 53 into a ring shape in advance.
It is fitted into the convex portion 11 and bonded by heating. On this occasion,
The oxynitride glass layer 51 is particularly made of inert materials such as argon and nitrogen! :1400℃~1850℃ in atmosphere
It is best to join with

The center electrode 6 is inserted across the leg assembly 1 and the corrugation insulator 2. Mana, center electrode 6
The conductive glass 61 filled above is heat-sealed together with the terminal electrode 63 with the resistor 62 sandwiched therebetween.

This spark plug D has the following functions and effects.

(G) The oxynitride-based glass layer 51 inside the ring-shaped bonded body 5, which is in contact with the leg length assembly 1 (silicon nitride), has physical properties similar to those of the leg length assembly 1-. High affinity. In addition, the outside Na2O, B2O3, Si
The physical properties of the dioxide glass layer 52 and the corrugation insulator 2 (alumina) are similar to each other. Furthermore, between these crow layers 51 and 52, N a 203 , B 203 , S
102 oxide-based glass layers 53 are supported. For this reason, the ring-shaped joined body 5 can ensure wettability between the leg length assembly 1 and the corplication section insulation 2. Therefore, the bonding strength between the two is excellent.

-) A fifth embodiment of the spark plug for an internal combustion engine according to the present invention is shown in FIGS. 9 and 10 (Claim 1.2.3.4)
(corresponding to).

This spark plug E has a cylindrical metal shell 4 and a rear end 1.
A cylindrical leg assembly 1 that is slightly narrower than the inner diameter of the metal shell 4 and has a convex portion 11; and a cylindrical corrugation portion that is slightly thinner than the inner diameter of the metal shell 4 at the tip and has a concave portion 21 formed therein. An insulator 2, a center electrode 6 fitted into each of the insulators 1.2, a ceramic bonding material size 7 of an insulating cross-section key fitted into the convex portion 11 and the concave portion 21, and a main metal μ4. It consists of silicone oil 8 placed in the gap between 1 and 2, and insulator 2.

The center electrode 6 is integrally heat-sealed with a terminal electrode 63 with a resistor 62 sandwiched therebetween.

Ceramic bonding material 7 is long leg insulator 1 (silicon nitride)
It has a coefficient of thermal expansion intermediate between that of the corrugation part insulator 2 (alumina) and the corrugation part insulator 2 (alumina). Moreover, this bonding material 7 is used for each insulator 1.
．． It is arranged so that all joint surfaces 16.25 of 2 are in contact with each other.

The silicone oil 8 is an insulator having a dielectric breakdown voltage of 50 kV/m 111 or higher.

(i) The spark plug F of this example had a significantly improved breakdown voltage limit.

(Icho margin) Table 1 Table 2

[Brief explanation of drawings]

FIG. 1 is a half sectional view showing a first embodiment of the present invention,
Assembling a spark plug for an internal combustion engine takes about two steps. FIG. 2 is a sectional view of a fitting portion of claim 1, and FIG. 3 is a sectional view of a fitting portion of claim 2, for explaining the function of each claim and the invention in detail. FIG. 4 is a half-sectional view showing a second embodiment and a third embodiment of a spark plug for an internal combustion engine according to the present invention. FIG. 5 is a sectional view showing a three-layer structure portion of a cylindrical glass according to a second embodiment of the present invention. FIG. 6 is a graph comparing bonding surface strength and bonding strength in the third embodiment of the present invention, with and without a silica layer. FIG. 7 is a half sectional view showing a fourth embodiment of a spark plug for an internal combustion engine according to the present invention. FIG. 8 is a cross-sectional view showing a ring-shaped joint according to a fourth embodiment of the present invention. FIG. 9 is a half sectional view showing a fifth embodiment of a spark plug for an internal combustion engine according to the present invention. FIG. 10 shows the fifth spark plug of the internal combustion engine of the present invention.
FIG. 3 is a cross-sectional view showing a fitting portion between a leg length insulator and a corrugation part insulator in an embodiment. In the figure: 1... Long leg insulator 2... Corrugation insulator 3... Cylindrical glass (insulating vitreous material) 4 - Metal shell 5... Ring-shaped joined body 6...
Center electrode 7 Ceramic bonding material (insulating ceramic material) 8 Silicone oil (paste-like insulator) 11 Convex portion 14 Convex outer surface (fitting surface) 15... Silica layer 16.25...joint surface (
Fitting surface) 21... Recess 24... Inner surface of the recess (fitting surface) 31... Outer oxide glass layer 32... Middle oxide glass layer 33... Inner oxygen Nitride glass layer 41...Caulked part 42...Packing contact surface A, B, C, D, F...Spark plug of internal combustion engine

Claims (1)

[Scope of Claims] 1) A cylindrical metal shell, a cylindrical leg insulator formed of silicon nitride ceramic and fitted into the tip side of the metal shell, and a rear part of the leg insulator. A spark plug for an internal combustion engine, comprising: a cylindrical corrugated part insulator made of alumina ceramic; and a center electrode fitted into each of the insulators; The bodies are fitted and joined by the concave portion and the convex portion, respectively, and a vitreous material or a ceramic material having a coefficient of thermal expansion intermediate between the silicon nitride ceramic and the alumina ceramic is interposed on the mating surface. A spark plug for an internal combustion engine characterized by: 2) The fitting of each insulator is performed between the caulking portion of the metal shell and the packing contact surface, and the glassy material or ceramic material is a combination of silicon nitride ceramic and alumina ceramic. The spark plug for an internal combustion engine according to claim 1, wherein the spark plug has a multilayer structure that asymptotizes the coefficient of thermal expansion. 3) The spark plug for an internal combustion engine according to claim 1 or claim 2, wherein the silicon nitride ceramic has a silica layer formed on a joint surface in an oxygen atmosphere. 4) The multilayer structure includes an inner oxynitride glass layer based on Al-Si-O-N and an outer Na_
Oxide glass layer such as 2O, B_2O_3, SiO_2 and the middle layer of Na_2O_3, B_2O_3, SiO_
4. The spark plug for an internal combustion engine according to claim 2, wherein the spark plug is a ring-shaped joined body comprising an oxide glass layer such as No. 2 or the like. 5) The spark plug for an internal combustion engine according to claim 1, wherein a paste-like insulator is filled in a gap between each of the insulators and the cylindrical metal shell.