JPH0355785A - Heater built-in spark plug and its manufacture - Google Patents

Abstract

PURPOSE:To prevent flashover effectively by forming a ceramic heater on the small dia. portion in the middle of a foot-length portion. CONSTITUTION:A heater built-in spark plug 100, that an insulator 1 made up with a center electrode 2 inserted in an axial hole 11 is fitted into a cylindrical metal shell 3, has a ceramic heater 4 arranged in the foot-length portion 12 of the insulator 1. The heater 4 is provided with an exothermic body 41 composed of burned mixture of metal powder 55wt.%-95wt.% and ceramic powder 5wt.%-45wt.% and burned aluminum 42 to coat it with. The pattern of the exothermic body 41 is formed of three ring portions which are arranged at almost equal spaces in an axial direction in contact with the surface of the small dia. portion 13 and two lead portions which are in parallel to an axial direction in connection with both ends thereof.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an electric heater that is integrally arranged in the long leg portion of the insulator in order to prevent contamination and to improve the low-temperature startability of an internal combustion engine that uses hard-to-ignite fuel. related to spark plugs for internal combustion engines.

[Prior Art] As shown in FIG. 7, Japanese Utility Model Application Publication No. 55-10239 discloses a method in which a mixed paste of metal powder and ceramic powder is applied so as to be wrapped around the outer peripheral surface of the long leg portion 111 of the insulator 110. , a spark plug 100 with a heater is disclosed in which a ceramic heater 120 is integrally fired by simultaneous sintering. [Problems to be Solved by the Invention] However, this spark plug with a heater has the disadvantage that spark discharge occurs between the heater and the center electrode, so-called flashover, which easily damages the heater and the insulator. An object of the present invention is to provide a spark plug with a heater that has excellent flashover resistance between the heater and the center electrode protruding from the tip of the insulator, and a method for manufacturing the same. [Means for Solving the Problems] In order to achieve the above object, the present invention adopts the following precepts. 1) A spark plug in which an insulator with a shaft hole is fitted into a cylindrical main metal fitting, a center electrode is inserted into the shaft hole, and a ceramic heater is integrally disposed on the long leg portion of the insulator. A small diameter part is provided in the middle part of the long leg part of the insulator, and this small diameter part is made of a mixed fired product of 55% to 95% by weight of metal powder and 5% to 45% by weight of ceramic powder. A heating element with an arbitrary pattern is arranged, and its outer periphery is covered with a ceramic insulating layer. Here, the above numerical limitation is due to the following reason. metal powder 55
If the amount is less than 45% by weight (ceramic powder exceeds 45% by weight), the electric resistance value of the heating element becomes too high and the heating element generates little heat, making it impossible to obtain the desired surface temperature of the long leg portion. If the metal powder exceeds 95% by weight (ceramic powder is less than 5% by weight), the electrical resistance of the heating element becomes too low and a large current flows through the heating element, making it easy for the heating element to overheat. 2) A tank arrangement in which unevenness is provided on the surface of the tip side portion of the ceramic heater installation portion of the long leg portion of the insulator to increase the creepage distance between the tip of the maturing body and the tip of the center electrode. 3) The ceramic heater installation portion of the long leg portion of the insulator is placed rearward from the tip of the metal shell, and the inner periphery of the tip of the metal shell protrudes inward, and the protruding surface and the corresponding surface of the insulator A configuration in which the distance between the corresponding insulator surface and the tip of the heating element is set smaller than the distance between the corresponding insulator surface and the tip of the heating element. 4) Ceramic heaters are manufactured using the following process. (a) A small diameter part is provided on the outer periphery of the intermediate part of the long leg part of the unfired insulator, (b) 55% to 95% by weight of metal powder is provided on the surface of a ceramic green sheet with a thickness of 0.2 mm to 2.0 mm. % and a ceramic powder of 5% to 45% by weight are kneaded together with a binder and applied in an arbitrary pattern to form an unfired ceramic heater; (c) coating the unfired ceramic heater; (d) The green ceramic heater and the green insulator are manufactured by simultaneously firing the green ceramic heater and the green insulator by wrapping it around the small diameter portion of the long leg portion of the green insulator so that the surface faces inside and closely joining it.

[Actions and Effects of the Invention] <Regarding Claim 1> A ceramic heater coated with a ceramic insulating layer,
The shape is defined by the small diameter part located in the middle of the long leg.
Therefore, the distance between the tip of the heating element and the tip of the center electrode is
An extra insulation distance can be gained by the thickness of the ceramic insulation layer, and the contact surface between the ceramic insulation layer and the insulator increases, resulting in tighter adhesion. This effectively prevents flashover.

Regarding Claim 2> An extra insulation distance can be gained between the tip of the heating element and the tip of the center electrode by the amount of distance increased by the unevenness. This can increase the effect of preventing flashover.

<Regarding Claim 3> Spark discharge to areas other than the outer electrode occurs mainly between the tip of the metal shell and flashover to the heating element is prevented. <Regarding Claim 4> A green sheet (thickness Q, 2 mm to 2.0 mm) with a small diameter portion provided on the outer periphery of the intermediate portion of the long leg portion of the unfired insulator and a green ceramic heater formed on the surface thereof. It is wrapped around the small-diameter portion so that it is on the inside, tightly bonded, and fired simultaneously.

As a result, the ceramic insulating layer and the insulator are tightly integrated, and the heating element is securely buried within the long legs, increasing the flashover prevention effect and reducing the firing process only once. Excellent productivity.

The thickness of the green sheet is limited here for the following reasons.
If the thickness is less than 0.2 mm, the distance between the tip of the ceramic heater and the tip of the center electrode is too short, resulting in poor flashover resistance. Moreover, if the thickness is 2.0 mm or more, the time required for the ceramic heater to be energized and for the surface temperature of the long leg portion to reach a temperature of 400° C. to 600° C. necessary for preventing adhesion of carbon, etc. will be too long.

[Embodiment] An embodiment of the heater-equipped spark plug of the present invention will be explained based on FIGS. 1 to 4. As shown in Figure 1,
The heater-equipped spark plug 100 is constructed by fitting an insulator 1 into a cylindrical metal shell 3 into which a central electric wire 2 is inserted into a shaft hole 11. A ceramic heater 4 is disposed on the long leg portion 12 of the insulator 1. The insulator 1 is formed of a ceramic sintered body mainly composed of alumina, and includes a large-diameter body 10 and its tip side (one side shown).
and the long leg portion having a small diameter. Leg length part 12
has a tapered shape whose outer shape gradually decreases toward the distal end, and a small-diameter portion 13 is formed in the middle portion thereof.

Here, the dimensions of each part after sintering are as follows. The length p of the long leg portion 12 is 11.0 mm, and the length q of the small diameter portion 13 is 5.
．． 0 mm, the distance r between the tip of the small diameter portion 13 and the tip surface 14 of the insulator 1 is 3.0 mm, the distance S between the rear end of the small diameter portion 13 and the base is 3.0 mm, and the depth of the small diameter portion 13 t is 0.5 mm.

The center electrode 2 is made of a nickel alloy, and its tip protrudes from the tip of the insulator 1, forming a discharge section 21. The metal shell 3 includes a large-diameter body 30 in which the body 10 of the insulator is housed, and a body 30 that extends from the body 30 toward the distal end and is threaded on the outer periphery, and has long leg portions of the insulator. and a threaded portion 31 encasing it.

The tip of the threaded portion 31 is a tip 32 of the metal shell 3, and a key-shaped outer electrode 33 is welded to the tip surface.

The ceramic heater 4 includes a heating element 41 made of a fired mixture of 55% to 95% by weight of metal powder and 5% to 45% by weight of ceramic powder, and an alumina fired body covering the heating element 41. It consists of 42. In this embodiment, the pattern of the heating element 41 includes three open annular portions that are in contact with the surface of the small diameter portion 13 and are arranged at approximately equal intervals in the axial direction, and three open annular portions that are connected to both ends of the annular portions and are arranged at approximately equal intervals in the axial direction. It consists of two lead parts that are parallel to each other.

Next, a method for manufacturing the heater-equipped spark plug 100 will be explained with reference to FIGS. 2, 3, and 4. ■Thickness U is 0.3mm using doctor blade method or mold press etc.
Ceramic green sheets are manufactured with a vertical V of 6.0 m.
m, cut the width W to 20.0 mm and make a heater sheet 51.
(See Figure 3).

■Three unfired heating elements 50 are placed on the heater sheet 51 at equal intervals using a screen printing method using a platinum paste made by kneading 65% by weight of platinum powder and 35% by weight of ceramic powder with a binder. Print on one side 52.

■ Print unfired electrode extraction portions 53 on both ends of the heater sheet 51 by screen printing using a platinum paste made by kneading 95% by weight of platinum powder and 5% by weight of ceramic powder with a binder. ．． ■ A groove (see Fig. 2) having a length An unfired ceramic heater 5 is placed on the unfired insulator 6 so that the printed surface is on the inside.
Wrap it around and fire at the same time (see Figures 2 and 4). (2) Insert the center electrode 2 into the shaft hole 11 of the insulator 1 and fix it, and then fit it into the cylindrical metal shell 3 and complete the process.

Next, the above-mentioned spark plug 10 with a heater is installed in the internal combustion engine.
I will explain the performance test with 0 installed.

(1> Pre-ignition resistance A comparison of a comparison product (BCPR7E, leg length 11 mm) with a single-cylinder 125cc, 4-cycle motorcycle engine and a spark plug with heater 100 showed the same pre-ignition resistance. .

The comparative product has the same shape and material as the plug 100, and the diameter of the center electrode (not shown) is 2.5 mm. (2) Pre-delivery fouling resistance (rapid fouling test) 4 cylinders 1600cc
, using a comparison product and a spark plug 100 with a heater in a 4-cycle four-wheel vehicle engine, at -10°C and a vehicle speed of 3.
A rapid soiling test was conducted in which one cycle was a driving pattern of 5 km/h x 60 seconds, idling for 20 seconds, and 15 km/h x 40 seconds. Spark Blag 100 with a heater had an infinite insulation resistance value (see Figure 5). In other words, this indicates that the ceramic heater 4 has burned out the carbon. (3) Ceramic heater temperature rise characteristics (temperature of the long legs of the insulator was measured using a radiation thermometer on a desk) The applied voltage was 1
2V, heater power consumption 15W, ceramic heater 4
The thickness is in the range of 0.1 mm to 3.0 mm (see Figure 6)
It was measured with Spark plug 10 with heater of this embodiment
0 has the following effects. (a) Platinum powder 65 is placed in the middle part of the long leg part 12 of the insulator
% by weight and ceramic powder 35% by weight
1, the surface temperature of the long leg portion 12 can be effectively raised during ignition, leading to improved low-temperature startability of an internal combustion engine using hard-to-ignite fuel. Furthermore, carbon and the like can be burned off to prevent their adhesion.

(a) Since the heater sheet 51 has a thickness U of 0.3 mm, the flashover voltage is high. Further, the surface temperature of the ceramic heater 4 reaches the saturation temperature in about 35 seconds (see Figure 6). The thickness U of the heater sheet 5l is O-
Since the distance is 2 mm or more, it is necessary to connect the ceramic heater 4 from the center electrode 2.
It can overcome flashover to (heating element 41). Furthermore, a more preferable thickness U is in the range of 0.3 mm to 1.0 mm. (C) The flashover voltage is high because the distance r between the tip of the small diameter portion 13 of the insulator 1 and the tip surface 14 of the insulator 1 is 3.0 mm. Here, if the distance r is 2.0 mm or less, the flashover voltage is 15
Flashover occurs at about kv to 20kv. (Engineering) The smaller the diameter of the small diameter portion 13, the more difficult it is for sparks from the center electrode 2 to wrap around, resulting in better flashover resistance. Here, if the distance t is less than 0.1 mm, flashover will occur even at a low voltage. In addition to the above embodiments, the present invention also includes the following embodiments.

a. When wrapping the heater sheet 51 around the long leg portion 12 of the insulator 1, alumina paste may be applied as an adhesive to improve bonding with the surface of the heating element 41.

b. Since platinum paste is expensive, tungsten paste (tungsten is very easily oxidized, so firing in a hydrogen atmosphere is required) may be used as the heating element 41.

[Modification] FIG. 8 shows the ceramic heater 4 of the long leg portion 12 of the insulator 1.
An embodiment is shown in which the surface of the distal end side portion of the disposed portion is provided with irregularities to increase the creeping distance between the distal end of the heating element 41 and the distal end portion (discharge portion) 21 of the center electrode.

A bulges the outer periphery of the tip 15 of the insulator 1 outward;
B makes the outer edge of the tip surface 14 of the insulator protrude forward;
In C, a corrugation 16 is provided on the outer periphery of the tip 15 of the insulator. In either case, the creepage distance between the tip 41a of the heating element 41 and the tip (discharge portion) 21 of the center electrode increases, and the effect of preventing the occurrence of flashover can be improved.

FIG. 9 shows that the ceramic heater 4 mounting portion of the long leg portion 12 of the insulator is arranged rearward from the tip 32 of the metal shell 3, and the inner periphery of the tip 32 of the metal shell 3 protrudes inward. , the distance L1 between the protruding surface 32a and the corresponding surface 12a of the insulator long leg portion 12, and the distance tll between the corresponding insulator surface 12a and the tip 41a of the heating element 41.
It is set smaller than L2.

In this embodiment, spark discharge (flashover) other than normal aerial spark discharge that occurs mainly between the discharge part 21 of the center electrode and the outer electrode 33 is caused by the metal shell tip 32 and the corresponding insulator. The flashover to the heating element 41 is prevented.
Therefore, the durability of the insulator 1 and the heating element 41 can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic assembly diagram of a heater-equipped spark plug showing an embodiment of the present invention, and FIG. 2 is a perspective view of an unfired insulator used in the heater-equipped spark plug. FIG. 3 is a perspective view of a green ceramic heater, and FIG. 4 is a perspective view of the green ceramic heater wrapped around a green insulator. Figure 5 is a graph showing pre-delivery contamination resistance characteristics;
The figure is a graph showing the temperature rise characteristics of a ceramic heater.
Figure 7 is a cross-sectional view of a conventional spark plug with a heater. 8A, B, and C are sectional views of essential parts of a modified example of the present invention, and FIG. 9 is a sectional view of essential parts of another modified example of the present invention. In the diagram 100...Spark plug with heater 1...
Insulator 2... Center electrode 3... Cylindrical metal shell 4
... Ceramic heater 5 ... Unfired ceramic heater 6 ... Unfired insulator l1 ... Shaft hole 12, 6
l... Long leg part l3, 62... Small diameter part 41...
Heating element 42...Alumina fired body (ceramic insulation layer)
50... Unfired or heating element 51... Heater sheet (ceramic green sheet)

Claims (1)

[Claims] 1) An insulator with a shaft hole is fitted into a cylindrical main metal fitting, and a center electrode is inserted into the shaft hole with the tip thereof protruding,
In the spark plug in which a ceramic heater is integrally arranged on the long leg portion of the insulator, the ceramic heater is provided with a small diameter portion in the middle portion of the long leg portion of the insulator, and metal powder is applied to the small diameter portion in the middle portion of the long leg portion of the insulator. It is composed of a fired mixture of 55% to 95% by weight and 5% to 45% by weight of ceramic powder, and is formed by arranging a heating element with an arbitrary pattern and covering the outer periphery with a ceramic insulating layer. , A spark plug with a heater. 2) In the heater-equipped spark plug according to claim 1, the surface of the distal end side portion of the ceramic heater disposed portion of the long leg portion of the insulator is provided with irregularities, and the creepage distance between the distal end of the heating element and the distal end portion of the center electrode is increased. A structure with increased . 3) In the heater-equipped spark plug according to claim 1 or 2, the ceramic heater disposed portion of the long leg portion of the insulator is arranged rearward from the tip of the metal shell, and the inner periphery of the tip of the metal shell projects inward; The distance between the protruding surface and the corresponding insulator surface,
A configuration in which the distance is set smaller than the distance to the tip of the heating element. 4) Manufacturing a spark plug with a heater in which an insulator with a shaft hole is fitted into a cylindrical main metal fitting, a center electrode is inserted into the shaft hole, and a ceramic heater is integrally disposed on the long leg portion of the insulator. In the method, the ceramic heater includes: (a) a small diameter portion is provided on the outer periphery of the intermediate portion of the long leg portion of the unfired insulator, and (b) metal powder is provided on the surface of a ceramic green sheet having a thickness of 0.2 mm to 2.0 mm. A paste prepared by kneading 55% to 95% by weight and 5% to 45% by weight of ceramic powder with a binder is applied in an arbitrary pattern to form a green ceramic heater, (c) the green ceramic The heater is wrapped around the small diameter part of the long leg part of the unfired insulator so that the coated surface faces inside, and the heater is tightly bonded to the long leg part of the unfired insulator, and (d) the unfired ceramic heater and the unfired insulator are manufactured by co-firing. A method for manufacturing a spark plug with a heater.