JPH04113121A - Glow plug - Google Patents

Abstract

PURPOSE:To provide a gentle temperature gradient between the surface and the interior of a base substance made of W and to enable reduction of a thermal stress by a method wherein a heat generating substance is formed in a filmy state on the outer surface of the base substance made of W. CONSTITUTION:A heat generating substance is formed of a W film 9, a base substance is formed of a base substance 7 made of W, and an AlN film 8 is located therebetween. Thereby, the thermal expansion coefficients of constituting materials of a heat generating part 5 approximately coincide with each other, and the occurrence of fatigue damage due to a heat cycle is reduced. Besides, since the W heat generating substance 9 is formed on an outer surface, in addition to high thermal conductivity of the base substance 7, a temperature gradient on the surface part of the base substance 7 is low and a thermal stress due to a temperature difference is also low. An SiC film 12 formed on the surface of the heat generating part 5 to prevent oxidation of W improves oxidation resistance and corrosion resistance of the heat generating part 5, and durability is sharply improved. Since the thermal coefficient of the heat generating part 5 approximately coincides with that of the film 12, a residual stress after adhesion to the film 12 is reduced. The film 12 has high thermal conductivity and a temperature difference between the interior and the exterior of the film 12 is low.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a glow plug that is suitably used as an ignition source for internal combustion engines that use fuel with poor ignitability, and in particular to a glow plug that has significantly improved high-temperature durability. Regarding plugs.

[Prior Art] Generally, in order to combust a fuel with poor ignitability in an internal combustion engine, such as a diesel engine, it is necessary to take measures to assist ignition. Glow plugs used in automobile diesel engines are often used to assist in ignition.

The glow plug used has a heat generating part made of a ceramic sintered body.

In a glow plug equipped with a heat generating part made of a ceramic sintered body, the heat generating part uses a high melting point metal wire such as W (tungsten) as the heating element, and the heat generating part is buried deep in the surface of the sintered body. It has a structure that is molded and sintered. Note that this heat generating portion is fixed to the cylindrical casing so as to protrude from the tip of the casing. This casing has a male thread cut on its outer periphery, and is screwed onto an internal combustion engine or the like.

As the ceramic sintered body constituting the heat generating part, 5is
N+ (silicon nitride) is often used.

[Problems to be Solved by the Invention] Glow plugs for automotive diesel engines are used to assist in starting the diesel engine. Since the fuel for automobile diesel engines is light oil, ignition is ensured when the surface temperature of the glow plug is around 900°C when the engine is started. Once the engine warms up after starting, self-ignition of the diesel fuel becomes stable, so the glow plug is controlled to stop generating heat.

If a glow plug from an automobile diesel engine that is used under such surface temperature and operating conditions is used as an ignition source for a diesel engine that uses fuel with poor ignitability, the surface temperature will be over 1000°C and it will constantly generate heat. Because they are used under such harsh conditions, their durability is significantly reduced. The reason for this is: ■ The heating element is buried deep from the surface of the sintered body ■ Due to the low thermal conductivity of Si3N+, when trying to maintain the surface temperature at a high temperature, the temperature difference between the inside and outside becomes large, and the heat dissipates. The stress increases and this results in
This is because the ceramic sintered body becomes easily damaged.

In this way, conventional glow plugs can be heated to 900°C, especially 1
There was a problem in that it could not be used at high temperatures exceeding 000°C.

An object of the present invention is to solve the above-mentioned conventional problems and provide a glow plug with improved heat resistance and durability.

[Means for Solving the Problem] The glow plug according to claim (1) has a rod-shaped heat-generating portion, and the heat-generating portion includes a rod-shaped base made of W and a portion of the surface of the base made of W. an electrically insulating film that covers the surface with the exception of the electrically insulating film; a w′$,a that is continuously formed from the electrically insulating film to the part of the surface of the base; The glow plug of claim (2) is characterized in that, in the glow plug of claim (1), an electrically insulating film is formed between the W film and the oxidation-resistant film. It is characterized by being

Incidentally, in the present invention, the W base body may be one containing W as a main component, and a commercially available W rod containing a trace amount of additives may be used.

The heating element made of the W film that covers the W base may cover the entire surface of the W base, or may partially cover the W base. In the case of partial coating, the W coating is preferably formed so as to be evenly distributed on the surface of the W substrate.

Further, the oxidation-resistant coating material is not particularly limited, but silicon carbide (S i C), silicon nitride (Si3N4), etc. may be mentioned, and a coating film formed by CVD is preferable in terms of film density and film thickness.

In addition, as the electrical insulating film, aluminum nitride (AuN), aluminum oxide (AJ22
03) v Si3N4 is mentioned, and a coating film formed by PVD or CVD is used in view of the denseness of the film.

The oxidation-resistant coating material for the heat generating part is ■ Excellent oxidation and corrosion resistance even at high temperatures.

■ The thermal expansion coefficient is close to that of the heat generating part (CW base).

■High thermal conductivity.

However, the SiC film produced by the CVD method is a suitable material that satisfies all of the above characteristics. That is, since the CVD-3iC film is r1i1 dense and highly pure, it has high oxidation resistance and corrosion resistance even at high temperatures. Therefore, the tungsten coating and the tungsten substrate are prevented from being oxidized, and the oxidation resistance and corrosion resistance of the heat generating part are improved.

II Thermal expansion coefficient is 4.5X10-8/(room temperature ~ 40
(0°C), the coefficient of thermal expansion is close to that of the W base.

Therefore, residual stress after SiC deposition by CVD method is small, and fatigue caused by thermal cycles is small.

Hl has a high thermal conductivity compared to other ceramics. Therefore, the temperature difference between the inside and outside of the SiC film is small, and the change in temperature distribution due to film formation is small.

It has excellent characteristics.

As an electrical insulating film formed between the W base and the W film, the AuN film has a high thermal conductivity and has a coefficient of thermal expansion similar to that of W as shown in Table 1 below. suitable.

Table 1 [Function] In the glow plug of the present invention, the heating element provided on the surface of the W base is attached to a heating element layer made of W coating on the outer surface of the W base via an electrically insulating coating such as an AfLN coating. is formed. In this way, since the heating element is formed in the form of a film on the outer surface of the W base, the temperature gradient between the surface and the inside of the W base becomes gentle even when used at high temperatures, reducing thermal stress. . (On the other hand, if the heating element is buried deep from the base surface as in the past, when the glow plug becomes high temperature, the temperature gradient between the inside of the base and the base surface becomes steep. , high tensile thermal stress is generated near the base surface, and this thermal stress causes separation.) Additionally, the heating element is located near the surface of the glow plug body, increasing thermal efficiency and reducing power consumption. Ru.

Furthermore, since the main body of the heating section is composed of a W base, it has high thermal conductivity and high strength.

By the way, the heating element layer of the W film formed on the surface of the W base body is oxidized and deteriorates if it is exposed to the outside as it is. Furthermore, if the surface of the W base is exposed, it will deteriorate due to oxidation, but since the outer surface of the heat generating part is coated with an oxidation-resistant coating, oxidation of the W base and the W coating is prevented.

In addition, in order to cover the outer surface of the heat generating part with an oxidation-resistant film with low electrical insulation, an electrically insulating film is formed between the W film and the oxidation-resistant film, so that the electrical insulation is improved. .

[Examples] Hereinafter, the present invention will be described in more detail with reference to examples shown in the drawings.

FIG. 1 is a longitudinal sectional view of a glow plug according to an embodiment of the present invention, and FIG. 2 is an enlarged view of the main part of FIG. Reference numeral 1 denotes a casing, which is cylindrical and has threads 2 carved on its circumferential surface. A center electrode holding member 4 is provided at the rear end of the casing 1 with an electrical insulating material 3 in between. A positive lead wire is connected to the center electrode holding member 4 via a nut (not shown).

Reference numeral 5 designates a rod-shaped heat generating portion, the proximal end of which is inserted into the casing 1, and the outer circumferential surface of the heat generating portion 5 and the inner circumferential surface of the casing 1 are fixed by brazing. The area marked with a dot and number 6 in the figure indicates the brazed portion.

In this embodiment, the heat generating part 5 is made of a base body 7 made of W and a base body 7 made of W.
l1N film 8, W film 9, AAN film 11, and Si
C coating 12. AflN coatings 8 and 11 are provided as electrically insulating layers. The Al1N coating 8 is formed almost on the gold-side peripheral surface of the W base body 7 except for the tip.

The W film 9 has a Joule heat generating portion 9A having a small layer thickness and a conductive LEAT portion 9B having a large layer thickness. The Joule heat generating portion 9A of the W coating 9 is formed in the region on the tip side of the heat generating portion 5 of the AnNnN forming portion, and further includes the A
The 4N coating 8 is continuously formed over the tip surface of the W base body 8 on which the 4N coating 8 is not provided. This Joule heat generating part 9
The lead portion 9B continuous with A is provided up to the brazed portion 6, and is electrically connected to the casing 1 by brazing at the brazed portion. An Aj2N film 11 and a SiC film 12 are formed on this surface.

A center electrode 13 is inserted through and held by the center electrode holding member 4, and the tip end surface of the center electrode 13 is connected to the end surface of the base body 7 made of W.

In such a glow plug, the thickness of the Joule heat generating portion 9A of the W coating 9 is preferably 0.1 to 10 μm, and the thickness of the leat portion 9B of the W coating 9 is preferably 1 to 100 μm. The thickness of the AuN coatings 8 and 11 is 1 to 100 μm, and the SiC coating 12 is an oxidation-resistant coating.
It is preferable that the film thickness of is 5 to 800 μm.

In such a glow plug, among the surfaces of the base body 7 made of W,
The AflN coating 8 is coated by PVD method while masking the parts that require conduction (the connecting part between the center electrode 13 and the solder joint 6 on one end, and the connection between the W coating 9 (9A) and the W base 7 on the other end). Or formed by CVD method, and furthermore, 1 on the center electrode 8i13 side.
A portion including the end of the J2N coating 8 is masked, a W coating 9 is formed by a PVD method or a CVD method, and finally a portion of the W coating (lead portion) 9E including the solder row portion 6 is masked on the central electrode 8i13 side. , AuN film 11 is formed by PVD method or CVD method.
According to the method, the SiC film 12 can be manufactured by forming the SiC film 12 by the CVD method.

In this example, the SiC coating 1 has relatively low electrical insulation properties.
Since Aj2N is used, the Aj2N coating 11 is provided.

This is to mainly generate Joule heat in the Joule heat generating section 9A. When an oxidation-resistant film having electrical insulation properties is used, the Al1N film 11 may be omitted and may be formed directly on the W film 9.

The glow plug of this embodiment is made of a heating element or a W coating 9, and the base is made of a W base 7, with an AuN coating 8 interposed therebetween, so that the thermal expansion coefficient of the constituent material of the heating part 5 is almost match, and there is little fatigue damage due to thermal cycles. Moreover, in addition to the high thermal conductivity of the base 7, W on the outer surface
Since the heating element 9 is provided, the temperature gradient in the surface portion of the base body 7 is small, and the thermal stress due to the temperature difference is also small.

Furthermore, since the SiC film 12 formed on the surface of the heat generating part 5 to prevent oxidation of W is dense and highly pure,
The oxidation resistance and corrosion resistance of the heat generating part 5 are enhanced, and the durability is significantly improved. Moreover, since the thermal expansion coefficients of the heat generating portion 5 and the coating 12 are almost the same, the residual stress after the coating 12 is attached is small. Further, the coating 12 has high thermal conductivity, and
The temperature difference between the inside and outside of 12 is J'X.

Therefore, the glow plug of the above embodiment does not suffer from cracking due to thermal stress even when used at a high temperature of about 1300° C., and can be used in good condition.

[Effects of the Invention] As detailed above, the glow plug of the present invention has excellent heat resistance, excellent oxidation resistance and corrosion resistance, and is highly durable. Therefore, it exhibits excellent durability even at high operating temperatures when used as an ignition source in diesel engines and the like that use difficult-to-ignite fuels, and can be used stably for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a glow plug according to an embodiment, and FIG. 2 is an enlarged view of the main part of FIG. 1. 1...Casing, 5...Heating part, 7...
・W base, 9 (9A)・W? tL membrane (Joule heat generating part), 9 (9
B)... W coating (lead part), 8.11.AJ2N coating, 12-SiC coating. Agent: Patent Attorney Tsuyoshi Shigeno

Claims (2)

[Claims] (1) In a glow plug having a rod-shaped heat generating part, the heat generating part comprises: a rod-shaped tungsten base; an electrically insulating coating covering all but a portion of the surface of the tungsten base; A glow plug comprising: a tungsten coating formed continuously from an electrically insulating coating to the part of the surface of the base; and an oxidation-resistant coating covering the tungsten coating. (2) The glow plug according to claim 1, wherein an electrically insulating film is formed between the tungsten film and the oxidation-resistant film.