JPS58106325A - Directly-heat type preheating plug for internal- combustion engine - Google Patents

Abstract

PURPOSE:To improve the rapid heating property and to improve the mechanical strength and the reliability in the operation by forming a heater which is exposed on the exterior of a metal plug as a substantially U-shaped current path having specific resistance. CONSTITUTION:A directly-heated preheating plug is composed of a metal plug body 1 formed of soft steel or the like, a conductor 2 of nichrome buried in insulation from the plug body 1 in the inner hole of the plug body 1, and a heater 3 which is connected to the end of the conductor 2 and has a resistance of approx. 0.1-10 ohms exposed on the exterior of the body 1. The conductor 2 is buried in insulating powder 5 which is filled in a sheath 4, is bent at one upper end 2A at the top of the sheath 4, and is hermetically fixed by silver brazing 6. The conductor 2 is further inserted at the other upper end 2B through a terminal shaft 9, and is hermetically sealed at 10 by argon arc welding or the like. The heater 3 is formed in U-shape, and is installed at the step 1C of the inner hole of the body 1 together with alumina holder 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct heating preheating plug for an internal combustion engine, and more particularly to a direct heating preheating plug for an internal combustion engine in which a heating element is exposed outside the plug for rapid heating.

As typical types of preheating plugs used in internal combustion engines, there are known indirect heating types in which a heating element is embedded in a sheath and direct heating types in which a coiled metal heating wire is exposed to the outside.

In the indirect heating type, the inside of the metal sheath is filled with ceramic insulating powder with a diameter of 0.4 (mm) and a length of 40 (mm).
mm) gold W4 wire (resistance value per wire: 0.39)
It is embedded in a coil shape and has great structural strength and durability against combustion gas, so it is currently the mainstream preheating plug for internal combustion engines. However, since heating is an indirect method, energy loss during heating is large, especially I
When rapid heating is required, the temperature of the internal heating element must be adjusted properly, which reduces durability and makes it difficult to raise the sheath surface temperature to 950C or higher. In recent years, there has been a demand for diesel engines to start as quickly as gasoline engines, and indirect heating type preheating plugs cannot adequately meet these demands.

On the other hand, a direct heating type preheating plug generally has a diameter of 2 (mm) and a length of 1.
It is formed by exposing a coiled metal of approximately 0.00100 as a heating coil, but although such a preheating plug with an exposed heating surface has good rapid heating properties, it does not heat up due to direct contact with combustion gas. The deterioration of the heating wire is a big problem, and short circuits are likely to occur due to unburned carbon adhesion during use.Furthermore, the resistance of the heating wire is about 0.04Ω, so in order to obtain an appropriate current, it is necessary to The disadvantage is that if one of the preheating plugs is disconnected due to the reasons mentioned above, the entire preheating plug becomes inoperable.Furthermore, the surface temperature of the heating element is approximately 900r was the limit.

It is an object of the present invention to provide a direct heating preheating plug for an internal combustion engine which takes advantage of the good rapid heating properties due to the exposed heating surface and has improved strength and operational reliability. be.

The present invention includes a conductive portion electrically insulated and housed in a metal stopper, and the conductor 1! A direct-coupled preheating plug for an internal combustion engine, which is connected to a part c and has a heating element exposed to the outside of the plug, and has an airtight sealing structure against high-temperature and high-pressure gas. Approximately 0.1 to 10
It is characterized in that it is designed as a substantially U-shaped current path with a resistance in the range of Ω.

An embodiment of the present invention will be described in detail below with reference to the drawings.

The basic structure of the direct-coupling preheating plug of this embodiment shown in FIG. The plug is equipped with a conductor 2 made of nichrome and a heating element 3 connected to the tip of the conductor 2 and exposed to the outside of the stopper.

The conductor 2 is embedded in an insulating powder (MgO, etc.) 5 that is minutely filled in a stainless steel sheath 4, and the upper end of the sheath 4 is located at the enlarged diameter part IA of the inner hole of the plug 1. It is exposed inside and forms an annular space between it and the inner wall of the plug body. One upper end of the conductive part 2 is bent into this space, and silver soldering 6 is applied to this part to provide an airtight sealing structure to prevent leakage of high temperature and high pressure gas. The other upper layer 2B of the conductor 2 is drilled out through a through hole in the terminal shaft 9 surrounded by insulating washers 7 and 8, and the tip [10] is sealed by argon arc welding. The upper periphery of the insulating washer 8 is caulked by the bent periphery @IB of the upper end of the plug body 1, and is tightened for earthquake resistance. A lock nut 11 is screwed into the thread groove of the terminal shaft 9, and is designed to identify a connection line from a power source that supplies heating current to the preheating plug.

In this embodiment, as shown in FIGS. 1 and 2, the heating element 3 is formed into a U-shape and is installed in the step IC of the inner hole of the plug body 1 together with the holder 12 behind the alumina. There is. Here, the current passing cross section of the heating element 3 is Z5X1.5
It has a flat U-shape with a length of 15 mm (4.5 mm in length) and can be assembled into a preheating plug with a 10 mm mounting screw. Further, the resistance value of the heating element 3 is set to about 0.8Ω in this embodiment by using 8iC obtained by a reaction sintering method.

An insulating thin film 3A is formed on the surface of the exposed portion of the heating element 3 in order to prevent current short-circuiting. Further, a heat-resistant metal thin film made of nickel is firmly fixed to the upper part of the heating element, and serves as an electrode outlet 3B at each lower end 2C, 2D of the conductive part 2.
It is connected to by nickel brazing 13.

Furthermore, the upper part of the heating element 3 is seismically fixed to the inner hole wall of the plug body 1 with heat-resistant and insulating solidified cement 14 such as aron ceramic. A protective louver 15 is provided on the outer periphery of the exposed portion of the lock heating element 3 with a predetermined radial gap to prevent the heating element 3 from being damaged by external force. In other figures, ID is a mounting screw for the plug.

In this embodiment, since the heating element 3 is exposed to the outside of the plug body 1, it is possible to obtain the good heating speed characteristic of a direct-coupled preheating plug and to effectively use electric energy. can be used. In particular, in this embodiment, the heating element 3 is formed as a flat U-shaped current path that provides a resistance value that allows for good heating speed and has a relatively simple structure. There is no risk of mutual short-circuiting or damage, and it is possible to operate satisfactorily with high reliability over a long period of time. Furthermore, in this embodiment, since the heating element is made of silicon carbide (8iC), which has excellent oxidation resistance, the heat resistance limit can also be increased to about 1oooc,
Moreover, its high thermal conductivity and small coefficient of thermal expansion allow it to have significantly excellent thermal shock resistance.

In this example, when a voltage of IIV is applied, 1000 tl? within 1 second? It was possible to obtain a heating temperature of .

The resistance value of the heating element is preferably about 0.1 to 10 Ω, particularly about 0.3 to 1 Ω, in order to obtain good heating properties. Therefore, in this example, SiC with a specific resistance of 0.01 to 0.02 Ω obtained by a reaction sintering method is used as the ceramic for the heating element, but any suitable metal may be used as the ceramic for the heating element. It is also possible to use oxides, carbides, borides, or even a mixed system of metal and gold II4 oxide, and these may be formed in any size so as to obtain a U-shaped electrical path with the required resistance value. In this specification, the U-shaped shape of the heating element refers to a simple shape that is inevitably formed by the outgoing and returning power supply paths including the heating part of the heating element, and therefore, in this sense, it is not meant to be a strict U-shape. Not needed.

In addition, the insulating thin film formed on the heating element part may be obtained by thermal spraying and vapor deposition of ceramic powder such as metal oxide, nitrite, and charcoal. When used, an insulating oxide thin film can be formed on the surface simply by heating it in the atmosphere.

As described above, according to the present invention, it is possible to obtain a direct heating type preheating plug for an internal combustion engine that has excellent rapid heating properties and extremely reliable operation during use.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of the present invention, and FIG. 2 is a view taken along the line ■--■ in FIG.

Claims (1)

[Claims] 1. A conductive part electrically insulated and housed in a metal plug body, and a heating element connected to the conductive part and exposed to the outside of the plug body, and a high-temperature, high-pressure device. A direct heating type preheating plug for an internal combustion engine that has an airtight sealing structure against gases,
1. A direct heating type preheating plug for an internal combustion engine as described above, characterized in that the exposed heating element is formed as a substantially U-shaped current path having a resistance in the range of about 0.1 to 10 Ω. 2. The direct heating type preheating plug for an internal combustion engine according to claim 1, wherein the heating element is made of a ceramic material. 3. A patented direct heating type preheating plug characterized in that the heating element is made of silicon carbide.