JPH06265144A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To provide a ceramic glow plug which can be easily removed from an internal combustion engine without breaking the plug even if carbon is fixed to a gap between a plug mounting hole of the engine and the plug. CONSTITUTION:A silicon resin layer 8 for preventing fixing of a ceramic glow plug to a plug mounting hole 12 is provided on an outer surface of a metal pipe 3 for holding a ceramic heater 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic glow plug for a diesel engine, which uses a ceramic heater for a heat generating portion.

[0002]

2. Description of the Related Art Conventionally, as ceramic heaters, various ceramic heaters have been proposed, such as one in which a high melting point metal is embedded in a ceramic as a heating element, or one in which a conductive ceramic is embedded in an insulating ceramic.

As a ceramic glow plug using such a ceramic heater, for example, a metal pipe is attached to the outer periphery of the ceramic heater by brazing, and the metal pipe is attached to one end of a cylindrical metal housing. Further, a structure in which they are joined by brazing or the like is widely adopted.

However, since such a ceramic glow plug is used in a diesel engine, carbon generated during operation is sequentially clogged in a slight gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug,
As a result, it is known that when the ceramic glow plug is removed from the internal combustion engine, the ceramic glow plug is broken due to the adhesion of carbon that is stuck in the gap between the plug mounting hole of the internal combustion engine and the ceramic glow plug.

As a countermeasure against this, conventionally, for example, as disclosed in Japanese Unexamined Patent Publication No. 4-161724, the temperature at the time of heat generation in the vicinity of the plug body of the end portion protruding from the plug body of the ceramic heater is determined by the ignition temperature of carbon. A method has been proposed in which the carbon is clogged in the gap between the glow plug mounting hole of the engine and the ceramic glow plug by burning it higher.

[0006]

However, even if the above measures are taken, it is still difficult to completely prevent breakage of the ceramic glow plug due to carbon sticking when the ceramic glow plug is removed.

In view of the above problems, the present invention provides a ceramic glow plug for an internal combustion engine without breaking the ceramic glow plug even if carbon is fixed in the gap between the plug mounting hole of the internal combustion engine and the ceramic glow plug. The present invention provides a ceramic glow plug that can be removed more easily.

[0008]

Therefore, the reason why we cannot completely prevent breakage of the ceramic glow plug by the conventional method is to intervene in the gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug. The cause was clarified by first investigating the state of carbon generation.

As a result, the carbon fixed in the gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug is not completely burned by the combustion of the light oil and the light oil / engine oil, but by the heat of combustion. It was found that it was formed from carbonized material.

That is, first, soft carbon generated by combustion is clogged between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug. Once the carbon is clogged, the fuel light oil and engine oil do not soak into the carbon and do not burn, but become the pyrolytic carbon by the heat of the glow plug and the heat at the time of combustion. By repeating this, carbon and pyrolytic carbon generated by combustion enter and fill a minute gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug, and as a result, the entire minute gap is covered by the carbon layer. Will be firmly fixed by.

As described above, the carbon interposed in the gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug is not only carbon after combustion but also carbon after combustion and pyrolysis carbon, so that it is better than conventionally thought. Since it is a stronger carbon, the structure of the ceramic heater has a structure in which the temperature at the time of heat generation in the vicinity of the plug body of the end portion protruding from the plug body of the ceramic heater is set higher than the ignition temperature of carbon, as in the past. It is impossible to completely prevent breakage of the ceramic glow plug because the temperature of only the portion near the plug body of the end portion protruding from the body is set higher than the ignition temperature of carbon and only the carbon in that portion is burned out.

Therefore, according to the present invention, in a ceramic glow plug having a housing and a ceramic heater held by the housing and protruding from one end side of the housing, the ceramic glow plug is mounted in a glow plug mounting hole of an internal combustion engine. In this case, the surface of the ceramic glow plug that faces the inner peripheral surface of the glow plug mounting hole is provided with a sticking prevention layer that prevents the ceramic glow plug and the inner peripheral surface of the glow plug mounting hole from sticking together. It is a glow plug.

[0013]

By adopting the above structure, even if carbon is firmly adhered to the gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug, the ceramic glow plug facing the inner peripheral surface of the plug mounting hole of the internal combustion engine. The surface of is provided with an anti-sticking layer that prevents sticking between the ceramic glow plug and the inner surface of the glow plug mounting hole, so that carbon does not directly contact the ceramic glow plug but through the anti-sticking layer. It will stick.

Therefore, when the ceramic glow plug is removed, the sticking prevention layer prevents sticking between the inner peripheral surface of the glow plug mounting hole and the ceramic glow plug, and even if the carbon is strong, the ceramic glow plug is broken. There is nothing to do.

[0015]

By adopting the present invention, even if carbon is firmly adhered to the gap between the glow plug mounting hole of the internal combustion engine and the ceramic glow plug, the ceramic glow plug can be provided to the internal combustion engine without breaking the ceramic glow plug. It has been possible to provide a ceramic glow plug that can be easily removed.

[0016]

EXAMPLES The present invention will be described below with reference to specific examples.
FIG. 1 is a cross-sectional view showing one structural example of the ceramic glow plug 1 of the present invention.

In FIG. 1, reference numeral 2 is a ceramic heater, which is made of an insulating ceramic in which a tungsten wire (not shown) such as a refractory metal or a heating wire made of a conductive ceramic is buried. Then, one end of the heating wire (not shown) is led to the end portion 2a of the ceramic heater 2, and the other end of the heating wire is led to the side surface 2b of the ceramic 2.

A side surface 2b of the ceramic heater 2 is plated with nickel, and a metal pipe 3 for holding the ceramic heater 2 is brazed and fixed so as to include the ceramic heater 2. . Then, one end of a cylindrical metal housing 4 having a mounting screw 4a for attaching to an engine (not shown) is joined to the outer periphery of the metal pipe 3 by brazing.

With this structure, one end of the metal wire led to the end 2a of the ceramic heater 2 is electrically connected to the metal cap 5 fitted to the end 2a of the ceramic heater 2. The metal cap 5 is electrically connected to a power source (not shown) via the nickel wire 6 and the center rod 7. Also, the ceramic heater 2
The other end of the metal wire led to the side surface 2b of the
Is electrically connected to. And this metal pipe 3
Is electrically grounded to a block of an internal combustion engine (not shown) through the metal housing 4.

On the outer surface 3a of the metal pipe 3 including the ceramic heater 2 projecting from the housing 4, a sticking prevention layer for preventing sticking of the ceramic heater 2 and the inner peripheral surface of the glow plug mounting hole of the internal combustion engine (not shown). A resin layer 8 made of a certain silicone resin is provided. The resin layer 8
Has a thickness of 0.2 mm and is formed on the entire surface of the metal pipe 3 in the longitudinal direction.

FIG. 2 is a diagram showing a main part when the ceramic glow plug 1 of the first embodiment shown in FIG. 1 is mounted on an engine 10 which is an internal combustion engine. Engine 10 is 2
It is a 200cc 4-cylinder diesel engine.

The ceramic glow plug 1 is connected to the engine 10
2, the heating portion 2c at the tip of the ceramic heater 2 is exposed in the combustion chamber 11, and the metal pipe 3 including the ceramic heater 2 is a plug mounting hole that is a glow plug mounting hole. 12 will be present. At this time, since the resin layer 8 is formed on the outer surface of the metal pipe 3 facing the inner peripheral surface of the plug mounting hole 12, the resin layer 8 is formed between the ceramic heater 2 of the ceramic glow plug 1 and the plug mounting hole 12. Has a structure in which the resin layer 8 is provided.

In FIG. 2, the gap A between the metal pipe 3 and the plug mounting hole 12 of the engine is 0.5 mm, the protective layer 3 is
The clearance B between the plug mounting hole 12 of the engine and the engine was 0.3 mm.

Next, the engine was operated in the mounted state shown in FIG. Considering the durability of the resin layer, the engine operating conditions are: a full load of 4000 rpm at which the glow plug is energized and the combustion temperature reaches its maximum, and a full load of 1000 rpm at which carbon is easily generated and adhered. The evaluation pattern was combined. Specifically, the glow plug is energized according to the evaluation pattern and the total load is 4000.
2 minutes rpm, full load 10 without glow plug energization
One cycle was performed at 00 rpm for 1 minute, a full load of 4000 rpm without energization of the glow plug for 1 minute, and a full load of 1000 rpm for 2 minutes without energization of the glow plug.

FIG. 3 shows the degree of clogging of carbon in the gap 13 between the plug mounting hole 12 of the engine 10 and the ceramic glow plug 1 after the test, and FIG. 4 shows the degree of clogging of the conventional ceramic glow plug.

As shown in FIGS. 3 and 4, after the engine 10 is operated under the above conditions, carbon 14 is entirely filled in the gap 13 in both the ceramic glow plug 1 of the first embodiment and the conventional ceramic glow plug.
Was jammed. In particular, in the case of the ceramic glow plug 1 of the first embodiment, the resin layer 8 was formed on the entire outer surface of the metal pipe 3 before the engine 10 was started, but due to the heat from the combustion chamber 11, A part of the metal pipe 3 on the heat generating portion 1c side was burnt out.

When these ceramic glow plugs are removed from the plug mounting holes 12, the conventional ceramic glow plugs that do not use the resin layer are the metal pipes 3.
The plug 13 of the engine 10 and the ceramic glow plug 1 are fixed by the carbon filled in the gap 13 between the plug and the plug 12 and the ceramic glow plug 1
When removing, the ceramic heater 2 etc. were broken.

However, in the case where the resin layer 8 which is the ceramic glow plug 1 of the first embodiment is provided, it is possible to remove the ceramic glow plug 1 without breaking the two of the four together with the resin layer 8. Further, the remaining two resin layers 8 remained in the plug mounting holes 12 of the engine 10, but could be removed without breaking the ceramic glow plug 1.

That is, only the portion where the resin layer 8 on the heat generating portion side of the metal pipe 3 of the ceramic glow plug 1 fixed to the plug mounting hole 12 is burned or carbonized, through the carbon 14, the metal pipe 3 and the plug mounting hole. 12 is only fixed, and the fixed length is sufficiently short, and the resin layer 8 and the plug mounting hole 12 are fixed via the carbon 14 in most of the lengthwise direction. . for that reason,
Since the resin layer 8 and the carbon 14 have a weak fixing force, the fixing force between the resin layer 8 and the plug mounting hole 12 becomes small. Therefore, when the ceramic glow plug is removed, the ceramic glow plug 1 can be easily removed due to the fixing force.

Further, even if the adhesion force between the surface of the resin layer 8 and carbon becomes strong for some reason, the metal pipe 3 comes off the resin layer 8 and leaves the resin in the plug mounting hole 12 of the engine 10. The ceramic glow plug 1 can be removed. And this engine 10
The resin layer 8 remaining in the plug mounting hole 12 is pushed into the combustion chamber 11 when the ceramic glow plug is mounted next time, and can be burnt out during engine operation.

Therefore, by adopting the first embodiment, even if the carbon 14 is firmly fixed in the gap between the plug mounting hole 12 of the engine 10 and the ceramic glow plug 1, when the ceramic glow plug 1 is removed, the ceramic glow plug 1 is removed. The breakage of the plug 1 does not occur.

From this, it was confirmed that the ceramic glow plug 1 of the first embodiment has a great effect on the fixation of the ceramic glow plug 1 to the plug mounting hole 12 of the engine 10 by carbon.

In the above embodiments, the silicone resin is used as the adhesion preventing layer, but the present invention is not limited to this. For example, in addition to silicone resin, any resin such as Teflon / polyolefin may be used. Good. Further, preferably, in consideration of the disappearance of the resin layer due to combustion in the combustion chamber, a layer made of a resin having a heat resistant temperature of 120 ° C. or higher can prevent breakage of the ceramic glow plug, More preferably, the heat resistant temperature of silicon resin or Teflon resin is 200 ° C. or higher.

Further, the thickness of the sticking prevention layer of the present invention is 5
It is preferably 0 μm or more. This is because if the thickness is 50 μm or less, the sticking prevention layer easily disappears due to heat and vibration from the combustion chamber.

In the above embodiment, the resin layer was formed by coating the silicone resin on the metal pipe by simple coating. However, a heat-shrinkable tube or the like may be wound around the metal pipe, or a strip shape may be formed. The anti-sticking layer may be attached. That is, any forming method may be used as long as the resin layer is provided between the ceramic glow plug and the plug mounting hole.

Further, although the sticking prevention layer is formed on the entire outer surface of the metal pipe 8 in the first embodiment, the present invention is not limited to this. For example, as shown in FIG.
By eliminating the gap between the metal pipe 3 and the plug mounting hole 12 of the engine 10 by the sticking prevention layer 15, carbon generated by combustion may be prevented from entering the gap between the glow plug and the plug mounting hole. With such a structure, it is possible to completely prevent the ingress of carbon and more reliably prevent the ceramic glow plug from being broken.

Further, as shown in FIG. 6, by forming the sticking prevention layer 16 only on the housing 4 side of the metal pipe 3,
From the beginning, the sticking prevention layer 16 may not be provided at the portion where the sticking prevention layer 16 disappears due to combustion in the combustion chamber.
With such a configuration, the disappearance portion of the sticking prevention layer 16 is eliminated from the beginning, and the same effect can be obtained by forming fewer sticking prevention layers 16.

Further, as shown in FIG. 7, the sticking prevention layer 17 may be formed only on the heat generating portion 2a side of the metal pipe 3, or as shown in FIG. 8, a tapered metal pipe 18 is formed. The sticking prevention layer 19 may be provided on the outer peripheral surface of the tapered metal pipe 18.

Furthermore, the sticking prevention layer of the present invention does not have to be provided on the outer peripheral surface of the metal pipe, but may be directly provided on the outer surface of the ceramic heater. That is, it is sufficient that the sticking prevention layer interposed between the ceramic glow plug and the plug mounting hole is not burned by the heat generated by energizing the ceramic glow plug and the engine operation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a ceramic glow plug showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram when the ceramic glow plug of the first embodiment of the present invention is mounted on an engine.

FIG. 3 is a state diagram showing a state after an engine test result of the ceramic glow plug of the first embodiment of the present invention.

FIG. 4 is a state diagram showing a state of a conventional ceramic glow plug after an engine test result.

FIG. 5 is a sectional view showing a ceramic glow plug showing another embodiment of the present invention.

FIG. 6 is a sectional view showing a ceramic glow plug showing another embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a ceramic glow plug showing another embodiment of the present invention.

FIG. 8 is a sectional view showing a ceramic glow plug showing another embodiment of the present invention.

[Explanation of symbols]

 1 Ceramic glow plug 8 Resin layer 12 Plug mounting hole 13 Gap

Claims (1)

[Claims] 1. A ceramic glow plug having a housing and a ceramic heater held by the housing and protruding from one end of the housing, wherein the ceramic glow plug is mounted in a glow plug mounting hole of an internal combustion engine, An adhesion preventing layer for preventing adhesion of the ceramic glow plug and the inner peripheral surface of the glow plug mounting hole is provided on a surface of the ceramic glow plug facing the inner peripheral surface of the glow plug mounting hole. Ceramic glow plug.