JPH09303773A - Ceramic glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic glow plug which displays an excellent perfor mance, and has a long life as well even when being used under a severe condi tion for diesel engine which uses aocohol and a natural gas, etc., as a fuel. SOLUTION: This ceramic glow plug comprises of a holding part 4 comprising a housing 41 or a metal sleeve 42 being provided in the housing 41, a heater 2 which is inserted in the holding part 4 and is directly held by the holding part 4, and a protective pipe 3 made of a metal, which is arranged so as to cover the leading end of the heater 2. The protective pipe 3 is fixed to the holding part 4. When the outer diameter of the protective pipe 3 is taken as E, the inner diameter is taken as D, and also, the outer diameter of the heater 2 is taken as (d), it is desirable satisfy the following relations 0.15mm<=(E-D)/2, and (E<2> -d<2> )/d<2> <=1.5.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a ceramic glow plug having excellent durability, which can be used for a diesel engine that uses a fuel such as alcohol or natural gas.

[0002]

2. Description of the Related Art As a glow plug for a diesel engine, as shown in FIG. 10, there is a ceramic glow plug 9 having excellent temperature raising performance, heat resistance, durability and the like. The ceramic glow plug 9 includes a heater 2 in which a heating element (not shown) made of an inorganic conductive material such as a refractory metal or a conductive ceramic is embedded in a ceramic skin 21 made of a silicon nitride sintered body. It is composed as the main part.

As shown in FIG. 10, the heater 2
Is held by a metal sleeve 42 provided inside the housing 41, and is also connected to the current-carrying inner shaft 6 via a connecting fitting 7. The center shaft 6 is attached to the housing 4 by the glass seal 84, the insulating bush 83 and the nut 82.
It is held while maintaining an insulating state from 1. Reference numeral 62 is a terminal screw portion of the center shaft 6.

On the other hand, from the viewpoint of environmental problems, diesel engines using alcohol, natural gas or the like as a clean fuel instead of light oil have been developed. However, although the above-mentioned conventional ceramic glow plug 9 has been found to have sufficient durability when used in a diesel engine that uses ordinary light oil as a fuel, it was used in a diesel engine that uses the above alcohol or natural gas. In this case, there is a problem of deterioration at an early stage.

That is, when alcohol or natural gas is used as the fuel, the ceramic skin 21 made of a silicon nitride sintered body on the surface of the heater 2 is thinned in a short time, and the heating element therein is exposed and oxidized. ， The function stops. It is considered that this is because the proportion of the glow plug 9 exposed to high temperature is higher in the case of using alcohol or natural gas than in the case of light oil, which promotes the oxidation and decomposition of silicon nitride. To be

On the other hand, conventionally, as shown in FIG.
There is a ceramic glow plug 92 having another structure (Japanese Utility Model Publication No. 55-171877). As shown in FIG. 11, the ceramic glow plug 92 is formed by enclosing the heater 2 similar to the above in a thin metal protection pipe 93 and joining the protection pipe 93 to the housing 41. In this case, the contact between the combustion gas and the heater 2 can be blocked in the combustion chamber, which is considered to be effective in preventing the above deterioration.

[0007]

However, the above conventional ceramic glow plug has the following problems. That is, in the ceramic glow plug 92 of the type having the conventional protection pipe 93, as described above, the heater 2 is enclosed in the thin protection pipe 93 and the protection pipe 93 is fixed to the housing 41. That is, the heater 2 is directly held by the protection pipe 93.

In this structure, the heater 2 may be gradually displaced due to the influence of the coefficient of thermal expansion and the like due to a severe thermal history during actual use. This misalignment causes various troubles such as pushing up the center shaft 6 located above the heater 2, leading to a reduction in life.

Further, as a means for improving the holding force between the protective pipe 93 and the heater 2, there is a method of brazing the protective pipe 93 and the heater 2. However, in this case, there are the following problems. That is, first, the tip end side of the protection pipe 93 is closed. Therefore, when the heater 2 and the protection pipe 93 are heated and the molten brazing material is poured between them, the air in the protection pipe 93 expands and blows out. Therefore, the productivity of the ceramic glow plug is greatly reduced.

Further, as described above, the protective pipe 93 is thin. Therefore, for the brazing above, the protective pipe 9
The strength problem of 3 also affects. That is, in the joining by brazing, a kind of shrink fitting effect is obtained by pouring the melted brazing material into the gap generated by heating due to the difference in the coefficient of thermal expansion between the protective pipe 93 and the heater 2 and then cooling. To secure the joining force. Therefore, if the protective pipe 93 is thin, it easily causes deformation and the like, and it is difficult to secure a strong shrink fitting force.

On the other hand, in order to secure a strong shrink fitting force, it is conceivable to thicken the protective pipe 93. However, in this case, the heat generated by the heater 2 is less likely to be transmitted to the surface of the protective pipe 93. Therefore, the performance of the ceramic glow plug itself is degraded.

As described above, in the conventional ceramic glow plug 92 having the protection pipe 93, there is no effective means for firmly holding the heater 2. Therefore, even though the life of the heater 2 itself can be improved by the protection pipe 93, the life of the heater 2 cannot be increased as a result of the problem of the holding force of the heater 2.

The present invention has been made in view of the above-mentioned conventional problems, and exhibits excellent performance and long-term performance even when used under severe conditions in a diesel engine using alcohol, natural gas or the like as a fuel. It is intended to provide a long life ceramic glow plug.

[0014]

According to a first aspect of the present invention, a holding portion formed of a housing or a metal sleeve provided inside the housing, a heater inserted into the holding portion and directly held by the holding portion, and a tip portion of the heater. The ceramic glow plug is characterized in that it is made of a metal protective pipe arranged so as to cover the above, and the protective pipe is fixed to the holding portion.

What is most noticeable in the present invention is that the heater is not directly held by the protection pipe covering the heater but is directly held by the holding portion, while the protection pipe is That is, it is fixed to the holding portion. The holding portion may be composed of only the housing, or may be composed of only the metal sleeve provided inside the housing. Further, it may be constituted by the housing and the metal sleeve.

Next, the function and effect of the present invention will be described. In the ceramic glow plug of the present invention, the heater is covered with the protective pipe. Therefore, in actual use, the heater is shut off from the combustion gas. Therefore, the heater does not oxidize or decompose, and its deterioration can be reliably prevented.

The heater is directly held by the holding portion without the protection pipe. for that reason,
For example, even if there is a difference in the amount of expansion and contraction between the heater and the protective pipe due to the difference in the coefficient of thermal expansion between them, the positional displacement of the heater does not occur. That is, the expansion and contraction of the protective pipe does not affect the heater. Therefore, there is no possibility that the heater will be displaced and the life of the ceramic glow plug will be shortened as in the conventional case.

As described above, the ceramic glow plug of the present invention has both excellent durability of the heater itself and excellent structural stability that does not cause displacement of the heater. Therefore, according to the present invention, it is possible to obtain a ceramic glow plug that exhibits excellent performance and has a long life even when used under severe conditions in a diesel engine that uses alcohol or natural gas as a fuel.

Next, when the outer diameter of the protective pipe is E, the inner diameter is D, and the outer diameter of the heater is d, as in the second aspect of the invention, 0.15 mm≤ (ED) It is preferable that / 2, and (E ² −d ² ) / d ² ≦ 1.5. Here, the value of (ED) / 2 corresponds to the thickness of the protective pipe. Further, the value of (E ² −d ² ) / d ² represents the ratio of the cross-sectional area represented by (cross-sectional area of the entire heat generating portion−cross-sectional area of the heater) to the cross-sectional area of the heater.

If (ED) / 2, that is, if the thickness of the protection pipe is less than 0.15 mm, corrosion of the protection pipe may be promoted by repeated heating and cooling in the combustion chamber. There is a problem, preferably 0.2 mm or more. The upper limit of the thickness is preferably set to 1 mm in consideration of heat conduction of heat generated by the heater.

Further, if the value of (E ² −d ² ) / d ² exceeds 1.5, there is a problem that durability against energization deteriorates. Here, the energization durability is evaluated by the time until the heater is broken so that the heater is continuously energized so that the surface of the protective pipe is maintained at a constant high temperature (for example, 1000 ° C.).

Further, as in the invention of claim 3, it is preferable that the protection pipe is fixed to the holding portion by welding. As a result, the fixed state between the protective pipe and the holding portion can be made very strong. As the welding method, there are laser welding, brazing, resistance welding and the like. The welding may be performed on the entire circumference of the protective pipe or may be performed partially.

Further, as in the invention of claim 4, it is preferable that the protective pipe is fixed to the housing so as to cover the heater and the metal sleeve. As a result, the fixed portion can be arranged outside the combustion chamber, and the fixed portion can be prevented from being heated during use.

Further, as in the fifth aspect of the invention, an inorganic material powder may be filled between the protective pipe and the heater. As a result, heat conduction between the heater and the protection pipe can be improved.

Further, as in the sixth aspect of the invention, silicon nitride can be used as the inorganic material powder. In addition, ceramic powder such as alumina or magnesium oxide may be used. Further, instead of powder, for example, a heat resistant metal pipe or the like can be filled.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 A ceramic glow plug according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the ceramic glow plug 1 of this example includes a holding portion 4 formed of a metal sleeve 42 provided inside a housing 41, and a holding portion 4.
The heater 2 inserted into the inside and directly held by the holding portion 4.
And a protective pipe 3 made of stainless steel (SUS310S) arranged so as to cover the tip of the heater 2.

As shown in FIG. 1, the protective pipe 3 is composed of a cap portion 32 for covering the tip of the heater 2 and a fixing portion 34 into which the holding portion 4 is inserted, and a step portion 33 is provided between them. is there. The step portion 33 contacts the tip of the metal sleeve 42 of the holding portion 4 and plays a role of positioning the protective pipe 3.

The protective pipe 3 is fixed to the holding portion 4 by welding the welded portion 35 of the fixed portion 34. The welding method is laser welding over the entire circumference. In addition, a slight gap 23 is provided between the protective pipe 3 and the heater 2 because of the assembling property.

The heater 2 has a heating resistor embedded in a ceramic skin 21 made of a silicon nitride sintered material. The heater 2 is provided with the metal sleeve 42 of the holding portion 4.
In contrast, it is firmly held directly by brazing.
The metal sleeve 42 and the housing 41 are also firmly joined by brazing.

Further, as shown in FIG. 1, the heater 2 is connected at its upper end to a current-carrying inner shaft 6 through a connecting fitting 7. Further, the center shaft 6 is fixed by a nut 82 while maintaining an insulating state with the housing 41 via a glass seal 84 and an insulating bush 83. Further, the center shaft 6 has a terminal screw portion 62 at its upper end.

Next, the function and effect of this example will be described. In the ceramic glow plug 1 of this example, the heater 2 is covered with a protective pipe 3. Therefore, in actual use, the heater 2 is shut off from the combustion gas. Therefore, the heater 2 is hardly oxidized or decomposed and its deterioration can be surely prevented.

The heater 2 is directly held by the holding portion without the protection pipe 3. That is, the heater 2 is
It is firmly brazed to the holding portion 4. On the other hand, the protective pipe 3 is directly welded and fixed to the holding portion 4. Therefore, even if a difference in expansion and contraction between the heater 2 and the protective pipe 3 occurs due to a difference in thermal expansion coefficient between them, the positional displacement of the heater 2 does not occur. That is, the expansion and contraction of the protection pipe 3 does not affect the heater 2.

Therefore, the life of the ceramic glow plug is not shortened due to the displacement of the heater 2 as in the conventional case. As described above, the ceramic glow plug 1 of this example has both excellent durability of the heater 2 itself and excellent structural stability in which the heater 2 is not displaced.

Therefore, according to this example, even if the diesel engine using alcohol, natural gas or the like as a fuel is used under severe conditions, it exhibits excellent performance.
Also, a long-life ceramic glow plug can be obtained.

Embodiment 2 In this embodiment, the ceramic glow plug 1 of Embodiment 1 was used, and a test was conducted on the relationship between its size and shape and durability. That is, when the outer diameter of the protective pipe 3 is E, the inner diameter is D, and the outer diameter of the heater 2 is d, (E-
The relationship between the value of D) / 2 and the value of (E ² −d ² ) / d ² and the durability was tested.

First, the value of (ED) / 2, that is, the thickness of the protective pipe 3 and the durability of the ceramic glow plug 1 were tested. As shown in Table 1, as the ceramic glow plugs for the test, those having a plurality of dimensions and shapes in which the above E, D and d values were variously changed were prepared (Sample No.
1-11). Nothing was particularly filled in the gap 23 between the heater 2 and the protection pipe 3.

The test was carried out by actually mounting each of the plurality of ceramic glow plugs on a diesel engine. Then, the corrosion state and the like of the protective pipe 3 after operating for 2000 hours under the condition that the surface temperature of the protective pipe 3 was 1000 ° C. were observed. Empirically, it can be judged that the ceramic glow plug has sufficient durability if there is no practical problem as a result of being used for 2000 hours under the above conditions.

The evaluation results are shown in Table 1. As is known from Table 1, when the value of (ED) / 2 was 0.15 mm or more, good results were obtained without any practical problems. Especially 0.
When the thickness was 2 mm or more, the oxidation of the protective pipe 3 was very slight, and there was no problem at all. On the other hand, when it was less than 0.15 mm, holes were formed due to corrosion.

From this result, the thickness of the protective pipe 3 was reduced to 0.
It can be seen that excellent durability can be obtained by setting the thickness to 15 mm or more, and further to 0.2 mm or more.

[0040]

[Table 1]

Next, the influence of the mounting of the protective pipe 3 having a relatively large heat capacity around the heater 2 on the current-carrying durability was tested. As shown in Table 2, a plurality of ceramic glow plugs for testing were prepared by changing the above E, D, and d variously (Sample Nos. 12 to 31).
Further, in the gap 23 between the heater 2 and the protection pipe 3,
I didn't fill anything in particular.

In the test, by keeping the heater energized, the surface temperature of the protective pipe was kept at 1000 ° C. at all times, and the time taken for the heater to break was examined. Empirically, the time until the disconnection is 200 under the above conditions.
If it is 0 hours or more, it can be judged that there is practically no problem.

Table 2 shows the results. As known from Table 2, regardless of each dimension, the above (E ² −d ² ) / d
^When the value of ² was less than 1.5, good results of over 2100 hours were obtained. On the other hand, when it exceeds 1.5, it is all less than 1900 hours, and the durability against energization is poor.

From this result, the above (E ² −d ² ) / d ²
It can be seen that excellent durability can be obtained by setting the value of to 1.5 or less.

[0045]

[Table 2]

Embodiment 3 As shown in FIG. 2, the ceramic glow plug 102 of this embodiment has the inorganic material powder 5 made of silicon nitride in the gap 23 between the protective pipe 3 and the heater 2 of Embodiment 1. Filled. Others were the same as those in the first embodiment. Then, the ceramic glow plug 102 was subjected to the current durability test shown in the second embodiment.

As shown in Table 2 above, the ceramic glow plugs used in the electrical durability test are as shown in the above (E ² -d
² ) / d ² was constant at a total of 1.12, and three types having different D dimensions were prepared (Sample No. 32).
~ 34). Note that these three types of ceramic glow plugs are the same as sample No. 1 in the second embodiment. 29 to 31, respectively, and the difference is that the gap 23
It is only whether or not the inorganic material powder 5 is filled.

The method of the electrical durability test was the same as in the second embodiment. Table 2 shows the results. As can be seen from Table 2, the durability time of all three types of ceramic glow plugs exceeded 2000 hours, which was a very good result. In addition, in this example, the sample No. Compared to 29-31, the durability life was slightly extended. This is considered to be an effect of improving heat transfer by the filler.

Fourth Embodiment As shown in FIG. 3, the ceramic glow plug 103 of this embodiment is configured such that a cap portion 323 covering the heater 2 is attached to the outer surface of the heater 2 instead of the protection pipe 3 of the first embodiment. A protective pipe 303 having a small inner diameter was used for the above. The heater 2 is press-fitted into the protective pipe 303. Others are the same as those in the first embodiment.

In this example, the heat transfer between the heater 2 and the protective pipe 3 can be improved without inserting a filling material, whereby the durability can be improved.
In addition, the same effects as those of the first embodiment can be obtained.

Embodiment 5 As shown in FIG. 4, the ceramic glow plug 104 of this embodiment has the cap portion 324 and the fixing portion 344 set to have the same diameter instead of the protection pipe 3 of the embodiment 1. The protection pipe 304 without the step was used. Further, the inner diameter of the protective pipe 304 is adjusted to the outer diameter of the metal sleeve 42 of the holding portion 4.

Then, the protection pipe 304 was attached to the tip of the heater 2 until it abuts, and the welded portion 35 of the fixed portion 344 was laser welded all around. The gap 234 between the protective pipe 304 and the heater 2 was filled with the silicon nitride powder 5. Others are the same as those in the first embodiment.

In this example, since the protective pipe is easily manufactured, the product of the present invention can be provided at low cost. In addition, the same effects as those of the first embodiment can be obtained.

Embodiment 6 As shown in FIG. 5, in the ceramic glow plug 105 of this embodiment, the cap portion 325 and the fixing portion 345 have the same diameter instead of the protection pipe 3 of the embodiment 1. The protection pipe 305 without the step was used. Further, the outer diameter of the protective pipe 305 is adjusted to the outer diameter of the metal sleeve 42 of the holding portion 4.

On the other hand, the tip of the metal sleeve 42 of the holding portion 4 is provided with a step portion 423 corresponding to the thickness of the protective pipe 305 and the tip thereof is thinned. And the protection pipe 305
Was attached until it abuts on the stepped portion 423 of the metal sleeve 42, and the entire circumference of the abutting portion 36 was butt welded by laser welding. Others are the same as those in the first embodiment.

In this example, the outer diameter of the metal sleeve portion does not become larger by the amount of the protection pipe, and it is particularly effective when the dimensional constraints on the engine side are severe. In addition, the same effects as those of the first embodiment can be obtained.

Embodiment 7 As shown in FIG. 6, in the ceramic glow plug 106 of this embodiment, instead of the protection pipe 305 in Embodiment 6, a protection pipe 306 with its fixing portion 345 removed is used. The outer diameter of the protection pipe 306 is adjusted to the outer diameter of the metal sleeve 42 of the holding portion 4 as in the sixth embodiment.

On the other hand, the tip of the metal sleeve 42 of the holding portion 4 has a constant thickness without the stepped portion as in the sixth embodiment. Then, the protective pipe 306 is connected to the metal sleeve 4
2 is attached until it abuts on the tip of 2 and its abutting portion 3
The entire circumference of 6 was butt welded by laser welding. Others are the same as those in the sixth embodiment.

In this example, the same effect as that of the sixth embodiment can be obtained, and the step processing of the sleeve in the sixth embodiment is not necessary, so that the cost can be reduced.

Embodiment 8 As shown in FIG. 7, the ceramic glow plug 107 of this embodiment is fixed to the housing 41 so as to cover the heater 2 and the metal sleeve 42 instead of the protection pipe 3 of Embodiment 1. The protective pipe 307 which is used is used.

That is, the protection pipe 307 has the cap portion 32 for covering the heater 2, the intermediate portion 347 via the step portion 33, and the fixing portion 38 via the step portion 37. The inner diameter of the intermediate portion 347 is adjusted to the outer diameter of the metal sleeve 42, and the outer diameter of the fixed portion 38 is adjusted to the outer diameter of the lower portion of the housing 41.

On the other hand, the lower portion of the housing 41 is provided with a step portion 413 corresponding to the thickness of the fixed portion 38 of the protective pipe 307, and the tip thereof is thinned. Then, the protection pipe 307 was mounted until it abuts against the stepped portion 413 of the housing 41, and the entire circumference of the abutting portion 36 is butt-welded by laser welding. Others are the same as those in the first embodiment.

In this example, the welded portion can be arranged outside the combustion chamber, and the welded portion can be prevented from being heated during use. Therefore, the reliability can be further enhanced. In addition, the same effects as those of the first embodiment can be obtained.

Embodiment 9 As shown in FIG. 8, the ceramic glow plug 108 of this embodiment uses a protection pipe 308 from which the fixing portion 38 of the protection pipe 307 of Embodiment 7 has been removed. On the other hand, the tip of the housing 41 of the holding portion 4 has a constant thickness without the stepped portion as in the eighth embodiment. Then, the step portion 358 of the protection pipe 308 was mounted until it abuts the tip of the housing 41, and the entire circumference of the welded portion 36 at the upper end of the protection pipe 308 was laser-welded. Others are the same as those in the eighth embodiment. Also in this example, the same effect as that of the eighth embodiment can be obtained.

Embodiment 10 As shown in FIG. 9, the ceramic glow plug 109 of the present embodiment has the cap portion 329 and the fixing portion 349 set to have the same diameter instead of the protection pipe 3 of the embodiment 1. The protection pipe 309 without the step was used. Further, the inner diameter of the protection pipe 309 was adjusted to the outer diameter of the holding portion 4.

On the other hand, the holding portion 4 is composed only of the housing 410, and the lower end side thereof has a reduced diameter to match the inner diameter of the protective pipe 309. And the protection pipe 3
09 until it touches the tip of the heater 2,
The welded portion 36 at the upper end of the protective pipe 309 is welded all around by laser welding. Others are the same as those in the first embodiment.

In this example, the welded portion is arranged in the combustion chamber, but the arrangement position is a low temperature portion. Therefore, also in this case, reliability can be improved.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view of a ceramic glow plug according to a first embodiment.

FIG. 2 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a third embodiment.

FIG. 3 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a fourth embodiment.

FIG. 4 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a fifth embodiment.

FIG. 5 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a sixth embodiment.

FIG. 6 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a seventh embodiment.

FIG. 7 is a partially cutaway sectional view of a ceramic glow plug tip portion according to an eighth embodiment.

FIG. 8 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a ninth embodiment.

FIG. 9 is a partially cutaway cross-sectional view of a ceramic glow plug tip portion according to a tenth embodiment.

FIG. 10 is a partially cutaway sectional view of a conventional ceramic glow plug.

FIG. 11 is a partially cutaway sectional view of another conventional ceramic glow plug.

[Explanation of symbols]

 1,102-109. . . Ceramic glow plug, 2. . . Heater, 21. . . Ceramic skin, 3. . . Protective pipe, 4. . . Holding part, 41. . . Housing, 42. . . Metal sleeve, 5. . . Silicon nitride powder, 6. . . Center axis,

Claims (6)

[Claims] 1. A holding portion formed of a housing or a metal sleeve provided inside the housing, a heater inserted into the holding portion and directly held by the holding portion, and a metal disposed so as to cover a tip portion of the heater. A ceramic glow plug comprising a protective pipe made of, and the protective pipe being fixed to the holding portion. 2. When the outer diameter of the protective pipe is E, the inner diameter is D, and the outer diameter of the heater is d, 0.15 mm ≦ (ED) / 2, and (E ² -D ² )
/ D ² ≦ 1.5 A ceramic glow plug characterized by the following: 3. The ceramic glow plug according to claim 1, wherein the protective pipe is fixed to the holding portion by welding. 4. The method according to claim 1, wherein:
The ceramic glow plug, wherein the protective pipe is fixed to the housing so as to cover the heater and the metal sleeve. 5. The method according to claim 1, wherein:
A ceramic glow plug, characterized in that an inorganic material powder is filled between the protective pipe and the heater. 6. The ceramic glow plug according to claim 5, wherein the inorganic material powder is silicon nitride.