JP2002243150A - Ceramic glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic glow plug in which consumed electric power is reduced without deteriorating temperature rise characteristics, and to reduce electric power loss owing to heat dissipation, and which is excellent in durability. SOLUTION: A ceramic glow plug A is provided, in which a heating electric conductive member 41 and electrodes 42, 43 electrically connected with the former member 41 are imbedded in an insulating ceramic 44, and which includes a heating device 4 extending axially and a metal outer cylinder 1 for holding the heating device 4 in the state where an exposed portion of the foregoing heating device is exposed to the outside. In the ceramic glow plug, the heating electric conductive member 41 is located in the exposed portion of the foregoing heating device 4, the foregoing electrodes 42, 43 form a reaction layer between the foregoing insulating ceramic 44 and the foregoing heating electric conductive member 41, and further side end surfaces of the foregoing electrodes 42, 43 are located in the exposed portion of the heating device 4 and an axial distance between the exposed portion side end surfaces of the electrodes 42, 43 and an exposed portion side end surface of the metal outer cylinder 1 exceeds 4.0 mm.

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 excellent in durability while reducing power loss due to heat radiation without lowering the temperature rise characteristics and reducing power consumption.

[0002]

2. Description of the Related Art Conventionally, a ceramic glow plug has an advantage that a ceramic element itself generates heat and can be rapidly heated as compared with a metal glow plug. As such a ceramic glow plug, for example, as shown in FIG.
Is known. The heating element 4 includes a substantially U-shaped heating conductive material 41 formed of conductive ceramic inside a rod-shaped insulating ceramic 44 having a round end and extending in the axial direction. The electrodes 42 and 43, which are electrically connected by being embedded in the distal end portion, are embedded. Then, by supplying electricity through the electrodes 42 and 43, the heating element 4
To generate heat.

[0003]

In a conventional ceramic glow plug A 'as shown in FIG.
The metal outer cylinder 1 expands / contracts due to repetition of energization to and heat and cooling during engine combustion, and compressive stress may be repeatedly applied to the heating element 4. This compressive stress tends to be particularly large in the vicinity of the exposed portion side end face 11 of the metal outer cylinder 1 which is susceptible to heat generation of the heat generating conductive material 41 and heat from the engine. Further, among the heat generating conductive materials 41,
At a place where the electrodes 42 and 43 are buried and electrically connected, for example, at the time of cooling after firing,
Fine gaps may be formed due to the difference in the coefficient of thermal expansion between the heat conductive material 43 and the heat generating conductive material 41.

[0004] When a compressive stress based on the expansion / contraction of the metal outer cylinder 1 repeatedly acts on such a connecting portion of the heat generating conductive material 41, cracks and the like are generated from the vicinity of the connecting portion of the heat generating conductive material 41, and the ceramic glow plug has The service life may be shortened. Conventionally, as a glow plug solving such a problem, for example, an exposed portion side end surface of an electrode is disposed so as to enter a metal outer cylinder side, and from the exposed portion side end surface of the metal outer cylinder to the exposed portion side end surface of the electrode. Distance of 2-10mm
(See Japanese Patent Application Laid-Open No. 9-18 / 1990)
4623).

However, in the case where the end face of the exposed portion of the electrode is disposed so as to enter the metal outer cylinder side as in the glow plug shown in the above-mentioned prior art, the metal outer cylinder holding the heating element when the temperature rises is reduced. Tends to increase heat dissipation. When the heat radiation increases, power consumption increases due to power loss due to the heat radiation, and the effect of the ceramic glow plug, which enables rapid heating, is reduced by half.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a ceramic glow plug which is excellent in durability while reducing power consumption without deteriorating the temperature rising characteristics, reducing power loss due to heat radiation. The purpose is to provide.

[0007]

The present inventors have studied the structure of a ceramic glow plug in consideration of the above-mentioned circumstances and the relationship between the temperature rise characteristics, power consumption, and durability. As a result, a reaction layer is formed on an electrode. By alleviating the stress caused by the difference in the coefficient of thermal expansion, furthermore, on the contrary to the conventional ceramic glow plug, on the side where the exposed portion side end face of the electrode is located outside the metal outer cylinder, By setting the axial distance between the exposed end face of the electrode and the exposed end face of the metal outer cylinder to be greater than 4.0 mm, the advantage of the ceramic glow plug that rapid heating is possible is impaired. It has been found that the power consumption can be reduced, the power loss due to heat radiation can be reduced, and a ceramic glow plug having excellent durability can be obtained.

A ceramic glow plug according to the present invention has a heating element extending in an axial direction by burying a heat-generating conductive material and an electrode electrically connected to the heat-generating conductive material inside an insulating ceramic; A metal outer cylinder that holds the heating element in a state where the exposed portion is exposed to the outside, wherein the heating conductive material is located in the exposed portion of the heating element, and the electrode is formed of the insulating material. A reaction layer is formed between the ceramic and the heat-generating conductive material, and the exposed portion-side end surface of the electrode is located within the exposed portion of the heating element, and the exposed portion-side end surface of the electrode and the metal outer cylinder are exposed. The axial distance from the part-side end face exceeds 4.0 mm.

An example of the ceramic glow plug of the present invention is shown in FIGS. As shown in FIG. 1, a ceramic glow plug A of the present invention includes a metal outer cylinder 1, a cylindrical metal shell 2 for holding the outer cylinder 1, and a terminal which is insulated and inserted into the cylindrical metal shell 2. An electrode 3 and a heating element 4 inserted into the metal outer cylinder 1 and held with the exposed portion exposed to the outside.
And. The rear portion of the metal outer cylinder 1 is fixed to the inner wall of the cylindrical metal shell 2 with silver brazing. In addition, terminal electrode 3
Is insulated and fixed from the cylindrical metal shell 2 by a glass seal.

As shown in FIG. 2, the heating element 4 has a U-shaped overall shape and a substantially circular cross-sectional shape, and is electrically connected to the heating conductive material 41. The electrodes 42 and 43 are embedded in an insulating ceramic 44. The heat-generating conductive material 41 includes a heat-generating portion 411 and a heat-generating portion holding portion 412 each having a substantially circular cross-sectional diameter. The above electrode 4
2, 43 are exposed portion side end surfaces 42A, as shown in FIG.
By embedding 43A in the heat-generating conductive material 41, it is electrically connected to the heat-generating conductive material 41.

In the glow plug of the present invention, the electrodes 42 and 43 form a reaction layer between the insulating ceramic 44 and the heat generating conductive material 41. The “reaction layer” can be generated in a firing step under predetermined conditions of the heating element 4. This reaction layer is formed in a somewhat porous state as compared with other portions, and the electrode 4
The joint strength between the insulating ceramics 2 and 43 and the insulating ceramics 44 and the heat generating conductive material 41 can be improved, and can also play a role of stress relaxation. That is, the heating conductive material 41 and the electrodes 42, 4
When the connection portion with the metal tube 3 is located outside the metal outer cylinder 1, the temperature rise during heating becomes remarkable. In order to alleviate the stress caused by the difference in the thermal expansion coefficient and improve the durability, This reaction layer becomes indispensable.

In the glow plug of the present invention, the "exposed portion of the heating element" means a portion of the heating element 4 which is located outside the metal outer cylinder 1 holding the heating element 4 and is exposed to the outside. Show. And in the glow plug of the present invention,
As shown in FIG. 2, the heating conductive material 41 and the exposed end faces 42A and 43A of the electrodes 42 and 43 are
Is located within the exposed part of the. With such a configuration, power loss due to heat radiation from the metal outer cylinder 1 that holds the heating element 4 at the time of temperature rise is suppressed, and rapid heating of the ceramic glow plug is enabled.

In the glow plug of the present invention, the axial distance (L1 in FIG. 2) between the exposed portion side end surfaces 42A and 43A of the electrode 4 and the exposed portion side end surface 11 of the metal outer cylinder 1 is:
Usually, it is more than 4.0 mm, preferably 5.0 mm or more, more preferably 6.0 mm or more. This distance is 4.0
mm or less, when the metal outer cylinder 1 expands and contracts due to energized heat generation of the heating element 4 and heat received from the engine, the compressive stress from the metal outer cylinder 1 accompanying the expansion / contraction causes heat generation conductor. As a result of adding to the connection between the electrode 41 and the electrodes 42 and 43, cracks are generated at this connection and the life of the ceramic glow plug is shortened, which is not preferable. still,
In the present invention, the axial distance between the exposed portion side end surface 11 of the metal outer cylinder 1 and the exposed portion side end surface 42A of the electrode 42, and the exposed portion side end surface 11 of the metal outer cylinder 1 and the exposed portion side end surface 4 of the electrode 43.
It is preferable that both the axial distance with 3A exceed 4.0 mm, but it is also possible to adopt a configuration in which one of the axial distances exceeds 4.0 mm.

The shape of the "heat generating conductive material" 4 is not particularly limited, and the cross-sectional shape may be the same as the whole. However, as shown in FIGS. A configuration including the unit 411 and the heat generating unit holding unit 412 can be adopted. The heat-generating portions 411 having different cross-sectional shapes as described above and the heat-generating portion holding portion 41
In the heat-generating conductive material 41 having the configuration of the heat-generating member 41, the exposed-side end surface 42 A of the electrode 42 and the heat-generating-portion holding portion 4
The axial distance (L2 in FIG. 2) of the surface 12 to the exposed surface 412A can be set to 2.0 mm or more, preferably 2.5 mm or more, and more preferably 3.0 mm or more. If this distance is short, the electrode 42 and the heat generating portion holding portion 41
The temperature at the connection with the electrode 2 tends to increase, and as a result, stress is generated due to the different effects of the thermal expansion of the insulating ceramic, the conductive material, and the electrode, causing cracks and disconnections at the electrode conductive material joint near the end face. However, the above configuration is preferable because crack generation and disconnection can be effectively suppressed and the life of the ceramic glow plug can be extended. In the present invention, the heat generating portion holding portion 412 is used.
And the exposed portion side end surface 42 of the electrode 42.
It is preferable that both the axial distance to A and the axial distance between the exposed portion side end surface 412A of the heat generating portion holding portion 412 and the exposed portion side end surface 43A of the electrode 43 be 2.0 mm or more, One of the axial distances is 2.0m
m or more.

The material of the "heat generating conductive material" 41 of the present invention is not particularly limited, and is usually WC, W, Ir, T
a, Pt, etc. are used. As the material of the “insulating ceramic” 44, Al ₂ O ₃ may be used.
A ceramic powder sintered body containing Si ₃ N ₄ or the like as a main component is preferable because the strength, toughness and the like are balanced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be specifically described with reference to examples and comparative examples. (1) Configuration of Ceramic Glow Plug of the Present Embodiment FIGS. 1 and 2 show a ceramic glow plug of the present embodiment. In the glow plug of the present embodiment, the metal outer cylinder 1 is a heat-resistant metal having a thickness of 0.6 mm, and the cylindrical metal shell 2 is made of carbon steel. Further, since the heat-generating conductive material 41 is embedded in the insulating ceramic 44 so that the distance from the surface to the surface of the heat-generating element 4 is 0.3 mm or more, the heat-generating conductive material 41 is kept at a high temperature during use. (800 ° C. to 1500 ° C.), oxidation of the heat generating conductive material 41 can be prevented and mechanical strength can be maintained high.

(2) Preparation of Ceramic Glow Plug of the Present Embodiment First, the raw material of the heat generating conductive material 41 is adjusted. The raw material of the heat generating conductive material 41 is composed of 60.0% by mass of WC and 40% by mass of ceramic raw material powder (Si ₃ N ₄ : 85 parts by mass, rare earth oxide: 10 parts by mass, SiO ₂ : 5 parts by mass). After adding a dispersing agent and a solvent thereto, pulverizing and drying, an organic binder is added to produce a granulated product. Next, the W line is cut into a predetermined length and formed into a predetermined shape to manufacture the electrodes 42 and 43. Then, as shown in FIG.
The above granulated material is injection-molded so as to be connected to the exposed portion side end surfaces 42A, 43A, thereby forming a unitary body of the U-shaped unsintered heat generating conductive material and the electrodes 42, 43 shown in FIG.

Next, the ceramic powder constituting the insulating ceramic 44 is prepared. The raw material of the ceramic powder is composed of 85 parts by mass of Si ₃ N _4, 10 parts by mass of rare earth oxide, and 5 parts by mass of SiO ₂ . An organic binder is added to these to produce granules. Then, a pair of half pressed bodies 44A and 44B are made from the granulated material, and the above-described integrated body shown in FIG. 4 is placed on the half pressed body 44A, and the half pressed body 44B is further placed thereon. By pressing and placing, a press-formed body 44C shown in FIG. 5 is formed. This press-formed body 44C was heated at 1750 ° C. in a nitrogen gas atmosphere.
Then, hot pressing is performed while applying a pressure of 20 MPa to form a substantially round bar-shaped ceramic sintered body having a hemispherical tip. Then, the outer surface of the ceramic sintered body is polished and finished to a predetermined cylindrical shape, and the other end surfaces 42B and 43B of the electrodes 42 and 43 are exposed to the surface of the ceramic sintered body. Thus, the heating element 4 is completed. In each of the examples and comparative examples, it was confirmed that a reaction layer was formed between the electrodes 42 and 43 and the insulating ceramic 44 and the heat generating conductive material 41.

After the heating element 4 is inserted into the metal outer cylinder 1 and electrically connected thereto, an assembly of the heating element 4 and the metal outer cylinder 1 is inserted into a cylindrical metal shell, and the metal outer cylinder 1 is inserted. The rear part of the tube 1 is fixed to the inner wall of the holding portion of the cylindrical metal shell 2 by silver brazing. Finally, the end of the metal shell is crimped to complete the ceramic glow plug A of this embodiment.

(3) Performance evaluation of ceramic glow plug by conducting durability test In the glow plug shown in FIG. 1 and FIG.
The axial distance (L) between the exposed portion side end surfaces 42A and 43A of the heat generating portion holding portion 412 and the exposed portion side end surfaces 42A and 43A of the heat generating portion holding portion 412.
2) was set to 3.0 mm, and the axial distance (L1) between the exposed portion side end surfaces 42A, 43A of the electrodes 42, 43 and the exposed portion side end surface 11 of the metal outer cylinder 1 was set to a value shown in Table 1 below. Using each of the glow plugs of Examples 1 to 4 and Comparative Examples 1 to 4, the performance was evaluated by examining the durability of the glow plug by a temperature rise time, power consumption, and a current-carrying durability test. The temperature was increased by energizing each of the glow plugs of Examples 1 to 4 and Comparative Examples 1 to 4 under the condition that the glow plugs were saturated at 1300 ° C. in the atmosphere.
It was measured as the time to reach 900 ° C (sec) at the time of saturation at 0 ° C. Power consumption was measured as power consumption (W) at 1300 ° C. saturation. In addition, the endurance test for energization
One minute (the temperature at the tip of the insulating part was 1400 ° C.)-One minute (cooling to room temperature) was stopped as one cycle, and the presence or absence of disconnection was confirmed. The results are shown in Table 1 below. In addition, the negative numerical value in the item of L1 in Table 1 is the above-mentioned electrode 4
The exposed portion side end surfaces 42A, 43A of the electrodes 42, 43 and the metal outer tube 1 in a state where the exposed portion side end surfaces 42A, 43A of the electrodes 2, 43 are retracted from the exposed portion side end surface 11 of the metal outer tube 1. It represents the axial distance from the heat-generating side end face 11.

[0021]

[Table 1]

In the glow plug shown in FIGS. 1 and 2, L1 is set to 8.0 mm and 5.5 mm.
Using the glow plugs of Examples 5 to 12 and Comparative Examples 5 and 6 in which 2 was the value shown in Table 2 below, the glow plugs were tested for temperature rise time, power consumption, and durability by conducting current durability tests. An evaluation was performed. The method of evaluating the durability of the glow plug by the temperature rise time, power consumption, and energization durability test is the same as the above case. The results are shown in Table 2 below.

[0023]

[Table 2]

(3) Effect of Example From Table 1, it is understood that L1 is shorter than 2.0 mm.
In each of the ceramic glow plugs of No. 4 in the current endurance test, the heat generating conductive material 41 was used at 6000 to 18000 cycles.
It can be seen that a disconnection is caused at the connection portion of FIG.
Further, when L1 is 4.0 mm, in the energization endurance test,
Since no disconnection is caused even after 20,000 cycles, it can be seen that the durability for energization is excellent, but the temperature rise time is slow and power consumption is still large as compared with Examples 1 to 4.

On the other hand, in each of the ceramic glow plugs of Examples 1 to 4 in which L1 exceeds 4.0 mm, in the current endurance test, no disconnection is caused even after 20,000 cycles. It turns out that it is excellent. Moreover, since the temperature rise time is faster than Comparative Examples 1 to 4 and the power consumption is smaller than Comparative Examples 1 to 4, the ceramic glow plugs of Examples 1 to 4 are different from Comparative Examples 1 to 4.
As compared with the above, it can be seen that the power consumption is reduced and the current-carrying durability is excellent without impairing the temperature rising characteristics. In particular, as shown in FIG. 7 and FIG.
When the distance exceeds 0 mm, the heating rate is rapidly increased, and the power consumption is significantly reduced. Therefore, it is understood that the influence of L1 on the heating rate and the power consumption is considerably large.

As shown in Table 2, in Comparative Examples 5 and 6 in which L2 was less than 2.0 mm, the heating rate was high and the power consumption was low, so that the heating property was maintained. Then, heat generation conductive material 4
It is found that the connection portion 1 is broken, and the connection durability is poor. On the other hand, when L2 is 2.0
mm or more in Examples 5 to 12 in which the temperature rise time is short,
Since the power consumption is low, the temperature rise characteristics are maintained, and furthermore, since no disconnection is caused up to 18000 cycles in the current durability test, the current durability is superior to Comparative Examples 5 and 6. It turns out that there is. That is, L
Each of the ceramic glow plugs of Examples 5 to 12 in which 2 is not less than 2.0 mm has a ceramic glow excellent in balance among the properties of the temperature rise time, the power consumption, and the current-carrying durability as compared with Comparative Examples 5 and 6. It turns out that it is a plug.

The glow plug of the present invention is not limited to the glow plug shown in the specific embodiment, but may be variously modified within the scope of the present invention depending on the purpose and application.

[0028]

According to the glow plug of the present invention, the power consumption can be reduced by the above structure without impairing the advantage of the ceramic glow plug that rapid heating is possible as compared with the conventional ceramic glow plug. A ceramic glow plug with reduced power loss due to heat radiation and excellent durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a glow plug according to an embodiment.

FIG. 2 is an enlarged longitudinal sectional view of a main part of the glow plug shown in FIG.

FIG. 3 is an explanatory view showing that an integrated body of a heating resistor and a lead wire is manufactured by injection molding.

FIG. 4 is an explanatory view of an integrated body of a heating resistor and a lead wire.

FIG. 5 is a longitudinal sectional view of a press-formed body.

FIG. 6 is an enlarged vertical sectional view of a main part of a conventional ceramic glow plug.

FIG. 7 shows distance L1 (mm) and heating time (sec) in Table 1.
6 is a graph showing a relationship with the graph.

FIG. 8 is a graph showing a relationship between a distance L1 (mm) and power consumption (W) in Table 1.

[Explanation of symbols] [Explanation of symbols]

A, A ': ceramic glow plug, 1: metal outer cylinder,
2; cylindrical metal shell; 3; terminal electrode; 4; heating element;
Reference Signs List 1: heat generating conductive material, 411; heat generating portion, 412; heat generating portion holding portion, 42, 43; electrode, 44; insulating ceramic

Claims (2)

[Claims] 1. A heat-generating conductive material and an electrode electrically connected to the heat-generating conductive material are embedded in an insulating ceramic.
In a ceramic glow plug including a heating element extending in an axial direction and a metal outer cylinder holding the heating element in a state where an exposed portion of the heating element is exposed to the outside, the heat generating conductive material is exposed to the heating element. And the electrode forms a reaction layer between the insulating ceramic and the heat-generating conductive material, and the exposed portion side end surface of the electrode is located in the exposed portion of the heating element, and A ceramic glow plug, wherein an axial distance between the exposed portion side end surface and the exposed portion side end surface of the metal outer cylinder exceeds 4.0 mm. 2. The heat generating conductive material includes a heat generating portion, and a heat generating portion holding portion having a different shape from the heat generating portion and electrically connected to the electrode. 2. The ceramic glow plug according to claim 1, wherein an axial distance between an end face and an end face on an exposed part side of the heat generating part holding part is 2.0 mm or more.