DE102014000633A1 - Glow plug, particularly ceramic glow plug for use in internal combustion engine, particularly diesel engine, has resistance heater that contains ceramic composition and generates heat on conducting electricity - Google Patents

Abstract

The glow plug (10) has a resistance heater (810) that contains a ceramic composition and generates heat on conducting electricity. A holding element (860) mainly contains another ceramic composition, which is different from the former ceramic composition. The holding element contains silicon nitride as a main component, in which the resistance heater is embedded, and holds the resistance heater. The latter ceramic composition contains a rare earth element and aluminum.

Description

BACKGROUND

1. Technical area

The present invention relates to a glow plug.

2. State of the art

Glow plugs exist as ceramic glow plugs with a ceramic heater (see, for example, Japanese Patent Application Laid-open JP 2009-287920 A (Patent Document 1)). The ceramic heater of the ceramic glow plug includes a resistance heater and a support member. The resistance heater includes a conductive ceramic composition and generates heat when electricity is passed through. The support member includes an electrically insulating ceramic composition. The support member supports the resistance heater embedded therein.

Japanese Patent Application Laid-Open JP 2011-66020 A (Patent Document 2) discloses a technology for avoiding damage to the ceramic heater due to the differential thermal expansion of the resistance heater and the support member. In this technology, the resistance heater is coated with a coating that has a hardness and density lower than that of the resistance heater and the support member. The coating according to Patent Document 2 mainly contains boron nitride (BN). The thermal expansion coefficient of the coating is smaller than that of the resistance heater and the support member.

As is well known, the coefficient of thermal expansion of the resistance heating element is greater than that of the support element (see, for example, Japanese Patent Application Laid-open JP 2010-108606 A ).

To shorten the starting time of an internal combustion engine, the glow plug must have the property of a rapid increase in temperature, so that the temperature rises rapidly to a desired temperature at the beginning of the flow of electricity. As for the characteristic of the rapid rise in the temperature of the glow plug, it is required that 1000 ° C. be reached within about two seconds. In recent years, demands have become more stringent and it is now required to reach 1000 ° C in about one second. To improve the property of rapid temperature rise, the initial resistance of the resistance heater is reduced by increasing the content of conductive components in the resistance heater.

When the content of conductive components in the resistance heater is increased to improve the property of rapid temperature rise, this causes an increased thermal load on the resistance heater due to the difference in thermal expansion from the support member in the glow plug according to Patent Document 1. Therefore, this has Glow plug the problem that the resistance heating deteriorates rapidly. The resistance of the resistance heater increases with the deterioration. Even if, in the glow plug according to Patent Document 2, the content of conductive components in the resistance heating is increased, the thermal stress occurring in the resistance heating by the coating can not be sufficiently mitigated. Therefore, there is also a problem with this glow plug that the resistance heating rapidly deteriorates. In addition, the strength of the resistance-heating coating in the glow plug according to Patent Document 2 is relatively low. Therefore, there is a problem that the strength of the ceramic heater can not be sufficiently ensured.

SUMMARY

The present invention aims to solve the above-mentioned problems. The present invention can be implemented as follows.

A glow plug according to an embodiment of the present invention is provided. In this embodiment, the glow plug includes: a resistance heater that includes a first ceramic composition and generates heat upon passage of electricity; and a support member mainly including a second ceramic composition different from the first ceramic composition, and containing silicon nitride (Si ₃ N ₄ ) as a main component in which the resistance heater is embedded and supporting the resistance heater. In the glow plug of this embodiment, the support member includes a neighboring region adjacent to the resistance heater, in which a plurality of particles are laterally unevenly distributed laterally of the resistance heater containing a component whose thermal expansion coefficient is larger than that of silicon nitride (Si ₃ N ₄ ).

According to this embodiment of the glow plug, different thermal expansions between the resistance heater and the support element in the neighboring area are buffered. This contributes to the suppression of thermal stress of the resistance heating due to that of the Supporting element different thermal expansion. Due to this, the longevity of the resistance heating can be improved.

In this embodiment of the glow plug, the component of the particles distributed in the neighboring area may include at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide Be (SiC).

• (1) Gemäß einer Ausführungsform der vorliegenden Erfindung wird eine Glühkerze bereitgestellt. Die Glühkerze gemäß dieser Ausführungsform beinhaltet: eine Widerstandsheizung, die eine erste Keramik-Zusammensetzung enthält und bei Durchleiten von Elektrizität Wärme erzeugt; und ein Halterungselement, das hauptsächlich eine zweite, von der ersten verschiedene Keramik-Zusammensetzung enthält, deren thermischer Ausdehnungskoeffizient kleiner ist als der der ersten Keramik-Zusammensetzung, in welches die Widerstandsheizung eingebettet ist, und welches die Widerstandsheizung haltert. In dieser Ausführungsform der Glühkerze beinhaltet das Halterungselement einen der Widerstandsheizung benachbarten Nachbarbereich, in welchem mehrere Partikeln verteilt sind. Die mehreren Partikeln enthalten eine dritte Keramik-Zusammensetzung, deren thermischer Ausdehnungskoeffizient größer ist als der der zweiten Keramik-Zusammensetzung. Gemäß dieser Ausführungsform der Glühkerze wird der Unterschied in der thermischen Ausdehnung zwischen der Widerstandsheizung und dem Halterungselement im Nachbarbereich abgepuffert. Dies trägt zur Unterdrückung der thermischen Belastung der Widerstandsheizung auf Grund der zu der des Halterungselements unterschiedlichen thermischen Ausdehnung bei. Auf Grund dessen kann die Langlebigkeit der Widerstandsheizung verbessert werden.
• (2) In der obigen Ausführungsform der Glühkerze kann die Dicke des Nachbarbereichs 10 bis 200 μm von der Widerstandsheizung betragen. Gemäß dieser Ausführungsform der Glühkerze trägt der Nachbarbereich effektiv zur Unterdrückung der thermischen Belastung der Widerstandsheizung bei.
• (3) In der obigen Ausführungsform der Glühkerze kann die Dicke des Nachbarbereichs 20 bis 100 μm von der Widerstandsheizung betragen. Gemäß dieser Ausführungsform der Glühkerze trägt der Nachbarbereich noch effektiver zur Unterdrückung der thermischen Belastung der Widerstandsheizung bei.
• (4) In der obigen Ausführungsform der Glühkerze kann der durchschnittliche Partikeldurchmesser der mehreren Partikeln weniger als oder gleich 5 μm sein.

This embodiment of the glow plug can effectively improve the longevity of the resistance heater supported by the support member.

• (1) According to one embodiment of the present invention, a glow plug is provided. The glow plug according to this embodiment includes: a resistance heater that includes a first ceramic composition and generates heat when passing electricity; and a support member mainly including a second ceramic composition other than the first one, the thermal expansion coefficient of which is smaller than that of the first ceramic composition in which the resistance heating is embedded, and which supports the resistance heating. In this embodiment of the glow plug, the mounting element includes a neighboring region adjacent to the resistance heater, in which a plurality of particles are distributed. The plurality of particles contains a third ceramic composition whose thermal expansion coefficient is greater than that of the second ceramic composition. According to this embodiment of the glow plug, the difference in thermal expansion between the resistance heater and the support member in the neighboring area is buffered. This contributes to the suppression of the thermal load of the resistance heating due to the thermal expansion different from that of the support member. Due to this, the longevity of the resistance heating can be improved.
• (2) In the above embodiment of the glow plug, the thickness of the neighboring portion may be 10 to 200 μm from the resistance heater. According to this embodiment of the glow plug, the adjacent area effectively contributes to the suppression of the thermal load of the resistance heater.
• (3) In the above embodiment of the glow plug, the thickness of the neighboring portion may be 20 to 100 μm from the resistance heater. According to this embodiment of the glow plug, the neighboring area contributes more effectively to the suppression of the thermal load of the resistance heater.
• (4) In the above embodiment of the glow plug, the average particle diameter of the plurality of particles may be less than or equal to 5 μm.

• (5) In der obigen Ausführungsform der Glühkerze kann die zweite Keramik-Zusammensetzung Siliziumnitrid sein, und die Hauptkomponente der dritten Keramik-Zusammensetzung kann ein Silizid von wenigstens einem von Chrom (Cr), Molybdän (Mo), Wolfram (W), Titan (Ti), Zirkonium (Zr) und Tantal (Ta), oder Siliziumcarbid (SiC) sein.

The glow plug according to this embodiment contributes to the suppression of pore formation in the neighboring area. In addition, this contributes to the suppression of fine cracks generated due to the different thermal expansion between the particles and their environment around the particles. Due to this, the longevity of the neighboring area can be increased and thus the longevity of the resistance heating can be improved.

• (5) In the above embodiment of the glow plug, the second ceramic composition may be silicon nitride, and the main component of the third ceramic composition may be a silicide of at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium ( Ti), zirconium (Zr) and tantalum (Ta), or silicon carbide (SiC).

• (6) In der obigen Ausführungsform der Glühkerze kann eine Beziehung zwischen der Querschnittsfläche S1 der Widerstandsheizung an einer Position, wo der Nachbarbereich gebildet ist, und der Querschnittsfläche S2 des Halterungselements 0.5% ≤ S1/(S1 + S2) × 100% ≤ 25% genügen.

According to this embodiment, the glow plug can improve the durability of the resistance heating supported by the mainly silicon nitride-containing supporting member.

• (6) In the above embodiment of the glow plug, a relationship between the cross-sectional area S1 of the resistance heater at a position where the neighboring area is formed and the cross-sectional area S2 of the supporting member can be 0.5% ≦ S1 / (S1 + S2) × 100% ≦ 25% suffice.

• (7) In der obigen Ausführungsform der Glühkerze kann eine Beziehung zwischen der Querschnittsfläche S1 der Widerstandsheizung an einer Position, wo der Nachbarbereich gebildet ist, der Querschnittsfläche S2 des Halterungselements, und der Dicke T des Nachbarbereichs T·(S1 + S2)/S1 ≥ 67 μm genügen.

According to this embodiment, the glow plug can improve the longevity of the while ensuring the property of rapid temperature rise.

• (7) In the above embodiment of the glow plug, a relationship between the cross-sectional area S1 of the resistance heater at a position where the neighboring area is formed, the cross-sectional area S2 of the supporting member, and the thickness T of the neighboring area T · (S1 + S2) / S1 ≥ 67 microns are sufficient.

• (8) In der obigen Ausführungsform der Glühkerze kann die Widerstandsheizung folgendes beinhalten: einen als Kehrschleife ausgebildeten Umkehrteil; und einen mit dem Umkehrteil verbundenen Zuleitungsteil mit einem größeren Querschnitt als der Umkehrteil, wobei der Nachbarbereich zumindest dem Umkehrteil benachbart sein kann.

According to this embodiment of the glow plug, the neighboring area contributes to the sufficient suppression of the thermal load of the resistance heater.

• (8) In the above embodiment of the glow plug, the resistance heater may include: a reversing part formed as a reverse loop; and a lead part having a larger cross section than the turn part connected to the turn part, wherein the neighboring part may be at least adjacent to the turn part.

• (9) In der obigen Ausführungsform der Glühkerze kann die Widerstandsheizung durch Spritzgießen oder Drucken gebildet sein.

This embodiment of the glow plug contributes to the suppression of the thermal load on the reversal occurs, the calorific value is relatively large.

• (9) In the above embodiment of the glow plug, the resistance heating may be formed by injection molding or printing.

• (10) In der obigen Ausführungsform der Glühkerze können die erste Keramik-Zusammensetzung und die zweite Keramik-Zusammensetzung eine beiden gemeinsame Komponente enthalten.

The design of the glow plug with a resistance heating formed by injection molding or printing can increase its longevity.

• (10) In the above embodiment of the glow plug, the first ceramic composition and the second ceramic composition may include a common component.

• (11) In der obigen Ausführungsform der Glühkerze kann die zweite Keramik-Zusammensetzung ein Seltenerdelement und Aluminium (Al) enthalten.

According to this embodiment of the glow plug, the connection between the resistance heater and the support member is strengthened, which contributes to an increased mechanical strength of the resistance heater. Therefore, the longevity of the resistance heating can be further increased.

• (11) In the above embodiment of the glow plug, the second ceramic composition may include a rare earth element and aluminum (Al).

This design of the glow plug can further increase the longevity of the resistance heating.

The present invention can be implemented in a variety of ways except as a glow plug. For example, the present invention may be implemented in the form of a glow plug component, a glow plug manufacturing method, and so on.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic view showing a partial cross section of the glow plug;

2 Fig. 10 is a schematic view showing a cross section of a resistance heater;

3 Fig. 10 is a schematic view showing a cross section of the ceramic heater;

4A Fig. 10 is a schematic view showing an example of a structure of the ceramic heater;

4B Fig. 10 is a schematic view showing an example of a structure of the ceramic heater;

4C Fig. 10 is a schematic view showing an example of a structure of the ceramic heater;

5 Fig. 10 is a flowchart showing a manufacturing method of the glow plug;

6 Fig. 12 is a table showing an evaluation result of the performance of the glow plug;

7 Fig. 12 is a table showing an evaluation result of the performance of the glow plug;

8th Fig. 10 is a schematic view showing a cross section of a ceramic heater according to a second embodiment;

9 Fig. 10 is a flowchart showing a manufacturing method of the glow plug according to the second embodiment; and

10 Fig. 10 is a schematic view showing an example of an image used for the sample analysis.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the illustrated embodiments. It will be appreciated, however, that one or more embodiments may do without these specific details. Elsewhere, well-known structures and devices are schematically illustrated to simplify the drawings.

A. First embodiment

A1. Configuration of the glow plug

1 is a schematic view showing a partial cross section of a glow plug 10 shows. In 1 is the outer shape of the glow plug 10 shown on the right side of the sheet, based on a through the center axis SC of the glow plug 10 given limit, while the cross-sectional shape of the glow plug 10 is shown on the left side of the sheet. In the description of the present embodiment is referred to in the sheet of the 1 lower side of the glow plug 10 as "front end", and on the upper side in the sheet of 1 referred to as "backend".

The glow plug 10 includes a ceramic heater 800 that generates heat. The glow plug 10 acts as a heat source that ignites the ignition when starting an internal combustion engine 90 , like a diesel engine, supported. The glow plug 10 includes, in addition to the ceramic heater 800 , a middle class 200 , a metal sleeve 500 , and an outer cylinder 700 , The center axis SC of the glow plug 10 indicates at the same time the center of each component of the glow plug 10 ,

The middle class 200 the glow plug 10 is a conductive metallic component. The middle class 200 has a columnar shape extending along the center axis SC as a center. The middle class 200 directs from outside the glow plug 10 the ceramic heater 800 supplied electrical energy on.

In the present embodiment, the middle shaft is taking 200 the power supply via the connector 100 from outside the glow plug 10 at the rear end of the central shaft 200 on. In another embodiment, the middle shaft 200 the power supply directly from outside the glow plug 10 at the rear end of the central shaft 200 take up.

In the present embodiment, the center shaft 200 electrically with the ceramic heater 800 over a ring 600 at the front end of the central shaft 200 connected. In another embodiment, the middle shaft 200 directly with the ceramic heater 800 at the front end of the central shaft 200 be connected.

The metal sleeve 500 the glow plug 10 is a conductive metallic component. The metal sleeve 500 has a cylindrical shape that extends along the center axis SC as its center. The metal sleeve 500 includes an axial hole 510 , a tool-engaging part 520 , and an external thread 540 ,

The axial hole 510 the metal sleeve 500 is a through hole extending along the center axis SC as its center. The inner diameter of the axial hole 510 is greater than the outer diameter of the central shaft 200 , The middle class 200 is on the center axis SC within the axial hole 510 arranged. Between the wall of the axial hole 510 and the middle class 200 Thus, a gap is provided to the central shaft 200 from the wall of the axial hole 510 electrically isolated. In the present embodiment, the center shaft 200 at the rear end side of the axial hole 510 via a cylindrical insulating member 300 and an annular insulating member 400 attached.

The tool-engaging part 520 the metal sleeve 500 is adapted to be able to engage with a (not shown) tool, which for the installation and removal of the glow plug 10 in or out of the internal combustion engine 90 is used. The external thread 540 the metal sleeve 500 is designed to be in the internal combustion engine 90 trained internal thread to be attached to the internal combustion engine 90 ,

The outer cylinder 700 the glow plug 10 is a conductive metallic component. The outer cylinder 700 has a cylindrical shape that extends along the center axis SC as its center. The outer cylinder 700 includes an axial hole 710 that the ceramic heater 800 stops in it. The rear end side of the outer cylinder 700 is at the front end side of the metal sleeve 500 welded. The ceramic heater 800 stands over the front end side of the outer cylinder 700 in front.

The ceramic heater 800 the glow plug 10 is a heating element (heater) containing a ceramic composition. The ceramic heater 800 includes a resistance heater 810 and a support member 860 ,

The resistance heating 810 of the ceramic heater 800 is a conductive ceramic containing a conductive first ceramic composition. The resistance heating 810 generates heat when electricity is flowing through. In the present embodiment, the resistance heater 810 a formed by injection molding component.

In the present embodiment, the first one includes the resistance heater 810 forming ceramic composition mainly tungsten carbide (WC). In the present embodiment, the first ceramic composition contains silicon nitride (Si ₃ N ₄ ) in addition to the tungsten carbide. The first ceramic composition contains 55 to 70 wt% tungsten carbide and 28 to 35 wt% silicon nitride. The remaining 2 to 10% by weight of the first ceramic composition may include erbium oxide (Er ₂ O ₃ ) and silicon oxide (SiO ₂ ). In another embodiment, the first ceramic composition may be a composition mainly of molybdenum silicide (MoSi ₂ ). By "more important" is meant by the way the component with the largest proportion by weight, in particular one which comprises more than 50% by weight.

The support element 860 of the ceramic heater 800 is an insulating ceramic mainly containing an electrically insulating second ceramic composition. The resistance heating 810 is in the support element 860 embedded. The support element 860 Insulates the resistance heater 810 electrically to the outside of the glow plug 10 , In addition, the support element passes 860 the heat from the resistance heating 810 outside the glow plug 10 ,

In the present embodiment, this includes the support member 860 forming second ceramic composition mainly silicon nitride (Si ₃ N ₄ ). In another embodiment, at least a portion of the silicon (Si) of the support member 860 silicon nitride (Si ₃ N ₄ ) by aluminum (Al), and at least part of the nitride (N) by oxygen (O) to be replaced. The second, the support member 860 forming ceramic composition 860 may contain rare earth oxide (eg, ytterbium (Yb) oxide, erbium (Er) oxide, or the like) and aluminum (Al) oxide as a sintering additive.

2 is a schematic view showing a cross section of the ceramic heater 800 shows. The cross section in 2 is a cross section of the ceramic heater 800 along the plane containing the center axis SC. The resistance heating 810 of the ceramic heater 800 includes a connector 811 , a supply line 812 , a reversal part 815 , a supply line 818 , and a connector 819 ,

The connection part 811 the resistance heating 810 is at the rear end side of the lead part 812 provided, and of the support member 860 exposed.

When on the metal sleeve 500 attached ceramic heater 800 is the connection part 811 electrically with the center shaft 200 connected.

The supply line 812 the resistance heating 810 has a linear shape along the center axis SC. The supply line 812 connects the connection part 811 with the reverse part 815 , The cross section of the supply line part 812 is larger than that of the reversing part 815 ,

The reverse part 815 the resistance heating 810 forms a sweeping loop in U-shape. A thigh of the U-shape of the reversing part 815 is with the lead part 812 connected, and the other leg of the U-shape is connected to the supply line part 818 connected. The cross section of the reversing part 815 is smaller than that of the lead part 812 and the supply line part 818 , Therefore, the electrical resistance of the reversing part 815 larger than that of the lead part 812 and the lead part 818 , Therefore, the resistance heater generates 810 at flow of electricity heat, the reverse part 815 represents the center of heat generation.

The supply line 818 the resistance heating 810 has a linear shape along the center axis SC. The supply line 818 connects the inverse part 815 with the connection part 819 , The cross section of the supply line part 818 is larger than that of the reversing part 815 ,

The connection part 819 the resistance heating 810 is at the rear end side of the lead part 818 provided, and of the support member 860 exposed. When on the metal sleeve 500 attached ceramic heater 800 is the connection part 819 is electric with the outer cylinder 700 connected.

3 is a schematic view showing the cross section of the ceramic heater 800 shows. The cross section in 3 is a cross section of the ceramic heater 800 along the plane perpendicular to the center axis SC at the turning part 815 , This cross section corresponds to the cross section along F3-F3 of FIG 2 ,

The diameter of the ceramic heater 800 is preferably 2.5 to 4.0 mm (millimeters). The diameter of the ceramic heater 800 can also be smaller than 2.5 mm or larger than 4.0 mm.

The long diameter L1 of the reversing part 815 in the resistance heating 810 is preferably 0.3 to 1.8 mm. The long diameter L1 of the reversing part 815 can also be smaller than 0.3 mm or larger than 1.8 mm.

The short diameter L2 of the reversing part 815 in the resistance heating 810 is preferably 0.2 to 1.0 mm. The short diameter L2 of the reversing part 815 may also be less than 0.2 mm or greater than 1.0 mm.

4A and 4B FIG. 12 are schematic views showing an example of the structure of the ceramic heater. FIG 800 demonstrate. The structure in 4A and 4B is the structure of the ceramic heater 800 in the vicinity of the border, at the reverse part 815 the support element 860 is adjacent, and corresponds to the part F4 of 3 ,

The support element 860 of the ceramic heater 800 has one of the resistance heating 810 neighboring area 866 on. In the neighboring area 866 are several particles 868 containing a third ceramic composition whose thermal expansion coefficient is greater than that of the second ceramic composition in a solid phase 862 containing the second ceramic composition containing the support member 860 forms. The main component of the third ceramic composition containing the particles 868 Preferably, a silicide is at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide (SiC). In the particles 868 may be the component of the support member 860 (For example, Si ₃ N ₄ ) or the component of the support member 860 can not be mixed.

In the example of 4A are the particles 868 formed such that the components of the particles 868 to the not yet sintered intermediate product of the resistance heating 810 be added, and during sintering of the ceramic heater 800 from the resistance heater 810 to the support element 860 diffuse out. Therefore, the tends Particle diameter of the particles 868 in addition, with the distance from the resistance heater 810 to decrease.

In the example of 4B , are the particles 868 formed such that the components of the particles 868 on the not yet sintered intermediate product of the resistance heating 810 (In particular, as a layer) are applied, and during sintering of the ceramic heater 800 from the material of the support element 860 be surrounded. Thus, the particle diameter of the particles 868 Essentially the same over the entire range.

4C is a schematic view showing an example of the structure of the ceramic heater 800 shows. The structure in 4C is the structure of the ceramic heater 800 in the vicinity of the border, at the reverse part 815 the support element 860 is adjacent, and corresponds to the part F4 in 3 , The view in field (A) of 4C schematically illustrates the structure of the ceramic heater 800 , The view in partial image (B) of 4C corresponds to the structure in partial image (A) and represents the crystal particles in the support member 860 specifically.

In the ceramic heater 800 from 4C contains the support element 860 mainly the second ceramic composition, which is different from the first ceramic composition, the resistance heating 810 forms. The second ceramic composition contains silicon nitride (Si ₃ N ₄ ) as a main component. In the support element 860 are several particles 862p , which are different from silicon nitride (Si ₃ N ₄ ), distributed as the second ceramic composition. The crystal particles of the particles 862p are relatively smaller than the crystal particles of the silicon nitride (Si ₃ N ₄ ). The support element 860 has the resistance heating 810 neighboring area on.

In the neighboring area 866 in 4C are several particles 868 distributed. In the particles 868 is that of the various components contained in the second ceramic composition (that of silicon nitride (Si ₃ N ₄ ) and the particles 862p different component) as a component for buffering the difference in the thermal expansion coefficient between the resistance heating 810 and the support member 860 contain. This component has a larger thermal expansion coefficient than silicon nitride (Si ₃ N ₄ ). The in the particles 868 The present component is preferably an element of at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide (SiC).

In the neighboring area 866 from 4C can the particles 862p and the particles 868 be mixed. The concentration of the particles 868 in the neighboring area 866 from 4C The closer you get to the resistance heater, the higher it can be 810 are, or may be lower, the farther they are from the resistance heater 810 ,

In the present embodiment, the neighboring area is 866 in which several particles 868 are distributed, only in the reverse part 815 educated. The neighboring area 866 at least in the reverse part 815 be educated. The neighboring area 866 can in a part of the reverse part 815 , or in the entire part of the reversing part 815 be educated. The neighboring area 866 can in addition to the reverse part 815 in a part of the supply line parts 812 and 818 , or in the entire supply line 812 and 818 be educated.

The thickness T of the neighboring area 866 is preferably 10 to 200 μm (microns) from the resistance heater 810 , The thickness T of the neighboring area 866 is more preferably 20 to 100 microns from the resistance heater 810 , The determination of the thickness T of the neighboring area 866 will be described later.

The average particle diameter of the multiple particles 868 is preferably less than or equal to 5 μm. The determination of the average particle diameter will be described later.

Preferably, the relationship is 0.5% ≦ S1 / (S1 + S2) × 100% ≦ 25% between the cross-sectional area S1 of the resistance heater 810 at the point where the neighboring area 866 is formed, and the cross-sectional area S2 of the support member 860 enough. The cross-sectional area S1 is the cross-sectional area which is the sum of a cross-sectional area S1a of the reversal area 815 and the other cross-sectional area S1b of the reverse area 815 results (see 3 ). The cross-sectional area S2 is the cross-sectional area including the neighboring area 866 , S1 / (S1 + S2) is the resistance aspect ratio Rs, which is the ratio of the cross-sectional area of the resistance heater 810 to the cross-sectional area of the ceramic heater 800 represents. The determination of the resistance-area ratio Rs will be described later.

Preferably, the relationship T · (S1 + S2) / S1 ≥ 67 μm between the cross-sectional area S1 of the resistance heater 810 , the cross-sectional area S2 of the support member 860 , and the thickness T of the neighboring area 866 enough. In other words, it is preferable that the relationship between the resistance aspect ratio Rs and the thickness T of the neighboring area 866 T / Rs 67 μm is sufficient is. The determination of the value T / Rs will be described later.

A2. Production method of the glow plug

5 FIG. 10 is a flowchart illustrating a method of manufacturing the glow plug. FIG 10 shows. In the production of the glow plug 10 The manufacturer first manufactures an intermediate product of the resistance heating 810 by injection molding (process P110).

After finishing the intermediate of resistance heating 810 (Process P110), the manufacturer carries a particulate material containing the material of the particles 868 is, on the reverse part 815 the intermediate of resistance heating 810 on (process P120). In the present embodiment, the manufacturer applies the particulate matter to the intermediate product of the resistance heater 810 by immersing the intermediate product of the resistance heater 810 in the liquid particulate material.

After application of the particulate material to the intermediate product of the resistance heating 810 (Process P120), the manufacturer manufactures the intermediate product of the support element 860 by molding with a metallic mold (process S130). In the present embodiment, the intermediate product of the support member includes 860 two halves divided at the plane containing the center axis SC. Within these halves is a groove for fitting the intermediate product of the resistance heater 810 educated. In another embodiment, the fabrication of the intermediate product of the support member 860 (Process P130) before the processes of manufacturing the intermediate product of the resistance heating 810 (Process P110) and the deposition of particulate matter (Process P120).

After fabrication of the intermediate product of the support member 860 (Process P130), the manufacturer manufactures a composite molded article as a combination of the resistance heating intermediate 810 and the intermediate product of the support member 860 (Process P140).

After fabrication of the composite molded article (process P140), the manufacturer sinters the composite molded article to the ceramic heater 800 to manufacture (process P150). After making the ceramic heater 800 (Process P150) the manufacturer fastens the ceramic heater 800 on other components (the middle shaft 200 , the metal sleeve 500 , the outer cylinder 700 , and the like) of the glow plug 10 (Process P190). This will cause the glow plug 10 completed.

There is the case that the melting point of the particles 868 component is lower than the sintering temperature during sintering (process P150). In this case, the manufacturer may be the intermediate of resistance heating 810 by injection molding using an injection molding material to which the particulate material is added, which is the raw material of the particles 868 is (process P115). That in the intermediate of resistance heating 810 contained particulate material diffuses during sintering to the support element 860 (Process P150) and forms the neighboring area 866 , In this case, the diameter of the particles tends to be 868 to be smaller, the farther they are from the resistance heater 810 are removed, as in 4A shown. In the case where the sintering temperature during sintering (process P150) is 1700 to 1900 ° C, the particulate material that can be added to the injection molding material is at least one element of chromium (Cr), titanium (Ti), and zirconium (Zr) , or silicide or oxide of at least one of these elements.

A3. Evaluation of the glow plug

6 and 7 Tables are the evaluation results of the performance of the glow plug 10 represent. The examiner has evaluated samples 1 to 25, namely the glow plug 10 with ceramic heaters 800 in various specifications.

Each cross-sectional area (S1 + S2) of the ceramic heater 800 in Samples 1 to 25 is equal to 7.54 mm ² . In the ceramic heater 800 Sample 1 is not an adjoining area 866 educated. In each of the ceramic heaters 800 Samples 2 to 25 is the neighboring area 866 educated.

Each support element 860 Samples 1 to 22 contains silicon nitride (Si ₃ N ₄ ) as a main component. In addition, each of these materials contains erbium (Er) oxide and silicon oxide (SiO ₂ ) as a sintering additive. The material of the support element 860 In Samples 23 and 24, silicon nitride (Si ₃ N ₄ ) as the main component contains ytterbium (Yb) oxide and alumina (Al ₂ O ₃ ) as a sintering additive. In addition, each of these materials contains molybdenum silicide (MoSi ₂ ) as an additive component for adjusting the difference in thermal expansion between the support member 860 and the resistance heater 810 , It is emphasized that the material of the support element 860 Tungsten silicide (WSi ₂ ) as the additive component for adjusting the difference in thermal expansion between the support member 860 and the resistance heater 810 may contain. The material of the support element 860 In Sample 25, silicon nitride (Si ₃ N ₄ ) as a main component contains erbium (Er) oxide and alumina (Al ₂ O ₃ ) as a sintering additive. In the crystal grain boundary in the support member 860 Samples 1 to 25, there is a component due to the particular sintering additive (for example, rare earth element, Aluminum element). The component due to the rare earth oxide of the sintering additive may be the rare earth element-containing disilicate and / or monosilicate.

Samples 1 to 22, 24, and 25 are made by sintering in nitrogen (N ₂ ). The sample 23 is made by sintering in argon (Ar).

In Samples 2 to 11 and 16 to 22 this is the material of the particles 868 one of chromium (Cr), molybdenum (Mo), tungsten (W), and chromium oxide (Cr ₂ O ₃ ). These particulate materials are used in the manufacture of the ceramic heater 800 by reaction with the silicon nitride of the support member 860 implemented during the sintering process to silicide. The particulate material of the sample 12 is silicon carbide (SiC), which is the particle composition of the main component of the particles 868 is. The particulate material of sample 13 is chromium silicide (CrSi ₂ ). The particulate material of sample 14 is molybdenum silicide (MoSi ₂ ). The particulate material of sample 15 is tungsten silicide (WSi ₂ ).

In sample 23, it is chromium (Cr), which is the particle material of the particles 868 serves. In the support element 860 The sample 23 is a plurality of particles 862p containing molybdenum silicide (MoSi ₂ ) dispersed in the crystal particles which, like In 4C shown containing silicon nitride (Si ₃ N ₄ ). Several particles 868 are in the neighboring area 866 in the support member 860 the sample 23 distributed. The examiner has the components of molybdenum (Mo), silicon (Si), and chromium (Cr) as in the particles 868 Sample 23 components were confirmed using an Electron Probe Micro-Analyzer (EPMA) and a Scanning Electron Microscope (SEM). In the sample 23 is, from the components of the particles 868 , the chromium (Cr), which is uneven in the neighboring area 866 is distributed.

In sample 24, it is chromium (Cr), which is the particle material of the particles 868 serves. In the support element 860 The sample 24 is a plurality of particles 862p containing molybdenum silicide carbide (Mo _4.8 Si ₃ C _0.6 ) dispersed in the crystal particles containing silicon nitride (Si ₃ N ₄ ) as in 4C shown. Several particles 868 are in the neighboring area 866 the support member 860 the sample 24 distributed. The investigator has confirmed that the components molybdenum (Mo), silicon (Si), carbon (C), and chromium (Cr) as the components in the particle 868 Sample 24 are present, by means of EPMA and SEM. In the sample 24 is from the components of the particles 868 Chromium (Cr) the one that is uneven in the neighboring area 866 is distributed. It is believed that the carbon (C) in the particles 862p and the particles 868 from the mold additive (binder) resulting from the molding of the resistance heating 810 and the support member 860 is added.

In sample 25, it is chromium (Cr) that acts as the particulate material of the particles 868 diet. This particulate material reacts with the silicon nitride of the support member 860 during the sintering process during the production of the ceramic heater 800 to chromosilicide (CrSi ₂ ).

The examiner evaluated the cross section along the center axis SC of the ceramic heater 800 vertical plane for samples 1 to 25 using an Electron Probe Micro-Analyzer (EPMA). The examiner calculated the thickness T of the neighboring area 866 , the average particle diameter of the particles 868 , the resistance aspect ratio Rs, and the value T / Rs by image analysis of the EPMA image.

The examiner prepared a plurality of samples for each of samples 2 to 25. For each sample, the investigator used a Scanning Electron Microscope (SEM) at 3000x magnification and evaluated the neighboring area 866 in the ceramic heater 800 in cross section along the plane perpendicular to the center axis SC level. The examiner calculated the proportion of samples with pores by image analysis of the SEM images. The proportion of the samples with pores is the proportion of the samples in which pores of 0.1 μm or more in the neighboring area 866 present, which are recognizable in the SEM image.

10 Fig. 12 is a schematic view showing an example of the image used for the sample analysis. Each analyzed image of 10 (A) . 10 (B) , and 10 (C) is an image obtained by analyzing the same part in the cross section along the plane of the sample 24 perpendicular to the center axis SC.

10 (A) is an image taken by SEM of the cross section of the ceramic heater 800 , 10 (B) is an assignment image obtained by means of EPMA, which shows the distribution of chromium (Cr) in the cross section of the ceramic heater 800 represents. 10 (C) is an assignment image obtained by means of EPMA, which shows the distribution of molybdenum (Mo) in the cross section of the ceramic heater 800 represents.

In EPMA image analysis, the first step is the EPMA WDM, which is a wavelength-dispersive X-ray spectrometer for qualitative analysis of the cross section of the ceramic heater 800 used. That in the cross section of the ceramic heater 800 contained element was identified by the qualitative analysis.

In the second step, a measurement condition for obtaining the mapping image which represents the distribution of each element identified in the first step was set. In this case, the analysis interval and the beam diameter were set as the measurement conditions of the mapping image by decomposing the evaluation area into a mesh pattern to the extent that the required analysis accuracy could be ensured. The beam intensity and the recording time as measurement conditions of the mapping image were set so that the X-ray intensity (in counts) was strong enough to visualize the change in the detection amount of low-frequency elements.

• – Beschleunigungsspannung: 15 kV (Kilovolt)
• – Probenstrom: 1.0 × 10^–7 A (Ampère)
• – Strahldurchmesser (Minimaldurchmesser): weniger als 0.003 μm
• – Auswertungsgebiet (vertikal × lateral): 100 μm × 100 μm
• – Analyseintervall: 0.4 μm
• – Messpunkte: 250 Punkte × 250 Punkte (62500 Punkte)
• – Hauptpeak-Messdauer: 15 ms (Millisekunden)
• – Untergrund-Messdauer: 15 ms

Specific measurement conditions are as follows.

• - Acceleration voltage: 15 kV (kilovolts)
• - Sample current: 1.0 × 10 ^-7 A (ampere)
• - Beam diameter (minimum diameter): less than 0.003 μm
• - Evaluation area (vertical × lateral): 100 μm × 100 μm
• - Analysis interval: 0.4 μm
• - Measuring points: 250 points × 250 points (62500 points)
• Main peak measurement time: 15 ms (milliseconds)
• - Underground measurement duration: 15 ms

In the third step, the detection amount in the evaluation area was measured for each element specified in the first step under the measurement conditions set in the second step. In particular, the background was picked up at the side of the smaller angles after the main peak was taken at each measurement point in the evaluation area. The assignment picture (see 10 (B) and 10 (C) ) of each element was represented by displaying the X-ray intensity which resulted when the background was subtracted from the main peak at each measurement point, two-dimensionally by color coding.

From the comparison of 10 (A) and 10 (C) it can be seen that several of the molybdenum (Mo) containing particles in the support member 860 are distributed. From the comparison of 10 (A) . 10 (B) , and 10 (C) it can be seen that several particles containing the element molybdenum (Mo) and the element chromium (Cr) in the neighboring area 866 in addition to the resistance heating 810 unevenly distributed, the reverse area 815 the resistance heating 810 is adjacent.

The examiner measured the resistance of an unused sample of the glow plug 10 , The examiner then applied a voltage of 11 V to the glow plug 10 to the surface temperature of the ceramic heater 800 to increase to 1000 ° C within one second of the beginning of the flow of electricity, and then further increased to 1350 ° C. Following this, the examiner cooled the ceramic heater 800 by means of supply air. The investigator performed a longevity test of 50,000 cycles for each sample, with one cycle ranging from raising the temperature to cooling the ceramic heater 800 , After the longevity test, the examiner again measured the resistance of the glow plug 10 , Thus, the resistance increase rate was calculated. The resistance increase rate represents the rate of increase of the resistance of the glow plug 10 before and after the longevity test. It is believed that increasing the resistance of the glow plug 10 due to the deterioration of the resistance heating 810 (especially the reversal area 815 ) is caused. The examiner evaluated the longevity of each sample according to the following criteria. The evaluation result is in 6 and 7 specified.

Double circle (excellent): Resistance increase rate less than or equal to 10% Single circle (good): Resistance increase rate greater than 10% and less than 20% X mark (unusable): Resistance increase rate greater than 20%

According to the comparison of the samples 1, 2, and 9 with the samples 3 and 5 to 8, a thickness T of the neighboring region becomes 866 from 10 to 200 μm from the resistance heater 810 in terms of ensuring the longevity of resistance heating 810 prefers. Moreover, according to the comparison of the samples 3 and 8 and the samples 5 to 8, a thickness T of the neighboring region becomes 866 from 20 to 100 μm from the resistance heater 810 in terms of ensuring the longevity of resistance heating 810 prefers.

According to the comparison of Samples 5 and 10-17 with Samples 18 and 19, an average particle diameter of the particles becomes 868 less than or equal to 5 μm in terms of ensuring the longevity of the resistance heating 810 prefers. For samples 18 and 19 are in the neighboring area 866 Pores in front of which the average particle diameter of the particles 868 Exceeds 5 microns. It is therefore assumed that the pores in the neighboring area 866 one of the causes of the deterioration of the resistance heating 810 are.

According to the comparison of the sample 18 with the sample 25, it is preferred if the support member 860 a component derived from erbium (er) oxide and alumina (Al ₂ O ₃ ) with respect to the suppression of the pores in the neighboring region 866 , This contributes to an increased longevity of resistance heating 810 at.

According to the comparison of the samples 4, 5, and 21 with the sample 20, the resistance increasing rate of the sample 20 whose resistance aspect ratio Rs is less than 0.5% is larger than that of the samples 4, 5, and 21. In the sample 22, whose resistance aspect ratio Rs exceeds 25% can be the resistance of the reverse region 815 can not be sufficiently ensured. Therefore, the sample 22 did not reach the fast temperature raising property of 1000 ° C within one second from the start of the electricity flow. Therefore, it is preferable that the resistance aspect ratio Rs be greater than, equal to or less than 0.5% and equal to or less than 25% in terms of ensuring the durability of the resistance heating 810 while ensuring the rapid temperature raising property.

According to the comparison of the sample 2 with the samples 3 to 8 and 10 to 22, it is preferable that the value T / Rs be larger than or equal to 67 μm in terms of ensuring the durability of the resistance heating 810 ,

According to the comparison of the sample 5 with the sample 13, the comparison of the sample 10 with the sample 14, and the comparison of the sample 11 with the sample 15 can be seen that the longevity of the resistance heating 810 Similarly, whether the particulate material is one that becomes silicide upon sintering or the particulate material is one that is silicide prior to sintering.

According to the result of Samples 23 and 24, it can be seen that the durability of the resistance heating 810 also by a structure of the support member 860 can be ensured at the particles 862p and the particles 868 as in 4C are shown distributed.

A4. Advantage:

According to the first embodiment described above, a difference in thermal expansion between the resistance heating becomes 810 and the support member 860 in the neighboring area 866 buffered, resulting in the suppression of the thermal load of the resistance heating 810 due to the difference in thermal expansion from that of the support member 860 contributes. As a result, the longevity of resistance heating 810 be increased.

Further contributes, when the thickness T of the neighboring area 866 from 10 to 200 μm from the resistance heater 810 is the neighbor area 866 to an effective suppression of the thermal load of the resistance heating 810 at. It also contributes when the thickness T of the neighboring area 866 from 20 to 100 μm from the resistance heater 810 is the neighbor area 866 to an even more effective suppression of the thermal load of the resistance heating 810 at.

Further, when the average particle diameter of the plurality of particles 868 less than or equal to 5 microns, the formation of pores in the neighboring area 866 be suppressed. This also contributes to the suppression of fine, due to the different thermal expansion between the particles and their environment around the particles 868 around formed cracks. As a result, the longevity of the neighboring area 866 be increased, resulting in the increased longevity of resistance heating 810 contributes.

Further, when the resistance aspect ratio Rs satisfies 0.5% ≤ Rs ≤ 25%, it can prolong the resistance heating life 810 increase while ensuring the rapid temperature increase characteristic.

Further, when the value T / Rs is greater than or equal to 67 μm, the neighboring area bears 866 for suppressing the thermal load of the resistance heating 810 at.

Further, the neighbor area 866 at least the reversal area 815 adjacent. This contributes to the suppression of the thermal load on the reverse portion 815 at, whose calorific value is relatively large.

Further, the first ceramic composition containing the resistance heating 810 forms, and the second ceramic composition containing the support member 860 forms, silicon nitride as two common component. This contributes to a stronger connection between the resistance heating 810 and the support member 860 at. This can be the mechanical strength of the resistance heating 810 , and thus the longevity of resistance heating 810 continue to increase.

B. Second Embodiment

8th is a schematic view showing a cross section of a ceramic heater 800B in the second embodiment. The glow plug 10 The second embodiment is similar to that of the first embodiment, except that it is used instead of the ceramic heater 800 the first embodiment, the ceramic heater 800B includes.

The ceramic heater 800B The second embodiment is similar to that of the first embodiment except that the shape of the resistance heater 810 is different. The resistance heating 810 The second embodiment is one by printing shaped component. The resistance heating 810 of the second embodiment is similar to that of the first embodiment, except that the shape of the cross section is different along a plane perpendicular to the center axis SC.

It is preferable if the long diameter L1 of the reversing part 815 in the resistance heating 810 0.4 to 1.0 mm. The long diameter L1 of the reversing part 815 may be less than 0.4 mm or greater than 1.0 mm.

It is preferable if the short diameter L2 of the reversing part 815 in the resistance heating 810 0.02 to 0.3 mm. The short diameter L2 of the reversing part 815 may be less than 0.02 mm or greater than 0.3 mm.

9 FIG. 10 is a flowchart illustrating a method of manufacturing the glow plug. FIG 10 in the second embodiment. In the production of the glow plug 10 The manufacturer first manufactures an intermediate product of the support element 860 by metal mold press forming (process P210). In the present embodiment, the intermediate product of the support member includes 860 two components divided at the plane containing the center axis SC. Within these components, a groove is formed, the resistance heating 810 equivalent.

After fabrication of the intermediate product of the support member 860 (Process P210), the manufacturer wears a particulate material on the groove of one of the components of the intermediate member of the support member 860 by printing on (process P220).

After applying the particulate material to the intermediate product of the support member 860 (Process P220) the manufacturer prints the resistance heater 810 on the particulate material acting on the intermediate product of the support element 860 by printing (process P230).

After printing the resistance heater 810 on the intermediate product of the support element 860 (Process P230), the manufacturer applies particulate material to the intermediate product of the support element 860 printed resistance heating 810 by printing on (process P240).

After application of the particulate material to the intermediate product of the resistance heating 810 acting on the intermediate product of the support element 860 was printed (process P240), the manufacturer manufactures a composite molded article by fitting the resistance heater 810 between the two components of the intermediate product of the support element 860 (Process P250).

After fabricating the composite molded article (P250 process), the manufacturer sinters the composite molded article to the ceramic heater 800B to form (process P260). After making the ceramic heater 800B (Process P260) the manufacturer fastens the ceramic heater 800B on other components (the middle shaft 200 , the metal sleeve 500 , the outer cylinder 700 , and the like) of the glow plug 10 (Process P290). This will be the glow plug 10 completed.

There is a case in which the melting point of the particles 868 Silica is lower than the sintering temperature during sintering (process P260). In this case, the manufacturer may, after manufacturing the intermediate product of the support member 860 (Process P210), the resistance heating 810 by printing on the groove in one of the components of the intermediate member of the support member 860 by means of a printing material containing the particulate material, which is the raw material of the particles 868 was added (process P235). That in the intermediate of resistance heating 810 Particulate material diffused during sintering (process P260) in the support member 860 and forms the neighboring area 866 , In this case, the particle diameter of the particles tends to be 868 to be smaller, the farther they are from the resistance heater 810 are removed, as in 4A _{, is} shown. When the sintering sintering temperature (Process P260) is 1700 to 1900 ° C, the particulate matter that can be added to the printing material may include silicide or oxide of at least one of chromium (Cr), titanium (Ti), and zirconium (Zr). be.

According to the second embodiment described above, the longevity of the resistance heating 810 can be increased as similar to the first embodiment.

C. Other Embodiments

The present invention is not limited to the above-described embodiments and their modifications. The present invention can be implemented in various configurations as long as they do not depart from the concept of the present invention. For example, the technical features in the embodiments, examples, and modifications that correspond to the technical features of each form described in the SUMMARY may be periodically replaced and / or combined to solve part or all of the problems described above, or a part or parts thereof to achieve all of the advantages described above. Further, the technical features may be omitted unless they are described as essential in the present specification.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2009-287920 A [0002]
• JP 2011-66020 A [0003]
• JP 2010-108606 A [0004]

Claims (11)

A glow plug, comprising: a resistance heater that includes a first ceramic composition and generates heat when passing electricity; and a support member mainly including a second ceramic composition different from the first ceramic composition and containing silicon nitride (Si ₃ N ₄ ) as a main component in which the resistance heater is embedded and supporting the resistance heater, the support member including a neighboring portion which is adjacent to the resistance heater and in which a plurality of particles are laterally unevenly distributed from the resistance heater including a component whose thermal expansion coefficient is larger than that of silicon nitride (Si ₃ N ₄ ). A glow plug according to claim 1, wherein the component in the particles distributed in the neighboring area comprises at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or Silicon carbide (SiC) is. A glow plug according to claim 1 or 2, wherein the thickness of the neighboring region is 10 to 200 μ from the resistance heating. Glow plug according to one of claims 1 to 3, wherein the thickness of the adjacent region is 20 to 100 microns from the resistance heater. A glow plug according to any one of claims 1 to 4, wherein the average size of the plurality of particles is less than or equal to 5 μm. A glow plug according to any one of claims 1 to 5, wherein a relationship between the cross-sectional area S1 of the resistance heater at a position where the neighboring area is formed and the cross-sectional area S2 of the supporting member satisfies 0.5% ≦ S1 (S1 + S2) × 100% ≦ 25% , A glow plug according to any one of claims 1 to 6, wherein a relationship between the cross-sectional area S1 of the resistance heater at a position where the adjacent area is formed, the cross-sectional area S2 of the supporting member, and the thickness T of the adjacent area T · (S1 + S2) / S1 ≥ 67 microns is enough. A glow plug according to any one of claims 1 to 7, wherein the resistance heater includes: a reversing part shaped as a reverse loop; and a supply part connected to the reversing part with a larger cross section than the reversing part, and wherein the neighboring area is at least adjacent to the reversal area. A glow plug according to any one of claims 1 to 8, wherein the resistance heater is an injection molded or a printed member. A glow plug according to any one of claims 1 to 9, wherein the first ceramic composition and the second ceramic composition contain a component which is common to both. A glow plug according to any one of claims 1 to 10, wherein the second ceramic composition contains a rare earth element and aluminum (Al).

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