GLOW PLUG

Abstract

A glow plug (10), comprising: a resistance heater (810) comprising a first ceramic composition and generating heat upon conduction of electricity; and a support member (860) mainly comprising a second ceramic composition different from the first ceramic composition and containing silicon nitride (Si3N4) as a main component, in which the resistance heater is embedded, and which supports the resistance heater, wherein the support member includes a neighboring region (866) adjacent to the resistance heater, characterized in that in the neighboring region, a plurality of particles (868) containing a component whose thermal expansion coefficient is greater than that of silicon nitride (Si3N4) are unevenly distributed laterally from the resistance heater, wherein the thickness, T, of the neighboring region is 10 to 200 µm.

Description

BACKGROUND 1. Technical field

[0001] The present invention relates to a glow plug. 2. State of the art

[0002] Glow plugs are available as ceramic glow plugs with a ceramic heater (see, for example, Japanese Patent Application Laid-Open No. 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 contains a conductive ceramic composition and generates heat when electricity passes through it. The support member contains an electrically insulating ceramic composition. The support member supports the embedded resistance heater.

[0003] Japanese Patent Application Laid-Open No. 2011-66020 (Patent Document 2) discloses a technology for preventing damage to the ceramic heater due to the difference in thermal expansion between the resistance heater and the support member. In this technology, the resistance heater is coated with a coating having a hardness and density lower than those 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 lower than that of the resistance heater and the support member.

[0004] As is generally known, the thermal expansion coefficient of the resistance heating element is larger than that of the support member (see, for example, Japanese Patent Application Laid-Open No. JP 2010 - 108 606 A).

[0005] To shorten the starting time of an internal combustion engine, the glow plug must have the rapid temperature rise characteristic, so that the temperature quickly rises to a desired temperature when the flow of electricity begins. Regarding the rapid temperature rise characteristic of the glow plug, it is required that 1000°C be reached within approximately two seconds. In recent years, the requirements have become more stringent, and it is now required that 1000°C be reached in approximately one second. To improve the rapid temperature rise characteristic, the initial resistance of the resistance heater is reduced by increasing the content of conductive components in the resistance heater.

[0006] Increasing the content of conductive components in the resistance heater to improve the rapid temperature rise property will cause increased thermal stress on the resistance heater due to the difference in thermal expansion compared to the support member in the glow plug according to Patent Document 1. Therefore, this glow plug has the problem of rapid deterioration of the resistance heater. The resistance of the resistance heater increases with deterioration. Even if the content of conductive components in the resistance heater is increased in the glow plug according to Patent Document 2, the coating cannot sufficiently alleviate the thermal stress occurring in the resistance heater. Therefore, this glow plug also has the problem of rapid deterioration of the resistance heater.In addition, the strength of the coating coating the resistance heater in the glow plug according to Patent Document 2 is relatively low. Therefore, there is a problem that the strength of the ceramic heater cannot be sufficiently guaranteed.

[0007] The published patent application US 2009 / 0 194 519 A1 discloses a ceramic heater with a heating element comprising molybdenum and tungsten silicide, nitride and / or carbide and a base of mainly silicon nitride and further 4 to 25 mass% of a rare earth oxide component, 1 to 8 mass% of chromium silicide and 0.02 to 1.0 mass% of aluminum nitride. SUMMARY

[0008] The present invention aims to solve the above-mentioned problems. The present invention can be implemented as follows.

[0009] A glow plug according to an embodiment of the present invention is provided. In this embodiment, the glow plug includes: a resistance heater comprising a first ceramic composition and generating heat upon conduction of electricity; and a support member mainly comprising a second ceramic composition different from the first ceramic composition and containing silicon nitride (Si3N4) as a main component, in which the resistance heater is embedded and which supports 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 containing a component whose thermal expansion coefficient is larger than that of silicon nitride (Si3N4) are unevenly distributed laterally from the resistance heater.

[0010] According to this glow plug design, differences in thermal expansion between the resistance heater and the support element are buffered in the adjacent region. This contributes to suppressing thermal stress on the resistance heater due to thermal expansion differing from that of the support element. As a result, the longevity of the resistance heater can be improved.

[0011] In this embodiment of the glow plug, the component of the particles distributed in the adjacent region may be at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide (SiC).

[0012] This embodiment of the glow plug can effectively improve the longevity of the resistance heater held by the support member.

[0013] (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 containing a first ceramic composition and generating heat upon conduction of electricity; and a support member mainly containing a second ceramic composition different from the first, whose thermal expansion coefficient is lower than that of the first ceramic composition, in which the resistance heater is embedded, and which supports the resistance heater. In this embodiment of the glow plug, the support member includes a neighboring region adjacent to the resistance heater in which a plurality of particles are dispersed. The plurality of particles contains a third ceramic composition whose thermal expansion coefficient is higher than that of the second ceramic composition.According to this glow plug design, the difference in thermal expansion between the resistance heater and the support element is buffered in the adjacent region. This contributes to suppressing thermal stress on the resistance heater due to the different thermal expansion compared to that of the support element. As a result, the longevity of the resistance heater can be improved.

[0014] (2) In the above embodiment of the glow plug, the thickness of the neighboring region of the resistance heater may be 10 to 200 µm.

[0015] According to this embodiment of the glow plug, the adjacent region effectively contributes to suppressing the thermal load of the resistance heater.

[0016] (3) In the above embodiment of the glow plug, the thickness of the neighboring region of the resistance heater may be 20 to 100 µm.

[0017] According to this embodiment of the glow plug, the adjacent area contributes even more effectively to suppressing the thermal load of the resistance heater.

[0018] (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.

[0019] The glow plug according to this embodiment contributes to the suppression of pore formation in the adjacent region. Furthermore, this contributes to the suppression of fine cracks generated around the particles due to the thermal expansion differences between the particles and their surroundings. As a result, the durability of the adjacent region can be increased, thus improving the durability of the resistance heater.

[0020] (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).

[0021] According to this embodiment, the glow plug can improve the durability of the resistance heater supported by the support member mainly containing silicon nitride.

[0022] (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 adjacent region is formed and the cross-sectional area S2 of the support member may satisfy 0.5% ≤ S1 / (S1 + S2) × 100% ≤ 25%.

[0023] According to this embodiment, the glow plug can improve the durability while ensuring the property of rapid temperature rise.

[0024] (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 region is formed, the cross-sectional area S2 of the support member, and the thickness T of the neighboring region may satisfy T·(S1 + S2) / S 1 ≥ 67 μm.

[0025] According to this embodiment of the glow plug, the adjacent region contributes to the sufficient suppression of the thermal load of the resistance heater.

[0026] (8) In the above embodiment of the glow plug, the resistance heater may include: a return part formed as a return loop; and a lead part connected to the return part and having a larger cross section than the return part, wherein the adjacent region may be at least adjacent to the return part.

[0027] This design of the glow plug contributes to the suppression of the thermal stress that occurs on the reversing part, whose calorific value is relatively high.

[0028] (9) In the above embodiment of the glow plug, the resistance heater may be formed by injection molding or printing.

[0029] Designing the glow plug with a resistance heater formed by injection molding or printing can increase its longevity.

[0030] (10) In the above embodiment of the glow plug, the first ceramic composition and the second ceramic composition may contain a component common to both.

[0031] According to this glow plug design, the connection between the resistance heater and the support element is reinforced, which contributes to increased mechanical strength of the resistance heater. Therefore, the longevity of the resistance heater can be further increased.

[0032] (11) In the above embodiment of the glow plug, the second ceramic composition may contain a rare earth element and aluminum (Al).

[0033] This design of the glow plug can further increase the longevity of the resistance heater.

[0034] The present invention can be implemented in various ways besides a glow plug. For example, the present invention can be implemented in the form of a glow plug component, a glow plug manufacturing method, and so on. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a partial cross section of the glow plug; Fig. 2 is a schematic view showing a cross section of a resistance heater; Fig. 3 is a schematic view showing a cross section of the ceramic heater; Fig. 4A is a schematic view showing an example of a structure of the ceramic heater; Fig. 4B is a schematic view showing an example of a structure of the ceramic heater; Fig. 4C is a schematic view showing an example of a structure of the ceramic heater; Fig. 5 is a flowchart showing a manufacturing method of the glow plug; Fig. 6 is a table showing an evaluation result of the glow plug performance; Fig. 7 is a table showing an evaluation result of the glow plug performance; Fig. 8 is a schematic view showing a cross section of a ceramic heater according to a second embodiment; Fig. 9 is a flowchart showing a manufacturing method for the glow plug according to the second embodiment; and Fig. 10 is a schematic view showing an example of an image used for sample analysis. DETAILED DESCRIPTION

[0035] 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. However, it will be appreciated that one or more embodiments may be omitted from these specific details. Elsewhere, well-known structures and devices are shown schematically to simplify the drawings. A. First Embodiment A1. Glow Plug Configuration

[0036] Fig. 1 is a schematic view showing a partial cross section of a glow plug 10.

[0037] In Fig. 1, the outer shape of the glow plug 10 is shown on the right side of the sheet, relative to a boundary defined by the center axis SC of the glow plug 10, 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, reference is made to the shape shown in the sheet of Fig. 1 lower side of the glow plug 10 as “front end side”, and on the upper side in the sheet of Fig. 1 referred to as “rear end page”.

[0038] The glow plug 10 includes a ceramic heater 800 that generates heat. The glow plug 10 acts as a heat source that assists ignition during the starting of an internal combustion engine 90, such as a diesel engine. In addition to the ceramic heater 800, the glow plug 10 includes a center shaft 200, a metal sleeve 500, and an outer cylinder 700. The center axis SC of the glow plug 10 also indicates the center of each component of the glow plug 10.

[0039] The center shaft 200 of the glow plug 10 is a conductive metallic component. The center shaft 200 has a columnar shape extending along the center axis SC as its center. The center shaft 200 conducts the electrical energy supplied from outside the glow plug 10 to the ceramic heater 800.

[0040] In the present embodiment, the center shaft 200 receives the power supply via the terminal 100 from outside the glow plug 10 at the rear end of the center shaft 200. In another embodiment, the center shaft 200 may receive the power supply directly from outside the glow plug 10 at the rear end of the center shaft 200.

[0041] In the present embodiment, the center shaft 200 is electrically connected to the ceramic heater 800 via a ring 600 on the front end side of the center shaft 200. In another embodiment, the center shaft 200 may be directly connected to the ceramic heater 800 on the front end side of the center shaft 200.

[0042] The metal sleeve 500 of the glow plug 10 is a conductive metallic component. The metal sleeve 500 has a cylindrical shape extending along the central axis SC as its center. The metal sleeve 500 includes an axial hole 510, a tool engagement portion 520, and an external thread 540.

[0043] The axial hole 510 of the metal shell 500 is a through hole extending along the central axis SC as its center. The inner diameter of the axial hole 510 is larger than the outer diameter of the center shaft 200. The center shaft 200 is arranged on the central axis SC within the axial hole 510. Thus, a gap is provided between the wall of the axial hole 510 and the center shaft 200, electrically insulating the center shaft 200 from the wall of the axial hole 510. In the present embodiment, the center shaft 200 is fixed to the rear end side of the axial hole 510 via a cylindrical insulating member 300 and an annular insulating member 400.

[0044] The tool engagement portion 520 of the metal sleeve 500 is configured to engage a tool (not shown) used for installing and removing the glow plug 10 from the internal combustion engine 90. The external thread 540 of the metal sleeve 500 is configured to fit into the internal thread formed in the internal combustion engine 90 for attachment to the internal combustion engine 90.

[0045] The outer cylinder 700 of the glow plug 10 is a conductive metallic component. The outer cylinder 700 has a cylindrical shape extending along the central axis SC as its center. The outer cylinder 700 includes an axial hole 710 that holds the ceramic heater 800 therein. The rear end of the outer cylinder 700 is welded to the front end of the metal sleeve 500. The ceramic heater 800 protrudes beyond the front end of the outer cylinder 700.

[0046] The ceramic heater 800 of 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 element 860.

[0047] The resistance heater 810 of the ceramic heater 800 is a conductive ceramic containing a conductive first ceramic composition. The resistance heater 810 generates heat when electricity passes through it. In the present embodiment, the resistance heater 810 is a component formed by injection molding.

[0048] In the present embodiment, the first ceramic composition forming the resistance heater 810 mainly contains tungsten carbide (WC). In the present embodiment, the first ceramic composition contains silicon nitride (Si3N4) 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 wt.% of the first ceramic composition may include erbium oxide (Er2O3) and silicon oxide (SiO2). In another embodiment, the first ceramic composition may be a composition mainly of molybdenum silicide (MoSi2). Incidentally, "mainly" means the component with the largest weight fraction, in particular one comprising more than 50 wt.%.

[0049] The support member 860 of the ceramic heater 800 is an insulating ceramic that primarily includes an electrically insulating second ceramic composition. The resistance heater 810 is embedded in the support member 860. The support member 860 electrically insulates the resistance heater 810 from the outside of the glow plug 10. Furthermore, the support member 860 conducts heat from the resistance heater 810 to the outside of the glow plug 10.

[0050] In the present embodiment, the second ceramic composition forming the support member 860 mainly contains silicon nitride (Si3N4). In another embodiment, at least a portion of the silicon (Si) in the silicon nitride (Si3N4) forming the support member 860 may be replaced with aluminum (Al), and at least a portion of the nitride (N) may be replaced with oxygen (O). The second ceramic composition forming the support member 860 may contain rare earth oxide (e.g., ytterbium (Yb) oxide, erbium (Er) oxide, or the like) and aluminum (Al) oxide as sintering additives.

[0051] Fig. 2 is a schematic view showing a cross section of the ceramic heater 800. The cross section in Fig. Figure 2 is a cross-section of the ceramic heater 800 along the plane containing the central axis SC. The resistance heater 810 of the ceramic heater 800 includes a terminal portion 811, a lead portion 812, a return portion 815, a lead portion 818, and a terminal portion 819.

[0052] The terminal part 811 of the resistance heater 810 is provided at the rear end of the lead part 812 and exposed from the support member 860. With the ceramic heater 800 attached to the metal sleeve 500, the terminal part 811 is electrically connected to the center shaft 200.

[0053] The supply part 812 of the resistance heater 810 has a linear shape along the central axis SC. The supply part 812 connects the connection part 811 to the reversing part 815. The cross-section of the supply part 812 is larger than that of the reversing part 815.

[0054] The reversing portion 815 of the resistance heater 810 forms a U-shaped loop. One leg of the U-shape of the reversing portion 815 is connected to the lead portion 812, and the other leg of the U-shape is connected to the lead portion 818. The cross-section of the reversing portion 815 is smaller than that of the lead portion 812 and the lead portion 818. Therefore, the electrical resistance of the reversing portion 815 is greater than that of the lead portion 812 and the lead portion 818. Therefore, the resistance heater 810 generates heat when electricity flows through it, with the reversing portion 815 being the center of heat generation.

[0055] The supply part 818 of the resistance heater 810 has a linear shape along the central axis SC. The supply part 818 connects the reversing part 815 to the connecting part 819. The cross-section of the supply part 818 is larger than that of the reversing part 815.

[0056] The connection part 819 of the resistance heater 810 is provided at the rear end of the lead part 818 and exposed from the support member 860. With the ceramic heater 800 attached to the metal sleeve 500, the connection part 819 is electrically connected to the outer cylinder 700.

[0057] Fig. 3 is a schematic view showing the cross section of the ceramic heater 800. The cross section in Fig. Figure 3 is a cross-section of the ceramic heater 800 along the plane perpendicular to the central axis SC at the inversion part 815. This cross-section corresponds to the cross-section along F3-F3 of Fig. 2.

[0058] 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.

[0059] The long diameter L1 of the reversing part 815 in the resistance heater 810 is preferably 0.3 to 1.8 mm. The long diameter L1 of the reversing part 815 may also be smaller than 0.3 mm or larger than 1.8 mm.

[0060] The short diameter L2 of the reversing part 815 in the resistance heater 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.

[0061] Fig. 4A and Fig. 4B are schematic views showing an example of the structure of the ceramic heater 800. The structure in Fig. 4A and Fig. Fig. 4B is the structure of the ceramic heater 800 in the vicinity of the boundary where the reversing part 815 is adjacent to the support member 860, and corresponds to part F4 of Fig. 3.

[0062] The support element 860 of the ceramic heater 800 has a neighboring region 866 adjacent to the resistance heater 810. In the neighboring region 866, a plurality of particles 868 containing a third ceramic composition whose thermal expansion coefficient is greater than that of the second ceramic composition are distributed in a solid phase 862 containing the second ceramic composition forming the support element 860. The main component of the third ceramic composition forming the particles 868 is preferably a silicide of at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide (SiC). The component of the support element 860 (for example, Si3N4) may be mixed into the particles 868, or the component of the support element 860 may not be mixed.

[0063] In the example of Fig. 4A, the particles 868 are formed such that the components of the particles 868 are added to the not-yet-sintered intermediate product of the resistance heater 810 and diffuse from the resistance heater 810 to the support member 860 during sintering of the ceramic heater 800. Therefore, the particle diameter of the particles 868 tends to decrease with distance from the resistance heater 810.

[0064] In the example of Fig. 4B, the particles 868 are formed such that the components of the particles 868 are applied to the not yet sintered intermediate product of the resistance heater 810 (in particular as a layer) and are surrounded by the material of the support element 860 during sintering of the ceramic heater 800. Thus, the particle diameter of the particles 868 is substantially the same over the entire area.

[0065] Fig. 4C is a schematic view showing an example of the structure of the ceramic heater 800. The structure in Fig. 4C is the structure of the ceramic heater 800 in the vicinity of the boundary where the reversing part 815 is adjacent to the support member 860, and corresponds to the part F4 in Fig. 3. The view in part (A) of Fig. 4C schematically illustrates the structure of the ceramic heater 800. The view in part (B) of Fig. Figure 4C corresponds to the structure in part (A) and specifically depicts the crystal particles in the support element 860.

[0066] In the ceramic heater 800 from Fig. 4C, the support member 860 mainly contains the second ceramic composition, which is different from the first ceramic composition constituting the resistance heater 810. The second ceramic composition contains silicon nitride (Si3N4) as the main component. A plurality of particles 862p other than silicon nitride (Si3N4) are dispersed in the support member 860 as the second ceramic composition. The crystal particles of the particles 862p are relatively smaller than the crystal particles of silicon nitride (Si3N4). The support member 860 has the adjacent region adjacent to the resistance heater 810.

[0067] In the neighboring area 866 in Fig. 4C, a plurality of particles 868 are distributed. The particles 868 contain the component other than that contained in the second ceramic composition (i.e., the component other than silicon nitride (Si3N4) and the particles 862p) as a component for buffering the difference in thermal expansion coefficient between the resistance heater 810 and the support member 860. This component has a larger thermal expansion coefficient than silicon nitride (Si3N4). The component present in the particles 868 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).

[0068] In the neighboring area 866 of Fig. 4C, the particles 862p and the particles 868 may be mixed. The concentration of the particles 868 in the neighboring region 866 of Fig. 4C may be higher the closer they are to the resistance heater 810, or may be lower the farther they are from the resistance heater 810.

[0069] In the present embodiment, the adjacent region 866 in which a plurality of particles 868 are distributed is formed only in the reversing part 815. The adjacent region 866 may be formed at least in the reversing part 815. The adjacent region 866 may be formed in a part of the reversing part 815, or in the entire part of the reversing part 815. The adjacent region 866 may be formed in a part of the supply parts 812 and 818 in addition to the reversing part 815, or in the entire supply parts 812 and 818.

[0070] The thickness T of the adjacent region 866 is preferably 10 to 200 µm (micrometers) from the resistance heater 810. The thickness T of the adjacent region 866 is more preferably 20 to 100 µm from the resistance heater 810. The determination of the thickness T of the adjacent region 866 will be described later.

[0071] The average particle diameter of the plurality of particles 868 is preferably less than or equal to 5 µm. The determination of the average particle diameter will be described later.

[0072] Preferably, the relationship 0.5% ≤ S1 / (S1 + S2) × 100% ≤ 25% between the cross-sectional area S1 of the resistance heater 810 at the location where the adjacent region 866 is formed and the cross-sectional area S2 of the support member 860 is satisfied. The cross-sectional area S1 is the cross-sectional area resulting from the sum of one cross-sectional area S1a of the reversal region 815 and the other cross-sectional area S1b of the reversal region 815 (see Fig. 3). The cross-sectional area S2 is the cross-sectional area including the adjacent region 866. S1 / (S1 + S2) is the resistance cross-sectional ratio Rs, which represents the ratio of the cross-sectional area of the resistance heater 810 to the cross-sectional area of the ceramic heater 800. The determination of the resistance cross-sectional ratio Rs will be described later.

[0073] Preferably, the relationship T·(S1 + S2) / S 1 ≥ 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 adjacent region 866 is satisfied. In other words, it is preferable that the relationship between the resistance cross-sectional ratio Rs and the thickness T of the adjacent region 866 is satisfied as T / Rs ≥ 67 µm. The determination of the value T / Rs will be described later. A2. Glow plug manufacturing process

[0074] Fig. 5 is a flowchart showing a manufacturing process of the glow plug 10. In manufacturing the glow plug 10, the manufacturer first produces an intermediate resistance heater 810 by injection molding (process P110).

[0075] After manufacturing the intermediate resistance heater 810 (process P110), the manufacturer applies a particulate material, which is the material of the particles 868, to the inversion portion 815 of the intermediate resistance heater 810 (process P120). In the present embodiment, the manufacturer applies the particulate material to the intermediate resistance heater 810 by immersing the intermediate resistance heater 810 in the liquid particulate material.

[0076] After applying the particulate material to the intermediate resistance heater 810 (process P120), the manufacturer manufactures the intermediate support member 860 by compression molding with a metallic mold (process P130). In the present embodiment, the intermediate support member 860 includes two halves split along the plane containing the central axis SC. A groove is formed within these halves for fitting the intermediate resistance heater 810. In another embodiment, the manufacturing of the intermediate support member 860 (process P130) may occur before the processes of manufacturing the intermediate resistance heater 810 (process P110) and applying the particulate material (process P120).

[0077] After manufacturing the intermediate support member 860 (process P130), the manufacturer produces a composite molded article as a combination of the intermediate resistance heater 810 and the intermediate support member 860 (process P140).

[0078] After manufacturing the composite molded article (process P140), the manufacturer sinters the composite molded article to produce the ceramic heater 800 (process P150). After manufacturing the ceramic heater 800 (process P150), the manufacturer attaches the ceramic heater 800 to other components (the center shaft 200, the metal sleeve 500, the outer cylinder 700, and the like) of the glow plug 10 (process P190). This completes the glow plug 10.

[0079] There is a case where the melting point of the component forming the particles 868 is lower than the sintering temperature during sintering (process P150). In this case, the manufacturer can produce the intermediate product of the resistance heater 810 by injection molding, using an injection molding material to which the particulate material, which is the raw material of the particles 868, is added (process P115). The particulate material contained in the intermediate product of the resistance heater 810 diffuses to the support element 860 during sintering (process P150) and forms the adjacent region 866. In this case, the diameter of the particles 868 tends to be smaller the further they are away from the resistance heater 810, as shown in Fig. 4A. 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. Glow plug evaluation

[0080] Fig. 6 and Fig. Figure 7 shows the evaluation results of the performance of glow plug 10. The investigator evaluated samples 1 to 25, namely glow plug 10 with ceramic heaters 800 in various specifications.

[0081] Each cross-sectional area (S1 + S2) of the ceramic heaters 800 in samples 1 to 25 is equally 7.54 mm 2 . In the ceramic heater 800 of Sample 1, no adjacent region 866 is formed. In each of the ceramic heaters 800 of Samples 2 to 25, the adjacent region 866 is formed.

[0082] Each support member 860 of Samples 1 to 22 contains silicon nitride (Si3N4) as the main component. Furthermore, each of these materials contains erbium (Er) oxide and silicon oxide (SiO2) as sintering additives. The material of the support member 860 in Samples 23 and 24 contains silicon nitride (Si3N4) as the main component, and contains ytterbium (Yb) oxide and aluminum oxide (Al2O3) as sintering additives. Furthermore, each of these materials contains molybdenum silicide (MoSi2) as an additive component for adjusting the difference in thermal expansion between the support member 860 and the resistance heater 810. It should be noted that the material of the support member 860 may contain tungsten silicide (WSi2) as the additive component for adjusting the difference in thermal expansion between the support member 860 and the resistance heater 810.The material of the support member 860 in Sample 25 contains silicon nitride (Si3N4) as the main component and also contains erbium oxide and aluminum oxide (Al2O3) as sintering additives. A component derived from the respective sintering additive (e.g., rare earth element, aluminum element) is present in the crystal grain boundary in the support member 860 of Samples 1 to 25. The component derived from the rare earth oxide of the sintering additive can be the rare earth element-containing disilicate and / or monosilicate.

[0083] Samples 1 to 22, 24, and 25 were sintered in nitrogen (N2). Sample 23 was sintered in argon (Ar).

[0084] In samples 2 to 11 and 16 to 22, the particulate material serving as the material of particles 868 is one of chromium (Cr), molybdenum (Mo), tungsten (W), and chromium oxide (Cr2O3).

[0085] These particulate materials are converted into silicide during the production of the ceramic heater 800 by reacting with the silicon nitride of the support element 860 during the sintering process. The particulate material of sample 12 is silicon carbide (SiC), which is the particle composition of the main component of particles 868. The particulate material of sample 13 is chromium silicide (CrSi2). The particulate material of sample 14 is molybdenum silicide (MoSi2). The particulate material of sample 15 is tungsten silicide (WSi2).

[0086] In Sample 23, it is chromium (Cr) that serves as the particle material of the particles 868. In the support member 860 of Sample 23, several particles 862p containing molybdenum silicide (MoSi2) are distributed in the crystal particles, which, as shown in Fig. 4C, which contains silicon nitride (Si3N4). Several particles 868 are distributed in the adjacent region 866 in the support member 860 of Sample 23. The examiner confirmed the components of molybdenum (Mo), silicon (Si), and chromium (Cr) as components present in the particles 868 of Sample 23 using an electron probe micro-analyzer (EPMA) and a scanning electron microscope (SEM). In Sample 23, among the components of the particles 868, chromium (Cr) is the one that is unevenly distributed in the adjacent region 866.

[0087] In Sample 24, it is chromium (Cr) that serves as the particle material of the particles 868. In the support element 860 of Sample 24, several particles 862p, which are molybdenum silicide carbide (Mo 4.8 Si3C 0.6 ) are distributed in the crystal particles containing silicon nitride (Si3N4), as in Fig. 4C. Several particles 868 are distributed in the adjacent region 866 of the support member 860 of Sample 24. The examiner confirmed that molybdenum (Mo), silicon (Si), carbon (C), and chromium (Cr) are present as the components in the particle 868 of Sample 24 using EPMA and SEM. In Sample 24, among the components of the particles 868, chromium (Cr) is the one that is unevenly distributed in the adjacent region 866. It is assumed that the carbon (C) in the particles 862p and the particles 868 originates from the molding additive (binder) added during the molding of the resistance heater 810 and the support member 860.

[0088] In Sample 25, it is chromium (Cr) that serves as the particulate material of particles 868. This particulate material reacts with the silicon nitride of the support element 860 during the sintering process in the manufacture of the ceramic heater 800 to form chromium silicide (CrSi2).

[0089] The examiner evaluated the cross-section along the plane perpendicular to the central axis SC of the ceramic heater 800 for samples 1 to 25 using an Electron Probe Micro-Analyzer (EPMA). The examiner calculated the thickness T of the adjacent region 866, the average particle diameter of the particles 868, the resistance-to-cross-sectional ratio Rs, and the T / Rs value by image analysis of the EPMA image.

[0090] The examiner prepared a plurality of samples for each of samples 2 to 25. For each sample, the examiner used a scanning electron microscope (SEM) with 3000x magnification and examined the adjacent region 866 in the ceramic heater 800 in cross-section along the plane perpendicular to the central axis SC. The examiner calculated the proportion of samples with pores by image analysis of the SEM images. The proportion of samples with pores is the proportion of samples in which pores of 0.1 µm or more are present in the adjacent region 866, which are visible in the SEM image.

[0091] Fig. Figure 10 is a schematic view showing an example of the image used for sample analysis. Each analyzed image of Fig. 10(A), Fig. 10(B), and Fig. 10(C) is an image obtained by analyzing the same part in the cross section along the plane perpendicular to the center axis SC of the sample 24.

[0092] Fig. Figure 10(A) is an SEM image of the cross section of the ceramic heater 800. Fig. 10(B) is an EPMA map showing the distribution of chromium (Cr) in the cross section of the ceramic heater 800. Fig. 10(C) is an EPMA map showing the distribution of molybdenum (Mo) in the cross section of the ceramic heater 800.

[0093] In the EPMA image analysis, the EPMA's wavelength dispersive X-ray spectrometer (WDS) is used in the first step to qualitatively analyze the cross-section of the ceramic heater 800. The element contained in the cross-section of the ceramic heater 800 was identified through the qualitative analysis.

[0094] In the second step, a measurement condition was defined to obtain the mapping image, which represents the distribution of each element identified in the first step. The analysis interval and beam diameter were determined as the measurement conditions of the mapping image by decomposing the evaluation area into a grid pattern to ensure the required analysis accuracy. The beam intensity and acquisition duration were set as the measurement conditions of the mapping image so that the X-ray intensity (in counts) was strong enough to visualize the change in the detection size for low-abundance elements.

[0095] Specific measurement conditions are as follows. - Acceleration voltage: 15 kV (kilovolts) - Sample flow: 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 duration: 15 ms (milliseconds) - Background measurement time: 15 ms

[0096] In the third step, the detection size in the evaluation area was measured for each element specified in the first step under the measurement conditions defined in the second step. Specifically, the background was recorded on the smaller angle side after the main peak was recorded at each measurement point in the evaluation area. The mapping image (see Fig. 10(B) and Fig. 10(C)) of each element was represented by displaying the X-ray intensity obtained when the background was subtracted from the main peak at each measurement point, two-dimensionally by color coding.

[0097] From the comparison of the Fig. 10(A) and Fig. 10(C) shows that several particles containing the element molybdenum (Mo) are distributed in the support member 860. From the comparison of the Fig. 10(A), Fig. 10(B), and Fig. 10(C) shows that several particles containing the element molybdenum (Mo) and the element chromium (Cr) are unevenly distributed in the neighboring region 866 adjacent to the resistance heater 810, which is adjacent to the reversal region 815 of the resistance heater 810.

[0098] The examiner measured the resistance of an unused glow plug sample 10. The examiner then applied a voltage of 11 V to the glow plug 10 to raise the surface temperature of the ceramic heater 800 to 1000 °C within one second from the start of the electricity flow, and then further raised it to 1350 °C. The examiner then cooled the ceramic heater 800 using forced air. The examiner conducted a durability test for each sample with 50,000 cycles, with one cycle from the temperature increase to the cooling of the ceramic heater 800. After the durability test, the examiner measured the resistance of the glow plug 10 again. This calculated the resistance increase rate. The resistance increase rate represents the increase rate of the resistance of the glow plug 10 before and after the durability test.The increase in resistance of glow plug 10 is believed to be caused by deterioration of resistance heater 810 (especially the reversing area 815). The investigator evaluated the durability of each sample using the following criteria. The evaluation results are shown in Figure 1. Fig. 6 and Fig. 7 is specified. Double circuit (excellent): resistance increase rate less than or equal to 10% Single circuit (good): resistance increase rate greater than 10% and less than 20% X-mark (unusable): Resistance increase rate greater than 20%

[0099] According to the comparison of Samples 1, 2, and 9 with Samples 3 and 5 to 8, a thickness T of the adjacent region 866 of 10 to 200 µm from the resistance heater 810 is preferred in terms of ensuring the longevity of the resistance heater 810. Furthermore, according to the comparison of Samples 3 and 8 and Samples 5 to 8, a thickness T of the adjacent region 866 of 20 to 100 µm from the resistance heater 810 is preferred in terms of ensuring the longevity of the resistance heater 810.

[0100] According to the comparison of Samples 5 and 10-17 with Samples 18 and 19, an average particle diameter of the particles 868 of less than or equal to 5 µm is preferred in terms of ensuring the longevity of the resistance heater 810. In Samples 18 and 19, there are pores in the adjacent region 866 in which the average particle diameter of the particles 868 exceeds 5 µm. Therefore, it is assumed that the pores in the adjacent region 866 are one of the causes of the deterioration of the resistance heater 810.

[0101] According to the comparison of Sample 18 with Sample 25, it is preferable for the support member 860 to contain a component derived from erbium (Er) oxide and aluminum oxide (Al2O3) in terms of suppressing the pores in the adjacent region 866. This contributes to increased longevity of the resistance heater 810.

[0102] According to the comparison of Samples 4, 5, and 21 with Sample 20, the resistance increase rate of Sample 20, whose resistance cross-sectional ratio Rs is less than 0.5%, is higher than that of Samples 4, 5, and 21. In Sample 22, whose resistance cross-sectional ratio Rs exceeds 25%, the resistance of the inversion region 815 cannot be sufficiently ensured. Therefore, Sample 22 did not achieve the rapid temperature increase characteristic of 1000°C within one second from the start of electricity flow. Therefore, it is preferable that the resistance cross-sectional ratio Rs be greater than or equal to 0.5% and less than or equal to 25% in terms of ensuring the longevity of the resistance heater 810 while ensuring the rapid temperature increase characteristic.

[0103] According to the comparison of Sample 2 with Samples 3 to 8 and 10 to 22, it is preferable that the value of T / Rs is greater than or equal to 67 µm in terms of ensuring the longevity of the resistance heater 810.

[0104] According to the comparison of Sample 5 with Sample 13, the comparison of Sample 10 with Sample 14, and the comparison of Sample 11 with Sample 15, it can be seen that the longevity of the resistance heater 810 can be ensured in a similar manner regardless of whether the particulate material is one that becomes silicide upon sintering or whether the particulate material is one that is already silicide before sintering.

[0105] According to the result of Samples 23 and 24, it can be seen that the durability of the resistance heater 810 can also be ensured by a structure of the support member 860 in which particles 862p and the particles 868 as in Fig. 4C shown. A4. Advantage:

[0106] According to the first embodiment described above, a difference in thermal expansion between the resistance heater 810 and the support member 860 is buffered in the adjacent region 866, which contributes to suppressing the thermal stress on the resistance heater 810 due to the difference in thermal expansion from that of the support member 860. As a result, the durability of the resistance heater 810 can be increased.

[0107] Furthermore, when the thickness T of the adjacent region 866 is from 10 to 200 µm to the resistance heater 810, the adjacent region 866 contributes to an effective suppression of the thermal load on the resistance heater 810. Furthermore, when the thickness T of the adjacent region 866 is from 20 to 100 µm to the resistance heater 810, the adjacent region 866 contributes to an even more effective suppression of the thermal load on the resistance heater 810.

[0108] Furthermore, when the average particle diameter of the plurality of particles 868 is less than or equal to 5 µm, the formation of pores in the adjacent region 866 can be suppressed. This further contributes to the suppression of fine cracks formed around the particles 868 due to the difference in thermal expansion between the particles and their surroundings. As a result, the longevity of the adjacent region 866 can be increased, which contributes to the increased longevity of the resistance heater 810.

[0109] Furthermore, if the resistance area ratio Rs satisfies the relationship 0.5% ≤ Rs ≤ 25%, this can increase the durability of the resistance heater 810 while ensuring the rapid temperature rise property.

[0110] Furthermore, when the value T / Rs is greater than or equal to 67 µm, the neighboring region 866 contributes to suppressing the thermal stress on the resistance heater 810.

[0111] Furthermore, the adjacent region 866 is at least adjacent to the reversal region 815. This contributes to suppressing the thermal stress at the reversal region 815, whose calorific value is relatively high.

[0112] Furthermore, the first ceramic composition forming the resistance heater 810 and the second ceramic composition forming the support member 860 contain silicon nitride as a common component. This contributes to a stronger bond between the resistance heater 810 and the support member 860. This can further increase the mechanical strength of the resistance heater 810 and thus the longevity of the resistance heater 810. B. Second embodiment

[0113] Fig. 8 is a schematic view showing a cross section of a ceramic heater 800B in the second embodiment. The glow plug 10 of the second embodiment is similar to that of the first embodiment, except that it includes the ceramic heater 800B instead of the ceramic heater 800 of the first embodiment.

[0114] The ceramic heater 800B of the second embodiment is similar to that of the first embodiment, except that the shape of the resistance heater 810 is different. The resistance heater 810 of the second embodiment is a component formed by printing. The resistance heater 810 of the second embodiment is similar to that of the first embodiment, except that the shape of the cross section along a plane perpendicular to the central axis SC is different.

[0115] It is preferable that the long diameter L1 of the reversing part 815 in the resistance heater 810 is 0.4 to 1.0 mm. The long diameter L1 of the reversing part 815 may be smaller than 0.4 mm or larger than 1.0 mm.

[0116] It is preferable that the short diameter L2 of the reversing part 815 in the resistance heater 810 is 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.

[0117] Fig. 9 is a flowchart showing a manufacturing process of the glow plug 10 in the second embodiment. In manufacturing the glow plug 10, the manufacturer first produces an intermediate support member 860 by metal compression molding (process P210). In the present embodiment, the intermediate support member 860 includes two components divided along the plane containing the center axis SC. A groove corresponding to the resistance heater 810 is formed within these components.

[0118] After manufacturing the intermediate support member 860 (process P210), the manufacturer applies a particulate material to the groove of one of the components of the intermediate support member 860 by printing (process P220).

[0119] After applying the particulate material to the intermediate support member 860 (process P220), the manufacturer prints the resistive heater 810 onto the particulate material that was applied to the intermediate support member 860 by printing (process P230).

[0120] After printing the resistance heater 810 onto the intermediate support member 860 (process P230), the manufacturer applies particulate material to the resistance heater 810 printed onto the intermediate support member 860 by printing (process P240).

[0121] After applying the particulate material to the intermediate resistance heater 810 printed on the intermediate support member 860 (process P240), the manufacturer produces a composite molded article by fitting the resistance heater 810 between the two components of the intermediate support member 860 (process P250).

[0122] After manufacturing the composite molded article (process P250), the manufacturer sinters the composite molded article to form the ceramic heater 800B (process P260). After manufacturing the ceramic heater 800B (process P260), the manufacturer attaches the ceramic heater 800B to other components (the center shaft 200, the metal sleeve 500, the outer cylinder 700, and the like) of the glow plug 10 (process P290). This completes the glow plug 10.

[0123] There is a case where the melting point of the silicide forming the particles 868 is lower than the sintering temperature during sintering (process P260). In this case, after manufacturing the intermediate support member 860 (process P210), the manufacturer can print the resistance heater 810 by printing on the groove in one of the components of the intermediate support member 860 using a printing material to which the particulate material, which is the raw material of the particles 868, has been added (process P235). The particulate material contained in the intermediate resistance heater 810 diffuses into the support member 860 during sintering (process P260) and forms the adjacent region 866. In this case, the particle diameter of the particles 868 tends to be smaller the farther they are from the resistance heater 810, as shown in Fig.4A. When the sintering temperature during sintering (process P260) is 1700 to 1900 °C, the particulate material that can be added to the printing material can be silicide or oxide of at least one of chromium (Cr), titanium (Ti), and zirconium (Zr).

[0124] According to the second embodiment described above, the durability of the resistance heater 810 can be increased similarly to the first embodiment. C. Other embodiments

[0125] The present invention is not limited to the above-described embodiments and modifications thereof. The present invention can be implemented in various configurations as long as they do not deviate from the concept of the present invention. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features of each form described in the SUMMARY may be regularly replaced and / or combined in order to solve some or all of the problems described above or to achieve some or all of the advantages described above. Furthermore, the technical features may be omitted unless they are described as essential in the present specification.

Claims

[1] Glow plug (10), with: a resistance heater (810) comprising a first ceramic composition and generating heat upon passing electricity; and a support member (860) mainly comprising a second ceramic composition different from the first ceramic composition and containing silicon nitride (Si3N4) as a main component, in which the resistance heater is embedded, and which supports the resistance heater, wherein the support member includes a neighboring region (866) adjacent to the resistance heater, characterized by in that in the adjacent region several particles (868) are unevenly distributed laterally from the resistance heater, which particles contain a component whose thermal expansion coefficient is greater than that of silicon nitride (Si3N4), the thickness, T, of the adjacent region being 10 to 200 µm. [2] Glow plug (10) according to claim 1, wherein the component in the particles (868) distributed in the adjacent region (866) is at least one of chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), zirconium (Zr), and tantalum (Ta), or silicon carbide (SiC). [3] Glow plug (10) according to claim 1 or 2, wherein the thickness of the adjacent region (866) is 20 to 100 µm from the resistance heater (810). [4] Glow plug (10) according to one of claims 1 to 3, wherein the average size of the plurality of particles (868) is less than or equal to 5 µm. [5] Glow plug (10) according to one of claims 1 to 4, wherein a relationship between the cross-sectional area S1 of the resistance heater (810) at a position where the adjacent region (866) is formed and the cross-sectional area S2 of the support member (860) 0.5%≤S1 / (S1+S2)×100%≤25% is enough. [6] Glow plug (10) according to one of claims 1 to 5, wherein a relationship between the cross-sectional area S1 of the resistance heater (810) at a position where the adjacent region (866) is formed, the cross-sectional area S2 of the support member (860), and the thickness T of the adjacent region (866) T⋅(S1+S2) / S1≥67 μm is enough. [7] Glow plug (10) according to one of claims 1 to 6, wherein the resistance heater (810) includes: a reversing part (815) shaped as a reversing loop; and a supply part (818) connected to the reversing part and having a larger cross-section than the reversing part, and wherein the neighboring region (866) is at least adjacent to the reversal region. [8] Glow plug (10) according to one of claims 1 to 7, wherein the resistance heater (810) is an injection-molded or printed element. [9] Glow plug (10) according to one of claims 1 to 8, wherein the first ceramic composition and the second ceramic composition contain a component common to both. [10] Glow plug (10) according to one of claims 1 to 9, wherein the second ceramic composition contains a rare earth element and aluminum (Al). [11] Glow plug (10) according to one of claims 1 to 10, wherein the concentration of the particles (868) in the adjacent region (866) is higher the closer they are to the resistance heater (810), or lower the further they are away from the resistance heater.

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