JPH0439195B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a preheating plug for a diesel engine,
This invention relates to ceramic keyers used in heaters for igniting fuel in space heaters. Conventionally, in ceramic heaters, a ceramic heating element is fixed to a housing. Usually, one of the lead wires of the pair of electrodes connected to the heating element is connected to the housing, and the other is passed through the interior and connected to the center electrode provided on the fixed part of the housing. In this case, the lead wire of the electrode connected to the center electrode needs to be electrically insulated from the housing and connected to the center electrode. For this reason, positioning between the housing and the heating element is important. Conventionally, a method has been adopted in which an insulating adhesive such as insulating glass or ceramic paste is poured between the heat generating pair and the housing to fix the heat generating pair and the housing. However, according to this method, the central axis of the heating element is not constant with respect to the central axis of the housing, which may cause the internal electrode to shift, resulting in poor conduction. For this reason, the positioning of the heating element and the housing during assembly becomes uncertain, which may make it difficult to attach the housing to the attachment member. Another problem is that the above-mentioned insulation work is troublesome. The present invention has been devised in view of the above circumstances, and provides a ceramic heater that facilitates communication between the electrodes of the ceramic heating element, facilitates assembly work, and uses a highly durable heating element. The purpose is to The ceramic heater of the present invention includes a ceramic insulator, a ceramic heating element provided at one end of the insulator, a pair of electrodes embedded in the insulator and connected at one end to the heating element, and a ceramic heating element provided at one end of the insulator. a housing made of a cylindrical conductive material fixed to the outer periphery of the insulator; and a housing made of a cylindrical conductive material fixed to the outer periphery of the insulator, the housing being brazed to the outer periphery of the insulator via a metallized layer, and also brazed to the inner periphery of one end of the housing. It comprises a cylindrical sleeve made of a conductive material and a terminal means arranged at the other end of the housing, and the other end of one of the integrated electrodes is connected to the housing through the sleeve. and the other end of the other electrode is connected to the terminal means. The ceramic heater of the present invention has a structure in which a ceramic heating element is provided at one end of a ceramic insulator, and a sleeve is provided between the outer circumferential side of the insulator and the inner circumferential side of one end of the housing. Electrical insulation between the ceramic heating element and the housing is achieved by an insulator without direct contact, and positioning of the heating element and the housing is achieved by a sleeve provided between the insulator and the housing. Further, for example, by forming the sleeve of metal and also forming the housing of metal, the insulator can be easily fixed to the housing by directly welding the two. A metallized layer is formed around the outer periphery of the insulator, and the sleeve is joined to the insulator by brazing via the metallized layer. This sleeve allows one of the pair of electrodes to be connected to the housing. The other electrode is passed through the insulator and connected to the end of the lead wire from the other end of the insulator using, for example, a metal cap, and electrically connected to the center electrode of the metal cap using a holding pin. The terminal means is constructed by burying the periphery with an insulating material to insulate the terminal portion from the housing.
Therefore, the current-carrying structure of the electrodes of the heating element can be simplified and shortening and disconnection can be prevented. The materials of the ceramic heating element of the present invention are MoSi ₂ and
Consists of a mixture with Si ₃ N ₄ . That is, when such a ceramic material is used as a heating element for a diesel engine, it is necessary to have a high temperature coefficient of resistance, and therefore it is necessary to add MoSi ₂ . but
Heating element materials made of MoSi ₂ alone have some drawbacks in high temperature strength and impact resistance. Therefore, it was found that it is good to add Si ₃ N ₄ to solve this problem. The mixing ratio of MoSi ₂ and Si ₃ N ₄ constituting the material of the ceramic heating element in the present invention is not particularly limited as long as it exhibits a heat generating function, but
_A composition of ~90 mol% _MoSi2 , 70-10 mol% _Si3N4 is preferred. When the proportion _{of Si3N4} exceeds 70 mol%, the nonresistance increases, while when it falls below 10 mol%
This is because the effect of adding Si ₃ N ₄ is lost. The ceramic heating element has a porosity of 8% or less, preferably 4% or less. In order to sufficiently and precisely control the temperature of ceramic heating elements used as preheating plugs in diesel engines using a current sensor method, safety must be considered.
1400 in the current situation where more durability is required.
The ceramic heater is normally required to have a resistance change rate of 8% or less after continuously generating heat at ℃ for 400 hours. As mentioned above, the porosity value of the ceramic heating element is 8% or less when the above-mentioned durability performance required in this current sensor system is satisfied. Also, this porosity is 4
% or less, the ceramic heater has almost no resistance change rate at room temperature even after continuous heat generation at 1400℃ for 400 hours (resistance change rate is 1% or less).
This is because it is extremely durable. The shape of this heating element is not particularly limited. However, in order to effectively use the heat inside the ceramic heating element or to reduce the temperature difference between the inner and outer surfaces of the heating element, the cross section of the heating element is made U-shaped, and one end of the ceramic insulator is placed in the center of the heating element. Preferably, it is integrated into the part. The material of the ceramic insulator of the present invention is not particularly limited as long as it is an insulator, but from the viewpoint of heat resistance, durability, and adhesion after integral sintering with the ceramic heating element, aluminum oxide and Si ₃ are used. A mixture with N ₄ or the like is used. Note that this ceramic insulator is sintered integrally with the ceramic heating element held at one end of the heating element. Heat-resistant metal lead wires forming a pair of electrodes are buried inside the insulator. This lead wire is made of molybdenum (called Mo) and tungsten (called W).
There are two lead wires made of a heat-resistant metal such as, for example, a thin plate or a wire, each of which is connected to the inside of the electrical insulator and the end of the heating element. A heating element composed of the above-mentioned heating element and insulator is manufactured as follows. That is, as shown in FIG. 3, the above raw sheet 21 and the raw sheet 3 of the heating element
A plurality of sheets 1 and 1 are prepared, and the sheets are stacked and the lead wires 4 are inserted between the sheets. Then, hot press at low temperature as shown by the arrow in the figure.
Glue each sheet. After bonding, it is fired at high temperature and pressure to form a dense sintered body. The porosity of the heating element in such a sintered body is determined by the temperature and pressure during sintering,
Adjusted by changing the particle size of Si ₃ N ₄ and MoSi ₂ . The heating element constituting the ceramic heater of the present invention is made of a ceramic mixture of MoSi ₂ and Si ₃ N ₄ , so it has better heat resistance and oxidation resistance than conventional metal wire heating elements, and has a good heat generation effect. death,
Compared to MoSi ₂ alone, it has extremely high-temperature strength and has a small coefficient of thermal expansion, so it also has excellent thermal shock resistance. According to the present invention, a ceramic heating element is provided at one end of a ceramic insulator, and a sleeve is provided between the outer periphery of the insulator and the inner periphery of one end of the housing. For this reason, electrical insulation between the heating element and the housing is achieved by the presence of the ceramic insulator, and positioning between the ceramic heating element and the housing is achieved by a sleeve provided between the ceramic insulator and the housing. can be achieved. Furthermore, by constructing the sleeve and the housing from a conductive material such as metal, the insulator can be easily fixed to the housing by directly welding them together. Further, since one of the pair of electrodes can be connected to the housing using the sleeve, the conduction structure of the electrode to the housing is simplified. By brazing the sleeve of the present application to the insulator through the metallized layer, one electrode can be reliably connected to the housing, and the strength of the bond between the insulator and the sleeve is improved. You can (Example) Hereinafter, the present invention will be explained with reference to Examples. FIG. 1 shows a sectional view of the ceramic heater. This ceramic heater includes a ceramic insulator 2,
A ceramic heating element 3 in which one end of the ceramic insulator 2 is buried, a pair of electrodes 4 connected to the ceramic heating element 3 through the ceramic insulator 2, and a cylinder fixed to the outer circumferential side of the ceramic insulator 2. a housing 6 made of a conductive material, and an inner peripheral side of one end of the housing 6 and a ceramic insulator 2.
A sleeve 5 made of a conductive material is provided between the outer peripheral side of the housing 6 and a center electrode 9 of a terminal means on the other end side of the housing 6. The end of the ceramic insulator 2 is inserted into the center of the ceramic heating element 3 and integrated to form the heating element 1. As shown in FIG. 2, lead wires 4 forming a pair of electrodes whose ends are connected to the heating element 3 are buried inside the ceramic insulator 2. As shown in FIG. One of the ends of the lead wire 4 is connected to the sleeve 5 with a portion exposed on the side as shown in FIG. 2a. The lead wire 4 is connected to the housing 6 through the sleeve 5, and the end of the other lead wire 4 is exposed on the other end surface of the ceramic insulator 3, and is connected to the center electrode 9 through the metal cap 7 and the holding pin 8. There is. Note that the area around the holding pin 8 is filled with insulating paste and is electrically insulated from the housing 6. Note that the ceramic heating element 3 has a cross-sectional shape of U.
It is a glyph. The heating element 1 is positioned on the outer peripheral side by a sleeve 5 and a housing 6 and fixed by welding or the like. The housing 6 is insulated and locked with the center electrode 9, an O-ring, and an insulating bush 10, and is integrally fixed with a mounting nut 11. With such a configuration, a ceramic heater having a single cylindrical current-carrying structure and excellent durability can be easily obtained. (Test Example 1) In order to exhibit high temperature strength and thermal shock resistance, the mixing ratio of the mixture of MoSi ₂ and Si ₃ N ₄ that constitutes the ceramic heating element was examined below, and the results are shown in Table 1. Indicated. The oxidation resistance test in Table 1 was conducted in air at 1000℃ for 15 hours.
High temperature fracture strength is sample 40 x 3 x 4 mm, loading rate 0.5
mm/min, 1300℃, 3-point bending test in air, it indicates the load when the sample is destroyed or significantly deformed, and the coefficient of thermal expansion refers to the average coefficient of thermal expansion from room temperature to 800℃. According to this test result, MoSi ₂ is 30-90
The mole% of Si ₃ N ₄ is preferably 70 to 10 mole%. Si ₃
When N ₄ exceeds 70 mol%, the specific resistance of the ceramic heater increases, while when it falls below 10 mol%, Si ₃
The effect of N ₄ addition disappears. (Test Example 2) The durability of ceramic heaters using ceramic heating elements having a composition of 80 mol% MoSi ₂ and 20 mol% Si ₃ N ₄ and having various porosities was investigated below. The heating element 1 shown in FIGS. 2a and 2b, which is made of ceramic heating elements with various porosities, is

【table】

【table】

[Table] Manufactured using the following method. That is, as shown in FIG. 3, a ceramic sheet 31 has a composition of 80 mol% MoSi ₂ with an average particle size of 10 μm and 20 mol% Si ₃ N ₄ with an average particle size of 1.0 μm, 20 mol% Si ₃ N ₄ and oxidation. Ceramic sheets 21 each having a composition of 80 mol % aluminum were laminated. Then, a lead wire 4 of a heat-resistant metal electrode of Mo or W is buried inside the laminate of each sheet, and the laminate is heated to a high temperature of 1500 to 1650°C and 100 to 500 kg/cm ²
Firing was carried out under various conditions as shown in Table 2 under high pressure. The heating element 1 shown in FIGS. 2a and 2b manufactured by the above method has a shape of 4 x 3 x 52 mm, and has a heating element 3 (4 x 3 x 10 mm) at one end. The electrode 4 is buried inside the insulator 2 and connected to the inside of the two ends of the heating element 3. As shown in FIG. 1, this heating element 1 was integrated into a housing 6 made of heat-resistant metal via a sleeve 5 made of heat-resistant metal. This sleeve 5 is brazed to the outer periphery of the insulator 2 of the heating element 1 via a metallized layer (not shown). The housing 6 is brazed to the sleeve 5. One of the electrode lead wires 4 is connected to the housing 6 through a sleeve 5, and the other electrode lead wire 4 is connected to the center electrode 9 through a metal cap 7 and a metal holding pin 8. Electric power is applied with the center electrode 9 as positive and the housing 6 as negative, so that the heating element 3 can generate heat. To explain the operation of the ceramic heater having the above structure, when the center electrode 9 is connected to a power source, for example, the positive electrode of a car battery, and the housing 6 is connected to the negative electrode of the battery, a current flows and the heating element 3 generates heat due to Joule heat. do. As a result, the fuel injected by the injector (not shown) is ignited. The heating element 3 with various porosities fixed to the housing 6 is continuously heated at 1200°C and 1400°C, taking safety into account, at the temperature actually used at about 1000°C, and the ceramic heater is heated to the room temperature. Changes in resistance values were investigated, and the results are shown in Table 3 and Figure 4. According to this result, under high pressure of 200 _~ 500mm/ ^cm2 and high temperature of 1550~1650℃, _MoSi2 and _Si3N4
(The molar ratio MoSi ₂ /Si ₃ N ₄ = 80/20)
When fired, a sintered body with a porosity of 8% or less was obtained. This porosity is a low value that has not normally been obtained in the case of conventionally known ceramic heating elements such as SiC. Also, according to the results in Table 3 and Figure 4, 1400
℃, if the room temperature resistance change rate of the ceramic heater after 400 hours of continuous heat generation is 8% or less, the porosity is 8.
% or less. In other words, the durability of conventionally used ceramic heaters is at most 1200℃,
Compared to 1000 hours, when the porosity of the ceramic heating element of this test example is 8% or less, the durability of the ceramic heater is quite good. In particular, when the porosity is 4% or less, the resistance change rate at room temperature of the ceramic heater is 1% or less even after continuous heating at 1400°C for 40 hours, and the ceramic heater of the present invention is extremely durable. good. Further, the same effect can be obtained even if the ceramic heating element has a different mixed composition of MoSi ₂ and Si ₃ N ₄ . Ceramic heating elements with various porosity
It can also be produced by changing the average particle size of MoSi ₂ and Si ₃ N ₄ . The results are shown in FIG. That is, the average particle size of MoSi ₂ is 1 to 50 μm, the average particle size of Si ₃ N ₄ is 0.3 to 10 μm, the pressure is 400 Kg/cm ² , and the firing temperature is 1625 μm.
By firing at a temperature of 1 hour, it was possible to produce a ceramic heating element with a porosity of 8% or less.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a ceramic heater showing an embodiment of the present invention, Fig. 2 shows the heating element of Fig. 1, Fig. 2a is a front view thereof, and Fig. 2b is a side view thereof. 3 are perspective views for explaining the manufacture of the heating element shown in FIG. 2. Figure 4 is a diagram showing the relationship between the porosity of the ceramic heater and the rate of change in resistance after 400 hours, and Figure 5 is a diagram showing the relationship between the average particle size of the ceramic heater raw material and the porosity of the ceramic heater obtained. be. 1... Heating element, 2... Ceramic insulator,
21... Raw sheet of ceramic insulator, 3... Ceramic heating element, 31... Raw sheet of ceramic heating element, 4... Lead wire, 5... Sleeve, 6...
... Housing, 7 ... Metal cap, 8 ... Holding pin, 9 ... Center electrode, 10 ... Electrical insulation bushing, 11 ... Mounting nut,

Claims (1)

[Scope of Claims] 1. A ceramic insulator, a ceramic heating element provided at one end of the insulator, a pair of electrodes embedded in the insulator and connected at one end to the heating element, and the insulator a housing made of a cylindrical conductive material fixed to the outer periphery of the insulator; and a housing made of a cylindrical conductive material fixed to the outer periphery of the insulator, the insulator being brazed to the outer periphery of the insulator via a metallized layer, and brazed to the inner periphery of one end of the housing. It comprises a cylindrical sleeve made of a conductive material and a terminal means arranged at the other end of the housing, and the other end of one of the pair of electrodes is connected to the housing via the sleeve. and the other end of the other electrode is connected to the terminal means. 2 Ceramic heating elements contain 30-90 mol% MoSi ₂
The ceramic heater according to claim 1, wherein the ceramic heater is formed of a sintered body of Si ₃ N ₄ containing 70 to 10 mol % of Si 3 N 4 . 3. The ceramic heater according to claim 1, wherein the ceramic heating element has a porosity of 8% or less. 4. The ceramic heater according to claim 1, wherein the ceramic heating element has a U-shaped cross-section, and one end of the ceramic insulator is inserted into the center of the ceramic heating element and integrated therewith.