JP2018194249A - Glow plug - Google Patents

Abstract

To provide a glow plug capable of keeping a heating temperature high, and also improving durability of a coil.SOLUTION: A glow plug comprises: a coil electrically connected to a middle shaft and mainly composed of W or Mo; a tube where a tip end side of the middle shaft is arranged, and whose tip connected to the coil is closed; a seal material interposed between the tube and the middle shaft; and insulation powder put into the tube where a gap between the tube abd the middle shaft is tightly closed by the seal material. The tube is mainly composed of Ni, and contains Fe, Cr, Al and Si. The insulation powder contains MgO and CaO, and the content of CaO in the insulation powder becomes 0.05-1.5 wt.% based on the total content of MgO and CaO.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a glow plug, and more particularly to a glow plug that can increase the heat generation temperature.

  Conventionally, a glow plug in which a coil is arranged inside a metal tube is known. This glow plug is used as an auxiliary heat source for an internal combustion engine such as a diesel engine using a compression ignition system. In addition, glow plugs are required to have a high heat generation temperature as regulations on internal combustion engines are tightened. Patent Document 1 discloses an insulating powder made of MgO in which a coil containing W or Mo as a main component is arranged inside a tube containing Ni, Cr, Al, and Si in order to meet the demand for higher heat generation temperature. A technique for filling a tube in a tube is disclosed. By using MgO for the insulating powder, the thermal conductivity from the coil to the tube can be improved.

Japanese Patent No. 5255706

However, Mg (OH) ₂ produced by absorbing MgO is decomposed around 370 ° C. and releases water. For example, when the temperature of the coil is higher than the temperature of the tube, such as when the temperature of the glow plug rises, the reaction speed of the coil surface, which is higher than the temperature of the tube, is fast, so the oxidation of the coil proceeds in the presence of water. However, the cross-sectional area of the coil decreases, the resistance value increases, and the coil may be disconnected due to overheating. Therefore, further improvement of the durability of the coil is desired.

  The present invention has been made to meet the above-described demand, and an object of the present invention is to provide a glow plug that can improve the durability of the coil while increasing the heat generation temperature.

  In order to achieve this object, the glow plug according to the present invention includes a metal center shaft, a coil electrically connected to the center shaft and the main component of W or Mo, and the tip side of the coil and the center shaft are disposed inside. A tube having a closed end to which a coil is connected, a sealing material interposed between the tube and the central shaft, and an insulating powder filled in the tube sealed between the central shaft and the sealing material. The tube includes Ni as a main component and contains Fe, Cr, Al, and Si. The insulating powder contains MgO and CaO, and the CaO content in the insulating powder is 0.05 to 1.5 wt% with respect to the total content of MgO and CaO.

According to the glow plug of claim 1, since Ca (OH) ₂ which is a reaction product of CaO and water is thermodynamically more stable than Mg (OH) ₂ , CaO has Mg (OH) ₂ of 370 Reacts with water released by decomposition at around 0 ° C. to produce Ca (OH) ₂ . Ca (OH) ₂ is decomposed at about 580 ° C. or more to release water. However, when the temperature of Ca (OH) ₂ is around 580 ° C., not only the temperature of the coil but also the temperature of the tube is sufficiently high, so the Cr and Al of the tube, which are more easily oxidized than W and Mo of the coil, Oxidized in the presence of When Cr and Al in the tube are oxidized, the oxygen partial pressure in the sealed tube is lowered. Thereby, the oxidation of the coil mainly composed of W or Mo can be prevented. Therefore, the durability of the coil can be improved while increasing the heat generation temperature.

  According to the glow plug of claim 2, since the coil has a total content of Al, Cr and Si of 0.1 wt% or less, Al, Cr and Si contained in the coil, CaO contained in the insulating powder, It is possible to suppress the formation of a low melting point compound formed by the reaction. When a low melting point compound is generated in the coil, the coil generates heat and the compound melts, the coil cross-sectional area decreases, the resistance increases, and the coil may overheat and break, but the low melting point Since the production | generation of a product can be suppressed, in addition to the effect of Claim 1, durability of a coil can further be improved.

  According to a third aspect of the present invention, the glow plug further includes the rear end coil connected to the rear end of the coil and the front end of the center shaft. The resistance ratio R1 which is the ratio of the resistance value at 1000 ° C. to the resistance value at 20 ° C. of the coil and the resistance ratio R2 which is the ratio of the resistance value at 1000 ° C. to the resistance value at 20 ° C. of the rear end coil The relationship of R1> R2 is satisfied. Therefore, when a voltage is applied, the coil and the tip side of the tube can be raised to a predetermined temperature (for example, 1000 ° C.) without excessively increasing the resistance value of the entire coil. The resistance ratio is “ratio of the resistance value at 1000 ° C. to the resistance value at 20 ° C. of the coil (or rear end coil)”.

  And since the emitted-heat amount of a coil and a rear end coil is proportional to each resistance value, when a coil rises to predetermined temperature, the temperature of a rear end coil can be made lower than the temperature of a coil. Since the rear coil has an Al content of 1 wt% or less, the reaction between Al contained in the rear coil and CaO contained in the insulating powder can be suppressed, and it is difficult for the rear coil to generate a low melting point compound. it can. Therefore, in addition to the effect of the first or second aspect, the durability of the rear end coil can be secured.

It is a half sectional view of a glow plug. It is sectional drawing of the glow plug which expanded a part.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. A glow plug 10 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a half sectional view of the glow plug 10, and FIG. 2 is a sectional view of the glow plug 10 with a part thereof enlarged. In FIGS. 1 and 2, the lower side of the drawing is referred to as the front end side of the glow plug 10, and the upper side of the drawing is referred to as the rear end side of the glow plug 10.

  As shown in FIG. 1, the glow plug 10 includes a center shaft 20, a metal shell 30, a tube 40, and a coil 50. These members are assembled along the axis O of the glow plug 10. The glow plug 10 is an auxiliary heat source used when starting an internal combustion engine (not shown) such as a diesel engine.

  The middle shaft 20 is a cylindrical metal conductor and is a member for supplying power to the coil 50. The middle shaft 20 has a coil 50 electrically connected to the tip. The middle shaft 20 is inserted into the metal shell 30 with the rear end protruding from the metal shell 30.

  In the present embodiment, the middle shaft 20 has a connecting portion 21 formed of an external thread at the rear end portion. The middle shaft 20 has an O-ring 22 made of insulating rubber, an insulator 23 which is a cylindrical member made of synthetic resin, a ring 24 which is a metallic cylindrical member, and a metal nut 25 in order from the front end side to the rear end portion. Is assembled. The connection unit 21 is a part to which a connector (not shown) of a cable that supplies power from a power source such as a battery is connected. The nut 25 is a member for fixing a connected connector (not shown).

  The metal shell 30 is a substantially cylindrical member formed of carbon steel or the like. The metal shell 30 has a shaft hole 31 extending along the axis O, and a threaded portion 32 formed on the outer peripheral surface. The metal shell 30 has a tool engagement portion 33 formed on the rear end side of the screw portion 32. The shaft hole 31 is a through hole into which the middle shaft 20 is inserted. Since the inner diameter of the shaft hole 31 is larger than the outer diameter of the middle shaft 20, a gap is formed between the middle shaft 20 and the shaft hole 31. The screw portion 32 is a male screw that fits into an internal combustion engine (not shown). The tool engaging portion 33 is a portion forming a shape (for example, hexagonal shape) with which a tool (not shown) used when the screw portion 32 is fitted or removed from a screw hole (not shown) of the internal combustion engine. .

  The metal shell 30 holds the middle shaft 20 via the O-ring 22 and the insulator 23 on the rear end side of the shaft hole 31. When the ring 24 is crimped to the middle shaft 20 with the ring 24 in contact with the insulator 23, the position of the insulator 23 in the axial direction is fixed. The insulator 23 insulates the rear end side of the metallic shell 30 from the ring 24. The metal shell 30 has a tube 40 fixed to the distal end side of the shaft hole 31.

  The tube 40 is a metal cylindrical body with the tip 41 closed. The tube 40 is fixed to the metal shell 30 by being press-fitted into the shaft hole 31. Examples of the material of the tube 40 include heat-resistant alloys such as nickel-based alloys and stainless steel.

  The composition of the tube 40 is, for example, Ni 50 wt% or more, Cr 18-30 wt%, Al 0.3 wt% or more, Si 0.2-1.5 wt%, C 0.04 wt% or less, and Fe 5 to 15 wt%. It may contain rare earth elements.

  The tube 40 can ensure the heat resistance of the tube 40 by containing 50 wt% or more of Ni. By containing 18 to 30 wt% of Cr, the workability of the tube 40 can be secured while securing the oxidation resistance of the tube 40 by the Cr oxide film formed on the surface of the tube 40. By containing 0.3 wt% or more of Al, the oxidation resistance of the tube 40 can be ensured by the Al oxide film formed on the surface of the tube 40. By containing 0.2 to 1.5 wt% of Si, the workability of the tube 40 can be ensured while ensuring the oxidation resistance of the tube 40. By suppressing the C content to 0.04 wt% or less and containing 5 to 15 wt% Fe, it is possible to improve the strength of the tube 40 at a high temperature and ensure workability.

  The tube 40 has a distal end side of the middle shaft 20 inserted therein. Since the inner diameter of the tube 40 is larger than the outer diameter of the middle shaft 20, a gap is formed between the middle shaft 20 and the tube 40. The sealing material 26 is a cylindrical insulating member sandwiched between the front end side of the middle shaft 20 and the rear end of the tube 40. The sealing material 26 maintains a distance between the middle shaft 20 and the tube 40 and seals between the middle shaft 20 and the tube 40. The coil 50 is accommodated in the tube 40 along the axis O. The insulating powder 60 is filled in the tube 40.

  As shown in FIG. 2, the coil 50 is formed in a spiral shape and generates heat when energized. The coil 50 has a tip joined to a portion on the tip 41 side of the tube 40 by welding. The rear end coil 51 is joined to the rear end of the coil 50 by welding. Between the coil 50 and the rear end coil 51, there is formed a melted portion 52 that is melted by welding and the weld metal is hardened. The rear end coil 51 is connected in series with the coil 50 via the melting part 52.

  The insulating powder 60 is a powder having electrical insulation properties and thermal conductivity at high temperatures. The insulating powder 60 is filled between the coil 50 and the rear end coil 51 and the tube 40, between the middle shaft 20 and the tube 40, and inside the coil 50 and the rear end coil 51. The insulating powder 60 has a function of transferring heat from the coil 50 to the tube 40, a function of preventing a short circuit between the coil 50 and the rear end coil 51 and the tube 40, and a difficulty in vibrating the coil 50 and the rear end coil 51 to prevent disconnection. There is a function.

The insulating powder 60 contains oxide powders of MgO and CaO. In addition to oxide powders of MgO and CaO, oxide powders such as Al ₂ O ₃ , ZrO ₂ and SiO ₂ and powders such as Si can be added. The content of CaO is 0.05 to 1.5 wt% with respect to the total content of MgO and CaO. Note that the total content of MgO and CaO is 98 to 100 wt% with respect to the entire insulating powder 60.

  The coil 50 is made of a refractory metal mainly composed of W and Mo. It should be noted that a simple substance of these elements or an alloy mainly containing any of these elements can be used as the coil 50. Note that “the main component is W or Mo” means that the total content of W or Mo with respect to the total content of the coil material is 50 wt% or more.

  The coil 50 preferably contains 99 wt% or more of W and Mo. This is for improving the heat resistance of the coil 50. In this case, inevitable impurities and intentional additives of about several ppm to several tens of ppm can be contained. In particular, pure W or pure Mo is preferably used. In this case as well, inevitable impurities can be contained. Of these, pure W is preferred. This is because pure W has a higher melting point than pure Mo. By using the pure W coil 50 having a high melting point, the effect of improving the durability of the coil 50 by adding CaO to the insulating powder 60 containing MgO can be enhanced.

  In the coil 50, the total content of Al, Cr and Si is set to 0.1 wt% or less. Thereby, the production | generation (corrosion of the coil 50) of the low melting point compound which Al, Cr, and Si contained in the coil 50 react with CaO contained in the insulating powder 60 can be suppressed. When a compound having a low melting point is generated in the coil 50, the cross-sectional area of the coil 50 decreases, the resistance value increases, and the coil 50 may be overheated and disconnected, but the corrosion of the coil 50 can be suppressed. 50 durability can be improved.

  The rear end coil 51 is formed of a conductive material having a resistance ratio R2 smaller than the resistance ratio R1 of the coil 50. Examples of the material of the rear end coil 51 include an FeCr alloy and a NiCr alloy. The rear end coil 51 is accommodated in the tube 40 along the axis O (see FIG. 1) and is joined to the middle shaft 20. The middle shaft 20 is electrically connected to the tube 40 via the rear end coil 51 and the coil 50.

When a voltage V is applied between the middle shaft 20 and the tube 40, a current I obtained by dividing the voltage V by the sum R ₁ + R ₂ of the resistance value R ₁ of the coil 50 and the resistance value R ₂ of the rear end coil 51 becomes the coil 50. And flows to the rear end coil 51. The amount of heat generated by the coil 50 per unit time is R ₁ · I ² , and the amount of heat generated by the rear end coil 51 per unit time is R ₂ · I ² .

The resistance value R ₂ of the rear end coil 51 at 20 ° C. is set to be larger than the resistance value R ₁ of the coil 50 at 20 ° C. This is because the current I (inrush current) flowing through the coil 50 at room temperature is ensured and the coil 50 generates heat.

The rear end coil 51 has a small resistance ratio R2 than the resistance ratio R1 of the coil 50, as the temperature rise due to heat generation of the coil 50 and the rear coil 51, the resistance the resistance value R ₁ of the coil 50 of the rear coil 51 It is larger than the value _{R 2.} As a result, the heat generation amount R ₁ · I ² per unit time of the coil 50 can be made larger than the heat generation amount R ₂ · I ² of the rear end coil 51 per unit time. Since the coil 50 is formed of a refractory metal mainly composed of W and Mo, the heat generation temperature can be increased. Thereby, the coil 50 can be heated to a desired temperature (for example, 1000 ° C.), and the vicinity of the tip 41 of the tube 40 can be locally heated to the desired temperature by the heat conduction of the insulating powder 60.

  The rear end coil 51 is set such that the total content of Al is 1 wt% or less. Since the heat generation amount per unit time of the rear end coil 51 is smaller than the heat generation amount per unit time of the coil 50, the temperature of the rear end coil 51 can be made lower than the temperature of the coil 50. As a result, the reaction rate between Al contained in the rear end coil 51 and CaO contained in the insulating powder 60 can be reduced, and the generation of a low melting point compound (corrosion of the rear end coil 51) can be suppressed. When a compound having a low melting point is generated in the rear end coil 51, the cross-sectional area of the rear end coil 51 is decreased, and the resistance value is increased, and the rear end coil 51 may be overheated and disconnected. Therefore, the durability of the rear end coil 51 can be improved.

  The glow plug 10 is manufactured as follows, for example. First, a resistance heating wire having a predetermined composition is processed into a coil shape, and the coil 50 and the rear end coil 51 are manufactured. Next, the ends of the coil 50 and the rear end coil 51 are joined together by welding, and the rear end coil 51 is joined to the front end of the middle shaft 20.

  On the other hand, a tapered tube precursor in which a metal steel pipe having a predetermined composition is formed to have a diameter larger than the final dimension of the tube 40 and the tip of the metal steel pipe is made smaller than the other part, and the tip is opened. Manufacturing. The coil 50 and the rear end coil 51 integrated with the middle shaft 20 are inserted into the tube precursor, and the tip of the coil 50 is disposed in the tapered opening of the tube precursor. The opening of the tube precursor and the coil 50 are melted by welding, the tip portion of the tube precursor is closed, and a heater precursor in which the coil 50 and the rear end coil 51 are housed is formed.

  Next, after filling the heater precursor tube 40 with the insulating powder 60, the sealing material 26 is inserted between the opening at the rear end of the tube 40 and the middle shaft 20 to seal the tube 40. Next, swaging is performed on the tube 40 until the tube 40 has a predetermined outer diameter.

  Next, the swaging tube 40 is press-fitted and fixed in the shaft hole 31 of the metal shell 30, and the O-ring 22 and the insulator 23 are fitted between the metal shell 30 and the medium shaft 20 from the rear end of the middle shaft 20. The glow plug 10 is obtained by caulking the middle shaft 20 with the ring 24.

In the present embodiment, MgO and CaO in the insulating powder 60 react with the water in the tube 40 to generate Mg (OH) ₂ and Ca (OH) ₂ . When the temperature of the glow plug 10 is raised, when the coil 50 and the rear end coil 51 are energized, the coil 50 mainly generates heat. The heat of the coil 50 is transmitted to the tube 40 through the insulating powder 60. When the insulating powder 60 is heated, Mg (OH) ₂ is decomposed and releases water at around 370 ° C.

On the other hand, since Ca _{(OH) 2} is Mg _{(OH) 2} thermodynamically stable than, CaO reacts with water to Mg _{(OH) 2} was released by decomposition at around 370 ° C. Ca and _{(OH) 2} Generate. Ca (OH) ₂ is decomposed at about 580 ° C. or more to release water. However, when the temperature of the insulating powder such as Ca (OH) ₂ is around 580 ° C., not only the temperature of the coil 50 but also the temperature of the tube 40 is sufficiently high, so that the tube is more easily oxidized than W or Mo of the coil 50. Forty Cr and Al are oxidized in the presence of moisture. When Cr and Al in the tube 40 are oxidized, the oxygen partial pressure in the sealed tube 40 is lowered. Thereby, oxidation of the coil 50 can be prevented. Therefore, the durability of the coil 50 can be improved while increasing the heat generation temperature of the glow plug 10.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Create samples 1-11)
A coil 50 having an outer diameter of Φ1.6 mm was prepared using a pure W wire having a diameter of Φ0.2 mm. Similarly, a rear end coil 51 was created using a wire made of a NiCr alloy, and the rear end coil 51 was joined to the coil 50 by welding.

A tube 40 is formed using a metal steel pipe made of 68.4Ni-23Cr-7Fe-0.5Al-1Si-0.1Y (wt%), and a glow plug having a structure similar to that of the glow plug 10 shown in FIG. Produced as described above. Thereby, the glow plugs of Samples 1 to 11 shown in Table 1 in which MgO and CaO of the insulating powder 60 were mixed at various ratios were obtained. The tube 40 had an inner diameter of Φ2.2 mm, and the volume (volume) of the tube 40 was 100 mm ³ .

チューブ４０に充填されたＭｇＯ及びＣａＯの比率は、試験後、以下の方法により求めた。まず、グロープラグから絶縁粉末（ＣａＯを含むＭｇＯ粉末）を取り出し、この粉末を炭酸カリウムナトリウム及びホウ酸と混合した後、バーナで加熱し融解させた。アルカリ塩となったＣａを酸の水溶液に溶解した後、ＩＣＰ発光分析法によって定量分析した。

The ratio of MgO and CaO filled in the tube 40 was determined by the following method after the test. First, the insulating powder (MgO powder containing CaO) was taken out from the glow plug, this powder was mixed with sodium potassium carbonate and boric acid, and then heated and melted with a burner. Ca dissolved as an alkali salt was dissolved in an acid aqueous solution and quantitatively analyzed by ICP emission spectrometry.

(Oxidation of coil)
A test method for evaluating the oxidation of the coil will be described. A DC voltage was applied between the connection part 21 of each sample and the metal shell 30 so that the temperature in the vicinity of the tip 41 of the tube 40 after 1000 seconds was 1000 ° C. Two seconds after the voltage was applied, the voltage application was stopped and the tip 41 of the tube 40 was air-cooled for 120 seconds. The test which repeats 10,000 cycles by making this into 1 cycle was done.

  The temperature near the tip 41 of the tube 40 was measured by a PR thermocouple bonded to a position 2 mm away from the tip 41 of the tube 40 of each sample on the rear end side in the axis O direction (surface of the tube 40). A radiation thermometer may be used instead of the PR thermocouple.

  For each sample (n = 5) after the test, the cut surface including the axis O is mirror-polished, and the thickness of the thickest portion of the oxide film formed on the surface of the coil 50 is measured using an electron microscope. The average was calculated.

  As shown in Table 1, Sample 1 having a CaO content of 0 wt% had an oxide film thickness (average value) of 23 μm. However, the thickness of the sample 2 with a CaO content of 0.01 wt% was gradually reduced to 20 μm, the thickness of the sample 3 with a CaO content of 0.05 wt% was 8 μm, and the CaO content was 0.1 wt% or more. Samples 4 to 11 showed no oxide film. Thereby, it was confirmed that the oxidation of the coil 50 can be prevented if the CaO content is 0.1 wt% or more.

(Tube corrosion)
A test method for evaluating the corrosion of the tube will be described. The voltage adjusted so that the temperature at the position 2 mm away from the tip 41 of the tube 40 of the samples 1 to 11 toward the rear end side in the axis O direction (surface of the tube 40) becomes 1200 ° C. is connected to the connection portion 21 of each sample. A test was conducted between the metal shell 30 and the metal shell 30 to continue application for 500 hours. Although the temperature was measured using a PR thermocouple, a radiation thermometer may be used instead of the PR thermocouple.

  For each sample after the test, the cut surface including the axis O was mirror-polished, and the coating film appearing on the inner surface of the tube 40 was subjected to WDS analysis using EPMA. The sample in which Ca contained in the film reached the interface of the tube 40 was determined to be corroded (NG), and the sample in which Ca did not reach the interface of the tube 40 was determined to be good (G).

  As shown in Table 1, the sample 10 with a CaO content of 1.8 wt% and the sample 11 with a CaO content of 2 wt% were judged as NG, whereas the CaO content was 1.5 wt%. The following samples 1 to 9 were judged as G. Thus, it was confirmed that the corrosion of the tube 40 can be prevented if the CaO content is 1.5 wt% or less.

  Therefore, it is confirmed that the prevention of the oxidation of the coil 50 and the prevention of the corrosion of the tube 40 can be achieved by setting the CaO content to 0.1 to 1.5 wt% with respect to the total content of MgO and CaO. It was done.

(Create samples 12-30)
A coil 50 having an outer diameter of Φ1.6 mm was prepared using various wire materials (wire diameter Φ0.2 mm) shown in Table 2. Similarly, a rear end coil 51 was created using a wire made of a NiCr alloy, and the rear end coil 51 was joined to the coil 50 by welding.

A tube 40 is formed using a metal steel pipe made of 68.4Ni-23Cr-7Fe-0.5Al-1Si-0.1Y (wt%), and a glow plug having a structure similar to that of the glow plug 10 shown in FIG. Produced as described above. The tube 40 was filled with an insulating powder 60 having a compounding ratio of 99MgO-1CaO (wt%), and samples 12 to 30 shown in Table 2 were obtained. The tube 40 had an inner diameter of Φ2.2 mm, and the volume (volume) of the tube 40 was 100 mm ³ .

（コイルの腐食）
コイルの腐食を評価した試験方法を説明する。サンプル１２〜３０のチューブ４０の先端４１から軸線Ｏ方向の後端側に２ｍｍ離れた位置（チューブ４０の表面）の温度が１２００℃になるように調整した電圧を、各サンプルの接続部２１と主体金具３０との間に、５００時間印加し続ける試験を行った。温度の測定はＰＲ熱電対を用いたが、ＰＲ熱電対の代わりに放射温度計を用いても良い。

(Coil corrosion)
A test method for evaluating the corrosion of the coil will be described. The voltage adjusted so that the temperature of the position (surface of the tube 40) 2 mm away from the tip 41 of the tube 40 of the samples 12 to 30 to the rear end side in the axis O direction is 1200 ° C. A test was conducted between the metal shell 30 and the metal shell 30 to continue application for 500 hours. Although the temperature was measured using a PR thermocouple, a radiation thermometer may be used instead of the PR thermocouple.

  About each sample after a test, the cut surface containing the axis line O was mirror-polished, and the coil 50 was WDS-analyzed using EPMA. The sample in which Ca reached the inside of the coil 50 was determined to be corroded (NG), and the sample in which Ca did not reach the inside of the coil 50 was determined to be good (G).

  As shown in Table 2, samples 12, 13, 16, 17, 20, 21, 23, 24, 26 to 28 in which the total content of Al, Cr, and Si contained in the coil 50 is 0.1 wt% or less. , 30 was G. On the other hand, the sample in which the total content of Al, Cr, Si exceeded 0.1 wt% was judged as NG. Therefore, it was confirmed that the corrosion of the coil 50 can be prevented if the total content of Al, Cr, Si in the coil 50 is 0.1 wt% or less.

  In this example, the sample including the coil 50 including W as a main component was evaluated, but it is assumed that the same result can be obtained for the sample including the coil 50 including Mo as a main component. This is because Mo is easily oxidized like W but has excellent mechanical strength at high temperatures.

  The present invention has been described above based on the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the spirit of the present invention. It is easy to guess that this is possible. For example, the shape of the tube 40 is not particularly limited as long as it is cylindrical, and the cross section orthogonal to the axis O may be circular, elliptical, polygonal, or the like.

  Although the case where the rear end coil 51 is connected to the coil 50 has been described in the above embodiment, the present invention is not necessarily limited thereto. Of course, it is possible to omit the rear end coil 51 and connect a coil mainly composed of W or Mo between the middle shaft 20 and the tip 41 side of the tube 40. In this case, the entire tube 40 can be heated, and the durability of the coil can be ensured while ensuring a high heat generation temperature.

  In the above-described embodiment, the case where the outer diameter and the inner diameter of the tube 40 are set to be the same over the entire length of the axis O has been described, but the present invention is not necessarily limited thereto. In consideration of the heat capacity of the tube 40 and the like, it is naturally possible to make the outer diameter and inner diameter on the distal end side of the tube 40 different from the outer diameter and inner diameter on the rear end side of the tube 40.

10 Glow plug 20 Middle shaft 40 Tube 42 Sealing material 50 Coil 51 Rear end coil 60 Insulating powder O Axis

Claims (3)

A metal shaft,
A coil that is electrically connected to the central shaft and has W or Mo as a main component;
A tube with a closed tip, in which the tip side of the coil and the central shaft is arranged inside and the coil is connected;
A sealing material interposed between the tube and the central shaft;
Insulating powder filled in the tube sealed between the middle shaft with the sealing material,
The tube is a glow plug containing Ni as a main component and containing Fe, Cr, Al and Si,
The insulating powder contains MgO and CaO,
A glow plug in which the content of CaO in the insulating powder is 0.05 to 1.5 wt% with respect to the total content of MgO and CaO.   The glow plug according to claim 1, wherein the coil has a total content of Al, Cr, and Si of 0.1 wt% or less. A rear end coil connected to a rear end of the coil and a front end of the middle shaft;
A resistance ratio R1 which is a ratio of a resistance value at 1000 ° C. to a resistance value at 20 ° C. of the coil and a resistance ratio R2 which is a ratio of a resistance value at 1000 ° C. to a resistance value at 20 ° C. of the rear end coil Satisfies the relationship of R1> R2,
The glow plug according to claim 1, wherein the rear end coil has an Al content of 1 wt% or less.

Images