JP2009162409A - Glow plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a constitution capable of improving durability of a heat generating resistor received inside of a sheath having an internal atmosphere wherein a nitrogen partial pressure is higher than an oxygen partial pressure by a partial pressure ratio, and achieving high durability as a glow plug without largely changing a constitution of a conventional glow plug. <P>SOLUTION: This glow plug comprises a body fitting 2 and a sheath heater 3. A heat generating coil 9 fused and joined to a tip of the sheath and a control coil 10 connected with a rear end of the heat generating coil 9 in series are sealed inside of the sheath 7 constituting the sheath heater 3 with insulating powder 11. The heat generating coil 9 is mainly composed of Fe, and includes Cr of 20 wt.% or less and Al of 8-15 wt.%. Thus intrusion of nitrogen to the inside of the heat generating resistor can be effectively blocked, and the task can be performed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a glow plug mainly used for assisting starting a diesel engine.

  Conventionally, in a diesel engine, a glow plug has been used for assisting engine startup, stabilizing combustion after startup, and purifying exhaust gas. The glow plug is a so-called metal glow plug in which a heating resistor is housed in a metal sheath and a control resistor (also simply referred to as a control coil) is housed to form a heater. There is. There is also a so-called ceramic glow plug in which the heater is made of ceramic. In order to increase the output of diesel engines and reduce environmental impact, it is generally advantageous that the operating temperature of the glow plug is high, so the ceramic glow plug is more durable than the metal glow plug. In recent years, the demand for ceramic glow plugs is increasing due to its superiority. On the other hand, the current situation is that metal glow plugs are still in demand because they are easy to manufacture and easy to control in terms of construction.

  When the metal glow plug is used, the sheath is exposed as a heater in the combustion chamber of the engine. Since the combustion chamber has an extremely high temperature and an atmosphere in which unburned gas / combustion gas mixed with fuel drifts, heat resistance such as high temperature corrosion resistance and high temperature strength of the sheath is required. In order to respond to this, a material having excellent heat resistance and corrosion resistance, mainly composed of Ni (nickel) or Fe (iron), such as SUS 310 or Inconel 601 (trade name), is used for the sheath.

  By the way, regarding the durability of the glow plug, importance is attached to the heating resistor that functions as a heater more than the sheath exposed to the combustion chamber, and material development is being conducted. In particular, Fe (iron) -Cr (chromium) -Al (aluminum) -based material is used as the heat generating coil material of the metal glow plug. For example, in Patent Document 1, a material having a composition of Fe-7.5Al-28Cr is used. It is disclosed. This material is used for multi-product glow plugs due to its excellent oxidation resistance.

  Although the above materials have excellent oxidation resistance, they cannot withstand actual use at a very high temperature of 1100 ° C. or higher required by recent engines, and the heating coil is disconnected. The cause of this disconnection is that granular AlN (aluminum nitride) is generated inside the heating coil material with use, and the proportion of the metal portion (ratio of the high conductivity portion) in the sectional area of the heating coil decreases. From the increase in the resistance value due to the above, it is clear that the heat generating coil is locally heated and becomes disconnected.

There is a technology corresponding to this (see, for example, Patent Document 2). Patent Document 2 describes that the rear end portion of the sheath of the metal glow plug is sealed with an elastic body having a small N ₂ (nitrogen) permeability. Certainly, by adopting this configuration, it is possible to effectively prevent N ₂ from entering from the outside of the glow plug. However, the durability is still not sufficient. This may be because oxygen or nitrogen contained in the atmosphere may be mixed during the process of filling the sheath with insulating powder during the manufacturing process, and components that can affect the coil material are enclosed in the sheath. It is done. It is difficult to eliminate this problem by using a conventional heating resistor material.

  However, there is also a configuration that is made to solve this problem without using a heat generating resistor as another material (for example, see Patent Document 3). In this configuration, TiO (titanium oxide) is mixed in MgO (magnesium oxide) powder, which is an insulating powder, and the surface layer of the heating resistor is positively oxidized by the role as an oxygen donor, and the oxide film generates heat of nitrogen. This is to prevent intrusion into the resistor. At first glance, this configuration seems to have solved the problem of durability of the heating resistor. However, mixing oxygen donors can cause the following problems.

  It plays a role as an oxygen donor, and there is a concern that the insulating function as an insulating powder is lowered due to the metal (Ti) from which oxygen is separated, or due to a change in thermal conductivity of the MgO insulating powder itself mixed with TiO, This is a problem that the desired performance of the surface temperature of the sheath cannot be exhibited and the original performance as a glow plug cannot be exhibited. In view of such a situation, it can be said that a technique for improving only the durability of the heating resistor while maintaining the same basic configuration as the glow plug is preferable.

Next, the Fe—Cr—Al alloy which is a heating resistor material will be mentioned.
FIG. 3 is an “influence on the life characteristics of Al and Cr in the Fe—Cr—Al-based heating element” described in Non-Patent Document 1. According to this, there may be a synergistic effect with Al, the degree of increase in the life value accompanying the increase in Cr content from the time when the Cr content exceeds 20% by weight, Cr is more than 20% by weight It seems desirable to include.
JP 54-141314 A JP-A-1-167529 JP 2005-507068 A Industrial heating Vol.20, No.4

  From the above, it can be said that the conventionally known metal glow plug has been sufficiently studied to improve the durability of the heating resistor. However, even if the heating resistor material disclosed in the above-mentioned patent document and the above-mentioned non-patent document 1 is used as it is, it cannot be said that the heat generation performance and durability as a glow plug are necessarily sufficient, and from the viewpoint of reliability. However, there is a market demand that does not like to change the basic configuration as a metal glow plug.

  As described above, an object of the present invention is to achieve high durability as a glow plug by improving the durability of the heating resistor while maintaining the same basic configuration as the glow plug as before.

The first configuration of the glow plug of the present invention is:
A cylindrical metal sheath that extends in the axial direction and has a closed tip side mainly composed of Ni or Fe;
A coiled heating resistor disposed along the axis within the sheath and electrically connected to the sheath;
Insulating powder filled around the heating resistor in the sheath;
A sealing member for sealing the rear end of the sheath;
With
A glow plug in which the internal atmosphere of the sheath sealed by the sealing member is an internal atmosphere having a partial pressure ratio and a nitrogen partial pressure larger than the oxygen partial pressure,
The heating resistor is
Fe is the main component, Cr is contained in an amount of 20% by weight or less, and Al is contained in an amount of more than 8% by weight and 15% by weight or less.

  In the first configuration described above, the invention is configured by an idea that sets a line in the technical field of the conventional glow plug. It is to propose a configuration for reducing the Cr content. This structure will be described from the mechanism.

The Fe-7.5Al-28Cr material, which is a conventional heating resistor material disclosed in Patent Document 1, is made of Al ₂ O ₃ (alumina) on its outer surface in an environment where oxygen is sufficiently present, such as in the atmosphere. It is formed and is effective as a protective oxide film. More specifically, a relatively thick Al ₂ O ₃ is formed on the outer surface of the heating resistor, but a large amount of Cr component is oxidized slightly under Al ₂ O _3. This suppresses the movement of oxygen into the alloy and produces dense Al ₂ O ₃ only on the surface. However, inside the glow plug sheath, where the partial pressure ratio of the nitrogen partial pressure is greater than the oxygen partial pressure and the absolute amount of oxygen is small, a sufficient amount of oxygen is not present, so the oxidation rate is slow, and the heating resistance Al ₂ O ₃ formed on the outer surface of the body can be formed thinner. For this reason, oxygen is depleted in a state where Al ₂ O ₃ is formed to be thin, resulting in an atmosphere of excess nitrogen. In this aspect, if the amount of Cr in the heating resistor is large, a chromium nitride film having a relatively poor protection is formed immediately below the thin film of Al ₂ O ₃ , and granular AlN is formed inside the heating resistor. This causes the problem of precipitation.

Therefore, by providing a configuration provided by the present invention, that is, a configuration with a relatively low Cr content of 20 wt% or less in the heating resistor, only a small amount of chromium nitride is generated immediately below the Al ₂ O ₃ film. Can be. Since the amount of Al with respect to Cr is larger than that of a conventional heating resistor material, an AlN film is formed immediately below the Al ₂ O ₃ film. Since this AlN film has a function of preventing nitrogen from entering the heating resistor, granular AlN is not generated inside the heating resistor. As a result, it is possible to prevent early disconnection of the heating resistor, and to improve durability. The Cr content may be intentionally not contained (that is, the Cr content is zero) by an evaluation test described later.

To form a good the Al ₂ O ₃ film, in order to be Al ₂ O ₃ film is formed immediately below, must be the content of Al 15% by weight more than 8 wt% or less It is. If Al is less than 8% by weight, a good film is not formed and nitriding proceeds inside, which may cause early disconnection. On the other hand, if it exceeds 15% by weight, it becomes extremely difficult to form a coil shape as a heating resistor. Further, even if the coil shape can be formed, the coil is not uniformly deformed in the swaging process, which may cause local heat generation, which is not preferable.

In addition, about Al content with respect to Cr content, it is desirable to set it as 0.65 <= _NAl / _NCr (weight ratio of Al content with respect to Cr content in a heating resistor) <= 1.4.

  As for the internal atmosphere of the first configuration described above, in the glow plug having the control resistor as in the following configuration 2, the glow plug is energized and the region where the control resistor is located is If the oxide film formed on the outer surface of the control resistor when the surface temperature of the sheath is kept at 900 ° C. for 20 hours is 5 μm or less, it can be said that the inside of the sheath is the above-described internal atmosphere.

  As for the internal atmosphere of the first configuration described above, the glow plug was energized as in Configuration 3 below, and the surface temperature of the sheath at the position where the control resistor was located was maintained at 900 ° C. for 20 hours. If the oxide film formed on the inner peripheral surface of the sheath is 5 μm or less, the inside of the sheath may be the above-described internal atmosphere as described above.

  Further, the heating resistor preferably contains 5 wt% or more of Cr (Configuration 4). This is because the temperature coefficient of resistance can be reduced by containing Cr, and quick heat performance can be secured.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is an overall view showing an example of a glow plug including a heating resistor according to the present invention, and FIG. 1B is a longitudinal sectional view thereof.

  As shown in FIGS. 1A and 1B, the glow plug 1 includes a cylindrical metal shell 2 and a sheath heater 3 attached to the metal shell 2.

  The metal shell 2 has a shaft hole 4 penetrating in the direction of the axis C1, and the outer peripheral surface thereof has a hexagonal cross section for engaging a screw portion 5 for attachment to a diesel engine and a tool such as a torque wrench. The tool engaging portion 6 is formed.

  The sheath heater 3 is configured by integrating a sheath 7 and a middle shaft 8 as a lead member in the direction of the axis C1.

  As shown in FIG. 2, the sheath 7 is a cylindrical sheath made of metal with a closed tip (particularly, metal made mainly of Ni or Fe and made of, for example, SUS310 or INC600). Inside, a heat generating coil 9 melt-bonded to the distal end of the sheath and a control coil 10 connected in series to the rear end of the heat generating coil 9 are enclosed together with an insulating powder 11 such as MgO. The rear end of the sheath 7 is sealed with a ring-shaped rubber 17 made of fluororubber between the central shaft 8. As described above, the heat generating coil 9 is electrically connected to the sheath 7 at the tip, but the outer peripheral surfaces of the heat generating coil 9 and the control coil 11 and the inner peripheral surface of the sheath 7 are insulated by the interposition of the insulating powder 11. It is in the state.

  The heating coil 9 is made of an Fe—Cr—Al alloy, and details will be described later. The control coil 10 is made of a material having a larger temperature coefficient of electrical specific resistance than the material of the heating coil 9, for example, a resistance heating wire mainly composed of Co or Ni represented by Co (cobalt) -Ni-Fe alloy. It is configured. Thereby, the control coil 10 increases the electric resistance value by receiving its own heat generation and heat generation from the heat generation coil 9, and controls the power supply amount to the heat generation coil 9. Therefore, relatively large electric power is supplied to the heating coil 9 in the initial stage of energization, and the temperature of the heating coil 9 rises rapidly. Then, the control coil 10 is heated by the heat generation, the electric resistance value increases, and the power supply to the heat generating coil 9 decreases. As a result, the temperature rise characteristic of the sheath heater 3 becomes a form in which the temperature is saturated after the temperature is rapidly raised in the initial stage of energization, and thereafter the power supply is suppressed by the action of the control coil 10. That is, the presence of the control coil 10 makes it possible to prevent the temperature of the heat generating coil 9 from excessively rising (overshoot) while improving the rapid temperature rise.

  Further, the sheath 7 is formed with a small-diameter portion 7a that accommodates the heating coil 9 and the like on the distal end side thereof by swaging or the like, and a large-diameter portion 7b that is larger in diameter than the small-diameter portion 7a on the rear end side. Has been. Then, the large diameter portion 7 b is press-fitted and joined to the small diameter portion 4 a formed in the shaft hole 4 of the metal shell 2, so that the sheath 7 is held in a state of protruding from the tip of the metal shell 2.

  The middle shaft 8 has its tip inserted into the sheath 7 and is electrically connected to the rear end of the control coil 10 and is inserted through the shaft hole 4 of the metal shell 2. The rear end of the middle shaft 8 protrudes from the rear end of the metal shell 2. At the rear end of the metal shell 2, the rubber-made O-ring 12, the resin-made insulating bush 13, and the insulating bush 13 are removed. The holding ring 14 for preventing and the nut 15 for connecting a cable for energization are structured to be fitted to the middle shaft 8 in this order.

Here, the material which comprises the heat generating coil 9 which is the main characteristic part of this invention is demonstrated in detail. In describing, the results of the tests conducted are also listed.
[Evaluation Test 1]
As the heating coil 9 in the present embodiment, a coil containing Fe as a main component and containing a relatively large amount of Al while suppressing a relatively small amount of Cr is employed. Table 1 shows both the compositions (comparative examples) prepared for investigating the mechanism of the present invention as well as showing compositions capable of carrying out the present invention. Table 1 also describes the thickness of the coating formed on the outer surface of the heating coil and the properties of the coating measured by the measurement method described later.

Each sample was produced as follows.
First, each composition is weighed and mixed as a raw material to produce a molten alloy. Next, a φ30 mm cylindrical ingot was formed by hot working, and a φ0.3 mm strand was produced by drawing. The produced wire was coiled by a conventionally known method to form a heating coil 9 shape.

Sample No. About 1-4, it was comprised as a binary system of Fe-Al, without containing Cr. sample. About 5-12, Cr was changed and contained stepwise and the compounding quantity of Al was changed, respectively. In addition, the ratio of each composition shown in Table 1 is weight%, and the sum total of each composition will be 100 weight%. The composition was analyzed using EPMA for the prepared samples (conditions: beam diameter: 10 μm, voltage: 20 kV, current: 2.5 × 10 ⁻⁸ A).

The following tests were performed on these samples. In order to simulate the use in a glow plug, each sample is placed in an electric furnace capable of gas replacement and held at 1200 ° C. for 5 hours. At this time, the atmosphere inside the electric furnace has an initial oxygen partial pressure of 0.2 × 10 ⁵ Pa, and after 3 minutes, 1.0 × 10 ⁻¹³ Pa. The test was performed using N ₂ gas containing a reducing gas such as CO (carbon monoxide) and H ₂ (hydrogen) for adjusting the oxygen partial pressure.

  Each sample after the test was observed. In the observation method, each sample is embedded in the resin block P1 (see FIG. 5), and the resin block P1 and the sample are cut and polished along the longitudinal direction C2 of the sample (of course, only polishing without cutting is performed). You can do it). At the time of polishing, first, rough polishing was performed with SiC water-resistant polishing paper (# 1500), and then mirror finishing was performed with 1 μm of diamond paste. For example, when the sample has a diameter of 0.3 mm, it is desirable to suppress polishing to the inside of about 0.1 to 0.15 mm of the sample. The mirror-finished sample was degreased and washed with an organic solvent such as acetone, and the structure was observed with a metal microscope or SEM, and the thickness of the nitrided portion was measured. Samples 5 and 7 are shown in FIGS. 4A and 4B as representative examples of the observed images.

  Moreover, about the analysis of the property of an oxide film, the element mapping using EPMA was performed with respect to the said sample, and the product was specified. As a result of this analysis, the film was an oxide or nitride mainly composed of Al, and was an oxide or nitride mixed with “Al”, Al and Cr in the “surface layer product” column. The thing is indicated as “Al, Cr”.

  As a result, for Samples 1 to 4 not containing Cr, the films formed on the surface layer of the sample were oxide films and nitride films made of only Al, but Sample 1 in which Al was 8 wt% or less. No dense film was formed, and nitriding had progressed to the inside. When a heat generating coil is formed using sample 1 in which nitriding has progressed and a glow plug is produced, the specific resistance of the internally nitrided portion increases with use, leading to early disconnection. Is predicted. On the other hand, no internal nitridation was observed for Samples 2-4.

For Samples 5 to 12 containing Cr, the film formed on the surface layer was only Al or an oxide film and a nitride film in which Al and Cr were mixed. Sample 12 having a Cr content exceeding 20% by weight has a film in which Al ₂ O ₃ , AlN, and chromium nitride are mixed on the surface layer, and as a result, it is not formed as a good film, and internal nitriding Has occurred. This is considered to be because, unlike the Al ₂ O ₃ coating, the chromium nitride coating has a high nitrogen gas permeability and could not effectively prevent the penetration of nitrogen into the interior. In addition, since the chromium nitride film is formed, the dense Al ₂ O ₃ film is not continuously formed, and the chromium nitride film and the Al ₂ O ₃ film are formed in a piecewise adjacent film. I guess.

  From the above results, it can be seen that the nitrogen partial pressure is higher than the oxygen partial pressure in the partial pressure ratio as in the glow plug sheath, and the oxygen partial pressure gradually decreases. In an environment in which oxygen in the sheath is consumed by oxidation of the sheath), the heating resistor is not contained in Cr or is contained at 20% by weight or less, and Al is contained in an amount of more than 8% by weight and 15% by weight or less. It was confirmed that it was possible to improve the durability of the glow plug.

  In addition, the point which made environmental temperature in this test 1200 degreeC is as follows. In a diesel engine that requires high durability as required by the present invention, the surface temperature of the sheath is as high as 900 ° C. to 1000 ° C. during use. In a glow plug provided with a control resistor, a temperature difference of about 100 ° C. at maximum occurs between the surface temperature of the sheath where the heating resistor is located and the surface temperature of the sheath where the control resistor is located. Further, a temperature difference of 100 ° C. or more is also generated between the surface temperature and the heating resistor and the control resistor housed inside. Taking these and temperature errors into consideration, in order to evaluate the durability of the heating resistor at high temperatures, if it is set to 1200 ° C., it is possible to perform a test assuming a use state.

[Evaluation Test 2]
Next, similarly to the sample of the heating coil shape prepared in the evaluation test 1, a sample for confirming the energization durability was similarly prepared, and the evaluation test 2 was performed. The sample evaluated was sample No. which is an example of the present invention. 2,8,10,13,14,15,16,17 (No. 13 to 17 are samples newly prepared for evaluation test 2) and comparative examples 5, 10 . The energization pattern was "DC 11V6 seconds-DC 14V180 seconds" as one cycle, and the number of cycles when disconnection was obtained in increments of 500 cycles. The results are shown in Table 2 together with the composition of each sample.

  As a result, all of Samples 2, 8, 10, 13 to 17 in which the Cr content is 20 wt% or less (including zero) and the Al content is more than 8 wt% and 15 wt% or less. It was confirmed that it had excellent durability exceeding 6000 cycles.

Among these, the sample 10 in which the _Al content ratio N _Al / N _Cr with respect to the Cr content was less than 0.65 had a durability of 6000 cycles or more, but in the film formed on the outer surface In addition to the formation of an oxide film and a nitride film in which Al ₂ O ₃ and chromium nitride are mixed in Test 1, N _Al / N _Cr is 0.65 or more. There was a tendency for the durability to be difficult compared to the other samples (for example, Sample 8).

On the other hand, the sample 13 in which N _Al / N _Cr exceeded 1.40 also had a durability of 6000 cycles or more, but the resistance value tends to be low due to the relatively small amount of Cr. It was difficult to obtain thermal properties, or the coil wire diameter had to be reduced. Under these influences, durability was lower than that of the sample 8 or the like. From this point of view, when Cr is contained appropriately, it is easy to realize rapid heat property as a glow plug, and it is preferable that Cr is contained, for example, by 5% by weight or more.

From the above results, it was confirmed that even better durability can be obtained when N _Al / N _Cr is 0.65 or more and 1.40 or less.

[Evaluation Test 3]
Next, the oxide film of the control resistor and the sheath was confirmed.
First, a heating coil is produced in the same manner as in the evaluation test 1. The composition of the heating coil to be produced is Sample 8 as an example and Sample 5 as a comparative example. Five sheath heaters are manufactured using a control coil that is separately manufactured. Five, 5-1, 5-2 using the sample 5, 8-1, 8-2 using the sample 8, and 8-3 using the sample 8 and having no control coil. These five sheath heaters were completed as sheath heaters in order to conduct an evaluation test, and then the part including the sealing member at the rear end of the sheath was removed by cutting so that the inside and outside of the sheath were not in an airtight state. It is said.

An evaluation test is performed on the manufactured five sheath heaters using the same apparatus as in the evaluation test 1. The test conditions are maintained at 1200 ° C. for 20 hours, but the two samples 5-1 and 8-1 are equal to the air atmosphere, and the oxygen partial pressure is 0.2 × 10 ⁵ Pa. On the other hand, for the three samples 5-2, 8-2, and 8-3, the oxygen partial pressure is 1.0 × 10 ⁻¹³ Pa assuming the atmosphere inside the sheath used as the glow plug.

  After holding in an electric furnace for 20 hours, each sample is disassembled and cut, and cross sections of the heating coil, control coil, and sheath are observed. When observing the cross section, each member to be observed is embedded in a resin block and observed in the same manner as in the evaluation test 1 (see FIG. 5). The observation results are shown in Table 3.

Consider this result.
Samples 5-1 and 8-1 compare the degree of nitridation due to the difference in the composition of the heating coil in an air atmosphere, that is, an environment where oxygen is sufficiently present and the atmosphere is not excessive with nitrogen. According to this, in the sample 5-1 corresponding to the conventional material and the sample 3-1 corresponding to the present invention, the nitriding degree of the heating coil does not proceed as 0%, There is no particular difference, and it can be judged that all have excellent durability. At this time, the thickness of the oxide film of the control coil and the thickness of the oxide film on the inner peripheral surface of the sheath are 113 μm and 17 μm using Sample 5-1, and are 117 μm and 19 μm using Sample 8-1. there were.

  On the other hand, when comparing 5-2, 8-2, and 8-3 assuming the inside of the sheath in which oxygen is not sufficiently present and the atmosphere is excessive in nitrogen, in the sample 5-2 as a comparative example, the nitriding of the heating coil is performed. Although the degree progresses to 82%, it can be determined that Samples 8-2 and 8-3, which are examples of the present invention, do not proceed with nitridation degree 0% and have excellent durability. Therefore, it was verified that the heating resistor of the present invention achieves excellent durability in a sheath having an internal atmosphere in which the nitrogen partial pressure is larger than the oxygen partial pressure. The thickness of the oxide film of the control coil at this time is 0.7 μm using Sample 5-2 and 0.8 μm using Sample 8-2, and the thickness of the oxide film on the inner peripheral surface of the sheath is All were 1 μm, and all were 5 μm or less.

In addition, this invention is not limited to the above Example at all, You may implement as follows.
That is, as the heating resistor, all of the above-described embodiments are composed of a ternary system of Fe—Cr—Al, but P (phosphorus) is an element that can be mixed depending on the refining of Fe. Although its characteristics are not largely lost due to the inevitable mixing, if it is segregated and contained, it can cause embrittlement, so its content is preferably 150 ppm or less.
In addition, S (sulfur) can be mixed in the same manner, but there is a possibility that the toughness may be lowered, and the content is preferably limited to 80 ppm or less.
Furthermore, Si (silicon) can also be mixed as an impurity. Si may excessively coarsen the crystal grains of the heating resistor during processing, which may reduce workability. From this viewpoint, it is preferably 0.8% by weight or less. However, when Si is contained at 0.8% by weight or less, the effect of promoting the movement of Al to the surface of the heating resistor can be exerted by the load of lattice strain, so an Al2O3 film is actively generated. In order to do so, it is also preferable to contain.

  Moreover, in the said embodiment, what is called a self-control type glow plug provided with the control resistor was illustrated, However, It cannot be overemphasized that it is not limited to this.

(A) is a figure which shows the glow plug 1 provided with the heat generating resistor concerning this invention, (b) shows the longitudinal cross-sectional view. FIG. 2 is a partially broken partial enlarged view for explaining the sheath heater 3. FIG. 3 shows the “influence on the life characteristics of Al and Cr in the Fe—Cr—Al heating element (in the atmosphere)” extracted from Non-Patent Document 1. (A) shows a cross-sectional observation after the evaluation test 1 of the comparative example (sample 5) according to the present invention, and (b) shows a cross-sectional observation after the evaluation test 1 of the embodiment of the present invention (sample 7). It is. It is the figure which buried the measuring object in resin block P1 in order to observe the section of each sample in an evaluation test.

Claims (5)

A cylindrical metal sheath that extends in the axial direction and has a closed tip side mainly composed of Ni or Fe;
A coiled heating resistor disposed along the axis within the sheath and electrically connected to the sheath;
Insulating powder filled around the heating resistor in the sheath;
A sealing member for sealing the rear end of the sheath;
With
A glow plug in which the internal atmosphere of the sheath sealed by the sealing member is an internal atmosphere having a partial pressure ratio and a nitrogen partial pressure larger than the oxygen partial pressure,
The heating resistor is
A glow plug comprising Fe as a main component, Cr containing 20 wt% or less, and Al exceeding 8 wt% and 15 wt% or less. The glow plug is
Comprising a control resistor electrically connected to the heating resistor;
When the glow plug is energized and the surface temperature of the sheath at the position where the control resistor is located is kept at 900 ° C. for 20 hours, the oxide film formed on the outer surface of the control resistor is 5 μm or less. The glow plug according to claim 1, wherein the glow plug is provided. When the glow plug is energized and the surface temperature of the sheath at the position where the control resistor is located is maintained at 900 ° C. for 20 hours, the oxide film formed on the inner peripheral surface of the sheath is 5 μm or less. The glow plug according to claim 1 or 2, characterized by the above. The glow plug according to any one of claims 1 to 3, wherein the heating resistor contains 5 wt% or more of Cr. The heating resistor has an Al content N _Al / N _{Cr with} respect to the _Cr content.
0.65 ≦ N _Al / N _Cr ≦ 1.4
The glow plug according to any one of claims 1 to 4, wherein:

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