JP5509017B2 - Glow plug - Google Patents

Description

  The present invention relates to a glow plug used for preheating a diesel engine.

  Glow plugs used for preheating diesel engines generally contain iron (Fe) as a main component, chromium, (Cr), aluminum (Al), etc. in a metal tube with a closed end. There is known one using a sheath heater in which a heating resistor made of an alloy is enclosed with an insulating powder (for example, magnesium oxide).

In addition, since the heating resistor contains Al, a film of aluminum oxide (Al ₂ O ₃ ) formed by a reaction between oxygen in the tube and Al is formed on the surface thereof. This Al ₂ O ₃ coating can prevent evaporation of material components of the heating resistor.

By the way, the Al ₂ O ₃ coating formed on the surface of the heating resistor is damaged by thermal shock caused by repeated heating and cooling. Here, when oxygen is sufficiently present in the tube, the Al ₂ O ₃ film is formed again. However, the formation and breakage of the Al ₂ O ₃ film is repeated and the oxygen in the tube is consumed. If this is done, there is a risk that the Al ₂ O ₃ coating will not be re-formed because the inside of the tube is sealed. If the Al ₂ O ₃ coating is not formed, the energizable portion of the heating resistor is reduced due to evaporation of the material components, which may increase the resistance value and eventually cause the heating coil to break.

Therefore, a technique for incorporating a metal oxide into the insulating powder in the tube has been proposed (see, for example, Patent Document 1). According to this technique, when oxygen in the tube is consumed, the metal oxide is reduced to generate oxygen in the tube. As a result, the Al ₂ O ₃ coating is regenerated for a longer period of time. Formation is possible.

Japanese Patent No. 4076162

However, even if more metal oxide is contained, the oxygen in the tube is eventually exhausted. That is, there is a limit to the method of preventing evaporation of material components by forming an Al ₂ O ₃ film on the surface of the heating resistor.

The present invention has been made in view of the above circumstances, and the object thereof is to effectively prevent evaporation of the material components of the heating resistor without the formation of an Al ₂ O ₃ film. An object of the present invention is to provide a glow plug that can achieve a long life.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The glow plug of this configuration has a cylindrical tube with a closed end and a sealed state inside,
A heating coil as a heating resistor that is disposed in the tube and whose tip is joined to the tip of the tube, and is connected to the rear end of the heating coil and has a temperature of electrical resistivity higher than the material of the heating coil A control coil made of a material with a large coefficient;
Glow plug with
The heating resistor is formed of an alloy containing nickel (Ni) as a main component and containing tungsten (W) less than Ni ,
The heating resistor has a tungsten content of 5 mol% or more and 15 mol% or less .

  “Main component” refers to a component having the highest mass ratio in the material (hereinafter the same).

According to the configuration 1, the heating resistor is formed of an alloy containing Ni as a main component and containing less W (Ni—W alloy). Here, since Ni is an element having a vapor pressure lower than that of Fe, the evaporation of the material components does not occur even under a high temperature in the operating temperature range of the glow plug, for example, at a high temperature where the temperature of the heating coil is 1300 ° C. Relatively difficult to occur. Further, even when Ni located on the surface layer of the heating resistor evaporates under such a high temperature, W having a very low vapor pressure is hardly evaporated and remains on the surface layer of the heating resistor. A film made of W (W film) is formed on the surface layer of the heating resistor. Therefore, further evaporation of Ni is suppressed by the W coating. That is, according to the present configuration 1, the property of Ni that is less likely to evaporate than Fe and the property of W that forms a film on the surface layer of the heating resistor act synergistically, thereby dramatically increasing the lifetime. Can be achieved.
In particular, the heating resistor contains a relatively large amount of W of 5 mol% or more. For this reason, the W film can be more reliably formed on the surface layer of the heating resistor, and evaporation of the material components can be more effectively suppressed. Further, the W content is 15 mol% or less. Therefore, the workability of the alloy constituting the heating resistor can be improved, and the heating resistor can be formed into a desired shape relatively easily.

  Note that the Ni—W alloy is an alloy that is relatively easily oxidized, but since the inside of the tube is in a sealed state, the entry of oxygen from the outside into the tube is suppressed as much as possible. In other words, a Ni—W alloy can be adopted as an alloy constituting the heating resistor because it is in an environment where oxygen intrusion is suppressed in the tube.

  In addition, instead of W, for example, it is conceivable that the heating resistor is composed of an alloy containing an element such as Mo in Ni as an element having a low vapor pressure. However, in this case, the film formed on the surface layer of the heating resistor is a mixture of Mo and Ni and is not stable. Therefore, there is a possibility that evaporation of material components cannot be sufficiently suppressed. On the other hand, when the heating resistor is made of a Ni—W alloy, a stable W film made of W is formed on the surface layer of the heating resistor. Therefore, evaporation of material components can be suppressed very effectively, and it can be said that it is significant to contain W from this point as well.

  In addition, considering the case where the heating resistor is made into a thin shape such as a coil shape, for example, when an alloy containing Fe as a main component is processed into a small diameter, the heating resistor is drawn while being heated (hot drawing). In the case of an alloy containing Ni as a main component, it can be drawn without heating. That is, the Ni—W alloy is more workable than the alloy containing Fe as a main component, and it is effective to use the Ni—W alloy also in this respect.

  It is preferable that phosphorus (P) is not substantially contained in the alloy constituting the heating resistor. If P is contained in the alloy constituting the heating resistor, Ni and P react with each other to generate a low melting point compound, which may reduce the high temperature strength. Further, in the Ni alloy, P is relatively easily segregated. However, since the location where P is segregated is fragile, there is a possibility that cracking or the like may occur in the heating resistor starting from the location. For this reason, it is preferable not to contain P in the alloy.

  However, since P is inevitably contained in the raw material, in order to prevent P from being contained in the raw material at all, a very expensive process such as increasing the refining degree of the raw material is required. Therefore, in consideration of such circumstances and the performance as a glow plug, it is preferable not to contain “substantially” P in the alloy constituting the heating resistor. Here, “substantially” means that the content of P is 0.05% by mass or less with respect to the total sum of materials (mass of the alloy). In view of only the performance of the glow plug, the P content in the material is preferably as small as possible. Therefore, it is more preferable that the P content is 0.03% by mass or less with respect to the total sum of the materials, and it is even more preferable that no P is contained in the material.

  Configuration 2. The glow plug of this configuration is characterized in that, in the above configuration 1, at least one of chromium (Cr), silicon (Si), and titanium (Ti) is contained in a portion in contact with the space in the tube. .

  In addition, “the portion in contact with the space in the tube” refers to what defines the space in the tube or is disposed in the space in the tube, for example, the tube itself, a heating resistor, Insulating powder for insulating between the tube and the heating resistor, or a metal film formed on the inner peripheral surface of the tube or the like can be used.

  Cr, Si, and Ti are elements that are relatively easily oxidized. Therefore, as in the above-described configuration 2, when these elements are contained in a portion in contact with the space in the tube, these elements function as oxygen getter elements, so that oxygen in the tube can be removed. Therefore, oxidation of the heating resistor can be prevented more reliably, and the durability can be further improved.

  Configuration 3. The glow plug of this configuration is the above configuration 1 or 2, wherein the heating resistor is made of 5 mol% or more and 30 mol% or less of Cr, 1 mol% or more and 10 mol% or less of Si, and 1 mol% or more and 5 mol% or less of Ti. It includes at least one kind.

  According to the said structure 3, the effect similar to the said structure 2 will be show | played fundamentally. In addition, according to the third configuration, the heating resistor contains Cr, Si, or the like. Therefore, when Cr, Si, etc. react with oxygen in the tube, an oxide film can be formed on the surface of the heating resistor. As a result, the oxide film prevents nitrogen and oxygen from entering the heating resistor. Can be prevented. As a result, disconnection of the heating resistor due to the formation of nitride or oxide inside the heating resistor can be more reliably prevented.

  Furthermore, evaporation of the material components of the heating resistor can be further suppressed by the oxide film. Therefore, combined with the effect of suppressing the formation of nitride or the like inside the heating resistor, it is possible to further extend the life.

  In addition, when Al is contained in the heating resistor, Al moves (diffuses) from the high potential side to the low potential side due to the potential difference generated in the heating resistor in a high temperature environment. There is a possibility that a cavity is formed inside the resistor (so-called electromigration occurs). In this regard, according to the present configuration 3, since a relatively large weight of W is contained in the heating resistor, the movement of Al can be prevented and the generation of cavities inside the heating resistor can be suppressed. That is, when Al is contained in the heating resistor, W in the heating resistor eliminates the disadvantages due to the Al content and sufficiently exerts the effects such as oxygen removal in the tube due to the Al content.

  In addition, when content, such as Cr and Si, is less than each lower limit, there exists a possibility that the above-mentioned effect may not be show | played fully. On the other hand, the upper limit of the content of Cr, Si, etc. indicates the solid solubility limit for the Ni—W alloy, and when the content of each element exceeds the upper limit, these elements are precipitated from the alloy. There is a risk of it. Therefore, the content of Cr, Si, or the like is desirably set to the upper limit value or less described above in order to prevent the workability from being lowered due to the hardening of the alloy.

  Configuration 4. In the glow plug of this configuration, in any one of the above configurations 1 to 3, the heating resistor is 5 mol% or more and 10 mol% or less of vanadium (V), 5 mol% or more and 10 mol% or less of molybdenum (Mo), 1 mol% or more. It contains at least one of niobium (Nb) of 5 mol% or less and tantalum (Ta) of 1 mol% or more and 10 mol% or less.

  According to the configuration 4, since the heating resistor contains V, Mo, or the like, the resistance value of the heating resistor can be increased. Therefore, it is possible to sufficiently increase the resistance value of the heating resistor without excessively reducing the diameter of the heating resistor, thereby realizing a sufficient heating performance. Further, since it is not necessary to excessively reduce the diameter of the heating resistor, the heating resistor can be made relatively thick, and the durability of the heating resistor can be improved.

  In addition, when content, such as V and Mo, is less than each lower limit, there exists a possibility that the above-mentioned effect may not fully be show | played. On the other hand, if the content of V, Mo, or the like exceeds the respective upper limit values, the workability may be reduced.

Configuration 5 . The glow plug of this configuration is characterized in that, in any one of the above configurations 1 to 4 , the phosphorus (P) content of the heating resistor is 0.05% by mass or less.

According to the configuration 5 , the P content in the heating resistor is 0.05% by mass or less. Therefore, it is possible to more reliably prevent a decrease in high-temperature strength due to the reaction between Ni and P to produce a low melting point compound, cracking of the heating resistor due to P segregation, and the like. Therefore, even when the heating resistor has a relatively thin shape (for example, φ0.2 mm or less), the heating resistor can be stably manufactured without causing cracks or the like. Moreover, the durability improvement effect by using the Ni-W alloy mentioned above can be exhibited more reliably.

(A) is the partially broken front view of the glow plug of this embodiment, (b) is the elements on larger scale of the glow plug front-end | tip part. It is a graph which shows the vapor pressure of Fe, Al, Cr, Ni, and W.

  Hereinafter, an embodiment will be described with reference to the drawings. Fig.1 (a) is a partially broken front view which shows an example of the glow plug concerning this invention, FIG.1 (b) is partial expanded sectional views, such as a sheath heater.

  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 CL1, and a hexagonal cross section for engaging a screw portion 5 for attachment to a diesel engine or the like and a tool such as a torque wrench on the outer peripheral surface thereof. A tool engaging portion 6 having a shape is formed.

  The sheath heater 3 is configured by integrating a tube 7 and a middle shaft 8 in the direction of the axis CL1.

  The tube 7 is a cylindrical tube formed of a metal (for example, Inconel, stainless steel alloy or the like) whose main component is iron (Fe) or nickel (Ni) and having a closed end. Inside the tube 7, a heating coil 9 as a heating resistor joined to the tip of the tube 7 and a control coil 10 connected in series to the rear end of the heating coil 9 are insulated with magnesium oxide powder or the like. It is enclosed with the powder 11. Although the heat generating coil 9 is electrically connected to the tube 7 at the tip, the outer peripheral surface of the heat generating coil 9 and the control coil 10 and the inner peripheral surface of the tube 7 are insulated from each other by the intervening insulating powder 11. It has become.

  Further, the rear end of the tube 7 is sealed with an annular rubber 16 between the tube 7 and the center shaft 8. That is, the inside of the tube 7 is sealed.

  The heating coil 9 is constituted by a resistance heating wire made of a predetermined alloy (the composition of the alloy will be described in detail later).

  The control coil 10 is made of a material having a temperature coefficient of electrical specific resistance larger than that of the material of the heating coil 9, for example, a resistance heating wire mainly composed of Co or Ni typified by a cobalt (Co) -Ni-Fe alloy. It is comprised by. 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.

  In addition, it is good also as controlling the heat_generation | fever of the heat generating coil 9 by adjusting the supply amount of the electric power with respect to the heat generating coil 9 using a predetermined | prescribed external controller. In addition, when the external controller fails, the amount of power supply is not adjusted, and overheating of the heat generating coil 9 is a concern. However, the amount of power supplied to the heat generating coil 9 is reduced by using the control coil 10. It is good also as preventing excessive temperature rise of the heat generating coil 9 by doing. That is, the control coil 10 can be used to positively adjust the amount of power supplied to the heating coil 9 or can be used to prevent an excessively large current from being supplied to the heating coil 9. it can.

  Further, the tube 7 is formed with a small-diameter portion 7a that accommodates the heating coil 9 and the like at its distal end 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. Is formed. 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 tube 7 is held in a state of protruding from the tip of the metal shell 2.

  The middle shaft 8 is inserted at its tip into the tube 7, 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.

  In addition, the heating coil 9 is made of an alloy containing Ni as a main component and containing less W (0.5 mol% or more and 15 mol% or less in this embodiment). That is, as shown in FIG. 2, the heating coil 9 is made of an alloy containing Ni and W whose vapor pressure is lower than the vapor pressure of each metal element constituting the Fe—Cr—Al alloy according to the prior art. .

  Moreover, at least one of 5 mol% to 30 mol% Cr, 1 mol% to 10 mol% Si, and 1 mol% to 5 mol% Ti is contained in the portion in contact with the space in the tube 7. . In this embodiment, these elements are contained in the alloy constituting the heating coil 9 located in the space in the tube 7.

  In addition to or in place of these elements, the alloy constituting the heating coil 9 includes 5 mol% to 10 mol% V, 5 mol% to 10 mol% Mo, 1 mol% to 5 mol% Nb, and It is good also as containing at least 1 type in 1 mol% or more and 10 mol% or less of Ta.

  In addition, the alloy constituting the heating coil 9 may contain inevitable impurities such as C, Mn, S, O, and N having a total content of 0.5% by mass or less. If the content of these inevitable impurities is 0.5% by mass or less, it is possible to more reliably prevent deterioration of workability and durability.

  In addition, in the present embodiment, the phosphorus (P) content in the alloy constituting the heating coil 9 is set to 0.05 mass% or less. That is, compared with the above-mentioned inevitable impurities, P is likely to be affected in terms of workability and durability even if its content is small, but its content is sufficiently small as 0.05% by mass or less. It is supposed to be. In view of workability and durability, the P content is preferably as low as possible, more preferably 0.03% by mass or less, and no P is contained in the material constituting the alloy. Even more preferably.

  As described above in detail, according to the present embodiment, the heat generating coil 9 is formed of an alloy containing Ni as a main component and containing less W. Here, since Ni is an element having a lower vapor pressure than Fe or the like as described above, evaporation of material components is relatively difficult to occur at high temperatures. Further, even if Ni located on the surface layer of the heating coil 9 evaporates at a high temperature, W having a very low vapor pressure remains on the surface layer of the heating coil 9 without being evaporated, and as a result, the surface layer of the heating coil 9 In this case, a film made of W (W film) is formed. Therefore, further evaporation of Ni is suppressed by the W coating. In other words, according to the present embodiment, the property of Ni that is less likely to evaporate than Fe and the property of W that forms a coating on the surface layer of the heating coil 9 act synergistically, resulting in a dramatically long life. Can be achieved.

  Note that the Ni—W alloy is an alloy that is relatively easy to oxidize, but the inside of the tube 7 is in a sealed state. In other words, the Ni—W alloy can be adopted as the alloy constituting the heating coil 9 because it is in an environment where oxygen intrusion is suppressed in the tube 7.

  In addition, when processing an alloy containing Fe as a main component into a coil shape, it is necessary to wire (hot drawing) while heating, but in an alloy containing Ni as a main component, It can be processed into a coil shape without heating. That is, the Ni—W alloy is more workable than the alloy containing Fe as a main component, and it is effective to use the Ni—W alloy also in this respect.

  Further, at least one of a predetermined amount of Cr, Si, and Ti is contained in a portion in contact with the space in the tube 7. Therefore, these elements function as oxygen getter elements, so that oxygen in the tube 7 can be removed. Therefore, even if the heat generating coil 9 is relatively easily oxidized, the oxidation can be prevented more reliably, and the durability can be further improved.

  In particular, in this embodiment, since the heating coil 9 contains Cr, Si or the like, an oxide film can be formed on the surface of the heating coil 9 by reacting Cr or Si with oxygen in the tube 7. . Therefore, the oxide film can prevent intrusion of nitrogen or oxygen into the heating coil 9 and can prevent the formation of nitrides or oxides in the heating coil 9.

  In addition, if the heating coil 9 contains a predetermined amount of at least one of V, Mo, Nb, and Ta, the electrical resistivity of the heating coil 9 can be increased. Therefore, in order to make the heating coil 9 have a desired resistance value, it is not necessary to reduce the diameter excessively. As a result, the durability of the heating coil 9 can be further improved.

  Furthermore, in this embodiment, the content of P in the alloy constituting the heating coil 9 is 0.05% by mass or less. Therefore, it is possible to more reliably prevent a decrease in high-temperature strength due to the reaction between Ni and P to produce a low melting point compound, cracking of the heating resistor due to P segregation, and the like. Thereby, while being able to prevent the fall of workability, the durable improvement effect by using the Ni-W alloy mentioned above can be exhibited more reliably.

  Next, in order to confirm the operational effects achieved by the above embodiment, a glow plug sample (corresponding to a comparative example) in which a heating coil is formed of an Fe—Al—Cr alloy, Ni as a main component, Samples of glow plugs (corresponding to Examples) in which heat generating coils were formed from an alloy containing a small amount of W were prepared, and durability evaluation tests were performed on the samples.

  The outline of the durability evaluation test is as follows. That is, the temperature of the portion 2 mm from the tip (measurement portion) of the tube is energized to increase the temperature to 1100 ° C., energized to maintain the temperature for 360 seconds, and then cooled for 120 seconds. As one cycle, the number of cycles until disconnection (disconnection cycle) was measured for each sample. Table 1 shows the composition of the alloy forming the heating coil and the disconnection cycle for each sample. The temperature was measured with a thermocouple attached to the measurement site. In addition, the wire diameter of the heating coil of each sample was adjusted to make the resistance values equal for each sample. Table 1 shows the composition when the contents of W, Mo, Al, etc. are expressed in mol% and the composition when expressed in mass%.

  As shown in Table 1, it was found that the sample according to the example in which the heat generating coil was formed of an alloy containing Ni as a main component and containing W has an excellent durability with a disconnection cycle exceeding 8000 cycles. This is presumably because after the Ni on the surface of the heating coil evaporates, a coating made of W having a very low vapor pressure was formed on the surface of the heating coil, and as a result, the Ni evaporation was effectively suppressed.

  In particular, a sample in which a heating coil is formed of an alloy composed of Ni and W, and the content of W is 5 mol% or more, it is confirmed that the disconnection cycle is 10,000 cycles or more and the durability is very excellent. It was.

  Furthermore, the sample in which the heating coil is formed from an alloy containing Mo, Cr, Ta, Nb, Ti, Si, V, or the like with respect to the Ni—W alloy is a case where the W content is relatively small. However, it has been found that it has extremely excellent durability. In addition, it is thought that this durability improvement was implement | achieved because each element functioned as follows. In other words, when Cr, Si, Ti, or the like is contained, these elements function as oxygen getter elements, so that oxygen in the tube can be removed, and thus oxidation of the heating coil can be suppressed. It is thought that. In addition, when V, Mo, Nb, or Ta is contained, the electrical resistivity of the alloy constituting the heating coil can be increased, and the wire diameter of the heating coil can be made relatively large. Conceivable.

  As mentioned above, it can be said that it is preferable to form the heating coil from an alloy containing Ni as a main component and containing less W from the viewpoint of improving durability by comprehensively considering the result of the evaluation test. . In particular, it can be said that it is more preferable to relatively increase the content of W to 5 mol% or more and to contain additional elements such as Mo and Cr from the viewpoint of further improving the durability.

  Next, whether or not a crack is generated in the manufactured wire when a φ1 mm wire rod is manufactured by reducing the diameter of a φ12 mm columnar alloy containing Ni as a main component and variously changing the W content. Thus, the superiority or inferiority of the workability due to the W content was evaluated. The diameter of the cylindrical alloy is reduced stepwise, and the heat treatment is performed at diameters of φ10 mm, φ8 mm, φ6 mm, φ4 mm, φ3 mm, φ2.3 mm, and φ1.8 mm, and wire drawing is performed. Sexual superiority or inferiority was evaluated.

  In addition, when a wire with a diameter of 1 mm can be obtained without cracking, a sample of a glow plug in which a heating coil is formed by the wire is prepared, and the following test is performed on the prepared sample. The durability was judged. That is, the temperature of the tube 2 mm from the tip (measurement site) is energized to increase the temperature to 1130 ° C., energized to maintain the temperature for 120 seconds, and the energization is stopped. Cooling by blowing for 120 seconds was taken as one cycle, and the number of cycles (disconnection cycle) until the heating coil was disconnected was measured. Table 2 shows the presence / absence of cracks at the time of manufacture and the disconnection cycle in each sample. Table 2 also shows the composition when the W content is expressed in mass%.

  As shown in Table 2, although the disconnection cycle increased as the W content increased, the sample in which the W content was larger than 15 mol% was cracked during production, and the above wire drawing process was performed. It was evaluated that it was inferior in the workability evaluation according to.

  From the above test results, it can be said that the W content is preferably 15 mol% or less in order to prevent deterioration of workability and durability.

  Next, for a cylindrical alloy having a diameter of 12 mm, containing Ni as a main component, containing 12 mol% (29.9 mass%) of W, and variously changing the P content (mass%). When the above-mentioned diameter reduction processing was performed and a φ1 mm wire was produced, whether the produced wire was cracked or not was evaluated for superiority or inferiority in workability and durability depending on the P content. Further, when a wire rod of φ1 mm can be obtained without cracking, a glow plug sample in which a heating coil is formed by the wire rod is manufactured, and the durability of the manufactured sample is tested as described above [ie, One cycle of energizing the tube so that the surface of the 2 mm portion (measurement site) from the tip is 1130 ° C., raising the temperature to maintain the temperature for 360 seconds, and then cooling for 120 seconds. As a test for measuring the number of cycles until disconnection]. Table 3 shows the presence / absence of cracks during production and the disconnection cycle in each sample.

  As shown in Table 3, it was confirmed that the samples (samples 1 to 5) having a P content of 0.05% by mass or less were excellent in workability and durability without cracking during production. . It was also found that the disconnection cycle can be increased as the P content is reduced.

  From the above test results, it can be said that the P content is preferably 0.05% by mass or less in order to more reliably prevent deterioration of workability and durability. Further, from the viewpoint of improving the durability, it is preferable to reduce the P content, and it is more preferable to set the P content to 0.03% by mass or less.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, Cr, Si, or Ti is contained in the alloy that constitutes the heating coil 9, but the alloy that constitutes the insulating powder 11 or the tube 7 contains Cr, Si, or the like. Alternatively, a metal film containing Cr, Si, or the like may be formed on the inner peripheral surface of the tube 7. Even in this case, Cr, Si, etc. can function as an oxygen getter, and oxygen in the tube 7 can be removed. Therefore, as in the case where the heating coil 9 contains Cr, the life can be further extended. Can be planned. In addition, when Cr, Ti, etc. are contained in the insulating powder 11, it is desirable to adjust the content of Cr, Ti, etc. so as not to impair the insulating properties of the insulating powder 11.

  (B) In the above embodiment, the alloy constituting the heating coil 9 contains an additive element such as Cr or Si, but without adding an additive element such as Cr or Si, the heating coil 9 is made of Ni--. It is good also as comprising from W alloy.

  (C) In the above embodiment, the metal material constituting the tube 7 is an alloy mainly composed of Fe or Ni. However, these are examples, and the metal material constituting the tube 7 is limited to this. Is not to be done. However, the metal material constituting the tube 7 needs to be a material capable of preventing oxygen from entering the tube 7.

  (D) The shape or the like of the glow plug 1 is not limited to the above embodiment. For example, the tube 7 is configured to omit the large-diameter portion 7b and form a straight shape with a substantially constant outer diameter. It is good as well. Further, the small diameter portion 4a of the shaft hole 4 of the metal shell 2 may be omitted, and the tube 7 may be press-fitted into the shaft hole 4 having a straight shape in the axial direction.

  (E) In the above embodiment, the glow plug 1 has the control coil 10, but the control coil 10 may be omitted and the rear end of the heating coil 9 may be directly joined to the middle shaft 8.

  (F) Moreover, the wire drawing performed in order to evaluate the superiority or inferiority of the workability is an example for evaluation, and limits the processing method when using the alloy constituting the heating resistor of the present invention. It is not a thing. Therefore, when drawing an alloy having relatively poor workability, the step of reducing the diameter may be further increased.

  DESCRIPTION OF SYMBOLS 1 ... Glow plug, 7 ... Tube, 9 ... Heat generating coil (heat generating resistor).

Claims (5)

A cylindrical tube having a closed end and a sealed inside,
A heating coil as a heating resistor that is disposed in the tube and whose tip is joined to the tip of the tube, and is connected to the rear end of the heating coil and has a temperature of electrical resistivity higher than the material of the heating coil A control coil made of a material with a large coefficient;
Glow plug with
The heating resistor is made of an alloy containing nickel as a main component and containing less tungsten than nickel ,
A glow plug, wherein the heating resistor has a tungsten content of 5 mol% or more and 15 mol% or less .   The glow plug according to claim 1, wherein at least one of chromium, silicon, and titanium is contained in a portion in contact with the space in the tube.   The heat generating resistor includes at least one of chromium of 5 mol% to 30 mol%, silicon of 1 mol% to 10 mol%, and titanium of 1 mol% to 5 mol%. Glow plug as described in.   The heating resistor includes at least one of vanadium of 5 mol% to 10 mol%, molybdenum of 5 mol% to 10 mol%, niobium of 1 mol% to 5 mol%, and tantalum of 1 mol% to 10 mol%. The glow plug according to any one of claims 1 to 3, wherein: The glow plug according to any one of claims 1 to 4 , wherein a content of phosphorus in the heating resistor is 0.05% by mass or less.

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