GLOW PLUG

Abstract

 To ensure oxidation resistance of a glow plug in a high temperature environment and simultaneously prevent a short circuit between a tube and a heat-generating coil in the high temperature environment.
The glow plug includes: a tube having a closed forward end; a heat-generating coil that is disposed inside the tube, has a forward end electrically connected to the forward end of the tube, and generates heat when energized; and an insulating material that contains MgO as a main component and fills the space between the inner surface of the tube and the heat-generating coil. The tube is formed of an alloy containing Ni in an amount of 50% by weight or more, Cr in an amount of 18% by weight to 30% by weight, Al, and at least one component selected from Y and Zr. The amount of Al is 1% by weight or less, and the total amount of the at least one component selected from Y and Zr is 0.01% by weight to 0.3% by weight.

Description

[0001] The present specification relates to a glow plug used for internal combustion engines, etc.

[0002] One known conventional glow plug used to, for example, assist the start of an internal combustion engine uses a sheath heater. One known sheath heater has a structure including a tube with a closed end, a heat-generating coil that is disposed inside the tube and generates heat when energized, and magnesia (MgO) that fills the space between the inner surface of the tube and the heat-generating coil (see, for example, Patent Document 2).

[0003] Patent Document 1 discloses, as the material of the tube of such a glow plug, an alloy containing 36 to 39% by weight of nickel, 20 to 23% by weight of chromium, and iron as main components and further containing 0 to 0.5% by weight of aluminum.

[0004] Patent Document 2 discloses, as the material of the tube of such a glow plug, an alloy containing more than 50% by weight of nickel, chromium, and iron as main components and further containing a small amount of aluminum (specifically, Ni-23Cr-14Fe-0.3Al-0.5Mn-0.2Si).

[Prior Art Documents]

[Patent Documents]

[0005] 

[Patent Document 1] Japanese Kohyo (PCT) Patent Publication No. 2014-522450

[Patent Document 2] WO2011/162074

[0006] In recent years, to reduce emissions from internal combustion engines and improve their fuel economy, there has been demand to further increase the temperature inside the combustion chambers of the internal combustion engines, and there has also been demand for glow plugs to operate in a higher temperature environment. The higher the temperature during operation, the higher the speed of progress of oxidation reaction. Therefore, the material of the tubes is required to have higher oxidation resistance. In the alloy disclosed in Patent Document 1, the amount of nickel having high oxidation resistance is relatively small, so that the relative amount of iron having lower oxidation resistance is large. Therefore, it is difficult to ensure oxidation resistance in a high temperature environment. In the alloy disclosed in Patent Document 2, the amount of nickel having high oxidation resistance is more than 50% by weight, and therefore the oxidation resistance of the alloy is superior to that of the alloy disclosed in Patent Document 1.

[0007] As the operating temperature of a glow plug increases, magnesia filling the tube becomes more likely to be reduced by aluminum contained in the tube. When the magnesia inside the tube is reduced, conductive magnesium is generated inside the tube, and this may cause a short circuit between the tube and the heat-generating coil. Therefore, as the operating temperature increases, there arises a stronger need for suppression of the reduction of magnesia by aluminum, as well as resistance to oxidation.

[0008] In the alloy disclosed in Patent Document 2, the amount of aluminum is relatively low. Therefore, formation of short circuit between the tube and the heat-generating coil can be prevented by suppressing reduction of magnesia by aluminum. However, the disclosed alloy may fail to have sufficient oxidation resistance. Specifically, in the alloy disclosed in Patent Document 2, although the amount of nickel having high oxidation resistance is more than 50%, the amount of aluminum is relatively low, so that an aluminum oxide film is less likely to be formed on the surface of the alloy. Therefore, it is difficult to ensure oxidation resistance in a high temperature environment.

[0009] The present specification discloses a technique that allows a glow plug to ensure oxidation resistance in a high temperature environment and simultaneously prevent occurrence of a short circuit between the tube and the heat-generating coil in the high temperature environment.

[0010] The technique disclosed in the present specification can be embodied in the following application examples.

[Application Example 1] A glow plug comprising:

a tube having a tubular shape with a closed forward end;

a heat-generating coil that is disposed inside the tube, has a forward end electrically connected to the forward end of the tube, and generates heat when energized; and

an insulating material that contains magnesia (MgO) as a main component and fills a space between an inner surface of the tube and the heat-generating coil,

wherein the tube is formed of an alloy containing

nickel (Ni) in an amount of 50% by weight or more,

chromium (Cr) in an amount of 18% by weight to 30% by weight,

aluminum (Al), and

at least one component selected from yttrium (Y) and zirconium (Zr), and wherein the amount of aluminum (Al) is 1% by weight or less, and

the total amount of the at least one component selected from yttrium (Y) and zirconium (Zr) is 0.01% by weight to 0.3% by weight.

In the above configuration, the alloy forming the tube contains 50% by weight or more of nickel. Therefore, this alloy is higher in oxidation resistance than alloys containing less than 50% by weight of nickel, e.g., Fe-based alloys containing Fe (iron) as a main component. The above alloy contains chromium in an amount of 18% by weight to 30% by weight. Therefore, an adequate chromium oxide (Cr₂O₃) film is formed on the surface of the alloy, and the oxidation resistance can be improved. In this alloy, the amount of aluminum is 1 % by weight or less, so that the reduction of magnesia can be suppressed. Therefore, a problem with a short circuit between the tube and the heat-generating coil can be prevented.
Since the amount of aluminum is 1 % by weight or less, the amount of an alumina (Al₂O₃) film formed on the surface of the alloy is small, so that the oxidation resistance can be low. However, this alloy contains at least one component selected from yttrium and zirconium in a total amount of 0.01 % by weight to 0.3% by weight. This can compensate for the deterioration in oxidation resistance due to the decrease in the amount of the alumina film formed on the surface of the alloy, and sufficient oxidation resistance can thereby be ensured.
The tube is formed using the above alloy. Therefore, the glow plug can ensure oxidation resistance in a high temperature environment, and simultaneously prevent formation of a short circuit between the tube and the heat-generating coil in the high temperature environment.

[Application Example 2] A glow plug described in Application Example 1, wherein
the alloy forming the tube further contains
at least one component selected from silicon (Si), titanium (Ti), and manganese (Mn), and
the total amount of the at least one component selected from silicon (Si), titanium (Ti), and manganese (Mn) is 0.2% by weight to 1.5% by weight.
In contrast to aluminum (Al), the free energy of oxide formation of each of silicon (Si), titanium (Ti), and manganese (Mn) is higher than that of magnesium even at high temperature, so that magnesia (MgO) is unlikely to be reduced by silicon (Si), titanium (Ti), and manganese (Mn). In addition, since the free energy of oxide formation of each of silicon (Si), titanium (Ti), and manganese (Mn) is lower than those of chromium (Cr) and nickel (Ni), an oxide film (e.g., a silica, titanium oxide, or manganese oxide film) can be formed on the surface of the alloy by adding such an element in a small amount. Therefore, in the glow plug configured as described above, the oxidation resistance of the tube can be improved without causing reduction of magnesia (MgO). In addition, since the formability of the alloy does not deteriorate, the tube can be easily formed.

[Application Example 3] A glow plug described in Application Example 1 or 2, wherein the alloy forming the tube further contains iron (Fe) in an amount of 5% by weight to 20% by weight.

[0011] In this case, the formability of the tube can be improved with no deterioration in the oxidation resistance of the tube.

[0012] The technique disclosed in the present specification can be embodied in various modes. For example, the technique can be embodied as a sheath heater, a tube of the sheath heater, an alloy for the tube of the sheath heater, etc.

[0013] The invention will be further described by way of example with reference to the accompanying drawings, in which:-

FIG. 1 is a cross-sectional view showing a glow plug which is one embodiment of the present invention.

FIG. 2 is an enlarged view of a forward end of a heater member 800 and the vicinity thereof.

A. Embodiment

A1. Structure of glow plug:

[0014] An embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a glow plug which is one embodiment of the present invention. The glow plug 10 functions as a heat source for, for example, assisting the start of an unillustrated internal combustion engine (e.g., a diesel engine). Specifically, an axial line CL shown in FIG. 1 represents the center axis of the glow plug 10. A direction parallel to the axial line CL is referred to also as an "axial direction." In FIG. 1, a first direction D1 and a second direction D2 are parallel to the axial line CL, and the second direction D2 is opposite the first direction D1. As will be described later, a heater member 800 that generates heat when energized forms an end portion of the glow plug 10 on a first direction D1 side. Hereinafter, the first direction D1 side is referred to also as a "forward end side," and a second direction D2 side is referred to also as a "rear end side." An end of each of various components of the glow plug 10 on the first direction D1 side is referred to also as a "forward end," and an end on the second direction D2 side is referred to also as a "rear end."

[0015] The glow plug 10 includes a metallic shell 20, a center rod 30, an O-ring 50, an insulating member 60, a terminal member 80, and the heater member 800.

[0016] The metallic shell 20 is a tubular member having a through hole 20x extending along the axial line CL and is formed using a conductive metallic material such as carbon steel. The metallic shell 20 includes a tool engagement portion 28 formed at an end portion on the second direction D2 side, a male screw portion 22 formed on the first direction D1 side of the tool engagement portion 28, and a trunk portion 21 that forms a portion on the first direction D1 side of the male threaded portion 22. The tool engagement portion 28 is to be engaged with an unillustrated tool when the glow plug 10 is attached or detached. The male screw portion 22 includes a screw thread that is to be threadingly engaged with a female screw in a mounting hole of an unillustrated internal combustion engine.

[0017] The center rod 30 is a round bar-shaped member and is formed using a conductive metallic material such as stainless steel. The center rod 30 is disposed inside the metallic shell 20, i.e., inside the through hole 20x. A rear end portion 319 of the center rod 30 protrudes in the second direction D2 from an opening OP2 of the metallic shell 20 on the second direction D2 side. A forward end portion of the center rod 30 is inserted into an axial hole AH of a tube 810 described later.

[0018] The O-ring 50 is an annular member and is formed using an electrically insulating elastic material such as rubber. The O-ring 50 is disposed near the opening OP2 of the metallic shell 20 and located between the outer circumferential surface of the center rod 30 and the inner circumferential surface of the metallic shell 20 that forms the through hole 20x.

[0019] The insulating member 60 is formed using an electrically insulating material such as a resin. The insulating member 60 includes a tubular portion 62 and a flange portion 68 disposed on the second direction D2 side of the tubular portion 62. The tubular portion 62 is inserted into the through hole 20x through the opening OP2 of the metallic shell 20, and the forward end of the tubular portion 62 is in contact with the O-ring 50. The center rod 30 is inserted into a through hole formed in the tubular portion 62. The flange portion 68 is in contact with a rear end surface of the metallic shell 20. The O-ring 50 and the insulating member 60 fix a rear end portion of the center rod 30 to the metallic shell 20 and electrically insulate the center rod 30 and the metallic shell 20 from each other.

[0020] The terminal member 80 is a cap-shaped member and is formed using a conductive metallic material such as nickel or a nickel alloy. The terminal member 80 is disposed rearward of the metallic shell 20. The flange portion 68 of the insulating member 60 is disposed between the terminal member 80 and the metallic shell 20 so as to electrically insulate the terminal member 80 and the metallic shell 20 from each other. The rear end portion 319 of the center rod 30 is inserted into the terminal member 80. The terminal member 80 is crimped, whereby the terminal member 80 is fixed to the rear end portion 319. In this manner, the terminal member 80 is electrically connected to the center rod 30.

[0021] The heater member 800 is press-fitted into a forward end portion of the metallic shell 20 (specifically into its opening OP1 on the first direction D1 side). In the present embodiment, the heater member 800 is a so-called sheath heater including a heat-generating coil 820 that generates heat when energized. Part of the heater member 800 on the second direction D2 side is press-fitted into the through hole 20x through the opening OP1 at the forward end of the through hole 20x. The heater member 800 includes the heat-generating coil 820, a control coil 830, an insulating powder 840, a packing 850, and the tube 810 that contains these members 820, 830, 840, and 850.

[0022] The tube 810 is formed using an electrically conductive Ni-based alloy described later in detail. For example, the tube 810 is formed into a cylindrical shape extending along the axial line CL and having an axial hole AH extending along the axial line CL. A forward end portion of the tube 810 (referred to as a "forward end portion 811 ") is closed, and a rear end portion of the tube 810 (referred to as a "rear end portion 819") is open.

[0023] The heat-generating coil 820 is a thin wire formed into a helical shape and is formed using tungsten in the present embodiment. The heat-generating coil 820 is disposed inside the tube 810, specifically in a forward end portion of the axial hole AH of the tube 810. A forward end portion 821 of the heat-generating coil 820 is welded or brazed to the forward end portion 811 of the tube 810 and thereby electrically connected thereto.

[0024] The control coil 830 is a thin wire formed into a helical shape and is formed using an iron-chromium-aluminum (Fe-Cr-Al) alloy in the present embodiment. In the present specification, a temperature coefficient of electrical resistivity is the quotient of the difference in electrical resistivity between room temperature (20°C) and a prescribed temperature after heating (an estimated temperature reachable during heating, e.g., a temperature equal to or higher than 1,100°C) divided by the difference in temperature. The control coil 830 is disposed inside the tube 810, specifically rearward of the heat-generating coil 820 within the axial hole AH of the tube 810. A forward end portion 831 of the control coil 830 is welded or brazed to a rear end portion 829 of the heat-generating coil 820 and thereby electrically connected thereto. A rear end portion 839 of the control coil 830 is wound around a forward end portion 321 of the center rod 30 inserted into the axial hole AH of the tube 810, welded to the forward end portion 321, and thereby electrically connected thereto.

[0025] The insulating powder 840 is magnesia (MgO, referred to also as magnesium oxide) powder and fills the inside of the tube 810, i.e., the axial hole AH of the tube 810. In other words, the insulating powder 840 fills the space between the inner surface (inner circumferential surface) of the tube 810 and the coils 820 and 830 and the space between the inner surface and the center rod 30.

[0026] The packing 850 is a member formed into a ring shape and is formed using an electrically insulating elastic material such as fluorocarbon rubber. The packing 850 is disposed between the rear end portion 819 of the tube 810 and the center rod 30.

[0027] The packing 850 and the insulating powder 840 electrically insulate the tube 810 and the center rod 30 from each other over their entire circumferences around the axial line CL. The insulating powder 840 prevents an unintended short circuit between the tube 810 and each of the heat-generating coil 820, the control coil 830, and the center rod 30.

[0028] FIG. 2 is an enlarged view of a forward end of the heater member 800 and the vicinity thereof. Specifically, FIG. 2 is a cross-sectional view showing, on an enlarged scale, a portion of the heater member 800 within a region X shown in FIG. 1. The glow plug 10 is assumed to operate at relatively high temperature in order to reduce emissions from an internal combustion engine and improve its fuel economy. Specifically, the maximum value of the surface temperature of the tube 810 in the vicinity of its forward end is preferably 1,000°C or higher, more preferably 1,100°C or higher, and particularly preferably 1,200°C or higher. Since the temperature of the heat-generating coil 820 becomes higher by 300°C or more than the surface temperature of the tube 810, the temperature of the heat-generating coil 820 reaches 1,300 to 1,500°C. An oxidation reaction can easily proceed in such a high temperature environment. Therefore, the material of the tube 810 is required to have high oxidation resistance. In addition, in such a high temperature environment, the reduction reaction of magnesia filling the tube 810 can easily proceed. When the magnesia in the tube 810 is reduced, conductive magnesium is generated in the tube 810. The generated magnesium may cause electrical continuity between the tube 810 and the heat-generating coil 820 at a position different from the forward end portion 821, i.e., may form a short circuit therebetween. If such a short circuit occurs, the glow plug 10 cannot exhibit its original performance.

[0029] To reduce the difference in temperature between the surface of the tube 810 and the heat-generating coil 820 to thereby decrease the temperature of the heat-generating coil 820, the distance between the inner surface of the tube 810 and the heat-generating coil 820 is set to be relatively small. For example, in the present embodiment, the distance between the inner surface of the tube 810 and the heat-generating coil 820 takes a minimum value ΔNt at a position close to the closed forward end of the tube 810, as shown in FIG. 2. In the present embodiment, the minimum value ΔNt is preferably 0.5 mm or less, more preferably 0.3 mm or less, and particularly preferably 0.2 mm or less.

[0030] Particularly in a portion in which the distance between the inner surface of the tube 810 and the heat-generating coil 820 is small as described above, only a small amount of magnesium generated by reduction of magnesia may cause a short circuit.

A2. Production method

[0031] The glow plug 10 described above can be produced using various methods. When a producer produces the heater member 800, the producer subjects, for example, a metal plate made of an alloy described later to deep drawing into a tubular shape to thereby form the tube 810. Then the producer welds the heat-generating coil 820 and the control coil 830 to each other and also welds the control coil 830 and the center rod 30 to each other to thereby integrate the heat-generating coil 820, the control coil 830, and the center rod 30. Then the producer places the control coil 830 and the heat-generating coil 820 integrated with the center rod 30 inside the tube 810. Then the producer welds the forward end portion 811 of the tube 810 and the heat-generating coil 820 to each other. For example, arc welding is performed from the outside of the tube 810 to thereby join the forward end portion 811 of the tube 810 and the forward end portion 821 of the heat-generating coil 820 together. Then the producer fills the insulating powder 840 into the tube 810 and fits the packing 850 into the rear end of the tube 810 filled with the insulating powder 840.

[0032] After the packing 850 is fitted into the rear end of the tube 810, the producer subjects the heater member 800 to swaging using a swaging machine having a chuck and rotary dies to thereby adjust the diameter of the heater member 800. To perform the swaging, the producer attaches the center rod 30 fixed to the heater member 800 to the chuck. Then the rotary dies strike the periphery of the tube 810 while the heater member 800 is moved along the axial line CL by moving the chuck. In this manner, the diameter of the heater member 800 is adjusted to a prescribed diameter, and the heater member 800 is completed.

[0033] The producer assembles the glow plug 10 using the completed heater member 800. Specifically, the producer press-fits the heater member 800 with the center rod 30 fixed thereto into the through hole 20x of the metallic shell 20 to thereby fix the heater member 800. Then the producer fits the O-ring 50 and the insulating member 60 into the rear end opening OP2 of the metallic shell 20. Then the producer crimps the terminal member 80 to fix the terminal member 80 to the rear end portion 319 of the center rod 30. The glow plug 10 is completed in the manner described above.

A3. Material of tube 810

[0034] The material forming the tube 810 will be described. The material of the tube 810 is an Ni-based alloy containing at least 50% by weight of nickel (Ni). This alloy contains, as additives, chromium (Cr) in an amount of 18% by weight to 30% by weight and aluminum (Al). The amount of aluminum (Al) is 1 % by weight or less. This alloy further contains, as an additive, at least one component selected from yttrium (Y) and zirconium (Zr). The total amount of the at least one component selected from yttrium (Y) and zirconium (Zr) is 0.01% by weight to 0.3% by weight.

[0035] When this alloy is used to form the tube 810, the glow plug 10 can ensure oxidation resistance of the tube 810 in a high temperature environment and simultaneously prevents occurrence of a short circuit between the tube 810 and the heat-generating coil 820 in the high temperature environment.

[0036] Specifically, the material of the tube 810 is an Ni-based alloy containing at least 50% by weight of nickel. The oxidation resistance of the Ni-based alloy is higher than that of, for example, an alloy containing less than 50% by weight of nickel, e.g., an Fe-based alloy composed mainly of iron (Fe). When, for example, an Fe-based alloy is used, the oxidation resistance of the base alloy is insufficient, so that sufficient oxidation resistance cannot be obtained even when the types and amounts of additives are controlled.

[0037] Since the Ni-based alloy contains at least 18% by weight of chromium, an adequate chromium oxide (Cr₂O₃) film is formed on the surface of the alloy. This allows an improvement of the oxidation resistance of the alloy.

[0038] As shown in the well-known Ellingham diagram (not shown), the standard free energy of formation (ΔG⁰) of alumina is sufficiently larger than the ΔG⁰ of magnesia at relatively low temperature. However, as the temperature increases, the difference in ΔG⁰ between alumina and magnesia becomes smaller. In a very high-temperature environment, the ΔG⁰ of alumina is lower than the ΔG⁰ of magnesia. Therefore, the higher the temperature, the more likely magnesia is reduced by aluminum. In the Ni-based alloy, the amount of aluminum is 1 % by weight or less, so that the reduction of magnesia can be suppressed. Therefore, a problem with a short circuit between the tube 810 and the heat-generating coil 820 through conductive magnesium generated by the reduction of magnesia can be prevented.

[0039] Since the amount of aluminum is 1 % by weight or less, the amount of an alumina (Al₂O₃) film formed on the surface of the alloy is small, so that the oxidation resistance can deteriorate. However, the above alloy contains at least one component selected from yttrium and zirconium in a total amount of 0.01 % by weight or more. This can compensate for the deterioration in oxidation resistance caused by the decrease in the amount of the alumina film formed on the surface of the alloy, so that sufficient oxidation resistance can be ensured. The reason for this may be as follows. Yttrium and zirconium are likely to concentrate at the interface between the surface of the alloy and the oxide film (such as the alumina or chromium oxide film) formed on the surface of the alloy and function as a tie that binds the alloy and the oxide film together at the interface. Therefore, the addition of a very small amount of yttrium or zirconium can enhance the binding between the alloy and the oxide film to thereby improve the oxidation resistance of the alloy.

[0040] From the viewpoint of oxidation resistance, it is preferable to form a small amount of the alumina film. Therefore, it is preferable that a small amount, i.e., 1% by weight or less, of aluminum is contained. For example, the amount of aluminum is particularly preferably from 0.5% by weight to 1% by weight.

[0041] As can be seen from the above description, when the above alloy is used to form the tube 810, oxidation resistance in a high temperature environment can be ensured, and simultaneously a short circuit between the tube 810 and the heat-generating coil 820 in the high temperature environment can be prevented.

[0042] In this alloy, since the amount of chromium is 30% by weight or less, the alloy is not excessively hardened. Therefore, workability during production of the tube 810 does not deteriorate, and the tube 810 can be formed easily.

[0043] In this alloy, the total amount of the at least one component selected from yttrium and zirconium is 0.3% by weight or less. Only a minute amount of yttrium and zirconium can dissolve in solid nickel. Therefore, if the amount of yttrium and/or zirconium with respect to nickel is excessively large, a precipitate composed mainly of yttrium and/or zirconium may be formed, and cracking starting from the precipitate may occur during working. When the total amount of the at least one component selected from yttrium and zirconium is 0.3% by weight or less, cracking does not occur, and the tube 810 can be easily formed.

[0044] Preferably, the alloy forming the tube 810 further contains at least one component selected from silicon (Si), titanium (Ti), and manganese (Mn). Preferably, the total amount of the at least one component selected from silicon, titanium, and manganese is 0.2% by weight to 1.5% by weight.

[0045] In contrast to aluminum, however, silicon, titanium, and manganese are unlikely to reduce magnesia because the ΔG⁰s of their oxides are sufficiently larger than the ΔG⁰ of magnesia even in a high temperature environment. In addition, since the ΔG⁰s of the oxides of silicon, titanium, and manganese are smaller than that of chromium oxide, an oxide film (e.g., a silica, titanium oxide, or manganese oxide film) can be formed on the surface of the alloy by adding these components in a small amount. Therefore, when the alloy used to form the tube 810 further contains at least one component selected from silicon, titanium, and manganese in a total amount of 0.2% by weight or more, the oxidation resistance of the tube 810 can be further improved without causing reduction of magnesia.

[0046] If the total amount of the at least one component selected from silicon, titanium, and manganese exceeds 1.5% by weight, solid solution hardening by these elements may cause excessive hardening of the alloy. When the total amount of the at least one component selected from silicon, titanium, and manganese is 1.5% by weight or less, the alloy is not excessively hardened. In this case, the workability during production of the tube 810 is not reduced, and the tube 810 can be easily formed.

[0047] Preferably, the alloy forming the tube 810 further contains iron (Fe) in an amount of 5% by weight to 20% by weight.

[0048] Iron has higher ductility than nickel and has high workability. Therefore, when the alloy used further contains 5% by weight or more of iron, the formability of the alloy can be improved, so that the tube 810 can be easily formed. When the amount of iron is 20% by weight or less, the oxidation resistance of the alloy does not deteriorate. Therefore, the formability of the alloy can be improved without deterioration in the oxidation resistance of the tube 810, so that the tube can be formed more easily.

A4. Evaluation tests

[0049] Evaluation tests for evaluating insulation, oxidation resistance, and workability were performed using glow plug samples. In the evaluation tests, 39 types of glow plug samples 1 to 39 shown in Table 1 were produced. Each of the samples has the same structure as the glow plug 10 described above, except for the material (alloy) forming the tube 810. The structure is the same among all the samples. For example, the following features are the same for all the samples.

Material of the insulating powder 840: MgO

Material of the heat-generating coil 820: tungsten

Control coil 830: Fe-22% by weight Cr-5% by weight Al

Minimum value ΔNt of the distance between the inner surface of the tube 810 and the heat-generating coil: 0.2 mm or less

[0050] For each of the samples, a 0.6 mm-thick plate was subjected to deep drawing to form a (non-swaged) tube 810 with an outer diameter of 5.15 mm and an axial length of 40 mm. Then a process including the swaging described above was performed using the non-swaged tube 810 to produce a heater member 800 of the sample.

[Table 1]

Sample No.	Fe	Cr	Al	Si	Mn	Ti	Y	Zr	Insulation	Oxidation resistance	Workability	Overall rating
1	14	23	1.5	0.1	0	0	0	0	C	B	A	C
2	10	18	2.5	0.1	0	0	0.1	0.1	C	B	A	C
3	10	23	2.5	0.1	0	0	0.1	0.1	C	B	A	C
4	10	30	2.5	0.1	0	0	0.1	0.1	C	B	A	C
5	10	23	1.1	0.1	0	0	0	0	C	B	A	C
6	10	23	1	0.1	0	0	0	0	A	C	A	C
7	10	23	0.5	0.1	0	0	0	0	A	C	A	C
8	10	23	0.1	0.1	0	0	0	0	A	C	A	C
9	10	23	0.5	0.1	0	0	0.01	0	A	B	A	B
10	10	15	0.5	0.1	0	0	0.1	0	A	C	A	C
11	10	18	0.5	0.1	0	0	0.1	0	A	B	A	B
12	10	23	0.5	0.1	0	0	0.1	0	A	B	A	B
13	10	30	0.5	0.1	0	0	0.1	0	A	B	A	B
14	10	33	0.5	0.1	0	0	0.1	0	A	B	B	C
15	10	23	0.5	0.1	0	0	0.3	0	A	B	A	B
16	10	23	0.5	0.1	0	0	0.4	0	A	B	B	C
17	10	23	0.5	0.1	0	0	0	0.01	A	B	A	B
18	10	18	0.5	0.1	0	0	0	0.1	A	B	A	B
19	10	23	0.5	0.1	0	0	0	0.1	A	B	A	B
20	10	30	0.5	0.1	0	0	0	0.1	A	B	A	B
21	10	23	0.5	0.1	0	0	0	0.3	A	B	A	B
22	10	23	0.5	0.1	0	0	0	0.4	A	B	B	C
23	10	23	0.5	0.1	0	0	0.1	0.01	A	B	A	B
24	10	23	0.5	0.1	0	0	0.05	0.1	A	B	A	B
25	10	23	0.5	0.2	0	0	0.1	0	A	A	A	A
26	10	23	0.5	1.5	0	0	0.1	0	A	A	A	A
27	10	23	0.5	2	0	0	0.1	0	A	A	B	B
28	10	23	0.5	0	0.2	0	0.1	0	A	A	A	A
29	10	23	0.5	0	1.5	0	0.1	0	A	A	A	A
30	10	23	0.5	0	2	0	0.1	0	A	A	B	B
31	10	23	0.5	0	0	0.2	0.1	0	A	A	A	A
32	10	23	0.5	0	0	1.5	0.1	0	A	A	A	A
33	10	23	0.5	0	0	2	0.1	0	A	A	B	B
34	0	23	0.5	0.5	0	0	0.1	0	A	A	B	B
35	2	23	0.5	0.5	0	0	0.1	0	A	A	B	B
36	5	23	0.5	0.5	0	0	0.1	0	A	A	A	A
37	10	23	0.5	0.5	0	0	0.1	0	A	A	A	A
38	20	23	0.5	0.5	0	0	0.1	0	A	A	A	A
39	25	23	0.5	0.5	0	0	0.1	0	A	B	A	B

[0051] In the 39 types of samples 1 to 39, different alloys are used for their tubes 810. The materials used in the samples are nickel-based alloys each containing at least some of additive elements (Fe, Cr, Al, Si, Mn, Ti, Y, and Zr) shown in Table 1 in amounts shown in Table 1 (unit: % by weight) with the balance being nickel. The 39 types of samples 1 to 39 are different in at least one of the types of the additive elements and their contents, as shown in Table 1. In all the 39 types of samples 1 to 39, the amount of nickel is 50% by weight or more.

[0052] Specifically, in samples 1 to 33 and 35 to 39, the alloys contain iron. In sample 34, the alloy contains no iron. In samples 1 to 33 and 35 to 39 containing iron, the amount of iron is any of 2% by weight, 5% by weight, 10% by weight, 14% by weight, 20% by weight, and 25% by weight.

[0053] In all samples 1 to 39, the alloys contain chromium, and the amount of chromium is any of 15% by weight, 18% by weight, 23% by weight, 30% by weight, and 33% by weight.

[0054] In all samples 1 to 39, the alloys contain aluminum, and the amount of aluminum is any of 0.1% by weight, 0.5% by weight, 1% by weight, 1.1% by weight, 1.5% by weight, and 2.5% by weight.

[0055] In all samples 1 to 39, the alloys contain any of silicon, manganese, and titanium. In samples 1 to 27 and 34 to 39 containing silicon, the amount of silicon is any of 0.1 % by weight, 0.2% by weight, 0.5% by weight, 1.5% by weight, and 2% by weight. In samples 28 to 30 containing manganese, the amount of manganese is any of 0.2% by weight, 1.5% by weight, and 2% by weight. In samples 31 to 33 containing titanium, the amount of titanium is any of 0.2% by weight, 1.5% by weight, and 2% by weight.

[0056] In samples 1 and 5 to 8, the alloys contain no yttrium and no zirconium. In samples 2 to 4 and 9 to 39, the alloys contain at least one of yttrium and zirconium. In samples 2 to 4,9 to 16, and 23 to 39 containing yttrium, the amount of yttrium is any of 0.01% by weight, 0.05% by weight, 0.1% by weight, 0.3% by weight, and 0.4% by weight. In samples 2 to 4 and 17 to 24 containing zirconium, the amount of zirconium is any of 0.01% by weight, 0.1% by weight, 0.3% by weight, and 0.4% by weight.

[0057] As one of the evaluation tests, a thermal test was performed, in which each sample of the glow plug 10 was repeatedly subjected to a heating-cooling cycle 10,000 times. Specifically, in each cycle, the sample of the glow plug 10 with the tube 810 being at room temperature (about 25°C) was energized to heat the sample such that the surface temperature of the tube 810 reached 1,000°C within 2 seconds. Then the surface temperature of the tube 810 was maintained at 1,050°C for 3 minutes. Then the sample was deenergized to cool the sample until the surface temperature of the tube 810 became room temperature.

[0058] For each of the samples, the occurrence of a short circuit between the tube 810 and the heat-generating coil 820 in the heater member 800 was checked after the thermal test. Specifically, for each of the samples, the resistance value between the terminal member 80 and the metallic shell 20 was measured. When the resistance after the test was smaller than that before the test by a reference value, a judgment was made that a short circuit occurred between the tube 810 and the heat-generating coil 820. When the resistance after the test was not smaller than that before the test by the reference value, a judgment was made that no short circuit occurred.

[0059] The insulation in a sample in which no short circuit occurred was rated "A," and the insulation in a sample in which a short circuit occurred was rated "C."

[0060] After the thermal test, the degree of deterioration of the tube 810 of the heater member 800 of each sample was examined. Specifically, the outer diameter of the tube 810 at a position located at a prescribed length L1 from the forward end in the axial direction (see FIG. 2) was measured before and after the thermal test to determine a decrease in the outer diameter by the thermal test. The prescribed length L1 was set to 5 mm. The measured decrease in the outer diameter was used to compute the rate of decrease in the wall thickness of the tube 810.

[0061] The oxidation resistance of a sample in which the rate of decrease in the wall thickness of the tube 810 was less than 10% was rated "A." The oxidation resistance of a sample in which the rate of decrease in the wall thickness was 10% or more and less than 15% was rated "B," and the oxidation resistance of a sample in which the rate of decrease in the wall thickness was 15% or more was rated "C."

[0062] In another evaluation test, a 0.6 mm-thick plate formed from one of the alloys in the samples was subjected to deep drawing to form a tube 810 having an outer diameter of 5.15 mm and an axial length of 40 mm, and this process was repeated 100 times. One hundred non-swaged tubes 810 were thereby produced for each sample. For each of the 100 tubes 810 for each sample, the presence or absence of cracking caused by deep drawing was visually checked.

[0063] When no cracking was found in all the 100 tubes 810, the workability of this sample was rated "A." When cracking was found in at least one tube 810, the workability of the sample was rated "B."

[0064] For each of the three ratings for the insulation, oxidation resistance, and workability, a score of 2 was given to "A," a score of 1 was given to "B," and a score of 0 was given to "C." Then the total score was computed. An "A" overall rating was assigned to a sample with a total score of 6, a "B" overall rating was assigned to a sample with a total score of 5, and a "C" overall rating was assigned to a sample with a total score of 4 or less.

[0065] The results of the evaluation tests are as shown in Table 1. In the case of samples 1 to 5 in which the amount of aluminum was more than 1% by weight, the insulation was rated "C." This may be because magnesia was reduced by aluminum, so that a short circuit between the tube 810 and the heat-generating coil 820 occurred. In the case of samples 6 to 39 in which the amount of aluminum was 1% by weight or less, the insulation was rated "A." This may be because magnesia was not reduced by aluminum, so that no short circuit between the tube 810 and the heat-generating coil 820 occurred.

[0066] In the case of samples 1 to 5 in which the amount of aluminum was more than 1% by weight, the oxidation resistance was rated "B," irrespective of whether or not yttrium and zirconium were added. This may be because, since an adequate alumina film was formed, the oxidation resistance was ensured irrespective of whether or not yttrium and zirconium were added.

[0067] Among samples 6 to 39 in which the amount of aluminum was 1% by weight or less, samples 6 to 8 contained no yttrium and no zirconium. In the case of these samples 6 to 8, the oxidation resistance was rated "C." This may be because, since the amount of aluminum was small, an adequate alumina film was not formed and because the binding between the surface of the alloy and an oxide film (e.g., the film of alumina or chromium oxide) was not enhanced by yttrium or zirconium.

[0068] Among samples 6 to 39 in which the amount of aluminum was 1% by weight or less, samples 9 to 39 contained at least one of yttrium and zirconium in a total amount of 0.01 % by weight or more. In the case of these samples 9 to 39 except for sample 10, the oxidation resistance was rated "B" or "A." This may be because of the following. Since the amount of aluminum was small, an adequate alumina film was not formed. However, the binding between the surface of the alloy and the oxide film was enhanced by yttrium or zirconium, and this compensated for the deterioration in oxidation resistance caused by the inadequate formation of the alumina film. Therefore, in samples 9 to 39 except for sample 10, no deterioration in oxidation resistance occurred.

[0069] Among samples 9 to 39, sample 10 had oxidation resistance rated "C." This may be because of the following. Although at least one of yttrium and zirconium was contained in a total amount of 0.01% by weight or more, an adequate chromium oxide film was not formed because the amount of chromium was 15% by weight.

[0070] As can be seen from the above results, it is preferable, in terms of ensuring the oxidation resistance and ensuring the insulation (preventing a short circuit) simultaneously, that the nickel-based alloy containing 50% by weight or more of nickel and used to form the tube 810 satisfies (1) to (3) below.

(1) The nickel-based alloy contains 18% by weight or more of chromium (Cr).

(2) The nickel-based alloy contains aluminum (Al), and the amount of aluminum (Al) is 1% by weight or less.

(3) The nickel-based alloy contains at least one component selected from yttrium (Y) and zirconium (Zr), and the total amount of the at least one component selected from yttrium and zirconium is 0.01% by weight or more.

[0071] Samples 9 and 11 to 39 satisfy the above (1) to (3). However, in the case of sample 16 containing more than 0.3% by weight of yttrium and sample 22 containing more than 0.3% by weight of zirconium, the workability was rated "B." Among samples 9 and 11 to 39, samples 9, 11 to 15, 17 to 21, and 23 to 39 contained yttrium and/or zirconium in a total amount of 0.3% by weight or less. In the case of these samples 9, 11 to 15, 17 to 21, and 23 to 39 except for samples 14, 27, 30, and 33 to 35 described later, the workability was rated "A." This may be because, since the amount of yttrium or zirconium was large in samples 16 and 22, the alloys were hardened.

[0072] Among samples 9 and 11 to 39 satisfying the above (1) to (3), sample 14 contained more than 30% by weight of chromium. In the case of sample 14, the workability was rated "B." Among samples 9 and 11 to 39, samples 9,11 to 13, and 15 to 39 contained chromium in an amount of 30% by weight or less. In the case of these samples 9, 11 to 13, and 15 to 39 except for samples 16 and 22 described above and samples 27,30, and 33 to 35 described later, the workability was rated "A." This may be because, since the amount of chromium in sample 14 was large, the alloy was hardened.

[0073] As can be seen from the above results, when the workability is also taken into consideration, it is preferable that the alloy used to form the tube 810 further satisfies (4) and (5) below.

(4) The amount of chromium is 30% by weight or less.

(5) The total amount of at least one component selected from yttrium and zirconium is 0.3% by weight or less.

[0074] Among samples 9 and 11 to 39 satisfying the above (1) to (3), samples 25 to 27 and 34 to 39 contained 0.2% by weight or more of silicon, samples 28 to 30 contained 0.2% by weight or more of manganese, and samples 31 to 33 contained 0.2% by weight or more of titanium. In the case of these samples except for sample 39 described later, the oxidation resistance was rated "A." Among samples 9 and 11 to 39 satisfying the above (1) to (3), samples 9 and 11 to 24 contained silicon, titanium, and manganese in an amount of less than 0.2% by weight. In the case of these samples 9 and 11 to 24, the oxidation resistance was rated "B." In the case of samples 31 to 38, the oxidation resistance was improved. This may be because the film of silicon, manganese, or titanium oxide was formed on the surface of the alloy. In the case of these samples 25 to 38, the insulation was rated "A," and no deterioration in insulation was found. This may be because silicon, manganese, and titanium did not reduce magnesia. Since silicon, manganese, and titanium may play the same role, it may be sufficient to consider the total amount of silicon, manganese, and titanium.

[0075] As can be seen from the above results, it is more preferable, in terms of ensuring the oxidation resistance and ensuring the insulation (preventing a short circuit) simultaneously, that the alloy used to form the tube 810 satisfy (6) below in addition to the above (1) to (3).

(6) The alloy contains at least one selected from silicon (Si), titanium (Ti), and manganese (Mn), and the total amount of the at least one component selected from silicon, titanium, and manganese is 0.2% by weight or more.

[0076] Among samples 25 to 39 satisfying the above (1) to (6), sample 27 contained more than 1.5% by weight of silicon, sample 30 contained more than 1.5% by weight of manganese, and sample 33 contained more than 1.5% by weight of titanium. In the case of these samples, the workability was rated "B." Among samples 25 to 39, samples 25, 26, 28, 29, 31, 32, 34 to 39 contained silicon, manganese, and titanium in an amount of 1.5% by weight or less. In the case of these samples except for samples 34 and 35 described later, the workability was rated "A." This may be because, since the amount of silicon, manganese, or titanium was large in samples 27,30, and 33, the alloys were hardened.

[0077] As can be seen from the above results, when the workability is also taken into consideration, it is more preferable that the alloy used to form the tube 810 satisfies (7) below.

(7) The total amount of at least one component selected from silicon, titanium, and manganese is 1.5% by weight or less.

[0078] Among samples 25, 26, 28, 29, 31, 32, and 34 to 39 satisfying the above (1) to (7), samples 34 and 35 contained iron in an amount of less than 5% by weight. In the case of these samples 34 and 35, the workability was rated "B." Among samples 25, 26, 28, 29, 31, 32, and 34 to 39 satisfying the above (1) to (7), samples 25, 26, 28, 29, 31, 32, and 36 to 39 contained iron in an amount of 5% by weight or more. In the case of these samples, the workability was rated "A." This may be because, when the amount of iron in an alloy is 5% by weight or more, the ductility of the alloy is improved, so that the workability is improved.

[0079] Among samples 25, 26, 28, 29, 31, 32, and 34 to 39 satisfying the above (1) to (7), samples 25, 26, 28, 29, 31, 32, and 34 to 38 contained iron in an amount of 20% by weight or less. In the case of these samples, the oxidation resistance was rated "A." Among samples 25, 26, 28, 29, 31, 32, and 34 to 39 satisfying the above (1) to (7), sample 39 contained iron in an amount of more than 20% by weight. In the case of sample 39, the oxidation resistance was rated "B." This indicates the following. When the amount of iron in an alloy exceeds 20% by weight, the oxidation resistance of the alloy can deteriorate because of the influence of iron inferior in oxidation resistance. However, when the amount of iron is less than 20% by weight, no deterioration in oxidation resistance occurs.

[0080] As can be seen from the above results, it is more preferable that the alloy used to form the tube 810 further satisfies (8) below.

(8) The alloy contains iron (Fe) in an amount of 5% by weight to 20% by weight.

[0081] Finally, the overall rating will be described. In the case of samples 9, 11 to 13, 15, 17 to 21, and 23 to 39 satisfying at least the above (1) to (5), the overall rating was "B" or "A." In the case of samples 1 to 8, 10, 14, 16, and 22 which do not satisfy at least one of the above (1) to (5), the overall rating was "C."

[0082] From a comprehensive point of view, it is preferable that the alloy used to form the tube 810 satisfies the above (1) to (5).

[0083] Among samples 9, 11 to 13, 15, 17 to 21, and 23 to 39 satisfying at least the above (1) to (5), samples 25, 26, 28, 29, 31, 32, and 36 to 38 further satisfy (6) to (8). In the case of these samples, the overall rating was "A."

[0084] From a comprehensive point of view, it is particularly preferable that the alloy used to form the tube 810 further satisfies (6) to (8). For example, in terms of oxidation resistance, it is particularly preferable to satisfy (6). In terms of workability, it is preferable to further satisfy any of (7) and (8).

B. Modifications

[0085] 

(1) The configuration of the glow plug 10 is not limited to that described in the above embodiment, and different configurations can be used. For example, although the heat-generating coil 820 is formed using tungsten, this is not a limitation. For example, the heat-generating coil 820 may be formed using an alloy containing tungsten and an additional component (such as rhenium or chromium) or may be formed using molybdenum or an alloy containing molybdenum and an additional component.
Although the control coil 830 is formed using the Fe-Cr-Al alloy, this is not a limitation. For example, the control coil 830 may be formed using tungsten.
The material of the insulating powder 840 is not limited to magnesia, and the insulating powder 840 may be formed using a material containing magnesia and an additional component (such as another ceramic). Generally, the insulating powder 840 may be formed from an insulating material composed mainly of magnesia. The material composed mainly of magnesia means that the percent by weight of magnesia in the insulating powder 840 is largest.
In the above embodiment, two coils, i.e., the control coil 830 and the heat-generating coil 820, are used. Instead, the control coil 830 may be omitted, and the heat-generating coil 820 may be connected directly to the center rod 30.

(2) The method of producing the glow plug 10 in the above embodiment is an example, and different production methods can be used. For example, when the heater member 800 is produced, the swaging may be omitted. The tube 810 may be formed using a method other than deep drawing. For example, the tube 810 may be formed by bending a metal plate into a round shape and then performing arc welding.

(3) The glow plug of the above embodiment is not limited to a glow plug used for assisting the start of an internal combustion engine and can be used as various glow plugs. For example, the glow plug of the above embodiment can be used as glow plugs used in exhaust gas heaters for heating exhaust gas, burner systems for regenerating catalysts or diesel particulate filters (DPFs), water heaters for heating cooling water, etc.

[0086] Although the present invention has been described on the basis of the embodiment and modifications thereof, the embodiment of the present invention is provided for facilitating an understanding of the present invention and does not limit the scope of the present invention. The present invention may be changed and improved without departing from the gist and scope of the present invention, and encompasses equivalents thereof.

[Description of Reference Numerals]

[0087] 

10: glow plug, 20: metallic shell, 20x: through hole, 21: trunk portion, 22: male threaded portion, 28: tool engagement portion, 30: center rod, 50: O-ring, 60: insulating member, 62: tubular portion, 68: flange portion, 80: terminal member, 319: rear end portion, 321: forward end portion, 800: heater member, 810: tube, 811: forward end portion, 819: rear end portion, 820: heat-generating coil, 821: forward end portion, 829: rear end portion, 830: control coil, 831: forward end portion, 839: rear end portion, 840: insulating powder, 850: packing

Claims

1. A glow plug (10) comprising:

a tube (810) having a tubular shape with a closed forward end;

a heat-generating coil (820) that is disposed inside the tube (810), has a forward end electrically connected to the forward end of the tube (810), and generates heat when energized; and

an insulating material (840) that contains magnesia (MgO) as a main component and fills a space between an inner surface of the tube (810) and the heat-generating coil (820),

wherein the tube (810) is formed of an alloy containing

nickel (Ni) in an amount of 50% by weight or more,

chromium (Cr) in an amount of 18% by weight to 30% by weight,

aluminum (Al), and

at least one component selected from yttrium (Y) and zirconium (Zr), and

wherein the amount of aluminum (Al) is 1% by weight or less, and

the total amount of the at least one component selected from yttrium (Y) and zirconium (Zr) is 0.01% by weight to 0.3% by weight.

2. Aglow plug (10) according to claim 1, wherein
the alloy forming the tube (810) further contains
at least one component selected from silicon (Si), titanium (Ti), and manganese (Mn), and the total amount of the at least one component selected from silicon (Si), titanium (Ti), and manganese (Mn) is 0.2% by weight to 1.5% by weight.

3. A glow plug (10) according to claim 1 or 2, wherein
the alloy forming the tube (810) further contains iron (Fe) in an amount of 5% by weight to 20% by weight.

Drawing