WO2011162074A1 - Glowplug, production method thereof and heating device - Google Patents

Abstract

The disclosed glowplug (1) is provided with a cylindrical tube (7) that is closed at the tip, a heating coil (9) that is inserted into the tube (7), and a seal (11) that is provided to the open rear end of the tube (7) and seals the tube (7). The heating coil (9) is formed by a metal member that has tungsten (W) or molybdenum (Mo) as the primary component and the tube (7) is formed from an alloy that contains 0.5-5.0 mass% aluminium (Al) and 20-40 mass% chromium (Cr). Due to the tube (7) containing Al and Cr in designated amounts, as well as the tube having high anti-oxidation properties, the oxygen partial pressure within the tube (7) is reduced and the oxidation of the heating coil (9) can be controlled. As a result, the durability of both the heating coil (9) and the tube (7) is increased and high temperature heating over a long period is possible.

Description

Glow plug, manufacturing method thereof, and heating device

The present invention relates to a glow plug used for preheating a diesel engine and the like, and a heating device.

Glow plugs used for diesel engine preheating and the like are generally formed of an alloy mainly composed of iron (Fe) or nickel (Ni), and Fe or Ni is placed in a tube having a closed end. As a main component, there is known one having a sheath heater in which a heating resistor formed of an alloy containing chromium (Cr), aluminum (Al), or the like is enclosed together with an insulating powder.

By the way, in recent years, there has been a demand for higher temperature in the combustion chamber in order to further reduce the emission. In order to meet this requirement, it is conceivable that the glow plug generates heat at a higher temperature (for example, the tube surface is heated to 1150 ° C. or higher), but the temperature difference between the tube surface and the heating resistor is about 300 ° C. In order to generate heat at a higher temperature, it is necessary to heat the heating resistor to an extremely high temperature (for example, 1450 ° C. or higher). However, the alloys mainly composed of Fe and Ni that have been used in the past have a melting point of around 1500 ° C. For this reason, when heated to an extremely high temperature as described above, there is a risk that the heating resistor will suffer from problems such as melting.

Therefore, in order to improve heat resistance, it is conceivable to form a heating resistor from high melting point tungsten (W) or molybdenum (Mo) (see, for example, Patent Document 1).

JP 58-158425 A

However, since W and Mo are very easily oxidized, there is a possibility that the heating resistor will deteriorate rapidly due to reaction with oxygen existing inside the tube.

Also, in order to enable the glow plug to generate heat at a higher temperature, it is necessary to improve not only the heating resistor but also the durability of the tube itself. However, Fe and Ni are likely to oxidize at high temperatures, and a tube made of an alloy that contains Fe or Ni as a main component but does not contain Al or Cr sufficiently may have insufficient durability. There is.

The present invention has been made in view of the above circumstances, and an object of the present invention is to endure both a heating resistor and a tube in a glow plug having a heating resistor formed of a metal material mainly composed of W or Mo. It is an object of the present invention to provide a glow plug, a method for manufacturing the same, and a heating device provided with the glow plug.

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

Configuration 1. The heating device of this configuration includes a glow plug having a heating resistor and constituting a heating unit,
A heating device that is configured to be capable of adjusting power supplied to the heating resistor and capable of controlling heat generation of the heating resistor by adjusting the power supply,
The energization control device supplies power to the heating resistor so that the temperature of the heating unit rises from room temperature to 1000 ° C. within 3 seconds,
The glow plug is
A cylindrical tube that has a distal end closed and the heating resistor is inserted into the heating tube;
Provided in a rear end side opening of the tube, and a seal portion for sealing the inside of the tube,
The heating resistor is formed of a metal material mainly composed of W or Mo,
The tube is formed of an alloy containing Al in an amount of 0.5% by mass to 5.0% by mass and Cr in an amount of 20% by mass to 40% by mass.

Note that the “heating section” means a tube through which a heating resistor is inserted, but the portion of the tube surface where the temperature is highest when energized may correspond to the “heating section”.

According to the above configuration 1, since the heat generating resistor is formed of a metal material mainly composed of W or Mo having a high melting point, excellent heat resistance can be realized in the heat generating resistor.

On the other hand, as described above, there is a concern about the decrease in oxidation resistance due to the use of W or Mo. However, according to Configuration 1, the tube contains 0.5% by mass or more of Al and 20% of Cr. It is contained by mass% or more. Therefore, during heat generation, Al and Cr that are more easily oxidized than W and Mo function as an oxygen getter element, and an oxide film made of Al ₂ O ₃ or Cr ₂ O ₃ is formed on the inner peripheral surface of the tube. As a result, since the inside of the tube is in a sealed state, the oxygen partial pressure inside the tube can be effectively reduced. As a result, it is possible to more reliably prevent the heating resistor mainly composed of W or Mo from being oxidized.

Further, by containing a predetermined amount or more of Al or Cr in the tube, an oxide film of Al ₂ O ₃ or Cr ₂ O ₃ can be formed over a wide range of the outer surface of the tube. The oxide film can more reliably prevent oxygen from entering the inside of the tube and improve the oxidation resistance of the tube. Furthermore, since the content of Al and Cr is sufficiently large, even if peeling or cracking occurs in the oxide film due to thermal stress due to repeated cooling and heating cycles, the oxide film is more reliably and for a longer period of time. Can be reformed over a period of time.

As described above, according to the above-described configuration 1, by adding a predetermined amount or more of Al or Cr to the tube, it is possible to effectively prevent oxidation of the heating resistor made of W, Mo, etc. In addition, it is possible to sufficiently exhibit the heat resistance and to maintain excellent oxidation resistance in the tube for a long period of time. As a result, the durability of both the heating resistor and the tube can be dramatically improved, and the glow plug can generate heat at a higher temperature over a long period of time.

Furthermore, according to the said structure 1, electric power is supplied with respect to a heating resistor so that the temperature of a tube surface (heating part) may rise from normal temperature to 1000 degreeC within 3 second by the electricity supply control apparatus. Thus, the thermal stress added to a tube can be increased by heating a tube rapidly. Therefore, the oxide film made of Al ₂ O ₃ or Cr ₂ O ₃ formed on the inner peripheral surface of the tube is easily broken, and an unoxidized metal surface is easily exposed from the oxide film on the inner peripheral surface of the tube. By newly oxidizing Al and Cr contained in the metal surface, the oxygen partial pressure inside the tube can be further reduced, and in turn, the oxidation of the heating resistor made of W or the like can be extremely effectively prevented. Can do.

Note that if the Al content in the tube is made larger than 5.0% by mass or the Cr content is made larger than 40% by mass, the workability may be lowered. Therefore, it is preferable that the Al content is 5.0% by mass or less and the Cr content is 40% by mass or less.

Configuration 2. The heating device of this configuration is the above-described configuration 1, wherein the heating resistor has an average value of normal temperature resistance in a portion between the tip of the heating resistor and the 6 mm rear end along the central axis of the tube. It is characterized by being larger than the average value of the whole room temperature resistance.

“The average value of the room temperature resistance in the portion of the heating resistor from the tip to the rear end of 6 mm along the central axis of the tube” is the tube from the tip of the heating resistor to the tube. The value obtained by dividing the room temperature resistance of the portion (tip-side heating element) between 6 mm along the center axis of the tube and the length of the tip-side heating element along the center axis of the tube (that is, the center axis of the tube The normal temperature resistance of the heating element on the tip side per unit length). The “average value of the room temperature resistance of the entire heating resistor” is the value obtained by dividing the room temperature resistance of the entire heating resistor by the length of the heating resistor along the central axis of the tube (ie, the center of the tube). Normal temperature resistance of heating resistor per unit length along the axis) (hereinafter the same).

In general, in a state where the glow plug is assembled to the internal combustion engine, a portion of the tube between the front end and the rear end up to about 4 mm (hereinafter referred to as “exposed portion”) protrudes from the inner wall of the combustion chamber and enters the combustion chamber. Be placed. Therefore, the temperature of the exposed portion is likely to be higher during heat generation than the other portion of the tube around which the components of the internal combustion engine are located. In addition, since the exposed portion rapidly rises in temperature compared to other portions of the tube and is rapidly cooled, a rapid temperature change is likely to occur. Therefore, at the time of supplying power to the heating resistor, the temperature of the exposed portion can be raised particularly so that the temperature of the tube can be raised, and a rapid temperature change can be caused in the tube. If the tube can be heated to a higher temperature or a sudden temperature change can be caused in the tube, the thermal stress generated in the tube can be further increased, and Al ₂ O ₃ and Cr ₂ formed on the inner peripheral surface of the tube The oxide film made of O ₃ can be further easily broken. As a result, the effect of preventing oxidation of the heating resistor according to Configuration 1 can be further enhanced.

In view of this point, according to the above-described configuration 2, the average value of the room temperature resistance in the portion of the heating resistor from the tip to the rear end of 6 mm along the central axis of the tube (tip-side heating member) is The average value of the room temperature resistance of the entire heating resistor is made larger. Here, by making the average value of the normal temperature resistance of the heating element on the front end side larger than the average value of the normal temperature resistance of the entire heating resistor, a portion of the tube about 2 mm from the front end to the rear end (that is, of the exposed portion). It is possible to positively raise the temperature of the central portion and the vicinity thereof. Therefore, according to the said structure 2, while being able to make a tube higher temperature, a sudden temperature change can be produced in a tube. As a result, the thermal stress generated in the tube can be further increased, and as a result, the antioxidant effect of the heating resistor can be further improved.

Also, in order to rapidly raise the temperature in the combustion chamber, it is desirable to raise the temperature of the exposed portion. Therefore, the above-described configuration 2 is also significant in this respect.

Configuration 3. The heating device of this configuration is the above configuration 1 or 2, wherein the heating resistor has a coil shape and a wire diameter of 0.2 mm or more.
Among the heating resistors, the average pitch in the region from the tip to the rear end of 6 mm along the center axis of the tube is 6 mm along the center axis of the tube from the tip of the heating resistor. It is characterized by being 0.9 mm or more smaller than the average pitch in the part located on the rear end side with respect to the rear end.

The “average pitch” means a distance (pitch) along the central axis (coil axis) between the centers of adjacent cross sections of the heating resistors in a cross section including the central axis (coil axis) of the heating resistors. ) Average (hereinafter the same).

According to the above-described configuration 3, the average pitch in the portion between the front end and the 6 mm rear end of the heating resistor (the front side heating element) is larger than the rear end portion of the heating resistor 6 mm from the front end. It is set to be smaller by 0.9 mm or more than the average pitch of the parts located on the side (rear end side heating element). Therefore, without making the tip side heating element excessively thin (while making the heating resistor wire diameter 0.2 mm or more), the average value of the room temperature resistance of the tip side heating element is the average value of the room temperature resistance of the whole heating resistor. Can be sufficiently larger. That is, according to the above-described configuration 3, the exposed portion can be heated more rapidly while maintaining the mechanical strength of the heating resistor sufficiently. As a result, the antioxidant effect of the heating resistor can be further improved.

Further, since it is not necessary to make the tip side heating element excessively thin, the heating resistor can be manufactured relatively easily, and the reduction in productivity can be prevented more reliably.

Configuration 4. In the heating device of this configuration, in any one of the above configurations 1 to 3, the glow plug includes an insulating powder filled around the heating resistor in the tube,
The insulating powder is a powder mainly composed of magnesium oxide (MgO).

According to the above configuration 4, since MgO having excellent thermal conductivity is used as the insulating powder, the thermal conductivity from the heating resistor to the tube can be improved. As a result, the glow plug (heating unit) can be heated at a higher temperature without excessively heating the heating resistor.

In addition, since the tube (heating part) can be heated to a higher temperature, the thermal stress applied to the tube can be further increased. As a result, the tube (heating portion) is made of Al ₂ O ₃ or Cr ₂ O ₃ formed on the inner peripheral surface of the tube. The oxide film becomes easier to break. Therefore, an unoxidized metal surface is more easily exposed on the inner peripheral surface of the tube, and the oxygen partial pressure inside the tube can be more effectively reduced by oxidation of Al or Cr contained in the metal surface.

Furthermore, MgO easily forms a composite oxide with Al ₂ O ₃ and Cr ₂ O ₃ formed on the inner peripheral surface of the tube. This composite oxide is composed of an oxide film made of Al ₂ O _{3 and the} like. Very coarse compared. Therefore, Al and Cr contained in the tube and oxygen inside the tube are more likely to react, and the oxygen partial pressure inside the tube can be further reduced.

In other words, the property of good thermal conductivity that MgO has and the property of easily forming composite oxides with Al ₂ O ₃ and the like act synergistically to extremely effectively reduce the oxygen partial pressure inside the tube. Can be reduced. As a result, the durability of the heating resistor can be further improved, and the glow plug can generate heat at a higher temperature for a longer period of time.

Configuration 5. In the heating device of this configuration, in any one of the above configurations 1 to 4, the seal portion is made of a material having an oxygen permeability of 2.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less. It is formed.

According to the configuration 5, the oxygen permeability of the seal portion is sufficiently small as 2.0 × 10 ⁻⁹ or less. Therefore, it is possible to effectively prevent oxygen from entering the inside of the tube without excessively thickening the seal portion.

Configuration 6. In the heating device of this configuration, in any one of the above configurations 1 to 5, the tip of the heating resistor is joined to the tip of the tube.
The distal end portion of the tube does not contain W and contains Cr equal to or more than the Cr content in the metal material.

In addition, it is good also as containing Cr in the metal material which comprises a heating resistor, and it is good also as not containing Cr.

A glow plug is known in which the tip of the heating resistor is joined to the tip of the tube. Here, as a method of joining the heating resistor to the tube, the tip of the tube is closed while the tip of the tube is closed by arc welding or the like after the heating resistor is inserted into the tube having the tip opened. There is known a technique of welding the portion and the tip of the heating resistor. If a heating resistor having W as a main component is joined to the distal end portion of the tube using this technique, W may be contained in the distal end portion of the tube. If W is contained in the tube tip (especially the outer surface), W may be oxidized rapidly, and the tube may be damaged.

In this regard, according to the configuration 6, the tip of the tube does not contain W, and the Cr content in the heating resistor (the heating resistor may not contain Cr) or more. Of Cr. Therefore, it is possible to prevent the occurrence of the above-mentioned problems due to the inclusion of W, and it is possible to more reliably form an oxide film made of Cr ₂ O _{3 on the} surface of the distal end portion of the tube with the contained Cr. As a result, it is possible to achieve sufficiently excellent durability at the distal end portion of the tube, and to prevent the tube from being damaged more reliably.

In order to realize the above-described configuration 6 while joining the distal end portion of the tube and the distal end portion of the heating resistor by the above-described method, for example, while not containing W, a metal piece containing Cr is used as the heating resistor. A method of welding the metal piece and the distal end portion of the tube after being previously welded to the distal end portion.

Configuration 7. The glow plug of this configuration has a cylindrical tube with a closed end,
A heating resistor inserted through the tube;
A glow plug provided at a rear end side opening of the tube and having a seal portion for sealing the inside of the tube;
The heating resistor is formed of a metal material mainly composed of W or Mo,
The tube is formed of an alloy containing Al in an amount of 0.5% by mass to 5.0% by mass and Cr in an amount of 20% by mass to 40% by mass.

According to the above-described configuration 7, the same function and effect as those of the above-described configuration 1 are basically obtained. That is, by containing a predetermined amount of Al or Cr in the tube, the oxidation of the heating resistor made of W, Mo, etc. can be effectively prevented, and the excellent heat resistance of W or Mo can be fully exhibited. And excellent oxidation resistance in the tube can be maintained over a long period of time. As a result, the durability of both the heating resistor and the tube can be dramatically improved, and the glow plug can generate heat at a higher temperature over a long period of time.

Configuration 8. In the glow plug of this configuration, the average value of the room temperature resistance in the portion from the tip of the heating resistor to the rear end of 6 mm along the central axis of the tube is the heating resistor in the configuration 7. It is characterized by being larger than the average value of the whole room temperature resistance.

According to the above-described configuration 8, the same function and effect as those of the above-described configuration 2 are basically obtained.

Configuration 9 The glow plug of this configuration is the above-described configuration 7 or 8, wherein the heating resistor has a coil shape and a wire diameter of 0.2 mm or more.
Among the heating resistors, the average pitch in the region from the tip to the rear end of 6 mm along the center axis of the tube is 6 mm along the center axis of the tube from the tip of the heating resistor. It is characterized by being 0.9 mm or more smaller than the average pitch in the part located on the rear end side with respect to the rear end.

According to the above-described configuration 9, basically the same function and effect as those of the above-described configuration 3 are achieved.

Configuration 10 The glow plug of this configuration includes an insulating powder filled around the heating resistor in the tube according to any one of the configurations 7 to 9,
The insulating powder is a powder mainly composed of MgO.

According to the above configuration 10, the same operational effects as the above configuration 4 are basically obtained.

Configuration 11 In the glow plug of this configuration, in any one of the above configurations 7 to 10, the seal portion is made of a material having an oxygen permeability of 2.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less. It is formed.

According to the above configuration 11, the same operational effects as the above configuration 5 are basically obtained.

Configuration 12. In the glow plug of this configuration, the tip of the heating resistor is joined to the tip of the tube in any of the above configurations 7 to 11,
The distal end portion of the tube does not contain W and contains Cr equal to or more than the Cr content in the metal material.

According to the above configuration 12, the same operational effects as the above configuration 6 are basically obtained.

Configuration 13 The manufacturing method of the glow plug of this configuration includes a cylindrical tube with a closed end,
A heating resistor inserted through the tube;
A glow plug manufacturing method comprising a seal portion provided in a rear end side opening of the tube and sealing the inside of the tube,
The heating resistor formed of a metal material mainly composed of W or Mo is formed of an alloy containing Al in a range of 0.5 mass% to 5.0 mass% and Cr in a content of 20 mass% to 40 mass%. A placement step of placing in the tube,
A sealing step of providing the seal portion at the rear end side opening of the tube and sealing the inside of the tube;
And a heating step of heating the outer surface of the tube after the sealing step.

According to the configuration 13, since the outer surface of the tube is heated in the heating step after the sealing step, Al and Cr in the tube can be led and reacted with oxygen inside the tube rather than the heating resistor. . As a result, the oxygen partial pressure inside the tube can be further reduced while suppressing the oxidation of the heating resistor, and the durability of the heating resistor can be further improved.

If the heating temperature of the tube outer surface is too low or the heating time is too short, the oxidation of Al or Cr in the tube may not be promoted sufficiently, and the heating temperature is too high, If the heating time is too long, the seal portion may be damaged. Therefore, in order to promote the oxidation of Al and Cr more reliably and prevent damage to the seal portion, it is preferable that the heating temperature is 700 ° C. or higher and 1300 ° C. or lower, and the heating time is 1 second or longer and 60 seconds or shorter. More preferably, the heating temperature is 800 ° C. to 1300 ° C., and the heating time is 3 seconds to 30 seconds.

It is a block diagram which shows schematic structure of a heating apparatus. (A) is a partially broken front view of the glow plug, and (b) is a partially enlarged sectional view of the tip end portion of the glow plug. It is a partial expanded sectional view for demonstrating the joining method of a tube front-end | tip part and a heating coil front-end | tip part. It is a partial expanded sectional view which shows the structure of the heating coil etc. in 2nd Embodiment. It is a partially broken enlarged view showing a glow plug or the like assembled to an internal combustion engine. It is a partial expanded sectional view which shows the structure of the heat generating coil etc. in 3rd Embodiment. (A), (b) is a partial expanded sectional view which shows the structure of a sample. (A), (b) is a partial expanded sectional view which shows the structure of a sample.

Hereinafter, embodiments will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram showing a schematic configuration of a heating device 21 according to the present invention.

The heating device 21 includes a glow plug 1 and a glow control device (GCU) 31 as an energization control device that controls energization of the glow plug 1. Although only one glow plug 1 is shown in FIG. 1, an actual engine is provided with a plurality of cylinders, and a glow plug 1 and a switch 33 described later are provided for each cylinder.

The GCU 31 is operated by electric power supplied from the battery VA, and includes a microcomputer 32 having a CPU, ROM, RAM, and the like, and a switch 33 that switches on / off of energization from the battery VA to the glow plug 1. Yes.

The energization control to the glow plug 1 by the GCU 31 is performed by PWM control, and the switch 33 switches on / off of energization to the glow plug 1 in accordance with an instruction from the microcomputer 32.

In the present embodiment, in order to measure the resistance value of the glow plug 1, the switch 33 is configured to operate an FET (field effect transistor) having a current detection function via an NPN transistor or the like. . In addition, a microcomputer 32 is connected to a terminal for power supply of the glow plug 1 via a voltage dividing resistor (not shown), and the microcomputer 32 is applied to the glow plug 1. A voltage obtained by dividing the voltage (voltage output from the GCU 31) is input. The microcomputer 32 can calculate the applied voltage to the glow plug 1 based on the input voltage, and the glow plug 1 can be calculated from the applied voltage and the current flowing through the glow plug 1 measured by the switch 33. The resistance value is obtained.

Further, the microcomputer 32 according to the present embodiment is configured so that when the engine key is turned on, the glow plug 1 is turned on for a predetermined time after the pre-glow energization for rapidly raising the temperature of the glow plug 1 and the pre-glow energization. It is set so that after-glow energization can be performed that is maintained at a predetermined temperature for a predetermined time.

In the present embodiment, in pre-glow energization, the surface of a tube 7 described later of the glow plug 1 is heated from room temperature to 1000 ° C. within 3 seconds so that the glow plug 1 is rapidly heated to a predetermined target temperature. Electric power is supplied to the glow plug 1.

In this pre-glow energization, a curve indicating the relationship between the electric power supplied to the glow plug 1 and the elapsed time is made to coincide with a reference curve prepared in advance, so that the glow plug 1 can be rapidly connected regardless of the characteristics of the glow plug 1. Raise the temperature to the target temperature. Specifically, using a relational expression or a table indicating a predetermined reference curve, the power to be input at each time point corresponding to the elapsed time from the start of energization is obtained. The voltage to be applied to the glow plug 1 is obtained from the relationship between the current flowing through the glow plug 1 and the value of power to be applied at that time, and the voltage applied to the glow plug 1 is controlled by PWM control. As a result, the power is input so as to draw the same curve as the reference curve, and the glow plug 1 generates heat according to the integrated amount of power input up to each point in the temperature raising process. Therefore, when the power supply along the reference curve is completed, the glow plug 1 reaches the target temperature in the time corresponding to the reference curve.

In addition, in the afterglow energization, the power supplied to the glow plug 1 is adjusted so that the surface temperature of the tube 7 becomes extremely high at 1150 ° C. or more for a relatively long period (for example, about 180 seconds). It has become.

In this after-glow energization, the energization of the glow plug 1 is controlled so that the resistance value of the glow plug 1 matches the resistance value (target resistance value) when the glow plug 1 is set to the target temperature. Specifically, the effective voltage to be applied to the glow plug 1 is calculated from the difference between the current resistance value of the glow plug 1 and the target resistance value, for example, by PI control, and the duty ratio is calculated based on the effective voltage. Is set. When the afterglow is energized, the surface of the tube 7 is maintained at a high temperature of 1150 ° C. or higher, so that emission can be reduced.

Next, the configuration of the glow plug 1 that is energized and controlled by the GCU 31 will be described in detail. As shown in FIGS. 2A and 2B, 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 material mainly composed of iron (Fe) or nickel (Ni) and having a closed end. Further, a heating coil 9 (corresponding to the “heating resistor” of the present invention) made of a predetermined metal material is provided in the tube 7, and the tip of the heating coil 9 is connected to the tip of the tube 7. (The metal material constituting the tube 7 and the metal material constituting the heating coil 9 will be described in detail later).

In addition, the tube 7 is configured so that the distal end portion thereof is closed when the heating coil 9 is joined, and the distal end portion of the tube 7 is in an open state before the heating coil 9 is joined. In the present embodiment, a metal piece MP (see FIG. 3), which will be described later, is welded in advance to the distal end portion of the heating coil 9, and then the metal piece MP is disposed at the distal end opening of the tube 7, and the metal piece is obtained by arc welding or the like. By melting MP or the like, the distal end portion of the tube 7 is closed, and the distal end portion of the heating coil 9 is joined to the distal end portion of the tube 7. Therefore, a melting portion 7 </ b> M is formed at the distal end portion of the tube 7.

In the present embodiment, the metal piece MP is formed of the same metal material as that of the tube 7. In addition, the tube 7 through which the heating coil 9 is inserted corresponds to the “heating unit” in the present invention. Of the surface of the tube 7, the portion where the temperature becomes highest by energization (in the present embodiment, the tip of the tube 7). 2 mm from the rear end side to the rear end side) may be equivalent to the “heating unit”.

In addition, insulating powder 10 is filled around the heating coil 9. Therefore, although the heat generating coil 9 is electrically connected to the tube 7 at the tip thereof, the outer peripheral surface of the heat generating coil 9 and the inner peripheral surface of the tube 7 are insulated by the interposition of the insulating powder 10. Yes.

Furthermore, the rear end of the tube 7 is sealed with an annular seal portion 11 between the tube 7 and the inside of the tube 7 is sealed.

Further, the shaft hole 4 has a large diameter portion 4a formed at the tip thereof, and a small diameter portion 4b formed at the rear end side of the large diameter portion 4a. The tube 7 is held in a state of protruding from the distal end portion of the metal shell 2 by being press-fitted and joined to the small diameter portion 4 b of the shaft hole 4.

The center shaft 8 has its tip inserted into the tube 7, is electrically connected to the rear end of the heating coil 9, 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.

Next, the metal material constituting the heating coil 9 and the composition of the metal material constituting the tube 7 will be described.

In the present embodiment, the heating coil 9 is a metal material mainly composed of tungsten (W) or molybdenum (Mo) [in this embodiment, pure metal of W or Mo (which may contain inevitable impurities). )].

In addition, the tube 7 contains Ni or Fe as a main component, and contains aluminum (Al) in an amount of 0.5 mass% to 5.0 mass% and chromium (Cr) in an amount of 20 mass% to 40 mass%. It is formed with the metal material which does. In the present embodiment, the Cr content in the tube 7 is greater than the Cr content in the heating coil 9, and the tube 7 does not contain W.

Furthermore, the insulating powder 10 is composed of a powder containing magnesium oxide (MgO) as a main component.

In addition, the seal portion 11 is made of an elastic material having an oxygen permeability of 2.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less [for example, ethylene propylene rubber (EPDM rubber) or fluororubber Etc.]. The thickness of the seal portion 11 along the direction of the axis CL1 is relatively small (for example, 10 mm or less).

Further, since the melting portion 7M (the tip portion of the tube 7) is formed by melting the tube 7 and the metal piece MP made of the same material, at least the outer surface thereof does not contain W. In addition, the metal material constituting the heating coil 9 is configured to contain Cr that is equal to or greater than the Cr content (the heating coil 9 in the present embodiment does not contain Cr).

Next, a method for manufacturing the above-described glow plug 1 will be described. In addition, a conventionally well-known method is employ | adopted about the site | part which is not specified clearly.

First, a resistance heating wire mainly composed of W or Mo is processed into a coil shape, and the heating coil 9 is manufactured. In addition, a cylindrical tube 7 whose tip is not closed is made of a metal material containing Ni or Fe as a main component, Al in an amount of 0.5% to 5.0% by mass, and Cr in an amount of 20% to 40% by mass. Make it.

Next, as shown in FIG. 3, after joining the metal piece MP made of the same metal material as the metal material constituting the tube 7 to the tip of the heating coil 9, in the arranging step, the cylindrical tube 7. Inside, the tip of the middle shaft 8 and the heating coil 9 integrated with the middle shaft 8 are arranged. Then, after the metal piece MP is disposed in the opening of the tube 7, the metal piece MP and the tube 7 are melted by arc welding or the like to close the tip of the tube 7, and the tip of the tube 7 is heated. The tip of the coil 9 is joined.

Thereafter, the insulating powder 10 is filled in the tube 7, and in the sealing step, the seal portion 11 is provided between the rear end opening of the tube 7 and the middle shaft 8 to seal the inside of the tube 7. Thereby, the tube 7 is integrated with the middle shaft 8 to complete the sheath heater 3. In addition, after sealing the inside of the tube 7, it is good also as giving a swaging process to the front-end | tip part of the tube 7, and reducing the diameter of the front-end | tip part of the tube 7. FIG. By performing the swaging process, the packing density of the insulating powder 10 can be further increased.

Finally, the sheath heater 3 formed as described above is press-fitted and fixed in the shaft hole 4 of the metal shell 2, and the O-ring 12, the insulating bush 13, etc. are fitted into the middle shaft 8 at the rear end portion of the metal shell 2. It is. Thereby, the glow plug 1 mentioned above is obtained.

In addition, it is good also as performing the preheating which heats the outer surface of the tube 7 in the obtained glow plug 1. FIG. In the preheating, the outer surface of the portion of the tube 7 where the heat generating coil 9 is located (for example, the range from the tip of the tube 7 to 1 mm on the rear end side in the axis CL1 direction) is 800 ° C. to 1300 ° C. It is heated by an electric furnace or a high-frequency heating device for 2 to 30 seconds.

As described above in detail, according to the present embodiment, the heat generating coil 9 is formed of a metal material mainly composed of W or Mo having a high melting point, so that the heat generating coil 9 can achieve excellent heat resistance. it can.

On the other hand, although there is a concern about the decrease in oxidation resistance due to the use of W or Mo, in this embodiment, the tube 7 contains 0.5% by mass or more of Al and 20% by mass or more of Cr. ing. Therefore, during heat generation, Al or Cr that is more easily oxidized than W or Mo functions as an oxygen getter element, and an oxide film made of Al ₂ O ₃ or Cr ₂ O ₃ is formed on the inner peripheral surface of the tube 7. Thus, since the inside of the tube 7 is in a sealed state, the oxygen partial pressure inside the tube 7 can be effectively reduced. As a result, it is possible to more reliably prevent oxidation of the heating coil 9 mainly composed of W or Mo.

Further, by containing a predetermined amount or more of Al or Cr in the tube 7, an oxide film of Al ₂ O ₃ or Cr ₂ O ₃ can be formed over a wide area on the outer surface of the tube 7. Oxygen intrusion into the tube 7 can be more reliably suppressed by the oxide film, and the oxidation resistance of the tube 7 can be improved. Furthermore, since the content of Al and Cr is sufficiently large, even if peeling or cracking occurs in the oxide film due to thermal stress due to repeated cooling and heating cycles, the oxide film is more reliably and for a longer period of time. Can be reformed over a period of time.

As described above, according to the present embodiment, when the tube 7 contains a predetermined amount of Al or Cr, the oxidation of the heating coil 9 made of W, Mo, or the like can be effectively prevented, and The excellent heat resistance can be sufficiently exhibited, and the excellent oxidation resistance in the tube 7 can be maintained for a long time. As a result, the durability of both the heating coil 9 and the tube 7 can be dramatically improved, and the glow plug 1 can generate heat at a higher temperature over a long period of time.

In addition, since power is supplied to the heating coil 9 so that the temperature of the surface of the tube 7 (heating unit) rises from room temperature to 1000 ° C. within 3 seconds by the GCU 31, the thermal stress applied to the tube 7 is increased. Can be made. Therefore, an oxide film made of Al ₂ O ₃ or Cr ₂ O ₃ formed on the inner peripheral surface of the tube 7 is likely to be broken, and an unoxidized metal surface is easily exposed from the oxide film on the inner peripheral surface of the tube 7. By newly oxidizing Al and Cr contained in the metal surface, the oxygen partial pressure inside the tube 7 can be further reduced, and as a result, oxidation of the heating coil 9 made of W or the like is extremely effectively prevented. be able to.

In particular, in the present embodiment, in after-glow energization, the surface temperature (heating part) of the tube 7 is a very high temperature of 1150 ° C. or more, and heat generation over a long period is difficult. By acting synergistically, it becomes possible to generate heat over a long period of time even at such a high temperature. In other words, the present invention is particularly significant when the surface temperature (heating portion) of the tube 7 is set to a high temperature of 1150 ° C. or higher in after-glow energization performed for a relatively long period of time.

Furthermore, since MgO having excellent thermal conductivity is used as the insulating powder 10, the thermal conductivity from the heating coil 9 to the tube 7 can be improved. As a result, the glow plug 1 (tube 7) can be heated at a higher temperature without excessively heating the heating coil 9.

Further, since the tube 7 can be heated to a higher temperature, the thermal stress applied to the tube 7 can be increased, and as a result, an oxide film made of Al ₂ O ₃ or Cr ₂ O ₃ formed on the inner peripheral surface of the tube 7. Becomes easier to crack. Therefore, unoxidized Al and Cr are more easily exposed on the inner peripheral surface of the tube 7, and the oxygen partial pressure inside the tube 7 can be reduced more effectively.

Further, MgO easily forms a composite oxide with Al ₂ O ₃ or Cr ₂ O ₃ formed on the inner peripheral surface of the tube 7, and this composite oxide is an oxide film made of Al ₂ O ₃ or the like. Very coarse compared to. Therefore, Al and Cr contained in the tube 7 and oxygen inside the tube 7 are more likely to react, and the oxygen partial pressure inside the tube 7 can be further reduced.

That is, by using a metal material mainly composed of MgO as the insulating powder 10, the property of good thermal conductivity of MgO and the property of easily forming a composite oxide with Al ₂ O ₃ and the like are synergistic. The oxygen partial pressure inside the tube 7 can be reduced extremely effectively. As a result, the durability of the heating coil 9 can be further improved, and the glow plug 1 can generate heat at a higher temperature for a longer period of time.

At the same time, the oxygen permeability of the material constituting the seal portion 11 is sufficiently small as 2.0 × 10 ⁻⁹ or less, so that oxygen does not enter the tube 7 without excessively thickening the seal portion 11. Intrusion can be effectively prevented.

In addition, the melting portion 7M (the tip portion of the tube 7) does not contain W at least on the outer surface thereof, and also contains Cr equal to or more than the Cr content in the metal material constituting the heating coil 9. Yes. Therefore, oxidation accompanying the inclusion of W can be prevented, and an oxide film made of Cr ₂ O ₃ can be more reliably formed on the surface of the tip of the tube 7. As a result, it is possible to achieve sufficiently excellent durability at the distal end portion of the tube 7 and to prevent the tube 7 from being damaged more reliably.

Furthermore, a material containing Cr is generally known as a material constituting the heat generating coil 9, but in the present embodiment, the heat generating coil 9 is formed from a pure metal such as W or Mo. For this reason, the formation of the Cr oxide film on the surface can prevent the occurrence of a change in the component of the heating coil 9 and the decrease in the resistance value of the heating coil 9. As a result, the durability of the heating coil 9 can be further improved.

Further, if preheating is performed at the time of manufacture, Al and Cr in the tube 7 can take the lead and react with oxygen inside the tube 7 rather than the heating coil 9. As a result, it is possible to further reduce the oxygen partial pressure inside the tube 7 while suppressing the oxidation of the heat generating coil 9, and to further improve the durability of the heat generating coil 9.
[Second Embodiment]
Next, the second embodiment will be described focusing on differences from the first embodiment. In the second embodiment, as shown in FIG. 4, the heating coil 49 extends from the tip to the rear end of 6 mm along the center axis CL <b> 2 of the tube 47 (in the present embodiment, coincides with the axis CL <b> 1). The wire diameter of the distal end side coil 49A located at the rear is made smaller than the wire diameter of the rear end side coil 49B of the heat generating coil 49 located on the rear end side of the distal end side coil 49A. Specifically, the distal end portion of the distal end side coil 94A is configured such that the wire diameter gradually decreases toward the distal end side.

And the average value of the room temperature resistance of the front end side coil 49A per unit length along the central axis CL2 of the tube 47 is made by making the wire diameter of the front end side coil 49A smaller than that of the rear end side coil 49B. Is larger than the average value of the room temperature resistance of the entire heating coil 49 per unit length along the central axis CL2. As described above, the average value of the normal temperature resistance in the distal end side coil 49A is made larger than the average value of the normal temperature resistance of the entire heating coil 49, so that when the power is supplied from the battery VA to the glow plug 1 (the heating coil 49), the tube 47, the portion X of about 2 mm and its vicinity can be positively heated from the front end to the rear end thereof, and the portion X and the vicinity thereof can be set to the highest temperature.

In the state where the glow plug 1 is assembled to the internal combustion engine EN, as shown in FIG. 5, a portion (hereinafter referred to as an “exposed portion”) of the tube 47 that is generally located between the front end and the rear end of the tube 47 is approximately 4 mm. 47E) is disposed in the combustion chamber ER. Therefore, the part X can be said to be a part located substantially at the center of the exposed portion 7E.

As described above in detail, according to the second embodiment, the temperature of the exposed portion 47E of the tube 47 that is likely to be higher and that is subject to a sudden temperature change can be positively increased. It is possible to make the temperature higher, and it is possible to cause a rapid temperature change in the tube 47. Therefore, the thermal stress generated in the tube 47 can be further increased, and the oxide film formed on the inner peripheral surface of the tube 47 can be further easily broken. As a result, the oxidation preventing effect of the heating coil 49 can be further improved.
[Third Embodiment]
Next, the third embodiment will be described focusing on differences from the second embodiment. In the second embodiment, in order to make the average value of the normal temperature resistance of the front end side coil 49A larger than the average value of the normal temperature resistance of the entire heating coil 49, the wire diameter of the front end side coil 49A is the wire of the rear end side coil 49B. It is smaller than the diameter. On the other hand, in the third embodiment, as shown in FIG. 6 (note that the heating coil is schematically shown in FIGS. 6 to 8), the average pitch of the front end side coil 59A is the rear end side. By making it 0.9 mm or more smaller than the average pitch of the coil 59B, the average value of the room temperature resistance in the tip coil 59A is sufficiently larger than the average value of the room temperature resistance of the entire heating coil 59 (this first example). In the third embodiment, the average value of the normal temperature resistance of the distal end side coil 59A is configured to be at least twice the average value of the normal temperature resistance of the entire heating coil 59). In the third embodiment, the heating coil 59 has a wire diameter of 0.2 mm or more, and the heating coil 59 is configured to have a substantially constant wire diameter from the front end to the rear end.

As described above, according to the third embodiment, the temperature of the exposed portion of the tube 57 can be positively increased, and the temperature of the tube 57 can be increased more rapidly. Therefore, the oxide film formed on the inner peripheral surface of the tube 57 can be further easily broken, and the oxidation preventing effect of the heating coil 59 can be further enhanced.

In addition, in the third embodiment, since the thickness of the distal end side coil 59A can be sufficiently secured, the mechanical strength of the heating coil 59 can be sufficiently maintained.

Furthermore, since it is not necessary to make the tip side coil 59A excessively thin, the heat generating coil 59 can be manufactured relatively easily, and a reduction in productivity can be prevented more reliably.

Next, in order to confirm the effects achieved by the above embodiment, the heating coil is formed of Fe-26Cr-7.5Al (Pyromax), W, or Mo, and the tube is mainly composed of Fe or Ni. At the same time, samples of glow plugs formed from metal materials with various contents of Al and Cr were prepared, and durability evaluation tests were performed on the samples. The outline of the durability evaluation test is as follows. That is, for each sample, the tube surface (heating portion) was heated from room temperature to 1000 ° C. in 2 seconds or 10 seconds and energized for 60 seconds so that the tube surface temperature was saturated at 1150 ° C. or 1200 ° C. Thereafter, air cooling for 180 seconds was taken as one cycle, and the number of cycles (disconnection cycle) until the heating coil was disconnected was measured. Here, when the tube surface temperature is saturated at 1150 ° C., the sample having a disconnection cycle of 10,000 cycles or more is evaluated as “◯” as having excellent durability, while the disconnection cycle is Samples with less than 10,000 cycles were evaluated as “x” because they were inferior in durability. In addition, when the tube surface temperature is saturated at 1200 ° C. (that is, under the condition that the heating coil is more likely to break), a sample with a break cycle of 5000 cycles or more is evaluated as “◯”, and the break cycle Samples with less than 5000 cycles were rated “x”. For samples in which the tube was damaged, “*” was given in the judgment column of Tables 1 to 3 below.

Table 1 shows the test results of the sample in which the heating coil is formed of Fe-26Cr-7.5Al. Table 2 shows the test results of the sample in which the heating coil is formed of W, and Table 3 shows the test result of the sample in which the heating coil is formed of Mo. When the temperature is raised from room temperature to 1000 ° C. in 2 seconds, the sample is energized at 11 V for 2 seconds, and when the temperature is raised from room temperature to 1000 ° C. in 10 seconds, 4.5 V is applied to the sample. Was energized for 5 seconds, and then energized at 7.5 V for 5 seconds. Moreover, when saturating the tube surface temperature at 1150 ° C., it was energized at 6.5 V for 60 seconds, and when saturating the tube surface temperature at 1200 ° C., it was energized at 7.5 V for 60 seconds. In each sample, the seal portion was formed of fluoro rubber, and the tube composition was specified by quantitative analysis using EPMA. For the sample in which the heating coil was formed of Fe-26Cr-7.5Al, only a test for raising the temperature from room temperature to 1000 ° C. in 2 seconds was performed.

As shown in Table 1, in the sample in which the heating coil is formed of Fe-26Cr-7.5Al (Pyromax), the heating coil is disconnected at an early stage regardless of the composition of the tube, particularly up to 1200 ° C. It was found that the heating coil melts when the temperature is raised. This is because the melting point of the metal material composing the heating coil is relatively low, about 1500 ° C., and when the tube surface was heated to a high temperature of 1150 ° C. or higher, the heating coil was heated to near its melting point. Conceivable.

In addition, as shown in Tables 2 and 3, even if the heating coil is made of W or Mo having a high melting point, if the Al content or Cr content of the tube is relatively low, the durability It became clear that became insufficient. This is presumably because W and Mo have the property of being relatively easy to oxidize, so that the oxidation consumption of the heating coil has rapidly advanced at high temperatures.

Further, it was confirmed that the sample in which the tube was formed of Ni-15Cr-8Fe-0.5Mn-0.2Si [Inconel (registered trademark) 600] would be damaged. This is because the tube does not contain Al and the Cr content in the tube is relatively low, so an oxide film formed by oxidation of Al or Cr is not sufficiently formed on the tube surface, and the tube has oxidation resistance. This is thought to be due to the fact that it was insufficient.

On the other hand, a sample in which the heating coil is formed of W or Mo and the Al content of the tube is 0.5 mass% or more and the Cr content is 20 mass% or more has excellent durability. It became clear. This is because Al and Cr contained in the tube are preferentially oxidized over W or Mo of the heating coil, so that the partial pressure of oxygen in the tube can be reduced, and hence the oxidation of the heating coil can be suppressed. In addition, according to the fact that an oxide film made of Al or Cr was sufficiently formed on the outer surface of the tube, and excellent oxidation resistance capable of withstanding a high temperature of 1150 ° C. or higher was realized in the tube over a long period of time. Conceivable.

In particular, it was confirmed that excellent durability can be realized as the content of Al and Cr in the tube is increased.

From the above test results, in order to improve the durability of both the heating coil and the tube and to enable heat generation at a higher temperature over a long period of time, the heating coil is made of a metal material mainly composed of W or Mo. While forming, it can be said that it is preferable to make Al content in a tube into 0.5 mass% or more, and to make Cr content into 20 mass% or more. In order to further improve the durability, the Al content is increased to 1.4% by mass or more and 2.4% by mass or more, or the Cr content is increased to 23% by mass or more and 26% by mass or more. It can be said that it is desirable to increase it. However, if the Al content is more than 5.0% by mass or the Cr content is more than 40% by mass, the workability may be deteriorated. Therefore, it is preferable that the Al content is 5.0% by mass or less and the Cr content is 40% by mass or less.

Next, a sample of a glow plug in which a heating coil is formed of W or Mo and a tube is formed of Ni-26Cr-11Fe-2.4Al-0.2C-0.2Ti-0.1Zr-0.1Y (Alloy 602) Several were produced. Then, the temperature of the tube is varied from room temperature to 1000 ° C. by changing the temperature raising time for each sample, and after reaching 1200 ° C., energization is performed to maintain the temperature for 60 seconds, and then air cooling is performed for 180 seconds. As one cycle, the disconnection cycle until the heating coil was disconnected was measured. Table 4 shows a test result of a sample in which the heating coil is formed of W, and Table 5 shows a test result of a sample in which the heating coil is formed of Mo. In each sample, the seal portion was formed of fluororubber.

As shown in Table 4 and Table 5, when the temperature rising time from room temperature to 1000 ° C. was more than 3 seconds, the disconnection cycle was around 7000 cycles, whereas the temperature rising from room temperature to 1000 ° C. It was found that when the time was within 3 seconds, the disconnection cycle was 8500 cycles or more, and further excellent durability could be realized. Moreover, it was confirmed that the disconnection cycle exceeded 9000 cycles and the durability was further improved by setting the temperature rising time from room temperature to 1000 ° C. within 2 seconds. This is because the thermal stress applied to the tube increases as the temperature rise time is shorter, so that the oxide film generated on the inner wall of the tube is likely to be destroyed (in other words, unoxidized Al and Cr are exposed on the inner surface of the tube). As a result, it is considered that the oxidation of oxygen inside the tube with Al and Cr was further promoted, and the oxygen partial pressure inside the tube was further reduced.

From the above test results, in order to further improve the durability, a glow plug in which a heating coil is formed of a metal material mainly composed of W or Mo and a tube is formed of a metal material containing a predetermined amount of Al or Cr. It is preferable to supply power so that the tube surface temperature rises from room temperature to 1000 ° C. within 3 seconds, and it is more preferable to supply power so that the temperature rises from room temperature to 1000 ° C. within 2 seconds. .

Next, a glow plug sample in which the insulating powder filled in the tube is made of MgO, aluminum oxide (Al ₂ O ₃ ), or silicon nitride (Si ₃ N ₄ ) is prepared and energized at 7.5 V for 65 seconds. (The temperature was raised from room temperature to 1000 ° C. in 5 seconds), and then air cooling for 180 seconds was taken as one cycle, and the disconnection cycle until the heating coil was disconnected was measured. Table 6 shows the results of the test. In each sample, the heating coil is formed of W, and the tube is formed of Ni-23Cr-14Fe-1.4Al-0.5Mn-0.2Si [Inconel (registered trademark) 601], Alloy 602, or SUS310s. did. In addition, the seal portion was formed of fluororubber, and the sample after preparation was preheated at 800 ° C. for 30 seconds.

As shown in Table 6, it was confirmed that the sample in which the tube was formed of Inconel 601 or Alloy 602 had excellent durability in any insulating powder. In particular, it has been clarified that the sample in which the insulating powder is formed of MgO is more excellent in durability than the sample in which the insulating powder is formed of Al ₂ O ₃ or Si ₃ N ₄ . This is because MgO is easy to form a composite oxide with Al and Cr oxides formed on the inner periphery of the tube. Since the composite oxide is very rough, Al and Cr in the tube and oxygen inside the tube As a result, the oxygen partial pressure inside the tube could be further reduced, and compared with Al ₂ O ₃ etc., MgO is superior in thermal conductivity. It is considered that a large thermal stress is applied, and as a result, the oxide film on the inner periphery of the tube is easily cracked, and the oxidation of oxygen inside the tube and Al and Cr in the tube is further promoted.

From the above test results, it can be said that it is preferable to use a material mainly composed of MgO as the insulating powder from the viewpoint of further improving the durability.

Next, glow plug samples in which the seal portion is made of EPDM or fluororubber are prepared, and each sample is energized at 7.5 V for 65 seconds (temperature rise from room temperature to 1000 ° C. in 5 seconds), and then for 180 seconds. Taking the air cooling as one cycle, the disconnection cycle until the heating coil was disconnected was measured. Table 7 shows the results of the test. The heating coil was made of W, and the tube was made of Inconel 601 or Alloy 602. Moreover, the thickness along the axial direction of the seal portion was set to 10 mm.

As shown in Table 7, it was clarified that each sample has excellent durability, and in particular, as the oxygen permeability of the seal portion is small, further excellent durability can be realized. This is considered to be because the invasion of oxygen that has passed through the seal portion into the tube is further suppressed.

From the above test results, in order to further improve the durability of the heating coil, the oxygen permeability of the seal portion should be 2.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less. It is preferable that the oxygen permeability is 1.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less.

Next, a plurality of glow plug samples in which the heating coil is formed of W and the tube is formed of Inconel 601 are produced, and the tip of the tube (range from the tip to 1 mm) is inserted into the electric furnace for each sample. The tube was preheated at 700 ° C. to 1400 ° C. for 1 second to 60 seconds. Then, for the preheated sample, the tube surface is heated from room temperature to 1000 ° C. in 2 seconds and energized for 60 seconds so that the tube surface temperature is saturated at 1200 ° C. (that is, at 11 V). After energizing for 2 seconds, energizing for 60 seconds at 7.5 V), and then cooling with air for 180 seconds was taken as one cycle, and the number of cycles until the heating coil was disconnected (disconnection cycle) was measured. Table 8 shows the results of the test. The seal portion was made of fluoro rubber. Moreover, in Table 8, the disconnection cycle of the sample which did not perform preheating is also shown as reference.

As shown in Table 8, it was found that the durability of the sample preliminarily heated at 800 ° C. or higher for 60 seconds or the sample preliminarily heated at 1400 ° C. was extremely lowered. This is considered to be due to the fact that the seal portion is melted by heating for a long time, or that the tube is thinned by heating at an extremely high temperature.

In contrast, samples that were preheated at 700 ° C. to 1300 ° C. for 1 second to 30 seconds, or samples that were preheated at 700 ° C. for 60 seconds were samples that were not preheated. It became clear that it had the further outstanding durability compared with. This is because heating the tube causes Al and Cr in the tube to take the lead and react with oxygen inside the tube rather than the heating coil. As a result, while suppressing oxidation of the heating coil, oxygen inside the tube This is probably because the partial pressure could be further reduced.

In particular, it was confirmed that the sample preliminarily heated at 800 ° C. to 1300 ° C. for 3 to 30 seconds has a disconnection cycle exceeding 9000 cycles and has extremely excellent durability.

From the above test results, it can be said that it is preferable to preheat the tube tip in order to further improve the durability. In particular, from the viewpoint of surely improving the durability, preheating at a relatively low temperature of 700 ° C. or lower, or preheating at 700 ° C. or higher and 1300 ° C. or lower for 1 second to 30 seconds. More preferably, it can be said that it is even more preferable to perform preheating at 800 ° C. or higher and 1300 ° C. or lower for 3 to 30 seconds.

Next, while preparing a plurality of glow plug samples with various wire diameters of the heating coil, using a radiation thermometer, the temperature at the 2 mm portion (center of the exposed portion) of the tube surface from the tip to the rear end is measured. While measuring, each sample was energized at 11 V for 2 seconds, and then energized at 6 V for 180 seconds. And the time (1000 degreeC arrival time) when the temperature in a 2 mm part (measurement object part) reached | attained 1000 degreeC from the front-end | tip to the rear end side among the tubes was measured. Here, the sample in which the measurement target portion reaches 1000 ° C. within 3 seconds can easily raise the temperature of the tube quickly and easily expose unoxidized Al and Cr to the inner peripheral surface of the tube. It can be said that it is preferable in terms of improving the chemical conversion. Table 9 shows the test results of the test. In each sample, the heating coil was made of Mo, the pitch of the heating coil was constant, the outer diameter of the heating coil was 2.5 mm, and the room temperature resistance of the entire heating coil was 300 mΩ. Further, in each sample, the length along the axis of the heating coil and the number of turns of the heating coil were changed according to the wire diameter of the heating coil in order to equalize the room temperature resistance of the entire heating coil. In Table 9, the length and the number of turns of the heating coil in each sample are also shown for reference.

As shown in Table 9, in the sample in which the wire diameter of the heating coil is 0.15 mm or less, the measurement target part becomes 1000 ° C. within 3 seconds, and it is easy to rapidly raise the temperature of the exposed part. It was.

Next, while changing the wire diameter of the portion (tip-side coil) located between the tip of the heating coil and the 6 mm rear end along the central axis of the tube, from the tip-side coil of the heating resistor Also, a plurality of glow plug samples with a constant wire diameter (0.2 mm) of the portion located on the rear end side (rear end side coil) were prepared, and each sample was energized at 11V for 2 seconds, The temperature was increased by energization at 6 V for 180 seconds. And the time when the temperature in the said measurement object part reached | attained 1000 degreeC was measured. Table 10 shows the test results of the test.

In each sample, the heat generating coil was formed of Mo, the outer diameter of the heat generating coil was 2.5 mm, the length of the front end side coil was 6 mm, and the length of the rear end side coil was 18 mm. In each sample, a heating coil was produced by welding a portion corresponding to the front end side coil to a portion corresponding to the rear end side coil. Furthermore, the average pitch of the tip side coil was changed in accordance with the wire diameter of the tip side coil, and the room temperature resistance of the tip side coil was adjusted to 150 mΩ. Further, the room temperature resistance of the rear end side coil was also set to 150 mΩ, so that the room temperature resistance of the entire heating coil was 300 mΩ, and the average value of the room temperature resistance of the entire heating coil was 12.5 mΩ / mm (= 300 mΩ / 24 mm).

As shown in Table 10, it was confirmed that in each sample, the measurement target part reached 1000 ° C. within 3 seconds, and rapid heating of the exposed part was easily possible.

Incidentally, in order to configure the heat generating coil to have sufficient mechanical strength, it is preferable that the wire diameter of the heat generating coil is set to 2.0 mm or more. Then, after making the wire diameter of the heating coil 2.0 mm, a plurality of glow plug samples in which the average value of the room temperature resistance of the tip side coil was changed by changing the pitch of the tip side coil, The sample was heated under the above-described energization conditions (energization at 11V for 2 seconds and energization at 6V for 180 seconds). The sample in which the measurement target portion reaches 1000 ° C. within 3 seconds is evaluated as “◯” because the exposed portion is easily heated rapidly. On the other hand, the temperature of the measurement target portion is 3 seconds. Samples that did not reach 1000 ° C. within the range were evaluated as “Δ” because the temperature of the exposed portion was somewhat difficult to raise. Table 11 shows the test results of the test.

Moreover, about the sample whose measurement object part became 1000 degreeC within 3 second, after energizing for 2 seconds at 11V, energizing for 180 seconds at 7.5V, and then stopping energization for 120 seconds as one cycle, The number of cycles until the heating coil was disconnected (disconnection cycle) was also measured. Table 11 also shows the measured disconnection cycle in addition to the results of the test.

In each sample, the heating coil was made of Mo, and the outer diameter of the heating coil was 2.5 mm. Further, as shown in FIGS. 7A and 7B, in each sample, the length of the front end side coil was 6 mm, and the length of the rear end side coil was 18 mm. The room temperature resistance of the rear end side coil is also changed by adjusting the pitch of the rear end side coil in accordance with the change of the room temperature resistance (pitch) of the front end side coil. It was. In Table 11, the normal temperature resistance of the front end side coil, the normal temperature resistance of the rear end side coil, the average pitch of the front end side coil, and the average pitch of the rear end side coil are also shown. In addition, the average pitch of the distal end side coil was calculated by excluding one turn adjacent to the distal end of the tube (the most distal portion of the heating coil) from the distal end side coil.

As shown in Table 11, in the sample in which the average value of the normal temperature resistance of the coil on the front end side is larger than the average value of the normal temperature resistance of the entire heating coil, the measurement target portion reaches 1000 ° C. within 3 seconds, and the exposed portion rapidly rises. It became clear that temperature could be easily achieved. In particular, in the sample in which the average pitch of the front end side coil is 0.9 mm or more smaller than the average pitch of the rear end side coil, the measurement target portion becomes 1000 ° C. within 2 seconds, and the rapid temperature rise performance of the exposed portion is further improved. I understood that.

Furthermore, it was confirmed again that the durability of the heating coil can be improved as the time to reach 1000 ° C. is shortened.

Next, both the normal temperature resistance of the front end side coil and the normal temperature resistance of the rear end side coil are set to 150 mΩ, and the length of the front end side coil is set to 6 mm as shown in FIGS. [In other words, the average value of the normal temperature resistance of the front coil is set to a constant value (25 mΩ / mm)], and the average value of the normal temperature resistance of the entire heating coil is changed by changing the length L of the rear coil. A sample of a glow plug with a modified length was prepared. Each sample was heated under the above-mentioned energization condition (energized at 11V for 2 seconds and energized at 6V for 180 seconds), and the sample whose measurement target part reached 1000 ° C. within 3 seconds was evaluated as “◯”. The sample whose measurement target part did not reach 1000 ° C. within 3 seconds was evaluated as “Δ”. Table 12 shows the test results of the test.

In addition, the sample with an evaluation of “◯” was energized at 11 V for 2 seconds, then energized at 7.5 V for 180 seconds, and then stopped for 120 seconds until the heating coil was disconnected. The number of cycles (disconnection cycle) was measured. Table 12 also shows the disconnection cycle in addition to the test results of the above test.

In each sample, the heating coil was formed of W, and the outer diameter of the heating coil was 2.5 mm.

As shown in Table 12, it was reconfirmed that the exposed portion can be rapidly heated rapidly by making the average value of the room temperature resistance of the coil on the tip side larger than the average value of the room temperature resistance of the entire heating coil. . In addition, it was confirmed again that the rapid temperature rising property of the exposed portion can be further improved by making the average pitch of the front end side coil 0.9 mm or more smaller than the average pitch of the rear end side coil.

Based on the above test results, in order to further increase the oxidation resistance of the heating coil, the average temperature resistance of the coil on the tip side is heated to positively raise the temperature of the exposed part of the tube, which is likely to be hot. It can be said that it is preferable to make it larger than the average value of the room temperature resistance of the entire coil. In order to further improve the oxidation resistance of the heating coil, it can be said that it is more preferable to make the average pitch of the front end side coil 0.9 mm or more smaller than the average pitch of the rear end side coil.

The test results in Tables 9 to 12 were obtained when energized at 11V for 2 seconds and then energized at 6V for 180 seconds as described above. Therefore, even in a sample where the exposed portion is evaluated to be slightly less likely to be rapidly heated under this energization condition, the surface temperature of the exposed portion should be 1000 ° C. or more within 3 seconds by changing the energization condition. Is possible. In addition, by changing the energization conditions and the configuration of the heating coil, the surface temperature of the portion of the tube other than the exposed portion can be set to 1000 ° C. or more within 3 seconds.

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, pure metals such as W and Mo are exemplified as the metal material constituting the heating coil 9, but the metal material constituting the heating coil 9 is an alloy mainly composed of W or Mo. If it is. Therefore, the heat generating coil 9 may be formed of a metal material mainly composed of W or Mo and containing rhenium (Re), thorium oxide (ThO ₂ ), Cr, or the like. By including Re in the range of several mass% to several tens mass%, the resistance value of the heating coil 9 is maintained without excessively reducing the diameter of the heating coil 9 (that is, maintaining the durability of the heating coil 9). Can be sufficiently increased, and sufficient heat generation performance can be realized. Further, by containing ThO ₂ by several mass%, it is possible to suppress the grain growth of the heat generating coil 9 at a high temperature, and the durability of the heat generating coil 9 can be further improved.

(B) In the above embodiment, the tip of the tube 7 and the tip of the heating coil 9 are joined, but the tip of the tube 7 and the tip of the heating coil 9 are configured without joining. Also good.

(C) In the above embodiment, EPDM rubber or fluororubber is exemplified as the material constituting the seal portion 11, but the material constituting the seal portion 11 is not limited to this. Accordingly, silicon rubber having a certain thickness may be used, or a glass material may be used as the seal portion 11 if the tube 7 is not subjected to swaging.

(D) In the above embodiment, the metal piece MP is formed of a material having the same composition as the material constituting the tube 7, but the composition of the metal piece MP is not limited to this. However, in order to configure the tube 7 so that no W is contained in the tip portion, the metal piece MP is preferably one containing no W. Moreover, like the said embodiment, in order to make Cr contain at the front-end | tip part of the tube 7, and to improve the oxidation resistance in the front-end | tip part of the tube 7, it is preferable to make the metal piece MP contain Cr.

(E) In the above embodiment, the insulating powder 10 is made of a metal material mainly composed of MgO. However, the insulating powder 10 is mainly made of another metal (for example, Al ₂ O ₃ or Si ₃ N ₄ ). It is good also as comprising with the material used as a component.

(F) The shape or the like of the glow plug 1 is not limited to the above-described embodiment. For example, the tube 7 may be configured to have a small-diameter portion at the tip. Alternatively, the large 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.

(G) In the above embodiment, the middle shaft 8 is directly joined to the rear end of the heating coil 9, but a metal material different from the heating coil 9 between the heating coil 9 and the middle shaft 8 [for example, cobalt (Co) It is also possible to provide a coil (so-called control coil) made of a metal material whose main component is Co or Ni represented by —Ni—Fe alloy or the like. In this case, when the temperature rises (relatively low temperature), the resistance value of the control coil is relatively low, and the heating coil 9 can be rapidly heated, while when the temperature is saturated, The resistance value becomes relatively high, the amount of power supplied to the heating coil 9 is suppressed, and as a result, the excessive heating of the heating coil 9 can be suppressed.

DESCRIPTION OF SYMBOLS 1 ... Glow plug, 7 ... Tube, 9 ... Heat generating coil (heat generating resistor), 10 ... Insulating powder, 11 ... Seal part, 21 ... Heating device, 31 ... GCU (energization control device).

Claims (13)

1. A glow plug having a heating resistor and constituting a heating unit;
   A heating device that is configured to be capable of adjusting power supplied to the heating resistor and capable of controlling heat generation of the heating resistor by adjusting the power supply,
   The energization control device supplies power to the heating resistor so that the temperature of the heating unit rises from room temperature to 1000 ° C. within 3 seconds,
   The glow plug is
   A cylindrical tube that has a distal end closed and the heating resistor is inserted into the heating tube;
   Provided in a rear end side opening of the tube, and a seal portion for sealing the inside of the tube,
   The heating resistor is made of a metal material mainly composed of tungsten or molybdenum,
   The said tube is formed with the alloy which contains aluminum 0.5 mass% or more and 5.0 mass% or less, and chromium contains 20 mass% or more and 40 mass% or less, The heating apparatus characterized by the above-mentioned.
2. Among the heating resistors, the average value of the room temperature resistance in the region from the tip to the rear end of 6 mm along the central axis of the tube is larger than the average value of the room temperature resistance of the entire heating resistor. The heating device according to claim 1, wherein
3. The heating resistor has a coil shape and a wire diameter of 0.2 mm or more,
   Among the heating resistors, the average pitch in the region from the tip to the rear end of 6 mm along the center axis of the tube is 6 mm along the center axis of the tube from the tip of the heating resistor. 3. The heating apparatus according to claim 1, wherein the heating device is 0.9 mm or more smaller than an average pitch at a portion located on the rear end side from the rear end.
4. The glow plug includes an insulating powder filled around the heating resistor in the tube,
   The heating apparatus according to any one of claims 1 to 3, wherein the insulating powder is a powder containing magnesium oxide as a main component.
5. The said seal | sticker part is formed with the material whose oxygen permeability is 2.0 * 10 < ^-9 > (cm < ³ > * cm / sec * cm < ² > * cmHg) or less, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. The heating device according to Item.
6. The tip of the heating resistor is joined to the tip of the tube,
   The heating device according to any one of claims 1 to 5, wherein a tip portion of the tube does not contain tungsten and contains chromium equal to or more than a chromium content in the metal material.
7. A tubular tube with a closed end,
   A heating resistor inserted through the tube;
   A glow plug provided at a rear end side opening of the tube and having a seal portion for sealing the inside of the tube;
   The heating resistor is made of a metal material mainly composed of tungsten or molybdenum,
   The glow plug is characterized in that the tube is formed of an alloy containing 0.5% by mass or more and 5.0% by mass or less of aluminum and 20% by mass or more and 40% by mass or less of chromium.
8. Among the heating resistors, the average value of the room temperature resistance in the region from the tip to the rear end of 6 mm along the central axis of the tube is larger than the average value of the room temperature resistance of the entire heating resistor. The glow plug according to claim 7, wherein the glow plug is characterized in that:
9. The heating resistor has a coil shape and a wire diameter of 0.2 mm or more,
   Among the heating resistors, the average pitch in the region from the tip to the rear end of 6 mm along the center axis of the tube is 6 mm along the center axis of the tube from the tip of the heating resistor. The glow plug according to claim 7 or 8, wherein the glow plug is smaller by 0.9 mm or more than an average pitch at a portion located on the rear end side with respect to the rear end.
10. In the tube, comprising an insulating powder filled around the heating resistor,
    The glow plug according to claim 7, wherein the insulating powder is a powder containing magnesium oxide as a main component.
11. 11. The seal part according to claim 7, wherein the seal part is made of a material having an oxygen permeability of 2.0 × 10 ⁻⁹ (cm ³ · cm / sec · cm ² · cmHg) or less. Glow plug according to item.
12. The tip of the heating resistor is joined to the tip of the tube,
    The glow plug according to any one of claims 7 to 11, wherein a distal end portion of the tube does not contain tungsten and contains chromium equal to or more than a chromium content in the metal material.
13. A tubular tube with a closed end,
    A heating resistor inserted through the tube;
    A glow plug manufacturing method comprising a seal portion provided in a rear end side opening of the tube and sealing the inside of the tube,
    The heating resistor formed of a metal material mainly composed of tungsten or molybdenum is formed of an alloy containing 0.5% by mass to 5.0% by mass of aluminum and 20% by mass to 40% by mass of chromium. A placement step of placing in the tube,
    A sealing step of providing the seal portion at the rear end side opening of the tube and sealing the inside of the tube;
    A method of manufacturing a glow plug, comprising a heating step of heating the outer surface of the tube after the sealing step.

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