JP2018096670A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug capable of restricting reduction in temperature when an applied voltage is decreased to saturate temperature while assuring a high temperature formation of heat generating temperature and a fast temperature increasing characteristic.SOLUTION: A glow plug includes an extremity end coil connected to an extremity end of a tube and having W or Mo as its chief constituent; and a rear end coil connected to a rear end of the extremity end coil. A resistance ratio that is a ratio of resistance at 1000°C in respect a resistance value at 20°C of the extremity end coil is larger than a resistance ratio that is a ratio of resistance at 1000°C in respect to a resistance value at 20°C at the rear end coil. A rate of resistance value at 20°C between the extremity end coil and the extremity end of the tube at a position of 4 mm from the extremity end of the tube toward the rear end side in an axial direction in respect to the resistance value at 20°C between the extremity end of the tube and the rear end of the extremity end coil is about 55 to 80%.SELECTED DRAWING: Figure 2

Description

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

  The glow plug is used as an auxiliary heat source for an internal combustion engine such as a diesel engine using a compression ignition system. The glow plug is required to have a capability of raising the temperature to a predetermined temperature in a short time (hereinafter referred to as “rapid temperature rise”) in order to improve the startability of the internal combustion engine. In addition, glow plugs are also required to have a high heat generation temperature as regulations on internal combustion engines are tightened. Patent Document 1 discloses a heat resistant metal whose main component is W or Mo having a melting point higher than that of an FeCrAl alloy or NiCr alloy in order to meet the demand for higher heat generation temperature in a glow plug having a coil joined to the tip of a central shaft. A technique for using a coil for a coil is disclosed.

International Publication No. 2014/206847

  However, since the resistance ratio of refractory metals such as W and Mo is larger than the resistance ratio of NiCr alloy, in the conventional technique, when a constant voltage is applied to the coil to raise it to a predetermined temperature, the resistance of the coil suddenly increases. Current value decreases rapidly. Here, the resistance ratio is “the ratio of the resistance value at 1000 ° C. to the resistance value at 20 ° C. of the coil”, and the resistance value at high temperature increases as the resistance ratio value increases. And since the emitted-heat amount is proportional to the square of an electric current value, there exists a problem that it is difficult to heat up to predetermined temperature in a short time, and rapid temperature rising property is missing.

  On the other hand, it is conceivable that a rear end coil made of FeCrAl alloy or NiCr alloy having a resistance ratio smaller than that of the heat resistant metal is joined to the rear end side of the coil made of the heat resistant metal (front end coil). Thereby, a tip coil can be raised to predetermined temperature, without making the resistance value of the whole coil increase excessively, and rapid temperature rising property can be ensured.

  However, if the applied voltage is lowered in order to saturate the temperature of the coil that has been heated to a predetermined temperature, the heat of the coil moves to the rear end coil, and the temperature of the front end coil tends to be temporarily greatly reduced. As a result, there are problems that the combustion of the engine becomes unstable and the emission of exhaust gas increases.

  The present invention has been made to solve the above-described problems, and suppresses a temperature drop when the applied voltage is lowered to saturate the temperature while ensuring a high exothermic temperature and rapid temperature rise. It aims to provide a glow plug that can be used.

  In order to achieve this object, the glow plug of the present invention includes a metal center shaft extending in the axial direction, a coil electrically connected to the tip of the center shaft, and the coil and the tip end side of the center shaft. And a metal tube having a closed end. The coil includes a front end coil that is electrically connected to the front end of the tube and mainly contains W or Mo, and a rear end coil that is electrically connected to the rear end of the front end coil. A resistance ratio R1 that is a ratio of the resistance value at 1000 ° C. to a resistance value at 20 ° C. of the front end coil, and a resistance ratio R2 that is a ratio of the resistance value at 1000 ° C. to the resistance value at 20 ° C. of the rear end coil Satisfies the relationship of R1> R2. Then, with respect to the resistance value at 20 ° C. between the distal end of the tube and the rear end of the distal end coil, 20 between the distal end coil and the distal end of the tube at a position of 4 mm from the distal end of the tube toward the rear end side in the axial direction. The ratio of the resistance value at 5 ° C. is 55 to 80%.

  According to the glow plug of claim 1, the tip coil at a position of 4 mm from the tip of the tube toward the rear end in the axial direction with respect to the resistance value at 20 ° C. between the tip of the tube and the rear end of the tip coil. Since the ratio of the resistance value at 20 ° C. between the tube and the tip of the tube is 55 to 80%, the heat generation amount of the tip coil up to 4 mm can be made larger than the heat generation amount of the remaining portion of the tip coil. Therefore, the temperature of the tip coil up to 4 mm can be rapidly raised, and rapid temperature rise can be ensured.

  Since the remaining part of the tip coil generates heat according to the ratio of resistance value (20 to 45%), the amount of heat that moves from the part up to 4 mm of the tip coil to the rear end when the applied voltage is lowered can be suppressed. . Therefore, a temperature drop when the applied voltage is lowered to saturate the temperature can be suppressed.

  Note that “the main component is W or Mo” means that the total content of W or Mo with respect to the total content of the coil material is 50 wt% or more.

  According to the glow plug of claim 2, since the resistance value between the tip of the tube and the rear end of the tip coil is 0.13Ω or less, in addition to the effect of claim 1, an excessive voltage is not applied to the coil. However, the value of the current flowing through the tip coil can be secured and the tip coil can generate heat.

  According to the glow plug of the third aspect, the tip coil has the same composition from its tip to the rear end, and the tip side pitch is smaller than the rear end side pitch. Therefore, in addition to the effect of Claim 1 or 2, the structure of the tip coil can be simplified.

  According to the glow plug of claim 4, since the resistance value at 20 ° C. between the tip of the tube and the rear end of the rear end coil is 0.36Ω or less, the current value at the time of inrush flowing through the front end coil is sufficiently secured. it can. Since the amount of heat generated by the tip coil can be secured, in addition to the effect of any one of claims 1 to 3, rapid temperature rise can be secured.

  According to the glow plug of the fifth aspect, the length in the axial direction from the tip of the tube to the rear end of the tip coil is 6 mm or more and 11 mm or less. Therefore, in addition to the effect of any one of claims 1 to 4, it is possible to easily set the ratio of the resistance value of the tip coil up to 4 mm.

  According to the glow plug of claim 6, since the outer diameter of the tube from the tip of the tube to the position of 4 mm toward the rear end in the axial direction is 3.5 mm or less, the vicinity of the tip of the tube where the tip coil is disposed The heat capacity of the can be prevented from becoming excessive. As a result, in addition to the effects of any one of claims 1 to 5, it is possible to easily ensure rapid temperature rise.

It is a half sectional view of a glow plug. It is sectional drawing of the glow plug which expanded a part. It is a schematic diagram which shows the relationship between the voltage applied to the glow plug, and the heat generation temperature.

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

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

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

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

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

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

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

  The tube 40 has a distal end side of the middle shaft 20 inserted therein. Since the inner diameter of the tube 40 is larger than the outer diameter of the middle shaft 20, a gap is formed between the middle shaft 20 and the tube 40. The sealing material 42 is a cylindrical insulating member sandwiched between the distal end side of the middle shaft 20 and the rear end of the tube 40. The sealing material 42 maintains the space between the middle shaft 20 and the tube 40 and seals between the middle shaft 20 and the tube 40. The coil 50 is accommodated in the tube 40 along the axis O. The insulating powder 60 is filled in the tube 40.

  As shown in FIG. 2, the coil 50 is formed in a spiral shape and generates heat when energized. The coil 50 includes a tip coil 51 joined to the tip 41 of the tube 40 and a rear end coil 52 joined to the tip of the middle shaft 20.

  The tip coil 51 is joined to the tip 41 of the tube 40 by welding at the tip. The material of the tip coil 51 is made of a refractory metal mainly composed of W and Mo. In addition, the simple substance of these elements, or the alloy which has either of these elements as a main component can be used as the front-end | tip coil 51. FIG. The rear end of the front end coil 51 is joined to the rear end coil 52 by welding. Between the front end coil 51 and the rear end coil 52, a molten portion 53 is formed in which the weld metal is melted by welding.

  The rear end coil 52 is a member connected in series with the front end coil 51 through the melting portion 53. The rear end coil 52 is formed of a conductive material having a resistance ratio R2 smaller than the resistance ratio R1 of the front end coil 51. Examples of the material of the rear end coil 52 include an FeCrAl alloy and a NiCr alloy. The rear end coil 52 is accommodated in the tube 40 along the axis O, and the rear end is joined to the front end of the middle shaft 20 by welding. The middle shaft 20 is electrically connected to the tube 40 via the rear end coil 52 and the front end coil 51.

The insulating powder 60 is a powder having electrical insulation properties and thermal conductivity at high temperatures. The insulating powder 60 is filled between the coil 50 and the tube 40, between the middle shaft 20 and the tube 40, and inside the coil 50. The insulating powder 60 has a function of transferring heat from the coil 50 to the tube 40, a function of preventing a short circuit between the coil 50 and the tube 40, and a function of making the coil 50 difficult to vibrate and preventing disconnection. Examples of the insulating powder 60 include oxide powders such as MgO and Al ₂ O ₃ . In addition to oxide powders such as MgO and Al ₂ O ₃ , powders such as CaO, ZrO _2, SiO ₂ and Si can be added. In the present embodiment, the insulating powder 60 contains 85% by mass or more and less than 100% by mass of MgO powder with respect to the total mass of the insulating powder 60, and also contains Si powder.

  The distal end coil 51 includes a first portion 54 from the distal end 41 of the tube 40 to a position 4 mm away from the distal end 41 in the direction of the axis O, and a rear end of the first portion 54 (from the distal end 41 of the tube 40 to the axis O The second portion 55 from the position 4 mm away from the rear end side in the direction) to the melting portion 53. In the tip coil 51, the resistance value at 20 ° C. between the tip 41 of the tube 40 and the rear end (melting portion 53) of the tip coil 51 is set to 0.13Ω or less. The resistance value is a value measured by a four-terminal method.

  In the tip coil 51, the ratio of the resistance value at 20 ° C. of the first part 54 to the resistance value at 20 ° C. between the tip 41 of the tube 40 and the rear end (melting portion 53) of the tip coil 51 is 55 to 80%. The ratio of the resistance value at 20 ° C. of the second part 55 is set to 20 to 45%.

  In the coil 50, the resistance value at 20 ° C. between the distal end 41 of the tube 40 and the rear end of the rear end coil 52 (the welded portion between the rear end coil 52 and the middle shaft 20) is set to 0.36Ω or less. In the present embodiment, the resistance value at 20 ° C. between the distal end 41 of the tube 40 and the rear end of the rear end coil 52 is set to 0.29Ω or more.

  Further, the tip coil 51 adds the length in the axis O direction from the tip 41 of the tube 40 to the melting portion 53, that is, the length in the axis O direction of the first portion 54 and the length in the axis O direction of the second portion 55. The total length is set to 6 mm or more and 11 mm or less.

  In the present embodiment, the tip coil 51 has the same composition from the tip 41 to the melted portion 53 except for the tip 41 of the tube 40 and the weld metal of the melted portion 53, and the pitch on the tip side of the tip coil 51 is reduced. By making the pitch smaller than the end-side pitch, the ratio of the resistance values of the first portion 54 and the second portion 55 is set. Thereby, the structure of the tip coil 51 can be simplified.

  The means for setting the ratio of the resistance values of the first part 54 and the second part 55 is not limited to the means for adjusting the pitch of the tip coil 51. Other means for setting the ratio of the resistance value include, for example, means for making the wire diameter on the front end side of the front end coil 51 smaller than the wire diameter on the rear end side, and 2 made of materials having different specific resistance at 20 ° C. For example, means for joining the two coils in series to form the tip coil 51 and joining the coil having the higher specific resistance to the tip 41 of the tube 40 may be used. Also in these cases, the resistance value on the front end side of the front end coil 51 can be made higher than the resistance value on the rear end side, so that the ratio of the resistance value of the first part 54 can be made larger than the ratio of the resistance value of the second part 55.

  Next, the relationship between the voltage V applied to the glow plug 10 and the heat generation temperature T of the glow plug 10 will be described with reference to FIG. FIG. 3 is a schematic diagram showing the relationship between the voltage V and the heat generation temperature T of the glow plug 10. In FIG. 3, the horizontal axis indicates time (seconds), the solid line indicates the heat generation temperature T, and the broken line indicates the voltage V.

When a voltage V is applied between the connecting portion 21 of the glow plug 10 and the metal shell 30, the voltage V is divided by the sum R ₁ + R ₂ of the resistance value R ₁ of the front end coil 51 and the resistance value R ₂ of the rear end coil 52. Current I flows through the coil 50. The amount of heat generated by the front end coil 51 per unit time is R ₁ · I ² , and the amount of heat generated by the rear end coil 52 per unit time is R ₂ · I ² .

Since the resistance value R ₁ at 20 ° C. of the tip coil 51 is 0.13Ω or less, the current I flowing through the tip coil 51 during heat generation is ensured even if the voltage applied between the connecting portion 21 and the metal shell 30 is not excessive. it can. Therefore, the heat generation amount of the tip coil 51 can be ensured. The coil 50, the resistance value _{R 2} at 20 ° C. of the rear coil 52, (specifically or 0.06Omu) greater than the resistance value _{R 1} at 20 ° C. of the tip coil 51 is set to . This is because the current I (inrush current) flowing through the coil 50 at room temperature is ensured and the coil 50 generates heat.

The rear end coil 52 has a small resistance ratio R2 than the resistance ratio R1 of the tip coil 51, as the temperature rise due to heat generation of the coil 50, the resistance value R ₂ of the resistance value R ₁ is a rear end coil 52 of the tip coil 51 Bigger than. As a result, the heat generation amount R ₁ · I ² per unit time of the front end coil 51 can be made larger than the heat generation amount R ₂ · I ² per unit time of the rear end coil 52.

Since the tip coil 51 is made of a high melting point metal mainly composed of W and Mo, the heat generation temperature T can be increased. In the glow plug 10, the ratio of the resistance value at 20 ° C. of the first portion 54 of the tip coil 51 to the resistance value R ₁ at 20 ° C. of the tip coil 51 is 55 to 80%. The amount of heat generated by the second portion 55 can be made larger. Therefore, the heat generation temperature T of the first portion 54 can be rapidly increased to a desired temperature (for example, 1000 ° C.), and rapid temperature increase performance can be ensured.

  After the heat generation temperature T reaches a desired temperature (1000 ° C. in this case), the voltage V applied to the glow plug 10 is decreased in order to set the heat generation temperature T to a stable saturation temperature (for example, 1100 ° C.). Since the heat generation amount of the rear end coil 52 is smaller than the heat generation amount of the front end coil 51, the heat amount of the front end coil 51 moves to the rear end coil 52 at the time of transition to decrease the voltage V. As a result, the exothermic temperature T, which is highly dependent on the tip coil 51, temporarily decreases by the temperature D. When the temperature D increases and the heat generation temperature T decreases significantly, engine combustion becomes unstable and exhaust gas emissions increase.

  In order to prevent this, in the glow plug 10, the ratio of the resistance value at 20 ° C. of the second portion 55 of the tip coil 51 is set to 20 to 45%. Since the second part 55 generates heat according to the ratio (20 to 45%) of the resistance value with respect to the tip coil 51, when the voltage V is lowered in order to shift to the saturated state, the second part 55 is changed from the first part 54 to the second part. The amount of heat transferred to 55 can be suppressed. Therefore, the temperature drop (temperature D) at the time of transition when the voltage V is lowered to saturate the heat generation temperature T can be suppressed. As a result, it is possible to suppress a decrease in temperature when the voltage V is lowered in order to saturate the heat generation temperature T while securing a high heat generation temperature T and rapid temperature rise. Accordingly, the glow plug 10 assists the combustion of the engine, can stabilize the idle operation of the engine after starting, and can reduce the emission of exhaust gas.

  The glow plug 10 has a resistance value at 20 ° C. between the front end 41 of the tube 40 and the rear end of the rear end coil 52 (coil 50) set to 0.36Ω or less, and therefore flows through the front end coil 51. A current value can be secured. Since the amount of heat generated by the tip coil 51 can be secured, rapid temperature rise can be secured.

  The glow plug 10 can suppress a temperature drop of the first portion 54 when the first portion 54 of the tip coil 51 rapidly generates heat by application of a voltage when entering, and further transitions to a saturated state. Therefore, power saving of the glow plug 10 can be realized.

  Further, since the resistance value at 20 ° C. between the front end 41 of the tube 40 and the rear end of the rear end coil 52 (coil 50) is set to 0.29Ω or more, the current value at the time of inrush can be regulated. As a result, it is possible to prevent an excessive inrush current from flowing to a controller (not shown) that controls the glow plug 10, so that the controller can be protected.

  Note that it is naturally possible to provide a protective resistor separately from the glow plug 10 in order to suppress the inrush current flowing through the controller. When providing a protective resistance, the resistance value of the glow plug 10 at 20 ° C. need not be set to 0.29Ω or more. However, since the protective resistance can be omitted by setting the resistance value of the glow plug 10 at 20 ° C. to 0.29Ω or more, the number of parts can be reduced accordingly.

  The tip coil 51 has a total length obtained by adding the length in the axis O direction from the tip 41 of the tube 40 to the melting portion 53, that is, the length in the axis O direction of the first portion 54 and the length in the axis O direction of the second portion 55. However, it is set to 6 mm or more and 11 mm or less. Thereby, the expansion | deployment length of the front end coil 51 can be set moderately. As a result, the ratio of the resistance value of the first portion 54 to the resistance value of the tip coil 51 can be easily set while preventing the resistance value of the tip coil 51 from becoming excessive.

  Since the insulating powder 60 contains Si powder, the thermal conductivity of the insulating powder 60 can be deteriorated as compared with the case where all of the insulating powder 60 is MgO powder. As a result, the heat dissipation of the first part 54 due to the heat conduction of the insulating powder 60 can be suppressed, so that heat can be generated from the tip 41 of the tube 40 to ensure rapid temperature rise at the time of entry and to suppress the temperature drop at the time of transition. The insulating powder 60 promotes the above.

  The glow plug 10 is manufactured as follows, for example. First, a resistance heating wire having a predetermined composition is processed into a coil shape, and the leading end coil 51 and the trailing end coil 52 are manufactured. Next, the ends of the front end coil 51 and the rear end coil 52 are joined together by welding to form a coil 50. Next, the rear end coil 52 of the coil 50 is joined to the front end of the middle shaft 20.

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

  Next, after filling the heater precursor tube 40 with the insulating powder 60, the sealing member 42 is inserted between the opening at the rear end of the tube 40 and the middle shaft 20 to seal the tube 40. Next, swaging is performed on the tube 40 until the tube 40 has a predetermined outer diameter.

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

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

<Creation of samples 1 to 10>
Using a wire with a wire diameter of Φ0.20 mm made of an alloy containing tungsten as a main component, adjusting the number of turns, pitch, and overall length, the resistance values at 20 ° C. of the first part 54 and the second part 55 are various. A tip coil 51 having a total length of 6 to 11 mm set in proportion was created. Similarly, various rear end coils 52 were formed using a wire made of a NiCr alloy. The rear end coil 52 was joined to the front end coil 51 by welding to create various coils 50 in which the rear end coil 52 and the front end coil 51 were connected in series.

  Using this coil 50, a glow plug having the same structure as the glow plug 10 shown in FIG. 1 was manufactured as described above, and glow plugs in samples 1 to 10 shown in Table 1 were obtained. The glow plugs in Samples 1 to 10 were MgO powder containing 0.2% by mass of Si powder as the insulating powder 60.

  The glow plugs in Samples 1 to 10 have an outer diameter of the tube 40 of Φ3.5 mm or less (that is, the portion of the tube 40 outside the first portion 54 of the coil 50 (from the tip 41 of the tube 40 to the rear end side). The outer diameter of the portion up to a position of 4 mm toward the end was set to φ3.5 mm or less.

各サンプルのチューブ４０の先端４１から軸線Ｏ方向に２ｍｍ離れたチューブ４０の表面の位置にＰＲ熱電対を接合し、チューブ４０の先端４１付近の温度を測定した。なお、ＰＲ熱電対の代わりに放射温度計を用いても良い。

A PR thermocouple was joined to the position of the surface of the tube 40 2 mm away from the tip 41 of the tube 40 of each sample in the axis O direction, and the temperature near the tip 41 of the tube 40 was measured. A radiation thermometer may be used instead of the PR thermocouple.

<Temperature at entry>
A DC voltage of 11 V was applied between the connection portion 21 and the metal shell 30 of each sample, and the temperature near the tip 41 of the tube 40 was measured 2 seconds after the voltage was applied. Evaluation is that samples with a temperature of 900 ° C. or higher are “Excellent: Excellent”, samples with a temperature of 850 ° C. or higher and lower than 900 ° C. are “Excellent”, and samples with a temperature of 800 ° C. or higher and lower than 850 ° C. Samples with “Δ: good” and temperature lower than 800 ° C. were evaluated as “x: inferior”. The results are shown in the column of “Temperature at entry” in Table 1.

<Temperature drop during transition>
A DC voltage is applied for 2 seconds between the connection part 21 of each sample and the metal shell 30 so that the temperature in the vicinity of the tip 41 of the tube 40 after application of the voltage is 1000 ° C. after 2 seconds. Reduced voltage. The applied voltage at this time was a rated voltage at which the temperature near the tip 41 of the tube 40 was saturated to 1100 ° C. When the applied voltage was lowered, the temperature of the tube 40 temporarily decreased and increased toward the saturation temperature of 1100 ° C. over time (see FIG. 3). A temperature difference (temperature D shown in FIG. 3) between the maximum temperature of the tube 40 at the time of rapid temperature rise and the temperature of the tube 40 at the time of transition with the applied voltage lowered was measured.

  Evaluation is that samples with a temperature difference of less than 30 ° C. are “Excellent”, samples with a temperature difference of 30 ° C. or more and less than 50 ° C. are “Excellent”, and the temperature difference is 50 ° C. or more and less than 80 ° C. The samples of “Δ: good” and samples having a temperature difference of 80 ° C. or more were “x: inferior”. The results are shown in the column “Temperature drop during transition” in Table 1.

<Comprehensive evaluation>
A glow plug that can achieve both a high “temperature during entry” and a small “temperature drop during transition” is required. Accordingly, the lower evaluation of the “temperature at entry” and the evaluation of “temperature drop at transition” is shown in the “Comprehensive” column of Table 1.

<Measurement of resistance value>
The tube 40 of each sample whose temperature has been measured is cut open in the direction of the axis O, the insulating powder 60 filled in the tube 40 is removed, and the coil 50 in which both ends are joined to the tip 41 of the tube 40 and the middle shaft 20 is formed. Exposed. The resistance values at 20 ° C. of the following parts (1) to (4) were measured by the four-terminal method. (1) A tip coil 51 between the tip 41 of the tube 40 and the melting part 53, (2) a first part between the tip 41 of the tube 40 and a position 4 mm away from the tip 41 of the tube 40 in the axis O direction. 54, (3) a second portion 55 between a position 4 mm away from the tip 41 of the tube 40 in the direction of the axis O and the melted portion 53, and (4) the tip 41 of the tube 40 and the rear end of the rear end coil 52 (medium shaft). Coil 20 between the tip of 20).

  After the measurement of the resistance value, the ratio of the resistance value at 20 ° C. of the first part 54 to the resistance value at 20 ° C. between the tip 41 of the tube 40 and the rear end (melting part 53) of the tip coil 51, and The ratio of the resistance value of 2 parts 55 at 20 ° C. was determined. The results are shown in Table 1. In addition, the resistance value in 20 degreeC of the coil 50 of all the samples was 0.33 (ohm).

<Result>
As shown in Table 1, in samples 1 to 8 in which the resistance value of the tip coil 51 is 0.13Ω, the ratio of the resistance value of the first part 54 exceeds 80%, and the ratio of the resistance value of the second part 55 is 20%. Samples 1 and 2 of less than% did not satisfy the evaluation criteria of the temperature drop at the time of transition, although the temperature at the time of entry satisfied the evaluation criteria. Since samples 1 and 2 have a small amount of heat generated in the second portion 55, when the applied voltage is lowered, the heat amount in the first portion 54 temporarily decreases due to heat conduction from the first portion 54 to the second portion 55, and the tube It was inferred that the temperature of 40 decreased.

  Samples 7 and 8, in which the ratio of the resistance value of the first part 54 is less than 55% and the ratio of the resistance value of the second part 55 exceeds 45%, the temperature drop during the transition satisfies the evaluation criteria, but the inrush The temperature at the time did not meet the evaluation criteria. It was inferred that samples 7 and 8 cannot secure the amount of heat generation required for rapid temperature increase of the first part 54 because the ratio of the resistance value of the first part 54 is small.

  On the other hand, samples 3 to 6 in which the ratio of the resistance value of the first part 54 is 55% to 80% and the ratio of the resistance value of the second part 55 is 20% to 45% The evaluation criteria for temperature drop were met. It was speculated that Samples 3 to 6 were able to secure the amount of heat necessary for rapid temperature increase of the first part 54 and to suppress the amount of heat transferred from the first part 54 to the second part 55.

  In Samples 9 and 10, the ratio of the resistance value of the first part 54 was 55% and the ratio of the resistance value of the second part 55 was 45%, but the temperature at the time of entry did not satisfy the evaluation criteria. Since the resistance value of the tip coil 51 in Samples 9 and 10 exceeds 0.13Ω, the current value necessary for rapid temperature rise of the tip coil 51 could not be secured with the DC voltage of 11 V applied in this example. Inferred.

  Therefore, it has been clarified that by setting the ratio of the resistance value of the first portion 54 to 55% to 80%, it is possible to suppress the temperature drop during the transition while ensuring the rapid temperature rise. Furthermore, it has been clarified that the heating value can be secured by applying a DC voltage of 11 V by setting the resistance value of the tip coil 51 to 0.13Ω or less. Further, by setting the outer diameter of the portion of the tube 40 from the distal end 41 of the tube 40 to the position of 4 mm toward the rear end side to be Φ3.5 mm or less, the heat capacity in the vicinity of the distal end 41 of the tube 40 does not become excessive. It was found that the rapid temperature rising property can be secured.

<Creation of Samples 11-14>
A tip coil 51 was prepared in the same manner as Sample 3. Various rear end coils 52 were prepared using a wire made of a NiCr alloy. The rear end coil 52 was joined to the front end coil 51 by welding to create various coils 50 in which the rear end coil 52 and the front end coil 51 were connected in series. The resistance value of the coil 50 at 20 ° C. was adjusted by adjusting the number of turns of the rear end coil 52. In addition, the measuring method of resistance value is as having demonstrated about samples 1-10, and measured resistance value after finishing the measurement of the temperature of each sample.

  Using this coil 50, a glow plug having the same structure as the glow plug 10 shown in FIG. 1 was manufactured as described above, and glow plugs in samples 11 to 14 shown in Table 2 were obtained. In addition, the glow plugs in Samples 11 to 14 were MgO powder containing 0.2% by mass of Si powder as the insulating powder 60.

各サンプルのチューブ４０の先端４１から軸線Ｏ方向に２ｍｍ離れたチューブ４０の表面の位置にＰＲ熱電対を接合し、チューブ４０の先端４１付近の温度を測定した。なお、ＰＲ熱電対の代わりに放射温度計を用いても良い。

A PR thermocouple was joined to the position of the surface of the tube 40 2 mm away from the tip 41 of the tube 40 of each sample in the axis O direction, and the temperature near the tip 41 of the tube 40 was measured. A radiation thermometer may be used instead of the PR thermocouple.

<Temperature at entry>
A DC voltage of 11 V was applied between the connection portion 21 and the metal shell 30 of each sample, and the temperature near the tip 41 of the tube 40 was measured 2 seconds after the voltage was applied. Evaluation is as follows: Samples with a temperature of 950 ° C. or higher are “Excellent: Excellent”, Samples with a temperature of 900 ° C. or higher and lower than 950 ° C. are “O: Excellent”, Samples with a temperature of 850 ° C. or higher and lower than 900 ° C. “△: Good”. The results are shown in the column “Temperature at entry” in Table 2.

<Result>
As shown in Table 2, samples 11 to 14 having a resistance value at 20 ° C. of the coil 50 (between the front end 41 of the tube 40 and the rear end of the rear end coil 52) of 0.29Ω to 0.36Ω are resistance. It was confirmed that the temperature increased as the value decreased, and the rapid temperature rise property improved. This is presumably because the current value at the time of inrush flowing through the tip coil 51 increases as the resistance value of the coil 50 at 20 ° C. decreases. As a result, since the amount of heat generated when the tip coil 51 enters can be increased, it is presumed that the rapid temperature rise can be improved.

  The present invention has been described above based on the embodiments and examples. However, the present invention is not limited to the above embodiments and examples, and various modifications can be made without departing from the spirit of the present invention. It is easy to guess that this is possible. For example, the shape of the tube 40 is not particularly limited as long as it is cylindrical, and the cross section orthogonal to the axis O may be circular, elliptical, polygonal, or the like. Further, the wire diameter and diameter of the coil 50 and the thickness and diameter of the tube 40 can be appropriately set in consideration of the heat capacity of the coil 50 and the tube 40 and the like.

  In the embodiment, the case where the entire tube 40 has the same outer diameter except for the portion of the tip 41 has been described. However, the present invention is not necessarily limited thereto. For example, a tube 40 having a different diameter in which the outer diameter of the inner portion of the metal shell 30 in the tube 40 is larger than the outer diameter at a position of 4 mm from the front end 41 toward the rear end side of the tube 40 is adopted. Is of course possible. By adopting a tube 40 of a different diameter with a small outer diameter on the distal end side, the heat capacity on the distal end 41 side of the tube 40 can be reduced, so that rapid temperature rise can be easily ensured.

  Furthermore, since the rear end side of the tube 40 having a larger outer diameter than the tip end 41 side is press-fitted into the metal shell 30, the inner diameter of the metal shell 30 does not have to be reduced according to the outer diameter of the tube 40 on the tip 41 side. . Further, since the tip of the middle shaft 20 is inserted into the rear end side of the tube 40, the diameter of the middle shaft 20 does not have to be reduced according to the inner diameter of the rear end side of the tube 40. That is, since the outer diameter of the middle shaft 20 and the inner diameter of the metal shell 30 can be set regardless of the outer diameter of the tube 40 on the tip 41 side, the degree of freedom in designing the middle shaft 20 and the metal shell 30 can be ensured.

DESCRIPTION OF SYMBOLS 10 Glow plug 20 Medium shaft 40 Tube 41 Front end 50 Coil 51 Front end coil 52 Rear end coil 54 1st part (part)
O axis

Claims (6)

A metal center shaft extending in the axial direction;
A coil electrically connected to the tip of the middle shaft;
A glow plug including a coil and a metal tube that houses the coil and the distal end side of the central shaft, and the coil is electrically connected and the distal end is closed,
The coil has a tip coil that is electrically connected to the tip of the tube and is mainly composed of W or Mo, and a rear end coil that is electrically connected to a rear end of the tip coil. ,
A resistance ratio R1 which is a ratio of a resistance value at 1000 ° C. to a resistance value at 20 ° C. of the front end coil and a resistance ratio which is a ratio of a resistance value at 1000 ° C. to a resistance value at 20 ° C. of the rear end coil R2 satisfies the relationship of R1> R2,
The resistance of the distal end coil and the tube at a position of 4 mm from the distal end of the tube toward the rear end side in the axial direction with respect to the resistance value at 20 ° C. between the distal end of the tube and the rear end of the distal end coil. A glow plug in which the ratio of the resistance value at 20 ° C. to the tip is 55 to 80%.   The glow plug according to claim 1, wherein the resistance value between the tip of the tube and the rear end of the tip coil is 0.13Ω or less.   The glow plug according to claim 1 or 2, wherein the tip coil has the same composition from its tip to the rear end, and a pitch on the front end side is smaller than a pitch on the rear end side.   The glow plug according to any one of claims 1 to 3, wherein a resistance value at 20 ° C between a front end of the tube and a rear end of the rear end coil is 0.36Ω or less.   The glow plug according to any one of claims 1 to 4, wherein an axial length from the tip of the tube to the rear end of the tip coil is 6 mm or more and 11 mm or less.   The glow plug according to any one of claims 1 to 5, wherein an outer diameter of the tube from the tip of the tube to a position of 4 mm toward the rear end side in the axial direction is 3.5 mm or less.

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