JP2017145990A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug capable of easily transmitting heat from a heating element to a tube.SOLUTION: A heating body is electrically connected to a tip of a metal center shaft, and a metal tube whose tip is closed stores the heating body and a tip side of the center shaft. The heating body is electrically connected to a tube. The tube is filled with insulating powder. A particle group arranged at a position opposite to the heating body, out of the insulating powder has at least one maximum value with frequency of 6% within a range of a particle diameter 12 μm or more, in particle size distribution based on a volume measured by a laser diffraction method, and the frequency of a particle diameter of 4-8 μm is within a range of 2.5-6%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a glow plug, and more particularly to a glow plug that can easily transfer heat from a heating element to a tube.

  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 filled in a metal center shaft, a heating element electrically connected to the tip of the center shaft, a metal tube having a closed tip for housing the heating element and the tip side of the center shaft, and the tube. Insulating powder. Since the heating element is electrically connected to the tube, when the current is passed between the central shaft and the tube, the heating element generates heat, and the heat moves to the tube through the insulating powder. In order to improve the fluidity and dust generation of the insulating powder, there are techniques disclosed in Patent Document 1 and Patent Document 2.

JP 63-21706 A Japanese Patent Publication No.2-18560

  However, in order to improve the startability of the internal combustion engine, the glow plug is heated to a predetermined temperature in a short time (hereinafter referred to as “rapid temperature increase”), and the predetermined temperature is set to a high temperature (hereinafter referred to as “rapid temperature increase”). This is called “higher heat generation temperature”. In order to increase the heat generation temperature while ensuring rapid temperature rise, it is necessary to more easily transfer heat from the heating element to the tube.

  The present invention has been made to meet the above-described demand, and an object thereof is to provide a glow plug that can easily transfer heat from a heating element to a tube.

  In order to achieve this object, the glow plug according to claim 1 is configured such that a heating element is electrically connected to a tip of a metal middle shaft, and a metal tube having a closed tip accommodates the heating element and the tip side of the middle shaft. To do. The heating element is electrically connected to the tube. A sealing material is interposed between the tube and the central shaft, and the sealing material seals between the central shaft and the tube. Insulating powder is filled into the tube. In the insulating powder, the particle group arranged at the position facing the heating element has at least one local maximum value with a frequency of 6% or more in a particle size range of 12 μm or more in a volume-based particle size distribution measured by a laser diffraction method. Having a particle size of 4 to 8 μm is 2.5 to 6%.

  A glow plug according to a second aspect of the present invention is the glow plug according to the first aspect, wherein the particle group has an accumulation of a frequency of a particle size of 34 μm or more in the particle size distribution of 4 to 26%.

  A glow plug according to a third aspect of the present invention is the glow plug according to the first or second aspect, wherein in the particle size distribution, the cumulative frequency of the particle size of 1.0 μm or less is 0.1 to 5%.

  According to the glow plug of the first to third aspects, since the packing property of the particle group can be improved, there is an effect that heat can be easily transmitted from the heating element to the tube.

It is a half sectional view of a glow plug. It is sectional drawing of the glow plug which expanded a part. It is an example of the particle size distribution of insulating powder.

  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 heating element 50. These members are assembled along the central 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 heating element 50. A heating element 50 is electrically connected to the tip of the middle shaft 20. 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 includes a shaft hole 31 penetrating along the central axis O, a screw portion 32, and 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.

  As shown in FIG. 2, the heating element 50 (heating coil) is accommodated in the tube 40 along the central axis O, and the tip is joined to the tip 41 of the tube 40 by welding. The heating element 50 is a spiral coil that generates heat when energized. Examples of the material of the heating element 50 include metals such as Fe, Ni, Mo, W, and Co, and alloys containing any one of these elements as a main component. The heating element 50 has a rear end joined to the control coil 51 by welding. Between the heat generating body 50 and the control coil 51, a melted portion 52 is formed which is solidified after being melted by welding.

  The control coil 51 is a member connected in series with the heating element 50 via the melting part 52. The control coil 51 controls the power supplied to the heating element 50 to prevent overheating of the heating element 50. The control coil 51 is made of a conductive material having a temperature coefficient of specific resistance higher than that of the material forming the heating element 50. Examples of the material of the control coil 51 include pure Ni, Ni alloy, and Co alloy. The control coil 51 is accommodated in the tube 40 along the central 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 control coil 51 and the heating element 50.

  The insulating powder 60 is a powder having electrical insulation properties and thermal conductivity at high temperatures, between the heating element 50 and the tube 40, between the control coil 51 and the tube 40, and between the middle shaft 20 and the tube 40. Between the control coil 51 and the heating element 50. The insulating powder 60 has a function of transferring heat from the heating element 50 to the tube 40, a function of preventing a short circuit between the heating element 50 and the control coil 51, and the tube 40, and making the heating element 50 and the control coil 51 difficult to vibrate and breaking the wire. There is a function to prevent.

Examples of the insulating powder 60 include oxide powders such as MgO and Al ₂ O ₃ . The insulating powder 60 preferably contains at least one of these oxide powders, and more preferably contains MgO powder in that the desired thermal conductivity can be maintained among these oxide powders. preferable. The insulating powder 60 preferably contains 85% by mass or more and 100% by mass or less of MgO powder with respect to the total mass of the insulating powder 60, more preferably 99% by mass or more and less than 100% by mass, and the balance is Al _2. O ₃ powder or other materials may be included. Examples of other substances include powders such as CaO, ZrO ₂ and SiO ₂ .

  The components contained in the insulating powder 60 (first particle group 61) and the content thereof can be obtained as follows. First, the component contained in the 1st particle group 61 is grasped | ascertained by conducting the qualitative analysis of the 1st particle group 61 by the powder X-ray diffraction method etc. Next, the elements contained in the first particle group 61 are quantitatively analyzed by ICP emission spectroscopy. When the component contained in the first particle group 61 is known to be an oxide by qualitative analysis, the content of the element obtained by quantitative analysis is converted into an oxide, and the content of the oxide Can be sought. In addition, when it is known from the qualitative analysis that the main component of the first particle group 61 is MgO, the components other than MgO are analyzed by ICP emission spectroscopy, and the MgO content is obtained as the remainder. be able to.

  The insulating powder 60 includes a first particle group 61 and a second particle group 62. The first particle group 61 is a plurality of particles arranged at positions facing the heating element 50, and specifically, is filled between the heating element 50 and the tube 40 and inside the heating element 50. A plurality of particles (below the broken line D in FIG. 2). The second particle group 62 is a plurality of particles filled between the control coil 51 and the tube 40, between the middle shaft 20 and the tube 40, and inside the control coil 51 (above the broken line D in FIG. 2). ).

  The first particle group 61 (particle group) is a plurality of particles for transferring heat from the heating element 50 to the tube 40. The first particle group 61 has a volume-based particle size distribution measured by a laser diffraction method. The particle size distribution of the first particle group 61 will be described with reference to FIG. FIG. 3 is an example of a volume-based particle size distribution of the insulating powder 60 (first particle group 61) measured using a laser diffraction particle size distribution measuring apparatus (HORIBA LA-750, manufactured by Horiba, Ltd.). FIG. 3 is plotted with the particle size (μm) on the horizontal axis and the frequency (%) on the vertical axis.

  As shown in FIG. 3, the first particle group 61 has at least one local maximum value 72 having a frequency of 6% or more in a range 71 having a particle size of 12 μm or more in a volume-based particle size distribution measured by a laser diffraction method. The frequency of particle sizes of 4-8 μm is all in the range 73 of 2.5-6%. Thereby, the packing density of the 1st particle group 61 can be raised and the porosity can be reduced. Since the thermal conductivity of the distal end side of the tube 40 (portion facing the heating element 50) can be increased, heat can be easily transferred from the heating element 50 to the tube 40 by heat conduction and heat transfer. Since the amount of heat generated at the distal end side of the tube 40 can be increased, the heat generation temperature can be increased while ensuring rapid temperature rise. Since the surface temperature of the tube 40 can be rapidly increased to a higher temperature without flowing a large current through the heating element 50, it is particularly suitable for an internal combustion engine that requires improved startability.

  Here, when there is no local maximum value with a frequency of 6% or more in the range 71 having a particle diameter of 12 μm or more, the ratio of particles having a particle diameter of less than 12 μm is large (relative particle amount with the whole being 100%). The number of particles present between 50 and the tube 40 increases. Since the boundary surface between the particles in contact with each other becomes a barrier for heat conduction, the number of particles existing between the heating element 50 and the tube 40 increases, so that the number of particles is small (the barrier is small). Compared to the case, there is a tendency that heat is not easily transmitted by heat conduction. By defining the particle size distribution of the first particle group 61, this can be prevented and heat can be easily transmitted.

  The maximum value 72 does not have to be a sharp peak as shown in FIG. 3, and may be a broad peak. Since at least one local maximum value 72 needs to be within the range 71, a plurality of broad peaks may exist within the range 71. This is because in any case, the proportion of particles having a particle size of 12 μm or more can be secured.

  In the range 71, the upper limit of the particle size is preferably 40 μm (that is, the particle size is 12 to 40 μm). When the maximum value of frequency 6% or more exists in a range exceeding the particle size of 40 μm, the ratio of particles having a large particle size is large, so that the gap between the filled particles is increased and the packing density of the first particle group 61 is increased. May be reduced. When the packing density of the first particle group 61 is reduced, the heating element 50 is likely to vibrate, and thus the heating element 50 may be easily disconnected. By making the maximum value having a frequency of 6% or more in the range of the particle diameter of 12 to 40 μm, it is possible to prevent the heating element 50 from being disconnected while facilitating heat transfer.

  In the range 71, the upper limit of the frequency is preferably 9% (that is, the frequency is 6 to 9%). Even when there is a maximum value exceeding 9% in the range of the particle size of 12 μm or more, since the ratio of particles having a large particle size is large, the gap between the filled particles is increased and the packing density of the first particle group 61 is increased. May be reduced. Also in this case, the heating element 50 is likely to vibrate, and the heating element 50 may be easily disconnected. By making the maximum value having a frequency of 6 to 9% in the range of the particle diameter of 12 μm or more, disconnection of the heating element 50 can be prevented while facilitating heat transfer.

  Even if at least one local maximum value 72 having a frequency of 6% or more is present in the range 71 having a particle diameter of 12 μm or more, if at least a part of the frequency of the particle diameter of 4 to 8 μm is less than 2.5%, the particle size 4 The ratio of small particles having a particle diameter of less than ˜8 μm increases, or the ratio of particles having a large particle diameter of 12 μm or more increases. In the former case, since the particle size of the particles filling the gaps between the particles generated by filling the particles having a particle size of 12 μm or more is small, the number of particles existing between the heating element 50 and the tube 40 is large. It becomes difficult to transfer heat by heat conduction. In the latter case, since the ratio of particles having a large particle size increases, there is a possibility that the gap between the filled particles increases and the packing density of the first particle group 61 decreases. When the packing density of the first particle group 61 is reduced, the heating element 50 is likely to vibrate, and thus the heating element 50 may be easily disconnected.

  Even if it has at least one maximum value 72 with a frequency of 6% or more in the range 71 with a particle size of 12 μm or more, if at least part of the frequency of the particle size of 4-8 μm exceeds 6%, the particle size is less than 4-8 μm The ratio of particles having a small particle diameter is reduced, or the ratio of particles having a large particle diameter of 12 μm or more is decreased. In the former case, it is difficult to fill the gaps between the particles, which are generated by filling the particles having a particle diameter of 12 μm or more, so that the packing density of the first particle group 61 may be lowered. When the packing density of the first particle group 61 is reduced, the heating element 50 is likely to vibrate, and thus the heating element 50 may be easily disconnected. In the latter case, the number of particles existing between the heating element 50 and the tube 40 increases, and heat is hardly transmitted by heat conduction.

  Therefore, by setting the frequency of the particle size of 4 to 8 μm to 2.5 to 6%, it is possible to prevent disconnection of the heating element 50 while making it easy to transmit heat.

  Further, in the first particle group 61, the integration 74 of the frequency of the particle size of 34 μm or more is 4 to 26%. By setting the ratio of the large particles to such a predetermined amount, it is possible to prevent the number of particles existing between the heating element 50 and the tube 40 from excessively increasing or decreasing. Therefore, the number of heat barriers can be reduced by reducing the number of particles existing between the heating element 50 and the tube 40, and it is possible to prevent heat from being easily transferred from the heating element 50 to the tube 40. Moreover, since the porosity (gap ratio) of the first particle group 61 can be reduced, disconnection of the heating element 50 can be prevented.

  As for the 1st particle group 61, the integration | accumulation 75 of the frequency of a particle size of 1.0 micrometer or less is 0.1 to 5%. By setting the ratio of particles having a particle diameter of 1.0 μm or less to such a predetermined amount, the porosity of the first particle group 61 can be reduced, and disconnection of the heating element 50 can be prevented. Further, by reducing the number of particles existing between the heating element 50 and the tube 40, the heat barrier can be reduced, and it is possible to prevent the heat from being easily transmitted from the heating element 50 to the tube 40.

  The D50 (50% particle diameter or median diameter) of the first particle group 61 is preferably 10 to 20 μm. If D50 of the first particle group 61 is 10 to 20 μm, heat is generated from the heating element 50 to the tube 40 when the maximum value 72, the range 73, and the integrals 74 and 75 of the first particle group 61 become the specified values. This is because it can be transmitted more easily. The frequency from the particle size 8 μm to the maximum value of the first particle group 61 is preferably 2.5% or more. This is because heat is more easily transferred from the heating element 50 to the tube 40.

  As the second particle group 62, a particle group having the same particle size distribution as that of the first particle group 61 can be used. As the second particle group 62, a particle group having a particle size distribution different from the particle size distribution of the first particle group 61 may be used. This is because the second particle group 62 is a particle group that is filled around the control coil 51, so that the requirement for the function of transferring heat to the tube 50 is low.

  The particle size distribution of the first particle group 61 can be measured as follows using a laser diffraction particle size distribution measuring device (HORIBA LA-750). First, the insulating powder 60 (first particle group 61) is taken out from the glow plug 10 to prepare a measurement sample. Specifically, first, the tube 40 is cut along a plane orthogonal to the central axis O and including the vicinity of the melting portion 52. After cutting the tube 40, the heating element 50 inside the tube 40 on the tip 41 side is pulled out from the tube 40, the shock is applied to the heating element 50, and particles (first particles) clogged inside the heating element 50 (heating coil). Remove group 61). Similarly, an impact is applied to the tube 40 and the particles (first particle group 61) in the tube 40 are taken out.

  Since the taken out particles (first particle group 61) are aggregated into a lump, the lump is crushed with a mortar. Since the particles are hard, it has been confirmed that the particles (primary particles) are not pulverized even if the first particle group 61 is rubbed using a mortar and a mortar held in the hand, and the measurement results are not affected. Impurities are removed while observing the particles (first particle group 61) after mortaring with a magnifier. Thus, 0.35 g or more of the sample of the first particle group 61 is prepared for one measurement.

  Next, the prepared sample of the first particle group 61 (for example, 2 to 4 cups of spatula) is dispersed in a dispersion medium (for example, 150 cc of a sodium hexametaphosphate 0.2% by mass solution). Examples of the method for dispersing the sample include a method of stirring for 3 minutes with an external homogenizer and then stirring for 2 minutes with an ultrasonic probe built in the laser diffraction particle size distribution measuring apparatus. Using a laser diffraction type particle size distribution measuring device, the particle size distribution of the sample dispersed in the dispersion medium is measured, the frequency distribution is 0.1 to 100 μm in particle size, the cumulative distribution (on the sieve) is 34 μm or more, the particle size An integrated distribution (under a sieve) of 1 μm or less is obtained. The particle size distribution is measured three times, and the obtained value is an average value of the three measurements.

  The first particle group 61 may exist as primary particles or as secondary particles. The first particle group 61 may be present in any form of primary particles and secondary particles, but is preferably present as primary particles. When the particles included in the first particle group 61 are present as secondary particles, there are a large number of voids in the secondary particles, so that these voids serve as a heat insulating layer (barrier) and the heat transfer of the first particle group 61 May decrease. MgO usually exists as primary particles without forming secondary particles. Therefore, also in this respect, the particles constituting the first particle group 61 are preferably MgO powder.

  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 a heating element (heating coil) 50 and a control coil 51 are manufactured. Next, the ends of the heating element 50 and the control coil 51 are joined together by arc welding or the like to obtain a coil member. Next, the control coil 51 of the coil members is joined to the tip 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. A coil member integrated with the central shaft 20 is inserted into the tube precursor, and the tip of the heating element 50 is disposed in the tapered opening of the tube precursor. The opening portion of the tube precursor and the tip portion of the heating element 50 are melted by arc welding or the like, the tip portion of the tube precursor is closed, and a heater precursor in which a coil member 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. The insulating powder 60 filled in the tube 40 is crushed and undergoes a change in particle size through a swaging process. Therefore, in consideration of the reduction rate of the outer diameter of the tube 40 when performing the swaging process, the first particle group 61 arranged around the heating element 50 is subjected to the swaging process (after the particles are crushed by the swaging). The tube 40 is filled with the insulating powder 60 so as to have a predetermined particle size distribution.

  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.

<Manufacture of glow plug and analysis of first particle group>
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 Experimental Examples 1 to 16 were obtained. In the glow plugs in Experimental Examples 1 to 16, MgO powder was used as insulating powder 60. The particle size of the first particles 61 (after filling) in each experimental example is adjusted before and after the swaging process in the manufacturing process of the glow plug 10 and the preparation of the particle size distribution of the insulating powder 60 filled in the tube 40 (before filling). The tube 40 was prepared by adjusting the reduction rate of the outer diameter.

  Using a laser diffraction particle size distribution measuring device (HORIBA LA-750), the volume-based particle size distribution of the first particle group 61 filled in the tube 40 of each experimental example is measured as described above, and the maximum value is obtained. The frequency of the particle size of 4 to 8 μm, the integration of the frequency of the particle size of 1.0 μm or less, and the integration of the frequency of the particle size of 34 μm or more were obtained. In addition, as a dispersion medium when analyzing the sample of the 1st particle group 61, 150 cc of sodium hexametaphosphate 0.2 mass% solutions were used. The sample was dispersed by stirring for 3 minutes with an external homogenizer, and then stirring for 2 minutes with an ultrasonic probe built in the laser diffraction particle size distribution analyzer. The particle size distribution of the sample was measured three times, and the average value of the three measured values obtained was determined.

In addition, about the glow plug in Experimental Examples 1-16, the component contained in the 1st particle group 61 and its content rate were measured as mentioned above by the powder X-ray diffraction method and ICP emission spectroscopy. All contained 99.4% by mass of MgO as a main component and 0.6% by mass of CaO, ZrO ₂ and SiO ₂ in total. Moreover, when the 1st particle group 61 was observed with the scanning microscope (1000 times), it was observed that particle | grains existed as a primary particle.

<Energization test>
The heat mobility (easy heat transfer) of the first particle group 61 is the difference (T1) between the temperature of the heating element 50 (hereinafter referred to as “T1”) and the surface temperature of the tube 40 (hereinafter referred to as “T2”). -Based on -T2). Specifically, a voltage difference is applied between the central shaft 20 and the metal shell 30 so that T2 becomes 1000 ° C. 2 seconds after energization, and a temperature difference between T1 and T2 2 seconds after energization. When the temperature difference between T1 and T2 is greater than 100 ° C and greater than 120 ° C, and when the temperature difference between T1 and T2 is greater than 120 ° C. ×: Inferior ”.

The temperature (T1) of the heating element 50 was measured by a thermocouple arranged at a position corresponding to the heating element 50. The thermocouple was disposed inside the heating element 50 when the glow plug in each experimental example was manufactured (before the heating element 50 was inserted into the tube 40). The thermocouple is disposed on the central axis O of the heating element 50 and at a position 2.0 mm away from the tip 41 in the direction of the central axis O.
The surface temperature (T2) of the tube 40 was measured by a thermocouple attached to the tube 40. The thermocouple was attached to the tube 40 after the glow plug in each experimental example was manufactured. The thermocouple is attached at a position 2.0 mm away from the tip 41 of the tube 40 in the direction of the central axis O.

  Table 1 shows the results of the analysis of the first particle group 61 of the glow plug and the current test in Experimental Examples 1 to 16. Table 1 shows the analysis results of the first particle group 61: “maximum particle size, frequency and determination result”, “frequency of particle size 4 μm, frequency of particle size 8 μm, and determination of frequency of particle size 4 to 8 μm. “Results”, “Results of determination of integration of frequency of particle size of 1.0 μm or less”, and “Results of determination of integration of frequency of particle size of 34 μm or more”.

  In Table 1, the determination result of the maximum value is OK when the particle size is 12 μm or more and the maximum value is 6% or more, and when the maximum value is less than 12 μm or the frequency is less than 6%. Is marked with NG. The determination result of the frequency of the particle size 4 to 8 μm is OK when the frequency of the particle size 4 to 8 μm is in the range of 2.5 to 6%, and NG when the frequency is out of the range. If the integrated value is within the range of 0.1 to 5%, the determination result for the frequency with a particle size of 1.0 μm or less is OK. If the integrated value is out of the range, which side is the integrated value? (<0.1% or> 5%). The determination result of the frequency integration with a particle size of 34 μm or more is OK when the integrated value is in the range of 4 to 26%, and on which side the integrated value is on the side when the integrated value is out of the range (<4 % Or> 26%).

  As shown in Table 1, in the particle size distribution of the first particle group 61, there is a maximum value of frequency 6% or more in the range of particle size 12 μm or more, and the frequency of particle size 4-8 μm is 2.5-6%. In Experimental Examples 1 to 8, the result of the energization test was “◎: excellent” or “◯: good” (temperature difference (T1-T2) is 120 ° C. or less). In particular, among Experimental Examples 1 to 8, Experimental Example 1 to which the cumulative frequency of the particle size of 1.0 μm or less is 0.1 to 5% and the cumulative frequency of the particle size of 34 μm or more is 4 to 26%. For No. 4, the result of the energization test was “◎: excellent” (temperature difference (T1-T2) is 100 ° C. or less).

  On the other hand, there is no maximum value with a particle size of 12 μm or more and a frequency of 6% or more (particle size is less than 12 μm, or there is a maximum value with a frequency of less than 6%). In Experimental Examples 11 to 16 where the frequency is out of the range of 2.5 to 6%, the result of the energization test was “x: inferior” (temperature difference (T1-T2) is greater than 120 ° C.) .

  According to this embodiment, in the volume-based particle size distribution of the first particle group 61, there is a maximum value of 6% or more in the range of the particle size of 12 μm or more, and the frequency of the particle size of 4 to 8 μm is 2. Since the heat mobility of the first particle group 61 becomes good when it is 5 to 6%, the surface temperature of the tube 40 can be rapidly raised to a higher temperature without flowing a large current through the heating element 50. I understand.

  In the volume-based particle size distribution of the first particle group 61, there is a maximum value of frequency 6% or more in the range of particle size 12 μm or more, and the frequency of particle size 4-8 μm is 2.5-6%, Furthermore, the heat mobility of the first particle group 61 is such that the integration of the frequency of the particle size of 1.0 μm or less is 0.1 to 5% and the integration of the frequency of the particle size of 34 μm or more is 4 to 26%. Therefore, it can be seen that the surface temperature of the tube 40 can be rapidly increased to a higher temperature without flowing a large current through the heating element 50.

  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 central axis O may be circular, elliptical, polygonal, or the like.

  In the above embodiment, the case where the heating element 50 is made of a spiral coil has been described. However, the present invention is not necessarily limited thereto. The shape of the heating element 50 is not particularly limited as long as it is a resistor that generates heat when energized.

  In the embodiment described above, the control coil 51 that prevents the heating element 50 from overheating has been interposed between the heating element 50 and the middle shaft 20. However, the present invention is not necessarily limited thereto, and it is naturally possible to omit the control coil 51 and directly join the heating element 50 to the middle shaft 20. In addition, instead of the control coil 51, it is naturally possible to connect a rear end coil in series between the heating element 50 and the middle shaft 20. Fe-Cr-Al, Ni-Cr, or the like can be used as the material for the rear end coil. Also in this case, the first particle group 61 is disposed at a position facing the heating element 50.

DESCRIPTION OF SYMBOLS 10 Glow plug 20 Middle shaft 40 Tube 42 Sealing material 50 Heat generating body 60 Insulating powder 61 1st particle group (particle group)
71 Range 72 Maximum value 74,75 Total

Claims (3)

A metal shaft,
A heating element electrically connected to the tip of the middle shaft;
A metal tube containing the heating element and the distal end side of the middle shaft, the tip of which is electrically connected to the heating element and closed;
A sealing material interposed between the tube and the central shaft;
Insulating powder filled in the tube sealed with the sealing material between the middle shaft,
In the insulating powder, the particle group arranged at a position facing the heating element has at least one local maximum of frequency 6% or more in a particle size range of 12 μm or more in a volume-based particle size distribution measured by a laser diffraction method. A glow plug having a value and a frequency of 4 to 8 μm and a frequency of 2.5 to 6%.   2. The glow plug according to claim 1, wherein in the particle size distribution, the accumulation of the frequency of the particle size of 34 μm or more is 4 to 26% in the particle size distribution.   3. The glow plug according to claim 1, wherein the particle group has an accumulation of a frequency of a particle size of 1.0 μm or less in the particle size distribution of 0.1 to 5%.