WO2019102708A1 - Glow plug - Google Patents

Abstract

The purpose of the present invention is to minimize power consumption while achieving a rapid increase in power. A glow plug (1) according to the present invention is characterized in comprising a ceramic heater (10) that has an electroconductive ceramic (11) and an insulating ceramic (16) that covers the electroconductive ceramic (11); the electroconductive ceramic (11) having a heat generation portion (12) disposed at the distal end, and a lead (14) connected to the rear end of the heat generation unit (12); and the thinnest portion (16a) of the insulating ceramic (16), at which the heat generation unit (12) and the outer peripheral surface of the insulating ceramic (16) are closest to each other in a cross-section perpendicular to the axis of the ceramic heater (10), measures 0.5 to 0.7 mm in thickness.

Description

Glow plug

TECHNICAL FIELD The present invention relates to a glow plug used as a start aid for an internal combustion engine such as a diesel engine.

A ceramic heater glow plug is known as a glow plug used for starting assistance of a diesel engine. Such a ceramic heater glow plug includes a ceramic heater and an outer cylinder that accommodates part of the ceramic heater such that at least the tip is exposed. The ceramic heater has a heat generating portion disposed at the front end of the heater and a lead connected to the rear end of the heat generating portion and having a resistivity lower than that of the heat generating portion. The heat generating portion and the leads are made of insulating ceramic It is covered. Further, the outer peripheral surface of the ceramic heater and the inner peripheral surface of the outer cylinder are electrically connected via a joint such as brazing (see, for example, Patent Document 1).

JP 2002-334768 A

By the way, in recent years, it has been desired to rapidly raise the temperature in the combustion chamber at the start of the internal combustion engine. However, in order to rapidly raise the temperature of the ceramic heater, for example, a large current may be supplied to the heat generating portion through the lead at the initial stage of energization to cause the heater to rapidly rise in temperature, resulting in large power consumption.

In the conventional ceramic heater, in order to achieve rapid temperature rise and power consumption reduction of the ceramic heater, insulation between the outer peripheral surface of the insulating ceramic in the ceramic heater and the conductive ceramic embedded in the insulating ceramic No consideration was given to the thickness of the ceramic. It is considered that reducing the thickness of the insulating ceramic is effective for rapid temperature rise. However, the aging of the insulating ceramic may expose the heat-generating portion inside, so the thickness may be simply reduced.

In addition, since the joint portion between the ceramic heater and the outer cylinder is formed of, for example, a high thermal conductivity brazing material, heat is easily transmitted from the ceramic heater to the outer cylinder. That is, heat tends to escape from the ceramic heater through the bonding portion, and focusing on this point, rapid heating and power consumption reduction with respect to the position of the heat generating portion in the ceramic heater, the bonding range of the ceramic heater and the outer cylinder, etc. It was not considered from the

Then, this invention is made in view of the said subject, and it aims at providing the glow plug which can suppress power consumption, achieving rapid temperature rise.

In order to achieve the above object, the present invention comprises a ceramic heater having a conductive ceramic and an insulating ceramic covering the conductive ceramic, wherein the conductive ceramic has a heat generating portion disposed at a tip thereof. And a lead connected to a rear end of the heat generating portion, wherein the insulating ceramic has a thickness of a thinnest portion where the outer peripheral surface and the heat generating portion are closest to each other in a cross section perpendicular to the axis of the ceramic heater. Is 0.5 to 0.7 mm.

The thickness of the thinnest portion is preferably 0.57 to 0.66 mm.

Preferably, the outer peripheral surface of the insulating ceramic is in a cylindrical shape having a diameter of 2.9 to 3.1 mm.

Moreover, it is preferable that the axial direction length from the front end of the said insulating ceramics to the rear end of the said heat-emitting part is 4.5 mm or less.

　を満たすことを特徴とする。 In order to achieve the above object, the present invention further provides a ceramic heater having a conductive ceramic and an insulating ceramic covering the conductive ceramic, and a part of the ceramic heater such that at least the tip is exposed. And an outer cylinder in which the inner peripheral surface is joined to the outer peripheral surface of the ceramic heater via the bonding portion, and the conductive ceramic includes a heat generating portion disposed at the tip and a rear portion of the heat generating portion And an axial length from the tip of the insulating ceramic to the rear end of the heat generating portion is a first length A, the junction from the tip of the insulating ceramic Assuming that the axial length to the tip of the joint is a second length B, and the axial length of the joint is a third length C, the following equation 1 and equation 2

It is characterized by satisfying.

　を満たすことが好ましい。 Also, the following Equation 3 and Equation 4

It is preferable to satisfy

According to the present invention, power consumption can be suppressed while achieving rapid temperature rise.

It is sectional drawing for demonstrating the structure of the glow plug which concerns on this Embodiment. FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. FIG. 3 is a cross-sectional view taken along the line III-III shown in FIG.

Preferred embodiments of the present invention will be described with reference to the drawings. Note that the embodiment shown below is one example, and various embodiments can be taken within the scope of the present invention. FIG. 1 is a cross-sectional view for explaining the configuration of the glow plug. FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. FIG. 3 is a cross-sectional view taken along the line III-III shown in FIG.

The glow plug 1 is, for example, a ceramic heater type glow plug, and as shown in FIG. 1, accommodates the ceramic heater 10 and a part of the ceramic heater 10 so that at least the tip is exposed and the outer peripheral surface of the ceramic heater 10 And a metal outer cylinder 20 whose inner circumferential surface is joined via the joint portion 21, and a housing 30.

The ceramic heater 10 assists the start of the internal combustion engine, and is disposed in the combustion chamber (pre-combustion chamber in the case of a pre-combustion internal combustion engine, combustion chamber of the internal combustion engine in the case of a direct injection internal combustion engine). The tip is inserted and fixed to the housing 30 via the outer cylinder 20. The ceramic heater 10 is formed of a ceramic.

The ceramic heater 10 has a conductive ceramic 11 and an insulating ceramic 16 covering the conductive ceramic 11.

The conductive ceramic 11 is heated in the glow plug 1 by energization, and has a heat generating portion 12 formed in a U shape disposed at the tip, and a lead 14 connected to the rear end of the heat generating portion 12; Have. The shape of the heat generating portion 12 is not particularly limited in a cross-sectional view perpendicular to the axis x of the ceramic heater 10, and may take various shapes such as a circle, an ellipse, an oval, and a polygon.

The heat generating portion 12 has a pair of extending portions 12a and 12b extending in parallel to each other along the axis x of the ceramic heater 10, and a curved portion 12c connecting the extending portions 12a and 12b. Heating unit 12 is located within the range of 4.5mm from the tip of the insulating ceramic 16, having dimensions of length _{l 1} of 3.5mm along the axis x of the ceramic heater 10.

The heat generating portion 12 is a heat generating resistor having high resistance to the lead 14, and is made of conductive ceramic. The heat generating portion 12 is formed of, for example, a material containing carbide, nitride, silicide or the like as a main component including tungsten (W), molybdenum (Mo), titanium (Ti) or the like. It is preferable that the heat generating portion 12 particularly contain tungsten carbide (WC) having inorganic heat conductivity in that it has high heat resistance and low specific resistance.

The heat generating portion 12 preferably contains silicon nitride (Si ₃ N ₄ ) in addition to the above main component, and the content of silicon nitride (Si ₃ N ₄ ) is preferably 20% by mass or more. For example, since the conductor component to be the heat generating portion 12 has a thermal expansion coefficient larger than that of silicon nitride (Si ₃ N ₄ ) in the insulating ceramic 16 containing silicon nitride ceramics, a tensile stress is usually applied. It is in. On the other hand, by adding silicon nitride (Si ₃ N ₄ ) into the heat generating portion 12, the thermal expansion coefficient is made close to the thermal expansion coefficient of the insulating ceramic 16, and the temperature rise and temperature drop of the ceramic heater 10. The stress due to the difference in the coefficient of thermal expansion can be relaxed.

When the content of silicon nitride (Si ₃ N ₄ ) contained in the heat generating portion 12 is 40% by mass or less, the resistance value of the heat generating portion 12 can be made relatively small and stable. Therefore, the content of silicon nitride (Si ₃ N ₄ ) contained in the heat generating portion 12 is preferably 20 to 40% by mass. More preferably, the content of silicon nitride (Si ₃ N ₄ ) is 25 to 35% by mass.

As a similar additive to the heat generating portion 12, 4 to 12% by mass of boron nitride (BN) may be added instead of silicon nitride (Si ₃ N ₄ ). Furthermore, in the heat generating portion 12, elements of the fourth, fifth, sixth, seventh and eighth groups of the fourth period of the periodic table of the elements (titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron ( At least one of Fe)) may be contained.

For example, the content of elements of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) in the heat-generating portion 12 is preferably 0.5 mol% or less.

The lead 14 is connected at its front end to the rear end of the heat generating portion 12 and exposed at its rear end from the insulating ceramic 16. The lead 14 includes a positive electrode lead 14 a and a negative electrode lead 14 b.

The positive electrode side lead 14 a and the negative electrode side lead 14 b are each formed of a conductive ceramic having low resistance to the heat generating portion 12. The positive electrode lead 14 a and the negative electrode lead 14 b extend in parallel with each other along the axis x of the ceramic heater 10. The positive electrode lead 14a and the negative electrode lead 14b are connected to both ends of the extension portions 12a and 12b of the heat generating portion 12 extending in a U-shape.

The positive electrode side lead 14 a is connected to the extending portion 12 a of the heat generating portion 12 at the tip. The positive electrode side lead 14 a extends inside the insulating ceramic 16 to the rear end of the insulating ceramic 16. The positive electrode side lead 14 a is exposed from the insulating ceramic 16 at the rear end of the ceramic heater 10 and is electrically connected to the lead wire 115 through the cap-like connection portion 114.

The negative electrode lead 14 b has an exposed portion 14 c which is connected to the extending portion 12 b of the heat generating portion 12 at its front end and partially exposed to the outer peripheral surface of the insulating ceramic 16 at its rear end. The exposed portion 14 c of the lead 14 is joined to the inner peripheral surface of the outer cylinder 20 by brazing or the like via a joining portion 21 described later. The lead 14 is electrically connected to the outer cylinder 20 formed of a conductive metal material through the exposed portion 14 c. The exposed portion 14c of the lead 14 functions as a negative electrode.

The lead 14 preferably contains tungsten carbide (WC), which is an inorganic conductor, as a main component, to which silicon nitride (Si ₃ N ₄ ) is preferably added so as to have a content of 15% by mass or more. As the content of silicon nitride (Si ₃ N ₄ ) increases, the thermal expansion coefficients of the positive electrode lead 14 a and the negative electrode lead 14 b approach the thermal expansion coefficient of silicon nitride (Si ₃ N ₄ ) contained in the insulating ceramic 16. be able to.

When the content of silicon nitride is 40% by mass or less, the resistances of the positive electrode lead 14a and the negative electrode lead 14b are reduced and stabilized. Therefore, the content of silicon nitride (Si ₃ N ₄ ) is preferably 15 to 40% by mass. More preferably, the content of silicon nitride (Si ₃ N ₄ ) is 20 to 35% by mass.

Furthermore, in the lead 14, an element (titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), group 4, 5, 6, 7, 8 of the 4th period of the element periodic table) )) May contain at least one oxide and / or nitride. For example, the content of the elements of titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), and iron (Fe) in the lead 14 is preferably 0.5 mol% or less.

The lead 14 is preferably a mixture containing, for example, a rare earth element compound such as chromium oxide (Cr ₂ O ₃ ) of about several tens of PPM, and is a sintered body formed by sintering.

The lead 14 is formed of the same material as the heat generating portion 12, but, for example, the lead 14 contains more of the forming material than the heat generating portion 12 or has a larger cross-sectional area than the heat generating portion 12. The resistance per unit length is low.

The insulating ceramic 16 is, for example, a sintered body having a cylindrical outer peripheral surface formed by sintering. The insulating ceramic 16 covers the conductive ceramic 11. More specifically, the insulating ceramic 16 covers the heat generating portion 12 and the lead 14. In other words, the heat generating portion 12 and the lead 14 are embedded in the insulating ceramic 16.

The insulating ceramic 16 has a diameter d of 2.9 to 3.1 mm and a cylindrical outer peripheral surface, and in particular, the diameter d is preferably 2.9 mm. Here, "the diameter d of the insulating ceramic 16" is the diameter at the portion of the cylindrical outer peripheral surface, and the diameter at the dome-shaped portion is excluded. Incidentally, the tip of the curved portion 12c of the heat generating portion 12, the distance between the tip of the insulating ceramic 16 (length) _{l 2} is about 0.97 mm.

Insulating ceramic 16, the thin part thickness t ₁ of the (the thinnest portion) 16a of the extending portion 12a of the outer peripheral surface and the heating portion 12, and a 12b closest of insulating ceramics 16 in the axial x perpendicular cross section It is in the range of 0.5 to 0.7 mm. The thickness _{t 1} of the thin portion 16a is more preferably a 0.57 ~ 0.66 mm.

Here, in the present embodiment, “closest” means the outer peripheral surface of the insulating ceramic 16 and the extending portions 12 a and 12 b of the heat generating portion 12 (here, the outer peripheral surfaces of the extending portions 12 a and 12 b). the thickness _{t 1} of the thin portion 16a of the insulating ceramic 16 between which means that in the range of 0.5 ~ 0.7 mm. Thinned portion 16a, as shown in FIG. 2, in a cross section perpendicular to the axis x, the thickness t ₁ of the shortest distance to the outer peripheral surface of the heat generating portion 12 from the outer circumferential surface of the insulating ceramic 16 is 0. It is a portion of 5 to 0.7 mm. The portion other than the thin portion 16a may be 0.5 to 0.7 mm.

In the insulating ceramic 16, the thickness t ₂ of the insulating ceramic 16 between the positive electrode lead 14 a and the negative electrode lead 14 b and the outer peripheral surface of the insulating ceramic 16 is 0.25 to 0 in the region covering the leads 14. It has a thin portion 16b in the range of .4 mm. The thin portion 16b is more preferably 0.25 to 0.35 mm.

Thin portion 16b, as shown in FIG. 3, in a cross section perpendicular to the axis x, the thickness t ₂ of the shortest distance from the outer peripheral surface of the insulating ceramic 16 to the outer peripheral surface of the lead 14 is 0.25 It is a portion which is ~ 0.4 mm.

The axial x direction length (first length) A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12, specifically, the rear ends of the extension portions 12 a and 12 b of the heat generating portion 12 is about 4 The axial length (second length) B from the tip of the insulating ceramic 16 to the tip of the joint 21 described later is 12 to 20 mm, and the length in the axis x direction of the joint 21 is .5 mm. The length (third length) C is 2.8 to 10.8 mm.

The length A with respect to the length B of the insulating ceramic 16 satisfies the following formula (Formula 1).

It is preferable that the length A with respect to the length B of the insulating ceramic 16 satisfy the following formula (Formula 3).

Moreover, the length B with respect to the total length (B + C) of the length B of the insulating ceramic 16 and the length C satisfy | fills the following numerical formula (Formula 2).

Moreover, it is preferable that the length B with respect to the length (B + C) of the sum total of length B of the insulating ceramic 16, and length C satisfy | fills the following numerical formula (Formula 4).

Further, the axial x direction length (l ₁ + l ₂ = A) from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12, specifically, the rear ends of the extension portions 12a and 12b of the heat generating portion 12 is , 4.5 mm or less. The heat generating portion 12 is located in the range of 4.5 mm in its entirety along the axis x from the tip of the insulating ceramic 16.

The insulating ceramic 16 made of ceramic enables provision of the ceramic heater 10 having high reliability at the time of rapid temperature rise. Specific examples of the ceramics include ceramics having electrical insulation such as oxide ceramics, nitride ceramics, carbide ceramics and the like.

In particular, in silicon nitride ceramics, silicon nitride, which is the main component, is excellent in terms of high strength, high toughness, high insulation and heat resistance. This silicon nitride ceramic is, for example, 3 to 12% by mass of yttrium oxide (Y ₂ O ₃ ), ytterbium oxide (Yb ₂ O ₃ ), eribium oxide (Yb ₂ O ₃ ) as a sintering aid with respect to silicon nitride as the main component. Rare earth element oxides such as Er ₂ O ₃ ), 0.5 to 3% by mass of aluminum oxide (Al ₂ O ₃ ), and further, 1.5 to 5 parts by mass of silicon dioxide (SiO ₂ ) contained in the sintered body % and comprising as silicon dioxide are mixed (SiO _2), obtained by hot press firing.

In the case of using a made of silicon nitride ceramics as the insulating ceramic 16, molybdenum disilicide (MoSi _2), it is preferable to be dispersed mixture of two tungsten silicide (WSi ₂₎ or the like. In this case, the coefficient of thermal expansion of the silicon nitride ceramic as the base material can be made close to the coefficient of thermal expansion of the heat generating portion 12, and the durability of the ceramic heater 10 can be improved.

The outer cylinder 20 is, for example, a cylindrical stainless steel such as SUS430. As shown in FIG. 1, the outer cylinder 20 accommodates the ceramic heater 10 in a state in which the tip of the ceramic heater 10 is exposed. In the state where the ceramic heater 10 is accommodated, the ceramic heater 10 and the outer cylinder 20 are provided on the inner peripheral surface of the outer cylinder 20 along the axis x of the ceramic heater 10 for a predetermined length, for example, brazing material such as silver solder. The joint part 21 joined by brazing using is formed.

The bonding portion 21 is formed by metalizing the outer peripheral surface of the insulating ceramic 16 by brazing of a brazing material such as silver brazing, and has a predetermined length (length C) along the axis x of the ceramic heater 10 Equivalent) is formed between the outer peripheral surface of the ceramic heater 10 and the inner peripheral surface of the outer cylinder 20. In the present embodiment, the joint portion 21 is formed from the front end of the outer cylinder 20 to a position where the insulating ceramic 16 is in contact with the inner peripheral surface of the front end portion 22 of the outer cylinder 20 at the rear end side. However, the joint portion 21 may be in the outer cylinder 20 even if the tip thereof is advanced from the outer cylinder 20 at the axis x.

The housing 30 is a fixture for a cylinder head of an engine (not shown), and accommodates the ceramic heater 10 together with the outer cylinder 20 as shown in FIG.

The housing 30 is formed of a thermally conductive metal material having excellent heat dissipation. The housing 30 is formed, for example, in a cylindrical shape, and the rear end side of the ceramic heater 10 is partially supported by the outer cylinder 20, and the outer cylinder 20 is disposed inside the housing 30. In this state, the tip end of the ceramic heater 10 protrudes outward from the tip of the housing 30.

Below, the comparative example based on the conventional glow plug and the specific Example of the glow plug 1 which concerns on the said embodiment are demonstrated. Furthermore, the present invention is not particularly limited to these examples. The following numerical values are numerical values obtained in the simulation.

Table 1 shows the diameter d (mm) of the insulating ceramic 16 in the ceramic heater 10, the thickness t ₁ (mm) of the thin portion 16a between the heat generating portion 12 and the outer peripheral surface of the insulating ceramic 16, and the lead 14 and the insulation examples 1 and 2 the thickness t ₂ of the thin portion 16b _{that (mm)} is the numerical range of the above embodiments between the outer peripheral surface of sexual ceramics 16, except in Comparative example 1 it various specifications and various It shows about the result of simulation.

In the glow plug 1 according to Examples 1 and 2 and Comparative Example 1, after the start of the simulation, a current of 11 V was applied for the first 2 seconds, and thereafter a current of 7 V was applied.

As a result, as can be seen from Table 1, the power consumptions of Examples 1 and 2 after 60 seconds of the simulation start are 35.2 W and 34.5 W, respectively, whichever is higher than the power consumption 35.6 W of Comparative Example 1. It was also found to be low.

Also, smaller than the diameter d of the ceramic heater 10 is 3.2mm, Examples 1 and 2 the thickness _{t 1} of the thin portion 16a is less than 0.7mm, the greater than 3.2mm diameter d, the thin portion 16a The temperature rising time up to 1000 ° C. was shorter as compared to Comparative Example 1 in which the thickness t ₁ exceeded 0.7 mm. In particular, in Example 2 in which the diameter d is 2.9 mm and the thickness t ₁ is 0.57 mm, the temperature rising time up to 1000 ° C. is less than 1 second, and excellent temperature rising characteristics are exhibited.

Furthermore, the temperatures of Examples 1 and 2 in the heat generating portion 12 two seconds after energization are both higher than the temperature of Comparative Example 1, and in Example 2 exceed 1500 ° C .; It turned out that it has a temperature characteristic.

The heat diffuses from the heating unit 12 the larger the volume of the insulating ceramic 16, as in Examples 1 and 2, the thickness _{t 1} of the thin portion 16a is a condition of 0.5 ~ 0.7 mm It was found that when satisfied, the temperature rising characteristics are excellent. Furthermore, it is more preferable that the diameter d satisfies the condition of 2.9 to 3.1 mm.

The thickness t ₁ is less than 0.5 mm, when the progress in corrosion of the insulating ceramic 16 with the passage of time, there is a possibility that the heat generating portion 12 is exposed at an early stage. When the heat generating portion 12 is exposed, tungsten (W) contained in the material of the heat generating portion 12 may be oxidized, and the heat generating portion 12 may be broken. The second embodiment achieves early temperature rise and power consumption reduction while avoiding the early exposure of the heat generating portion 12 and achieving the long life of the glow plug 1.

Next, Table 2 shows the same diameter d (mm) of the insulating ceramic 16 as in Example 2, the thickness t ₁ (mm) of the thin portion 16a between the heat generating portion 12 and the outer peripheral surface of the insulating ceramic 16, The thickness t ₂ (mm) of the thin portion 16 b between the lead 14 and the outer circumferential surface of the insulating ceramic 16, the axial length B from the tip of the insulating ceramic 16 to the tip of the joint 21, bonding The axial length C of the part 21 shows the result of various specifications and various simulations of Examples 3 to 5 and Comparative Examples 2 and 3 different from each other. The axial length A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12 is the same in Examples 3 to 5 and Comparative Examples 1 and 2.

As can be seen from Table 2, the temperature at a point 2 mm from the tip of the ceramic heater 10 after 60 seconds of simulation start has a large proportion of the ceramic heater 10 exposed from the outer cylinder 20, that is, brazing with the outer cylinder 20 It was found that the smaller the area of the ceramic heater 10 being made, the higher.

Specifically, as in Examples 3 to 5, the ratio (A / B) of the length A to the length B in the insulating ceramic 16 is 0.2 to 0.4, and the insulating ceramic 16 The ceramic heater 10 satisfying the ratio of the length C to the length B + C (C / B + C) in the range of 0.1 to 0.5 reached a temperature of about 1200 ° C. after 60 seconds.

Example 3 has a value of A / B of 0.375, C / B + C has a value of about 0.474, and Example 4 has a value of A / B of about 0.321; The value of B + C was about 0.386, the value of A / B was 0.225, and the value of C / B + C was about 0.123. Even when Comparative Examples 2 and 3 which do not satisfy the conditions of any of the above-mentioned ratios and Examples 3 to 5 are compared, it is found that the temperature rise characteristics are excellent in Examples 3 to 5.

Furthermore, the power consumption after 60 seconds of the simulation start becomes 29 W or less when the condition of the above ratio is satisfied as in the examples 3 to 5, and the power consumption in the examples 3 to 5 is the consumption in the comparative examples 2 and 3 It was found to be small compared to the power.

Furthermore, in Examples 3 to 5, the structure in which the heat from the ceramic heater 10 is less likely to be released is suppressed because the bonding area between the bonding portion 21 formed of high thermal conductivity silver solder and the ceramic heater 10 is reduced. It has become. Therefore, high heat retention in the vicinity of the heat generating portion 12 can be exhibited.

In particular, in Examples 3 to 5, since the temperature near the heat generating portion 12 can be maintained at a high temperature, the temperature at the joint portion 21 between the negative electrode side lead 14b and the outer cylinder 20, that is, the exposed portion 14c of the lead 14 The temperature could be kept below 450 ° C. On the other hand, in Comparative Examples 2 and 3, the temperature at the exposed portion of the lead was 450 ° C. or higher. From the above, it was found that in Examples 3 to 5, the negative influence of the heat given to the brazing material of the joint portion 21 can also be reduced.

Next, Table 3 shows the same diameter d (mm) of the insulating ceramic 16 as in Example 2, the thickness t ₁ (mm) of the thin portion between the heat generating portion 12 and the outer peripheral surface of the insulating ceramic 16, and the lead. Example 6 and Comparative Example 4 having a thickness t ₂ (mm) of the thin portion 16a between the outer peripheral surface of the insulating ceramic 16 and the heat generating portion 12 and having different lengths l ₁ and Comparative Example Various Examples of Comparative Example 5 having the same diameter d (mm), thickness t ₁ (mm), and thickness t ₂ (mm) as ₁ and having the same length 11 of the heat generating portion 12 as in Example 6 The original and simulation results are shown.

As can be seen from Table 3, in Example 6 in which the axial direction x length A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12 is 4.5 mm or less (A ≦ 4.5 (mm)) The temperature rising time to 1000 ° C. was 0.98 seconds, which was less than 1 second.

On the other hand, in Comparative Example 4, the axial direction length A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12 exceeds 4.5 mm (A> 4.5 (mm)). The temperature rise time was 1.08 seconds, which exceeded 1 second.

From this also, the temperature rise time up to 1000 ° C. in the ceramic heater 10 is shortened if the axial x direction length A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12 is 4.5 mm or less It turned out that

As in Comparative Example 5, even if the axial direction length A from the front end of the insulating ceramic 16 to the rear end of the heat generating portion 12 is 4.5 mm or less (A ≦ 4.5 (mm)), the diameter d It is found that the temperature rising time to 1000 ° C. is 1.32 seconds and the temperature rising characteristic is inferior to that in Example 6 in the case where is 3.22 mm (more than 2.9 mm).

According to the glow plug 1 as described above, by the thickness t ₁ of the thin portion 16a of the outer peripheral surface of the insulating ceramic 16 and the heating portion 12 is closer is in the range of 0.5 ~ 0.7 mm, As compared with a glow plug in which the thin portion 16a is out of the above range, the temperature rising characteristic can be greatly improved, and the power consumption can be suppressed. The thickness _{t 1} of the thin portion 16a is preferable to be 0.57 ~ 0.66 mm, further, it is more preferred diameter d of the insulating ceramic 16 is 2.9 ~ 3.1 mm.

The axial x direction length A from the front end of the insulating ceramic 16 to the rear ends of the extension portions 12a and 12b of the heat generating portion 12 is 4.5 mm or less, in other words, within 4.5 mm from the front end of the insulating ceramic 16 Since the entire heat generating portion 12 is positioned, the time until the temperature reaches 1000 ° C. is the length A in the axial line x direction from the front end of the insulating ceramic 16 to the rear ends of the extension portions 12 a and 12 b of the heat generating portion 12. Can be shortened compared to when it exceeds 4.5 mm.

　を満たすと、昇温特性及び消費電力低減に加えて、負極側リード１４ｂの露出部１４ｃと外筒２０との接触部における温度を低くすることができる。これにより、セラミックヒータ１０と外筒２０とを接合する接合部２１のろう材への熱による負荷を軽減することができる。 Further, according to the glow plug 1, an axial x-direction length A from the front end of the insulating ceramic 16 to the rear ends of the extended portions 12 a and 12 b of the heat generating portion 12, the front end of the insulating ceramic 16 to the front end of the joint 21 Up to the axial line x direction length B, and the axial line x direction length C of the joint portion 21, the following equation 1 and equation 2

If the above condition is satisfied, the temperature at the contact portion between the exposed portion 14c of the negative electrode side lead 14b and the outer cylinder 20 can be lowered in addition to the temperature rise characteristics and the reduction of the power consumption. Thereby, the load by the heat to the brazing material of the junction part 21 which joins the ceramic heater 10 and the outer cylinder 20 can be reduced.

　を満たすことが、昇温特性及び消費電力低減の観点からさらに好ましい。 Also, the following Equation 3 and Equation 4

Is more preferable from the viewpoint of temperature rise characteristics and power consumption reduction.

<Others>
The present invention is not limited to the above embodiment. For example, the cross-sectional shape of the ceramic heater 10 perpendicular to the axis x is not limited to a circle, but may be another shape such as an ellipse or a polygon. Further, as shown in FIGS. 2 and 3, the stepped surface shape of the heat generating portion 12 and the lead 14 is not limited to an elliptical shape, and may be another shape such as a circle or a polygon such as a rectangle.

Claims (6)

A ceramic heater having a conductive ceramic and an insulating ceramic covering the conductive ceramic,
The conductive ceramic has a heat generating portion disposed at a front end, and a lead connected to a rear end of the heat generating portion.
The glow is characterized in that, in the insulating ceramic, in a cross section perpendicular to the axis of the ceramic heater, the thickness of the thinnest portion where the outer peripheral surface and the heat generating portion are closest to each other is 0.5 to 0.7 mm. plug. The glow plug according to claim 1, wherein the thickness of the thinnest portion is 0.57 to 0.66 mm. The glow plug according to claim 1 or 2, wherein the outer peripheral surface of the insulating ceramic is cylindrical with a diameter of 2.9 to 3.1 mm. The glow plug according to any one of claims 1 to 3, wherein an axial length from a front end of the insulating ceramic to a rear end of the heat generating portion is 4.5 mm or less. A ceramic heater having a conductive ceramic and an insulating ceramic covering the conductive ceramic;
And an outer cylinder that accommodates a portion of the ceramic heater such that at least the tip is exposed, and the inner peripheral surface is joined to the outer peripheral surface of the ceramic heater via a bonding portion,
The conductive ceramic has a heat generating portion disposed at a front end, and a lead connected to a rear end of the heat generating portion.
The axial length from the front end of the insulating ceramic to the rear end of the heat generating portion is a first length A,
The axial length from the tip of the insulating ceramic to the tip of the joint is a second length B,
The axial length of the joint is a third length C,
And the following Equation 1 and Equation 2

Glow plug characterized by satisfying. Equation 3 and Equation 4 below

The glow plug according to claim 5, characterized in that:

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