JP2003056849A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug where good airtightness is maintained by binding firmly a ceramic heater and a metal outer cylinder by press-fitting engagement. SOLUTION: The glow plug 50 in this invention is provided with the rod-like ceramic heater 1 where a resistance heating element 11 is embedded in its own inside, the metal outer cylinder 3 installed on the outer circumferential face of the ceramic heater 1 by press-fitting engagement, a main metal fitting 4 holding the metal outer cylinder 3. The glow plug 50 is adjusted so that load necessary for extracting the ceramic heater 1 from the metal outer cylinder 3 is more than 1000 N.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a glow plug for preheating a diesel engine.

[0002]

2. Description of the Related Art Heretofore, as a glow plug for preheating a diesel engine, there has been widely used one in which a rod-shaped ceramic heater is arranged so as to protrude inside a tip of a tubular metal shell. Electricity is supplied to the ceramic heater through a metal shaft (which is connected to a power source) provided at the rear end of the metal shell and a metal lead portion which connects the metal shaft and the ceramic heater. In the conventional glow plug, the connection between the ceramic heater and the metal lead is
For example, JP-A-10-205753 or JP-A-2
As disclosed in Japanese Patent Publication No. 000-356343,
This has been done by forming the front end of the metal lead portion into a coil shape, inserting the rear end of the ceramic heater with the heater terminal formed exposed therein, and brazing the two. In addition, a structure in which the other terminal of the ceramic heater is connected to the metal shell via a metal outer cylinder and grounded via an engine block to which a glow plug is attached is often adopted. It is joined to the ceramic heater by brazing.

However, the joining mode by brazing has a drawback that it is inefficient because many steps are required such as a step of assembling the materials to be joined by sandwiching the brazing material and a heating step of melting the brazing material. In addition, since the ceramic is joined to a metal member such as a metal lead or a metal outer cylinder, an expensive active brazing material must be used, and the heating temperature and atmosphere for brazing are also subtly adjusted. Combined with the problem of increased man-hours described above, the manufacturing cost is likely to increase. Therefore, Japanese Unexamined Patent Publication No. 2000-356343 discloses a method in which the metal outer cylinder is assembled to the ground side terminal of the ceramic heater by shrink fitting.

[0004]

Even in interference fit fitting such as shrink fitting or press fitting, it is important to ensure the same joining strength as brazing. If the joint strength is insufficient, when the glow plug is attached to the engine and receives a strong pressure due to compression / explosion, the ceramic heater causes pushback to the metal outer cylinder, which causes deterioration of startability, Problems such as disconnection of metal leads and short circuit with the metal shell occur.

An object of the present invention is to provide a glow plug in which a ceramic heater and a metal outer cylinder are firmly joined by press-fitting and which is attached to an engine and does not cause pushback even after long-term use. It is in.

[0006]

Means for Solving the Problems and Actions / Effects In order to solve the above problems, a glow plug according to the present invention comprises a rod-shaped ceramic heater having a resistance heating element embedded therein.
A metal outer cylinder attached to the outer peripheral surface of the ceramic heater by press-fitting and a metal shell for holding the metal outer cylinder are provided, and a load P required to remove the ceramic heater from the metal outer cylinder is 1000 N or more. It is adjusted so that

In the glow plug of the present invention, the ceramic heater and the metal outer cylinder are joined by press fitting. When the glow plug is attached to the engine and receives a strong pressure due to compression / explosion, the metal outer cylinder receives heat from the resistance heating element embedded inside the ceramic heater and heat from combustion. That is, it receives pressure while receiving heat. However, when various investigations were made as to whether pushback occurs, it was found that it was not directly related to whether or not heat was received, and that it was approximately proportional to the extraction load at room temperature. That is, by adjusting the extraction load at room temperature within the above range, it is possible to obtain reliability that pushback does not occur even when heat is received from the combustion chamber. It should be noted that pushback means that the ceramic heater receives pressure from the combustion chamber and retracts relatively to the outer side of the combustion chamber with respect to the metal outer cylinder.

Further, the glow plug of the present invention, in the axial direction thereof, is defined as a portion on the combustion chamber side with respect to the contact position with the cylinder head closest to the combustion chamber when it is attached to the internal combustion engine. A part of the metal outer cylinder, which consists of a part, a front part exposed in the combustion chamber that is defined as a part following the part, and a subsequent part that follows the part. Is defined as a partial ceramic heater, and in the axial direction, when the total length of the metal outer cylinder is L and the length of the partial metal outer cylinder is L1, the partial ceramic heater located in the partial metal outer cylinder is defined as the partial metal heater. It is desirable that the partial withdrawal load Pk necessary for withdrawing from the inside of the outer cylinder is adjusted so as to satisfy Pk ≧ (P × L1) / L (unit: N) with respect to the withdrawal load P. . As a result, even if heat is received from the combustion chamber of the engine and the tight binding force of the metal outer cylinder to the ceramic heater is weakened, pushback does not occur because the ceramic heater is reliably held by the metal outer cylinder in the subsequent portion.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the glow plug of the present invention together with its internal structure. Also,
FIG. 2 is an enlarged view of the main part. The glow plug 50 has a ceramic heater 1 and a metal shell 4 that holds the ceramic heater 1. The ceramic heater 1 has a rod-like shape, and the resistance heating element 11 is embedded in the tip portion 2 of the ceramic heater 1. A first heater terminal 12a for energizing the resistance heating element 11 is formed on the outer peripheral surface of the rear end portion of itself. The metal outer cylinder 3 is formed in a cylindrical shape, and the ceramic heater 1
Are held inside themselves in such a manner that the rear end portion and the front end portion 2 respectively project in the direction of the axis O. Metal shell 4
Is formed in a cylindrical shape that is coaxially coupled to the metal outer cylinder 3.

Next, on the outer peripheral surface of the metal shell 4, a screw portion 5 as a mounting portion for fixing the glow plug 50 to an engine block (not shown) is formed, and a metal shaft 6 is mounted on the rear end portion. Has been. The metal shaft 6 has a rod shape, is inserted in the rear end portion of the metal shell 4 in the direction of the axis O, and has its front end surface 65 in the direction of the axis O.
Are arranged so as to face the rear end surface 2r of the ceramic heater 1. On the other hand, on the outer peripheral surface of the rear end portion of the ceramic heater 1, a metal terminal ring 14 electrically connected to the first heater terminal 12a is provided in an interference fit state in the first heater terminal 12a.
It is attached so as to cover a. And the metal shaft 6
And the first heater terminal 12a, one end of which is coupled to the terminal ring 14 and the other end of which is coupled to the metal shaft 6
It is electrically connected by 7.

An axis O is formed on the outer peripheral surface of the ceramic heater 1.
A second heater terminal 12b for energizing the resistance heating element 11 is exposed and formed on the front side of the first heater terminal 12a in the direction. Then, the second heater terminal 12b
The cylindrical metal outer cylinder 3 that covers the
The ceramic heater 1 is attached to the outer peripheral surface of the ceramic heater 1 by press-fitting with the rear end of the ceramic heater 1 protruding toward the rear side of the ceramic heater 1. The metal shell 4 is attached to the outer peripheral surface of the metal outer cylinder 3 at the cylindrical heater holding surface 4a.

According to the above construction, by using the metal outer cylinder 3 inserted between the metal shell 4 and the ceramic heater 1 as a spacer, the ceramic heater protruded rearward of the metal outer cylinder 3. A suitable gap can be formed between the outer peripheral surface of the rear end portion 1 and the inner peripheral surface of the metal shell 4 on the rear side of the heater holding surface 4a. This makes it easier to arrange the terminal ring 14 at the rear end of the ceramic heater 1.

Next, with respect to the assembling form of the metal shell 4 and the metal outer cylinder 3, for example, brazing is performed so as to fill the gap between the inner and outer peripheral surfaces of the both, or the inner edge of the opening of the metal shell 4 and the metal. Although it may be fixed to the outer peripheral surface of the outer cylinder 3 by laser welding all around, in the embodiment shown in FIGS. 1 and 2, the metal shell 4 also has a heater holding surface 4a.
The metal outer cylinder 3 is attached to the outer peripheral surface in an interference fit state. Thereby, the assembly process of the glow plug 50 can be further simplified.

Further, as shown in FIG. 7, it is also possible to exemplify a form in which the rear end portion of the metal outer cylinder 3 has an enlarged diameter at the joining position with the metal shell 4. In the form shown in FIG. 7,
The inner diameter of the metallic shell 4 at the tip portion is reduced so that the enlarged diameter portion 3c of the metal outer cylinder 3 is seated. In such a form, it is difficult to join the metal shell 4 and the metal outer cylinder 3 by interference fitting, so brazing is preferable.

Specifically, regarding the bonding strength between the ceramic heater 1 and the metal outer cylinder 3, a withdrawal load P of 1000 N or more must be required to extract the ceramic heater 1 from the metal outer cylinder 3. Extraction load P is 100
For those of less than 0 N, pushback is likely to occur when assembled in an engine and subjected to a durability test.
In addition, the extraction load P is improved by improving various requirements.
For example, it is possible to improve the ratio up to about 30,000 N easily. However, if it is too high, the tight binding force of the metal outer cylinder 3 becomes too strong, and there is a concern that the bending strength of the ceramic heater 1 may be reduced. Therefore, it is preferably less than 30,000N.

Although it is possible to adjust as a whole as described above, normally, when the glow plug 50 is assembled to an engine, the reduced diameter surface 4k of the metal shell 4 is a cylinder as shown in FIG. The head 40 is fixed in a seating contact with the mounting hole of the head 40. When the cylinder head 40 and the reduced diameter surface 4k come into contact with each other, the glow plug 50 receives the heat from the combustion chamber and the cylinder head 40.
It can be efficiently released. In the direction of the axis O, a space S is formed on the combustion chamber side with respect to the reference line HL indicating the contact start position, the gap S extending between the cylinder head 40 and the combustion chamber. Therefore, the environment to be placed is significantly different depending on whether or not it is closer to the combustion chamber than the reference line HL.

It is possible to consider the following with the reference line HL as a boundary. That is, the glow plug 50
Is a front-stage portion 50a defined as a portion closer to the combustion chamber than the contact position with the cylinder head closest to the combustion chamber when attached to the internal combustion engine in the direction of the axis O.
And a subsequent portion 50b which is defined as a subsequent portion. A part of the metal outer cylinder 3 forming the subsequent portion 50b is defined as a partial metal outer cylinder 3b, and a part of the ceramic heater 1 is also defined as a partial ceramic heater 1b. You can

In the embodiment shown in FIG. 5, the reduced diameter surface 4k of the metal shell 4 is seated in the mounting hole of the cylinder head 40. On the other hand, in another example shown in FIG. 9, the reduced diameter surface 3k of the metal outer cylinder 3 plays the same role as the reduced diameter surface 4k of the metal shell 4.

During engine operation, the front part 50a may reach a high temperature of, for example, 500 to 700 ° C.
On the other hand, on the cylinder head 40 side (subsequent part 50b), since heat is drawn well, the temperature is kept sufficiently lower than that. Therefore, when the total length of the metal outer cylinder 3 is L and the length of the partial metal outer cylinder 3b is L1 in the axis O direction (see FIG. 4), the partial ceramic heater 1b located in the partial metal outer cylinder 3b is The partial withdrawal load Pk necessary for withdrawing from the inside of the partial metal outer cylinder 3b is adjusted so as to satisfy Pk ≧ P × (L1 / L) (unit: N) with respect to the above-mentioned withdrawal load P. If this is done, there is no risk of pushback occurring when the engine is operating.

Incidentally, FIG. 4 shows an outline of a method for measuring the above-mentioned extraction load P and partial extraction load Pk. That is, the assembly of the metal outer cylinder 3 and the ceramic heater 1 removed from the metal shell 4 is cut at the boundary HL between the preceding stage portion 50a and the following portion 50b. Then, each of them is fixed to a pedestal 41 whose dimensions are adjusted so that they fit exactly,
Pressure is applied to the end surfaces of the divided ceramic heaters 1a and 1b, and the value at the time of starting relative movement with respect to the divided metal outer cylinders 3a and 3b is measured. The sum of both measured in this way is defined as the extraction load P, and on the other hand,
The value of only the subsequent portion 50b is set as the partial extraction load Pk.

As a material for the terminal ring 14 and the metal outer cylinder 3, an Fe-based alloy having hardness and heat resistance above a certain level may be used in consideration of the balance between high temperature strength and material cost. desirable. In particular, in order to secure a sufficient elastic binding force, Vickers hardness (JIS-Z2244
(Value measured with a load of 10 N by the method specified in (1998)) Hv of 170 or more (desirably 350 or more)
The use of e-based alloys is recommended. As such an Fe-based alloy, precipitation hardening stainless steel such as SUS630 or SUS631 can be preferably used. For example, SUS63
0 is H defined in JIS-G4303 (1988).
Aging precipitation hardening can be performed by heat treatment of any one of 900, H1025, H1075, and H1105, and in particular, H900 treatment can secure Hv350 or higher. On the other hand, SUS631 is TH105 of the same standard.
Aging precipitation hardening can be performed by heat treatment of 0 or RH950, and both can secure Hv of 350 or more.
Further, although it is slightly inferior in hardness, ferritic stainless steel such as SUS430 can also be used.

When it is required to secure higher heat resistance and further suppress a decrease in tight binding force at high temperature, an iron-based super heat-resistant alloy (for example, Incoloy 909 (trade name of Inco) is used. )) Age-hardened product, Ni-base super heat-resistant alloy (for example, Waspaloy (trade name of United Technology)), or non-age-hardened Ni.
Base heat-resistant alloy (Inconel 625 (trade name of Inco))
It is also possible to use a work-hardened product of the above. However,
These materials are expensive, and in the normal use environment of the glow plug, the ultimate temperature of the terminal ring 14 is 50 to 20.
When the temperature reached at 0 ° C. and the metal outer cylinder 3 remains within the range of about 500 to 700 ° C., Ni, Cr, Cu, Nb or Al, such as the above precipitation hardening stainless steel,
It is desirable that the total content of alloying elements added for matrix solid solution strengthening or formation of precipitates is made of a Fe-based alloy limited to a range of 50 mass% or less. However, the total content of these is preferably 20% by mass or more from the viewpoint of securing high temperature strength or corrosion resistance.

Next, as shown in FIG. 2, the metal lead portion 1
7 is arranged in a bent shape between the metal shaft 6 and the terminal ring 14. As a result, even when a heating / cooling cycle is applied due to the heat generation of the ceramic heater 1, the metal lead portion 17 can absorb expansion / contraction at the bent portion thereof, and by extension, the metal lead portion 17 and the terminal ring 1.
It is possible to prevent excessive stress from concentrating on the joint portion with 4 and causing problems such as poor contact and disconnection. On the other hand, in order to easily and firmly join the metal lead portion 17 and the metal shaft 6, the joining end portion of the metal lead portion 17 with the metal shaft 6 has a planar shape with respect to the tip end portion of the outer peripheral surface of the metal shaft 6. Are joined with the joint surface of. For example, when the metal lead portion 17 and the metal shaft 6 are joined by resistance welding, it is necessary to make the joining surface flat so that the pressure applied during the resistance welding is evenly applied to form a weld portion with few defects. But it will be advantageous.

On the other hand, the metal lead portion 17 and the terminal ring 14
In order to join with the ceramic heater 1, the terminal ring 14 is first assembled to the ceramic heater 1 so as not to interfere with the assembly of the terminal ring 14 into the ceramic heater 1 by press fitting or the like. It is desirable to join the end portion of the metal lead portion 17 to the outer peripheral surface. In this case, resistance welding or brazing can be used as the joining method.

Next, the ceramic heater 1 has a resistance heating element 11 in a ceramic base 13 made of an insulating ceramic.
Is embedded as a rod-shaped ceramic heater element. In this embodiment, the ceramic heater 1
Is configured such that a ceramic resistor 10 made of a conductive ceramic is embedded in a ceramic base 13 made of an insulating ceramic. Ceramic resistor 1
Reference numeral 0 denotes a first conductive ceramic portion which is arranged at the tip 2 of the ceramic heater 1 and which functions as a resistance heating element, and a ceramic at the rear side of the first resistive portion 11. The second conductive member is arranged so as to extend in the direction of the axis O of the heater 1 and has a tip end joined to both ends of the first resistor portion 11 in the energizing direction and having a lower resistivity than the first conductive ceramic. And a pair of second resistor portions 12, 12 made of a conductive ceramic. Then, the pair of second resistor portions 12, 12 of the ceramic resistor 10 have branch portions formed at different positions in the direction of the axis O, and the branch portions have
The exposed portions of the ceramic heater 1 on the surface form a first heater terminal 12a and a second heater terminal 12b, respectively.

The resistance heating element 11 is energized by, for example, as shown in FIG. 6, embedded lead wires 18 and 19 made of a refractory metal wire material such as W embedded in the ceramic substrate 13.
Can also be done via. In this case, the first heater terminal is formed of the embedded lead wire 18, and the second heater terminal is formed of the embedded lead wire 19 as the exposed portions 18a and 19a.

Next, in this embodiment, a silicon nitride ceramic is used as the insulating ceramic forming the ceramic base 13. The structure of the silicon nitride ceramic is such that main phase particles containing silicon nitride (Si ₃ N ₄ ) as a main component are bonded by a grain boundary phase derived from a sintering aid component described later. The main phase may be one in which a part of Si or N is replaced with Al or O, and further, one in which metal atoms such as Li, Ca, Mg, and Y are solid-dissolved in the phase. .

For silicon nitride ceramics, 3 of the periodic table is used.
At least one selected from the group of elements of each group of A, 4A, 5A, 3B (for example, Al) and 4B (for example, Si) and Mg is used as the cation element, and the oxide is contained in the whole sintered body. It can be contained in an amount of 1 to 10 mass% in terms of conversion. These components are added mainly in the form of oxides,
In the sintered body, it is contained mainly in the form of oxide or complex oxide such as silicate. If the sintering additive component is less than 1% by mass, it is difficult to obtain a dense sintered body, and if it exceeds 10% by mass, the strength, toughness, or heat resistance becomes insufficient. The content of the sintering aid component is preferably 2 to 8% by mass.
It is good to say When a rare earth component is used as the sintering aid component, Sc, Y, La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
u can be used. Among these, Tb, D
y, Ho, Er, Tm, and Yb have the effect of promoting crystallization of the grain boundary phase and improving high-temperature strength, and thus can be preferably used.

Next, the first resistor portion 11 and the second resistor portions 12, 12 constituting the ceramic resistor 10 are made of conductive ceramics having different electric resistivities as described above. The method of making the electric resistances of both conductive ceramics different from each other is not particularly limited, and, for example, a method of making the contents different from each other while using the same kind of conductive ceramic phase; There are various examples, such as a method of adopting a conductive ceramic phase;
In this embodiment, the method of is adopted.

Examples of the conductive ceramic phase include tungsten carbide (WC) and molybdenum disilicide (MoSi).
₂ ) and tungsten disilicide (WSi ₂ ) can be used. In this embodiment, WC is adopted.
In order to reduce the difference in linear expansion coefficient from the ceramic base 13 and improve the thermal shock resistance, an insulating ceramic phase, which is the main component of the ceramic base 13, here a silicon nitride ceramic phase can be blended. Therefore, by changing the content ratio of the insulating ceramic phase and the conductive ceramic phase, the electric resistivity of the conductive ceramic forming the resistor portion can be adjusted to a desired value.

Specifically, the first conductive ceramic material of the first resistor portion 11 forming the resistance heating portion has a conductive ceramic phase content of 10 to 25% by volume, and the balance of insulating ceramic phase. It is good to say If the content rate of the conductive ceramic phase exceeds 25% by volume, the electrical conductivity becomes too high and a sufficient calorific value cannot be expected, and if it is less than 10% by volume, the electrical conductivity becomes too low and the calorific value becomes the same. Can not be secured enough.

On the other hand, the second resistor portions 12 and 12 serve as conduction paths to the first resistor portion 11, and the material of the second conductive ceramic has a conductive ceramic phase content of 15%. ˜30% by volume, and the balance is preferably an insulating ceramic phase. If the content rate of the conductive ceramic phase exceeds 30% by volume, it becomes difficult to densify it by firing, resulting in insufficient strength, and even if the temperature range normally used for engine preheating is reached, the electrical resistivity The rise may be insufficient, and the self-saturation function for stabilizing the current density may not be realized. On the other hand, if it is less than 15% by volume, the heat generation in the second resistor portions 12 and 12 becomes too large, which leads to deterioration in heat generation efficiency of the first resistor portion 11. In the present embodiment, the content ratio of WC in the first conductive ceramic is 16% by volume (55 mass%), and the content ratio of WC in the second conductive ceramic is 20% by volume (7%).
0% by mass) (the rest are all silicon nitride ceramics (including a sintering aid)).

In this embodiment, the ceramic resistor 10
Is arranged such that the first resistor portion 11 has a U-shape, and the U-shaped bottom portion is located on the tip side of the ceramic heater 1, and the second resistor portions 12 and 12 have the U-shaped first portion. It is a rod-shaped portion that extends rearward from both ends of the one resistor portion 11 along the axis O direction and is substantially parallel to each other.

In the ceramic resistor 10, the first resistor portion 11 has a tip portion 11a which should have the highest temperature during operation.
In order to concentrate the electric current, the tip portion 11a has a smaller diameter than the both end portions 11b and 11b. The joint surface 15 with the second resistor portions 12 and 12 has a tip portion 1
It is formed on both ends 11b, 11b having a diameter larger than that of 1a.

As shown in FIG. 6, the embedded lead wires 18,
In the structure in which 19 is arranged in ceramic, when the voltage for driving the heater is applied at high temperature, the embedded lead wires 18,
The metal atoms forming 19 may be consumed by the so-called electromigration effect of being forcibly diffused to the ceramic side by receiving an electrochemical driving force due to the electric field gradient thereof, which may cause disconnection and the like. However, FIG.
Since the embedded lead wire is abolished in the above configuration, there is an advantage that it is essentially not affected by the electromigration effect.

Next, as shown in FIG. 1, inside the rear end portion of the metal shell 4, the metal shaft 6 for supplying electric power to the ceramic heater 1 is insulated from the metal shell 4 as described above. It is arranged. In this embodiment, the ceramic ring 3 is provided between the outer peripheral surface of the metal shaft 6 on the rear end side and the inner peripheral surface of the metal shell 4.
1 is arranged, and a glass filling layer 32 is formed on the rear side of the No. 1 and fixed. A ring-side engagement portion 31a is formed on the outer peripheral surface of the ceramic ring 31 in the form of a large diameter portion, and a metal fitting formed in the shape of a circumferential step portion near the rear end of the inner peripheral surface of the metal shell 4. By engaging with the side engaging portion 4e, the retaining to the front side in the axial direction is prevented. Further, the outer peripheral surface portion of the metal shaft 6 which is in contact with the glass filling layer 32 is provided with unevenness by knurling or the like (a shaded area in the drawing). Further, the rear end portion of the metal shaft 6 extends rearward of the metal shell 4, and the terminal metal fitting 7 is fitted into the extending portion via an insulating bush 8. The terminal fitting 7 is fixed to the outer peripheral surface of the metal shaft 6 in a conductive state by a caulking portion 9 in the circumferential direction.

The glow plug 50 is attached to the cylinder head of the diesel engine at the attachment portion 5 of the metal shell 4. Then, by connecting the terminal metal fitting 7 to a power source, the current flows in the order of the metal shaft 6 → the metal lead 17 → the terminal ring 14 → the ceramic heater 1 → the metal outer cylinder 3 → the metal shell 4 → (grounded through the engine block). And the tip portion 2 of the ceramic heater 1 generates heat to preheat the combustion chamber.

The method of manufacturing the glow plug 50 will be described below. First, as shown in FIG. 3A, a resistor powder molding portion 34 to be the ceramic resistor 10 is manufactured by injection molding. Further, the raw material powder for forming the ceramic base 13 is press-molded in advance with a die to prepare divided preforms 36 and 37 as separate base upper and lower bodies. A concave portion 37a having a shape corresponding to the resistor powder molding portion 34 (a concave portion on the divided preliminary molded body 36 side is not shown in the drawing) is formed on the mating surface of each of the divided preliminary molded bodies 36 and 37. , The resistor powder molding part 34 is housed therein, and the divided preform 3
As shown in FIG. 3B, by fitting 6, 37 on the mating surface, and further pressing and compressing,
A composite molded body 39 in which these are integrated is produced.

The composite molded body 39 thus obtained is subjected to binder removal processing, and is then fired at a temperature of 1700 ° C. or higher, for example, around 1800 ° C. by a hot press or the like to obtain a fired body, and rough polishing for size adjustment is performed. After that, the ceramic heater 1 is finely ground by using fixed abrasive grains.
Is obtained. Then, the terminal ring 14 and the metal outer cylinder 3 are press-fitted into the ceramic heater 1, and necessary parts such as the metal lead portion 17 and the metal shell 4 are assembled, whereby the glow plug 50 shown in FIG. 1 is completed. To do.

When the ceramic heater 1 is press-fitted into the metal outer cylinder 3 and the terminal ring 14, if at least one of the joint surfaces thereof is coated with a lubricant whose lubricity disappears by heating, the press-fitting will be smoother. This is preferable because it can be performed. After completion of the press-fitting process, heat treatment is performed. As such a lubricant, for example, stearic acid, sodium fatty acid which is a substance containing carboxylic acid or carboxylic acid salt, oxidized microwax, and the like can be used. Regarding the heat treatment conditions and the like, for example, the technique disclosed in Japanese Patent Publication No. 8-5728 can be preferably adopted.

[0041]

EXAMPLES Example 1 The results of experiments conducted to confirm the effects of the present invention will be described below. First, Fig. 1
The ceramic heater 1 having the form shown in was prepared by the method described above. However, the length of the ceramic heater 1 is 40 mm, the outer diameter is 3.5 mm, and the second resistor portion 1
The thickness of 2 and 12 is 1 mm, and the first heater terminal 12a
The second heater terminal 12b is a circular area having a diameter of 0.8 mm. On the other hand, the above-mentioned SUS630 (H900
Age-hardened product: Hv = approx. 400)
Was produced. However, the thickness was fixed to 0.9 mm and the length L in the direction of the axis O was fixed to 20 mm.

Then, the above metal outer cylinder 3 was assembled by press-fitting at a predetermined position of each ceramic heater 1. It should be noted that, with respect to the metal outer cylinder 3 and the ceramic heater 1 in the assembled state, the extraction load P described above is 1000 N by variously adjusting their manufacturing requirements (press fitting margin, surface roughness, etc.).
The adjustment is made as described above. Further, they were assembled by pressing into a predetermined position of the metal shell 4 to obtain a glow plug 50 of the present invention. At the time of press-fitting, an appropriate amount of lubricant (Paskin M30 (trade name: Kyoeisha Chemical Co., Ltd.)) was applied to the inner surface and the outer surface of the metal outer cylinder 3. Under these test conditions, 300 ° C after press-fitting unless otherwise specified.
The lubricant is decomposed. In addition, the ceramic heater 1 and the metal outer tube 3 adjusted to exactly the same conditions
Was used to produce three sets of the glow plugs 50. Further, the glow plug 50 adjusted so that the extraction load P is less than 1000 N was similarly manufactured as a comparative product.

The following tests were conducted on the three sets of glow plugs 50 obtained as described above. First, the extraction load P was measured by the method described above. Next, the engine was mounted on a diesel engine for a glow plug endurance test with a displacement of 200 cc and a four cylinder, and the engine was stopped for 480 seconds with the throttle fully open at 5000 rpm for 6 seconds.
After maintaining for 0 second and repeating this for 100 cycles, the pushback amount of the ceramic heater 1 with respect to the metal outer cylinder 3 was measured. It should be noted that the energization of the ceramic heater 1 is synchronized with the start of the throttle fully opening as described above.
The applied voltage of 1 V is applied for only 15 seconds.

Next, the flexural strength test of the ceramic heater 1 was conducted on the glow plug whose pushback amount was measured. The bending strength test was conducted as follows. That is, as shown in FIG. 8, the metal shell 4 is held by an aluminum jig, and a static load is gradually applied to the tip end portion 2 of the ceramic heater 1 at the fitting portion mouth 40 with the metal outer cylinder 3. The load (limit load) applied until the breakage was measured and used as the bending strength. The results are shown in Table 1.

[0045]

[Table 1]

The extraction load P of the ceramic heater 1 is 100
The product of the present invention adjusted to 0 N or more (Examples 1-1 to 1-
Regarding 5), pushback did not occur in the durability test, which was good. However, the extraction load P is 300
With respect to those of 00N or more, the transverse rupture strength after the endurance test was remarkably reduced, and no favorable result was obtained.

(Embodiment 2) Next, in the same manner as in Embodiment 1, glow plugs 50 adjusted to various extraction loads P were produced. Then, the engine was assembled in the same engine for durability test as in Example 1, and the throttle was opened at 5000 rpm to 300
Continuous operation was performed for an hour. Energization of the ceramic heater 1 was always continued during the durability test. After the durability test, the pushback amount of the ceramic heater was examined. Then, the extraction load P and the partial extraction load Pk of the ceramic heater 1 were obtained by the method described above. As shown in FIG. 4, the length L1 of the partial metal outer cylinder 3b is 7 mm, 10 mm, 15 m.
It is adjusted to m. The results are shown in Table 2.

[0048]

[Table 2]

As described above, in the products of the present invention (Examples 2-1 to 2-12) in which the partial extraction load Pk in the partial metal outer cylinder 3b is adjusted to be larger than P × (L1 / L). In the above durability test as well, pushback did not occur and good durability was exhibited.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a glow plug of the present invention.

FIG. 2 is a vertical sectional view showing a main part of FIG.

FIG. 3 is an explanatory view of a manufacturing process of the glow plug of FIG.

FIG. 4 is a diagram showing a method for measuring an extraction load and a partial extraction load.

FIG. 5 is a view showing a mounted state of a glow plug in an internal combustion engine.

FIG. 6 is a longitudinal sectional view of a main part showing a first modified example of the glow plug of FIG.

FIG. 7 is a vertical cross-sectional view of a main part of a glow plug of the present invention in which a rear end portion of a metal outer cylinder has a diameter-expanding shape.

FIG. 8 is a diagram illustrating a method of measuring bending strength.

FIG. 9 is a diagram showing another example of a mounted state of a glow plug in an internal combustion engine.

[Explanation of symbols]

1 Ceramic heater 1b Partial ceramic heater 3 metal outer cylinder 3b Partial metal outer cylinder 4 metal shell 11 Heating resistor 50 glow plug 50a front part 50b subsequent part O axis

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroyuki Suzuki             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company (72) Inventor Masaya Ito             14-18 Takatsuji-cho, Mizuho-ku, Nagoya City, Aichi Prefecture             Inside this special ceramics company

Claims (2)

[Claims] 1. A rod-shaped ceramic heater (1) having a resistance heating element (11) embedded therein, and a metal outer tube (3) attached to the outer peripheral surface of the ceramic heater (1) by press fitting. ) And a metal shell (4) for holding the metal outer cylinder (3), and an extraction load P required to extract the ceramic heater (1) from the metal outer cylinder (3) is 1000 N or more. A glow plug (50), characterized in that it is adjusted to 2. The glow plug (50) as a portion on the combustion chamber side with respect to the direction of the axis (O) of the glow plug (50), when attached to the internal combustion engine, is closer to the cylinder head than the contact position with the cylinder head. A part of the metal outer cylinder (3), which comprises a front part (50a) defined and a subsequent part (50b) defined as a part following the part, and which constitutes the subsequent part (50b) is a partial metal outer tube (50). 3b), similarly, a part of the ceramic heater (1) is replaced by a partial ceramic heater (1
On the other hand, when the total length of the metal outer cylinder (3) is L and the length of the partial metal outer cylinder (3b) is L1 in the axis (O) direction, the partial metal outer cylinder ( 3b) the partial ceramic heater (1b) is replaced by the partial metal outer cylinder (3b).
b) The partial withdrawal load Pk required to pull out from inside is
The glow plug (50) according to claim 1, wherein the glow plug (50) is adjusted so as to satisfy Pk ≧ P × (L1 / L) (unit: N) with respect to the extraction load P.