JP2002364844A - Glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glow plug allowing a metal ring and a ceramic heater to be assembled simply and moreover allowing the energization to a resistance heating element to be performed well. SOLUTION: When the contact resistance between the first and the second terminal rings 14 and 3 of the first and the second heaters for energizing the resistance heating element 11 and the first and the second heater terminals 12a and 12b is the value R1-R2 that is obtained by subtracting the value R2 of the energizing resistance of the resistance heating element 11 measured in such a form that the first and the second terminal rings 14 and 3 are detached from the ceramic heater 1 for the direct energization from the first and the second heater terminals 12a and 12b from the value R1 measured in such a state that the first and the second terminal rings 14 and 3 are fitted to the ceramic heater 1, a condition 1 of (R1-R2)/R2×100<=20% is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glow plug for preheating diesel engines.

[0002]

2. Description of the Related Art Conventionally, as the above-mentioned glow plug, a glow plug in which a tip portion of a rod-shaped ceramic heater is protruded inside a tip portion of a cylindrical metal shell is widely used. The energization of the ceramic heater is performed by a metal shaft (connected to a power source) provided at the rear end of the metal shell,
This is performed via a metal lead portion connecting the metal shaft and the ceramic heater. In a conventional glow plug, the connection between a ceramic heater and a metal lead is described in, for example,
0-205753 or JP-A-2000-356
As disclosed in Japanese Patent No. 343, the tip of the metal lead is formed in a coil shape, the rear end of the ceramic heater with the heater terminals exposed is inserted into the inside, and both are brazed. It has been done by. In many cases, the other terminal of the ceramic heater is connected to a metal shell via a metal ring and grounded via an engine block to which a glow plug is attached. This metal ring is also brazed. To the ceramic heater.

[0003]

However, the joining form by brazing has a disadvantage that the efficiency is poor due to a large number of steps such as a process of assembling the material to be joined with the brazing material sandwiched therebetween and a heating process of melting the brazing material. . Also, since it is a joining of ceramic and metal members such as metal leads or metal rings, expensive active brazing materials must be used,
Further, the adjustment of the heating temperature and atmosphere for brazing is delicate, and there is a problem that the production cost is likely to increase due to the above-mentioned problem of an increase in the number of steps.

In order to generate heat in the ceramic heater of the glow plug, a current is applied to a resistance heating element embedded in the ceramic heater. As described above, when the assembly of the ceramic heater and the metal ring is fitted by an interference fit, power is supplied to the resistance heating element via the metal ring. Therefore, there is a problem of contact resistance caused by the contact between the metal ring and the ceramic heater. This contact resistance may hinder the application of a desired current to the resistance heating element. If the contact resistance is too large, heat is generated at the contact portion between the metal ring and the ceramic heater. There is a possibility. In particular, when fitting is performed by interference fit, the contact resistance tends to be higher than that of brazing.

An object of the present invention is to provide a glow plug in which a metal ring and a ceramic heater can be easily assembled, and in which electric current is well supplied to a resistance heating element.

[0006]

In order to solve the above-mentioned problems, a glow plug according to the present invention has a rod-like form, and a resistance heating element is buried in a tip end of the glow plug. A heater terminal for energizing the heating element has a ceramic heater exposed on its outer peripheral surface, and a metal fitting for covering and conducting with the heater terminal exposed on the outer peripheral surface of the ceramic heater. In a glow plug in which the joining member is attached to the outer peripheral surface of the ceramic heater in an interference fit state, the energization resistance of the resistance heating element is set in a state where the metal fitting member is attached to the ceramic heater. While measuring at room temperature through the metal fitting member,
When the metal fitting member is detached from the ceramic heater, the heater terminal is exposed, and a value measured at room temperature in a state where current is directly supplied from the heater terminal is R2, (R1-R2) / R2 × 100 ≦ 20 (%) Condition 1 is satisfied.

[0007] In the glow plug of the present invention as described above, the contact resistance caused by the fitting between the metal fitting member such as the metal ring and the ceramic heater, which is generated when the resistance heating element is energized, can be reduced. . As a result, it is possible to easily conduct current to the resistance heating element, and it is possible to satisfactorily generate heat in the resistance heating element. In addition, it also suppresses undesired heat generation at the fitting portion between the metal fitting member and the ceramic heater, and as a result,
The expansion or the like of the metal fitting member due to heat generation can be suppressed, and good fitting between the metal fitting member and the ceramic heater can be maintained.

In the above specified contact resistance, (R1-R
2) / R2 × 100 ≦ 20 (%): A metal fitting member is manufactured and the ceramic heater is fitted so as to satisfy the condition 1. At this time, by fitting the metal fitting member, a contact resistance within a range of 20% or less with respect to the conduction resistance of only the ceramic heater is allowed. If the contact resistance after the fitting exceeds 20% of the energization resistance before the fitting (resistance of only the ceramic heater), the fitting of the metal fitting member greatly increases the contact resistance. As a result, energization of the resistance heating element is hindered, and the resistance heating element does not generate heat sufficiently. In turn,
The temperature of the ceramic heater does not rise sufficiently and a good glow plug is not used. Further, at the contact surface between the metal fitting member and the ceramic heater, the contact resistance causes an excessive rise in temperature at the contact surface. As a result, the contact surface is easily oxidized with an increase in the temperature, and a vicious cycle occurs in which the contact resistance increases. On the other hand, when the above condition 1 is satisfied, the power supply to the resistance heating element is also performed well, and the resistance heating element generates heat sufficiently. As a result, the maximum temperature of the ceramic heater does not decrease, and the ceramic heater can be suitably used as a glow plug. Note that the contact resistance is (R1-R2)
If the condition of / R2 × 100 ≦ 10 (%) is further satisfied, the above effect can be obtained more effectively.

Further, in this specification, the contact resistance between the metal fitting member and the ceramic heater means the resistance at room temperature through the metal fitting member when the metal fitting member is attached to the ceramic heater. From the measured value R1 of the energization resistance when energizing the heating element, the metal fitting member is removed from the ceramic heater, the heater terminal is exposed, and the energization resistance when energizing the resistance heating element directly from the heater terminal is determined. A value obtained by subtracting the measured value R2 (that is, R1-R2).

Further, in the present invention, it is preferable that the following condition is satisfied: R1−R2 (contact resistance) ≦ 50 mΩ. Thereby, it is possible to sufficiently suppress the occurrence of contact resistance based on the contact between the metal fitting member and the ceramic heater. When starting the engine, it is preferable to raise the temperature of the ceramic heater of the glow plug to 1000 ° C. or higher. However, when the contact resistance becomes high to some extent, when the engine is started, power is not sufficiently supplied to the resistance heating element, and it takes a long time for the ceramic heater to generate heat. By satisfying the above condition 2, energization to the resistance heating element is performed well, and the time required to reach the target temperature (1000 ° C.) is reduced.
On the other hand, if the contact resistance exceeds 50 mΩ, sufficient current conduction to the resistance heating element is not performed, so that it takes a long time for the temperature of the ceramic heater to reach the target temperature (1000 ° C.). Further, heat is easily generated at a fitting portion between the metal fitting member and the ceramic heater, which is not preferable in securing durability. The contact resistance is more desirably suppressed to 25 mΩ or less, and still more desirably limited to 10 mΩ or less.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment 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.
FIG. 2 is an enlarged view of a main part thereof. The glow plug 50 has the ceramic heater 1 and the metal shell 4 holding the ceramic heater 1. The ceramic heater 1 has a rod-like shape, and a resistance heating element 11 is buried in the tip 2 of itself. In addition, a first heater terminal 12a for energizing the resistance heating element 11 is formed to be exposed on the outer peripheral surface of the rear end portion of the first heater terminal 12a. The metal shell 4 is formed in a cylindrical shape that covers the outside of the ceramic heater 1 coaxially, and the front end of the inner peripheral surface in the direction of the axis O is a heater holding surface 4a. The ceramic heater 1 is held on the heater holding surface 4a indirectly via the second terminal ring 3 and in a form in which the tip 2 protrudes. Further, the heater holding surface 4
A ring arrangement gap G is formed between the outer peripheral surface of the rear end portion of the ceramic heater 1 and the inner peripheral surface of the metal shell 4 on the rear side of a.

Next, on the outer peripheral surface of the metal shell 4, a screw portion 5 is formed as a mounting portion for fixing the glow plug 50 to an engine block (not shown), and a metal shaft 6 is mounted on a rear end portion. Have been. The metal shaft 6 has a rod-like shape, is inserted into the rear end of the metal shell 4 in the direction of the axis O, and has its own front end surface 6f in the direction of the axis O.
Are disposed so as to face the rear end face 2r of the ceramic heater 1. On the other hand, in the ring arrangement gap G, the first heater terminal 12a
And a first terminal ring 14 that is electrically connected to the first heater terminal 12a in an interference fit state. One end of the metal shaft 6 and the first heater terminal 12 a are connected to the first terminal ring 14, and the other end is electrically connected by a metal lead 17 connected to the metal shaft 6.

The outer peripheral surface of the ceramic heater 1 has an axis O
A second heater terminal 12b for energizing the resistance heating element 11 is exposed and formed in front of the first heater terminal 12a in the direction. And, the second heater terminal 12b
The cylindrical second terminal ring 3 that covers and conducts with the rear end portion of the ceramic heater 1 protrudes rearward of itself, and is tightly fitted to the outer peripheral surface of the ceramic heater 1. Installed. The metal shell 4 is attached to the outer peripheral surface of the second terminal ring 3 on the cylindrical heater holding surface 4a.

In the present invention, the heater terminal is formed by fitting the first terminal ring 14 and the second terminal ring 3 (hereinafter simply referred to as rings 14 and 3) as metal fitting members to the ceramic heater 1. The contact resistance with 12a and 12b is determined by the above condition 1 ((R1−R2) / R2 × 10
0 ≦ 20 (%)). Further, it is preferable to satisfy the above condition 2 (R1-R2 ≤ 50 mΩ).
The method of measuring the contact resistance by the second terminal ring 3 is as follows. First, as shown in FIG. 8A, the ceramic heater 1 with the second terminal ring 3 still attached is taken out from the glow plug 50. At this time, the second heater terminal 12b and the second terminal ring 3 are in a conductive state. Then, the second terminal ring 3 and the first heater terminal 12a
And a resistance is measured by passing a current between the two, and the measured value is defined as a resistance before decomposition R1 (Ω). Next, as shown in FIG. 8B, the fitted second terminal ring 3 is detached from the ceramic heater 1 to be in a disassembled state. The second heater terminal 12b exposed on the outer peripheral surface of the ceramic heater 1
The resistance between the first heater terminal 12a and the first heater terminal 12a is measured, and is set as a post-decomposition resistance R2 (Ω). The contact resistance between the second terminal ring 3 as the metal fitting member and the second heater terminal 12b is R2
Expressed as -R1 (Ω). Further, the contact resistance of the first terminal ring 14 can be measured in the same manner. The resistance before disassembly (R1) is a current-carrying resistance with the first terminal ring 14 and the second terminal ring 3 attached, and is based on both the first terminal ring 14 and the second terminal ring 3 based on this. This contact resistance may be the contact resistance in this specification.

The reduction in contact resistance also depends on the material and thickness t, t 'of the metal fitting members, that is, the rings 3, 14. As shown in FIG. 5, in the disassembled state where the first terminal ring 14 or the second terminal ring 3 as the metal fitting member is removed from the ceramic heater 1,
The inside diameter of the metal fitting member is d1 (d1 ′), and the first heater terminal 12a (second heater terminal 1
The outer diameter of the ceramic heater 1 at the formation position of 2b) is d2
As (d2 '), d2-d1 (d2'-d1') (hereinafter referred to as post-decomposition interference: in the present specification, means a value in a room temperature state) is 8 μm or more and the metal fitting member 2% of the outer diameter of the ceramic heater at the mounting position
It is desirable that the thickness be adjusted to the following range, particularly 8 to 100 μm. Further, as described later, the metal shell 4
The same rule can be applied when is a metal fitting member.

The interference after the disassembly is set by the ceramic heater 1
It can be seen as a parameter reflecting the amount of elastic return of the rings 14, 3 when removed from the ceramic heater 1, that is, the elastic binding force of the rings 14, 3 to the ceramic heater 1. If the interference after the disassembly is less than 8 μm, when the temperature of the ring 3 or 14 rises to the normal operating temperature range of the glow plug,
Necessary tightness cannot be secured. For example, an increase in contact resistance with the first heater terminal 12a in the first terminal ring 14 and an increase in contact resistance with the first heater terminal 12b in the second terminal ring 3 occur as specific problems. Leads to. On the other hand, if the interference after disassembly exceeds 2% of the outer diameter of the ceramic heater 1 at the mounting position of the first terminal ring 14 or the second terminal ring 3 (for example, 70 μm when the outer diameter is 3.5 mm). An excessive tightening force acts on the ceramic heater 1, which may lead to the occurrence of cracks, cracks, and the like. If the thickness of the rings 3 and 14 is small, the amount of plastic deformation of the rings themselves increases, so that it may be essentially impossible to set the interference after disassembly to 100 μm or more. The post-disassembly interference d2-d1 or d2'-d1 'is more desirably adjusted to a range of 15 to 40 [mu] m. Also, even with the same post-disassembly interference value, a larger ring thickness is more advantageous from the viewpoint of increasing the value of elastic binding force, which in turn contributes to a reduction in contact resistance. Become. In the present embodiment, the thickness t ′ of the second terminal ring 3 required to be airtight is changed to the thickness t of the first terminal ring 14.
It is set larger than.

The materials constituting the first and second terminal rings 14, 3 and the like as metal fitting members include high-temperature strength,
In consideration of the balance with material costs, it is desirable to use, for example, an Fe-based alloy having a certain degree of hardness and heat resistance. In particular, in order to increase the tightening margin after disassembly and sufficiently secure elastic binding force, Vickers hardness (JIS: Z2
It is recommended to use an Fe-based alloy having an Hv of 170 or more (preferably 350 or more) (value measured at a load of 10 N according to the method specified in H.244 (1998)). Such Fe
As a system alloy, a precipitation hardening stainless steel such as SUS630 or SUS631 can be suitably used. For example, S
US630 is H900, H1025, H1075 or H11 specified in JISG4303 (1988).
Aging precipitation hardening can be achieved by any of the heat treatments of No. 05, and particularly, those subjected to H900 treatment can secure Hv 350 or more. On the other hand, SUS631 is TH1 of the same standard.
Aging precipitation hardening can be performed by heat treatment of 050 or RH950, and Hv350 or more can be ensured in each case. In addition, ferrite stainless steel such as SUS430 can be used although the hardness is slightly inferior.

When it is required to ensure higher heat resistance and further suppress the decrease in the binding force at a high temperature, an iron-based super heat-resistant alloy (for example, Incoloy 909 (trade name of Inco) )), An age-hardened product of a Ni-base super heat-resistant alloy (for example, Waspaloy (trade name of United Technology)), or a non-age-hardened Ni
Base heat-resistant alloy (Inconel 625 (trade name of Inco))
It is also possible to use a work hardened product or the like. However,
These materials are expensive, and are in a normal use environment of the glow plug.
About 200 ° C., the temperature reached by the second terminal ring 3 is 500 to
When the temperature is kept up to 700 ° C., the total content of alloying elements added for matrix solid solution strengthening or precipitate formation, such as Ni, Cr, Cu, Nb or Al, such as the above precipitation hardening stainless steel, , 50 mass% or less is desirably made of an Fe-based alloy. However, from the viewpoint of ensuring high-temperature strength or corrosion resistance, it is preferable that the total content of these components be 20% by mass or more.

Further, from the viewpoint of reducing contact resistance,
When the metal fitting member is removed from the ceramic heater 1, the surface roughness Rz1 of the fitting surface on the gold fitting member side is 1
The thickness is preferably set to 0 μm or less. When the metal fitting member is removed from the ceramic heater 1, the surface roughness Rz2 of the fitting surface on the ceramic heater 1 side is 5 μm.
m. If the surface roughness of the mating surface after removal exceeds the above range, the contact area between the metal fitting member and the ceramic heater 1 decreases, and the two cannot be sufficiently fitted, and as a result, the contact resistance increases. Lead to. Desirably, Rz1 is 6 μm or less and Rz2 is 3 μm or less.

In this specification, the surface roughness Rz (Rz
1 and Rz2) refer to the ten-point average roughness (Rz) of each surface measured by the method specified in JIS-B0601 (1994). The measurement length is 3.2 mm and the cutoff value is 0.8 mm. In addition, in order to define the surface roughness of each fitting surface, it is naturally possible to adopt an arithmetic average roughness Ra, a maximum height Rmax, and the like, in addition to the ten-point average roughness Rz. Arithmetic mean roughness (Ra1 and Ra
2) and the maximum heights (Rmax1 and Rmax2) also refer to those measured by the method specified in the above JIS, and the cutoff value, the reference length, and the evaluation length are also specified in the above JIS. Shall be used.

The case of contact resistance between the first and second terminal rings 14, 3 as metal fitting members and the ceramic heater 1 has been described above. However, the present invention is not limited to this, and the present invention is not limited thereto. This is the same even when 4 is a metal fitting member. In this case, the contact resistance is defined as the difference in the current-carrying resistance between the heater terminals before and after the metal shell 4 is removed.

That is, as shown in FIG.
It is also possible to adopt a configuration in which the outer peripheral surface of the ceramic heater 1 is directly held by the interference fitting on the heater holding surface 4a. In this case, the metal shell 4 can be a metal fitting member. In order to form the ring arrangement gap G, the distal end of the inner peripheral surface of the metal shell 4 in the direction of the axis O is reduced in diameter by the reduced diameter portion 4r, and the inner peripheral surface of the reduced diameter portion 4r is formed as the heater holding surface 4a. can do. In addition,
1 and 2, a small diameter portion 4r 'is formed in the metal shell 4 in order to enlarge the ring arrangement gap G, but by increasing the thickness of the second terminal ring 3, The reduced diameter portion 4r 'can be omitted.

Next, as to the manner of assembling the metal shell 4 and the second terminal ring 3, for example, brazing is performed so as to fill the gap between the inner and outer peripheral surfaces of the metal shell 4 and the second terminal ring 3. The outer peripheral surface of the second terminal ring 3 may be fixed by laser welding all around. In the present embodiment, the metal shell 4 is also fixed on the heater holding surface 4a.
The outer peripheral surface of the second terminal ring 3 is fitted in a tight fit. Thereby, the assembly process of the glow plug 50 can be further simplified. Further, the fitting surface (heater holding surface 4 a) of the metal shell 4 with the second terminal ring 3 overlaps with the fitting surface of the second terminal ring 3 with the ceramic heater 1. The tightness of the metal shell 4 is superimposed on the tightness of the terminal ring 3, and the airtightness of the fitting between the second terminal ring 3 and the ceramic heater 1 can be further enhanced.

Each terminal ring 1 to ceramic heater 1
As shown in FIG. 4, for example, as shown in FIG. 4, the individual terminal rings 14 or 3 can be assembled by press-fitting the ceramic heater 1 while inserting the terminal rings 14 or 3 from the ends in the axial direction. Note that shrink fitting may be used instead of press fitting. Among them, the first terminal ring 14 only needs to have a sufficient binding force to ensure conduction with the first heater terminal 12a. On the other hand, for the second terminal ring 3, in addition to ensuring conduction with the second heater terminal 12b, it is necessary to ensure airtightness on the mating surface. Can be In any case, it is important that the necessary and sufficient binding force is secured even at room temperature and also when the temperature of the ceramic heater 1 where the thermal expansion occurs in each part increases. In general, when comparing ceramic and metal, the metal has a higher linear expansion coefficient except for a special alloy such as invar, and the terminal rings 14 and 3 tend to loosen the binding force when the temperature rises. The temperature reached by the terminal rings 14 and 3 varies depending on the operating condition of the engine to which the glow plug 50 is attached, but is, for example, about 50 to 200 ° C.

As shown in FIG. 2, the metal lead 17 is
It is arranged in a bent form between the metal shaft 6 and the first terminal ring 14. As a result, even when a heating / cooling cycle is applied due to the heat generated by the ceramic heater 1, the metal lead portion 17 can absorb the expansion / contraction at the bent portion, so that the metal lead portion 17 and the first terminal ring 14 can be absorbed. It is possible to prevent excessive stress from concentrating on the joint portion with the contact member, thereby preventing problems such as poor contact and disconnection. On the other hand, in order to easily and firmly join the metal lead 17 and the metal shaft 6, the joint end of the metal lead 17 with the metal shaft 6 has a flat shape with respect to the tip of the outer peripheral surface of the metal shaft 6. Are joined together. For example, the metal lead 17 and the metal shaft 6
In the case of joining by means of resistance welding, it is advantageous to form the joining surface in a plane shape, in order to uniformly apply the pressing force at the time of resistance welding and to form a weld having few defects.

On the other hand, when joining the metal lead portion 17 and the first terminal ring 14, the first terminal ring 14 is first attached to the ceramic heater 1 so that the first terminal ring 14 is not obstructed when the first terminal ring 14 is assembled into the ceramic heater 1 by press fitting or the like. After being assembled to the ceramic heater 1, it is desirable to join the terminal end of the metal lead 17 to, for example, the outer peripheral surface of the assembled first terminal ring 14. In this case, resistance welding can be adopted as the joining method.

Next, the ceramic heater 1 includes a resistance heating element 11 in a ceramic base 13 made of insulating ceramic.
Are embedded as rod-shaped ceramic heater elements. In the present 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 resistor portion 11 made of a first conductive ceramic disposed at the tip of the ceramic heater 1 and functioning as a resistance heating element. The second conductive member is arranged so as to extend in the direction of the axis O of the first conductive member. A pair of second resistor portions made of ceramic. In the pair of second resistor portions 12 and 12 of the ceramic resistor 10, branch portions are respectively formed at different positions in the direction of the axis O, and the branch portions are exposed to the surface of the ceramic heater 1. Are respectively formed with a first heater terminal 12a and a second heater terminal 12b.

The energization of the resistance heating element 11 is performed, for example, as shown in FIG. 6, by burying lead wires 18 and 19 made of a refractory metal wire such as W embedded in the ceramic base 13.
Can also be performed via In this case, the first heater terminal is formed as the exposed portion 18a and the second heater terminal is formed as the exposed portion 18a of the embedded lead wire 19. In this case, also in this case, the first terminal ring 14
The contact resistance between the second terminal ring 3 and the ceramic heater 1 is within the scope of the present invention.

Next, as the insulating ceramic constituting the ceramic base 13, a silicon nitride ceramic is employed in this embodiment. The structure of the silicon nitride ceramic has a form in which main phase particles mainly composed of silicon nitride (Si ₃ N ₄ ) are bound by a grain boundary phase derived from a sintering aid component described later. The main phase may be a phase in which Si or N is partially substituted by Al or O, or a phase in which metal atoms such as Li, Ca, Mg, and Y are dissolved in the phase. .

In the silicon nitride ceramics, 3 of the periodic table is used.
A, 4A, 5A, 3B (for example, Al) and 4B (for example, Si) and at least one element selected from the group consisting of Mg and Mg as the above-mentioned cation element, in terms of the content in the whole sintered body, It can be contained in a conversion of 1 to 10% by mass. These components are mainly added in the form of oxides,
In the sintered body, it is mainly contained in the form of an oxide or a composite oxide such as silicate. If the sintering aid component is less than 1% by mass, it is difficult to obtain a dense sintered body, and if it exceeds 10% by mass, insufficient strength, toughness or heat resistance is caused. The content of the sintering aid component is desirably 2 to 8% by mass.
It is good to do. When a rare earth component is used as a sintering aid component, Sc, Y, La, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
u can be used. Among them, Tb and D
Since y, Ho, Er, Tm, and Yb have the effect of promoting crystallization of the grain boundary phase and improving the high-temperature strength, they can be suitably 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 resistivity as described above. The method of making the electric resistivity of both conductive ceramics different from each other is not particularly limited. For example, a method of using the same kind of conductive ceramic phase and making the contents different from each other; Various methods, such as a method employing a conductive ceramic phase;
In this embodiment, the following method is adopted.

As the conductive ceramic phase, for example, tungsten carbide (WC), molybdenum disilicide (MoSi
₂ ) and known materials such as tungsten disilicide (WSi ₂ ). In the present embodiment, WC is adopted.
In order to reduce the difference in linear expansion coefficient from the ceramic base 13 and increase the thermal shock resistance, an insulating ceramic phase which is a main component of the ceramic base 13, here, a silicon nitride ceramic phase can be blended. Therefore, by changing the content ratio between the insulating ceramic phase and the conductive ceramic phase, the electric resistivity of the conductive ceramic constituting the resistor portion can be adjusted to a desired value.

Specifically, the first conductive ceramic, which is the 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 remainder is an insulating ceramic phase. It is good to do. When the content of the conductive ceramic phase exceeds 25% by volume, the conductivity becomes too high and a sufficient calorific value cannot be expected. When the content is less than 10% by volume, the conductivity becomes too low. Cannot be secured sufficiently.

On the other hand, the second resistor portions 12, 12 serve as a conduction path to the first resistor portion 11, and the second conductive ceramic, which is a material thereof, has a conductive ceramic phase content of 15%. -30% by volume, with the balance being an insulating ceramic phase. If the content of the conductive ceramic phase exceeds 30% by volume, it becomes difficult to densify by firing, and the strength tends to be insufficient. In addition, even when the temperature reaches the temperature range usually used for preheating the engine, the electric resistivity is low. In some cases, the rise becomes insufficient and the self-saturation function for stabilizing the current density cannot be realized. On the other hand, when the volume is less than 15% by volume, the heat generation in the second resistor portions 12 and 12 becomes too large, and the heat generation efficiency of the first resistor portion 11 is deteriorated. In the present embodiment, the content of WC in the first conductive ceramic is 16% by volume (55% by mass), and the content of WC in the second conductive ceramic is 20% by volume (7%).
0% by mass) (all the rest are silicon nitride ceramics (including a sintering aid)).

In this embodiment, the ceramic resistor 10
Are 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 a U-shaped shape. Bar-shaped portions extending substantially in parallel with each other in the direction of the axis O from both ends of the one resistor portion 11 are formed.

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

Note that, as shown in FIG.
In the structure in which the heater 19 is disposed in the ceramic, when a voltage for driving the heater is applied under a high temperature,
In some cases, the metal atoms constituting 19 are consumed by the so-called electromigration effect that they are forcibly diffused toward the ceramic side by receiving the electrochemical driving force due to the electric field gradient, and the disconnection or the like is likely to occur. However, FIG.
Since the buried lead wire is eliminated in the above configuration, there is an advantage that the effect of the electromigration effect is essentially low.

Next, as shown in FIG. 1, a metal shaft 6 for supplying electric power to the ceramic heater 1 is insulated from the metal shell 4 inside the rear end of the metal shell 4 as described above. Are located. In the present embodiment, the ceramic ring 3 is placed between the outer peripheral surface on the rear end side of the metal shaft 6 and the inner peripheral surface of the metal shell 4.
1, and a glass-filled layer 32 is formed and fixed on the rear side thereof. A ring-side engaging portion 31a is formed on the outer peripheral surface of the ceramic ring 31 in the form of a large-diameter portion. By engaging with the side engaging portion 4e, the axially forward side is prevented from coming off. In addition, the outer peripheral surface portion of the metal shaft 6 that comes into contact with the glass-filled layer 32 is provided with unevenness by knurling or the like (a hatched area in the figure). Further, the rear end of the metal shaft 6 extends rearward of the metallic shell 4, and the terminal fitting 7 is fitted into the extended portion via an insulating bush 8. The terminal fitting 7 is fixed in a conductive state to the outer peripheral surface of the metal shaft 6 by a circumferential caulking portion 9.

The glow plug 50 is attached to the diesel engine such that the tip 2 of the ceramic heater 1 is located in the combustion chamber at the attachment portion 5 of the metal shell 4. Then, by connecting the terminal fitting 7 to a power source, the metal shaft 6 → the metal lead 17 → the first terminal ring 14 → the ceramic heater 1 → the second terminal ring 3 → the metal shell 4 → (ground via the engine block). The current flows in this order, and the tip 2 of the ceramic heater 1 generates heat, so that the combustion chamber can be preheated.

Hereinafter, a method of manufacturing the glow plug 50 will be described. First, as shown in FIG. 3, a resistor powder molding section 34 to be the ceramic resistor 10 is formed by injection molding. In addition, by dividing the raw material powder for forming the ceramic base 13 into a die press in advance, divided preformed bodies 36 and 37 are separately prepared as base formed bodies formed separately in the upper and lower parts. These divided preforms 3
6, 37, a concave portion 37a having a shape corresponding to the resistor powder molded portion 34 (the concave portion on the divided preformed body 36 side is not shown in the drawing) is formed on its mating surface, and the resistor The divided preform 36 containing the powder molding part 34
37 are fitted on the mating surface, and further pressed and compressed to produce a composite molded body 39 in which these are integrated as shown in FIG. 3B.

The thus obtained composite molded body 39 is subjected to a binder removal treatment and then fired at 1700 ° C. or more, for example, about 1800 ° C. by a hot press or the like, thereby obtaining a fired body and further polishing the outer peripheral surface to a cylindrical shape. Thus, a ceramic heater 1 is obtained. Then, as shown in FIG. 4, the first terminal ring 14 and the second terminal ring 3 are tightly fitted to the ceramic heater 1 by, for example, press-fitting, and necessary parts such as the metal lead portion 17 and the metal shell 4 are further mounted. When assembled, the glow plug 50 shown in FIG. 1 is completed.

[0042]

EXAMPLES The results of experiments conducted to confirm the effects of the present invention will be described below. First, the ceramic heater 1 having the configuration shown in FIG. 1 was manufactured by the method described above. However, the length of the ceramic heater 1 is 40 mm, the outer diameter is 3.5 mm, the thickness of the second resistor portions 12, 12 is 1 mm, and the first heater terminal 12a and the second heater terminal 12b each have a diameter. It was a 0.8 mm circular area.

On the other hand, the first terminal ring 14 and the second terminal ring 3 were manufactured using SUS630 (H900 age hardened product: Hv = about 400). The thickness of the first terminal ring 14 is 0.3 mm, and the inner diameter d1i is 3.
One having a size of 45 mm was prepared. On the other hand, the thickness of the second terminal ring 3 is 0.85 mm, and the inner diameter d1i ′ is 3.
One having a size of 45 mm was prepared.

Next, the first terminal ring 14 and the second terminal ring 3 were assembled into the ceramic heater 1 at a predetermined position by press fitting. At the time of press-fitting, an appropriate amount of a lubricant (Paskin M30 (trade name: manufactured by Kyoeisha Chemical Co., Ltd.)) was applied to the inner surface of each ring, and the lubricant was decomposed at 300 ° C. after press-fitting.

The press-fitted first terminal ring 14
Was removed, the first heater terminal 12a was exposed, and the resistance when a current was applied between the second terminal ring 3 and the first heater terminal 12a was measured to obtain the resistance R1 before disassembly. Next, the first terminal ring 14 and the second terminal ring 3 are removed from the ceramic heater 1, the first heater terminal 12a and the second heater terminal 12b are exposed, and a current is applied between the terminals to measure the resistance. The post-resistance is R2. All of these measurements were performed at room temperature (20 ° C.). By subtracting R2 from R1, the value of the contact resistance (R1-R2) due to the fitting of the second terminal ring 3 and the ceramic heater was determined.

In the glow plug 50 before the first terminal ring 14 and the second terminal ring 3 were removed, a DC voltage of 11 V was continuously applied between these terminal rings for 60 seconds. By conducting such an energization, the temperature becomes constant and a steady state is reached after 60 seconds. Example 1 As Example 1, the highest temperature in the steady state at the tip of the ceramic heater 1 at this time was measured. Table 1 and FIG. 9 show the results of the obtained contact resistance and the maximum attained temperature.

[0047]

[Table 1]

In Table 1 and FIG. 9, in the glow plug of the present invention that satisfies the condition 1, the maximum attainable temperature is maintained at 1200 ° C. or more in the steady state. On the other hand, it can be seen that, if the value falls outside the range of the present invention where the condition 1 is not satisfied, the maximum temperature rapidly decreases.

(Embodiment 2) In the embodiment 1 above, those satisfying the condition 1 show almost no change in the maximum attained temperature and show a good maximum attained temperature in any of the embodiments. In the examples,
There was a difference in the time required to reach the target temperature. That is, the product of the present invention satisfying the condition 1 is the product of the present invention. Start engine for 1 to 3 (ignite fuel)
The time required for the temperature of the ceramic heater to reach the target attainment temperature (10000 ° C.) required for the measurement was measured. Obtained contact resistance (mΩ) and time to reach 1000 ° C (sec)
Are shown in Table 2 and FIG.

[0050]

[Table 2]

According to Table 2 and FIG. In the embodiment No. 1, which satisfies the condition 2 among the cases Nos. 1, 2, and 3, In 1 and 2, since the time required to reach 1000 ° C. is 4 seconds, the engine can be started quickly. Example No. 2 which does not satisfy the condition 2. In the case of Example No. 3 from the viewpoint of the time to reach the target attainment temperature. It turns out that it is less than 1 and 2.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing one embodiment of a glow plug of the present invention.

FIG. 2 is a longitudinal 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 an explanatory view following FIG. 2;

FIG. 5 is a view for explaining parts used for calculating a post-disassembly interference.

FIG. 6 is an essential part longitudinal cross sectional view showing a first modification of the glow plug of FIG. 1;

FIG. 7 is a longitudinal sectional view of a main part showing a second modified example.

FIG. 8 is a diagram illustrating a method for measuring contact resistance.

FIG. 9 is a first graph showing experimental results of the example.

FIG. 10 is a second graph showing experimental results of the example.

[Explanation of symbols]

 Reference Signs List 1 ceramic heater 2 tip 3 second terminal ring (metal fitting member) 4 metal shell (metal fitting member) 4a heater holding surface 10 ceramic resistor 11 first resistor portion (resistance heating element) 12, 12 second Resistor portion 12a First heater terminal (heater terminal) 12b Second heater terminal (heater terminal) 14 First terminal ring (metal fitting member) 41 Metal coating layer 50 Glow plug

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Suzuki 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside Nihon Special Ceramics Co., Ltd. (72) Inventor Masaya Ito 14 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture No. 18 Inside Japan Special Ceramics Co., Ltd.

Claims (3)

[Claims] 1. A ceramic heater having a rod-like shape, a resistance heating element buried at a tip end thereof, and a heater terminal for energizing the resistance heating element formed exposed on its outer peripheral surface. And a metal fitting member that covers the heater terminal exposed on the outer peripheral surface of the ceramic heater and conducts with the heater terminal,
In the glow plug attached to the outer peripheral surface of the ceramic heater in a tight fit state, the energization resistance of the resistance heating element may be adjusted in a state where the metal fitting member is attached to the ceramic heater. Measured at room temperature through the member, the value was set to R1, the metal fitting member was removed from the ceramic heater, the heater terminal was exposed, and the temperature was measured at room temperature in such a way that the heater terminal was directly energized. A glow plug characterized in that, when the value obtained is R2, (R1-R2) / R2 x 100 ≤ 20 (%). 2. The glow plug according to claim 1, wherein R1−R2 ≦ 50 mΩ. 3. The metal fitting member is formed in a ring shape, and when the metal fitting member is removed from the ceramic heater, the inner diameter of the metal fitting member is d1, and the metal fitting member is in the disassembled state. Where d2-d1 is at least 8 m and 2% of the outer diameter of the ceramic heater at the mounting position of the metal fitting member, where d2 is the outer diameter of the ceramic heater at the position where the heater terminal is formed.
The glow plug according to claim 1, wherein the glow plug is adjusted to the following range.