JPH07217881A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To prevent a crack from being generated at a ceramic heater caused by a thermal expansion difference between a metallic outer cylinder and a ceramic heater. CONSTITUTION:A ceramic heater having a heater buried within a ceramic sintered member therein is projected out at its extremity end from a metallic outer cylinder 4 inserted into and fitted to an outside part of the ceramic heater and connected to its inner cavity. This metallic outer cylinder 4 is connected to the inner cavity at the extremity end of a fixing fitting 5 so as to form a ceramic glow plug. A thickness of the metallic outer cylinder 4 inserted into and fitted to an outer side of the ceramic heater 1 is made thinner at its' heat generating section as compared with that of the fixing fitting 5, and a section where the thickness is transmitted from the thin part to the thick part is formed into a tapered section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic glow plug mounted on a diesel engine mainly for starting.

[0002]

2. Description of the Related Art Generally, a diesel engine has a poor startability at a low temperature. Therefore, a glow plug is attached to an auxiliary chamber or the like provided in an engine head. There is a method to increase the temperature by burning to improve the engine startability, and it tends to be used as an afterglow for a long time to stabilize the combustion even after starting, improving the durability of the glow plug. In particular, the heater part is liable to be damaged under the conditions such as the heat cycle of severe rapid heating and quenching in the room and vibration shock during operation, so it is reinforced by the metal outer cylinder to increase the mechanical strength. However, improvements were still required.

A glow plug consisting of a ceramic heater 1 and a metal outer cylinder 4 and a fitting 5 for reinforcing the base of the ceramic heater 1 is a cylinder so that the ceramic heater 1 of the glow plug is directly exposed in the engine sub-chamber or the main combustion chamber. It is used by being attached to the head, and the metal outer cylinder 4 is cylindrical and is configured to cover the base side of the ceramic heater.

When operated in such an attached state, the ceramic heater 1 having a heating resistance wire made of tungsten, tungsten-rhenium alloy or the like embedded in a sintered body mainly composed of silicon nitride is exposed to a long-term heat history. If it receives, peeling may occur at the boundary surface between the heating resistance wire and the ceramic material of the ceramic heater due to a difference in thermal expansion between the two, or a minute crack may occur.

The ceramic heater 1 will be described with reference to an enlarged view of FIG.
In particular, the connection portion 21 wound with is large in cross-sectional area of the electrode with respect to the cross-sectional area of the ceramic heater 1, and has a high rate of peeling or cracking at the boundary surface.

In order to prevent the separation and the generation of minute cracks at the boundary surface, Japanese Patent Laid-Open No. 61-179084 discloses a method of adding various inclusions to the material of the ceramic heater. Kaihei 1-157084 discloses a method of forming an intermediate layer on the surface of a heating resistance wire.

[0007]

Conventionally, however, only the material of the ceramic heater and the electrode lead-out wires 3 and 3'and the heating resistance wire 2 which have the thermal expansion difference when the ceramic heater is subjected to the thermal history are heated. Since the countermeasure is applied to the target and the thermal stress applied to the ceramic heater 1 from the metal outer cylinder 4 is not taken into consideration, the above method cannot sufficiently prevent the occurrence and development of peeling and microcracks.

In Japanese Utility Model Laid-Open No. 61-181956, a countermeasure is taken by suggesting that the cause of the damage of the ceramic heater part is a sharp temperature gradient at the end of the metal outer cylinder. The stress generated by the difference in thermal expansion between the outer cylinder and the ceramic heater is considerably large, and the stress is transmitted to the ceramic heater through the brazing material 6 existing between the metal outer cylinder and the ceramic heater, so that the above-mentioned peeling occurs. Occurrence and development of minute cracks.

The present invention provides a shape of a metal outer cylinder for alleviating stress caused by a difference in thermal expansion between the metal outer cylinder and the ceramic heater.

[0010]

In order to achieve the above object, the invention of claim 1 is such that a ceramic heater having a heating element embedded in a ceramic sintered body is provided with a tip end from a metal outer cylinder inserted into the outside thereof. A ceramic glow plug formed by projecting a portion and being joined to the inner cavity thereof, and the metal outer tube being joined to the tip end inner cavity of the mounting member, wherein the thickness of the metal outer tube to be fitted outside the ceramic heater is It is a gist of the invention to provide a ceramic glow plug in which the heat generating portion side is thinner than the mounting metal portion side, and a portion transitioning from a thin portion to a thick portion is formed in a tapered shape.

A second aspect of the present invention provides the ceramic glow plug according to the first aspect, wherein the thickness of the metal outer cylinder on the heat generating portion side is 0.3 mm or more.

According to a third aspect of the present invention, the thickness (T) of the metal outer cylinder on the side of the mounting bracket is 0.5 to 1.0 mm, and the step difference with the thickness (t) on the side of the heat generating portion is 0. 2 mm or more,
The length (L) of the thin portion of the metal outer cylinder is 1.0 to 2.0 times the distance (l) from the end surface of the metal outer tube on the heat generating portion side to the end surface of the electrode lead wire on the heat generating portion side. The gist of the invention is the ceramic glow plug according to claim 1 and claim 2.

[0013]

According to the present invention, the thickness of the metal outer cylinder 4 inserted into the outside of the ceramic heater is smaller on the heat generating portion side than on the mounting metal fitting side, and the portion transitioning from the thinner portion to the thicker portion is tapered. Since it is formed into a shape, the longitudinal compressive stress applied to the ceramic heater due to the difference in thermal expansion between the ceramic heater and the outer cylinder, which is generated in the thin portion of the metal outer cylinder, is equal to the thickness of the metal outer cylinder over the entire length. And the thickness T on the side of the mounting bracket is the same as when it is the same.

Further, since the transition portion from the thick portion to the thin portion of the metal outer cylinder 4 is formed into a tapered shape, the ceramic heater 1 and the metal outer cylinder 4 are prevented from changing in abrupt cross-sectional area. The longitudinal compressive stress applied to the ceramic heater 1 by heating and cooling due to the difference in thermal expansion between
It is not discontinuous and the stress concentration area is reduced.

Further, when the stress is applied in the direction perpendicular to the major axis direction, the taper portion of the metal outer cylinder 4 prevents the strength against bending from decreasing.

The length L of the thin portion of the metal outer cylinder 4 on the heat generating portion side is set to 1.0 from the distance l from the end surface of the metal outer casing 4 on the heat generating portion side to the end surface of the electrode lead wire on the heat generating portion side. By making it 2.0 times, the connecting portion 21 in which the heating resistance wire 2 is wound around the electrode lead-out wires 3 and 3 ′ inside the ceramic heater is
The cross-sectional area of the electrode is large relative to the cross-sectional area of the ceramic heater, and the rate of peeling and cracking at the boundary surface is high. It is possible to relieve the tensile / compressive stress due to the difference in thermal expansion between the outer cylinder and the ceramic heater in a particularly weak part. .

The thickness T of the metal outer cylinder 4 on the side of the mounting bracket is set to 0.5.
The reason for setting 1.0 to 1.0 mm is to provide a step with the heat generating portion side of the metal outer cylinder 4 when it is less than 0.5 mm, and to provide the heat generating portion side with a minimum required strength. If it is larger than 0 mm, the glow plug mounting bracket 5 is restricted due to the inner diameter of the glow plug mounting hole in the cylinder head on the engine side.
Since the maximum value of the inner diameter is inevitably determined and the maximum value of the outer diameter of the metal outer cylinder 4 inserted on the inner diameter side of the mounting bracket 5 is determined,
There is no choice but to reduce the outer diameter of the ceramic heater 1, and to reduce the outer diameter with the heating resistance wire 2 inside the ceramic heater 1 is to review the firing conditions of the ceramic and the dimensions of each part inside the ceramic heater 1. This is because changes are required and manufacturing difficulties are involved.

The thickness t of the metal outer cylinder 1 on the heating portion side is 0.3 mm.
The reason for the above is that it is desirable to be at this level or more in order to secure the strength of the outer cylinder for protecting the ceramic heater.

The length L of the thin portion of the metal outer cylinder 4 is such that the electrode lead-out lines 3, 3'from the end face 41 of the metal outer cylinder on the heat generating portion side.
1.0 to 2.0 times the distance 1 to the end face of the heat generating part on the side of is that the distance between the end face of the electrode lead wire on the heat generating part side and the end face of the outer tube on the heat generating part side is taken into consideration. If it is less than 0.0 times, it becomes impossible to cover the connecting portion 21 where the electrode lead-out wires 3 and 3'and the heating resistance wire 2 are wound, and if it is more than 2.0 times, the thickness of the metal outer cylinder is thin. The lengthening of the portion makes it impossible to ensure sufficient strength as a protective outer cylinder for protecting the ceramic heater 1, and the ceramic heater 1 cracks when stress is applied in a direction perpendicular to the long axis direction, This is because cracks may occur and disconnection may occur inside the ceramic heater 1.

[0020]

【Example】

Embodiment 1 FIG. 1 is a vertical sectional view of a ceramic glow plug showing an embodiment of the present invention, in which reference numeral 1 is a ceramic heater serving as a heating element, such as tungsten, molybdenum,
In addition to exothermic wires of refractory metals such as tungsten-rhenium alloys, molybdenum silicide, Ti, Zr, Hf, La, V, Nb, Ta, which are transition elements of IVa group, Va group, and VIa group,
-A heating wire 2 formed by using a conductive ceramic or the like containing one or more carbides and / or nitrides of a metal selected from the group consisting of Cr, Mo, and W, and bending it in a U-shape in the central portion 2 Has electrode lead-out lines 3 and 3'welded to both ends thereof and embedded in a ceramic sintered body containing, for example, Si ₃ N ₄ as a main component, and preferably the heater has a perfect circle. It is formed in a rod shape.

The ceramic heater 1 is fitted with a pipe-shaped metal outer cylinder 4 having a step, and a portion of the ceramic heater 1 and a silver brazing material 6 are attached to the electrode lead-out line 3 of the heating resistor.
The ceramic heater 1 is held by being appropriately protruded (preferably not more than 3 times the outer diameter of the heater) from the tip of the metal outer cylinder 4.

Further, the metal outer cylinder 4 and the silver brazing material are inserted into the inner cavities of the metal outer cylinder 4 and the mounting bracket 5 so as to have a step portion at least on the tip side of the end surface on the ignition side of the mounting bracket 5. The negative electrode is formed by brazing with the material 7 or the like.

On the other hand, at the rear end of the ceramic heater 1, a metal cap 9 provided with the other lead rod 8 of the heating resistor 2 brazed together with the metal outer tube 4 is abutted and electrically connected. The other end of the lead rod 8 is welded to the center shaft 10 and the insulator 11 is interposed between the mounting member 5 and the nut 12, and is tightened and fixed. The negative electrode of the mounting member 5 and the positive electrode on the nut side are It is insulated to form a glow plug.

Further, the ceramic heater 1 is provided with a heating resistor having a heating portion in which a line interval is closely wound in a molded body formed into a rod shape having a semicircular cross section, and then another cross section is placed on the upper surface thereof. A semi-circular rod-shaped molded body is overlaid, pressure-fired and integrated.

The connecting portion 21 around which the electrode lead wire and the heating resistance wire are wound has a large cross-sectional area of the electrode with respect to the cross-sectional area of the ceramic heater 1 and a high rate of peeling or cracking at the boundary surface, resulting in high strength. Therefore, it is installed and protected so as to be located inside the metal outer cylinder.

Since the wound portion is the weakest portion in terms of strength, it is positioned closer to the fitting side than the end face 41 on the heat generating portion side of the metal outer tube, and the metal outer tube 4 reinforces the ceramic heater 1. For this reason, it is usually located within about 3 mm from the end surface 41 of the metal outer cylinder on the heat generating portion side.

As the material of the metal outer cylinder 4, a heat-resistant alloy containing Ni as a main component (trade name Inconel 601) is used.
Samples for evaluation were prepared with various outer diameters of the outer cylinder on the side of the mounting bracket and on the outer cylinder tip side, and the outer diameter of the ceramic heater 1 was constant (φ 3.5 mm).

Using the sample for evaluation, the glow plug is heated by repeating ON and OFF of energization so that the temperature of the tip of the ceramic heater 1 becomes a heat curve as shown in the graph of FIG. The ceramic heater 1 was repeatedly heated and cooled and evaluated by the number of crack generation cycles of the ceramic heater 1.

The results are shown in FIG. 5, which shows a situation in which the number of crack generation cycles changes when the number of crack generation cycles when there is no step is set to 1 and the steps are sequentially increased. is there

As a result, the thickness of the metal outer cylinder 4 inserted into the outer side of the ceramic heater 1 is made thicker on the side of the mounting fitting than on the side of the heat generating portion, and the portion transitioning from the thinner portion to the thicker portion is tapered. By doing so, cracks are less likely to occur as compared with the case where the thickness is constant, and it is particularly desirable that the thickness T on the mounting metal side is 0.5 to 1.0 mm. The step is preferably 0.2 mm or more, and the length L of the thin portion of the metal outer cylinder is a distance l from the end surface of the metal outer tube on the heat generating portion side to the end surface of the electrode lead wire on the heat generating portion side. It is desirable to be within a dimensional range of 1.0 to 2.0 times.

In this embodiment, the diameter of the screw for mounting the engine is 10 mm.

Embodiment 2 In this embodiment, the section modulus of the metal outer cylinder when the thickness of the heat generating portion side of the metal outer cylinder 4 is changed is shown in FIG. 4, and as described above, the ceramic heater is protected. By securing the strength of the outer cylinder for achieving the above, in addition to the effects of the first embodiment,
In order to prevent the occurrence of cracks in the ceramic heater 1 due to an external force, the thickness of the metal outer cylinder is preferably 0.3 mm or more.

In both the first and second embodiments, the maximum thickness of the metal outer cylinder 4 can be determined by the inner diameter of the plug hole for mounting the ceramic glow plug on the engine side. Although it is not uniquely determined by the plug alone, if the inner diameter of the plug hole becomes large, swirl at the time of combustion is hindered and smoothness of combustion is hindered, resulting in a decrease in output.

[0034]

As described above, according to the present invention, as compared with the conventional ceramic glow plug, the metal outer cylinder has a two-step shape, that is, the heating portion side is thin and the mounting bracket side is thick.
The absolute value of the thermal stress generated due to the difference in thermal expansion between the metal outer cylinder and the ceramic heater is reduced, and the peeling and cracks that occurred between the electrode lead wire and the ceramic heater base material can be prevented. It has an excellent effect of being able to prevent the damage of.

In this embodiment, the material of the metal outer cylinder is Inconel 601 only, but Incoloy 80
0, SUS430 or the like may be used.

Further, in the structure of the ceramic glow plug, the respective parts are joined by silver brazing in the present embodiment, but the brazing material is not limited to silver brazing, but may be copper brazing, gold brazing, or the like. A method such as caulking may be used.

As long as the electrode lead-out lines 3 and 3'are surely electrically connected to the positive electrode and the negative electrode, not only the joining by the brazing material but also the method by the glass seal may be used.

In short, any method may be used as long as it is electrically connected to the ceramic heater, can be energized, and has an airtightness so that combustion gas during engine operation does not blow through to the nut side of the glow plug.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of essential parts of the ceramic heater and the metal outer cylinder of FIG.

FIG. 3 is a graph showing a temperature curve of a tip portion of a ceramic heater when an evaluation test of a ceramic glow plug according to the present invention is performed.

FIG. 4 shows the section modulus when the thickness of the metal outer cylinder on the heat generating portion side is changed.

FIG. 5 shows the number of cycles in which cracks are generated in the ceramic heater portion when the steps of the metal outer cylinder are variously changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramic heater 2 Heating wire 3, 3'electrode take-out wire 4 Metal outer cylinder 5 Mounting bracket 41 End surface of metal outer cylinder on heating part side

Claims (3)

[Claims] 1. A ceramic heater in which a heating element is embedded in a ceramic sintered body, a tip of which is protruded from a metal outer cylinder inserted and fitted to the outside thereof and joined to the inner cavity thereof, and the metal outer cylinder is attached. A ceramic glow plug that is joined to the inner cavity of the tip of the metal fitting, wherein the thickness of the metal outer tube inserted into the outside of the ceramic heater is smaller on the heating portion side than on the mounting metal fitting side, and from the thin portion Ceramic glow plug with a tapered portion that transitions to a thicker portion. 2. The thickness of the metal outer cylinder on the heat generating portion side is 0.3.
The ceramic glow plug according to claim 1, having a diameter of at least mm. 3. The thickness (T) of the metal outer cylinder on the side of the mounting bracket.
Is 0.5 mm or more and 1.0 mm or less, the step difference from the thickness (t) on the heat generating portion side is 0.2 mm or more, and the length (L) of the thin portion of the metal outer cylinder is Distance (l) from the end face of the metal outer tube to the heat generating part to the end face of the electrode lead wire to the heat generating part
The ceramic glow plug according to claim 1 or 2, which is 1.0 to 2.0 times of the above.