JPH07239123A - Ceramic glow plug - Google Patents

Abstract

PURPOSE:To obtain a self-saturation type glow plug for a diesel engine in which a ceramic heat generator is not easily broken against an impact to be applied to the ceramic plug and which can endure against thermal impact at the time of continuously operating for a long time and has effective ignition and excellent durability and reliability for obtaining safety. CONSTITUTION:When a length from an adherence starting point 6 to a support fitting 5 to a corner 7 of a substantially U-shaped heat generating resistor 4 connected to a lead 9 near an outer periphery of the end of the resistor 4 is ln a maximum length from a center 8 of a section including the corner 7 of the resistor 4 to each corner is Wn, a length from the point 6 to an end of a ceramic heat generator 2 is L and an outer diameter or width of an electric insulation ceramic sintered unit 3 of the corner 7 is D, D/2Wn>=2(L-ln)/L (where 2Wn< D, 0<ln<L, n is integer) is satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-saturation type ceramic glow plug which rapidly preheats a sub combustion chamber at the time of starting a diesel engine or idling.

[0002]

2. Description of the Related Art Conventionally, as a glow plug used for accelerating the starting of a diesel engine, a heat-generating resistor made of a refractory metal wire mainly composed of nickel (Ni) -chromium (Cr) or the like is provided in a heat-resistant metal sheath. A sheathed heater filled and embedded with heat resistant insulating powder was used.

However, since the sheathed heater transfers heat of the heat-generating resistor through the heat-resistant insulating powder filled in the sheath made of heat-resistant metal, heat conduction is poor and rapid temperature rise in a short time is difficult. In addition, there is a problem that durability such as wear resistance, heat resistance, and corrosion resistance is poor.

Therefore, a heating resistor made of an inorganic conductive material is used as a glow plug excellent in durability such as wear resistance, heat resistance, corrosion resistance, etc. Ceramic heating elements embedded in an insulating ceramic sintered body have been widely used as glow plugs for internal combustion engines.

For example, as shown in FIG. 12, a non-oxide ceramic such as a silicon nitride sintered material, which is significantly superior in thermal shock resistance and high temperature strength to other ceramics, is used as the insulating substrate 11, and tungsten (W) is generally used. ) Or molybdenum (Mo) or other high melting point metal or a compound thereof is used to print a resistor pattern composed of a heat generating portion 12 and lead portions 13 on the insulating substrate 11 using a heat generating resistor paste. A ceramic heating element has been proposed in which another insulating substrate is overlaid and integrally fired (Japanese Patent Laid-Open No. 2-75).
188).

[0006]

However, when the ceramic heating element is used as a glow plug of a diesel engine, the glow plug generally has a maximum heat generating portion 14 which is red-heated by energizing so as not to impair startability. Are exposed in the auxiliary combustion chamber.

Therefore, when the ceramic heating element is impacted by hitting or dropping the glow plug when the ceramic heating element is attached to the cylinder head, the ceramic heating element may be broken below the breaking strength of the electrically insulating ceramic sintered body. However, there is a problem that durability remains uncertain and reliability is poor.

[0008]

SUMMARY OF THE INVENTION The present invention has been developed in view of the above problems, and an object thereof is to easily deal with an impact that is considered to be applied to a glow plug due to an unexpected situation that occurs during the operation of handling the glow plug. An object of the present invention is to provide a ceramic glow plug having excellent durability and reliability without breaking the ceramic heating element.

[0009]

In the ceramic glow plug of the present invention, a ceramic heating element in which a heating resistor made of an inorganic conductive material formed in a substantially U-shape is embedded in an electrically insulating ceramic sintered body and a cylinder head are attached. The length from the bonding start point where the supporting metal fittings connected to the metal fittings are fixed to the corner near the outer circumference of the end of the substantially U-shaped heating resistor connected to the embedded lead wire is 1 _n , and the corner of the heating resistor is The maximum length from the center of the cross-section including the part to each corner is W _n , the length from the bonding start point to the tip of the ceramic heating element is L, and the electrical insulation corresponding to the outer peripheral corner of the heating resistor when the outer diameter or width of the ceramic sintered body is D, the exposed ceramic heating element and the heating resistor and the relationships _{D / 2W n ≧ 2 (L} -l n) / L where, 2W _n <D 0 < l _n <L n is characterized by satisfying the integer Than it is.

In the case of a ceramic heating element in which a substantially U-shaped heating resistor made of at least two layers of inorganic conductive material is embedded in an electrically insulating ceramic sintered body, the ceramic heating element is attached to a cylinder head. The length from the adhesion starting point fixed by the supporting metal fitting connected to the metal fitting to the corner near the outer periphery of the end portion of at least two layers of the heating resistor connected to the embedded lead wire is l _n , and each of the layered heating resistances The maximum length from the center of the cross section including the corners of the body to each corner is W _n ,
When the length from the bonding start point to the tip of the ceramic heating element is L and the outer diameter or width of the electrically insulating ceramic sintered body corresponding to the corner is D, the exposed ceramic heating element and heating resistor relationship _{D / 2W n ≧ 2 (L} -l n) / L _{where, 2W n <D 0 <l} n <L n are those characterized by satisfying the integer.

[0011]

According to the ceramic glow plug of the present invention, the positional relationship between the ceramic heating element and the heating resistor embedded in the ceramic heating element from the bonding start point where the ceramic heating element and the support fitting are fixedly attached, or the ceramic heating element. In the case where the number of the heating resistors in the inside is at least two layers, the positional relationship between the ceramic heating element from the adhesion starting point and the layered heating resistor embedded in the ceramic heating element is D / 2W _n ≧ 2 (L -l _n) / L _{where, 2W n <D 0 <l} n <L n from be configured to satisfy the integer, stress generated by the impact applied to the ceramic heating element, heating resistors embedded therein It becomes to concentrate on the adhesion starting point that has almost no effect on the above, acts to withstand a stress close to the rupture strength of the electrically insulating ceramic sintered body, and resists as a ceramic glow plug. Sex and reliability is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A ceramic glow plug of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing a ceramic glow plug according to an embodiment of the present invention with a main part broken away.
2 to 4 are plan views of a main part broken view showing another embodiment in which the end shape of the heating resistor of the ceramic glow plug of the present invention and the starting point of adhesion by the support fitting are changed, and FIGS. It is sectional drawing which shows the typical cross section of the corner | angular part of FIGS.

FIG. 7 is a plan view of a broken main part showing another embodiment in which the heating resistor of the ceramic glow plug of the present invention is different, and FIGS. 8 and 9 are typical corner portions of FIG. It is sectional drawing which shows a cross section.

1 to 9, reference numeral 1 denotes a substantially U-shaped heating resistor 4 made of an inorganic conductive material and a lead wire 9 connected to both ends thereof in an electrically insulating ceramic sintered body 3. It is a ceramic glow plug in which the ceramic heating element 2 is fixed by a support fitting 5 connected to the cylinder head mounting fitting 10.

The ceramic glow plug 1 of the present invention is connected to a lead wire 9 from a starting point 6 of bonding with a support fitting 5 and is substantially U-shaped.
The length up to the corner 7 near the outer periphery of the end of the character-shaped heating resistor 4 is l _n , and the maximum length from the center 8 of the cross section including the corner 7 of the heating resistor 4 to each corner is W _n. When the length from the bonding start point 6 to the tip of the ceramic heating element 2 is L and the outer diameter or width of the electrically insulating ceramic sintered body 3 of the corner portion 7 is D, the respective relationships are D / 2W _n ≧ _{2 (L-l n) /} L _{where, 2W n <D 0 <l} n <L n are those satisfying the integer.

In the present invention, the corner portion is in the vicinity of both ends of the substantially U-shaped heat generating resistor 4 connected to the lead wire 9 and outside the end portion of the heat generating resistor 4 at the connecting portion with the lead wire 9. Refers to all bending points formed on the outer periphery including the corner portion, and is shown in FIGS. 1, 2 and 4 including the outer corner portion of the end portion of the heating resistor 4 at the connection portion with the lead wire 9. In the case of a corner portion of such an end portion or in the case where the corner portion is chamfered to form an arc shape as shown in FIG. 3, the position of the intersection of the straight line portions is used, and as shown in FIG. When the resistor 4 is a coil of wire material wound in a spiral shape, it means a point where the winding diameter changes.

Further, in the present invention, the center of the cross section including the corner portion means a point located on the center line of the electrically insulating ceramic sintered body 3 in the cross section including the substantially U-shaped heating resistor 4. is there.

On the other hand, FIG. 10 and FIG. 11 are cross-sectional views showing a cross-section in which at least two layers of heating resistors are embedded in the ceramic glow plug of the present invention.
Similar to FIG. 4, the corners and the center of the vertical section are defined in the same manner as above.

10 and 11 show at least two layers of heating resistors 4 made of an inorganic conductive material in an electrically insulating ceramic sintered body 3 with respect to the diameter d of a circle indicated by a chain double-dashed line. When the outer diameter or width of the united body 3 is D,
It is sectional drawing which shows the typical cross section of the ceramic heating element 2 embedded in d / D of 0.3-0.9.

In the ceramic glow plug 1 of the present invention, the ceramic heating element 2 is attached to the cylinder head fitting 10.
To the corner 7 near the outer periphery of the end of the heating resistor 4 of at least two layers of substantially U-shape connected to the embedded lead wire 9 from the adhesion start point 6 with the supporting metal 5. The length is l _n , the maximum value from the center 8 to the corner 7 of the longitudinal section including the corner 7 of the layered heating resistor 4 is W _n , and the length from the bonding start point 6 to the tip of the ceramic heating element 2 is L, when the outer diameter or width of the electrically insulating ceramic sintered body corresponding to the corner portion 7 was _{D, D / 2W n ≧ 2} (L-l n) / L _{where, 2W n <D 0 <l} n <L n is an integer.

For the electrically insulating ceramic sintered body of the present invention, a silicon nitride sintered body or sialon having silicon nitride (Si ₃ N ₄ ) as a main component, which is excellent in oxidation resistance and strength, is suitable.

The main component of the heating resistor made of an inorganic conductive material is a refractory metal such as tungsten (W), molybdenum (Mo) or rhenium (Re) or an alloy such as tungsten-rhenium (W-Re). Besides, there are, for example, tungsten carbide (WC), titanium nitride (TiN), zirconium boride (ZrB ₂ ), and the like, and carbides or nitrides of Group 4a, Group 5a, and Group 6a, among others, especially tungsten carbide (WC). Is most preferable in terms of ease of design and durability.

When the electrically insulating ceramic sintered body is a silicon nitride sintered body containing silicon nitride (Si ₃ N ₄ ) as a main component, the heating resistor is mainly made of tungsten carbide (WC). It is desirable to use the component as a component. For example, when the heating resistor is formed by the screen printing method or the like, silicon nitride (Si ₃₎ which is the main component of the electrically insulating ceramic sintered body is used.
A mixture obtained by appropriately adding N ₄ ) powder is preferable from the viewpoint of thermal expansion.

That is, when the heating resistor made of the inorganic conductive material is formed by the screen printing method or the like, considering the coefficient of thermal expansion, tungsten carbide (WC) is 65 to 95% by weight, silicon nitride (Si ₃ It is preferable that the composition of N ₄ ) is 5 to 35% by weight, especially tungsten carbide (W
C) is 75 to 90% by weight, and silicon nitride (Si ₃ N ₄ ) is 1
A composition of 0 to 25% by weight is most preferable from the viewpoint of the coefficient of thermal expansion as a ceramic heating element for high temperature.

Further, in order to prevent the heat generating resistor from being broken during manufacturing, when the heat generating resistor is formed by a screen printing method or the like, the thickness thereof should be at least 2.3 at the highest heat generating portion. It is preferable that the thickness of the heating resistor is at least 8 to 53 μm at least at the maximum heating portion in order to prevent cracks and the like from occurring in the heating resistor during sintering and integration. The range of is desirable.

On the other hand, in the lead portion, tungsten (W), molybdenum (Mo), and rhenium (R) are used as refractory metals.
In addition to e) and the like, alloys such as tungsten-rhenium (W-Re) can be cited. However, a wire rod made of tungsten (W), which has a low specific resistance and whose characteristics are hard to change even after firing and integration, is preferable, The resistance value is preferably about 80 to 120Ω, and the wire diameter is preferably about 6 to 15% of the outer diameter of the ceramic heating element.

When the heating resistor is formed by the screen printing method, each end of the heating resistor made of a substantially U-shaped inorganic conductive material has a resistance lower than that of the heating resistor and has substantially the same width. A heat generating resistor having a low resistance is formed by stacking heat generating resistors and forming an end of the heat generating resistor having a low resistance narrower than a width of the heat generating resistor serving as a heat generating portion so as to protrude from each end of the heat generating resistor. It is desirable to connect a lead wire made of a refractory metal wire material such as tungsten (W) or molybdenum (Mo) through the wire.

The ceramic heating element of the present invention has been described above in detail with a circular cross section and a rectangular cross section. However, the cross sectional shape of the ceramic heating element may be an elliptical shape or an oval shape other than that shown in the drawing. .

In evaluating the ceramic glow plug according to the present invention, first, high-purity silicon nitride (Si
₃ N ₄ ) powder, yttria (Y
₂ O ₃ ) or an oxide of a rare earth element is added and mixed to form a flat plate-shaped ceramic molded body containing silicon nitride as a main component by a well-known molding method such as a press molding method. .

Next, a solvent was added to a raw material powder prepared by mixing a predetermined amount of each fine powder of tungsten carbide (WC) and silicon nitride (Si ₃ N ₄ ) to prepare a paste, and the paste was prepared by screen printing based on the designed resistance value. , A substantially U-shaped pattern of various sizes and a pattern having a protruding portion having a narrow width overlapping the end portion of the substantially U-shaped pattern are sequentially formed on the surface of the ceramic molded body to form a ceramic heating element and a support fitting. Various positional relations were set between the ceramic heating element from the bonding start point where the solid state was fixed and the heating resistor embedded in the ceramic heating element.

Next, a tungsten (W) wire having a diameter of 0.25 mm is used as a lead wire between the ceramic molded body on which the heating resistor is formed by printing and another ceramic molded body, and the substantially U-shaped inorganic conductive material. It is sandwiched so as to be connected to the heating resistor formed in a substantially U-shape through a low-resistance heating resistor formed by overlapping a heating resistor made of a material, and the same tungsten (W ) Insert the wire with another ceramic molded body that does not print the heating resistor,
A heating resistor having one layer and a heating resistor having two layers were prepared and subjected to 1750 in a reducing atmosphere containing carbon (C).
Pressure baking was performed at a temperature of ° C for 1 hour.

Further, a tungsten (W) wire having a diameter of 0.2 mm is wound into a coil shape and formed into a substantially U shape as a heating resistor, and an end portion of the tungsten (W) wire having a diameter of 0.3 mm is used. What was wound around the lead wire consisting of was embedded in a ceramic molded body similar to the above was also fired under pressure in the same manner.

The periphery of the ceramic sintered body, in which the respective heating resistors thus obtained were embedded, was ground to make the tip a substantially spherical surface and processed into a circular cross section, with diameters of 2.6 mm and 3.0.
A ceramic heating element having a size of mm and 3.4 mm and a length of about 54 mm was produced.

Next, after a metal coating such as nickel (Ni) is formed on the ceramic heating element by a metallizing method or a plating method, the ceramic heating element is connected to one electrode connecting portion exposed on the side surface of the ceramic heating element. A support metal fitting was fitted on the outside and joined with silver brazing in a reducing atmosphere to produce a ceramic glow plug for evaluation.

A comparative example was also manufactured in which a supporting metal was joined to the same electrically insulating ceramic sintered body without burying the heating resistor therein.

Then, using the ceramic glow plug for evaluation, a cantilever bending test was carried out in which a supporting metal fitting was gripped and a load was applied to the exposed end of the ceramic heating element to break it. Was calculated.

Further, the starting point of the destruction of the ceramic heating element was investigated, and the one which was destroyed from the adhesion starting point was designated as S, and the one which was destroyed by the exposed ceramic heating element was designated as H.

Further, from the cantilever bending strength of the comparative example measured prior to the measurement of the ceramic glow plug for evaluation and the starting point of breakage, a cantilever bending strength of 50 kg / mm ² or more, in which a deviation of 3σ is expected. Those having the above and having the starting point of destruction as the starting point of adhesion to the supporting metal fitting were evaluated as good, and the others were evaluated as defective.

At the corners near the adhesion starting point and the outer periphery of the end portion of the heating resistor, an X-ray transmission photograph of the film is magnified and confirmed by a magnifying projector, and each of D, W _n , L, and l _n is confirmed. The value was measured and the design dimension was confirmed.

The above results are shown in Tables 1 to 4. Further, Table 1 to Table 4, based on the result D / 2W _n and 2 (L-l _n) /
The relationship of L is shown in FIG. 13, and those within the claims of the present invention are indicated by ● and those outside the claims are indicated by X.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

A self-saturating glow plug produced by connecting a cylinder head mounting bracket to the above-mentioned ceramic glow plug for evaluation was dropped onto a concrete floor from a predetermined height, and then a predetermined torque torque wrench was used. It was installed in a 4-cylinder diesel engine bench test device by tightening force and the fuel was directly contacted with the exposed ceramic heating element by changing the fuel injection angle, and the diesel engine was operated for 100 hours under the conditions of maximum rotation speed and full load. Although a durability test was conducted, the ceramic glow plug according to the present invention was confirmed to be operating normally during the test, the exposed ceramic heating element was not broken, and further non-destructive after the test. No abnormalities such as cracks were found in any of the inspections.

[0046]

As described above, in the ceramic glow plug of the present invention, the positional relationship between the ceramic heating element from the bonding start point where the ceramic heating element and the supporting metal fitting are fixed and the heating resistor embedded in the ceramic heating element. , Or when the heating resistor in the ceramic heating element is at least two layers,
Positional relationship between the heating resistor layer which is embedded in the ceramic heating element and the ceramic heating element from the adhesive starting _{point, D / 2W n ≧ 2 (} L-l n) / L where, 2W _n <D 0 <l _{Since n} <L n is configured so as to satisfy an integer, the ceramic heating element is easily broken due to an impact that is considered to be applied to the glow plug due to an unexpected situation that occurs when the glow plug is handled. It is possible to obtain a self-saturating glow plug for a diesel engine that has excellent durability and reliability that can withstand thermal shock during long-term continuous operation without failing, and reliably ignites to ensure safety. it can.

[Brief description of drawings]

FIG. 1 is a plan view with a main part broken, showing an embodiment of a ceramic glow plug according to the present invention.

FIG. 2 is a view showing another embodiment in which the end of the heating resistor of the ceramic glow plug according to the present invention is narrowed through a taper provided on the outer periphery and the tip of the supporting metal fitting is arcuate. It is a top view.

FIG. 3 shows another embodiment in which a corner portion of a heating resistor of a ceramic glow plug according to the present invention is formed in an arc shape, and a starting point of bonding with a ceramic heating element is set to an inner back side of a support fitting. It is a top view.

FIG. 4 is a plan view of a main part fractured showing another embodiment in which the end portion of the heat generating resistor of the ceramic glow plug according to the present invention is narrowed inward through a taper.

FIG. 5 is a cross-sectional view showing a circular cross section of a corner portion of FIGS.

FIG. 6 is a cross-sectional view showing a rectangular cross section of a corner portion of FIGS. 1 to 4;

FIG. 7 is a plan view of a main part fractured showing another embodiment in which the heating resistor of the ceramic glow plug according to the present invention is a coiled metal wire.

8 is a cross-sectional view showing a circular cross section of a corner portion of FIG. 7.

9 is a cross-sectional view showing a rectangular cross section of a corner of FIG.

FIG. 10 is a cross-sectional view showing a circular cross section in which at least two layers of heating resistors of the ceramic glow plug according to the present invention are embedded.

FIG. 11 is a cross-sectional view showing a rectangular cross section in which at least two layers of heating resistors of a ceramic glow plug according to the present invention are embedded.

FIG. 12 is a plan view with a main part broken showing a conventional ceramic glow plug.

FIG. 13: D / of the ceramic glow plug according to the present invention
It is a diagram showing the relationship between 2W _n and _{2 (L-l n) /} L.

[Explanation of symbols]

 1 Ceramic Glow Plug 2 Ceramic Heating Element 3 Electric Insulating Ceramic Sintered Body 4 Heating Resistor 5 Supporting Metal 6 Starting Point of Adhesion 7 Corner 8 Center 9 Lead Wire

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[Submission date] March 3, 1994

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[Submission date] July 12, 1994

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Claims (2)

[Claims] 1. A ceramic glow plug comprising a ceramic U-shaped heating resistor made of an inorganic conductive material embedded in an electrically insulating ceramic sintered body and a ceramic glow plug fixed by a supporting metal member. The length from the starting point of adhesion to the support fitting to the corner near the outer circumference of the end of the heating resistor connected to the lead wire is l _n , the maximum from the center of the cross section including the corner of the heating resistor to each corner. The length is W _n , the length from the bonding start point to the tip of the ceramic heating element is L, and the outer diameter or width of the electrically insulating ceramic sintered body at the corner is D.
When _{a, D / 2W n ≧ 2 (} L-l n) / L where ceramic glow plug _{2W n <D 0 <l n} <L n which satisfies the integer. 2. A ceramic glow plug having a ceramic U-shaped heating resistor made of an inorganic conductive material embedded in an electrically insulating ceramic sintered body fixed to a ceramic fitting by a supporting member. The length from the adhesion starting point with the support fitting to the corner near the outer circumference of the end of at least two layers of the heating resistor connected to the lead wire is l _n , and the length of the cross section including the corner of the at least two layers of heating resistor is The maximum length from the center to each corner is W _n , the length from the bonding start point to the tip of the ceramic heating element is L, and the outer diameter or width of the electrically insulating ceramic sintered body at the corner is D. _{when, D / 2W n ≧ 2 (} L-l n) / L However, _{2W n <D 0 <l n} <L n ceramic glow plug, characterized by satisfying the integer.