JP2001173953A - Ceramic glow plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic glow plug which does not cause such a trouble that the temperature of a cathode fitting rises and a brazing material fixing a ceramic heating element to the cathode fitting melts, resulting in the melting of the fitting by the brazing material and the deterioration of a brazing material section depending upon the running condition of a vehicle, even when the diameter and protruded length of the heating elements are reduced following the diameter reduction of the plug. SOLUTION: The ceramic glow plug has an outside diameter of 2.0-3.0 mm and is provided with first and second exothermic resistors. The ratio of the resistance of the first exothermic resistor to that of the second exothermic resistor is adjusted to >=2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-saturated ceramic glow plug for maintaining fuel ignition and stable combustion when starting or idling a diesel engine.

[0002]

2. Description of the Related Art Conventionally, as a glow plug used for accelerating the starting of a diesel engine, a heat-resistant alloy sheath is filled with a heat-resistant insulating powder, and nickel (Ni) -chromium (Cr) is contained in the heat-resistant insulating powder. A sheathed heater in which a heat-generating resistor made of a high-melting-point metal wire whose main component is etc. is embedded has been used.

However, in the sheathed heater, it is difficult to quickly raise the temperature in a short time because the heat of the heating resistor is transmitted through the insulating powder filled in the heat-resistant metal sheath. In addition, there is a problem that the abrasion resistance and the oxidation resistance are inferior.

[0004] Therefore, as a reliable glow plug capable of rapidly increasing the temperature in a short time and having excellent wear resistance and oxidation resistance, a heating resistor made of an inorganic conductive material is sintered with an electrically insulating ceramic sinter. Ceramic glow plug buried in the body,
It has been widely used as a glow plug for an internal combustion engine.

For example, as shown in FIG. 3, a ceramic body 3 mainly composed of silicon nitride (Si ₃ N ₄ ) having high strength and excellent oxidation resistance is used as a heating resistor 4 such as tungsten carbide (WC) or the like. It has been proposed that a ceramic heating element 2 in which a conductive ceramic is buried and which takes into consideration the difference in thermal expansion between a ceramic body 3 and a heating resistor 4 made of the buried conductive ceramic is suitable as the ceramic glow plug 1. (See Japanese Utility Model Application Laid-Open No. 2-20293).

In this ceramic glow plug 1, a heating resistor 4 and a lead pin 6 made of tungsten are embedded in an electrically insulating ceramic sintered body 3, a cathode side electrode lead-out portion 7 is joined to a cathode metal fitting 8, and an anode The side electrode lead-out part 7 is joined to a coil-shaped anode metal fitting 10,
1 and the rod-shaped electrode 12.
The rod-shaped electrode 12 is fixed with mounting screws 15 via insulating seals 14 and 16 in order to secure electrical insulation between the cathode metal fitting 8 and the housing metal fitting 9 joined thereto. Has become. A screw part 13 is formed on the outer periphery of the housing fitting 9, and by tightening this part, the ceramic glow plug 1 is mounted in the cylinder of the engine.

However, as a movement related to automobiles to prevent global warming, recently, measures to reduce the emission of harmful exhaust gas, especially measures to clean exhaust gas when starting the engine, have been studied. There has been a demand for improvement of the glow plug startup characteristics at the time of starting. A conventional ceramic glow plug 1 in which a heating resistor 4 made of a high melting point metal wire of a nickel-chromium alloy is buried requires a starting time required for heating from room temperature to 800 ° C. of about 30 seconds. In the ceramic glow plug 1 of the type proposed in Japanese Utility Model Laid-Open Publication No. 2-229393, this was reduced to 4 to 5 seconds. However, recently, the rise time was 3
Something less than a second is required.

The mainstream of the ceramic glow plug 1 currently used is that the ceramic heating element 2 has an outer diameter of 3.5 m from the viewpoint of workability of the ceramic body 3 and the heating resistor 4.
Those having a diameter of about mφ are used. However, when the outer diameter is as large as this, the starting time is inevitably 4 to 5 seconds. If the starting time is further reduced, the durability of the ceramic glow plug 1 is significantly reduced due to excessive temperature rise at the time of starting. I knew it would.

[0009] Further, as another movement for reducing the size of a diesel engine, conventionally, an auxiliary combustion chamber is provided,
Here, a two-stage combustion was adopted in which the fuel was ignited and the combustion was transmitted to a combustion chamber filled with a rich air-rich gas, but the auxiliary combustion chamber was abolished and the combustion chamber was replaced with a combustion chamber. Direct injection engines that directly ignite fuel are being put into practical use. Such an engine is a system in which the fuel injection in the combustion chamber generates a concentration variation, ignites the fuel at a portion having a high concentration, and spreads the fuel over the entirety where the fuel concentration is low. Further, the number of valves has been increased to four in order to improve combustion efficiency and output.

However, in the engine of such a system, the fuel injection nozzle, the intake / exhaust valve, etc. are dense, the space for installing the glow plug is narrow, and the conventional ceramic glow plug cannot be used due to its size. There were challenges. The ceramic glow plugs required at present have a large outer diameter, and there is a problem that the engine must be designed with a reduced capacity in order to be installed in an engine cylinder. The currently required ceramic glow plug is 8 mm or less in diameter of the housing fitting, and in consideration of the overall holding strength including the cathode fitting, the outer diameter of the ceramic heating element needs to be 2-3 mm.

Another important feature of such a system is a performance called afterglow. Since the concentration of the fuel concentration is intentionally generated in the combustion chamber, the combustion characteristics are particularly unstable during a cold start, and unburned harmful substances may be exhausted as exhaust gas. This should be improved not only for global warming but also for improving the performance of diesel engine vehicles. That is, the afterglow is a method for stabilizing combustion in the combustion chamber at the time of cold start. This is for continuously heating the glow plug even after the fuel is ignited to achieve complete combustion of the unburned components.

[0012]

As described above, as described above, the glow plug is reduced in diameter with the downsizing of the diesel engine.
In order to reduce the amount of harmful substances contained in the exhaust gas during the cold start of the diesel engine, the start time from room temperature to 800 ° C. during the cold start of the ceramic glow plug is set to 3.0 seconds or less, There is a problem that a self-saturated ceramic glow plug with excellent durability that can be used for afterglow must be provided to the market.

However, the outer diameter of the ceramic heating element is limited to 2-3.
When the length is reduced to mm, it is necessary to shorten the protruding length of the porcelain in order to maintain the cantilever strength of the porcelain. In this case, the temperature of the cathode metal fitting rises because the heat-generating part is close, and the brazing material for fixing the ceramic heating body to the cathode metal fitting may melt and deteriorate depending on the driving conditions of the vehicle. Has to be suppressed.

[0014]

Means for Solving the Problems The present inventors have conducted intensive studies and as a result, have found that a ceramic heating element having a heating resistor made of an inorganic conductive material which generates heat by energization and an electrode lead portion is provided on a silicon nitride sintered body. In the ceramic glow plug having: the outer diameter of the portion in which the heating resistor is embedded is 2.0 to
A ceramic glow plug having a thickness of 3.0 mm, wherein the heat-generating resistor comprises first and second heat-generating resistors, and wherein a resistance ratio of the first heat-generating resistor to the second heat-generating resistor is 2 or more. It has been found that the above-mentioned problem can be solved.

[0015] This makes it possible to reduce the temperature rise time of the ceramic glow plug from room temperature to 800 ° C for 3 seconds or less.

[0016]

Embodiments of the present invention will be described with reference to FIG.

FIG. 1 is a sectional view of a ceramic glow plug 1 according to the present invention. The ceramic heating element 2 has a first heating resistor 4, a second heating resistor 5, a lead pin 6, and an electrode lead portion 7 embedded in a ceramic body 3, and these electrode lead portions 7 are interposed via a brazing material (not shown). To the cathode metal fitting 8 and the anode metal fitting 10. The cathode fitting 8 is further connected to a housing fitting 9. Also, on the anode side,
It is connected to a substantially cap-shaped anode fitting 10 via an electrode lead-out portion 7. The anode fitting 10 is further connected to a rod-shaped electrode 12 via a metal terminal 11. The housing metal 9 and the rod-shaped electrode 12 are electrically insulated by insulating seals 14 and 16, and are electrically insulated from the housing metal 10 by the mounting screws 15 via the ring-shaped insulating seals 14 and 16. It is tightened and fixed.

A feature of the present invention is that the outer diameter a of the ceramic 2 is reduced to 2.0 to 3.0 mm so as to withstand rapid temperature rise and to cope with downsizing of the engine. Is reduced to 6 to 7.5 mm or less, and the resistance ratio of the first heating resistor 4 to the second heating resistor 5 is 2 or more, that is, the first heating resistor 4 and the second heating resistor The first heating resistor 4 has a resistance ratio of 2: 1 or more.
The point is that the resistance is increased.

If the outer diameter of the ceramic heating element 2 is less than 2.0 mm, the first heating resistor 4 comes close to the cathode metal fitting 10 to maintain the cantilever strength of the ceramic heating element 2, and It is not preferable because the metal fitting 10 is directly heated by the first heating resistor 4. Also,
If it is 3.0 mm or more, it cannot respond to miniaturization.

If the resistance ratio of the first heating resistor 4 to the second heating resistor 5 is less than 2: 1 and the resistance of the first heating resistor is small, the vicinity of the cathode metal fitting is undesirably heated.
When the resistance of the first heating resistor 4 becomes greater than the resistance ratio of 7: 1, silicon nitride of the same quality as the ceramic body 3 as a buffer material is used to reduce the resistance of the second heating resistor 5. And the amount of boron nitride to be added is not preferable because cracks are generated in the second heating resistor 5 due to thermal shock at the time of temperature rise and fall. Therefore, the above resistance ratio is 2: 1 to 7: 1.
Is preferable.

A conventional ceramic glow plug 1 is shown in FIG.
As shown in (1), the anode fitting 10 is formed of a coil-shaped metal wire, and is joined to the cathode fitting 8 using a brazing material. A clearance is provided so that the anode fitting 10 does not contact the housing fitting 9.
Conventionally, in order to form this clearance, a step is provided at the joint between the cathode metal fitting 8 and the housing metal fitting 9 to secure the clearance. On the other hand, according to the present invention, as shown in FIG. 1, the anode fitting 10 is formed of a thin metal cap and the step is eliminated, so that the cathode fitting 8 is formed.
The thickness is reduced only by securing the clearance only by the thickness of the housing metal fitting 9 and eliminating the step of the housing metal fitting 9 near the joint with the cathode metal fitting 8.

The ceramic body 3 of the present invention contains silicon nitride as a main component, 3 to 10% by weight of a rare earth element oxide, 0.3 to 3% by weight of aluminum oxide as a sintering aid,
0.5-8.5% by weight molybdenum disilicide and 1-5
Those containing silicon oxide by weight are preferred. The rare earth element oxide improves the melting point of the grain boundary phase and improves the high temperature durability of the ceramic glow plug. Further, aluminum oxide greatly promotes sintering of silicon nitride, and greatly affects the increase and decrease in the amount of grain boundary phase. More preferably, the content is preferably 0.5 to 2% by weight. Silicon oxide is composed of oxygen contained as an impurity of a raw material, a substance mixed from an atmosphere during firing, and a substance to be added. Silicon oxide also has the effect of greatly promoting the sintering of silicon nitride. However, if the content exceeds 5% by weight, it tends to collect on the anode side due to the electric field during energization, and deteriorates the durability of the ceramic glow plug.

The above-mentioned raw material is formed into a predetermined structure, and a first heating resistor 4, a second heating resistor 5 and an electrode lead portion 7 are formed on the surface of the molded body. Body 5
After the lead pin 6 made of W is installed so as to connect the electrode lead portion 7 and another formed body, another molded body is stacked and fired integrally by hot press firing. The reason why the second heating resistor 5 is provided is that when the first heating resistor 4 and the lead pin 6 made of W are directly connected, the temperature of the connecting portion becomes extremely high. This is because the brazing portion of the metal fitting 8 is melted and deteriorated, and the reliability of holding the ceramic heating element 2 is reduced. In order to prevent this, a second heating resistor 5 having a lower resistance than the first heating resistor 4 is formed at the connection portion to lower the temperature of the connection portion with the lead pin 6. When a plurality of layers of the first heating resistor 4 and the second heating resistor 5 are provided, a plurality of the compacts are prepared, and then they are stacked and integrally fired by hot pressing.

The compact thus prepared is fired by a hot press to obtain a rectangular ceramic heating element 2 having a built-in heating resistor 4. The shrinkage ratio of the heating resistor 4 in the thickness direction is approximately 40 to 60% with respect to the print thickness.
About.

Further, the rectangular ceramic heating element 2 was processed into a columnar shape, the electrode lead-out portion 7 was exposed, and the cathode metal fitting 8, the anode metal fitting 10, the anode terminal 11, the bar-shaped electrode 12, and the housing metal fitting 9 were sequentially joined. Thereafter, the rod-shaped electrode was fixed to the housing fitting via an insulating seal with a screw to obtain a ceramic glow plug 1.

[0026]

EXAMPLE 1 An appropriate amount of silicon oxide was mixed with 5% by weight of ytterbium oxide (Yb ₂ O ₃ ), 3% by weight of molybdenum disilicide, and 0.5% by weight of aluminum oxide, which are one of the rare earth element oxides. A flat silicon nitride compact is prepared by press molding using the granulated powder. A first heating resistor 4 and a second heating resistor 5 and an electrode lead-out portion 7 are printed on one side of the molded body, and a molded body on which lead pins 6 are further placed is formed.
Prepare a pair. At this time, the resistance ratio of the first heating resistor 4 and the second heating resistor 5 was varied between 1.3: 1 and 7: 1 to produce a sample.

The dimensions of the first heating resistor 4 and the second heating resistor 5 are 1.8 mm, 2.0 mm,
Print was formed by adjusting the diameter to 2.5 mm, 3.0 mm, and 3.5 mm.

Thereafter, the above-mentioned molded bodies were stacked in two stages, another silicon nitride-based molded body was further laminated on the upper molded body, and further hot-fired to obtain a ceramic heating element 2 having a square cross section. .

Thereafter, the ceramic heating elements 2 having a square cross section are respectively provided with an outer diameter of 1.8 mm, 2.0 mm, 2.5 mm,
It was rounded to 3.0 mm and 3.5 mm. Thereafter, the cathode metal fitting 8 was set on the electrode lead-out portion 7 on the cathode side, and the brazing material was melted to fix the cathode metal fitting 8. Further, as for the anode, after the cap-shaped anode fitting 10 was put on the electrode lead-out portion 7 on the anode side, the brazing material was melted and integrated.

Further, the housing fitting 9 is placed on the cathode fitting 8.
After mounting, this was brazed, and a mounting screw 15 installed on the end of the anode fitting 10 opposite to the ceramic heating element 2 was fixed via insulating seals 14 and 16 to obtain a ceramic glow plug. Ten samples were prepared for each, and the temperature of the tip of the cathode fitting 8 on the ceramic body 2 side during the heating time from room temperature to 800 ° C. and during continuous heating were measured. Table 1 shows the results.

[0031]

[Table 1]

As can be seen from Table 1, No. 1 having an outer diameter of 1.8 mm was processed. For 1 to 5, the heating time up to 800 ° C.
Although it is 2.2 seconds or less, since the protruding length of the ceramic heating element 2 from the cathode fitting 8 is reduced to 4.5 mm, the temperature of the cathode fitting 8 becomes 700 ° C. or more, which is not preferable. In addition, the outer diameter of the ceramic heating element 2 was processed to 3.5 mm, and No. In Nos. 21 to 25, although the temperature of the cathode metal fitting 8 is 700 ° C. or less, the temperature rise time up to 800 ° C. is 3 seconds or more, which is not preferable. Further, the outer diameter of the ceramic heating element 2 was set to 2.0 to 3.0 mm, and the resistance ratio of the first heating resistor 4 to the second heating resistor 5 was set to 1.3: 1. 6, 1
Nos. 1 and 16 are not preferred because the temperature of the cathode metal fitting 8 is 700 ° C. or higher. On the other hand, the outer diameter of the ceramic heating element 2 is 2.0 to 3.0 mm, and the resistance ratio is 2: 1 to 7:
No. 1 being No. 1 7-10, 12-15, 17-20
In each case, the temperature raising time up to 800 ° C. was 3 seconds or less, and the tip temperature of the cathode metal fitting 8 was 700 ° C. or less, which was good.

Example 2 The outer diameter of the ceramic heating element 2 is 2.5, 3.0, 3.5 m.
m, three samples each were prepared, and
The heating time up to 00 ° C. is changed between 2 and 5 seconds, and the temperature of the highest temperature portion on the surface of the ceramic heating element 2 at this time and the cycle of turning on the voltage for 5 minutes and turning off the voltage for 3 minutes are 10,000. The rate of change in resistance before and after the cycle was measured. The resistance ratio between the first heating resistor 4 and the second heating resistor 5 was 3: 1. Further, the sample was mounted on a diesel engine, and the effect of afterglow during cold start was examined. In the evaluation, the time from when the engine was started until the white smoke in the exhaust gas disappeared in an idling state was measured. The criterion for the 800 ° C. heating time is 3 seconds or less, the criterion for the resistance change rate is 1% or less, and the after-glow activation time is
It was determined whether it would be 30 seconds or less. If it was within the above range, it was determined to be OK.

The results are shown in Table 2.

[0035]

[Table 2]

As shown in Table 2, as shown in FIG.
N with an outer diameter of 3.5 mm and a temperature rise time of 800 ° C. for 2 to 3 seconds
o. Samples Nos. 48 and 49 have good afterglow activation time, but are not preferred because the resistance change rate in the intermittent durability test exceeds 1%. In addition, No. In the case of No. 49, the rate of change in resistance in the intermittent durability test is 1% or less, but it is not preferable because the time required for raising the temperature up to 800 ° C. becomes as slow as 5 seconds. On the other hand, N in which the outer diameter of the ceramic heating element 2 is 2.5 to 3.0 mm is used.
o. Samples Nos. 41 to 46 were favorable under a voltage application condition where the temperature rise time at 800 ° C. was 2 to 3 seconds, the resistance change rate after the intermittent test was 1% or less, and the afterglow activation time was 30 seconds or less.

[0037]

According to the present invention, a silicon nitride sintered body is
In a ceramic glow plug provided with a heating resistor made of an inorganic conductive material that generates heat when energized and a lead portion, an outer diameter of a portion in which the heating resistor is embedded is 2.0 to 3.0 mm.
The heat-generating resistor is composed of first and second heat-generating resistors, and the resistance ratio of the first heat-generating resistor to the second heat-generating resistor is 2 or more. Can provide a ceramic glow plug having good durability.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a ceramic glow plug of the present invention.

FIG. 2 is a view showing a heating resistor of the ceramic glow plug of the present invention.

FIG. 3 is a structural sectional view of a conventional ceramic glow plug.

[Explanation of symbols]

 1: Ceramic glow plug 2: Ceramic heating element 3: Ceramic body 4: First heating resistor 5: Second heating resistor 6: Lead pin 7: Electrode lead-out section 8: Cathode fitting 9: Housing fitting 10: Anode fitting 11: anode terminal 12: rod-shaped electrode 13: screw part 14, 16: insulating seal 15: mounting screw

Claims (2)

[Claims] 1. A ceramic glow plug having a heating resistor made of an inorganic conductive material that generates heat by energization and a lead portion in a silicon nitride sintered body, wherein the outside diameter of a portion where the heating resistor is embedded is 2. 0 to 3.0 mm, and the heating resistor is composed of first and second heating resistors,
A ceramic glow plug, wherein a resistance ratio of the first heating resistor to the second heating resistor is 2 or more. 2. A ceramic glow plug comprising a heat generating resistor made of an inorganic conductive material which generates heat by energizing a silicon nitride sintered body and a lead portion, wherein a temperature rise time from room temperature to 800 ° C. is 3 seconds or less. A ceramic glow plug characterized by the following.