JPH04124467A - Self-control type glow plug - Google Patents

Abstract

PURPOSE:To obtain a self-control type glow plug excellent in durability and rapid temperature rising characteristic so as to further heighten its reliability by burying control resistors, series-connected to an exothermic pattern, into a ceramic body, or forming an exothermic part of a ceramic heater with a part of the exothermic pattern exposed on a ceramic body. CONSTITUTION:A self-control type glow plug is provided with an exothermic pattern formed at least one kind of the carbide, nitride, silicide and boride of the periodic table No. IVa, Va, VIa group metal so as to have a small resistance temperature coefficient from the normal temperature to 1000 deg.C being not more than four times as an exothermic body. A control resistor 3 having a larger positive resistance temperature coefficient compared to the exothermic pattern 2 is formed of such a high fusing point metal wire that the resistance value of the control resistor 3 per unit volume of a ceramic heater 1 corresponding to the buried part of the current control resistor 3 is smaller than the same resistance value of the exothermic pattern 2. Such control resistors 3 are series- connected to the exothermic pattern 2 and buried into a ceramic body 4. The self-control glow plug can be also formed of a ceramic heater 1 with a part of the exothermic pattern 2 exposed on the surface of the ceramic body 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a self-control glow plug that is installed in a diesel engine and rapidly preheats the inside of a sub-combustion chamber at the time of startup.

[Conventional technology 1] Conventionally, a glow plug has been installed in the auxiliary combustion chamber in the cylinder head as a starting aid for diesel engines.When starting the diesel engine, the glow plug is energized to generate heat and start the auxiliary combustion. Preheats the interior of the vehicle to ensure starting, especially at low temperatures. In recent years, in order to improve the operability of diesel engines to the same level as gasoline engines, glow plugs have tended to be energized for a long time to provide stable heating even when starting a diesel engine as an afterglow to stabilize combustion. After warming,
There is a need for a self-control glow plug that can control the energization so that it saturates at a constant temperature, and there is an increasing demand for improved durability.

Conventional self-regulating glow plugs include a resistor made of high melting point gold wire having a higher positive temperature coefficient of resistance than the heating element, connected in series to the heating element, and the connected portion sealed with glass. There is one in which the heating current of the heating element is controlled when the temperature is increased by energization.

Self-regulating glow plugs with a curved structure are characterized by repeated heat generation and cooling, which creates a crank in the glass due to the difference in thermal expansion coefficient between the resistor and the sealing glass, which impairs the sealing properties of the glow plug. This had the disadvantage of decreasing durability.

Therefore, in an attempt to eliminate the above-mentioned drawbacks and improve durability, the connecting portion 24 between the ceramic heater 21 in which the heating element 22 is buried and the resistor 23 is inserted into the metal tube 25, as shown in FIG. A self-control glow plug is disclosed in Japanese Patent Publication No. 1-55369, etc., which is an integral assembly in which a powder 26 of a heat-resistant insulating material is filled and integrated.

Problem B1 to be Solved by the Invention However, in the self-regulating glow plug, the connecting portion 24 between the heating element 22 and the resistor 23 is buried in the powder 26 of the heat-resistant insulating material, and sealing portions 27. 27
Since ゛ is composed of organic materials, the temperature of 100℃
If heat generation and cooling are repeated over a long period of time until reaching a temperature exceeding In addition to the problem of corrosion of the 24 and lack of long-term durability, the self-regulating glow plug of the present invention has insufficient rapid temperature rise characteristics. A heating pattern made of at least one of carbides, nitrides, silicides, and borides of metals in groups rVa, Va, and Vla of the periodic table with a temperature coefficient as small as 4 times or less, and a positive temperature coefficient of resistance larger than the heating pattern. The resistance value of the control resistor per unit volume of the ceramic heater corresponding to the buried portion of the current control resistor is smaller than the similar resistance value of the heat generating pattern. The heating element is characterized by comprising a ceramic heater connected in series with a control resistor and embedded in the ceramic body, or with a part of the heating pattern exposed on the surface of the ceramic body. be.

[Effect 1] The heating pattern having a relatively small temperature coefficient of resistance of 4 times or less is provided at the tip of the glow plug, that is, the tip of the ceramic heater, and the heating pattern is made of tungsten (with a large temperature coefficient of resistance of 5 times or more). Since current control resistors made of high-melting point metal wires such as W) and molybdenum (Mo) are connected in series, the heating pattern with the large resistance value per unit volume rapidly generates heat at the tip of the glow plug when energized. do.

On the other hand, since the heat generating pattern and the control resistor are either embedded in the ceramic body or a part of the heat generating pattern is exposed on the surface of the ceramic body, the temperature of the control resistor itself increases when energized. In addition, the temperature of the control resistor further increases due to heat conduction from the heating pattern to the ceramic body, and the resistance value of the control resistor increases due to the large temperature coefficient of resistance.On the other hand, the temperature coefficient of resistance is small. Since the resistance increase rate of the heat generating pattern is small even when the temperature increases, the voltage applied to the heat generating pattern decreases, thereby exhibiting a self-control function.

Furthermore, sealing properties are maintained by embedding both the heating pattern and the current control resistor in the ceramic body.

[Example 1] Hereinafter, a self-regulating glow plug of the present invention will be explained in detail based on the drawings.

FIG. 1 is a vertical cross-sectional view showing the main parts of the self-regulating glow plug of the present invention, FIG. 2 is an enlarged cross-sectional view of the main parts of the ceramic heater shown in FIG. 1, and FIG. 3 is a heat generation pattern. FIG. 2 is an enlarged cross-sectional view of a main part of the ceramic heater of the self-regulating glow plug of the present invention in which the glow plug is exposed on the surface of the ceramic body.

1 to 3, reference numeral 1 is a ceramic heater installed in the inner hole 6 of the mounting bracket 5 of the glow plug. 4, or by exposing the - part of the heating pattern 2".
The ceramic heater 1 is brazed to the inner hole 8 of the metal pipe 7, and one end of the lead 1s9 of the control resistor 3 is electrically connected to form one electrode, and the other end is brazed to the mounting bracket 5. A lead shaft 12 is electrically connected to an electrode shaft 13 via a metal cap 11 joined to a rear end portion 10 of the ceramic heater 1, forming the other electrode to constitute a self-control glow plug.

The above-mentioned ceramic heater 1 is manufactured by printing a heat generating pattern 2.2" in a thick film at a predetermined position using a screen printing method on a silicon nitride molded body formed into a flat plate shape.
Place the coiled control resistor 3 and the lead wire 9 connected to the control resistor 3 so that the end of the coil and the tip of the coiled control resistor 3 are connected in series. Another silicon nitride molded body is stacked on the top surface and then baked under pressure to be integrated.

Note that it is desirable to form grooves into which the control resistor 3 and the lead wire 9 enter during or after molding in the silicon nitride molded body into which the heat generating pattern 2.2'' is thickly printed.

On the other hand, for the thick film printing of the heating pattern 2.2', carbides, nitrides, silicides, and metals of groups rVa, Va, and VIa of the periodic table whose temperature coefficient of resistance from room temperature to 100°C is four times or less are used. Made of at least one type of boride, such as tungsten carbide (WC), titanium nitride (TiN)
), molybdenum silicide (MoSiz) or zirconium boride (ZrBz) can be used as the conductor, and the remainder can be used as silicon nitride.

Further, the coil-shaped current control resistor 3 has a resistance value per unit volume of the control resistor 3 connected in series with the heat generating pattern 2.2', which is equal to or greater than the unit volume of the heat generating pattern 2.2'. It is preferable to use a wire made of a high-melting point metal mainly composed of tungsten or molybdenum, which has a relatively large resistance temperature coefficient of 5 times or more, which is designed to be smaller than the normal resistance value.

(Experiment example) The heating pattern material shown in Table 1 was applied on the surface of a silicon nitride molded body formed into a flat plate shape, which mainly contains silicon nitride Si3N4, yttrium oxide Yz03, and alumina Alz03, near one tip. Using a heating pattern paste containing silicon nitride 5i3Na and yttrium oxide Y2O3 as its main components, the ratio ρ of the respective resistance values per unit volume of the ceramic heater with the control resistor material shown in the same table was calculated. A heat generation pattern set to a target of 0.02 to 1°0 is thick-film printed using a screen printing method.

Next, a coil-shaped control resistor made of the control resistor material shown in the construction table and a lead wire connected to the resistor are placed in the pre-formed groove so as to be connected in series to the heat generating pattern. A flat silicon nitride molded body having the same composition as the above was placed on top of the molded body and fired using a hot press firing method. Obtained a body. Thereafter, the ceramic heater sintered body was polished to produce a cylindrical ceramic heater with a diameter of 4.3 m and a length of 35 m+a.

Each of the electrodes was connected to each of the five ceramic heaters manufactured under the same conditions as described above, and a voltage that reached saturation at 1100°C was applied to each ceramic heater, so that the heating pattern at the tip of the ceramic heater The time taken to reach 800°C was measured, and the temperature increase characteristics of each were evaluated based on the average value. After that, the ceramic heater is cut at the connection between the heating pattern and the coiled control resistor, and at the connection between the coiled control resistor and the lead wire, and the resistance values of the heating pattern and the control resistor are determined. From the heat generation pattern in the longitudinal direction of the ceramic heater and the volume of the cylindrical ceramic heater corresponding to the length of the buried part of the control resistor, the resistance value per unit volume of each is calculated, and the resistance value for each unit volume is calculated. The ratio of the resistance value per unit volume of the control resistor was determined as the resistance ratio ρ.

Furthermore, each of the five ceramic heaters under the same conditions as described above was subjected to metallization treatment, a metal pipe and a metal cap were soldered to a predetermined position of the ceramic heater, and one end of the lead wire of the control resistor was connected from the metal pipe to the mounting bracket. The rear end of the ceramic heater is electrically connected to the metal cap to form one electrode, and the other end is soldered to the mounting bracket via a metal pipe.The lead shaft is electrically connected to the electrode shaft via the metal cap. do. Next, a heat-resistant resin and a backing were inserted into the electrode shaft, and then the outer periphery of the end of the mounting bracket was caulked to produce a self-control glow plug for durability evaluation.

Next, using the above-mentioned self-control type glow plug, conduct a process of energizing the glow plug to rapidly raise the temperature to 1100'C, keeping the temperature at that temperature for 3 minutes under self-control, and then stopping the energization for 1 minute. One cycle was used, and the resistance change of the self-regulating glow plug after 5000 cycles was measured to evaluate durability.

In addition, the heating element is made of tungsten (W)-rhenium (Re).
Comparative examples include a ceramic heater in which a coiled wire bent into a U-shape is embedded, and a self-control glow plug in which a control resistor is a Japanese wire connected in series to the ceramic heater.

The above results are shown in Table 1.

(Leaving space below) Table 1 As is clear from Table 1, the comparative example is a self-control glow plug in which a ceramic heater with a heating element made of a coiled wire is embedded and a control resistor are connected in series.
Although the maximum time required to reach a temperature of 800°C is 5.5 seconds, the resistance change after 5000 cycles was extremely large at 213 mΩ, indicating that the control resistor wire was oxidized. On the other hand, in the self-regulating glow plug of the present invention, if the resistance ratio ρ is 0.85 or less, the time to reach 800°C is 5.5 seconds or less, and the No abnormality was observed in either the heat generation pattern or the control resistor.

Therefore, if the resistance ratio ρ per unit volume of the present invention is 0°85 or less, the time to reach a temperature of 800°C will be 5.5 seconds or less, but setting the resistance ratio ρ to 0.02 or less will cause heat generation. Since the width of the pattern becomes extremely small and thick film printing becomes difficult due to dimensional accuracy, the resistance ratio ρ is set in the range of 0.02 to 0.85.
, more preferably from 0.05 to 0.85.

[Effects of the Invention] As mentioned above, the self-regulating glow plaque of the present invention has a small temperature coefficient of resistance, Va = Vi of the periodic table.
A heating pattern made of at least one of carbides, nitrides, silicides, and borides of Group A metals, and a control resistor made of a high melting point metal with a large temperature coefficient of resistance connected in series with the heating pattern, are made of a ceramic body. Since the heat generating part is a ceramic heater that is buried in the ceramic heater or has a part of the heat generating pattern exposed, it is possible to further improve heat resistance and corrosion resistance under harsh usage conditions, and also to improve the heat resistance more rapidly. To provide a self-regulating glow plug with a higher performance, which has many advantages such as being able to obtain a temperature increase characteristic, and which does not require an expensive control mechanism and is excellent in durability and rapid temperature increase characteristics. be able to.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the main parts of the self-regulating glow plug of the present invention, Fig. 2 is an enlarged cross-sectional view of the main parts of the ceramic heater shown in Fig. 1, and Fig. 3 is a part of the heating pattern. FIG. 4 is an enlarged sectional view of a main part of a ceramic heater of another self-regulating glow plug of the present invention in which the glow plug is exposed on the surface of the ceramic body.
The figure is a sectional view showing the main parts of a conventional self-regulating glow plug. 2.2゛ ・ ・ 6.8 ・ ・ 10 ・ ・ 11 ・ ・ 12 ・ ・ 13 ・ ・ Ceramic heater Heat generation pattern control resistor Ceramic body mounting bracket Inner hole Metal pipe Lead wire rear end Metal cap Lead shaft Electrode shaft

Claims (1)

[Claims] A heating pattern made of at least one of carbides, nitrides, silicides, and borides of group IVa, Va, and VIa metals of the periodic table, and a control material made of a high melting point metal having a positive temperature coefficient of resistance larger than that of the heating pattern. The heating pattern and the control resistor are both embedded in a ceramic body with resistors connected in series, or a ceramic heater is configured with a part of the heating pattern exposed. Self-regulating glow plug.