JPS61237918A - Quick raised temp.-saturated temp. type ceramic glow plug - Google Patents

Abstract

PURPOSE:To improve starting performance of engines and durability with control ling the generation of cracks by installing heating resistance elements in such a manner that U-shape heating resistance elements having two pieces are buried longitudinally in a rod-like ceramic body and heating resistance elements are so arranged as in a primary, secondary, third, and fourth quadrants when X, Y axes co-ordinates are set up through a center of the rode as the origin. CONSTITUTION:When X, Y axes co-ordinates are set up through a center of a cross section of heating resistance elements having circular or oval shape as the origin, each heating resistance element 302 is buried in the cross section area of a heating body 301 corresponding to a primary, secondary, third, and fourth quadrants thereof respectively. In relation between glow plug peak temp. and generation rate of cracks in case of circular cross section, cracks start to occur as temp. exceeds 1,100 deg.C in a comparison example 1, almost occur at 1,300 deg.C, and almost all occur at 1,500 deg.C in a comparison example 3, however, cracks start to occur from about 1,460 deg.C in an embodiment example 1 and almost all occur at about 1,750 deg.C. Thus, remarkable effect is obtained compared as those in the past.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a ceramic glow plug used as a starting ignition device for a diesel engine.

"Conventional technology" Glow plugs used as starting ignition devices for diesel engines use a large current at the beginning of energization to achieve a rapid rise in temperature, thereby preventing damage due to glow plug cranking under high temperatures. In order to achieve ignition, it is generally adopted to maintain a stable temperature by controlling the current to flow at a low level after reaching a temperature that allows ignition. For example, the temperature is raised to about 900° C. in 3.5 seconds after the start of energization, and then the temperature is maintained at a constant temperature.

A conventional current control device is shown in FIG. That is, at the initial stage of energization, power is applied from the power source 101 to the glow plug 103 via the relay contact 102, but after the temperature rises, the power is applied from the power source 101 to the glow plug 103 via the resistor 104 and the relay contact 105, and the current passes through the resistor 104. By doing so, the current decreases, the amount of heat generated decreases, and the temperature of the glow plug does not rise and remains almost constant. There is also one shown in FIG. Electricity is supplied from a power source 101 to a glow plug 107 via a braking coil 106 having a positive temperature coefficient of resistance. Since the resistance of the braking coil 106 increases as the temperature increases,
When the temperature increases, the resistance increases, the current to the glow plug 107 decreases, and the amount of heat generated decreases.

On the other hand, in a conventional glow plug made of a ceramic sintered body, as shown in FIGS. 3 and 4, a heating resistor 126 is placed in a ceramic sintered body 125 and is bent at its tip along the axis line so that it is parallel to the body. In the cross section perpendicular to the axis, the heating resistors 126 are located at two locations, and the required amount of heat is supplied from these two locations, thereby increasing the ceramic sintered body. 125 and the heat generating resistor 126 increases, which poses a problem in durability.

Furthermore, the heating resistor 1 is
There is variation in the distance up to 26, and therefore the temperature distribution in the cross section of the sintered body becomes non-uniform. Furthermore, heating resistor 1
When two 26 exist in one cross section, the heating resistor 126
has a relatively large wire diameter, and the heating resistor 126 and the ceramic sintered body 125 have different linear expansion coefficients, so that the thermal stress on the ceramic sintered body 125 and the thermal stress on the heating resistor 126 becomes considerably large.

In order to solve the above-mentioned problems, the applicant proposed
According to Japanese Patent Application No. 60-33489 "Ceramic Heater" filed on May 20th, in a heater in which a heating resistor is embedded in a ceramic sintered body, a plurality of said heating resistors are provided in the ceramic sintered body, and these heating resistors are We proposed a rapid temperature rise/temperature saturation type ceramic heater that connects the body to the power supply in parallel when the initial voltage is applied and in series when the temperature is saturated.

The glow plug is shown in FIGS. 5 and 6.

Two heating resistors 2 and 3 made of W, No%Pe, Ni or Cr are buried in a ceramic sintered body 1 such as 5iJ4 or SiCs Alto, AIN, etc.
The positive electrode lead wires 4 and 5 are interposed to connect to the positive electrode lead metal fitting 6 on the proximal end side of the ceramic sintered body 1, and further to the lead wire 7. The other ends of the heating resistors 2 and 3 are connected to the electrode lead wire, and the heating resistor 2 is connected to the metal outer cylinder 1 through the cathode lead pipe 10 in the middle of the ceramic sintered body 1.
Connect to 1. On the other hand, the heating resistor 3 is connected to a lead wire 13 via an electrode extraction tube 12 attached to the base end of the ceramic sintered body 1.

When applying the initial voltage, the heating resistors 2 and 3 are energized,
The combined calorific value of these heating resistors 2 and 3 causes rapid temperature rise.

After the rapid temperature rise, the heating elements 3 and 2 are connected in series, the combined resistance increases, the amount of current is reduced, and the amount of heat generated is also reduced, so that the temperature does not rise and is maintained at a constant temperature.

However, as the applicant conducted repeated experiments on ceramic glow plugs, he discovered the following.

As shown in FIG. 7 (Comparative Example 3) and FIG. 8 (Comparative Example 4), some of the many production lofts are equipped with heating resistors.
3 will be located unevenly and the desired characteristics will not be obtained.

The reason for this is thought to be that the following problems arise in the manufacturing method. When the ceramic powder is filled obliquely as shown in Figure 9, or as shown in Figure 10, areas H and low density of the ceramic powder grains are formed, which are compressed. will occur from time to time.

In general, in glow plugs made of ceramic sintered bodies, the heating element at the tip of the metal outer cylinder is made of silicon nitride or the like and is made of a substantially round bar-shaped ceramic sintered body. A heating resistor (coil-shaped heating wire) made mainly of tungsten metal is buried in the ground, and by supplying electricity to the heating resistor, the heating element made of the ceramic sintered body becomes red hot and the fuel to be sprayed is heated. I'm trying to ignite it.

Such ceramic glow plugs are required to have rapid temperature rise characteristics in order to quickly start the engine, and on the other hand, ceramic glow plugs that occur due to the difference in thermal expansion between the heating resistor and the ceramic heating element (sintered body) at high temperatures are required. In order to prevent the generation of cracks in the heating element, it is necessary to control the current so that the temperature does not rise above a certain temperature after the heating element reaches an ignitable temperature.

As shown in FIG. 11, the ceramic glow plug currently on the market has a ceramic heating element 203 made of silicon nitride or the like fixed to the tip of a metal outer cylinder 201 via a metal tube 202. This ceramic heating element 203 is made of a ceramic sintered body in the shape of a substantially round bar, and a heating resistor 204 (coil-shaped heating element) mainly made of tungsten metal is bent into a plane U-shape along the inside of this sintered body in the longitudinal direction. One is buried. For example, in the case of a body ground type as shown in FIG. 11, this heating element 204 is connected to
+) voltage is applied and short-circuited to the body ground (-) side via lead wire 207, metal tube 202, and metal outer cylinder 201.

Ceramic heating elements 203 used in such glow plugs are conventionally available in two types, circular or oval in cross section, due to differences in processing methods, as shown in Figure 12 (Comparative Example 1) and Figure 13 (Comparative Example 2). provided. Both are rod-shaped ceramic sintered bodies 203a.

U-shaped heating resistor 20 along the longitudinal direction inside 203b
One each of 4a and 204b is buried, and when viewed in cross section, each appears at two locations. For these heating resistors 204a and 204b, the distance from the heating resistor to the surface of the ceramic heating elements 203a and 203b (2
08a, 209a, 208b, 209b") is relatively large and the distance between them is uneven, the heat distribution in the cross section of the ceramic heating elements 203a, 203b is also uneven, and the heating element as a whole is insufficient. It is not possible to obtain a sufficient amount of heat to be supplied. This has a great effect on the rapid temperature rise characteristic at the time of engine startup. Also, this also causes the heating resistors 204a, 20
It is necessary to increase the amount of heat generated by the inner body 4b, and therefore, the wire diameter of the heating resistors 204a and 204b must be relatively large and the resistance value must be small. This means that the heating resistors 204a and 204b
The amount of heat generated per one of the ceramic heating elements 203a and
Due to the difference in thermal expansion between the ceramic heating element 203b and the heating resistors 204a and 204b, cranks occur in the ceramic heating element, particularly near the heating resistors 204a and 204b, resulting in poor durability.

This point will be explained in more detail based on FIG. 14.

The temperature saturation curve of the glow plug shows the temperature saturation characteristics of a general glow plug, in which the temperature rapidly increases to around 900°C in about 3 seconds, and then reaches a high temperature peak of about 1350°C. Such characteristics are still not sufficient. On the other hand, if the wire diameter of the heating resistor is increased to lower the resistance value in order to raise the temperature to 900° C. in a faster period, the temperature saturation curve Y will be obtained. In this case, a rapid temperature rise up to 900°C is achieved in a relatively short period, but on the other hand, the high temperature peak at saturation is 135°C.
If the temperature exceeds 0°C, the thermal expansion of the resistor inside the ceramic heating element becomes severe and cranking is likely to occur. In addition, in order to suppress the high temperature peak to a lower temperature and further reduce the occurrence rate of cranking, for example, if the wire diameter of the heating resistor is made thinner and the resistance value is increased, the temperature saturation curve becomes as shown in Z. . In this case, the peak of relatively high temperature can be suppressed to a low level, but on the other hand, the period during which the temperature rises to 900°C is
, and the rapid temperature rise characteristics deteriorate.

As described above, the distribution of heat from the heating resistor in the cross-sectional area of the ceramic heating element is determined by the distance to the surface of the heating resistor 204a, 204b (208a, 209a, 208b, 209b) as shown in FIGS. 12 and 13.
) is large and the distance varies, no matter how much the wire diameters of the heating resistors 204a and 204b are changed, it is not possible to obtain rapid temperature rise characteristics superior to the above temperature saturation curve X. However, it is difficult to further suppress the high temperature. It was also difficult to maintain a high temperature after temperature saturation (afterglow).

"Problems to be Solved by the Invention" In view of the above points, the applicant has conducted extensive research and found that two U-shaped heating resistors are installed in parallel along the longitudinal direction of the ceramic sintered body. It has been found that the above-mentioned characteristics can be further improved by embedding the heating resistor and arranging the buried position of the heating resistor in a certain area in the substantially circular or oval cross section of the heating element.

Therefore, in the present invention, by further improving the rapid temperature rise characteristics of the glow plug and further suppressing the high temperature peak at temperature saturation, it is possible to improve engine startability and suppress the occurrence of cranking, thereby improving durability. The purpose is to provide ceramic glow plugs that can.

According to the present invention, a glow plug has a rod-shaped ceramic heating element in which two U-shaped heating resistors are embedded in parallel in the longitudinal direction of a ceramic sintered body. If the center of the cross section of the ceramic heating element is set as the XY axis coordinate, the position where the heating resistor is buried is in the first quadrant, second quadrant, third quadrant, and fourth quadrant of each coordinate. A ceramic glow plug is provided which is characterized in that it is located in a region in the cross-sectional area of the corresponding heating element.

Further, according to the present invention, the average outer diameter of the ceramic heating element is
On the other hand, there is provided a ceramic glow plug in which the circumscribed circle D2 of the heating resistor located in each quadrant region centered on the origin is located within a ratio range of 0.5 to 0.9.

When two U-shaped heating resistors are embedded in a ceramic heating element, the cross section of the heating element (sintered body) will be circular as shown in Figure 15 or oval shaped as shown in Figure 16. These resistors are located at four locations. When creating a ceramic glow plug with such a configuration, a hot press firing method is usually used. That is, the bottom of a rectangular mold of a hot press machine is filled with ceramic powder to a certain thickness, a first-grain U-shaped heating resistor is placed on top of it, and a certain thickness of ceramic powder is placed on top of it. is filled, another U-shaped heating resistor is placed on top of it, and the top is filled with ceramic powder, which is compressed to create a green body, which is then fired under high temperature and high pressure. As a result, the ceramic glow plug of the present invention can be obtained. However, due to various conditions such as the amount and thickness of the ceramic powder to be filled, the pressure during hot pressing, and shrinkage after sintering, it is not possible to obtain the same configuration as the initial state set in the hot press mold after firing. It's not easy.

The cross section of the ceramic heating element thus produced is as shown in FIGS. 15 and 16, for example.

In the cross section of the ceramic heating element (sintered body 301) having a circular cross section as shown in FIG. 15 or an oval cross section as shown in FIG.
The buried position of 02 is the first quadrant, the second quadrant of each coordinate,
It is located in a region in the cross-sectional area of the heating element 301 corresponding to the third and fourth quadrants.

With respect to the average outer diameter of the ceramic heating element 301 (in the oval-shaped cross section shown in FIG. 16, the length on the X axis is approximately the diameter), the area of each quadrant centered on the origin is The diameter D2 of the circumscribed circle of the located heating resistor 302 is 0.5
~0.9 ratio.

As shown in FIG. 17, the surface of the heating resistor 302 is covered with a tungsten silicide layer 303 (S
The layer formed by the reaction between i and tungsten during firing has a maximum thickness of 50 μm, and this tungsten silicide generation layer 3
Since 03 has conductivity, the distance between the tungsten wires must be approximately 50 μm.

If the above ratio is less than 0.5, there is a risk that the heat generating resistors 302 or the tungsten silicide layers will come into contact with each other and cause a short circuit, while if it is 0.9 or more, the heat generating resistors 302 may come into contact with each other and cause a short circuit.

The particle size distribution of the ceramic particles outside the body 302 is poor;
It is difficult to become dense.

"Effects of the Invention" FIGS. 18 and 19 show temperature increase characteristics. FIG. 18 shows a circular cross section, and Comparative Example 1 has a speed of 900 in 3.2 seconds.
℃, and the maximum temperature was about 1300℃, and the one in Comparative Example 3 with a biased heating resistor reached 900℃ in 4.2 seconds, indicating that the temperature rise time was slow. 2
The temperature reaches 900°C in seconds, and the temperature is maintained at about 1000°C even after afterglow. The one in Figure 19 has an oval cross section, and the one in Comparative Example 2 has a 3.0
It reaches 900°C in seconds, then rises to about 1300°C, and then rapidly drops. There are four heating resistors of Comparative Example 4. The temperature reached 900℃ in 4.2 seconds, and the temperature rise time was slow, and the device of the present invention reached 900℃ in 2 seconds.
The temperature reaches 0°C, the temperature rises quickly, and then the temperature is maintained at approximately 1000°C.

Next, FIGS. 20 and 21 show the relationship between the glow pump temperature and the crank occurrence rate. FIG. 20 shows a circular cross section, and the one of Comparative Example 1 starts to crack when the temperature exceeds 1100°C, and most of them start to crack at 1300°C. In addition, in Comparative Example 3, 12
Cracks start to occur at about 80°C, and at 1500°C, cranks almost always occur, but in Example 1 of the present invention, 1
Cranks begin to occur at about 460°C, and most of them occur at about 1750°C. The temperature distribution is concentrated in the extreme parts, and a difference in thermal expansion occurs in the cross section of the sintered body, making it easy for cranks to occur. In addition, in Fig. 21, a heating element with an oval cross section starts to crank at around 1300°C in Comparative Example 2.
Crank occurs in most cases at 1520-1530°C. In addition, in Comparative Example 4, cracks start to occur at about 1370°C and most cracks occur at about 1600°C, whereas in Example 2 of the present invention, cranks start to occur at about 1570°C and most of the cracks occur at about 1800°C. A crank appears in the product, and as you can see, it has a remarkable effect compared to conventional products.

As described above, the present invention can improve rapid temperature rise characteristics and can also suppress high temperature peak temperature at temperature saturation. Furthermore, the temperature after temperature saturation (afterglow) can be maintained high.

[Brief explanation of drawings]

Figure 1 is a system diagram of a conventional glow plug, Figure 2 is a system diagram of another conventional glow plug, Figure 3 is a vertical cross-sectional view of a conventional glow plug, and Figure 4 is IV-IV of Figure 3. 5 is a longitudinal sectional view of a glow plug developed by the applicant, FIG. 6 is an enlarged sectional view of the part ■-v in FIG. 5, and FIG. 7 is a longitudinal sectional view of a ceramic heating element with a circular cross section. 8th longitudinal cross-sectional view showing Comparative Example 3 showing a state in which the heating resistor is biased in the plan view.
The figures are a longitudinal cross-sectional view of Comparative Example 4 showing a state in which the heating resistor is biased in the ceramic heating element with an oval-shaped cross section, Figure 9, and Figure 1.
Figure 0 is a diagram explaining the manufacturing method of ceramic glow plugs.
FIG. 11 is a plan sectional view of a conventional ceramic glow plug, and FIG. 12 is a vertical sectional view of Comparative Example 1 showing a state in which two heating resistors are arranged in a ceramic heating element with a circular cross section.
FIG. 13 is a vertical cross-sectional view of Comparative Example 2 in which two heating resistors are arranged in a ceramic heating element with an oval-shaped cross section;
Figure 4 is a diagram explaining the temperature increase state of the ceramic glow plug, Figure 15 is a vertical cross-sectional view of Example 1 in which four heating resistors are arranged in a ceramic heating element with a circular cross section, and Figure 16 is an oval diagram. FIG. 17 is a vertical cross-sectional view of Example 2 in which four heating resistors are arranged in a ceramic heating element with a shaped cross section, and FIG. 17 is a diagram showing a tungsten silicide generation layer on the surface of the heating resistance wire.
The figure is a diagram comparing the temperature increase state of Comparative Examples 1 and 3 with the present invention, Figure 19 is a diagram comparing the temperature increase state of Comparative Examples 2 and 4 with the present invention, and Figure 20 is a diagram comparing the temperature increase state of Comparative Examples 1 and 3 with the present invention. FIG. 21 is a diagram comparing the ratio of crack occurrence between Comparative Examples 2 and 4 and the present invention.

Claims (2)

[Claims] (1) When two U-shaped heating resistors are embedded in the longitudinal direction of a rod-shaped ceramic body, and the center of the cross section of the ceramic heating element is set as the origin and the XY axis coordinates are set, the heating resistors are located at these coordinates. A rapid temperature rise-temperature saturation type ceramic glow plug characterized by having a ceramic heating element in which the resistor is arranged in areas corresponding to a first quadrant, a second quadrant, a third quadrant, and a fourth quadrant. (2) In a cross section perpendicular to the longitudinal direction of the rod-shaped ceramic body, the ratio of the diameter of the circumscribed circle of the heating resistor centered at the origin to the average outer diameter of the ceramic body is 0.5 to 0.9.
A rapid temperature rise-temperature saturation type ceramic glow plug according to claim 1 falling within the scope of