JPH01114622A - Self-controlling type ceramic glow plug - Google Patents

Abstract

PURPOSE:To prevent an over-heating, prohibit a crack from being generated in a ceramic heater rod and further prevent a heater from being melted cut by a method wherein both heater buried in the ceramic heater rod and controlling resistor are arranged at a location spaced apart from an extremity end of a metallic pipe by more than a specified distance. CONSTITUTION:Both heater buried in a ceramic heater rod and a controlling resistor are arranged at a location spaced apart from an extremity end of a metallic pipe by more than 2mm. Applying this self controlling type ceramic grow plug causes a rapid increasing in temperature to be attained. Since the controlling resistor 4 is placed at a location spaced apart from a metallic pipe 7, the controlling resistor 4 may also show an increased temperature as the ceramic heater rod 1 increases its temperature and further a proper current control can be attained, so that an over-heating can be prevented. In addition, a ratio between a length l1 of a connected part between the heater and the resistor and a length l of a projecting part of the ceramic heater rod is set to have a relation of 0.2<=l/l<=0.5, a temperature increasing time up to 900 deg.C is less than 5 second and thus a ceramic grow plug which is not overheated by more than 1200 deg.C can be attained.

Description

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

[Conventional technology]

Diesel engines generally have poor starting performance at low temperatures, so a glow plug is installed in the auxiliary combustion chamber or combustion chamber, and by passing an electric current through it and generating heat, a portion of the fuel injected into the interior is temporarily combusted. , a method is used to improve engine startability by heating the interior of the vehicle.

Instead of the conventional seeded type glow plug, a wire made of tungsten, molybdenum, etc. is embedded as a heating element in a ceramic body such as silicon nitride or sialon, which has high thermal shock resistance, and the wire is connected to the outside. Ceramic glow plugs, which allow a large current to flow through the terminals and reach high temperatures, are often used.

In addition, the characteristics of glow plugs are such that the temperature rises rapidly to about 900° C., and the maximum temperature is required to be controlled to 1200° C. or less so that the heating element etc. do not melt. Therefore, as shown in Japanese Patent Application Laid-open No. 60-218, a self-controlling ceramic glow plug has been developed in which a heating element and a current control resistor are connected in series and embedded in a ceramic body. This utilizes the fact that the resistance value of the current control resistor increases as the temperature rises to suppress the amount of current and prevent overheating of the glow plug.

[Problems with conventional technology]

However, in such conventional self-control ceramic glow plugs, the current control resistor was located inside the metal pipe that supported the ceramic heater rod, so the temperature of the current control resistor was difficult to rise due to the cooling effect of the metal pipe. ,
The effect of preventing overheating as described above was small. Therefore, the ceramic heater rod tends to reach a high temperature of 1,200° C. or higher, and as a result, there is a risk that cracks may occur or the heating element may melt.

[Means for solving problems]

In view of the above, the present invention provides a self-regulating ceramic glow plug that includes a heating element embedded in a ceramic heater rod,
Both control resistors are placed at a distance of 211I11 or more from the tip of the metal pipe.

Furthermore, the length of the connection between the heating element and the resistor is jll
and the length l of the protruding part of the ceramic heater rod is 0.
．． 2≦1. /It≦0.5 to 900℃
It is possible to provide a ceramic glow plug that takes 5 seconds or less to heat up and does not overheat to 1200° C. or higher.

〔Example〕

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

In FIG. 1, numeral 1 is a ceramic heater rod that serves as a heating element, and a coil-shaped heating element 2 bent in a 0-shape is embedded in the tip of the rod, and a connecting part 3 is connected to each end of the heating element 2. A coil-shaped control resistor 4 is connected thereto, and is further connected to electrode lead lines 6a, 6b via a connecting line 5 which is the same line as the control resistor 4 and whose pitch is 1.5 times or more coarser.

This ceramic heater rod 1 is brazed to a metal pipe 7 through a metallized layer, and its rear end is brazed to a terminal cap 8 through a metallized layer. The metal pipe 7 to which the electrode lead wire 6a is brazed is brazed to the inner cavity of the tip end of the mounting bracket 9 to constitute a cathode, while the terminal cap 8 to which the electrode lead wire 6b is brazed is brazed to the lead rod 10. In addition, this lead rod 10
is welded to the center shaft 11 and serves as an anode.

Moreover, the heating element 2 is -ReJ-CosW-Mo+W-Zr
Tungsten (-) with a high melting point and a small temperature coefficient of resistance, such as
The control resistor 4 is made of an alloy that has a high melting point, such as pure metal, and has a higher temperature coefficient of resistance than the heating element 2.

The connecting portion 3 is a cylindrical body made of conductive ceramic, and the heating element 2 and the resistor 4 are inserted from both end faces for connection.

After embedding these in ceramic powder such as silicon nitride and preforming them into an elliptical shape, the ceramic heater rod 1 is formed by sintering the ceramic and integrally molding it using the hot bures method. Since it is coiled, there is no risk of wire breakage due to differences in sintering expansion even when cooling after sintering.

If the self-regulating ceramic glow plug according to the embodiment of the present invention is used, the temperature rises rapidly at the initial stage of energization, and since the control resistor 4 is located further away from the metal pipe 7, the temperature of the ceramic heater rod 1 increases. As the temperature increases, the temperature of the control resistor 4 also increases, and the amount of current can be controlled appropriately, so overheating can be prevented.

Further, as shown in another embodiment in FIG. 2, the heating element 2, the control resistor 4, and the connecting wire 5 are wavy, and the connecting portion 3 is a structure in which the heating element 2 and the control resistor 4 are directly connected by diffusion bonding or the like. The heating element 2 and the control resistor 4 may have various other shapes, and the connecting portion 3 may also have various structures such as a winding connection.

Furthermore, although not shown, the heating element 2, the connecting portion 3, the control resistor 4, and the connecting wire 5 may all be formed by printing, and the resistance value may be adjusted by changing the line width or printing material. good.

Next, regarding the self-regulating glow plug shown in Figure 1,
Prototypes were manufactured with various distances d between the control resistor 4 and the metal pipe 7, and experiments were conducted to investigate the temperature rise characteristics of each. The globe lug to be used has a ceramic heater rod 1 cross section with a major axis of 4.4 mm, a minor axis of 3.51 mm, and a protrusion length 2 of 14 mm+, and the temperature rise characteristics when a voltage of 11 V is applied are shown in Figure 3. As shown in (a) to (e).

3(a) shows the case where the control resistor 4 is located inside the metal pipe 7, and FIGS. 3(b) to (e) show the case where the distance between the control resistor 4 and the metal pipe 7 [d is θ~31II11 Each case is shown.

Here, the characteristics required for a self-regulating glow plug are that the maximum temperature is 1200°C or less and the time to reach 900°C is 5 seconds or less, but as shown in Figure 3 (d) and (e), The distance d between the control resistor 4 and the metal pipe 7 is 2 m.
It can be seen that if it is greater than or equal to m, the above-mentioned required characteristics are satisfied.

Next, in the self-regulating glow plug shown in Fig. 1,
The length i of the protruding portion of the ceramic heater rod 1 and the length 11 of the connecting portion 3 were varied, and the time required to reach 900° C. was measured for each. Note that the distance d between the control resistor 4 and the metal pipe 7 was 3 ml, and the other conditions were the same as in Experimental Example 1. The results are shown in Table 1.

As mentioned above, the required characteristic of a glow plug is that the time to reach 900°C is 5 seconds or less, but the first characteristic is
From the table, it can be seen that when 1,7N is 0.2 or more, the above requirements are almost satisfied. If 11/l is smaller than 0.2, the heating element 2 and the control resistor 4 are too close;
The temperature of the control resistor 4 tends to rise due to the heat generated by the heating element 2.
The overheating prevention effect works before the temperature reaches its peak.
Rapid temperature rise cannot be achieved.

On the other hand, if 11/1 is too large, the ratio occupied by the heat dissipating element 2 and the control resistor 4 will become smaller, making it impossible to obtain excellent characteristics. /(l was preferably 0.5 or less.

To summarize the above experimental examples, in the self-control ceramic glow plug shown in FIG. It can be seen that if the ratio of the length of the protrusion to l is 0.2≦β+/l≦0.5, an excellent glow plug that satisfies the required characteristics can be obtained.

In addition, the length of the heating element 2 is R, the length of the connecting part 3 is β3, and the limit is 4.
As a result of various experiments, the ratio of the length R2 of the B resistor 4 is R1:#1:
Rz・1:0.5~1.5:Q, 5~1.5 is excellent, especially R1: e +: Rz=1:1:
The one rated 1 was the best.

Although the above embodiments have been described only with respect to the self-regulating ceramic glow plug shown in FIG. 1, the same applies to the self-regulating ceramic glow plug shown in FIG.

Further, although only a configuration in which two control resistors 4 are provided on the cathode side and an anode side of the heating element 2 is shown, the same applies even if only one of them is provided.

〔Effect of the invention〕

As described above, according to the present invention, in a self-regulating ceramic glow plug, both the heating element embedded in the ceramic heater rod and the control resistor are placed at least 2 mm away from the tip of the metal pipe. The temperature can be raised quickly, taking less than 5 seconds, and it can prevent overheating to over 1200℃, so there is no risk of the ceramic heater rod cranking or the heating element melting. A high performance self-regulating ceramic glow plug can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a self-regulating ceramic glow plug according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing only a ceramic heater rod constituting a self-regulating ceramic glow plug according to another embodiment of the present invention. It is a diagram. FIGS. 3(a) to 3(e) are graphs showing the temperature increase characteristics of self-regulating ceramic glow plugs. 1: Ceramic heater rod 2: Heating element 3: Connection part 4: Control resistor, 5: Connection wires 6a, 6b: Electrode lead wire 7: Metal pipe

Claims (1)

[Claims] (1) A self-controlling ceramic glow plug that has a heating element and a control resistor connected in series to the heating element, and a ceramic heater rod in which the heating element and the control resistor are embedded is held by a metal pipe, A self-controlling ceramic glow plug characterized in that the heating element and the control resistor are arranged at a distance of 2 mm or more from the tip of the metal pipe of the ceramic heater rod. (2) The ratio of the length l_1 of the connection part between the heating element and the control resistor to the length l of the part of the ceramic heater rod protruding from the metal pipe is 0.2≦l
A self-regulating ceramic glow plug according to claim 1, characterized in that _1/l≦0.5.