JPS61195580A - Ceramic heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

"Problems to be Solved by Prior Art and the Invention" Glow plugs used as starting ignition devices for diesel engines require a large current to be applied at the initial stage of energization in order to achieve a rapid rise in temperature. After reaching the ignition temperature to prevent the glow plug from cranking,
It is generally employed to maintain a stable temperature by controlling the current to be low. This is shown in Figure 10, which shows that the temperature reaches 900°C in 2.0 seconds after electricity is applied.
It maintains a fairly constant temperature. Such characteristics are desired.

A conventional glow plug is shown in FIGS. 11 and 12. That is, the ceramic sintered body 101
A heating resistor 102, a positive electrode lead wire 103, and a negative electrode lead wire are buried therein, a positive electrode lead metal fitting 104 is fixed to the base end side of the ceramic sintered body 101, and a lead wire 105 is connected thereto. On the other hand, a cathode extraction tube 106 is interposed in the middle part of the ceramic sintered body 101, and the metal outer cylinder 1
07 and take out the negative electrode. The heating resistor 102 is arranged along the axis of the front wheel portion of the ceramic sintered body 101 and is bent at the tip, so that the heating resistor 102 is arranged at two locations in the cross section as shown in FIG. has been done.

Since the required amount of heat must be supplied by the heating resistors 102 at two locations in the cross section, the amount of heat supplied per one becomes considerably large, resulting in a large thermal load on the ceramic sintered body 101 and the heating resistor 102, resulting in poor durability. It lacks character. Further, the distance from the surface of the ceramic sintered body 101 to the heating resistor 102 is
Since the difference in distance becomes large depending on the location on the surface of 1, the temperature distribution becomes non-uniform as shown in FIG. Furthermore, since there are two heating resistors 102 in the cross section of the ceramic sintered body 101, the wire diameter of the heating resistor 102 becomes large because it is necessary to heat the entire body. Since the coefficient of linear expansion is different from that of the heat generating resistor 102, the thermal stress on the ceramic sintered body 101 and the thermal stress generated in the heat generating resistor become large, causing problems in terms of durability.

1. In view of the above-mentioned circumstances, the present invention has been developed by embedding a plurality of heat generating resistors in a ceramic sintered body, so that the amount of heat supplied from these heat generating resistors is reduced to the surface of the ceramic sintered body. This is a ceramic heater that evenly distributes the amount of heat.

1. The amount of heat supplied from the heating resistor is distributed uniformly on the surface of the ceramic sintered body (that is, it is uniformly averaged in the cross section).

"First Embodiment" A glow plug used as a starting ignition device for a diesel engine is shown in FIGS. 1 and 2, and its circuit diagram is shown in FIGS. 3 and 4. S 2LSiCXAIN
Two heating resistors 2 and 3 such as WlMo are embedded in a ceramic sintered body 1 such as, and a positive electrode attached to the base end side of the ceramic sintered body 1 with positive electrode lead wires 4 and 5 interposed. It is connected to the electrode extraction fitting 6 and further connected to the lead wire 7. The other ends of the heating resistors 2 and 3 are connected to electrode lead wires 8 and 9.
The heating resistor 2 is connected to the metal outer cylinder 11 via the electrode lead wire 8 and the cathode lead pipe 10 in the middle of the ceramic sintered body 1, and the cathode is taken out.

On the other hand, the heating resistor 3 is connected to a lead wire 13 via an electrode lead-out tube 12 attached closer to the proximal end of the ceramic sintered body 1 than the electrode lead-out wire 9 is.

At the time of initial voltage application, as shown in FIG. 3, electricity is applied from the power source 14 through the relay contact 15, through the lead wire 7 and the positive electrode extraction fitting 6 to the heating resistors 2 and 3, and the electrode extraction tubes 10 and 12 are energized. After that, electricity is applied to the heating resistors 2 and 3.
are connected in parallel to the power supply 14, and the power supply 14 is directly applied to the heating resistors 2 and 3.

After the rapid temperature rise, the switching is performed by a timer or the like as shown in FIG. 9. Heat generating resistor 3, positive electrode lead wire 5, positive electrode lead wire 6, then positive electrode lead wire 4, heat generating resistor 2, positive electrode lead wire 9
, the electrode extraction tube 10 is energized, and the heating resistors 3 and 2
are connected in series, the combined resistance of the glow plug as a whole increases, the current flowing through it decreases, the amount of heat supplied also decreases, and the temperature of the glow plug is maintained constant. In the present invention, the heating resistor 2 is present in four or more locations in the ceramic sintered body I as shown in FIG. 2, whereas in the conventional product, the heating resistor 2 is present in two locations as shown in FIG. Compared to the ceramic sintered body 1 and the heat generating resistors 2 and 3, the heat capacity is the same because the cross-sectional area is the same, so each heat generating resistor needs to supply less heat, and the heat load on the ceramic sintered body 1 and the heat generating resistors 2 and 3 is reduced. It is smaller and has improved durability. FIG. 5 shows the results of a glow plug overvoltage test at the glow plug's peak temperature. Conventionally, cracks begin to appear at a little less than 1,300℃, and cracks occur in most items at 1,450℃, but experiments have shown that with this product, cracks often occur only after the temperature exceeds 1,500℃. Confirmed.

In addition, compared to conventional glow plugs, the distance from the ceramic sintered body surface to the heating resistor is not much different at any position on the ceramic sintered body surface, so the temperature distribution on the ceramic cross section is As shown in Figure 6, since there is uniformity, the amount of heat supplied to the surface of the sintered body is also uniform. In addition, this glow plug has more heating resistors embedded in the ceramic sintered body than conventional glow plugs, so the wire diameter of the heating resistor can be made smaller than in conventional glow plugs. Even if there is a difference in the coefficient of linear expansion between the ceramic sintered body and the heating resistor, the thermal stress of the ceramic sintered body and the thermal stress generated in the heating resistor are small, resulting in excellent durability.

- In Section 2, we talked about embedding multiple heating resistors in a ceramic sintered body used for glow plugs, and connecting them in parallel or series, but it is not limited to this. From connection to single resistor connection, from resistor body to single resistor, from parallel connection to parallel connection,
It is also possible to change from series connection to series connection or from a single resistor to parallel connection. In this case, in order to obtain an arbitrary or optimal amount of heat to be supplied during rapid temperature rise and temperature saturation, and to sufficiently suppress thermal stress on the ceramic sintered body and the heat-generating resistor, the connection form and heat-generating resistor You can select the resistance value.

"Second Example" Adding a solvent to powder containing tungsten (W),
As shown in Figure 7, mix the kneaded slurry with alumina (810
) The heating resistors 2o and 21 are formed by screen printing on a ceramic green sheet substrate mainly composed of
A sintered body containing two heat generating resistor circuits was obtained by laminating a total of three sheets, two sheets of 8.19 and the upper green sheet 17, and firing them. In addition, the material of the heating resistor mentioned above includes WSi, Mo, MoSi,
It may be composed of one or more selected from Fe-, Ni, Cr, etc. Furthermore, the connection form can be arbitrarily selected as described above.

In this heating element, as described in the first embodiment, when the initial temperature rises, the heating resistors 20 and 21
are connected in parallel, and after startup, the heating resistors 20 and 21
can be connected in series to maintain a predetermined temperature.

Therefore, compared to conventional heating elements, the thermal load on the ceramic sintered body and the heating resistor is reduced, and durability is improved. Figure 9 shows the temperature rise test results for alumina heaters. Conventionally, cracks began to appear at about 180'C, and at 250'C.
℃, most of the products developed cracks, but according to the products of the present invention, the rate of cracking gradually started to increase from about 250°C, and therefore the durability improved. is confirmed by the experimental results.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a vertical cross-sectional view of a glow plug according to a first embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view taken along nn of FIG. 1, and FIGS. Figures 1 and 2 are glow plug circuit diagrams, Figure 5 is a diagram of glow plug overvoltage test results, Figure 6 is a temperature distribution diagram based on calculation results when the glow plug is stably heated,
Fig. 7 is an exploded perspective view of the heating element of the second embodiment, Fig. 8 is a perspective view of the heating element of the second embodiment, Fig. 9 is a diagram showing the temperature rise test results of the alumina heater, and Fig. 10 is the glow plug. Figure 11 is a longitudinal cross-sectional view of a conventional glow plug, Figure 12 is a temperature characteristic diagram of
The figure is a sectional view taken along the line X[I-XI in FIG. 11, and FIG. 13 is a temperature distribution diagram based on calculation results during stable heating of a conventional glow plug.

Claims (2)

[Claims] (1) A ceramic heater characterized in that a plurality of heating resistors are embedded in a ceramic sintered body, and the amount of heat supplied from these heating resistors is uniformly distributed over the surface of the ceramic sintered body. (2) The ceramic heater according to claim 1, wherein the heating resistor is one or more selected from W, WSi, Mo, and MoSi.