JPS5836154Y2 - Positive temperature coefficient thermistor for heating elements - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a heating element device using a positive temperature coefficient thermistor, which has a uniform temperature distribution and a large amount of heat generation.

For example, a positive temperature coefficient thermistor for a heating element is known in which electrodes are provided on both opposing sides of a square plate-shaped positive temperature coefficient thermistor element.

However, in such devices, since the distance between the electrodes is long, when a voltage is applied between both electrodes to generate heat, the surface temperature of the device often becomes non-uniform.

In other words, a high resistance portion is locally generated in the element.

This may occur, for example, in some high-resistance areas caused by uneven pore distribution that inevitably occurs after firing a molded element, or in areas with poor heat dissipation, where the temperature is higher than other areas. This refers to a region where the resistance becomes high, and this is not limited to a certain location.As shown in FIG. (X direction) and may occur across both electrodes 2 and 3.

In this case, the high resistance portion 4 has a high resistance value, the other low resistance portions have a low resistance value, and the resistance values in the X direction are uniform.

Therefore, when a current is passed through this element 1, the temperature distribution of the element 1 in the X direction becomes uniform because its resistance value is uniform.

The resistance-temperature characteristic of the high-resistance portion 4 is as shown by curve A in FIG. 2, and that of the other portions is as shown by curve A.

However, when the current begins to flow, although a predetermined current flows through the low-resistance portion, not much current flows through the high-resistance portion, and as shown by curve A in FIG. Direction perpendicular to the direction of current flow (Y direction)
A temperature distribution occurs in the region, and the temperature of the high-resistance portion 4 becomes lower than that of other portions.

However, in this element, after a while after starting to flow current, the temperature of the low resistance part further rises, and its resistance value increases beyond the Curie point, reaching a level similar to the resistance value of the high resistance part 4. will be reached.

In this case, since the amount of current flowing through the high resistance part 4 is smaller than that in other parts, heat generation is delayed, and the resistance increase in the low resistance part easily follows, and the high resistance part is no longer a high resistance part. .

As a result, the temperature distribution of the element 1 in the Y direction at the time of final stable operation becomes almost negligible, as shown by curve B in FIG.

The part where the temperature is slightly lower in curve B in Fig. 3 coincides with the stable operation point A' of curve A in Fig. 2, which is slightly smaller than the stable operation point A' at the beginning of the curve. As long as the temperature is low, it is not a problem at all.

Therefore, if a high resistance portion 4 in the X direction as shown in FIG. 1 occurs in the element 1, there will be no practical problem at all.

There is simply a difference in the time it takes to reach a stable state of operation.

As shown in FIG. 4, the high resistance portion 4 may occur in the element 1 over both end faces of the element 1 in the direction (Y direction) orthogonal to the direction in which the current flows.

In this case, the high resistance part 4 has a high resistance value, and the other low resistance parts have a low resistance value, and the resistance values in the Y direction are uniform. Therefore, when current is passed through this element 1, the Y
The directional temperature distribution becomes uniform.

However, in the current flow direction (X direction) of this element 1, since there is always a high resistance part 4 in a part, both electrodes 2 and 3
When a voltage is applied to the high resistance portion 4 in the X direction, the voltage is concentrated in the high resistance portion 4, as shown in FIG.

As a result, the temperature of this high resistance part 4 (voltage concentration part) becomes higher than other parts, so voltage concentration accelerates there (Figure 6), and the resistance value of the high resistance part 4 increases. This increases the resistance value of the low resistance part and widens the difference between the resistance value and the resistance value of the low resistance part.

Therefore, as shown in FIG. 7, the temperature distribution of the element 1 in the X direction is such that the temperature of the high resistance part 4 is extremely high, making it impossible to equalize the temperature, and also making it impossible to increase the amount of current flow. This was a big problem in practice.

As yet another form of high resistance portion 4 occurring in element 1, as shown in FIG. 8, high resistance portion 4 may occur at a point only in a portion between electrodes 2 and 3.

In this case, since the high resistance part 4 exists only in a small area, it seems that it can be ignored in practical terms like the one shown in FIG. The result will be something like the one shown in Figure 4.

This operation will be explained step by step below.

First, the area where the high resistance part 4 exists (X1 area) in the X direction where the current flows, and the high resistance part 4 very adjacent to this area.
Looking at the relationship with the area that does not include (X2 area),
The resistance value distribution in the Xl region is as shown in FIG. 9a, and the resistance value distribution in the X2 region is as shown in the same figure.

If a voltage is applied between electrodes 2 and 3 in this state, the voltage distribution will originally correspond to the resistance value distribution of each electrode, but in reality, since the X1 region and the X2 region are adjacent to each other, they interfere with each other. , the voltage distribution is as shown in Fig. 10 a, l).

That is, the unevenness of the voltage distribution in the X1 region is alleviated and reduced by the X2 region, and conversely, the unevenness occurs in the X2 region due to the reaction thereof.

This is because the heat of the high voltage section in the X1 region is conducted to the X2 region, increasing the temperature of that region and increasing the resistance value.

As a result, the heat generation rate in the X2 region is no longer uniform,
The result will be the same as if a high resistance portion 4 with a high resistance value were formed there.

However, as explained in the case of Figure 4 above,
If there is a high resistance part (high temperature part) in the direction of current flow,
The voltage concentration in that part occurs at an accelerated rate, and the high temperature part becomes even hotter, so once a high resistance part occurs in the X2 region, the temperature in that part increases at an accelerated rate (Figure 11). ).

Since this high-resistance region (high-temperature region) is formed instantaneously, the same phenomenon will next transfer to the region adjacent to the X2 region, which will also transfer to the next region, and so on. A resistance portion is formed, and finally, as shown in FIG. 12, a high resistance portion is formed over both ends of the element 1, over the entire Y direction.

This FIG. 12 ends up being substantially the same as that shown in FIG.

Therefore, in this case as well, it was not possible to equalize the temperature of the element 1, and it was not possible to obtain a large amount of heat generation.

Therefore, in an attempt to eliminate this defect, as shown in FIG.
There was one in which a heat equalizing plate 5 was brought into contact.

However, in this conventional device, it is difficult to bring the element 1 and the heat equalizing plate 5 into close contact with each other, which poses a problem in effectively dissipating the heat generated by the element 1.

In addition, in this conventional type, the heat taken out from the positive temperature coefficient thermistor element 1 is almost equalized by the heat equalizing plate 5, but since the temperature of the element 1 itself is not equalized, there are still localized high-temperature parts. However, when used as a heat generating element, there were various disadvantages in terms of heat cycles and the like.

The main purpose of the present invention is to prevent voltage concentration from occurring even if there is a high resistance part in the direction of current flow of a positive temperature coefficient thermistor element, as shown on each side of Figures 4 and 8 above. It is an object of the present invention to provide a positive temperature coefficient thermistor for a heating element in which the temperature is reduced.

In other words, a resistor is provided on at least one plane of a positive temperature coefficient thermistor element having electrodes provided on opposing sides, and a resistor is provided over almost the entire length between the two electrodes, and the resistance value of this resistor is determined by the amount of heat generated by the entire element. set higher than the average resistance value of the stable operation point at the time, and lower than the resistance value per unit length of the voltage concentrated portion that occurs in the direction of current flow of the element,
If a voltage concentration portion occurs in the element in the direction in which the current flows, the voltage concentration in that portion is suppressed by the resistor.

A specific example of the present invention will be described below in detail with reference to the drawings.

In FIG. 14, 11 is a square plate-shaped positive temperature coefficient thermistor element made of, for example, a barium titanate-based ceramic semiconductor; 12.
Reference numeral 13 indicates a pair of electrodes provided on opposing side surfaces of the element 11, and reference numeral 14 indicates a resistor provided over the entire surface of the element 11. The resistance value of the resistor 14 is equal to It is set higher than the average resistance value at the stable operation point when the entire element 11 generates heat, and lower than the resistance value per unit length of the voltage concentrated portion.

In such a configuration, if a voltage is applied between the electrodes 12 and 13, most of the current will flow through the element 1 since the resistance value of the element 11 is lower than that of the resistor 14.
1 and starts generating heat.

Then, after a certain period of time, the resistance value of the element 11 increases beyond the Curie point, and stabilizes at a predetermined resistance value (operational stability point).

However, if the above-mentioned high-resistance portion exists (at a point or across a gold mine) in the direction of current flow in the element 11, voltage will be applied to that portion in a concentrated manner, and the temperature will be higher than other portions. do.

However, on the surface of the element 11 in this voltage concentrated area, a resistor 14 whose resistance value is lower than that of this area is provided over the entire area, so the voltage applied to this area is applied to the resistor 14.
The resistance value of element 1 flows through this part.
The current No. 1 mainly flows through the resistor 14 and generates a certain amount of heat, and no acceleration phenomenon of voltage concentration occurs in the element 11, so that the element 11 does not generate heat locally and can become scorching.

It is not possible to predict in which part of the element 11 the high resistance part will occur, but as mentioned above, the resistance will occur over the entire or almost the entire surface of the element 11, or over the entire length or almost the entire length between the electrodes 12 and 13. By providing the voltage body 14, voltage concentration can be effectively suppressed no matter where it occurs.

Further, even when a plurality of new high-resistance portions are generated, similarly good results can be obtained.

Needless to say, at least the resistor 14 needs to be substantially conductively connected to the element 11.

Note that the drawings and the above-mentioned embodiments merely show one specific example of the present invention, and the present invention is not limited thereto.

In particular, the shapes of the element 11 and the electrodes 12, 13 are arbitrary; for example, using a disk element and providing electrodes at opposing positions on the circumferential surface of this element is simply a matter of design.

Further, the resistor 14 may be applied to both planes of the element 11, and both ends thereof may be directly connected to both electrodes 12.13. Furthermore, the resistor 14 may be applied by any method such as coating or pasting. It's okay.

In this case, if the resistor 14 and the element 11 are directly electrically connected, it is not necessary to connect the electrodes 12, 13 of the element 11 and the resistor 14.

Further, the shape of the resistor 14 is not limited to the one provided on the entire surface of the element 11, but may be in the shape of a band as shown in FIGS. 15 and 16.

In short, in the present invention, since it is difficult to anticipate in advance the high-resistance portion that will occur in the element 14, no matter where the high-resistance portion occurs on the surface of the element, it is possible to prevent voltage concentration from occurring at that portion. It is only necessary to provide the resistor in a similar shape, and there is no need for the resistor to be shaped like the above-mentioned shapes on each side.

Furthermore, in the present invention, in order to improve the heat dissipation of the element 11, the outer surface of the resistor 14 provided on the surface is roughened to increase its heat dissipation area, thereby increasing the amount of heat generated by the element 11. It's easy.

In other words, the current that flows through the element flows perpendicularly to its thickness, so if there is more heat dissipated from the surface, a commensurate amount of current will flow to the area near the surface of the element 11, and the amount of heat generated will increase accordingly, but the surface will become relatively rough. In the present invention, which only requires roughening the surface of the resistor 14, this effect is surprisingly large.

As described above, the present invention provides a resistor on one plane of the element, and the resistance value of this resistor is higher than the average resistance value at the stable point of operation when the entire element generates heat, and the voltage concentration of the element is The resistance value is set lower than the resistance value per unit length of the part, and voltage concentration in the high resistance part of the element is well suppressed, so the element does not generate heat locally and the temperature is equalized. This has the effect of expanding its usage.

In addition, in this invention, local heat generation is prevented, so
This has the effect of solving problems such as cracking of the element due to heat cycling.

Furthermore, in the present invention, by providing the resistor, it is possible to generate a certain amount of heat all the time, so that the overall amount of heat generated can be further increased.

In addition, in this invention, since the resistor can be applied in advance, it has the effect of improving productivity, and is a device that has many practical effects.

[Brief explanation of drawings]

Figure 1 is a perspective view of a positive temperature coefficient thermistor element, which is the background of the present invention, Figure 2 is its resistance temperature characteristic diagram, and Figure 3 is the same as Figure 1.
Figure 4 is a perspective view of another positive temperature coefficient thermistor element that forms the background of the present invention, Figures 5 and 6 are voltage distribution diagrams in the X direction in Figure 4, and Figure 7 is a diagram of the voltage distribution in the X direction. Similarly, the temperature distribution diagram, Figure 8 is a perspective view of yet another positive temperature coefficient thermistor element which is the background of the present invention, Figure 9 is the resistance value distribution diagram in the X direction of Figure 8, and Figure 10 is the same voltage distribution diagram. , FIG. 11 is the temperature distribution diagram, FIG. 12 is a perspective view of the device in FIG. 8 when its operation is stable,
Fig. 13 is a side view showing a conventional PTC thermistor for a heating element, Fig. 14 is a side view showing an example of the shape of the PTC thermistor for a heating element of the present invention, and Figs. 15 and 16 are It is a perspective view showing other examples. 11-positive temperature coefficient thermistor element, 12, 13-electrode, 14
resistor.

Claims (1)

[Scope of utility model registration request] A resistor is provided on at least one plane of a positive temperature coefficient thermistor element having electrodes provided on opposing sides thereof, and a resistor is provided along almost the entire length between the two electrodes, and the resistance value of this resistor is determined when the entire element generates heat. The voltage is set higher than the average resistance value at the stable operating point of the element and lower than the resistance value per unit length of the voltage concentrated part that occurs in the current flow direction of the element, and the voltage concentration in the current flow direction of the element is set. 1. A positive temperature coefficient thermistor for a heating element, characterized in that, when a portion occurs, voltage concentration at that portion is suppressed by the resistor.