JPS6146746B2 - - Google Patents

Description

Detailed Description of the Invention The present invention is used in refrigerators, air conditioners, etc., which are equipped with a refrigeration system consisting of a compressor, a condenser, a capillary tube, and an evaporator (hereinafter referred to as a cooler). This invention relates to a defrosting device that removes frost that has formed.

Generally, cooling of refrigerators, air conditioners, etc.
Warm air is brought in, cooled by passing through a cooler, and then discharged into the refrigerator or indoors. For this reason, the moisture contained in the warm air causes frost to form on the cooler. When frost adheres to the cooler, the heat exchange efficiency of the cooler decreases and the cooling capacity decreases. Therefore, in refrigerators, as shown in FIG. 1, a defrosting heater 2 is conventionally provided in a heat exchange fin 3 attached to a refrigerant pipe 1a of a cooler 1, and a , the operation of the cooling device of the refrigerator is stopped, the defrosting heater 2 is energized, and the defrosting heater 2 is heated to perform defrosting, thereby preventing the cooling capacity from decreasing. In the case of an air conditioner, when frost forms, the operation of the air conditioner is stopped for a certain period of time, and the frost is defrosted by melting the frost with heat from the outside air.

As the defrost heater 2 of the refrigerator, nichrome wire,
A heater is used in which a metal heater wire such as nickel or copper wire is housed in a protective tube such as an aluminum pipe.
This conventional defrosting heater 2 is a heater that does not have a self-temperature control function, and has the characteristic of maintaining a constant amount of heat regardless of the amount of frost attached to the cooler and the frost distribution state. The time point at which defrosting is completed for each part of 1 is different. In other words, defrosting is delayed in areas where a large amount of frost has adhered. Therefore, conventionally, in order to detect when defrosting has been completed, a temperature detection device such as a thermistor is installed at the part of the cooler 1 where defrosting is completed the latest, and the temperature is detected while defrosting is performed. Defrosting is considered to have been completed when this is reached. Furthermore, in consideration of cases where the amount of frost increases due to seasonal changes, or cases where the distribution of frost changes due to differences in the arrangement of stored items, sufficient defrosting is performed in both cases. It was necessary to set defrosting conditions such as temperature and time to ensure that defrosting was carried out. For this reason, the temperature of the portion of the cooler 1 where the amount of frost is small and defrosting is completed quickly becomes unnecessarily high as the energization time increases. That is, at the time when the heater 2 is no longer energized, the temperature of each part during cooling 1 has a large temperature difference as shown in FIG. In FIG. 2, curves 4, 5, and 6 indicate the temperature distribution of the defrosting heater 2, refrigerant pipe 1a, and heat exchange fin 3 at the upper, middle, and lower positions of the cooler 1, respectively. If the temperature of the cooler 1 becomes unnecessarily high as shown in curves 4, 5, and 6 in Fig. 2, when the cooling operation is restarted after defrosting is completed, the temperature of the cooler 1 will be lowered. This method has the drawbacks that it takes a long time and consumes a lot of power. Furthermore, there is a drawback that the electric power required to heat the defrosting heater 2 is unnecessarily large. Another disadvantage is that the temperature of foods stored in the refrigerator tends to rise.

As a solution to the above drawback, a part of the defrosting heater is made of a positive temperature coefficient thermistor having a large positive temperature coefficient of resistance, and when the current of the heater decreases to a predetermined constant value, the heater is turned off. A frost control device is disclosed in Japanese Patent Application Laid-Open No. 54-101533. However, the resistance of the heater provided near the cooler section changes over a long period of operation because the heater is subjected to severe cooling and heating cycles such as frost, ice, water, heating, and cooling. Therefore, if the resistance value of the heater increases due to long-term operation, in the heater control method, heat generation of the heater ends with incomplete defrosting. Furthermore, if the resistance value decreases, the heater will continue to generate heat even after defrosting is completely completed. That is, even in the defrosting control device disclosed in Japanese Patent Application Laid-Open No. 54-101522, it is necessary to provide a margin for increasing the defrosting time at a certain threshold value for controlling the heater off.
The same problem as when a metal heater wire was used as a defrosting heater occurred, although to a lesser extent.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a defrosting device that can defrost efficiently.

In the present invention, in order to achieve the above-mentioned object,
Using a defrosting heater that has a positive temperature coefficient of resistance and a characteristic that changes suddenly at a certain temperature, the defrosting heater automatically defrosts the temperature by utilizing the characteristic change during heating operation of the defrosting heater itself. It ends the frost.

First, the heater used in the present invention will be explained. FIG. 3 shows a cutaway perspective view of this heater. In FIG. 3, 7 and 7' are electrical conductors for power supply such as tinned copper wire, 8 is a heater section made of a mixture of an organic material such as high-density polyethylene and a conductive material such as carbon, and 9 is a For example, the insulating coating part 10 is made of urethane rubber or the like, and the reference numeral 10 is a flame-retardant coating part made of polyethylene or the like. Next, the operation of this heater 2' will be explained. When a rated voltage is applied between the power supply electric conductors 7 and 7' of the heater 2', a current flows through the heater section 8, which is made of a kneaded mixture of an organic material and a conductive material such as carbon, and the heater section 8 generates heat due to Joule heat. The organic material thermally expands due to the temperature rise due to this heat generation, and the specific resistance value of the heater section 8 increases accordingly, and as it approaches the softening temperature determined by the organic material used, the resistance value increases rapidly. FIG. 4 shows changes in the resistance value of the heater section 8, with temperature plotted on the horizontal axis. Fourth
In the figure, a curve 11 shows the resistance value change characteristic of the heater section 8, and a curve 12 shows the temperature at which the temperature coefficient of the resistance value suddenly changes (operating sudden change temperature). The specific resistance value of the heater section 8 rapidly increases as the temperature rises, so the current decreases, and the temperature rise stops and stabilizes at a constant temperature determined by the organic material.

Next, the operation of the defrosting heater 2' described above during defrosting will be explained. FIG. 5 shows temporal changes in the current flowing through the defrosting heater 2' and changes in the temperature of the cooler. In FIG. 5, the horizontal axis shows the time from the start of energization to the defrosting heater 2', and the vertical axis shows the current flowing through the defrosting heater 2' and the temperature of the cooler.
Curve 13 shows the heater current, and curve 14 shows the cooler temperature. Immediately after the defrosting heater 2' is energized, an inrush current flows and the temperature rapidly rises, and accordingly, the heater current 13 begins to decrease, the temperature of each part of the cooler rises, and defrosting is started. When defrosting of each part of the cooler starts, the temperature of each part of the cooler changes from -0℃ to ++ due to the heat of melting of the frost at point A in Figure 5.
At 0° C., the rate of change of the heater current 13 also changes from decreasing to increasing. After point A, the temperature of the defrosting heater 2' gradually increases to further advance defrosting, and at the same time, the rate of change of the heater current 13 increases,
Defrosting ends at point B in FIG. Although the time during which the heater 2' is energized varies, the heater current at point A in FIG. 5 and the heater current at the end of defrosting are at a constant ratio. Defrosting detection in the defrosting device according to the present invention is performed using this newly discovered phenomenon.

Next, embodiments according to the present invention will be described. A block diagram of the defrosting device is shown in FIG. In the figure, 15
16 is a switch for supplying power to the defrost heater 15; 17 is a current detection circuit for detecting the current flowing to the defrost heater 15; 18 is a memory for storing the output of the current detection circuit 17 at a predetermined time. The memory circuit 19 is the output of the current detection circuit 17,
A comparison calculation circuit 20 compares and calculates the outputs of the storage circuit 18, and a defrost termination circuit 20 terminates power supply to the defrost heater 15 based on the result of the comparison calculation circuit 19.
1 is a power source. In this device, in order to start defrosting, the power supply switch 16 is closed by defrosting start detection means (not shown) such as a timer. When the power supply switch 16 is closed,
A current flows from the power supply 21 to the heater 15, the heater 15 generates heat, and defrosting begins. The current value of the current flowing through the heater 15 is detected by a current detection circuit 17. The output of the current detection circuit 17 is supplied to a memory circuit 18 and a comparison calculation circuit 19, and the memory circuit 18 detects the time when a predetermined time has elapsed since power supply to the heater 15 was started and defrosting was started. The current value of the current at the time (time around point A in FIG. 5) is stored as a reference current value, and the value is supplied to the comparison calculation circuit 19. Current detection circuit 17
The comparison circuit 19, which is supplied with the output of the memory circuit 18, compares and calculates the current value flowing through the heater 15 and the reference current value, and when the ratio of the two reaches a predetermined value, sends a signal to the defrosting termination circuit 20. The defrost end circuit 20 outputs a defrost end signal and outputs a defrost end signal to the power supply switch 16.
is cut off, power supply to the heater 15 is stopped, and defrosting is completed. Here, the time for the memory circuit 18 to memorize the current must be the time it takes to reach point A in FIG. 5, but in reality, the time to reach point A changes depending on the amount of frost formation. Therefore, it is not possible to set a constant memorization time. However, since the rate of change in current near point A is small, if a predetermined time is set as point A at the average amount of frost formation, it will hardly matter even if the amount of frost formation occurs, and the current at point A will change. Can be memorized.

As described above, according to the defrosting device according to the present invention, defrosting completion can be appropriately detected by the heater 2' itself, without separately providing another defrosting completion detection element. FIG. 7 shows the temperature distribution in each part of the cooler 1 when defrosting is completed when a heater 2' having a self-temperature control function is installed in the cooler 1 of the refrigerator shown in FIG. In Figure 7, curve 2
2 is the temperature of the heater 2' having a self-temperature control function, curve 23 is the temperature of the refrigerant pipe 1, and curve 24 is the surface temperature of the heat exchange fin 3.The temperature distribution of each part of the cooler 1 is shown in FIG. Compared to the results obtained using the conventional defrosting device shown in Figure 2, it can be seen that the temperature is uniform and there are no areas that become unnecessarily high in temperature.

As described above, according to the present invention, a heater having at least a positive temperature coefficient of resistance value and a characteristic that the temperature coefficient of resistance value changes suddenly at a certain temperature is used, and changes in the current flowing through the heater are utilized. It is possible to detect the end of defrosting and prevent unnecessary temperature rise of the cooler at the end of defrosting. As a result, the power consumed by the defrosting heater of the refrigerator is reduced, and furthermore, the power consumption during recooling is greatly reduced. Further, in the present invention, the current value of the heater current at the end of defrosting is determined based on the current value of the current during defrosting of the heater, and the heater power source is cut off. Therefore, it is possible to automatically determine the current at the end of defrosting by using changes in the resistance value of the heater, so it is possible to automatically determine the current at the end of defrosting. It also has the great effect of being able to deal with changes over time.

[Brief explanation of the drawing]

Figure 1 is a front view showing the structure of a cooler in a refrigerator, Figure 2 is a characteristic diagram showing the temperature distribution of each part of the cooler at the end of defrosting when a conventional defrosting heater is used, and Figure 3 is a A partially cutaway perspective view of a defrosting heater used in a defrosting device according to an embodiment of the present invention, FIG. 4 is a characteristic diagram of the defrosting heater, and FIG. FIG. 6 is a block diagram showing the configuration of the defrosting device according to the present invention; FIG. 7 is a characteristic diagram showing the temperature distribution of each part of the cooler according to the present invention. . 15... Defrost heater, 16... Power supply switch, 17... Current detection circuit, 18... Memory circuit,
19... Comparison calculation circuit, 20... Defrosting end circuit.

Claims (1)

[Claims] 1 A defrosting device for removing frost adhering to a cooler such as a refrigerator or an air conditioner, which is at least installed on the cooler and has a positive temperature coefficient of resistance value, and A heater having a characteristic that changes suddenly at a certain temperature, a defrosting start means for supplying power to the heater to start defrosting, a current detecting means for detecting the current value of a current flowing through the heater, storage means for storing the current value of the current flowing through the heater detected by the current detection means as a reference current value after a predetermined time has elapsed; The current value of the current flowing through the heater detected by the current detection means and the reference current value stored in the storage means are compared and calculated, and the ratio of the current value flowing through the heater and the reference current value is a predetermined value. and a defrost termination means that stops power supply to the heater when the defrost termination signal is supplied from the comparison calculation means. Defrost equipment.