JPS6140905B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a defrosting method for removing frost attached to a cooler such as a refrigerator or an air conditioner that is equipped with a refrigeration system consisting of a compressor, a condenser, and an evaporator (hereinafter referred to as a cooler). It is related to the device.

In general, refrigerator coolers or air conditioner coolers are operated by water vapor generated from the items stored in the refrigerator, damp air that enters the refrigerator when the door is opened or closed, or by the interaction between outside air and indoor air. Frost formation occurs due to the temperature difference. When frost adheres to the cooler, the heat exchange efficiency of the cooler decreases and the cooling capacity decreases. For this reason, conventionally in refrigerators, as shown in Fig. 1, a defrosting heater 2 is provided on a heat exchange fin 3 attached to a refrigerant pipe 1a of a cooler 1, and a Stop the operation of the cooling device, energize the defrosting heater 2,
Defrosting is performed by heating the defrosting heater 2 to prevent the cooling capacity from decreasing. In the case of air conditioning equipment, when frost forms, the operation of the air conditioning equipment is stopped for a certain period of time, and the frost is melted and defrosted using the heat of the outside air. As the defrost heater 2 of the refrigerator,
Conventionally, heaters have been used in which metal heater wires such as nichrome wires, nickel/copper wires, etc. are housed in protective tubes such as aluminum pipes.

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 differs for each part. In other words, defrosting is delayed in areas where a large amount of frost has adhered. Therefore, conventionally, in order to detect when defrosting is completed, a temperature detection device such as a thermistor is installed at the part of the cooler 1 where defrosting is completed latest, and the temperature is detected while defrosting.
Defrosting is considered complete when a certain temperature is reached. Furthermore, in consideration of cases where the amount of frost increases due to seasonal changes, or when the distribution of frost changes due to differences in the arrangement of stored items,
In either case, defrosting conditions such as temperature and time had to be set to ensure sufficient defrosting. For this reason, the temperature of the portions of the cooler 1 where the amount of frost is small and defrosting is completed quickly increases unnecessarily as the energization time increases. That is, at the time when the heater 2 is no longer energized, there is a large difference in temperature between the various parts of the cooler 1, 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. As shown in curves 4, 5, and 6 in Figure 2, if the temperature of cooler 1 becomes unnecessarily high, it takes time to lower the temperature of cooler 1 when restarting cooling operation after completing defrosting. The defrosting heater 2 has the drawback that the length of the defrosting heater 2 is long and the power consumption is large.Furthermore, the 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-mentioned drawbacks, a positive characteristic thermistor having a positive temperature coefficient of resistance is used as the defrosting heater or a part of the defrosting heater, and when the current of the heater decreases to a predetermined constant value, A defrosting control device that cuts off the current flowing to a defrosting heater is disclosed in Japanese Patent Application Laid-open No. 101533/1983. However, the resistance value of the heater provided near the cooler section changes over a long period of operation because the heater is subjected to severe cooling/heating cycles such as frost, ice, water, and heating. Therefore, when the resistance of the heater increases due to long-term operation, in the heater control device, heat generation of the heater ends with incomplete defrosting. Furthermore, if the resistance decreases, the heater will continue to generate heat even after defrosting is completely completed. In other words, even in the defrosting control device described above, it is necessary to provide a certain threshold value for controlling the heater off with a margin to lengthen the defrosting time. Similar shortcomings occurred.

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 order to achieve the above-mentioned object, the present invention uses a defrost heater whose resistance value has a positive temperature coefficient and whose temperature coefficient changes suddenly at a certain temperature. This is to automatically end defrosting by utilizing the change.

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, for example, An insulating covering part such as urethane rubber, and 10 a flame retardant covering part such as polyethylene. 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 made of a mixture of organic material and carbon, and the heater section 8 generates heat due to Joule heat. Due to the temperature rise due to this heat generation, the organic material thermally expands, and the specific resistance of the heater section 8 increases accordingly, and the resistance value increases rapidly as it approaches the softening temperature determined by the organic material used. FIG. 4 shows changes in the resistance value of the heater section 8, with the resistance value plotted on the vertical axis and the temperature plotted on the horizontal axis. In FIG. 4, a curve 11 shows the resistance change characteristic of the heater section 8, and a curve 12 shows the temperature (operation setting temperature) at which the temperature coefficient of the resistance value suddenly changes. Since the specific resistance value of the heater section 8 rapidly increases as the temperature rises, the current decreases, and the temperature rise stops and stabilizes at a constant temperature determined by the organic material.

Next, a defrosting device using the defrosting heater 2' described above will be described. 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 since the start of electricity supply to the defrosting heater 2', the vertical axis shows the current flowing through the defrosting heater 2' and the temperature of the cooler, and the curve 13 shows the heater current,
Curve 14 shows the temperature of the cooler. Immediately after the defrosting heater 2' is energized, an inrush current flows and the temperature 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, A in Fig. 5
At this point, the temperature of each part of the cooler changes from -0°C to +0°C due to the heat of melting the frost, and at the same time the rate of change of the heater current 13 changes from decreasing to increasing. After point A, the temperature of the defrosting heater 2' gradually increases to further defrost, and at the same time the heater current 1
The rate of change of 3 increases, and defrosting is completely completed at point B in FIG. 5, when the defrosting heater 2' reaches an arbitrary temperature. If the defrosting heater 2' is operated continuously after this point, all the frost adhering to the cooler will have melted, so the temperature of the defrosting heater 2' will rise until all parts reach thermal equilibrium. Therefore, the current change rate of the defrosting heater 2' after the point B in FIG. 5, that is, after the completion of defrosting, shows a decreasing tendency. As described in detail above, the defrosting completion point has a characteristic in which the current change rate of the defrosting heater 2' changes from an increasing tendency to a decreasing tendency.

Defrosting completion detection in the defrosting device according to the present invention is performed using this phenomenon.

Next, an embodiment of the defrosting device according to the present invention will be described with reference to FIG. In the figure, 15 is a defrosting heater;
16 is a switch for supplying power to the defrosting heater 15; 17;
18 is a current detection circuit for detecting the current flowing through the defrosting heater 15; 18 is an arithmetic processing circuit equipped with instructions for processing a signal responsive to the heater current generated by the current detection circuit 17; and 19 is an arithmetic processing circuit. 1
8 is a control circuit for cutting off the current flowing through the defrosting heater 15 in accordance with the generated signal; 20 is a power supply; In this device, when the power supply switch 16 is closed, current flows from the power supply 20 to the defrosting heater 15 via the power supply switch 16. Defrost heater 1
When current flows through the defrosting heater 15, the defrosting heater 15 generates heat.
The current flowing through the defrosting heater 15 is then supplied to the current detection circuit 17. The current detection circuit 17 detects the current flowing through the defrosting heater 15 using a minute time ΔT as a unit time, and supplies a signal responsive to this current to the arithmetic processing circuit 18. Suppose that the signal is I _T at time T, and time T+ ΔT has elapsed after time T.
I _T+ 〓 _T at ΔT, and I _T+2 〓 _T at time T+2ΔT after ΔT has elapsed. The arithmetic processing circuit 18 that receives this signal stores the signal and calculates the difference between the signal I _T and the signal I _T+ 〓 _T (I _T −I _T
+ 〓 _T ) or decreasing slope (IT − I _{T +} 〓 _T )/ΔT
Similarly, with the following signal, (I _T+ 〓 _T −
I _T+2 〓 _T ) or decreasing slope (I _T+ 〓 _T −I _T+2 〓
Find _T )/ΔT. Next, the difference between these two calculation results is determined. For example, the signal difference is ( _IT − I _T+
〓T )−(IT _{+ 〓T} − _{IT+2〓T )} is obtained. Assuming that this value is I'', I'' indicates the tendency of increase/decrease in the current flowing through the defrosting heater 15, and the point where this value I'' changes from negative to positive is point B in FIG. 5, that is,
This indicates the point at which the current rate of change changes from an increasing trend to a decreasing trend. Next, the arithmetic processing circuit 18 issues a signal to the control circuit 19 as soon as this signal I'' changes from negative to positive.The control circuit 19 receives this signal and opens the power supply switch 16. When it is opened, the current supplied to the defrosting heater 15 is cut off and defrosting ends.The current flowing through the defrosting heater 15 is C in FIG.
The rate of change of the current changes from an increasing trend to a decreasing trend near the point, but the current circuit 17 detects the current after a predetermined time has elapsed after the power supply switch 16 is closed, or If the arithmetic processing circuit 18 is configured to perform arithmetic operations, the power supply switch 16 will not be opened near point C. In the above-mentioned embodiment, the operation was explained using the heater current, but the same effect could be obtained even if the operation was performed using the electric power supplied to the heater.

As described above, according to the defrosting device according to the present invention, it is possible to appropriately detect the completion of defrosting using the heater 2' itself, without separately providing another defrosting completion detection element. When a heater 2' with a self-temperature control function with an operating temperature setting of 65°C is installed in the cooler 1 of the refrigerator shown in Figure 1, the temperature distribution in each part of the cooler 1 when defrosting is completed is shown. It is shown in FIG. In FIG. 7, a curve 21 is the temperature of the heater 2' having a self-temperature control function, a curve 22 is the temperature of the refrigerant pipe 1a, a curve 23 is the surface temperature of the heat exchange fin 3, and the temperature of each part of the cooler 1. It can be seen that the distribution is more uniform compared to the results obtained by the conventional defrosting device shown in FIG. 2, and there are no areas that become unnecessarily high temperature.

Although an organic heater was used as an example of the present invention, it goes without saying that similar effects can be obtained using an inorganic positive temperature coefficient thermistor such as barium titanate.

As described above, according to the present invention, a heater is used which has a positive temperature coefficient of resistance value and a characteristic that the temperature coefficient of resistance value changes suddenly at a certain temperature, and the temperature coefficient of the resistance value is removed by using a change in the current flowing through the heater. It is possible to detect the completion of frosting, and prevent unnecessary temperature increases in the cooler when defrosting is completed. As a result, the power consumed by the defrosting heater is reduced, and the power consumption during recooling is also greatly reduced.

Further, in the present invention, since the completion of defrosting is detected based on the turning point at which the rate of change of the heater current changes from an increasing tendency to a decreasing tendency, there is no problem even if the resistance value of the defrosting heater changes at a certain temperature. Therefore, it is possible to provide a margin for variations in defrosting heater resistance.
Costs can be reduced, circuit adjustment for each individual defrosting device can be simplified, and productivity can be improved. Furthermore, even if the resistance value changes over time due to long-term operation in harsh conditions such as frost, ice, water, and heating, no problems occur and the device is also excellent in reliability.

[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 when defrosting is completed when a conventional defrosting heater is used, and Figure 3 is a A partially cut away perspective view of a defrosting heater used in an embodiment of the defrosting device according to the present invention, FIG. 4 is a characteristic diagram of the defrosting heater,
FIG. 5 is a characteristic diagram showing changes in temperature and current flowing through the defrosting heater in the defrosting device of the present invention, and 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 in the present invention. 15... Heater, 17... Current detection circuit, 18
... Arithmetic processing circuit, 19 ... Control circuit.

Claims (1)

[Claims] 1. A heater having a characteristic that the temperature coefficient of the low resistance value is positive and the temperature coefficient of the resistance value suddenly changes at a certain temperature, and a means for detecting the turning point at which the current change rate of the heater changes from an increasing tendency to a decreasing tendency. and a control means for cutting off power to the heater at the conversion point.