JPS624628B2 - - 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 conditioning equipment coolers are affected by water vapor generated from the items stored in the refrigerator, damp air that enters the refrigerator when the door is opened, or air from outside and indoors. Frost formation occurs due to the temperature difference between the 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.
The defrosting heater 2 is attached to the heat exchange fan 3 attached to the
is installed, and every time the refrigerator is operated for a certain period of time, the operation of the refrigerator's cooling device 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. is prevented. 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 using the heat of the outside air.
Defrosting is being carried out. As the defrosting heater 2 of a refrigerator, a heater in which a metal heater wire such as a nichrome wire, a nickel wire, or a copper wire is housed in a protective tube such as an aluminum pipe is conventionally used.

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 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,
Defrosting conditions such as temperature and time had to be set to ensure sufficient defrosting in all cases. 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, heater 2
As shown in FIG. 2, there is a large temperature difference in the temperature of each part of the cooler 1 at the time when the power supply to the cooler 1 is finished. In FIG. 2, curves 4, 5, and 6 indicate the temperature distribution of the defrosting heater 2, the cooling pipe 1a, and the heat exchange fin 3 at the upper, middle, and lower positions of the cooler 1, respectively. Curve 4 in Figure 2,
As shown in 5 and 6, if the temperature of the cooler 1 becomes unnecessarily high, it will take longer to lower the temperature of the cooler 1 when the cooling operation is resumed after defrosting has been completed, resulting in lower consumption. It had the disadvantage of requiring a large amount 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 means to solve the above-mentioned drawbacks, the defrosting heater or a part of the defrosting heater is configured with a positive temperature coefficient thermistor having a large positive resistance temperature coefficient, and when the current flowing through 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 value of the heater increases due to long-term operation, in the heater control device described above, the 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. In other words, even in the defrosting control device disclosed in JP-A No. 54-10533, it is necessary to provide a certain threshold for heater-off control with a margin to lengthen the defrosting time. The same problem as when a 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 order to achieve the above object, the present invention uses a heater whose resistance value has a positive temperature coefficient and whose resistance value suddenly changes at a certain temperature as a defrosting heater,
Defrosting is automatically terminated by utilizing changes in the characteristics of the defrosting heater itself during heating operation.

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', the heater part 8 made of a mixture of organic material and carbon is activated.
A current flows through the heater section 8, 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 the resistance value increases rapidly as the softening temperature determined by the organic material used is approached. 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 at which the temperature coefficient of resistance suddenly changes (operating sudden change temperature). 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 energizing 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, the temperature of each part of the cooler changes from -0℃ to +0℃ due to the heat of melting of the frost, starting from point A in Figure 5, and at the same time The rate of change in heater current 13 changes from decreasing to increasing. After point A, the temperature of the defrosting heater 2' gradually rises to further advance defrosting, and at the same time, the rate of change of the heater current 13 increases, and the temperature of the defrosting heater 2' reaches the level shown in FIG. When the temperature reaches point B, defrosting is completely completed.

The time that the heater 2' is energized varies depending on the amount of frost, but the decrease in heater current from point A to point B in Figure 5 is due to the relationship between the degree of frost melting and the heat capacity of the heater. It is determined by a time constant, which shows a nearly constant trend.

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

Next, a block diagram of the defrosting device according to the present invention and characteristic diagrams showing output signals converted into voltages at various parts are shown in FIGS. 6 and 7.

In FIG. 6, 15 is a defrost heater, 16 is a switch for power supply to the defrost heater 15, and 17 is a current detection circuit 18 for detecting the current flowing through the defrost heater 15, which is a predetermined function that changes over time. A signal generator that generates a decreasing signal; 19 a timer circuit that controls the start time of the signal output of the signal generator 18; 20 that subtracts the outputs of the current detection circuit 17 and the signal generator 18, and the result is predetermined. a comparator circuit that outputs a signal when the specified value is reached; 21;
22 is a control circuit which opens the power supply switch 16 to the defrosting heater 15 based on the output of the comparator circuit 20; and 22 is a power supply. In this device, when the power supply switch 16 is closed, current flows from the power supply 22 to the defrost heater 15 via the power supply switch 16, and the defrost heater 15 generates heat. And defrost heater 15
The current flowing through is supplied to the current detection circuit 17.
The current detection circuit 17 converts the current value into a voltage value as shown by the curve υ ₁ in FIG. 7 using a current transformer or the like,
The signal is supplied to the comparator circuit 20 and the signal generator 18. The signal generator 18, like the curve ν ₂ shown in FIG.
The timer circuit 19 generates a signal whose initial value is the output of the current detection circuit 17 at a predetermined time to, starting from time to. Further, the output of the signal generator 18 described above upon completion of defrosting is smaller than the output of the current detection circuit 17. next,
A comparator circuit 20 to which the outputs of the current detection circuit 17 and the signal generator 18 are supplied subtracts the value of the curve υ ₂ from the value of the curve υ ₁ as shown in the curve υ ₃ shown in FIG. After the maximum value of subtraction has passed the maximum value, the stored maximum value is compared with the subtraction result obtained by subtraction, and the subtraction result and the memorized maximum value of subtraction are When a certain predetermined ratio is reached, a defrosting completion signal is generated and supplied to the control circuit 21. At that point, the control circuit 21, which has been supplied with the defrosting completion signal from the comparison circuit 20,
Open the power supply switch 16. When the power supply switch 16 is opened, the current supplied to the defrosting heater 15 is cut off and defrosting ends. Here, the curve υ ₂ in FIG. 7 in the above-mentioned embodiment uses the discharge characteristics of the charger when the signal generator 18 is a charger composed of a capacitor and a resistor. The initial value of the signal 18 is the output of the current detection circuit at a time predetermined by the timer circuit 19, and the final value of the signal is less than or equal to the output of the current detection circuit at the time of completion of defrosting. It is sufficient if the signal includes a straight line connecting the value and the closing price and is convex downward with respect to the straight line.

Furthermore, the comparator circuit 21 in the above embodiment is such that the subtracted value between the signal responsive to the heater current obtained by the current detection circuit 17 and the signal from the signal generator 18 is a predetermined ratio with respect to the maximum value of the subtracted value. A heater control signal is issued at this point, but the relationship between the subtracted value and the maximum value is determined by the signal of the signal generator 18, the characteristics of the defrosting heater 15, the shape of the cooler to be defrosted, etc. It should be noted that in some cases, the same effect can be obtained even if defrosting is completed when the subtracted value has decreased by a certain level with respect to the maximum value, rather than the ratio of the subtracted values.

In the above embodiment, the operation was explained using the heater current, but it goes without saying that the same effect can be obtained even if the defrosting completion detection operation is performed using the electric power supplied to the heater.

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. 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. 8, a curve 23 indicates the temperature of the heater 2' having a self-temperature control function, and a curve 24 indicates the temperature of the refrigerant pipe 1.
2, the curve 25 is the surface temperature of the heat exchange fin 3, and the temperature distribution of the cooler 1 is made more uniform and unnecessary compared to the result of the conventional defrosting device shown in FIG. It can be seen that there are no parts that reach high temperatures.

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, defrosting completion is detected using a change in the current flowing through the heater, using a heater having a temperature at which the temperature coefficient of the resistance is positive and the temperature coefficient of the resistance changes suddenly. This makes it possible to prevent unnecessary temperature rises 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.

In addition, the present invention does not use the absolute value of the heater current, but effectively utilizes its changing state to detect the completion of defrosting, so there is no problem even if there is a change in the fluctuation characteristics of the defrost heater resistance value. . Therefore, it is possible to provide a margin for variations in the defrosting heater resistance, thereby reducing costs, simplifying circuit adjustment for each defrosting device, and improving productivity. Further, even if the resistance of the defrosting heater changes over time due to long-term operation, no problem occurs as described above, and the defrosting heater is excellent in terms of reliability.

[Brief explanation of the drawing]

Fig. 1 is a front view showing the structure of a cooler in a refrigerator, Fig. 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 Fig. 3 The figure is 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. Characteristic diagram showing changes in temperature and current flowing through the defrosting heater in the defrosting device,
Fig. 6 is a block diagram showing the configuration of the defrosting device according to the present invention, Fig. 7 is an example of operating characteristics showing the output voltage of each part in Fig. 6, and Fig. 8 is a temperature diagram of each part of the cooler in the present invention. It is a characteristic diagram showing distribution. 15... Heater, 17... Current detection circuit, 18
...Timer circuit, 19...Signal generator, 20...
Comparison circuit, 21...control circuit.

Claims (1)

[Claims] 1. At least a heater that has a positive temperature coefficient of resistance and a characteristic that the temperature coefficient of resistance changes suddenly at a certain temperature, a current detection circuit that detects the value of the current flowing through this heater, and a current detection circuit that detects the value of the current flowing through the heater. A signal generator that generates a signal whose initial value is the output signal of the current detection circuit after a predetermined period of time has elapsed after the output signal is supplied and current begins to be supplied to the heater, and whose value decreases over time. and subtracting the signal of the signal generator and the output signal of the current detection circuit to generate a subtracted value, and
The maximum value of the subtraction value is memorized, and after the subtraction value reaches the maximum point, the memorized maximum value is compared with the above subtraction value, and output when the two reach a predetermined ratio or difference. a comparison circuit that generates a signal;
A defrosting device comprising: a control circuit that is connected to a comparison circuit and cuts off current to a heater based on an output signal of the comparison circuit.