JPS5816173A - Defroster - 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 The present invention relates to a defrosting device for removing frost attached to cooler traps of refrigerators, air conditioners, refrigeration showcases, etc., which are equipped with a refrigeration system consisting of a compressor, a condenser capillary tube, and an evaporator. It is something.

In general, the evaporator of a refrigerator (hereinafter referred to as a cooler) or the cooler of an air conditioner, etc., is operated by water vapor generated from the items stored in the refrigerator or damp air that enters the refrigerator when the door is opened or closed. , or frost formation occurs due to the temperature difference between outside air and indoor air. When frost adheres to the cooler, the heat exchange efficiency of the cooler decreases and the cooling capacity decreases.

Therefore, in refrigerators, a defrosting device that performs heating and defrosting is provided to prevent the cooling capacity from decreasing. That is, as shown in FIG.

A waste removal heater 2 is provided on the heat exchange fin 3 attached to the refrigerant pipe 1α of the cooler 1, and each time the refrigerator operates for a certain period of time, the operation of the refrigerator cooling device is stopped and the defrosting heater 2 is energized. Then, defrosting is performed by heating the defrosting heater 2. As the defrosting heater 2 of a refrigerator, a heater in which a metal heater wire such as a nichrome wire or a nickel/copper wire is housed in a protective tube such as an aluminum pipe has conventionally been used.

This conventional removal 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. Conventionally, in order to detect that 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 latest, and the temperature is detected while defrosting is being performed.
Defrosting is considered complete when a certain temperature is reached. 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 represent the defrosting heater 2.5, respectively. The temperature distribution of the refrigerant pipe 1α and the heat exchange fins 3 at the upper, middle, and lower positions of the cooler 1 is shown. Cooler 1 as shown in curves 4 and 5 of FIG.
If the temperature of the cooler 1 becomes unnecessarily high, it takes a long time to lower the temperature of the cooler 1 when the cooling operation is resumed after defrosting is completed, resulting in an increase in power consumption. 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,
JP-A-54-101533 discloses a defrosting control device that controls stopping power supply to the heater when the current value of the heater decreases to a predetermined constant value. This JP-A-5
The defrosting completion method according to No. 4-105533 has no problem if the defrosting heater does not deteriorate in characteristics under harsh usage conditions for a long period of time, but in reality, it is difficult to defrost after repeated heating and cooling over a long period of time. The resistance of the frost heater changes, and the defrosting end point gradually changes, causing problems such as excessive defrosting or incomplete defrosting. As a means of solving this problem, the present inventors have proposed that the heater current of the heater having a self-temperature control function at the time when the frost adhering to the cooler 1 is defrosted and thereafter is a constant current regardless of the frost amount 6 and the frosting state. A new defrosting device (Japanese Patent Application No. 55-160788) has been newly discovered that exhibits a decreasing slope, and the defrosting is completed when the heater current reaches a constant current decreasing slope. This defrosting device can maintain stable defrosting performance for a long period of time, and when defrosting is completed, the temperature distribution in each part of the cooler 1 is made uniform, and there are no parts that become unnecessarily high temperature. This is a good defrosting device that has a great effect on reducing power consumption. However, heaters with a self-temperature control function have the characteristic that when power supply starts, a large current called inrush current flows, causing the heater temperature to rise rapidly. I had a problem.

An object of the present invention is to provide a defrosting device that can defrost efficiently with low power consumption.

In order to achieve the above object, the present invention provides a defrosting heater having a positive temperature coefficient of resistance and a temperature at which the temperature coefficient of the resistance suddenly changes; The present invention is characterized by having a control means for starting power supply to the defrosting heater.

First, the basic operating characteristics of the defrosting heater used in the present invention will be explained. FIG. 3 shows the current-voltage characteristics of the defrosting heater during power supply. In FIG. 3, curve 7 shows the characteristics when the ambient temperature is 7', and curve 8 shows the characteristics when the ambient temperature is 11° C. (here, Tt>T+). When a rated voltage (for example, 100 V) is supplied to a defrosting heater having the characteristics of curve 7, the characteristics at the rise of curve 7 are extended, and a current I instantaneously flows at point A1 where it intersects with the rated voltage. ．． Due to the Joule heat generated by Tic, the temperature of the defrosting heater rises rapidly. As the temperature rises, the defrosting heater's specific resistance rises, the current decreases, and when the ambient temperature is I'1°C, it stabilizes at point A2 of curve 7. Next, the ambient temperature rises to T, due to the heat generated by the defrosting heater. As the temperature rises to ℃, the curve 8
Move to the Et point. The defrosting heater used in the present invention is
As shown above, 2 to 3 during stable operation when power is turned on.
This heater has a so-called self-temperature control function, in which a current about twice as large flows through it, and after the temperature rises rapidly, it operates at a constant temperature determined by the material used.

Next, a defrosting device according to the present invention will be explained.

FIG. 4 shows temporal changes in the current flowing through the defrosting heater having a self-temperature control function and changes in the temperature of the cooler 1. In FIG. 4, the horizontal axis shows the time since the compressor stopped and the defrost cycle started, the vertical axis shows the current flowing through the defrosting heater and the temperature of the cooler 1, and curve 9 shows the heater current. , curve 10 shows the temperature of the cooler. When the defrosting heater starts energizing a certain period of time (t,) after the compressor stops, an inrush current flows immediately after the energization, and the temperature rises rapidly.As the heater current 9 begins to decrease, the temperature of the cooler rises. Defrosting begins. When each part of the cooler starts to be removed from the register, the heater current 90 reduction rate decreases due to the heat of melting the frost.
The current value is almost constant. Then, once defrosting is complete, the cooler temperature begins to rise again and the heater current begins to decrease again. Point 0 is the point of completion of defrosting, and point 11 indicates the decreasing slope of the heater current after completion of defrosting. In FIG. 5, curve 12 and curve 13 are shown for comparison.
It shows the heater current and the temperature of the cooler when the defrosting heater starts to be energized at the same time as the compressor stops, and the time point at which defrosting is completed is C'. At the start of the expulsion cycle.

From the example, power supply to the defrosting heater is started after a certain period of time (tl) after the compressor has stopped. Since the temperature of the cooler is higher than when the machine is stopped, the current of the defrosting heater becomes smaller and the time from the start of defrosting to the completion of defrosting becomes slightly longer, but we found that the amount of power consumed for defrosting can be reduced. It should be noted that if the above-mentioned certain time (tl) is more than 5 minutes, the natural temperature rise rate of the cooler will be low and the power saving effect will be reduced, so it is desirable that the certain time (tl) be within 5 minutes.

Next, a block diagram of the defrosting device according to the present invention and a time diagram showing the operations of the defrosting device and the compressor are shown in FIGS. 5 and 6. In FIG. 5, 14 is a power supply, 15 is a compressor, 16 is a switch for supplying power to the compressor 15, 17 is a control circuit for controlling the compressor, and 18 is a control circuit for controlling the compressor 15 when the accumulated operating time reaches a certain time. , a defrosting start circuit that commands the start of defrosting when the compressor 15 stops; 19 a timer circuit that generates a signal after a certain period of time after receiving a command signal from the defrosting start circuit; and 18 a timer circuit 20 a defrosting circuit. 21 is a heater for expulsion 20
22 is a current detection circuit 23 for detecting the current flowing through the defrosting heater 20, and 24 is an arithmetic processing circuit equipped with instructions for arithmetic processing of the detection signal generated by the current detection circuit 22. Due to the noise generated by the processing circuit, the power supply switch 21 to the defrosting heater 20 is disconnected,
t is a defrosting heater control circuit for closing the power supply switch 21 to the defrosting heater 20 in response to the signal from the timer circuit 19; In FIG. 6, (A) is a waveform diagram of a signal indicating the operation of the compressor 15 (1), ,D,,D.

(b) is a waveform diagram E of the signal output from the defrosting start circuit when the cumulative operating time of the compressor 15 reaches a certain value and the compressor 15 is stopped, and (c) is a waveform diagram E of the signal output from the defrosting start circuit 18. A waveform diagram F (←) of a signal generated by the timer circuit 19 after a certain period of time after receiving the signal shows that upon receiving the signal from the timer circuit 19, the removal heater control circuit 24 closes the power supply switch 21, and the defrosting heater 20 A signal waveform diagram 0° (E) showing that the is in the energized state is a defrosting completion signal waveform diagram H of the arithmetic processing circuit 23.

In this device, when the integrated value of the signals , , n, indicating the operating time of the compressor 15 reaches a predetermined constant pressure, the compressor control circuit 17 disconnects the power supply switch 16 and the power supply to the compressor 15 is turned off. When the power supply is stopped, the dark blue removal start circuit M18 generates a signal E to the timer circuit 19, and the timer circuit power i operates. When the timer circuit reaches a predetermined period of time, it generates a signal I' to the defrosting heater control circuit j824, the defrosting heater control circuit 24 closes the power supply switch 21, and the defrosting heater 20 starts generating heat. Note that the compressor control circuit 17
The compressor 15 is controlled to be inactive while the defrosting heater 20 is operating, and to operate normally while the defrosting heater 20 is inactive.

The current flowing through the defrosting heater 20 is supplied to a current detection circuit 22. The current detection circuit 22 uses a current transformer or the like to generate a signal responsive to current and supplies it to the arithmetic circuit 23 . The current detection circuit 22 detects the current JT flowing through the defrosting heater 20 at time T and the current I (T0ΔT) at time (T0ΔT).
T) is detected and a signal corresponding to this current 11.1<T+Δr)K is supplied to the arithmetic processing circuit 23. The arithmetic processing circuit 23 stores the input signal and calculates the decreasing slope C1r-ICr+ΔT)/Δ7゛) of the current JT, and after the decreasing slope becomes a value smaller than a predetermined value α. , when the decreasing slope increases again and reaches a value larger than α, an output signal is generated and this output signal is supplied to the expulsion heater control circuit 24. Calculation surface 745
When the output signal 23 is supplied to the control circuit 2tK, the control circuit 24 opens the power supply switch 21. When the power supply switch 21 is opened, the current supplied to the defrosting heater 20 is cut off, and defrosting ends. Note that the arithmetic processing circuit performs calculations after a predetermined period of time has elapsed after the power supply switch 21 is closed to prevent malfunctions due to the current decreasing gradient immediately after the start of power supply.

Next, FIG. 7 shows the temperature distribution of each part of the cooler 1 at the time when defrosting is completed by the defrosting device K according to an example of the present invention. In FIG. 7, a curve 25 is the temperature of the pig box heater 2' having a self-temperature control function, a curve 26 is the temperature of the refrigerant pipe 1α, and a curve 27 is the surface temperature of the heat exchange fin 30, which is shown in FIG. Compared to the results obtained by conventional defrosting devices, the results are more uniform and there are no areas that become unnecessarily hot.

As described above, according to the present invention, in a defrosting device that heats pig boxes using a heater, at least the temperature coefficient of the resistance is positive and the temperature coefficient of the resistance changes rapidly. VC starts energizing the pig box heater, which has a so-called self-temperature control function, not at the same time as the compressor stops, but after a predetermined period of time.By VC, it is possible to reduce the power consumption of defrosting, and to reduce the power consumption of the cooler. It is also possible to prevent unnecessary temperature rises in frozen food products, etc. during the defrosting cycle.

[Brief explanation of the drawing]

Figure 1 shows the structure of a cooler in a refrigerator. 11 A front view, 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. FIG. 3 is a characteristic diagram of the defrosting heater used in the defrosting device of the present invention, and FIG. 4 is a characteristic diagram showing changes in heater current flowing through the defrosting heater and cooler temperature in the defrosting device of the present invention. , FIG. 5 is a block diagram showing the configuration of a defrosting device according to an example of the present invention, FIG. 6 is a waveform diagram of signals of the main parts of the defrosting device according to the present invention during operation, and FIG. 7 is a temperature distribution of each part of the cooler. FIG. 20: Defrosting heater representative patent attorney Usui 1) Tori, - Shizuku 2 Figure 1 Figure 2 Upper middle and lower Toja

Claims (1)

[Claims] A defrosting device that performs heating defrosting using a heater includes at least a defrosting heater that has a positive temperature coefficient of resistance and a characteristic that the temperature coefficient of resistance suddenly changes at a certain temperature;
A defrosting device comprising: a control means for starting power supply to the defrosting heater after a predetermined period of time has passed after the refrigeration cycle stops operating.