JPS6140907B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for removing frost attached to coolers such as refrigerators and air conditioners equipped with a refrigeration system consisting of a compressor, a condenser capillary tube, and an evaporator (hereinafter referred to as a cooler). This relates to a frost device.

Generally, frost forms on coolers such as refrigerators and air conditioners due to moisture contained in the air around the cooler when the cooler is in operation. When frost adheres to the cooler, the heat exchange efficiency of the cooler decreases and the cooling capacity decreases. For this reason, a heater is arranged around the cooler, and the heater generates heat, which melts and defrosts the frost that has adhered to the cooler.
Conventionally, in a refrigerator, 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 when defrosting, the defrosting heater 2 is energized. The defrosting heater 2 is heated to perform defrosting and prevent the cooling capacity from decreasing. The important issue here is deciding when to start defrosting. It is extremely difficult to detect when to start defrosting, as the amount and distribution of frost, which are factors that reduce the cooling capacity of the cooler, change with seasonal changes and the operating status of the cooler. It is.
Therefore, in the past, it was necessary to defrost the cooler every time the cooler operated for a certain period of time, and the time was designed to ensure that the cooling capacity of the cooler would not decrease even during periods with a large amount of frost. There is.

However, a defrost control device with such a means defrosts during periods when the amount of frost is small, even though the cooling capacity of the cooler has not decreased.
This results in wasted power. In addition, the electricity required for defrosting causes the temperature of the cooler to rise unnecessarily, and when cooling operation is resumed, it takes longer to lower the temperature of the cooler, which also has the disadvantage of increasing power consumption. are doing.

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 control device that can defrost efficiently.

In the present invention, in order to achieve the above-mentioned object,
By using a defrosting heater that has a positive temperature coefficient of resistance and a characteristic that the temperature coefficient of resistance changes suddenly at a certain temperature, the defrosting key point and It determines that it is unnecessary and ends defrosting.

First, the heater used in the present invention will be explained. FIG. 2 shows a cutaway perspective view of this heater. In FIG. 2, 4 and 4' are electrical conductors for power supply such as tinned copper wire, 5 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 6 is, for example, An insulating covering part such as urethane rubber, and 7 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 4 and 4' of the heater 2', a current flows through the heater section 5 made of a mixture of organic material and carbon, and the heater section 5 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 5 increases accordingly, and the resistance value rapidly increases as the softening temperature determined by the organic material used is approached. FIG. 3 shows changes in the resistance value of the heater section 5, with the resistance value plotted on the vertical axis and the temperature plotted on the horizontal axis. In FIG. 3, a curve 8 shows the resistance change characteristic of the heater section 5, and a curve 9 shows the temperature at which the temperature coefficient of resistance changes suddenly (operating sudden change temperature). Since the specific resistance value of the heater section 5 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. Defrost heater 2'
FIG. 4 shows a temporal change in the current flowing through the cooling device and a characteristic diagram of the change in the temperature of the cooler. In Figure 4,
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 10 shows the heater current,
Curve 11 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 10 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°C to +0°C due to the heat of melting the frost at point A in Figure 4, and at the same time the temperature of each part of the cooler changes from -0°C to +0°C. The rate of change of current 10 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 0 increases, and defrosting is completely completed at point B in FIG. 4 when the defrosting heater 2' reaches a certain temperature. Here, although the time constant of the current reduction portion from the maximum heater current immediately after the power is turned on differs depending on the amount of frost formation, there is a correspondence between the slope of the heater current and the amount of frost formation.

The defrosting control device according to the present invention utilizes this phenomenon.

Next, embodiments according to the present invention will be described. A block diagram of the defrosting control device of the present invention and a time diagram showing the operation of each part of the device and the cooler are shown in FIGS. 5 and 6.

In FIG. 5, 12 is a defrosting heater, 13 is a switch for supplying power to the defrosting heater 12, 14 is a current detection circuit for detecting the current flowing through the defrosting heater 12, and 15 is a current detection circuit 14 generating electricity. 16 is a determination circuit that determines whether defrosting is necessary or unnecessary based on the signal generated by the calculation circuit 15; 17 is a discriminating circuit that disconnects the power supply switch 13 to the defrosting heater 12; 18 is a power supply start circuit for closing the power supply switch 13 to the defrosting heater 12 at regular intervals, 1
9 is a defrost completion detection circuit for detecting that defrosting is completed by the defrost heater 12, and 20 is a power supply.
In addition, in FIG. 6, A is a waveform diagram of a signal indicating the operation time of the cooler in the power supply start circuit 18, B is a waveform diagram of a signal indicating the calculation result of the calculation circuit 15,
C is a waveform diagram of the power supply stop signal to the defrosting heater 12 obtained by the determination circuit 16 comparing the calculation result E of the calculation circuit 15 with a predetermined value J, and D is the defrosting completion detection circuit 19. FIG. 5 is a waveform diagram of a signal, E is a waveform diagram of a signal indicating the operation of the defrosting heater 12 and the operation of the power supply switch 13, and F is a waveform diagram of a signal indicating the operation of the cooler.

In this device, when the signals C ₁ , C ₂ , C ₃ , and C ₄ indicating the operating time of the cooler reach a predetermined reference value I, the power supply start circuit 18 closes the power supply switch 13 and at the same time, the power supply start circuit 18 closes the power supply switch 13 . Operating signals C ₁ , C ₂ , C ₃ , C ₄
is returned to zero and the operation of the cooler is integrated. Although not shown, the cooler is controlled by a separately provided cooler control function to stop while the defrosting heater 12 is operating and to perform a cooling operation while the defrosting heater 12 is stopped. At signal _C1 in FIG. 6, the cooling operation of the cooler is stopped, as indicated by signal _H1 in the same figure. When the power supply switch 13 is closed, current flows from the power supply 20 to the defrosting heater 12 via the power supply switch 13. The current flowing through the defrosting heater 12 is then supplied to a current detection circuit 14. The current detection circuit 14 uses a current transformer or the like to generate a signal responsive to current, and supplies it to the arithmetic circuit 15.
The arithmetic circuit 15 detects when the signal reaches the maximum value, and calculates the rate of change of the signal in response to the current at a point after a certain period of time has elapsed,
As a result, the signal D ₁ is supplied to the discrimination circuit 16 . The discrimination circuit 16 receives this signal D ₁ and determines this signal D ₁
is a predetermined value J or more, a signal that causes the power supply stop circuit 17 to cut off the supply of current to the defrosting heater 12
Supply E ₁ . Upon receiving this signal _E1 , the power supply stop circuit 17 opens the power supply switch 13 and causes the defrosting heater 15 to stop generating heat. Next, as soon as the power supply switch 13 is opened, the cooler starts cooling operation as shown by signal H in FIG. 6 by a separately provided cooler control function. As a result, the power supply start circuit 18 starts measuring the operating time of the cooler, and when the signal _C2 in FIG. Each part of the device operates. Next, the cooler is activated and signal C ₃ again sets the predetermined reference value I.
When the power supply start circuit 18 reaches the power supply switch 1
3 is closed, and at the same time, the operation signal C of the cooler is returned to zero, and the operation of the cooler is integrated. When the power supply switch 13 is closed, current flows from the power supply 20 to the defrosting heater 12 via the power supply switch 13.
At the same time, the cooler is deactivated by the cooler control function.
The current flowing through the defrosting heater 12 via the power supply switch 13 is supplied to the current detection circuit 14. The current detection circuit 14 uses a current transformer or the like to generate a signal responsive to current, and supplies it to the arithmetic circuit 15 . The arithmetic circuit 15 detects that the signal has reached the maximum value, calculates the rate of change of the signal in response to the current at a point after a certain period of time has elapsed, and supplies the resulting signal _D3 to the discrimination circuit 16. do. The determination circuit 16 receives this signal D ₃ and, if this signal D ₃ is smaller than a predetermined value J, the power supply stop circuit 1
7, the power supply stop signal E to the defrosting heater 12 is not issued. If the power supply stop signal E is not input, the power supply stop circuit 17 continues in that state without opening the power supply switch 14. Since the power supply switch 14 remains closed, the defrosting heater 12 continues to receive current supply and continues to generate heat, which melts the frost attached to the cooler. When the attached frost is completely removed, the defrosting completion detection circuit 19 supplies a defrosting completion signal F ₁ to the stop circuit 17 . The stop circuit 17 receives the signal _F1 and switches the power supply switch 1.
Open 3. When the power supply switch 13 is opened, the cooler starts cooling operation by the cooler control function.

As described above, the defrosting control device according to the present invention has the following features:
Each time the operating time of the cooler reaches a predetermined time, one of the above two types of operations is performed depending on the presence or absence of the output signal E of the discrimination circuit 16, and this is repeated. is designed so that when the output signal D of the arithmetic circuit 15 is larger than a predetermined value J, the signal E is output, and when it is smaller, the signal E is not output. Here, the output signal D of the arithmetic circuit 15 is in response to the rate of change of the current at a certain time point after the current flowing through the defrosting heater 12 reaches its maximum value, and this output signal D is as follows: This corresponds to the differential value of the defrost heater current at the above point, and this differential value approximately corresponds to the reciprocal of the time constant when the defrost heater current decreases from its maximum value. Here, the time constant of the defrost heater current corresponds to the thermal time constant of the defrost heater 12, and the thermal time constant of the defrost heater 12 corresponds to the thermal time constant of the defrost heater 12.
This heat capacity is proportional to the heat capacity of the defrosting heater 12.
It corresponds to the heat capacity of the cooler attached to the cooler and is proportional to the amount of frost formed on the cooler, so if the amount of frost formed is small, the time constant of the current flowing through the defrosting heater 12 becomes small, and conversely, the time constant of the current flowing through the defrosting heater 12 becomes smaller. The larger the amount, the larger the time constant. Therefore, when the value of the signal D from the arithmetic circuit 15 is large, it indicates that the time constant of the current flowing through the defrosting heater 12 is small, and at the same time, it also indicates that the amount of frost formation is small. If it is small, it indicates that the amount of frost is large, and the presence or absence of the output signal E from the above-mentioned discrimination circuit 16 indicates whether the amount of frost is less than the reference amount. Note that the above reference amount is preferably an amount that does not reduce the cooling capacity. That is, when there is an output signal E from the discrimination circuit 16, it indicates that defrosting is not necessary because the amount of frost is small, and when there is no output signal, it indicates that defrosting is necessary because the amount of frost is large. It is the same as having

As explained above, the defrosting control device according to the present invention estimates the amount of frost from the current change rate at the point where the current flowing through the defrosting heater 12 decreases after passing through the maximum value, and from this result determines the necessity of defrosting. The defrosting heater 12 operates to control the power supply to the defrosting heater 12 based on the presence or absence of the defrosting heater 12 .

In addition, defrosting completion detection in the defrosting control device described above may be performed by detecting the surface temperature of the cooler, or may be performed simply by using a timer, and the setting time of the timer may be detected by the output of the arithmetic circuit. The determination may be made to correspond to the reciprocal of the magnitude of the signal D, or alternatively, the determination may be made by detecting with a current sensor that the current flowing through the defrosting heater 12 has decreased below a certain threshold value.

Moreover, in the above-mentioned embodiment, the defrosting heater 12
The operation was explained using the current flowing to the defrosting heater 12.
The same effect can be obtained by using power supplied to the

Further, in the present invention, an organic heater 12 is used, but it goes without saying that the same effect can be obtained using an inorganic material such as a barium titanate positive temperature coefficient thermistor.

Furthermore, in the above embodiment, the operation of the cooler was simply shown as two operations, operating and stopping, but the cooler also has a state in which it temporarily stops in order to control the temperature even when it is in the operating state. Even if the cooler does not always operate to cool down when it enters the operating state, and the cooler starts to cool down after the temperature of the cooler is naturally cooled by the defrosting heater 12, There are no problems with the operation of the invention.

As described above, according to the present invention, a heater is used that 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 frost formation is achieved by utilizing changes in the current flowing through the heater. If the amount of frost does not reduce the cooling capacity, defrosting is stopped, and if the amount of frost does reduce the cooling capacity, defrosting can be carried out. As a result, optimal defrosting control can be performed without unnecessary defrosting, resulting in a large power saving effect.

In addition, in the present invention, if the operation time of the cooler that starts energizing the defrosting heater is adjusted to be suitable for the summer when there is a large amount of frost, as has been done in the past, the amount of frost can be reduced and the amount of frost can be removed. In winter, when there is less need for frost, the number of times defrosting is reduced, so the number of times the cooler is heated is also reduced, and the power required to recool the cooler is also reduced, which also produces a power effect.

[Brief explanation of the drawing]

FIG. 1 is a front view showing the structure of a cooler in a refrigerator, FIG. 2 is a partially cutaway perspective view of a defrosting heater used in a defrosting control device according to an embodiment of the present invention, and FIG. 3 is a front view showing the structure of a cooler in a refrigerator. Characteristic diagram of the defrosting heater, No. 4
Figure 5 is a characteristic diagram showing changes in defrost heater current and cooler temperature in the defrost control device of the present invention.
FIG. 6 is a block diagram showing the configuration of the defrosting control device according to the present invention, and FIG. 6 is a waveform diagram of signals in the main parts of the defrosting control device when the defrosting control device according to the present invention is in operation. 12... Heater, 14... Current detection circuit, 15
... Arithmetic circuit, 16 ... Discrimination circuit, 17 ... Power supply stop circuit, 18 ... Power supply start circuit, 19 ... Defrost completion detection circuit.

Claims (1)

[Claims] 1. A defrosting heater consisting of 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, and a power supply for supplying current to the defrosting heater or cutting off the current. With the switch,
Current detecting means detects the current value of the current flowing through the defrosting heater and generates a signal responsive to the current value, and a signal responsive to the current value obtained by the current detecting means is supplied, and the current value reaches the maximum value. a calculation means that detects that the current value has reached the maximum value and calculates the rate of change on the current side when a predetermined time has elapsed after the current value reaches the maximum value, and a change in the current value obtained by the calculation means. If the rate of change is less than a predetermined value, no power supply stop signal is generated, and if the rate of change in current value is greater than a predetermined value, the current supply to the defrosting heater is cut off. A determination means for generating a power supply stop signal; and when the power supply stop signal is supplied from the determination means, a power supply switch is opened to interrupt the current flowing to the defrosting heater and interrupting the supply of current to the defrosting heater. A power supply stop means detects that defrosting is completed, generates a defrost completion signal, supplies the defrost completion signal to the power supply stop means, opens the power supply switch by the defrost completion signal, and starts the defrosting heater. A defrosting device comprising: defrosting completion detection means for interrupting current flowing through the defrosting device.