JPS6140904B2 - - 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 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 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 fin 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. Furthermore, in the case of air conditioning equipment, when frost occurs, the operation of the air conditioning equipment is stopped for a certain period of time, and the frost is melted by heat from the outside air to perform defrosting. 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. In addition, taking into account 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,
It was necessary to set defrosting conditions such as temperature and time so that sufficient defrosting could not be carried out in any case. 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, 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 are
The temperature distributions of the defrosting heater 2, the refrigerant pipe 1a, and the heat exchange fin 3 at the upper, middle, and lower positions of the cooler 1 are shown, 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 resumed after defrosting is completed, the 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 means to solve the above-mentioned drawbacks, a positive temperature coefficient thermistor having a positive temperature coefficient of resistance value is used in the defrosting heater or a part of the defrosting heater, and the current of the heater is reduced to a predetermined constant value. When the defrost control device cuts off the current flowing to the defrost heater,
It is disclosed in Japanese Patent Application Laid-Open No. 54-101533. but,
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 above-described heater control device, the 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 for heater-off control with a margin to lengthen the defrosting time. There were some shortcomings.

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 value of the heater section 8 increases accordingly, and the resistance value rapidly increases 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 resistance 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 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, the temperature of each part of the cooler decreases to - due to the heat of melting of the frost, starting from point A in Fig. 5.
Changes from 0℃ to +0℃, and at the same time heater current 1
The rate of change in 3 changes from a decreasing trend to an increasing trend.
After point A, the temperature of the defrosting heater 2' gradually increases and defrosting progresses further, 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 fifth point.
When reaching point B in the figure, defrosting is completely completed. Although the time during which the heater 2' is energized varies depending on the amount of frost, the heater current at point A in FIG. 5 and the heater current at point B in the same figure are at a constant ratio. Also, the time required from when the heater 2' is energized until it reaches point A in FIG.
There is also a certain relationship between the time required to reach point B in FIG. 5, where defrosting is completed.

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

Next, a first embodiment of the defrosting device according to the present invention will be described with reference to FIG.

In FIG. 6, 15 is a defrosting heater, 16 is a power supply switch that supplies current to the defrosting heater 15,
17 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 detection signal generated by the current detection circuit 17; and 19 is a signal generated by the arithmetic processing circuit 18. The control circuit 20 is a power source for cutting off the defrosting heater 15 in response to a signal. In this device, when the power supply switch 16 is closed, the defrosting heater 15 is connected from the power supply 20 via the power supply switch 16.
A current flows through. 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 an arbitrary time ΔT.
The value of the current flowing through the defrosting heater 15 is detected every time lapses, and a signal corresponding to this current value is supplied to the arithmetic processing circuit 18. Here, suppose that the current value at an arbitrary time T is the signal I _T , and the time (T+Δ
The current value at T) is the signal I _(T+ 〓 _T) , and the time (T
The current value at +2ΔT) is indicated by a signal I _(T+2 〓 _T) . The arithmetic processing circuit 18 that receives these signals I _T and T _(T+2 〓 _{T )} stores the signals and calculates the difference ₍ I _{T −}
I _(T+ 〓 _T) ) or decreasing slope (I _T −I _(T+ 〓 _T
) )/ΔT is calculated, and similarly the signal I _(T+ 〓
_T) and the signal I _(T+2 〓 _T) (I _(T+ 〓 _T) −I _(T+2 〓 _T
) or decreasing slope (I _(T+ 〓 _T) −I _(T+2 〓 _T) )/
Find ΔT. Next, the difference between the results of both calculations is determined. For example, to explain it in terms of signal differences, first,
(I _T −I _(T+ 〓 _T) )−(I _(T+ 〓 _T) −I _(T+2 〓 _T) ) is obtained. If this value is I'', then this value
I'' indicates the tendency of increase/decrease in the current flowing through the defrosting heater 15, and the point at which this value I'' changes from positive to negative indicates point A in FIG. Next, the arithmetic processing circuit 18 multiplies and stores the signal corresponding to the heater current at the time when I'' changes from positive to negative by a predetermined value. Compare the stored values, and when both values match, B in Figure 5
It is assumed that the point has been reached and an output signal is generated.
When the output signal of the arithmetic processing circuit 18 is supplied to the control circuit 19, the control circuit 19 switches the power supply switch 16
to open. When the power supply switch 16 is opened, the current supplied to the defrosting heater 15 is cut off, and defrosting ends.

In the above-described embodiment, the operation was explained using the heater current, but the same effect can be obtained even if the operation is performed using the electric power supplied to the heater.

As described above, according to the defrosting device of the present invention, it is possible to appropriately detect the completion of defrosting using the heater 2' itself, without providing it separately from other defrosting completion detection elements. 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, and a curve 23 is the surface temperature of the heat exchange fin 3, and the temperature distribution in each part of the cooler 1. However, compared to the results obtained by the conventional defrosting device shown in FIG. 2, the results are more uniform and there are no parts that become unnecessarily high temperature. In addition, in the present invention, an organic substance-based defrosting heater has been described, but there are also devices that have a positive temperature coefficient and whose resistance temperature coefficient changes suddenly at a certain temperature, such as a barium titanate-based positive temperature coefficient thermistor. It goes without saying that similar effects can be obtained even with inorganic materials.

As described above, according to the present invention, by using 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, changes in the current flowing through the heater can be suppressed. This can be used to detect the completion of defrosting, and prevent unnecessary temperature increases in the cooler when defrosting is complete. 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 a decreasing tendency to an increasing 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 the resistance value of the defrosting heater, thereby reducing costs, and making it easy to adjust the circuits of each individual defrosting device, thereby improving productivity. It also has excellent reliability because it operates without any problem even if the resistance value 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 the cooler when defrosting is completed when a conventional defrosting heater is used, and Figure 3 is a diagram showing the temperature distribution of the cooler when defrosting is completed when a conventional defrosting heater is used. FIG. 4 is a partially cutaway perspective view of a defrosting heater used in a defrosting device according to an embodiment of the invention; FIG. 4 is a characteristic diagram of the defrosting heater; FIG.
FIG. 6 is a characteristic diagram showing changes in temperature and current flowing through the defrosting heater in the defrosting device of the present invention, FIG. 6 is a block diagram showing the configuration of the defrosting device according to the present invention, and FIG.
The figure is a characteristic diagram showing the temperature distribution of each part of the cooler in the present invention. 15... Heater, 16... Current detection circuit, 18
... Arithmetic processing circuit, 19 ... Control circuit.

Claims (1)

[Claims] 1. At least a heater having a characteristic that the temperature coefficient of the low resistance value is positive and the temperature coefficient of the resistance value changes suddenly at a certain temperature, a current detection circuit that detects the value of the current flowing through the heater, and a current detection circuit that detects the value of the current flowing through the heater. Detect a turning point where the rate of change of current changes from a decreasing tendency to an increasing tendency, generate a reference signal by multiplying the value of the current flowing through the heater at the turning point by a predetermined value, and calculate the value of this reference signal. An arithmetic processing circuit stores the value of the reference signal and compares the value of the current flowing through the heater, and generates an output signal when the two values match, and the current to the heater is controlled by the output signal of the arithmetic processing circuit. A defrosting device characterized by having a control means for shutting off.