JPH0317191Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention relates to a defrosting control device equipped with an oscillation circuit that detects frost formation on a frost detector attached to an evaporator of a refrigerator, etc. as a change in an electrical signal. It is.

Conventional structure and its problems Generally, frost adhering to the evaporator of a refrigerator, etc. is removed at regular intervals by integrating the operating time of the compressor, or by counting the number of times the refrigerator and freezer compartment doors are opened and closed. When the number of times reached was reached, defrosting was performed. However, the formation of frost on the evaporator of a refrigerator, etc. is greatly affected by the outside temperature and humidity of the refrigerator, the frequency of opening and closing of the refrigerator and freezer compartment doors, and the contents stored in the refrigerator. There were disadvantages such as defrosting was not performed when necessary, and defrosting was not performed even though a large amount of frost formed on the evaporator and the cooling capacity was reduced.

Therefore, in order to eliminate such drawbacks, as a means of directly detecting frost formation, we have developed a frost detector in which a piezoelectric element is attached to a vibrating surface, and a method in which the piezoelectric element is oscillated to generate resonance due to frost formation on the frost detector. A defrosting control device has been proposed that includes a separately excited oscillation circuit (not including a frost detector in the oscillation circuit) that detects a change in resistance as a change in circuit output. For example, as shown in FIG. 1, such a defrosting control device includes a separately excited oscillation circuit 2, an amplifier circuit 3 that amplifies the oscillation signal of the separately excited oscillation circuit 2,
A frost amount detection circuit 4 includes a frost detector 1 whose resonant resistance increases when frost is deposited, and a resistor R, and outputs an oscillation signal correlated to the amount of frost on the frost detector 1; and the frost amount detection circuit. It consists of a detection circuit 5 which selectively switches between defrosting operation and cooling operation based on the output of . Since this defrosting control device always performs defrosting with a constant amount of frost throughout the year, significant power savings can be achieved compared to conventional defrosting methods that occur at regular intervals. However, from a more strict point of view, the optimal defrosting starting point for the evaporator of a refrigerator, etc. changes depending on the temperature outside the refrigerator, so it is better to set the optimal defrosting starting point according to the outside temperature for cooling efficiency. This is more desirable from the viewpoint of improved performance and power saving. In other words, as shown in Fig. 2, compared to the optimal defrosting start frost formation amount V ₁ (cc) at normal temperature T ₁ (°C), at low temperature T ₂ (°C)
Since the operating rate of the compressor is low and there is plenty of cooling capacity, the cooling efficiency is less likely to decrease even if frost forms, so the optimal defrosting start frost amount V ₂ (cc) increases, and conversely, the high temperature T ₃ (°C), the operating rate of the compressor is high and there is not enough cooling capacity to spare, so if frost forms, the cooling efficiency tends to drop, so the optimal defrosting start frost volume V ₃ (cc) will be small.

Purpose of the invention Therefore, the purpose of the present invention is to provide a defrosting control device that accurately detects changes in the resonance resistance of a frost detector due to frost formation and always starts defrosting at the optimal defrosting starting point. It is something to do.

Structure of the invention In order to achieve this objective, the amplitude of the oscillation signal applied to the frost detector is changed by changing the amplification factor of the amplifier circuit that amplifies the oscillation signal of the separately excited oscillation circuit according to the temperature outside the refrigerator. When the optimum amount of frost is reached according to the outside temperature, defrosting is started.

DESCRIPTION OF EMBODIMENTS FIG. 3 shows a frost detector 1 according to an embodiment of the present invention.
6 is a metal casing with good thermal conductivity; 7 is a vibrating surface having a piezoelectric element 8 attached to the inner surface of the casing 6; 9 is a defrosting heater that removes frost adhering to the vibrating surface 7 during defrosting; 10 11 is a molding material such as epoxy resin that is packed into the metal casing and fixes the heater 9; and 11 is an airtight plate that airtightly separates the vibrating part where the piezoelectric element 8 is located and the molded part of the lower heater 9. 12 is the piezoelectric element 8
and a lead wire of the heater 9. As is well known, such a frost detector 1 is installed in an evaporator (not shown) or the like that is subject to frost formation, and its operation is performed when the amount of frost adhering to the frost detector 1 (frost amount) is determined as shown in FIG. As the resistance increases, the resonance resistance increases.

Next, the defrosting control circuit according to one embodiment of the present invention includes a separately excited oscillation circuit 13, an amplifier circuit 14, and a frost amount detection circuit 1.
5. It consists of a detection circuit 16, which is shown in FIG. In the figure, the separately excited oscillation circuit 13 includes a transistor TR ₁ , capacitors C ₁ to C ₃ , and resistors R ₁ to
Tunable LC consisting of R ₃ and transformers L ₁ and L ₂
It is an oscillation circuit, in which C ₁ and L ₁ constitute a resonant circuit, and L ₂ and C ₂ constitute a positive feedback circuit. Further, the separately excited oscillation circuit 13 is not limited to the tuned LC oscillation circuit, but may be of other types. Oscillation signal output terminal 1 of the separately excited oscillation circuit 13
7 is connected to the base of the transistor TR ₂ of the amplifier circuit 14 through a DC cut capacitor C ₄ . The transistor TR ₂ is connected to the power supply Vc.c. and ground through the collector resistor R ₄ , the thermistor TH as an outside temperature detector that detects the ambient temperature of the refrigerator, and the emitter resistor R ₅ , and at this time, the amplification factor is determined by the ratio of the resistance value of the thermistor TH and the sum of the resistance values of the resistor _R4 to the resistance value _of the resistor _R5 . That is, when the amplification factor is A, it is expressed as A=R ₄ +R _TH /R ₅ .

As shown in Figure 6, the thermistor TH has the characteristic that the resistance _RTH decreases as the temperature rises, so the collector side resistance value of the transistor _TR2 (sum of the resistance _R4 and thermistor TH) is the seventh As shown in the figure, as the temperature rises, the resistance value decreases. Here, since the emitter resistance _R5 of the transistor _TR2 is constant regardless of the temperature, the amplification factor A of the transistor _TR2 is
tends to decrease as the temperature rises, as shown in FIG.

Further, the bias of the base of the transistor TR ₂ is determined by the resistors R ₆ and R ₇ connected between the power supply V _CC and the ground. Then, the output terminal 1 of the amplifier circuit 14
8 is connected to the frost detector 1 and the resistor _R8 of the frost amount detection circuit 15 through the DC cut capacitor _C5 , and the output terminal 19 of the frost amount detection circuit 15 is connected to the diode D1 of the detection circuit ₁₆ . It is connected.
The diode _D1 is connected to the capacitor _C6 , and the output terminal 19 of the frost amount detection circuit 15 is connected to the capacitor C6.
rectifies the sine wave oscillation output into DC voltage. The base of the transistor TR ₃ is connected to the diode D ₁ through a resistor R ₉ , the emitter is grounded,
The collector is connected to the power supply V _CC through a resistor R ₁₀ and grounded through a capacitor C ₇ .
The base of the transistor TR ₄ is connected to the collector of the transistor TR ₃ through a resistor R ₁₁ , the emitter is grounded, and the collector is connected to the relay RY
(switching means) is connected to one end of the primary coil, and the other end of this coil is connected to the power supply V _CC . Additionally, a heater 20 disposed in the evaporator (not shown)
and the heater 9 built into the frost detector 1 is a relay
It is connected to the power supply via the normally open contact a of the RY, and the compressor 21 of the cooling cycle is connected to the power supply via the normally closed contact b of the relay RY and the thermostat 22, which opens and closes by sensing the temperature inside the refrigerator. has been done.

The operation in such a configuration will be explained. When the power is turned on, the separately excited oscillation circuit 13 oscillates at the resonant frequency of the frost detector 1, and a sine wave oscillation signal is obtained at the output terminal 17 of the separately excited oscillation circuit 13. and,
The oscillation signal is amplified by the amplifier circuit 14 with an amplification factor depending on the temperature as shown in FIG _.
Only the sine wave oscillation signal from which the DC bias has been removed is input to the frost amount detection circuit 15. This sine wave oscillation signal is shown in FIG.

When there is a small amount of frost on the frost detector 1, the resonant resistance is small as shown in _FIG .
Regardless of the amplification factor, the sine wave oscillation output of the output terminal 19 of the frost amount detection circuit 15 increases. and,
It is converted to a DC voltage by diode D ₁ and capacitor C ₆ , and the base potential of transistor TR ₃ is at the cut-off potential (for example, in a silicon transistor
(approximately 0.6V) or higher, transistor TR ₃ turns on. The collector potential smoothed by the capacitor _C7 is a low potential of about 0.2V, and the base potential of the transistor _TR4 is also a low potential of about 0.2V, so the transistor _TR4 is turned off and the relay RY does not operate. Therefore, the compressor 21 is energized and performs cooling operation.

As the amount of frost on the frost detector 1 increases, the resonant resistance gradually increases as shown in Fig. 4, and the resonant resistance of the frost detector 1 becomes larger than the resistor _R8 , so the frost amount detection circuit The sine wave oscillation output at the output end 19 of the output terminal 15 gradually decreases. Then, the DC voltage rectified by the diode _D1 and the capacitor _C6 also decreases, the base potential of the transistor _TR3 becomes below the cut-off potential, the transistor _TR3 is turned off, and the collector potential becomes a value close to the power supply V _CC . and,
The base potential of transistor TR ₄ also rises to a value close to the power supply V _CC , transistor TR ₄ turns on,
The excitation current flows and the relay RY operates to start energizing the evaporator defrosting heater 20 and the frost detector built-in heater 9 to defrost. When the frost adhering to the vibrating surface 7 of the frost detector 1 is removed by defrosting, the defrosting ends and cooling operation starts.

In this case, when the outside temperature of the refrigerator is lower than room temperature, the amplification factor A of the amplifier circuit 14 is as shown in FIG.
is higher than the room temperature, so the amount of frost detection circuit 15
The sine wave oscillation output inputted to the frost sensor 1 increases, and even if frost forms on the frost detector 1, the sine wave oscillation output at the output end 19 of the frost amount detection circuit 15 becomes difficult to decrease. Therefore, the amount of frost formed at the start of defrosting is greater than that at room temperature. On the other hand, when the outside temperature of the refrigerator is higher than room temperature, the amplification factor A of the amplifier circuit 14 is
is smaller than the room temperature, so the amount of frost detection circuit 15
When the sine wave oscillation output input to the frost detector 1 becomes smaller and frost forms on the frost detector 1, the sine wave oscillation output at the output terminal 19 of the frost amount detection circuit 15 tends to decrease. Therefore, the amount of frost formed at the start of defrosting is smaller than at room temperature. Here, the amplification factor of the excitation system, that is, the amplification circuit 14, was changed depending on the outside temperature of the refrigerator, but the same effect can be obtained by changing the detection level of the vibration receiving system, that is, the detection circuit 15, depending on the outside temperature of the refrigerator.

In this way, since the amplification factor of the amplifier circuit 14 that amplifies the oscillation signal of the separately excited oscillation circuit 13 is changed according to the outside temperature of the refrigerator, the amount of frost formed at the start of defrosting at room temperature is higher than that at low temperatures. The amount of frost formation increases at the onset of frost, and decreases at high temperatures. Therefore, the same tendency as the optimal defrosting start frost formation amount characteristic shown in FIG. 2 is obtained, and it is possible to improve cooling efficiency and save power.

Effects of the Invention As is clear from the above explanation, the present invention provides a frost detector which is placed in an evaporator of a refrigerator, etc., and which has a built-in piezoelectric element and whose resonant resistance increases when frost adheres to the frost detector. an outside temperature detector for detecting the ambient temperature of the frost detector; a separately excited oscillation circuit that oscillates at the same frequency as the resonant frequency of the frost detector; An amplifier circuit that reduces the amplification factor as the outside temperature detected by a temperature sensor rises, and a frost detector and a voltage dividing resistor connected in series between the output terminal of the amplifier circuit and ground, a frost amount detection circuit that inputs an oscillation signal from the amplifier circuit and outputs an oscillation signal correlated to the amount of frost on the frost detector from an output terminal provided at an intermediate point between the frost detector and the voltage dividing resistor; , outputting a switching signal to a switching means for switching the operation of a compressor of a cooling system of the refrigerator or the like and a defrosting heater installed in the evaporator in accordance with the voltage level of the output end of the frost amount detection circuit; Since it is composed of a detection circuit that allows defrosting to occur when defrosting is necessary, it is possible to defrost when necessary.In particular, compared to the amount of frost formation at the start of defrosting at room temperature, the amount of frost formation at the start of defrosting increases at low temperatures and decreases at high temperatures. , which can improve cooling efficiency and save power.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional defrosting control device, Fig. 2 is a graph showing the outside temperature of the refrigerator and the optimum amount of frost formation at the start of defrosting of the evaporator, Fig. 3 is a cross-sectional view of the frost detector, and Fig. 4 The figure is a graph showing the relationship between the amount of frost and the resonant resistance in the frost detector. Figure 7 is a graph showing the relationship between temperature and the collector side resistance value of transistor TR ₂ , Figure 8 is a graph showing the relationship between temperature and amplification factor of transistor TR ₂ , and Figure 9 is input to the frost amount detection circuit. A sinusoidal oscillation signal is shown. 1...Frost detector, 8...Piezoelectric element, 13...Separately excited oscillation circuit, 14...Amplifier circuit, 15...Frost formation detection circuit, 16...Detection circuit, TH...Thermistor (outside temperature detection vessel).

Claims (1)

[Scope of utility model registration request] A frost detector is placed in an evaporator of a refrigerator, etc., and has a built-in piezoelectric element so that resonance resistance increases when frost adheres to it; an outside temperature sensor that detects the ambient temperature of the refrigerator, etc.; and the frost detector. a separately excited oscillation circuit that oscillates at the same frequency as the resonant frequency of the device; and a separately excited oscillation circuit that is connected to the output terminal of the separately excited oscillator circuit and amplifies the oscillation signal, and decreases the amplification factor as the outside temperature detected by the temperature sensor rises. the frost detector is connected in series between the output end of the amplifier circuit and ground, and a voltage dividing resistor, and the oscillation signal from the amplifier circuit is input to the frost detector. a frost amount detection circuit that outputs an oscillation signal correlated to the amount of frost from an output terminal provided at an intermediate point between the frost detector and the voltage dividing resistor; A defrosting control device comprising a detection circuit that outputs a switching signal to a switching means that switches between a compressor of a cooling system of the refrigerator or the like and a defrosting heater installed in the evaporator.