JPH01312378A - Frost sensor for heat exchanger - Google Patents

Abstract

PURPOSE:To enable accurate detection of a frosted condition and contrive rationalization of control of the start and end of defrosting by providing a temperature sensing element in proximity to a heat exchanger, heating the element and comparing the rate of change in resistance. CONSTITUTION:A frost sensor 4 provided between cooling fins in proximity to the fin comprises a thermistor 8 as a temperature sensing element and a heater 9, and is connected to plus and minus terminals of a comparator 13 through resistances 10, 11 and 12. When the heater 9 is energized in an unfrosted condition, the resistance of the thermistor 8 is lowered, whereas when the heater 9 is energized in a frosted condition, the resistance is raised. It is thus possible to energize the heater 9 for, for instance, 5sec, detect the rate and amount of change in the resistance of the thermistor 8 and check whether the rate of change is higher or lower than a preset threshold. It is thereby possible to detect directly whether the degree of frosting is at such a level as to require defrosting, and to control accurately the timing for starting and ending the defrosting.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a frost sensor for an automatic defrosting device for a heat exchanger such as a refrigerator.

(Prior art) Conventionally, automatic defrosting of a refrigerator is performed by energizing the defrosting heater to defrost when the accumulated operating time of the compressor reaches a predetermined time, and the defrosting operation is similarly terminated after the elapse of a predetermined time. It is generally known that power supply to the defrosting heater is later terminated. According to this method, the start of defrosting is controlled by time, but the actual frosting state depends on the usage conditions of the refrigerator, such as the temperature around the refrigerator, humidity, frequency of opening and closing of the door, heat generation and heat capacity of the object to be cooled. Due to the various differences K, etc., defrosting cannot be controlled simply by time. In addition, since this method does not directly detect the actual frosting state, defrosting is performed even if there are no boxes, and defrosting is not performed even if there is excessive frosting. There will be situations where there is no such thing. Further, even at the end of the defrosting operation, the defrosting heater continues to be energized more than necessary, or even when frost remains, the defrosting heater is no longer energized, resulting in an inefficient defrosting operation.

Therefore, an automatic defrosting device described in Japanese Patent Publication No. 42-4181 is generally used. As shown in FIGS. 8 and 9, this automatic defrosting device has an evaporator 100 which is one heat exchanger, and the frost 101 that forms on this evaporator 100
The temperature-sensitive resistance element 102 is placed at a position Kv buried in the j
ll The temperature-sensitive resistance element 102 and the temperature-sensitive resistance element 103 are configured with the other temperature-sensitive resistance element 103 installed in a position where they do not come into contact with OIK.
It is connected to the.

In FIG. 9, temperature-sensitive resistance elements 102 and 103 constitute two sides of the bridge circuit, and the other two sides are resistors 106.
and 107. This electric bridge circuit is equipped with a control circuit 108 that controls a defrosting control device (not shown), and a timer circuit 109 that applies an intermittent trap voltage to the electric bridge circuit.

110 is a power source.

In the automatic defrosting device configured as described above, when a voltage is applied to the temperature-sensitive resistance elements 102 and 103, when frost 101 is not generated, there is no relative difference in the internal temperature of the pixel elements, and the electric bridge circuit maintains a balance. Therefore, no current flows through the control circuit 108 and the n removal device does not operate. However, n101 generated in the evaporator 100 increases and the temperature-sensitive resistance element 102 becomes frost 10.
When a voltage is applied to the pixel element when the pixel element 102 is buried in frost 101, the element 102 buried in the frost 101 loses heat due to the melting of n, so the temperature does not rise, and the resistance value is high and the electric bridge circuit 102-
Although the voltage division ratio between the element 102 and the resistor 106 on the 106th side does not change significantly, the temperature of the element 103 increases due to the applied voltage.
A self-heating state occurs in which the resistance value decreases and the current further increases, and the element 103 and the resistor 10 on the bridge circuit 103-107 side
7 changes significantly, the balance of the electric bridge circuit collapses, and a detection current flows to the control circuit 108, activating the defrosting device.
It defrosts the air.

However, with this defrosting device, dust and other particles adhere to one of the elements, which creates a temperature difference between the elements and upsets the balance of the electric bridge circuit, causing the defrosting device to malfunction and reducing the efficiency of the evaporator. Sometimes.

(Problem to be Solved by the Invention) As described above, in the conventional defrosting device for a heat exchanger, the defrosting device malfunctions due to dust etc. adhering to the temperature-sensitive resistance element, reducing the cooling efficiency of the heat exchanger. It will lower it.

The present invention was made in view of the above circumstances, and provides a heat exchanger box sensor that can directly detect the presence or absence of frost, perform defrosting operation for an appropriate time, and increase the cooling efficiency of the heat exchanger. The purpose is to provide.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the frost sensor for a heat exchanger of the present invention includes a temperature sensing element provided close to the heat exchanger, and a frost sensor for heating the temperature sensing element. comprising a heating means provided close to the temperature sensing element, and a control means for detecting the resistance value of the temperature sensing element and controlling the defrosting means of the heat exchanger according to the detected amount,
This control means is characterized in that it turns on the defrosting means when the resistance value detected by the temperature sensing element is within a predetermined value, and stops the defrosting means when the resistance value is greater than or equal to a predetermined value.

(Function) In the device configured as described above, when there is no frost on the heat exchanger, the resistance value of the thermistor of the temperature sensing element changes greatly and rapidly due to the heat of the heating means. On the other hand, in a state where frost is attached, the heat from the heating means is absorbed by ffK, and the change in the resistance value of the thermistor of the temperature sensing element is small. A certain threshold value is set for the difference in this rate of change, and the detected value is compared with the threshold value. Depending on whether the detected value is above or below the threshold value, it is determined whether the frost is above the level required for defrosting. It is possible to directly detect defrosting and accurately control when defrosting starts and ends.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of the interior of a refrigerator equipped with a frost sensor of a heat exchanger according to the present invention. In the figure, an evaporator 2 which is a heat exchanger and a defrosting heater 3 which is a defrosting means are installed in a refrigerator main body 1. The fin sensor 4 is provided close to the cooling fin of the evaporator 2.

As shown in the schematic diagrams of the frost sensor of the heat exchanger according to the present invention in FIG. 2 and FIG. It is provided closely between the fins 7. This frost sensor 4
It is composed of a thermistor 8 which is a temperature sensing element and a heater 9 which is a heating means provided close to the thermistor 8.

The thermistor 8 of the temperature sensing element and the heater 9 of the heating means
is connected to a control means for controlling a defrosting heater 3 which is a defrosting means. This control means is constructed as shown in the circuit diagram of FIG. 4 which shows the control means for the box sensor of the heat exchanger according to the present invention. In the figure, the frost sensor 4 composed of a thermistor 8 and a heater 9 includes a resistor 10, a resistor 11,
It is connected to a plus terminal and a minus terminal of a comparator 13 via a resistor 12.

The oscillator 14 sends out an output having a period of, for example, 30 minutes and a width of 0.1 seconds, and this output is input to the input of the flip-flop 15. When the output of the oscillator 14 enters the input of the 7 lip-flop 15, the output Q of the 7-lip flop 15 passes through the resistor 16, turns on the transistor 17, and causes current to flow through the heater 9. At the same time, the output q of the 7-lip flop 15 passes through the inverter 18,
It enters one input of the ND gate 19. AND gate 19
The input to the other side of
The counter 21 is configured to count the output of the counter 20 when the AND gate 19 is opened.

Provided close to the heater 9 (at an interval of about 5 mm)
When the thermistor 8 is heated by the heater 9 and its resistance value decreases, the power supply voltage is divided by the thermistor 8, the resistor 10, and K, and is input to the negative terminal of the comparator 13, and the voltage decreases.

When this voltage becomes lower than the voltage that is input to the positive terminal of the comparator 13 by dividing the power supply voltage by the resistor 11 and the resistor 12, the output of the comparator 13 becomes Low and clears the flip-flop 15.

When flip 70 knob 15 is cleared, flip 70
The output Q of the cup 15 becomes HI, the AND gate 19 closes, and the counter 21 stops counting. The relationship between the count number counted by this counter 21 and the amount of frost is shown in the fifth figure.
This is shown in the characteristic diagram of count number vs. amount of frost in the figure.

Next, the operation of the frost sensor for a heat exchanger according to the present invention having the above configuration will be explained with reference to the operation flowchart of an embodiment of the frost sensor for a heat exchanger according to the present invention shown in FIG.

First, the resistance value of the thermistor 8 is detected before the heater 9 of the resistance sensor is energized (step 5o).

Thereafter, the heater 9 provided close to the thermistor 8 of the frost sensor 4 is energized (C step 52).

The power is supplied to the heater 9 for, for example, 5 seconds, and then the power to the heater 9 is cut off to stop heating the thermistor 8 (step 53). Detect and store the resistance value of the thermistor 8 at this time (step 54) (step 55)
. The resistance value of the thermistor 8 after being heated by the heater 9 stored in step 55 is compared with the resistance value of the thermistor 8 before heating stored in step 51 (step 56).
.

In addition, a threshold value X (a predetermined deviation value from the resistance value of the thermistor 8 before heating by the heating heater 9) is set and stored in advance as the division π level, and the heating value is compared with this threshold value X in step 56. The difference between the resistance value of the previous thermistor 8 and the resistance value of the thermistor 8 after being heated by the heater 9 is compared (step 57).

FIG. 7 is a time-thermistor resistance characteristic diagram of the frost sensor of the heat exchanger according to the present invention. As shown in the figure, the threshold value X is set to a predetermined resistance value from the resistance value of the thermistor 8 before the heater 9 is energized. Since the temperature of the thermistor 8 increases due to the heat from the heater 9, the low resistance value of the thermistor 8 decreases. Furthermore, when the heater 9 is energized during frost formation, the temperature of the thermistor 8' does not rise because heat is lost due to the melting of the frost that has adhered, so the resistance value of the thermistor 8 is high. Therefore, it is possible to energize the heater 9 for a certain period of time (for example, 5 seconds) and detect the rate and amount of change in the resistance value of the thermistor 8 at that time. A constant threshold value X is set for this difference in rate of change, and it is possible to compare whether the rate of change is larger or smaller than this threshold value X, and the presence or absence of frost formation can be detected.

In addition, by providing a plurality of frost sensors in combination with the heater 9 and thermistor 8, it is possible to detect differences in the frost formation state at the refrigerant inlet and refrigerant outlet of the evaporator 2, which is a heat exchanger, and the degree of melting during defrosting. Defects in detection can be eliminated. Therefore, the comparison with the threshold value X in step 57 is performed using the frost sensors 4 installed at several locations, and the one with a smaller change in resistance value than the threshold value It is determined whether the number is smaller or larger than the number N (step 58). When this result is less than the set number N, it is assumed that the amount of frost adhesion is small, and the defrosting heater 3 is not energized and the cooling operation is continued without performing the N removal operation (steps 59 and 60).

Then, in order to leave a certain interval until the next sensing (for example, 3 minutes), a timer is set (step 61), the timer is started (step 62), and the next sensing is performed.

If the comparison result in step 58 is greater than the set number N, it is determined that the amount of frost adhesion is large, and the defrosting heater 3 is energized to start defrosting operation (step 63). This communication to the defrosting heater 3 is controlled by the number counted by the counter 21 of the control means.

During the defrosting operation, sensing is repeated until the end of the defrosting operation, so the heater 9 of the frost sensor 4 is set and started (step 64). At the same time, a thermistor 8 is also set near the defrosting heater 3, the resistance value of this thermistor 8 is detected (step 65), the detected resistance value is memorized (step 66), and the thermistor 8 is again set after 5 seconds, for example. Step 67), step 6 to detect the resistance value of
The difference from the resistance value obtained in step 5 is taken (step 68) and compared with the threshold value X (step 57). Thereafter, steps 58 to 68 are repeated. When the data from the thermistor 8 of the frost sensor 4 attached to the evaporator 2 reaches the threshold value X, it is assumed that defrosting has ended, and the power to the defrost heater 3 is stopped and normal cooling operation is performed. , it is possible to perform accurate expulsion operations. Note that defrosting can normally be performed in about one hour when the defrosting heater 3 is energized.

〔Effect of the invention〕

According to the present invention, the temperature sensing element is provided in close proximity to the heat exchanger,
By installing a heating means in close proximity to this temperature sensing element, the heating means heats the temperature sensing element, and by comparing the rate of change in resistance value, it is possible to know the exact frosting state and start defrosting. , the termination can be precisely controlled.

Therefore, defrosting can be performed only when necessary, making it possible to maintain efficient cooling operation.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the inside of a refrigerator equipped with a frost sensor for a heat exchanger according to the present invention, Figures 2 and 3 are schematic diagrams showing a frost sensor for a heat exchanger according to the present invention, and Figure 4 is A circuit diagram showing the control means for the frost sensor of the heat exchanger according to the present invention, FIG. 5 is a characteristic diagram of the count number-box amount of the frost sensor according to the present invention, and FIG. 6 is a diagram showing the frost sensor control means according to the present invention. An operation flowchart showing an embodiment of the frost sensor, 81 yen 7 Figure is a time-thermistor resistance value characteristic diagram of the frost sensor of the heat exchanger according to the present invention,
FIG. 8 is a schematic diagram showing a conventional defrosting device, and FIG. 9 is a control circuit diagram relating to the conventional defrosting device. 1... Refrigerator body, 2... Evaporator, 3...
Defrosting heater, 4...Frost sensor, 7...Cooling fin, 8...Thermistor, 9...Heating heater. Agent Patent Attorney Nori Chika Ken Yudo Uji Hiroki 1 Figure 3rd 25th 092;'T Tsuji-Misku Resistance 8th/62 Sagi 9 Figure

Claims (3)

[Claims] (1) A temperature-sensitive element provided close to a heat exchanger, a heating means provided close to the temperature-sensitive element that heats the temperature-sensitive element, and a resistance value of the temperature-sensitive element detected; A frost sensor for a heat exchanger, comprising: a control means for controlling a defrosting means of the heat exchanger according to a detected amount. (2) The control means operates the defrosting means when the resistance value detected by the temperature sensing element is within a predetermined value, and the defrosting means when the resistance value detected by the temperature sensing element is greater than or equal to the predetermined value. The frost sensor for a heat exchanger according to claim 1, wherein the frost sensor stops the frost sensor. (3) Claim 1 characterized in that it has at least two or more sets of the temperature sensing element and the heating means, and at least one of the sets of the heating means is also used as a defrosting means. Frost sensor for the heat exchanger described.