JPS60200070A - Detector for frost - 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 Field of the Invention The present invention relates to a frost detection device for optically detecting frost adhering to an evaporator of an electric refrigerator or the like.

Structure of conventional example and its problems A conventional frost detection device of this type (K) is as shown in Fig. 1, with a light emitting element (A) and a light receiving element (■) facing each other and mounted on a substrate with a predetermined spacing between them. )), and this is housed in a case (e) that transmits the emission wavelength of the light emitting element (a), and sealed with mold resin (ii). In addition, the electric circuit includes a light emitting element (A) and a light receiving element (T) as shown in Figure 2.
Connect current-limiting resistors (1) and (a) in series with each, and connect both ends to a DC power supply (2), and create a light-receiving element (series resistance of two) that changes depending on the amount of frost on the evaporator. The terminal voltage of is set as the frost detection device output v0.

Then, as shown in Fig. 3, the frost detection device output ■. When voltage decreases due to frost formation and reaches a predetermined voltage v1, the defrosting heater is energized to perform defrosting operation, and the frost disappears and the frost detection device outputs ■.

When the voltage returns to the original voltage v2, the defrosting operation is terminated and the cooling operation is restarted.

Therefore, there were the following drawbacks.

1 The detection sensitivity of a frost detection device must be highly sensitive regardless of the ambient temperature, as it is necessary to accurately detect frost thickness.
Therefore, the detection sensitivity is high even immediately after defrosting when the ambient temperature is high, and even if defrosted water droplets block the optical axis, they tend to detect this and malfunction. Therefore, there was a risk that the food would be put into the defrosting operation again and the temperature inside the refrigerator would rise, reducing the freshness of the food.

2 The end of defrosting is detected when the amount of light between the elements is no longer blocked by frost, so even if the frost detection device is installed in the position of the evaporator where frost is most likely to remain, there will be no variation in the heat generated by the defrost heater or Due to frost distribution, etc., boxes tend to remain in some areas, and there is a risk that excessive frost formation caused by residual frost may lead to a decrease in cooling efficiency or freezing of the fan inside the refrigerator. . One way to deal with this is to install a separate temperature detector such as a thermostat and detect the end of defrosting based on the temperature rise in the vicinity of the evaporator as the frost melts, but this increases the number of parts and increases costs.

Purpose of the Invention Therefore, the present invention aims to reduce the detection sensitivity only when the ambient temperature is high to eliminate false detection after defrosting, and to provide a reliable defrosting system that can perform complete defrosting operation without any frost residue at low cost. Aims to provide a high frost detection device.

Structure of the Invention In order to achieve this object, the present invention provides a temperature-sensitive resistance element whose resistance value changes depending on the ambient temperature inside the frost detection device.
In the cooling mode that detects frost formation, this temperature-sensitive resistance element is connected in parallel or series with either the light-emitting element or the light-receiving element, and the detection sensitivity is reduced only when the ambient temperature is high. On the other hand, in the defrosting mode for detecting the completion of defrosting, the temperature-sensitive resistance element detects the rise in ambient temperature upon completion of defrosting, thereby preventing residual frost.

DESCRIPTION OF THE EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 4 schematically shows a refrigerating machine such as a refrigerator, and 1 is an evaporator of the cooling cycle. In the evaporator 1, 2 is a pipe through which a refrigerant passes, 3 is a fin plate disposed orthogonally to this pipe, and 4 is an end plate located on both sides of the fin plate. Reference numeral 6 indicates a frost detection device composed of a light emitting element and a light receiving element, and 6 indicates an internal fan of the chamber in which the evaporator 1 is installed. The frost detection device 6 will be explained in further detail with reference to FIGS. 7 is a light emitting element, and 8 is a light receiving element. Both terminals of each are soldered to a substrate 9 and housed in a case 10 made of a material that transmits the emission wavelength range of the light emitting element 7. A temperature-sensitive resistance element 11 with positive temperature characteristics is added on the substrate 9 in series with the light-receiving element 8, and after the substrate 9 is attached to the case 10, it is sealed with a molding resin 12. 13 is a conducting wire.

Next, an electric circuit of a refrigerator to which the frost detection device 6 is applied will be explained with reference to FIG. Reference numeral 14 denotes a commercial AC power source, and 16 indicates an internal temperature regulator which opens when the internal temperature falls below a predetermined temperature.

Reference numeral 16 denotes a two-pole, double-throw relay that is switched by a signal from a defogging control circuit 17, which will be described later.A heater 18 for defrosting the evaporator is connected in series to the normally open contact 16a of the first pole. A compressor 19 is connected in series to the normally closed terminal 16b.

Next, the defrosting control circuit 17 will be described. 2Q is a power transformer, 21 is a rectifying diode, 22 is a smoothing capacitor, and 23 is a constant voltage diode, forming a DC constant voltage circuit. 16C is a normally closed contact of the second pole of the above-mentioned two-pole double-throw relay, to which the frost detection device 6 is connected in series, a current limiting resistor 24 is connected in series to the light emitting element 7, It is connected to the DC constant voltage circuit together with a series circuit of the light receiving element 8 and the temperature sensitive resistance element 11. 16d is a normally open contact of the second pole of the above-mentioned two-pole double-throw relay, and the voltage dividing resistor 26 with the temperature-sensitive resistance element 11 is connected in series. 2
6 is a comparator that compares the terminal voltage 26a of the temperature-sensitive resistance element 11 in the frost detection device 6 with a reference voltage 28b determined by the resistor 27.28; , a transistor that drives the two-pole double-throw relay 16.

The operation in the above configuration will be explained. As frost builds up on the evaporator 1, the amount of light received by the light-receiving element 8 decreases, and as a result, the terminal voltage 26a of the temperature-sensitive resistance element 11 decreases, and when it falls below the reference voltage 26b of the comparator 26, the comparator 26 A defrosting start signal (H level) is output, transistor 29 is turned on, and two-pole, double-throw relay 16 is closed. At this time, when the ambient temperature of the frost detection device 6 after defrosting operation is high, the resistance value of the temperature-sensitive element 11 is high and the current of the light-receiving element 8 is small, so the sensitivity is low; The resistance value is low, the current of the light receiving element 8 is large, and the sensitivity is high.

Next, when the two-pole double-throw relay 1e is closed, the first pole normally closed contact 16b opens, the normally open contact 16a closes, and the commercial power supply 1
The compressor 19 is disconnected from the compressor 4 to stop the cooling operation, and the evaporator defrosting heater 18 is connected to the power source. At the same time, the second pole normally closed contact 16C+ opens and the normally open contact 16d closes, disconnecting the frost detection device 6 from the DC constant voltage circuit, and connecting the series constant voltage circuit to the series circuit of the temperature sensitive resistance element 11 and its voltage dividing resistor 26. Connecting.

Then, the temperature of the evaporator 1 rises, and as a result, the resistance value of the temperature-sensitive resistance element 11 rises, and its terminal voltage 26a rises.
When the voltage exceeds the reference voltage 26b of the comparator 26, the comparator 26 outputs a termination signal (L level), the transistor 29 is cut off, and the two-pole double-throw relay 16 is opened. That is, the normally closed contacts 16b of the first pole and the second pole,
16c is closed, the compressor 19 is energized, and the frost detection device 6 is energized to enter cooling operation.

Therefore, immediately after defrosting when the ambient temperature is high, the frost detection device 6
The detection sensitivity is low due to the function of the built-in temperature-sensitive resistance element 11.
Even if defrosted water droplets block the optical axis, high detection reliability can be obtained regardless of whether they are detected, while the sensitivity is automatically increased when the evaporator 1 is at a low temperature where frosting is progressing, ensuring reliable defrosting. You can get the action.

Furthermore, regarding the completion of defrosting, the state of defrosting can be detected by the rise in evaporator temperature using the temperature-sensitive resistance element 11 without using any separate parts, so that the defrosting can be completed reliably at low cost.

Further, in the illustrated embodiment, a temperature-sensitive resistance element is connected in series with the light-receiving element 8, but the present invention is not limited to this, and a resistance element connected to the light-emitting element side may be connected in series, or a resistance element having opposite characteristics may be connected in series. If a temperature-sensitive resistance element is used, the same effect can be obtained even when connected in parallel.

Effects of the Invention As is clear from the above description, the present invention comprises a light-emitting element and a light-receiving element that are arranged opposite to each other at a predetermined interval and that detect frost based on changes in the amount of transmitted light between them, and a case that houses these elements. , This case is equipped with a temperature-sensitive resistance element for detecting the end of defrosting that changes its resistance value according to the ambient temperature, and this temperature-sensitive resistance element is connected in series or parallel with the light emitting element or light receiving element to determine the evaporator temperature. The sensitivity can be adjusted as a frost detection device, and when the evaporator temperature is high, such as immediately after defrosting, the sensitivity is automatically lowered to 9, and even if removed water droplets block the optical axis, it will be detected. While high detection reliability is obtained without any damage, the sensitivity is automatically increased when the evaporator is at a low temperature where frosting is progressing, ensuring reliable defrosting operation. On the other hand, regarding the end of defrosting, the defrosting state can be detected based on the rise in evaporator temperature without using any separate parts, so defrosting can be completed reliably at low cost, and the practical effect is extremely great.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional frost detection device, Fig. 2 is an electric circuit diagram of the same device, Fig. 3 is an operation time chart of the device, and Fig. 4 is frost detection in an embodiment of the present invention. Figure 5 is a plan view of the evaporator with the device, and Figure 6 is a cross-sectional view of the same device.
The figure is an internal perspective view of the device, FIG. 7 is an electric circuit diagram of an electric refrigerator to which the device is applied, and FIG. 8 is an operating time chart of the device. 7... Light emitting element,
8... Light receiving element, 10... Case, 1
1... Temperature-sensitive resistance element. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] A light-emitting element and a light-receiving element that face each other at a predetermined interval and detect frost by changes in the amount of transmitted light between them, a case that houses these elements, and a resistance value inside this case that changes according to the ambient temperature. A frost detection device comprising a temperature-sensitive resistance element for detecting the end of defrosting, and the temperature-sensitive resistance element is connected in series or parallel with the light emitting element or the light receiving element.