Refrigeration – Automatic control – By accumulation on freezing surface – e.g. – ice
Patent
1998-06-12
2000-03-21
Tanner, Harry B.
Refrigeration
Automatic control
By accumulation on freezing surface, e.g., ice
62156, 62158, F25D 2102
Patent
active
060388722
DESCRIPTION:
BRIEF SUMMARY
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a frost detecting device used in various industrial machines and refrigerators.
2. Related Art
Frost on the surface of the cooling fan of a heat exchanger incorporated into a refrigerator reduces the cooling efficiency. A continuous operation with the frost uneconomically increases energy consumption, and often causes failure. In view of this, a frost detecting method generally used includes the steps of: switching on and off the compressor by detecting the inner temperature of a refrigerator; cooling for a predetermined period of time using a timer; after the cooling is performed for a predetermined period of time, switching to a heating operation to defrost; and, after the defrosting for a predetermined period of time, stopping the heating operation.
Although the start of defrosting can be controlled in the above method, the frosting condition cannot be controlled, because it changes depending on ambient temperature, humidity, frequency of opening the door, and the content of the refrigerator. Since the actual frosting condition cannot be detected by the above method, defrosting is performed even in non-frosting condition, or it is not performed in an over-frosting condition. This unnecessarily increases energy consumption.
In order to solve the problems in the conventional defrosting method, various frost detecting methods have been developed. However, they have many drawbacks in practical use, such as faulty operation and detection inaccuracy. FIG. 6 shows an example of a frost and dew detecting device produced for a freezer or refrigerator. Japanese Patent Application Laid-Open No. 2-115678 discloses such frost and dew detecting device.
The frost and dew detecting device is provided with a pair of thermal sensitive elements R1 and R2 adjacent to each other. Each thermal sensitive element has a current supply source. One of the thermal sensitive elements R1 and R2 is provided with an electric current source which generates heat in the air so as to cause a temperature rise, while the other thermal sensitive element is provided with a set electric current source which is not affected by the temperature rise. The thermal sensitive element that receives current from the electric current source is kept at a temperature higher than that of the other thermal sensitive element that receives current from the set electric current source.
If frost or dew forms on the pair of thermal sensitive elements that are kept at different temperatures, heat diffusion occurs through the frost or dew on the surface of the thermal sensitive element of the higher temperature, as the heat conductivity of a solid or liquid material is higher than that of air. The temperature of the thermal sensitive element is lowered due to the heat diffusion, and the temperature difference between the two thermal sensitive elements becomes smaller. The temperature difference is determined by an arithmetic circuit and compared with a predetermined reference value. If the determined temperature difference is smaller than the reference value, it is judged to be in a frosting and dewing condition.
PROBLEMS TO BE SOLVED BY THE INVENTION
The conventional frost and dew detecting device mounted to a refrigerator has drawbacks as follows. Generally, a refrigerator has a compressor and a cooling fan which operate at the same time in a cooling operation. FIG. 7A shows a frost and dew detecting device. The frost and dew detecting device 10 is a series circuit made up of thermal sensitive elements 10a and 10b. The output voltage Va of the series circuit is inputted into an amplifier circuit 11, whose output voltage V1 is inputted into a comparator circuit 12. A reference voltage Vr outputted from a level setting circuit 13 is inputted into the comparator circuit 12. As shown in FIG. 7B, the compressor repeats an on-off operation so that the inner temperature becomes constant through temperature detection by a temperature sensor disposed inside the refrigerat
REFERENCES:
patent: 4345441 (1982-08-01), Hansen
patent: 4373349 (1983-02-01), Mueller
patent: 4882908 (1989-11-01), White
patent: 5345775 (1994-09-01), Ridenour
patent: 5522232 (1996-06-01), Nojiri
patent: 5564286 (1996-10-01), Suse
Nojiri Toshiyuki
Saito Shin-ichi
Ishizuka Electronics Corporation
Tanner Harry B.
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