Overheat preventing method for prescribed displacement type compressor and apparatus for the same

An overheat preventing apparatus for a fixed displacement compressor comprising:

• a condensor of a refrigeration cycle;
• a connecting pipe for introducing a part of a high pressure coolant liquified in said condensor into a compression chamber for controlling a flow rate of the liquified coolant through said connecting pipe to thereby cool the compressor, said connecting pipe having a first end communicating with an outlet of the condensor and a second end communicating with the compression chamber at a position thereof wherein a pressure ratio of the gas to an evaporation pressure is in a range of 3.0 to 3.5;
• means for controlling the flow of the high pressure liquefied coolant through said connecting pipe in dependence upon a detected temperature of an evaporator;
• and
• a second connecting pipe in fluid communication with a higher pressure side of the compressor than said first mentioned connecting pipe,
• wherein said connecting pipes are controlled in accordance with a temperature of the evaporator, and
• wherein said second connecting pipe is in fluid communication in a low evaporation temperature region within the operational pressure range, while said first-mentioned connecting pipe is in fluid communication in a high evaporation temperature region within the operational pressure range.

A method for preventing an overheating of a fixed displacement type compressor, the compressor including a compressor overheat preventing means including a connecting pipe for introducing a part of high pressure liquified coolant, liquified in a condenser of a refrigeration cycle, into a compression chamber maintained under a compression stroke of the compressor and for controlling a flow rate of the liquified coolant flowing through the connecting pipe to cool the compressor at a level of an operational pressure value not less than 3.5, the method comprising the steps of:

• providing a electromagnetic valve within said connecting pipe;
• communicating said connecting pipe with an interior of the compression chamber of the compressor at a position thereof wherein a pressure in the compression chamber is always less than a condensing pressure in an operational range of the refrigeration cycle;
• detecting a temperature of discharged gas from the compressor by a thermostat mounted on the compressor;
• and
• controlling said electromagnetic valve according to the detected temperature so as to maintain the temperature of discharge gas lower than a predetermined temperature of 110.degree. C.