Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to refrigeration systems using different refrigerants that dissolve lubricant, and with compressors having a casting for storing oil delivered by a pump for lubrication of their bearings, and more specifically to a method for controlling compressor oil pressure in the systems where oil is returned to the compressor from the evaporator. 
     2. Background of the Prior Art 
     Oil is usually used to lubricate refrigeration compressors. The oil pressure of a compressor must be sufficient to support the minimal necessary amount of oil lubricant. If the oil pressure falls below a pressure necessary to support that minimal required amount of lubricant, the compressor can be damaged. That is why refrigeration systems have a special device to turn the compressor off when the pressure of the oil in the system reaches the minimum level. The oil from the compressor is evacuated with the refrigerant vapor. After the evaporation of the liquid refrigerant has taken place in the evaporator of the refrigeration system, the oil returns to the compressor either by refrigerant vapors or separately from the refrigerant. 
     In U.S. Pat. No. 3,978,685 by M. Taylor, issued Jul. 14, 1975, the oil returns to the compressor with the refrigerant vapors from the evaporator. In this case a certain amount of liquid refrigerant can enter the compressor along with the oil. This cannot be evaporated by the same method as in the evaporator. The oil pressure drops and a blocking device turns the compressor off. A certain amount of time and special preparations are required to restart the compressor again. 
     A similar situation is described in U.S. Pat. No. 4,631,926 by Goldstein, et. al., issued on Dec. 30, 1986, which states that when the oil carrying liquid refrigerant separates from the vapor, the refrigerant moves to the compressor through a special thermal exchange heater. A significant amount of the refrigerant returns with the oil to the compressor due to the existing inertia of the system, which supports a temperature level of the mixture of the oil and the refrigerant. It leads to the same disadvantages of the system as in U.S. Pat. No. 3,978,685. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a method of controlling the oil pressure in a compressor in order to allow it to work without interruption. This can be accomplished by the use of the following method. Practice shows that the oil pressure changes step-wise when the liquid refrigerant is accessing into the compressor. At the beginning, the pressure does not drop significantly and stays higher then the allowed minimum. As the liquid refrigerant continues to enter the compressor, the oil pressure drops significantly and reaches a critically low level. When the oil along with the liquid refrigerant is prevented from entering the compressor immediately after the first drop of pressure, the oil pressure will be elevated. The elevation in pressure is due to the extraction of the excess amount of liquid refrigerant from the oil in the compressor. Thereafter, the compressor can continue to work without interruption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1 illustrates a schematic representation of the unit in which oil together with the liquid refrigerant is returned to the compressor. 
     FIG. 2 illustrates a schematic representation of an alternative embodiment of the unit where oil is returned to the compressor together with refrigerant vapor. 
     FIG. 3 illustrates a schematic representation of an alternative embodiment of the unit where oil is returned to the compressor together with refrigerant vapor, with a controller placed on the line connected to a condenser and an evaporator. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 depicts a closed circuit system consisting of a compressor  1  with casting  1   a , suction line  8 , condenser  2 , evaporator  3 , suction accumulator  7  with inlet  5  connected to said evaporator  3  by line  4 , two outlets  6  and  9 , said outlet  6  connected to said compressor  1  by said suction line  8 , said outlet  9  connected to said casting  1   a  by oil return line  10 , and controller  11  placed on said oil return line  10  to adjust the oil-refrigerant mixture flow. Regulator  13  with set-point adjustment  14  is connected to said compressor  1  by line  15  and electrically connected to said controller  11  by line  12 . 
     Refrigerant vapor compressed in the compressor  1  enters the condenser  2  where it becomes a liquid and enters the evaporator  3  where it is boiled. The refrigerant vapor containing oil enters the suction accumulator  7  through line  4  and then through inlet  5 . The mixture is separated in said suction accumulator  7  into a vapor and a liquid part containing mainly oil and some liquid refrigerant. The mixture containing oil and liquid refrigerant is drawn to the compressor  1  from the suction accumulator  7  through outlet  9  by return line  10 . When the initial part of this mixture, containing an excess of liquid refrigerant, enters said casting  1   a  of said compressor  1 , the oil pressure in said compressor  1  immediately decreases to a level that is still above the minimum level allowed for the bearings (not shown) of said compressor  1  to work safely. Regulator  13  monitors the oil pressure value of the compressor  1  and compares this pressure value to that installed on set-point adjustment  14 . When this first reduction of oil pressure occurs, the controller  11  closes the line  10  and prevents the entrance of liquid oil-refrigerant mixture into the compressor  1 . In a short period of time liquid refrigerant in the compressor  1  evaporates, the oil pressure increases, the regulator  13  opens the controller  11 , and the oil continues to return to the compressor  1 . This system provides an uninterrupted safe operation of the compressor. 
     FIG. 2 depicts a closed circuit system consisting of compressor  1  with casting  1   a , suction line  16 , condenser  2 , evaporator  3  connected by said suction line  16  to said compressor  1  and to said condenser  2 , and controller  11  which is placed on said suction line  16 . Regulator  13  with set-point adjustment  14  is connected to said compressor  1  by line  15  and electrically connected to said controller  11  by line  12 . 
     Refrigerant vapor becomes compressed in the compressor  1  and enters the condenser  2  where it becomes a liquid and enters the evaporator  3  where it is boiled. The refrigerant vapor containing oil is drawn to the compressor  1  by suction line  16 . When the initial part of this mixture containing an excess of liquid refrigerant enters the casting  1   a  of said compressor  1 , and the oil pressure in said compressor  1  immediately decreases to a level that is still above the minimum level allowed for the bearings (not shown) of said compressor  1  to work safely. The regulator  13  monitors the oil pressure value of the compressor  1 , comparing this pressure value to the one established on set point adjuster  14 . Controller  11  closes the line  16  when the target pressure is reached. This prevents the entrance of liquid oil-refrigerant mixture into the compressor  1 . In a short period of time liquid refrigerant in the compressor  1  evaporates, the oil pressure increases, the regulator  13  opens the controller  11  and the oil continues to return to the compressor  1 . This system provides uninterrupted safe operation of the compressor. 
     FIG. 3 depicts a closed circuit system consisting of compressor  1  with casting  1   a , suction line  16 , condenser  2 , evaporator  3  connected by said suction line  16  to said compressor  1  and connected to said condenser  2  by line  17 , and controller  11  which is placed on said line  17 . Regulator  13  connected to said compressor  1  by line  15 , and electrically connected to said controller  11  by line  12 . 
     Refrigerant vapor compresses in the compressor  1  and enters the condenser  2  where it becomes a liquid and enters the evaporator  3  where it is boiled. The refrigerant vapor containing oil is drawn to the compressor  1  by suction line  16 . When the initial part of this mixture containing an excess of liquid refrigerant enters the casting  1   a  of said compressor  1 , the oil pressure in said compressor  1  immediately decreases to a level that is still above the minimum level allowed for the bearings (not shown) of said compressor  1  to work safely. The regulator  13  monitors the oil pressure value of the compressor  1 , comparing this pressure value to the one installed on the set-point adjuster  14 , and closes the line  17  by means of controller  11 . Controller  11  closes the line  16  when the target pressure is reached. This prevents the entrance of liquid oil-refrigerant mixture into the compressor  1 . In a short period of time liquid refrigerant in the compressor  1  evaporates, the oil pressure increases, the regulator  13  opens the controller  11 , and the oil continue to return to the compressor  1 . This system provides an uninterrupted safe operation of the compressor. 
     While this invention has been illustrated and described in accordance with the preferred embodiments, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.

Technology Category: 2