Abstract:
A portion of the condensed liquid in a condenser is diverted to a generator where it supplies heat to boil off refrigerant from a refrigerant oil mixture and is thereby subcooled. The subcooled liquid is supplied to the motor for cooling. The boiling off of refrigerant in the generator results in an “oil rich” liquid which is supplied to the bearings, etc. for lubrication. One, or more, jet or ejector pumps are preferably used to supply the oil rich liquid to the lubrication distribution system.

Description:
BACKGROUND OF THE INVENTION 
     In closed refrigeration and air conditioning systems, the refrigerant and lubricant are normally in contact. Because there is an affinity between lubricants and refrigerants, they are present in refrigeration and air conditioning systems as a mixture of varying composition. The composition will depend upon many factors such as the temperature, whether the system is running or not, whether oil is separated by flow through an oil separator or circuitous path, whether the refrigerant undergoes a phase change, etc. The lubricant in the refrigerant tends to coat the surfaces of the system and deteriorates the heat transfer properties of the system. The refrigerant not only dilutes the lubricant, but is subject to outgassing which results from a pressure reduction and produces a froth which can interfere with lubrication. 
     SUMMARY OF THE INVENTION 
     A small heat exchanger is preferably located below the cooler or evaporator of a closed refrigeration or air conditioning system and defines an oil rich generator or still. Alternatively, the still may be located at a higher level but would require a pump, or the like. The oil rich generator takes mixed liquid made up of refrigerant and oil from the cooler. A portion of the relatively warm liquid from the condenser is diverted into the generator vessel. In flowing through the tubes in the generator vessel, heat is given up by the flow from the condenser causing the refrigerant in the generator vessel to boil. Alternatively, a supplemental heat source such as electric resistance heat may be used. The resulting refrigerant vapor is vented from the vessel and flows to the compressor suction due to the pressure differential between the compressor suction and the cooler. The boiling off of refrigerant results in an “oil rich” liquid. The oil rich liquid is supplied to the lubrication system via one, or more, ejectors which cause the oil rich liquid to be entrained in high pressure gas diverted from the compressor. The pressure driving the ejectors is, preferably, the higher of the discharge pressure or the last closed lobe rotor pressure. 
     In passing through the generator, the refrigerant flow from the condenser is subcooled. This relatively high pressure, subcooled flow is supplied to the motor for cooling. In cooling the motor, the subcooled flow is heated and expanded and is subsequently supplied to the suction flow to the compressor. 
     It is an object of this invention to generate an oil rich fluid to lubricate screw compressor bearings. 
     It is an additional object of this invention to provide separate lubrication circuits for the rotors and bearings of a screw compressor. 
     It is another object of this invention to reduce the refrigerant content of an oil-refrigerant mixture. 
     It is an object of this invention to eliminate the complexity of typical oil separation systems thereby lowering the cost and improving the system reliability. 
     It is a further object of this invention to generate subcooled liquid for motor cooling. These objects, and others as will become apparent hereinafter, are accomplished by the present invention. 
     Basically, supplemental heat or a portion of the condensed liquid in a condenser is diverted to a generator or still where it supplies heat to boil off refrigerant from a refrigerant oil mixture and is thereby subcooled. The subcooled liquid is supplied to the motor for cooling. The boiling off of refrigerant in the generator results in an “oil rich” liquid which is supplied to the bearings for lubrication. One, or more, jet or ejector pumps are preferably used to supply the oil rich liquid to the lubrication distribution system for lubricating the bearings. Preferably, an oil rich zone in the cooler supplies lubricant for lubrication and/or sealing of the rotors via a second lubrication distribution system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a schematic diagram of a closed refrigeration or air conditioning system employing the present invention; 
     FIG. 2 is a more detailed schematic diagram of the FIG. 1 system; 
     FIG. 3 is a partially cutaway sectional view of a screw rotor showing a portion of the lubricant path; 
     FIG. 4 is a schematic diagram of a modified lubrication system; and 
     FIG. 5 is a schematic diagram of a portion of the lubrication flow path of the FIG. 4 system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, the numeral  10  generally designates a closed refrigeration or air conditioning system. As is conventional, there is a closed circuit serially including compressor  12 , discharge line  14  connected to the discharge port, condenser  16 , line  18  which contains expansion device  20 , cooler or evaporator  22  and suction line  24  leading to the suction port. Compressor  12  is a multi-rotor, hermetic, screw compressor and is driven by electric motor  26  which is connected to a source of electric power (not illustrated). As is best shown in FIGS. 2 and 5, screw compressor  12  has a plurality of intermeshing rotors with three rotors  121 ,  131  and  141  being illustrated. Referring specifically to FIG. 3, rotor  121  has end shafts  1211  and  121 - 2  and an axial bore  121 - 3  extending the full length of rotor  121  and shafts  121 - 1  and  121 - 2 . End shafts  121 - 1  and  121 - 2  are connected to rotor  121  through intermediate shafts  121 - 1   a  and  121 - 2   a,  respectively. Intermediate shafts  121 - 1   a  and  121 - 2   a  are in a tight clearance relationship with labyrinth seals  122  and  123 . Labyrinth seal  122  seals rotor bore  12 - 1  from bearing chamber  12 - 2 . Similarly, labyrinth seal  123  seals rotor bore  12 - 1  from bearing chamber  12 - 3 . Shaft  121 - 1  is supported in bearing chamber  12 - 2  by a plurality of bearings  124 - 1 ,  124 - 2  and  124 - 3 . Similarly, shaft  121 - 2  is supported in bearing chamber  12 - 3  by bearing  125 - 1 . 
     Rotor  121 , as illustrated in FIG. 3, and described above, is representative of rotors  131  and  141  relative to bearing support and lubrication. The only differences would be that there are both male and female rotors and that one rotor would be driven by motor  26  and would, in turn, drive the other rotors. In gears the driving gear is the “sun” and the driven gears are the “planets”. The rotors can be driven through gears rather than directly through the rotors. 
     Referring again to FIG. 1, according to the teachings of the present invention, a portion of the relatively warm liquid in condenser  16  passes via line  30  to generator vessel or still  32 . Preferably, generator vessel or still  32  is located below or at a lower level than cooler  22 . If necessary, or desirable, generator vessel or still  32  can be located at a higher level but would require pumping to supply the still. The liquid from condenser  16  supplied via line  30  passes through a plurality of tubes  34  in a heat exchange relationship with the refrigerant-oil mixed liquid which flows into generator vessel  32  from cooler  22  via line  36 . After passing through the tubes  34 , the flow is supplied via line  35  to motor  26  for cooling motor  26  and subsequently combines with the suction gas supplied via line  24 . The diverted flow from the condenser  16  gives off heat to the refrigerant-oil mixture in generator  32  causing the refrigerant to boil while the flow from the condenser  16  is cooled. The vapor resulting from the boiling of refrigerant is vented out of generator vessel  32  via line  38  which connects to the compressor suction line  24  and flows into the compressor suction due to the pressure differential between the compressor suction and cooler  22 . 
     Due to the boiling off of refrigerant, an oil rich liquid  40  is produced in generator vessel  32 . The oil rich liquid  40  is supplied via line  42  to ejector  44 . A portion of the compressor discharge or last closed lobe rotor fluid is diverted to ejector  44  via line  46  and entrains oil rich liquid from generator  32  and carries it into line  48  which may contain one or more filters  50 . Line  48  branches into a plurality of lines. Lines  48 - 1 ,  48 - 2  and  48 - 3 , respectively, are connected to the upper portion of the bearing housings, as best shown in FIG. 3 with respect to line  48 - 1 , and feed the bearing chambers  12 - 2 ,  12 - 2   a  and  12 - 2   b  located on the discharge or high pressure side of compressor  12 . 
     Referring specifically to FIG. 3 as typical of the supplying of lubrication to bearing chambers  12 - 2 ,  12 - 2   a  and  12 - 2   b,  it will be noted that branch  48 - 1  connects with the top of bearing chamber  12 - 2 . The lubricant supplied via branch  48 - 1  flows through and over bearings  124 - 1 ,  124 - 2  and  124 - 3  thereby lubricating them. The oil and gaseous refrigerant in bearing chamber  12 - 2  flows into and through axial bore  121 - 3  in rotor  121  and flows into bearing chamber  12 - 3 . The oil flowing into bearing chamber  12 - 3  flows over and through bearing  125 - 1  before passing into branch line  60 - 1  which connects with line  60  and, ultimately, still  32 . Similarly, oil passes from bearing chambers  12 - 3   a  and  12 - 3   b  via branch lines  60 - 2  and  60 - 3 , respectively, into line  60 . Line  60  connects with second ejector  144  and a portion of the compressor discharge or last closed lobe rotor fluid is diverted to ejector  144  via line  146  and entrains oil drawn from cavities  12 - 3 ,  12 - 3   a  and  12 - 3   b  and, preferably, returns the oil to still  32 . If necessary, or desired, the oil can be carried into cooler  22  instead of still  32 . 
     FIG. 2 adds to the illustrated structure of FIG. 1 the feeding of the higher of discharge and last closed lobe rotor pressure to ejectors  44  and  144  as the motive fluid. Line  46  which feeds ejector  44  is feed from one of two branch lines  46 - 1  and  46 - 2 , containing check valves  46 - 1   a  and  46 - 2   a,  respectively. Line  46 - 1   a  supplies compressor discharge pressure to ejector  44  and line  46 - 2   a  supplies the last closed lobe pressure to ejector  44  with the higher of the two pressures being supplied to the ejector  44 . The oil return path  148  is to still  32 . 
     System  110  of FIGS. 4 and 5 differs from system  10  of FIGS. 1 and 2 by adding the supplying of lubricant for lubricating and/or sealing the rotors being drawn from cooler  22  via line  122  and supplied to a third ejector  244 . Specifically, line  246  branches off of line  46  and supplies the higher of discharge pressure and last closed lobe rotor pressure to ejector  244  causing oil in a refrigerant oil mixture to be drawn from cooler  22  via line  122  and to be supplied via line  248 - 1  to compressor  12  for lubricating rotors  121 ,  131  and  141 . FIG. 5 provides a more detailed view of the rotor lubrication path. This embodiment takes advantage of the fact that the rotors  121 ,  131  and  141  do not require the oil rich mixture that is required by the bearings since its major function is sealing rather than lubrication. Advantage is also taken of the fact that an oil rich zone tends to form in cooler  22  such that the fluid connection of line  122  to cooler  22  can be located so as to withdraw oil from this zone. Additionally, the use of three ejectors reduces the demand placed on them. Referring specifically to FIG. 5 it will be noted that line  248 - 1  divides into line  248 - 2  which lubricates rotors  121  and  131  and line  248 - 3  which lubricates rotors  131  and  141 . As noted, branch lines  60 - 1 ,  60 - 2  and  60 - 3  lead from the upper portion of the bearing chambers  12 - 3 ,  12 - 3   a  and  12 - 3   b  on the suction or low pressure side of the compressor  12  and combine in line  60  which returns the oil to still  32 . 
     Although preferred embodiments of the present invention have been illustrated and described, other changes will occur to those skilled in the art. It is therefore intended that the scope of the present invention is to be limited only by the scope of the appended claims.