Abstract:
The entire discharge flow in a high side, vertical, hermetic rotary compressor is directed into the oil sump which generates foam for sound attenuation and heats the oil to reduce its viscosity and to drive off refrigerant dissolved in the oil.

Description:
BACKGROUND OF THE INVENTION 
     Commonly assigned U.S. Pat. Nos., 4.900,234; 4,907,414 and 5,077,981 each disclose a low side hermetic compressor in which a portion of the discharge of the compressor is bled into the oil sump. The high pressure gas being bled into the oil sump represents a loss but, because the interior of the compressor shell and the oil sump are at suction pressure, the foam generated by the high pressure gas expanding to suction pressure in the oil provides sound attenuation. 
     Discharge gas pulsation in the shell cavity beneath the motor in a high side vertical, hermetic rotary compressor has been found to be one of the major noise sources. In current compressor designs, the compressed gas discharges from the pump structure into the muffler cavity and then passes into the lower shell cavity. The discharge gas passes from the lower shell cavity to the discharge at the top of the compressor shell by passing through the gap between the rotor and stator and/or passing through passages between the stator and the compressor shell. 
     SUMMARY OF THE INVENTION 
     According to the teachings of the present invention the discharge gas in a high side rotary compressor passes from the pump structure into the muffler cavity and then passes via tubes into the oil sump located beneath the pump structure. Discharging the hot high pressure gas into the oil sump heats the oil and thereby reduces its viscosity. Additionally, the discharging of the high pressure gas into the oil sump, which is also at discharge pressure, generates foam roughly in the volume of the gas discharged from the pump structure. The foam will pass from the oil sump, through the pump structure to the upper part of the lower shell cavity, i.e. the part below the motor. Any foam entering the gap between the rotor and stator will tend to be collapsed and the oil will tend to be centrifugally separated such that it collects on the stator and drains due to gravity. 
     It is an object of this invention to reduce rotary compressor noise due to discharge gas pulsation. 
     It is another object of this invention to provide additional attenuation without reducing efficiency. 
     It is a further object of this invention to improve oil lubrication capability by increasing oil temperature in the sump. These objects, and others as will become apparent hereinafter, are accomplished by the present invention. 
     Basically, the entire discharge flow in a high side, vertical, hermetic rotary compressor is directed into the oil sump which generates foam for sound attenuation and heats the oil to reduce its viscosity and to drive off refrigerant dissolved in the oil. 
    
    
     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 partially sectioned view of a compressor employing the present invention schematically located in a refrigeration circuit; 
     FIG. 2 is a sectional view taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a partially cutaway view of the discharge muffler of the present invention; 
     FIG. 5 is an enlarged view of a portion of FIG. 1; and 
     FIG. 6 is a sectional view taken along line  6 — 6  of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIGS. 1-3 and  5 , the numeral  10  generally designates a vertical, high side, rolling piston compressor. Compressor  10  is in a refrigeration circuit serially including compressor  10 , discharge line  60 , condenser  70 , expansion valve  80  and evaporator  90 . The numeral  12  generally designates the shell or casing. Suction tube  16  is sealed to shell  12  and provides fluid communication between suction accumulator  14 , which is connected to evaporator  90 , and suction chamber S. Cylinder  20 , piston  22 , pump end bearing  24 , motor end bearing  28  and vane  30  collectively make up the pump structure. Suction chamber S and compression chamber C are defined by bore  20 - 1  in cylinder  20 , piston  22 , bearings  24  and  28 , and vane  30  which separates suction chamber S and compression chamber C. 
     Eccentric shaft  40  includes a portion  40 - 1  supportingly received in bore  24 - 1  of pump end bearing  24 , eccentric  40 - 2  which is received in bore  22 - 1  of piston  22 , and portion  40 - 3  supportingly received in bore  28 - 1  of motor end bearing  28 . Oil pick up tube  34  extends into sump  36  from a bore in portion  40 - 1 . Stator  42  is secured to shell  12  by a shrink fit, welding or any other suitable means. Commonly there will be passages in the form of slots or grooves  42 - 2  in the outer surface of the stator  42  running its entire length to provide flow paths for refrigerant gas across the motor defined by stator  42  and rotor  44  and for the return flow of oil to oil sump  36 . Rotor  44  is suitably secured to shaft  40 , as by shrink fit, and is located within bore  42 - 1  of stator  42  in a spaced relationship and coacts therewith to define a variable speed motor. Vane  30  is biased into contact with piston  22  by spring  31 . 
     Discharge port  28 - 2  in motor end bearing  28  is overlain by normally closed valve  29 . Valve  29  is within and opens into muffler  32 . As described so far, compressor  10  is generally conventional. The present invention differs in the details of muffler  32  and the resultant differences in operation of compressor  10 . Referring specifically to FIGS. 3 and 4 it will be evident that muffler  32  differs from conventional mufflers in that it has two downwardly directed discharge tubes  32 - 1  and  32 - 2  which are blocked at their ends and which have a plurality of ports  32 - 1   a  and  32 - 2   a , respectively, which are each located within the portion of the 180° perimeter of tubes  32 - 1  and  32 - 2  which is not directed towards the other one of discharge tubes  32 - 1  and  32 - 2  or pick up tube  34 . The reason for these locations of ports  32 - 1   a  and  32 - 2   a  is to avoid discharging gas towards oil pick up tube  34 . Referring specifically to FIG. 3, it will be noted that discharge tubes  32 - 1  and  32 - 2  extend into oil sump  36  and that all of ports  32 - 1   a  and  32 - 2   a  are located above the intake of oil pick up tube  34 . This is to prevent the generation of foam from uncovering oil pick up tube  34  and thereby interfering with compressor lubrication. 
     Although two discharge tubes  32 - 1  and  32 - 2  are illustrated with each having a plurality of ports  32 - 1   a  and  32 - 2   a , respectively, one discharge tube and any convenient number of ports may be employed. The critical consideration is to avoid unnecessary restrictions. Accordingly, the discharge tubes should have a combined cross section at least equal to that of discharge port  28 - 2  and the ports  32 - 1   a  and  32 - 2   a  should be at least 0.25 inches in diameter and have a total cross sectional area on the order of 1.2 to 1.5 times the area of discharge port  28 - 2 . 
     As best shown in FIGS. 1,  5  and  6 , an oil separator  50  is suitably secured to the top of the interior of shell  12  in a surrounding relationship to discharge line  60 . Referring specifically to FIGS. 5 and 6, oil separator  50  includes: (1) a flat portion  50 - 1  facing rotor  44  and having a plurality of ports  50 - 1  a for oil drainage; (2) an inner annular wall member  50 - 2  having a plurality of ports  50 - 2   a  and being welded or otherwise suitably secured to the interior of shell  12 ; and, (3) outer annular wall member  50 - 3  having a plurality of ports  50 - 3   a  and being spaced from the interior of shell  12 . 
     Initially, compressor  10  will be charged with oil up to, or a little above, the top surface of motor end bearing  28 . During operation of compressor  10 , some oil will be carried off to the refrigeration circuit due to the affinity between oil and refrigerant. The generation of foam by the discharge gas will temporarily remove oil from the sump as the foam moves into the space above motor end bearing  28 . Foam will be continuously generated, collapsed and drained back into sump  36  but the oil level will drop due to the removal of oil as foam. To prevent the excess loss of oil due to foam generation, ports  32 - 1   a  and  32 - 2   a  must be located above the inlet of oil pick up tube  34  by a minimum of a quarter of an inch. If the level of oil in sump  36  drops below ports  32 - 1   a  and  32 - 2   a , no foam is generated and compressor  10  will be noisier but will operate without problems as long as the oil is able to circulate for compressor lubrication. 
     In operation, rotor  44  and eccentric shaft  40  rotate as a unit and eccentric  40 - 2  causes movement of piston  22 . Oil from sump  36  is drawn through oil pick up tube  34  into bore  40 - 4  which acts as a centrifugal pump. The pumping action will be dependent upon the rotational speed of shaft  40 . As best shown in FIG. 2, oil delivered to bore  40 - 4  is able to flow into a series of radially extending passages, in portion  40 - 1 , eccentric  40 - 2 , and portion  40 - 3  exemplified by passage  40 - 5  in eccentric  40 - 2 , to lubricate bearing  24 , piston  22 , and bearing  28 , respectively. The excess oil flows from bore  40 - 4  and either passes downwardly over the rotor  44  and stator  42  to the sump  36  or is carried by the gas flowing from the annular gap between rotor  44  and stator bore  42 - 1  and impinges and collects on the inside of cover  12 - 1  or oil separator  50  before draining to sump  36 . 
     Piston  22  coacts with vane  30  in a conventional manner such that refrigerant gas is drawn through suction tube  16  and passageway  20 - 2  to suction chamber S. The gas in suction chamber S is compressed after suction chamber S has been cut off from suction tube  16  and has been transformed into a compression chamber C while a new suction chamber is being formed. The hot compressed gas in compression chamber C passes through discharge port  28 - 2  unseating discharge valve  29  and enters into the interior of muffler  32 . The compressed gas divides in muffler  32  with part flowing into tube  32 - 1  and out ports  32 - 1   a  and part flowing into tube  32 - 2  and out ports  32 - 2   a . The gas, at discharge pressure, passing from muffler  32  via ports  32 - 1   a  and  32 - 2   a  enters oil sump  36  which is also at discharge pressure. Depending upon the oil level in sump  36  and the location of ports  32 - 1   a  and  32 - 2   a  relative to the oil in sump  36 , foam may or may not be generated. The passing of the hot discharge gas into oil sump  36  increases the temperature of the oil in sump  36  and tends to generate foam. Under certain operating conditions, such as those encountered in heat pump operation, the solubility of the refrigerant in the oil could be very high due to low ambient temperature. In such a case, the oil lubrication capability may be compromised but refrigerant solubility will be significantly reduced due to the heating of the oil thereby improving its lubricating effectiveness. Additionally, the discharge of the gas into the oil sump  36  produces a foam which has a greater volume than the oil forming the foam and so tends to flow through the passages defined by recessed portions  20 - 3  and  20 - 4  and the interior of shell  12 , as best shown in FIG.  2 . There will be a tendency for the lower shell, i.e. the portion of shell  12  below rotor  44  and stator  42  to fill with foam. Because the gas/liquid impedance is ineffective for sound transmission and because there is no direct path for sound to travel, the compressor  10  is quieter than conventional compressors. If ports  32 - 1   a  and  32 - 2   a  are located above the surface of the oil in sump  36 , no foam will be generated but the oil will be heated by the hot discharge gas thereby improving the lubricating effectiveness of the oil. 
     If excessive oil passes from compressor  10  with the discharge gas it can interfere with heat transfer in the refrigeration system and can leave an inadequate amount of oil in oil sump  36  for proper lubrication. The presence of foam greatly increases the amount of oil present with the discharge gas. The discharge gas must however go past the motor and this can only be done by passing through the clearance between rotor  44  and stator bore  42 - 1  or by passing through the slots or grooves  42 - 2  in the outer surface of stator  42 . Because the clearance between rotor  44  and stator bore  42 - 1  is small and because the relative movement of rotor  44  with respect to stator  42  results in a shearing force on any foam bubbles entering the clearance, the foam tends to collapse in passing between the rotor  44  and stator  42 . Additionally, the relative rotation of rotor  44  with respect to stator  42  tends to cause the discharge gas to move in a spiral path that tends to centrifugally remove oil from the gas. The swirling flow tends to persist into the space between rotor  44  and discharge line  60 . Oil separator  50  tends to collect oil and prevents its being entrained with the gas passing from compressor  10  through discharge line  60  to the condenser  70  of the refrigeration circuit. Specifically, refrigerant, oil and any remaining foam passing between rotor  44  and stator  42  tends to be moving in a spiral path which tend to move any oil outward. The refrigerant and any entrained oil will flow either through ports  50 - 3   a  or between wall member  50 - 3  and the interior of shell  12  before passing through ports  50 - 2   a  and the changes in flow direction will tend to separate out entrained oil which will drain through drainage ports  50 - 1   a . The refrigerant and any entrained oil passing through ports  50 - 2   a  will undergo a change in flow direction prior to flowing into discharge line  60  which will tend to separate out entrained oil which will drain through drainage ports  50 - 1   a . The oil draining through drainage ports  50 - 1   a  will tend to fall into the swirling flow passing between rotor  44  and stator  42  and will thereby be directed towards the interior of casing  12 . While discharge gas may flow past stator  42  via grooves  42 - 2 , it is more likely to be the location of return oil flow to sump  36  given the fact that there is no pressure gradient so that gravity flow of the oil will take place and because of the centrifugal effect on oil in the gap between rotor  44  and stator bore  42 - 1 . 
     Although the present invention has been illustrated and described in terms of a vertical, high side, variable speed compressor, other modifications will occur to those skilled in the art. For example, the invention is applicable to both horizontal and vertical compressors. The only significant difference would be the location of the oil sump relative to the muffler and the discharge from the muffler could be straight down into the portion of the oil sump between the pump structure and the stator which would be well removed from the appropriate oil pick up tube. It is therefore intended that the present invention is to be limited only by the scope of the appended claims.