US 3796526 A
An improved hermetic screw compressor incorporating hydraulic means for balancing the axial thrust of the screw rotors. The cooperating screw rotors are disposed in a working space in a compressor housing supported in a sealed outer casing. The screw rotors are journalled at least in part by support members secured to the compressor housing and extending into longitudinal openings or recesses in the screw rotors. The rotor support members are relatively close together and consequently the problem of rotor support shaft deflection as occurred when the rotor shafts extended from the rotors is minimized. The effective screw length is reduced and thus the overall screw compressor can be more compact than heretofore.
Description (OCR text may contain errors)
United States Patent 1191 C wl y 1 Mar. 12, 1974 [5 SCREW COMPRESSOR 3,462,072 8/1969 Schibbye; 418/98  Inventor: Richard E. Cawley Hurst Tex. 3,658,452 4/1972 Kita 418/203  Assignee: Lennox Industries Inc., fic J Husar Marshantown Iowa Attorney, Agent, or Firm-Molinare, Allegretti, Newitt 122 Filed: Feb. 22, 1972 & wltcoff  Appl. No.: 227,764
-  ABSTRACT  US. Cl 418/97, 418/201, 418/203, An improved hermetic screw compressor incorporat- 417/424 ing. hydraulic means for balancing the axial thrust of  Int. Cl. Ftllc 21/04 the screw rotors. The cooperating screw rotors are dis-  Field of Search 418/97-99, posed in a working space in a compressor housing sup- 418/94, 201, 203; 417/424 ported in a sealed outer casing. The screw rotors are journalled at least in part by support members secured  References Cited to the compressor housing and extending into longitu- UNITED STATES PATENTS dinal openings or recesses in the screw rotors. The 3,105,446 10/1963 Blomgren, Sr. et al 418/152 rotor Support members are relatvely Close together 3 55s 24s 1/1971 Parker 418/201 and consequently the Problem of rotor support shaft 1:698:802 1/1929 Montelius........,...........: 418/203 deflection as Occurred when the Shafts extended 2 71 794 2 1959 4 3 20 from the rotors is minimized. The effective screw 2,924,181 2/1960 Sennet 418/203 length is reduced and thus the overall screw compres- 3,161,349 12/1960 Schibbye 1 1 418/203 sor can be more compact than heretofore. 3,307,777 3/1967 Schibbye 418/201 3,434,656 3/1969 Bellmer 418/94 9 Claims, 3 Drawing Figures SCREW COMPRESSOR BACKGROUND OF THE INVENTION This invention relates to a screw compressor and more particularly, to an improved hermetic screw compressor incorporating hydraulic means for balancing the axial thrust of the screw rotors.
Screw compressors are finding increased use in refrigeration applications because they are a positive displacement type of compressor that can handle high compression ratios with efficiencies approaching those of the reciprocating compressor. Essentially, a screw compressor consists of a housing having two intermeshing male and female rotors therein, with the male rotor corresponding to the piston and the female rotor to the cylinder of a reciprocating compressor. At constant speed, the screw compressor has almost constant volume for variable pressure ratio. Advantages of the screw compressor are absence of wearing parts, a high specific output, positive displacement to provide for surge-free compression under all operating conditions, ability to utilize high-pressure refrigerants as used by reciprocating compressors, such as R12 and R22, and the ability to pass liquid refrigerant. Because of operation at high speeds and having balanced rotary motion, the screw compr'esso'riscompact and has no externally unbalanced forces.
Certain mechanical problems arise in a rotary screw compressor which limits its more widespread use today. Due to deflection and bearing loading problems, the screw compressor is limited in the maximum pressure ratio that can be handled. Various types of labyrinth or similar seals have been used on the rotor shaft to maintain the pressure and thrust bearings have been utilized to take up some of the bearing loading. Deflection of the rotors is an important consideration because it affects the clearances between the rotors and to obtain the maximum pressure difference, the shafts must be as stiff as possible.
An object of the present invention is to provide an improved hermetic compressor incorporating hydraulic means for balancing the axial thrust of the screw ro tors.
Another object of this invention is to provide an improved hermetic screw compressor incorporating rotor supports extending within the rotors so as to minimize deflection thereof.
Still another object of the present invention is to provide an improved hermetic screw compressor wherein the rotor supports are at least partially within the rotors so as to minimize the problem of shaft deflection.
Yet another object of the present invention is to provide an improved screw compressor having rotor support means at least partially within the rotors whereby the overall screw compressor can be more compact than heretofore.
A further object of this invention is to provide a hermetic screw compressor with a novel compressor housing support arrangement including seal means between a discharge chamber and a suction chamber in the compressor. Other objects and advantages of the present invention will be made more apparent hereafter.
BRIEF DESCRIPTION OF THE DRAWING There is shown in the attached drawing presently preferred embodiments of the present invention wherein:
FIG. 1 is a crosssectional view of a hermetic screw compressor embodying principles of the present invention;
FIG. 2 is a cross-sectional view of a modified her metic screw compressor incorporating a pump operative from the drive shaft of the compressor motor for forwarding lubricant from the sump to the bearings of the rotors and to the working space; and
FIG. 3 is a cross-sectional view of a further modification of hermetic screw compressor, with a pump being operatively attached to the drive shaft of the compressor motor for delivering lubricant to the bearings of the rotors, with lubricant injection to the working space within the compressor housing being provided by pressure differential;
DETAILED DESCRIPTION OF THE PRESENT INVENTION Referring now to FIG. 1, there is illustrated a rotary screw compressor 10 embodying principles of the present invention. The screw compressor 10 comprises a sealed outer housing having an upper casing portion 12 an da lower casing portion 14 joined together in sealed relationship as, for example, by welding. Support members or legs 15 may be secured to the lower casing portion 14 for retaining the compressor in an upright position for use.
Compression mechanism 16 is supported within the outer housing by means of support means 17 and 18. The compression mechanism 16 comprises a block or housing member which includes an annular portion 20 closed at the ends by plate members 22 and 24. The plate member 22 is secured to the annular member 20 by suitable fastening means, for example, bolts 25. The plate member 24 is secured to the annular member by suitable fastening means, for example, bolts 26 and 44. Defined within the compression mechanism 16 is a working space 28 and the rotors 30 and 32 cooperate with one another within the working space 28.
The compression mechanism 26 also includes an annular housing portion 34 which receives an electric drive motor 36. The drive motor 36 includes a stator 38 fixedly secured to the housing portion 34 and a rotor 39 inductively connected to the stator 38. A drive shaft 40 is secured to the rotor 39 for rotation therewith. The
annular portion 34 of the compression mechanism 16 is secured to the end plate 24 by suitable fastening means, for example, bolts 42 and 44. It is noted that several bolts 44 will serve the function of connecting annular member 34, end plate 24 and annular member 20. i
A suitable O-ring seal 46 is provided to seal between the end plate 24 and the annular member 34. A similar O-ring seal 48 is adapted to seal between a surface of the annular portion 34 and the interior surface of the lower casing portion 14 so as to separate the discharge chamber 47 from the suction chamber 49.
It will be understood that there are a plurality of spaced support members 17 within the interior of the upper casing portion 12. Likewise, there are a plurality of lower support members 18 provided within the lower casing portion 14. In one form of the invention, each support means 17 and 18 comprises three equidistantly spaced members. Dowel pins 19 are provided to help locate the end member 24 relative to the support members 17. The dowel pins T9 are staked in place after properly orienting the end plate 24 relative to the support members 17.
A feature of the present invention is the method of lubricating the bearing surfaces between the rotors and the supports therefor and also the means for injecting the lubricant so as to seal the clearance between the two rotors 30 and 32 and between the rotors and the surrounding housing in order to increase the efficiency of compression. Another feature of the present invention is the manner of supporting the rotors within the housing so as to minimize shaft deflection and the clearance problems occurring in prior devices.
The cooperating male and female rotors 34 and 32 are each provided with lands and grooves which cooperate with the housing portion 20 so as to define diminishing chambers extending from the inlet (not shown) in the end plate 22 through the outlet (not shown) in the end plate 24. Suction gas is returned from the refrigeration system to the suction chamber 49 defined within the upper portion of the outer housing of compressor through the inlet 50 and discharge gas is forwarded from the discharge chamber 47 within the compressor 10 through the outlet opening 52.
The drive shaft 40 is operatively connected to the extension 30a of the rotor 30 for driving same. The portion 30a of the rotor 30 is journalled in a stationary bearing 59 disposed between the rotor portion 30a and a central hub portion of the end plate 24. The opposite end of the rotor 30 is provided with a longitudinally ex- -tending recess or opening 56, which is adapted to receive therein a support or shaft 58 that is affixed at an end to the end plate 22. A bearing liner 60 is disposed between the walls defining opening 56 within the rotor 30 and the exterior of the support 58 and is adapted to rotate with the rotor. A thrust washer 62 is provided between the upper end of the rotor 30 and the inner surface of the end plate 22 and its operation will be more fully explained later.
The rotor 32 has a pair of recessed axially aligned openings 66 and 68 therein for receiving the supports 70 and 72, respectively, that are secured within openings in the end plates 22 and 24, respectively. Bearing liners 74 and 75 are disposed between the bearing or supports 70 and 72 and the recesses or openings 66 and 68 within the rotor 32 and are adapted to rotate with rotor 32. By virtue of supporting the rotors 3t) and 32 at least partially within the length of the respective rotors as shown, the compressor is made more compact, that is, the overall length may be reduced, as contrasted with prior designs wherein the rotors were supported on shafts extending outwardly from the rotors. In addition, since the shaft supports are closer together, there is virtually no rotor shaft deflection and, therefore, less clearance problems than in prior constructions.
If desired, a thrust washer 78 may be provided between the end surface of the bearing or support 58 and a wall of the recess 56. Likewise, thrust washers 79 and 80 may be utilized between the respective ends of the supports 70 and 72 and the recesses 66 and 68, respectively, in the rotor 32.
The means for hydraulically balancing the axial thrust of the screw compressor rotors comprises a conduit 82 that receives fluid from a heat exchanger (not shown) and supplies same to act against the washer 62 in opposition to axial forces on rotor 30 during operation thereof. The heat exchanger may be supplied by the conduit 83 that is operatively connected to the lu-- bricant sump defined in the bottom of the lower casing portion 14. By virtue of the pressure differential between the discharge pressure on top of the fiuid contained within the lubricant sump and the suction pressure in the suction chamber 49 in the upper housing portion 12 of the compressor, lubricant will be ported from conduit 83 through the heat exchanger and then through conduit 82 to lubricate the bearing surfaces, to hydraulically balance the axial thrust of the screw rotors, and to provide a sealing lubricant to the working space 28. The conduit 82 communicates with the conduit 84 which opens into the working space 28 at a point along the intersection of the rotors 30 and The lubricant from the conduit 84 is discharged through the outlet 86 into the working space 28 to provide a seal between the rotors 30 and 32 and between the rotors and the interior of the housing 20.
Also communicated with conduit 82 is a conduit 88 which has communication with passages within rotor 31) and also passages within the rotor 32. Provided within the rotor 34) is a longitudinally extending passageway 90 that connects with the transverse passages 91 and 92 for lubricating the bearing surface between liner 59 and shaft portion 30a. Excess fluid from the exterior of the bearing liner 59 may flow back to the low side or suction chamber 49 of the compressor 10 through a passage 93 provided in the end plate 24. The longitudinally extending passage 90 in the rotor 30 communicates with the longitudinally extending passage 94 in the bearing support 58. A transverse passage 95 in the bearing support 58 communicates with the longitudinally extending passage 94 and provides lubricant to the space between the thrust washer 62 and the end plate 22 for pressurizing the thrust washer 62 and counterbalancing the axial thrust forces. The hydraulic fluid between the thrust washer 62 and end plate 22, coupled with the extended surface of the thrust washer 62, provides the hydraulic means for balancing the axial thrust of the screw rotor 30. i
Longitudinally extending passages 96 and 97 are provided in each of the bearing supports 70 and 72. The longitudinally extending passage 96 cooperates with a transverse passage 98 for supplying lubricant between the bearing liner 74 and the bearing or support 70. Similarly, a transverse passage 99, which cooperates with the passage 97, forwards lubricant. to the journal surface between the bearing support 72 and the bearing liner 75. The longitudinally extending passages 96 and 97 are connected to one another via a communicating passage me within the rotor 32. The bleed passage 102 in the end plate 24', provides a bleed for returning lubricant from about the journal 72 to the low side of the compressor. The end of the passage 1102 may communicate with a transverse recess or bleed port 1102a between the end plate 24 and the upper casing portion 12 to effectuate the desired return of lubricant.
Another feature of the present invention is the manner of construction wherein a simple tl-ring seal 48 is provided to seal between the high side or discharge chamber 47 of the compressor and the low side or suction chamber 49 of the compressor. Seal 48 is disposed in a recess in a flange on the lower part of the annular member 34.
It will be understood that the oil is forced from the lubricant sump to'the bearing surfaces, the hydraulic axial thrust balancing means, and injection port 86 by meansof the pressure differential between the dis- 'tive from the drive shaft of the compressor motor in order to force lubricant to the bearings, the hydraulic axial thrust balancing means, and the injection port. Accordingly, like numerals will be utilized to indicate the like parts in the embodiments of FIGS. 1 and 2. The pump 110 comprises a body having an upper portion 112 secured to a lower portion 114 by suitable fastening means as, for example, bolts 116. Body portion 114 is suitably secured to the lower casing portion 14. An inlet tube 118 communicates with the housing portion 112 and a discharge tube 120 communicates with the housing portion 114. Gear or impeller means 122 are provided within the pump 110 for compressing lubricant ingested from the sump and forcing same through the heat exchanger, through conduit 82 and then through the conduit 88 for lubricating the bearing surfaces and pressurizing washer 62 and through the conduit 84 and the port 86 for ejecting fluid into the working space 28. The gearor impeller means 122 includes a shaft 124 is driven from shaft 40 by means of a pin 125 connected to shaft 124 and eccentrically connected to the shaft 40. Then whenever the shaft 40 rotates, pump 110 will be operative. I
With reference 'to FIG. 3, there is shown a further modification ofhermetic screw compressor including a pump 110. In the embodiment of FIG. 3, the pump 110 is utilized to pump refrigerant directly to the bearing surfaces and to the thrust washer 62 through a conduit identified as 88. A separate conduit 83' carries lubricant from the sump and passes it to the heat exchanger, from which heat exchanger the fluid passes through conduit 82' to the conduit 84' for discharge through the outlet 86 into the working space 28. In
other constructional aspects, the compressor is.
vides lubricant to the bearings, the hydraulic axial thrust balancing means, and the injection port. In a third modification, a pump mechanism is provided within the compressor and driven by the electric drive motor of the compressor to force lubricant to the bearing surfaces, and to the hydraulic axial thrust balancing means with pressure differential being relied on to provide fluid to the injection port. Another feature of this invention is journalling the rotors at least partially internally, whereby shaft deflection problems are obviated andthe size of the compressor can be made more compact with the elimination of the rotor shaft ends extending outwardly'from the .rotors, as is common in prior art devices. While I have shown a presently preferred embodiment of the invention, it will be understood that the invention is not limited thereto, since it may be otherwise embodied within the scope of the following claims.
The claims; I I
1. In a screw compressor having a housing defining a working space, and at least two cooperating screw rotors disposed in the working space for compressing the fluid, one rotor being drivingly engaged with a drive motor and the second rotor being engaged with said one rotor to be driven thereby, an axial thrust resulting along the axes of the rotors from the cooperation thereof in use, the improvement comprising hydraulic means for balancing the axial thrust of the rotors, said rotors each journalled at least in part by a support member secured to the housing and having an axial opening therein, said support member being received in said axial opening, a thrust member between the housing and said one rotor remote from the drive motor, said hydraulic means actuating the thrust member to balance the axial .thrust of said one rotor.
2. A screw compressor as in claim 1 wherein the hydraulic means includes passage means in the support member for the said one rotor for supplying pressurizing fluid to the thrust member. I
3. A screw compressor as in claim 1 including drive shaft means connecting the drive :motor and the said oneroton the drive shaft means being journalled in said I housing, and passage means in the said one rotor and drive shaft means, the hydraulic means communicating with said passage means for supplying lubricant to lubricate the journal surfaces between the drive shaft means and said housing.
4. A screw compressor as in claim 1 including an outer casing having a lubricant sump therein, said housing being carried in said casing, and pump means operatively connected to the drive shaft means for supplying lubricant from the sump to said hydraulic means.
5. A screw compressor as in claim 1 including means for communicating lubricant toth-e working space to seal the clearance between the screw rotors and between the screw rotors and the housing in order to increase the efficiency of operation.
6. A screw compressor as in claim 5 wherein the pump means are operatively connected to both the hydraulic means and the communicating means.
7. In a screw compressor having. a housing defining a working space, and a least two cooperating screw rotors disposed in the working space for compressing the fluid, an axial thrust resulting along the axes of the rotors from the cooperation thereof in use, the improvement comprising hydraulic means for balancing the axial thrust of the rotors, said rotors each journalled at least in part by support members secured in the housing and having an axial opening therein, said support member being received in said axial opening, said housing including an annular member and end plates defining the working space, an electric drive motor, means for supporting the electric drive motor secured to an end plate, an outer casing enclosing said housing, support means affixed to said outer casing and bearing against an end plate and supporting means: to retainthe housing in place within the outer casing, said supporting means including a portion having a recess therein, a seal in the recess for sealing between the outer casing and the said portion so as to define a discharge chamber and a suction chamber within said outer casing.
8. In a screw compressor having a housing defining a working space and at least two cooperating screw rotors disposed in the working space for compressing the fluid, an axial thrust resulting along the axes of the rotors from the cooperation thereof in use, the improvement comprising hydraulic means for balancing the axial thrust of the rotor, said rotors-each journalled at least in part by support members secured to the housing and having an axial opening therein, said support member being received in said axial opening, said housing including an annular member and endplates defining the working space, an electric drive motor, means for supporting the electric drive motor secured to an end plate, an outer casing enclosing said housing, and support means affixed to said support means and bearing against an end plate and said supporting means to retainthe housing in place within the outer casing, the support means affixed to the outer casing comprising spaced apart sets of support members, one set engaging an end plate and the other set engaging the supporting means.
9. A screw compressorv as in claim 8 wherein alignment means extend between one set of support members and associated end plate to properly orient the housing within the outer casing.