Screw Compressor

Abstract

A liquid injected screw compressor having an intermediate housing member which supports a detachable screw rotor housing portion, a thrust bearing housing, and a pressure fluid control actuator for a sliding capacity control valve. The intermediate housing member also includes a cavity for distributing lubricating and cooling oil to the compressor. The screw compressor includes a substantially cylindrical casing fabricated of steel plate which is bolted to the intermediate housing member and encloses the screw rotor housing portion to serve as a pressure vessel for compressor inlet gas and for gas vented by the capacity control valve. A separate casing portion is bolted to the intermediate housing member and encloses the thrust bearing housing and the pressure fluid control actuator. The compressor is adapted to be mounted on a base or frame by means of legs attached to the cylindrical casing.

Description

BACKGROUND OF THE INVENTION

Liquid injected gas compressors of the helical screw rotor type are well known and are used in many applications including refrigeration and other gas process systems. In particular, in applications such as vapor-compression refrigeration systems, it is desirable to have high efficiency capacity control devices whereby the compressor may be operated economically at part load conditions. To this end there has been developed what is known in the art as the axial slide valve capacity control. Such a control device is generally characterized by an axially movable portion of the screw rotor housing wall which in effect shortens the length of the intermeshing screw rotors and thereby reduces their swept volume in compression. Examples of axial slide valve controlled screw compressors are disclosed in U.S. Pat. Nos. 3,314,597 and 3,432,089 to L.B. Schibbye.

Generally, axial slide valve controlled screw compressors are also designed to operate with compressor inlet pressures substantially greater than atmospheric pressure. Accordingly, in prior art screw compressors the compressor housing containing the screw rotors and the axial slide valve has been formed as a substantially thick walled metal casting. Cast prior art compressor housings have not only been of heavy section thickness to withstand high gas pressures but the gas return passages communicating gas vented from the slide valve back to the compressor inlet have resulted in a rather complicated and difficult to clean casting.

A related problem in the art of liquid injected screw compressors concerns the leakage of gas and the injection liquid from the numerous piping connections normally required, and from the flanged joints between compressor housing pieces. Leakage of gas under pressure to the exterior of the compressor is particularly unwanted in a closed system and when the gas being compressed is toxic or flammable. Of course, leakage of the injection liquid is also unwanted. Therefore, it is desirable to minimize the number of compressor housing joints and to make such joints easily sealable. Furthermore, the numerous external piping connections and conduits found in prior art compressors precludes the effective application of noise suppression coatings or wrappings on the compressor housing.

In certain prior art screw compressor designs the liquid injection system is substantially contained within the screw rotor housing portion wherein a cavity is formed in the housing proper adjacent to the rotor bores. All liquid injection and lubricant flow passages are internally formed to be in communication with said cavity. Such an arrangement is disclosed in U.S. Pat. No. 3,178,104 to R.F. Williams, et al. However, the benefits of this type of liquid distribution arrangement have not heretofore been enjoyed in compressors having the afore-mentioned sliding valve capacity control device. Moreover, in prior art screw compressors used for refrigeration and other high pressure gas service the problem of gas and liquid leakage has in some cases been dealt with by placing the entire compressor in a hermetically sealed enclosure which greatly increases the bulk of the machine and makes servicing difficult and time consuming.

SUMMARY OF THE INVENTION

The present invention is directed to an improved housing construction for liquid injected helical screw gas compressors which provides for a minimum number of housing joints required to be hermetically sealed and which provides for a liquid distribution system which is substantially contained within the compressor housing.

The present invention also provides for a housing construction for a helical screw gas compressor of the sliding valve capacity control type wherein an inlet casing portion is separately formed as a fabricated metal member for enclosing the screw rotor housing to form a chamber for compressor inlet gas and for gas vented by the capacity control valve. The fabricated casing portion is also formed to provide for supporting the compressor unit on a frame and the compressor may be bodily detached from the fabricated casing portion without disturbing the alignment thereof with respect to the compressor drive motor.

The present invention further provides a housing construction for a liquid injected helical screw compressor in which an intermediate housing member comprises a support for the basic compressor proper and which is readily detachable from the fabricated casing portion. The intermediate housing member also includes a liquid distribution cavity or manifold which provides for a minimum number of liquid conduit connections to be located on the exterior of the compressor. The arrangement of a liquid distribution cavity in an intermediate housing member together with hermetically sealable casing portions mounted thereon provides for substantially all liquid conduits to be located within enclosed areas which are normally exposed to the compressor gas-liquid mixture. The compressor housing construction of the present invention also provides a structure which is aesthetically pleasing as well as being easily covered with externally applied sound absorbing and insulating blankets or coatings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exterior longitudinal elevation of a helical screw compressor in accordance with the present invention.

FIG. 2 is an exterior transverse elevation of the compressor of FIG. 1.

FIG. 3 is a longitudinal section of a helical screw compressor according to the present invention taken substantially along the line 3--3 of FIG. 4.

FIG. 4 is a transverse section taken along the line 4--4 of FIG. 3.

FIG. 5 is a section taken along the line 5--5 of FIG. 4.

FIG. 6 is a perspective view showing the compressor disassembled from the exterior casing portions.

FIG. 7 is a schematic of the liquid injection and lubrication system of the compressor of the present invention.

FIG. 8 is a fragmentary view taken along the line 8--8 of FIG. 3 with the high pressure casing removed.

FIG. 9 is a section view taken along the line 9--9 of FIG. 3 with the low pressure casing removed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-4 and 6, a liquid injected screw compressor according to the present invention is illustrated and generally designated by the numeral 10. The compressor 10 is of a type generally well known in which a pair of cooperating rotors, a male rotor 12, and a female rotor 14, are rotatably housed in a rotor housing 16 having parallel intersecting bores 18 and 20 surrounding in close fitting relationship the respective rotors 12 and 14. The male rotor 12 has four helical lobes 22 and intervening grooves 24 and the female rotor 14 has six helical lobes 26 and intervening grooves 28. Various rotor lobe profiles and lobe wrap angles as well as combinations of numbers of lobes on the respective rotors are known and used in the art of screw compressors. However, for high pressure ratio liquid injected screw compressors a male-female lobe combination of four and six respectively with respective wrap angles of 300.degree. and 200 degrees have been found desirable. The rotors 12 and 14 are drivably interengaged to operate without synchronizing gears.

The rotor housing 16 is removably bolted to an intermediate housing 30 having a first transverse face 32 which forms the high pressure end wall of the compression or working chamber comprising the bores 18 and 20. The opposite end of the rotor housing 16 is partially closed by a bearing housing 34 removably bolted thereto and including a low pressure or inlet port 36 which opens through the end wall 37 into the working chamber. The inlet port 36 is primarily axial in accordance with known design practice for helical screw compressors. The rotor housing 16 also includes an integral wall portion 38 forming a bore 40 for an axially slidable valve member 42 which comprises a portion of the wall defining the working chamber formed by the intersecting bores 18 and 20. The valve member 42 is similar to the axially slidable valve disclosed in U.S. Pat. No. 3,314,597. The valve member 42 is axially slidable in the bore 40 from the closed position shown, viewing FIG. 3, to a position to the right whereby an opening is formed between the edge 44 and the valve member through which gas entrapped in the rotor grooves 24 and 28 may be vented from the compressor working chamber. The axially slidable valve member 42 thereby operates as a control over the swept volume or compressed gas throughput of the compressor 10. The valve member 42 is guided by a cylindrical pin 46 fitted in cooperating grooves 48 and 50 in the valve member 42 and in the wall portion 38, respectively.

As may be seen in FIG. 3 the male rotor 12 is rotatably supported in a radial sleeve type bearing 52 on the low pressure end of the rotor and in a similar bearing 54 on the high pressure end of the rotor. The bearings 52 and 54 are respectively located in the bearing housing 34 and the intermediate housing 30. Axial forces acting on the rotor 12 are partially taken by a pair of angular contact ball bearings 56. The bearings 56 are suitably housed in a bearing housing 58 which is removably bolted to the intermediate housing 30 on a second transverse face 59 spaced from and parallel to the face 32. The bearing housing 58 includes a cylindrical chamber 60 in which is located a thrust piston 62 which is attached to the high pressure end portion 63 of the male rotor 12. Pressure fluid such as the compressor injection liquid is conducted to the chamber 60 to act on the piston 62 to offset the thrust forces due to the high pressure gas acting on the end face 64 of the rotor 12. The opposite end of the male rotor 12 includes an integral shaft portion 66 to which a prime mover may be connected by means of a coupling 68 as shown in FIG. 1. The female rotor 14 is similarly supported by sleeve bearings and rolling element thrust bearings, not shown. The female rotor also includes a thrust piston formed by the end of the rotor shaft extension, not shown, located in the bearing housing 34. The thrust piston on the female rotor 14 also acts in a known way to oppose the axial thrust forces acting on the female rotor.

The bearing housing 58 also includes a cylindrical bore forming a chamber 70 for a pressure liquid operated actuator. A piston 72 slidable in the chamber 70 comprises an integral portion of the sliding valve member 42 and is connected to the valve member by spaced apart longitudinal webs 74, one shown in FIG. 3. The webs 74 extend through an open area 76 in the intermediate housing 30 which forms a passageway for a high pressure gas-liquid mixture being discharged from the compressor working chamber through a discharge port 78 formed in the face 32 of the intermediate housing 30 and by the edge 80 of the sliding valve member 42. The piston 72 includes a member 82 removably attached thereto comprising a nut threadedly engaged with a rotatable screw 84. The screw 84 is rotatably journaled in a bearing 86 located in a cover member 88 for the chamber 70. The screw 84 is operable to be connected to suitable mechanism, not shown, for indicating the position of the piston 72 and sliding valve member 42. The piston 72 is operable to move the sliding valve member to the left, as shown in FIG. 3, in response to the admission of pressure fluid to the chamber 70.

The sliding valve member 42 is biased against the forces acting on the piston 72 due to pressure fluid in the chamber 70 by a coil spring 90 supported by a tubular guide 92 attached to the bearing housing 34. The coil spring 90 operates to move the valve member 42 to the full open or minimum capacity position in the absence of pressure fluid being applied to act on the piston 72. Moreover, the axial projected area of the piston face 94 is greater than the axial projected area of the face 96 of the valve member 42 so that a bias force tending to open the valve to reduce compressor throughput is created by the high pressure gas in the area 76. This feature provides for assuring that the valve member 42 will move to reduce the required work input to the compressor in the absence of pressure fluid in the chamber 70 such as during compressor startup.

A particularly advantageous feature of the compressor 10 in accordance with the present invention is realized with the construction wherein a substantially cylindrical low pressure casing 98 is formed to be detachably bolted to the transverse face 32 of the intermediate housing 30 and enclosing the rotor housing 16 and the bearing housing 34. The casing 98 includes a flanged inlet opening 100 for compressor inlet gas. The interior area 102 between the rotor housing 16 and the casing 98 comprises an inlet flow chamber to the compressor inlet port 36 and also for receiving gas vented from the working chamber by the sliding capacity control valve 42. The casing 98 is preferably formed of fabricated metal such as steel in accordance with accepted pressure vessel design practices and includes an annular flange 104 for fastening the casing to the intermediate housing 30. The casing 98 includes a sleeve 106 suitably welded to the casing and forming an opening through which the male rotor shaft extension 66 projects. The sleeve 106 sealingly engages the exterior of a rotary mechanical seal assembly 108 for the male rotor shaft. The casing 98 also includes a plurality of legs 110 for supporting the compressor on a frame 112 as shown in FIGS. 1 and 2. Contrary to prior art screw compressors of the axial slide valve capacity controlled type the compressor 10 of the present invention comprises a rotor housing 16 which may be a metal casting of comparatively simple construction and being relatively easy to manufacture. Thanks to the provision of the fabricated casing 98 as a member separable from the rotor housing 16, and which is lighter in weight and inherently less susceptible to structural defects as compared to a casting, the compressor 10 is less costly to manufacture and, furthermore, enjoys ease of assembly and disassembly as will be explained herein.

The screw compressor according to the present invention also includes a high pressure casing 114 removably fastened to the transverse face 59 of the intermediate housing 30. The casing 114 is characterized by a hollow interior 116 forming a discharge flow chamber which is in communication with the area 76 in the intermediate housing 30 through openings 118 in the transverse face 59, FIG. 8. The casing 114 also includes a flanged opening 120 for connecting a suitable conduit to the compressor 10 to conduct high pressure gas and liquid from the compressor. As may be noted in FIG. 3 the casing 114 encloses the bearing housing 58 and includes a boss 122 having a cylindrical opening for sealingly receiving a cylindrical portion 124 of the cover member 88.

The casings 98 and 114 are easily disassembled from the intermediate housing 30 by removing the screws 126 around the flanges 104 and 128 respectively. The cylindrical flanged joints between the casings 98 and 114 and the intermediate housing 30 are also easily sealed by conventional O-rings 130 located in suitable grooves in the intermediate housing. As best illustrated in FIG. 6 the compressor 10 may be disassembled, without disturbing the alignment of the casing 98 with respect to a prime mover, by unbolting the flanged joint between the intermediate housing 30 and the casing 98 whereby the entire compressor with the exception of the casing 98 may be moved to a suitable location for servicing and further disassembly. Moreover, if access to the bearing housing 58 or any of the components located in the interior of the casing 114 is desired the casing 114 may be easily removed from the intermediate housing. Alignment of the casings 98 and 114 with respect to the compressor assembly comprising the intermediate housing and the housing members fastened thereto may be achieved by conventional means such as dowel pins 132, one shown in FIG. 6.

As previously mentioned the compressor 10 is of a well known type in which liquid is injected into the working chamber formed by the bores 18 and 20 to be mixed with the gas being compressed for absorbing some of the heat of compression and for sealing the clearances between the cooperating rotors 12 and 14. The liquid is usually a suitable oil which also serves as a lubricant for the interengaged rotors and the rotor bearings. The liquid used for lubrication as well as what is directly injected into the compressor working chamber is discharged with the high pressure gas, separated from the gas, cooled and recirculated through the compressor in a known manner.

In accordance with the present invention there is provided a housing construction which provides for an improved liquid distribution system which is substantially enclosed within the casings 98 and 114, and thereby minimizes leakage of liquid to the exterior of the compressor. In the compressor 10 the intermediate housing 30 includes a plurality of passages for conducting liquid to various locations in the compressor. The intermediate housing 30 also includes a cavity or manifold 134 from which pressure liquid is distributed. Referring in particular to FIGS. 3 through 7 liquid is introduced into the compressor proper through a conduit 136 and a passageway 138 in the intermediate housing 30 to a suitable pump 140 driven by an extension, not shown, of the female rotor. The pump 140 provides for increasing the pressure of the liquid to a value sufficient to provide adequate force on the thrust piston 62 as well as liquid flow to all desired locations within the compressor. A discharge conduit 142 from the pump 140 is connected to a passage 144 in the intermediate housing which is in communication with a filter 146 fastened to the intermediate housing. Liquid from the filter 146 flows into the cavity 134 in the intermediate housing.

The cavity 134 serves as a manifold for distributing pressure liquid to the compressor bearings and seals, the thrust pistons, the working chamber formed by the intersecting bores 18 and 20, and the chamber 70 of the actuator for the capacity control valve 42. Pressure liquid is supplied to the chamber 70 from the cavity 134 through conduits 148, 150, passage 152 and conduit 154. A suitable valve 156 is interposed in the conduit 148 to control the flow of pressure liquid to the chamber 70 of the capacity control valve actuator. Pressure liquid is vented from the chamber 70 by operation of valve 158 interposed in the conduit 160. The conduit 160 is in communication with conduit 150 and a passage 162 in the intermediate housing which opens into the interior 102 of the casing 98. A substantial portion of the liquid discharged into the interior 102 is eventually entrained with the inlet gas flowing to the compressor working chamber. The cavity 134 also is in communication with a pressure relief valve 163 shown in FIG. 5 and schematically shown in FIG. 7. The pressure relief valve 164 is operable to limit the liquid pressure in the cavity 134 and operates to vent liquid into the interior 116 of the casing 114. The relief valve 164 is of a type which operates basically on the pressure differential existing between the interior 116 and the cavity 134.

The cavity 134 includes a portion 166, FIG. 5, interconnected by a passage 168 to the cavity and including a passage 170 leading to the bearings 54 located in the intermediate housing. A conduit 172 also leads from the cavity portion 166 to the thrust piston chamber 60 for supplying pressure liquid to act on the thrust piston 62. Liquid leaking past the periphery of the thrust piston to a chamber 174 formed by the cover portion 175, FIG. 3, is conducted away from said chamber by a conduit 176 which is connected, via a suitable passage in the intermediate housing, to a conduit 178 leading to the bore 20. A conduit 180 also connected to the cavity portion 166 supplies liquid to the bearings 52 in the bearing housing 34 and to a thrust piston on the female rotor 14 which as previously mentioned is also located in the bearing housing 34. Liquid is also supplied to the shaft seal assembly 108 by way of conduit 182 and is drained from the seal to the conduit 178 through a connecting conduit 184.

Liquid draining from the compressor bearings and from the thrust pistons and the seal 108 flows into the working chamber comprising the intersecting bores 18 and 20. The primary source of liquid injected into the working chamber is, however, from a conduit 186 in communication with the cavity portion 166 and connected to a passageway 188 located in the integral wall portion 38 of the rotor housing 16. The passageway 188 is in communication with an annular area 190 and intersecting passages 192, 194, and 196 in the locating pin 46. As shown in FIG. 4 the passage 196 in the pin 46 opens into an annular area 198 which is in communication with peripheral grooves 200 which open into the bores 18 and 20. The grooves 200 conduct injection liquid into the working chamber of the compressor in a region which is normally subject to high pressure gas under compression. The location of the grooves 200 in the bore 40 also serves to provide liquid for lubricating the bearing surface formed by the bore 40 to facilitate easy movement of the axial sliding valve member 42.

The compressor 10 is adapted to be used in various vapor-compression refrigeration systems utilizing different types of refrigerants. The ratio of injection liquid mass flow to refrigerant gas mass flow for optimum compressor performance has been determined to be dependent on the type of refrigerant used in the system. The flow rate of injection liquid to the grooves 200 is controlled by means comprising an orifice plug holder 202 which, as shown in FIG. 5, is removably insertable from the exterior of the intermediate housing 30 into the cavity portion 166. The holder 202 includes a removable plug 204 having an orifice 206 which opens into a passageway 208 in the holder from the cavity portion 166. The passage 208 in the holder opens into the annular area 210 formed by the holder and the cavity portion 166. The area 210 is in communication with the conduit 186. As may be appreciated from the foregoing the arrangement of the holder 202 in the intermediate housing 30 provides for interchanging the plug 204 with similar plugs having different orifice sizes without disassembly of the compressor.

Referring to FIG. 9, a second set of grooves 212 are also formed in the wall portion 38 and open into the intersecting bores 18 and 20. In FIG. 9 an alternate embodiment of a cylindrical locating pin 214 is shown in which is formed an annular recess 216 in communication with the grooves 212 and the passage 188. The grooves 212 and the pin 214 are used to provide an alternate location for liquid injection into the compressor working chamber for use with alternate embodiments of the axial sliding valve member 42. Such alternate embodiments of the sliding capacity control valve are used for changing the so-called built-in volume ratio of the compressor.

As may be appreciated from the foregoing description of the liquid injection and lubrication system the provision of a distribution cavity or manifold in the intermediate housing 30 and the location of substantially all conduits within the casings 98 and 114 eliminates, to a large extent, leakage of the injection liquid to the exterior of the compressor 10. Moreover, the joints formed between the intermediate housing, the rotor housing 16 and the bearing housings 34 and 58 are not required to be completely fluid tight. Gas and liquid leakage between the connection flanges of the aforementioned housing, small amounts of which can be tolerated from a compressor performance standpoint, merely flows into the chambers formed by the interiors of the casings 98 and 114.

Claims

What is claimed is:

1. In a screw compressor:

a rotor housing having two parallel intersecting bores forming a working chamber;

an inlet port and a discharge port opening into said working chamber;

a high pressure end wall at one end of said working chamber and a low pressure end wall at the opposite end of said working chamber;

interengaged male and female screw rotors located in said bores and operable to entrap and compress gas admitted to said working chamber through said inlet port, one of said rotors including a shaft extension for connecting said one rotor to compressor driving means;

valve means characterized by a movable wall portion of said working chamber and operable to vent gas from said working chamber; and,

a housing portion comprising an intermediate housing having a first transverse face thereon, said first transverse face forming said high pressure end wall of said working chamber, and said rotor housing is removably fastened to said intermediate housing on said first transverse face,

low pressure casing means including a gas inlet opening and means defining an opening through which said shaft extension projects to the exterior of said compressor, said compressor including sealing means surrounding said shaft extension and sealingly engaged with said means defining said opening, said low pressure casing means including means for supporting said compressor on a frame, said low pressure casing means substantially enclosing said rotor housing and being removably fastened to said intermediate housing and in sealing engagement to said first transverse face to form an interior area between said rotor housing and said low pressure casing means, said interior area defining a flow chamber in communication with said inlet port and said valve means, and said low pressure casing means comprises a member separable from said intermediate housing whereby said compressor may be removed from said low pressure casing means without moving said low pressure casing means with respect to said frame.

2. The invention set forth in claim 1 wherein:

said low pressure casing means is fabricated of metal plate.

3. The invention set forth in claim 1 wherein:

said housing portion includes bearing means for rotatably supporting the high pressure ends of said rotors.

4. The invention set forth in claim 1 wherein:

said intermediate housing includes a second transverse face spaced from said first transverse face and a passageway opening through said first and second transverse faces and being in communication with said discharge port, said compressor includes housing means including a chamber for a pressure fluid actuator, said actuator being operable to move said valve means to vent gas from said working chamber, said housing means being removably fastened to said intermediate housing on said second transverse face, and said compressor includes high pressure casing means including a discharge opening, said high pressure casing means being adapted to be removably fastened to said second transverse face in sealing engagement therewith and substantially enclosing said housing means and defining a discharge flow chamber in communication with said passageway in said intermediate housing for receiving compressed gas from said working chamber.

5. In a screw compressor:

a rotor housing having two parallel intersecting bores forming a working chamber;

an inlet port and a discharge port opening into said working chamber;

a high pressure end wall at one end of said working chamber and a low pressure end wall at the opposite end of said working chamber;

interengaged male and female screw rotors located in said bores and operable to entrap and compress gas admitted to said working chamber through said inlet port;

a housing portion including bearing means for supporting the high pressure ends of said rotors, said housing portion having a first transverse face and a second transverse face spaced from said first transverse face;

low pressure casing means removably fastened to said first transverse face and substantially enclosing said rotor housing and forming an interior area between said low pressure casing means and said rotor housing defining a gas inlet flow chamber;

high pressure casing means removably fastened to said second transverse face, said high pressure casing means forming with said second transverse face a compressor gas discharge flow chamber; and,

means for conducting liquid to said working chamber including a cavity in said housing portion, conduit means for conducting liquid from an external source to said cavity, and conduit means for conducting liquid from said cavity to said working chamber.

6. The invention set forth in claim 5 wherein:

said compressor includes liquid pump means supported by said housing portion and disposed within said discharge flow chamber formed by said second transverse face and said high pressure casing means.

7. The invention set forth in claim 5 wherein:

said conduit means for conducting liquid from said cavity are disposed within the chambers defined by said casing means.

8. The invention set forth in claim 5 wherein:

said housing portion includes flow control means disposed in flow communication with said cavity and operable to limit the flow of liquid from said cavity to said working chamber.

9. The invention set forth in claim 8 wherein:

said flow control means comprises a plug having an orifice therein, a holder for said plug, said plug and said holder being removably insertable in said housing portion.

10. The invention set forth in claim 9 wherein:

said cavity includes a portion opening to the exterior of said compressor and said holder is removably insertable in said cavity portion from the exterior of said compressor.