Screw compressor and gas compression facility

Abstract

This screw compressor comprises: a rotor shaft; and a radial slide bearing which includes a sleeve having a bearing surface on an inner circumference, and which rotatably supports the rotor shaft. The bearing surface of the sleeve has a non-circular contour defined by a long axis and a short axis in a cross section orthogonal to the axial direction of the rotor shaft, and includes an oil supply passage communicating with an oil reservoir part formed between a part including an end part of the long axis of the bearing surface and the outer circumferential surface of the rotor shaft.

Description

Screw compressors and gas compression equipment

[0001] The present disclosure relates to screw compressors and gas compression equipment.

[0002] 2. Description of the Related Art Slide bearings are used as radial bearings in rotating machines.

[0003] Patent Document 1 discloses a radial sliding bearing in which the bearing surface has a contour that is a perfect circle in a cross section perpendicular to the axial direction of the rotating shaft.

[0004] Japanese Patent Application Publication No. 7-332364

[0005] Meanwhile, screw compressors, which are subject to heavy loads, use rotor shafts with large diameters. A larger diameter rotor shaft increases the peripheral speed of the rotor shaft, resulting in increased friction loss between the rotor shaft and the radial bearings. This also requires the supply of a large amount of oil to remove the heat generated by friction. Furthermore, in screw compressors, some of the oil supplied to the bearings enters the compression section and is pressurized together with the gas. Therefore, as mentioned above, a large oil supply volume increases the churning loss in the compression section.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide a screw compressor and gas compression equipment that can appropriately support a rotor shaft while reducing the amount of oil supplied to the bearings or enabling the bearings to be made smaller.

[0007] A screw compressor according to at least one embodiment of the present invention comprises: a rotor shaft; and a radial plain bearing including a sleeve having a bearing surface on its inner circumference and rotatably supporting the rotor shaft, wherein the bearing surface of the sleeve has a non-circular outline defined by a major axis and a minor axis in a cross section perpendicular to the axial direction of the rotor shaft, and an oil supply passage communicating with an oil reservoir formed between a portion of the bearing surface including the end of the major axis and the outer peripheral surface of the rotor shaft.

[0008] Furthermore, a gas compression facility according to at least one embodiment of the present invention comprises the above-mentioned screw compressor configured to compress gas, and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor, and is configured so that the oil from the oil separator is supplied to the oil reservoir.

[0009] According to at least one embodiment of the present invention, there is provided a screw compressor and gas compression equipment that can adequately support a rotor shaft while reducing the amount of oil supplied to the bearings or enabling the bearings to be made smaller.

[0010] Fig. 3 is a schematic diagram of a gas compression facility according to one embodiment. Fig. 4 is a schematic cross-sectional plan view of a screw compressor according to one embodiment. Fig. 5 is a schematic diagram showing a cross section perpendicular to the axial direction of a rotor shaft and a radial plain bearing of a screw compressor according to one embodiment. Fig. 6 is a diagram showing a B-B cross section of the radial plain bearing shown in Fig. 3. Fig. 7 is a diagram showing a B-B cross section of the radial plain bearing shown in Fig. 3. Fig. 8 is a schematic diagram showing a cross section perpendicular to the axial direction of a rotor shaft and a radial plain bearing of a screw compressor according to one embodiment.

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0012] 1 is a schematic diagram of a gas compression facility including a screw compressor according to some embodiments. As shown in the figure, the gas compression facility 1 includes a screw compressor 2, an oil separator 4, a cooler 6, and a pump 8.

[0013] The screw compressor 2 is configured to compress and discharge the gas that it has drawn in. In the drawing, the symbol Ps indicates the suction pressure of the screw compressor 2, and the symbol Pd indicates the discharge pressure of the screw compressor 2. Oil is supplied to the screw compressor 2 via an oil supply line 10 for cooling, lubrication, etc. The oil supplied to the screw compressor 2 is discharged together with the compressed gas.

[0014] The configuration of the screw compressor 2 will be described later, but generally, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) each including a rotor shaft 14, 16, and radial plain bearings 18 for rotatably supporting the rotor shafts 14, 16. The radial plain bearings 18 include a radial plain bearing 18A located on the suction side in the axial direction, and a radial plain bearing 18B located on the discharge side in the axial direction. Oil is supplied to the radial plain bearings 18 via an oil supply line 10 for lubrication and cooling.

[0015] The oil separator 4 is configured to separate oil from a mixture of compressed gas and oil discharged from the screw compressor 2. The oil separated in the oil separator 4 is supplied again to the screw compressor 2 (radial plain bearing 18, etc.) via an oil supply line 10. Typically, the oil separated in the oil separator 4 is pressurized by a pump 8 and then supplied to the screw compressor 2 via the oil supply line 10. In this case, the pressure Poil of the oil supplied to the screw compressor 2 is higher than the discharge pressure Pd (Poil = Pd + α). The oil separated in the oil separator 4 may also be cooled in a cooler 6 and then pressurized by the pump 8.

[0016] (Configuration of screw compressor) Fig. 2 is a schematic cross-sectional plan view of a screw compressor according to one embodiment. As shown in Fig. 2, the screw compressor 2 includes a pair of screw rotors (a male rotor 15 and a female rotor 17) including a pair of rotor shafts 14, 16, and a casing 12 that houses the pair of screw rotors.

[0017] The pair of rotor shafts 14, 16 are rotatably supported by radial plain bearings 18A, 18B and thrust bearings 20. Oil at a pressure Poil is supplied to each bearing via an oil supply line 10.

[0018] The male rotor 15 and the female rotor 17 have helical teeth that mesh with each other. The meshing of the teeth of the male rotor 15 and the female rotor 17 and the casing 12 form a plurality of tooth gap spaces (chambers) along the axial direction of the rotor shafts 14, 16.

[0019] The rotor shaft 14 that constitutes the male rotor 15 is connected to the output shaft of a motor (not shown) and is configured to be rotationally driven by the motor. The female rotor 17 that meshes with the male rotor 15 is rotationally driven by the rotation of the male rotor 15. The female rotor 17 rotates in the opposite direction to the rotation of the male rotor 15. When the male rotor 15 and female rotor 17 rotate in their meshed state, the tooth groove space moves axially from the suction side to the discharge side.

[0020] A shaft seal 24 for suppressing gas leakage through the penetration portion of the casing 12, which is formed by the rotor shaft 14, is provided at the penetration portion. Oil at a pressure Poil may be supplied to the shaft seal 24 through the oil supply line 10.

[0021] The oil supplied to the bearings and shaft seals 24 is discharged from the casing 12 and returned to the relatively low-pressure space of the screw rotor housing portion of the casing 12 via a return line 28 (see FIGS. 1 and 2). Note that the oil supply lines branching off from the oil supply line 10 to the bearings and shaft seals, and the return lines 28 from each portion are shown as external lines in FIG. 2, but may also be lines provided inside the casing.

[0022] Gas is drawn into the tooth groove spaces from suction spaces 50 formed in the casing 12 via suction ports 52. When the male rotor 15 and female rotor 17 rotate, the tooth groove spaces move axially from the suction side to the discharge side in accordance with the rotation of these screw rotors. During this process, the volume of the tooth groove spaces decreases after the suction ports 52 are closed, compressing the gas in the tooth groove spaces. When the tooth groove spaces reach the discharge ports 54 and are connected to a discharge space (not shown) formed in the casing 12, the compressed gas in the tooth groove spaces is discharged into the discharge space. The discharge ports 54 are formed by openings provided in the end faces of the casing 12.

[0023] The screw compressor 2 may include a balance piston 30 provided on at least one of the pair of rotor shafts 14, 16. The balance piston 30 is accommodated in an accommodation space 45 formed inside the casing 12. In the exemplary embodiment shown in FIG. 2 , the balance piston 30 is provided at the discharge-side end of the rotor shaft 14 constituting the male rotor 15. Relatively high-pressure oil is supplied from the oil supply line 10 to a balance piston chamber 42 facing the suction-side end face of the balance piston 30. As a result, a force (a force in the axial direction from the suction side to the discharge side) opposite to the thrust gas load acting on the rotor shaft 14 (a thrust load acting on the rotor shaft 14 in the axial direction from the discharge side to the suction side due to the difference between the suction pressure Ps and the discharge pressure Pd of the screw compressor 2) acts on the rotor shaft 14 via the end face of the balance piston 30. This reduces the load on the thrust bearing 20.

[0024] Fig. 3 is a schematic diagram showing a cross section perpendicular to the axial direction of the rotor shaft 14 and radial plain bearings 18 (18A, 18B) of the screw compressor 2 according to one embodiment. Figs. 4 and 5 are diagrams showing the B-B cross section of the radial plain bearing shown in Fig. 3. Fig. 4 shows a cross section of the suction-side radial plain bearing 18A, and Fig. 5 shows a cross section of the discharge-side radial plain bearing 18B.

[0025] In the following, the radial plain bearings 18 (18A, 18B) that support the rotor shaft 14 that constitutes the male rotor 15 will be described with reference to the figures, but the same explanation can be applied to the radial plain bearings 18 (18A, 18B) that support the rotor shaft 16 that constitutes the female rotor 17.

[0026] 3 to 5, the radial plain bearing 18 includes a sleeve 60 having a bearing surface 62 on its inner periphery. As shown in Figures 4 and 5, the sleeve 60 has an end face 60a on the suction side and an end face 60b on the discharge side in the axial direction.

[0027] 4 and 5, the suction side end 62a and the discharge side end 62b of the bearing surface 62 in the axial direction do not have to coincide with the suction side end face 60a and the discharge side end face 60b of the sleeve 60. In other words, as shown in Figures 4 and 5, the bearing surface 62 may be formed only in a partial region of the extension range of the sleeve 60 in the axial direction.

[0028] The sleeve 60 may include a flange 61 for axial positioning of the sleeve 60. As shown in the figure, the flange 61 of the radial plain bearing 18A provided on the suction side in the axial direction may be provided at the suction side end of the radial plain bearing 18A. The flange 61 of the radial plain bearing 18B provided on the discharge side in the axial direction may be provided at the discharge side end of the radial plain bearing 18A.

[0029] 3, the bearing surface 62 of the sleeve 60 has a non-circular profile defined by a major axis AL and a minor axis AS in a cross section perpendicular to the axial direction of the rotor shaft 14. In the exemplary embodiment shown in FIG. 3, the profile of the bearing surface 62 in the cross section perpendicular to the axial direction has a generally elliptical shape having the major axis AL and the minor axis AS.

[0030] An oil reservoir 64 is formed between a portion of the bearing surface 62 including the ends EL1, EL2 of the major axis AL and the outer peripheral surface 19 of the rotor shaft 14. The oil reservoir 64 is a portion where the distance between the bearing surface 62 and the outer peripheral surface 19 of the rotor shaft 14 is relatively wide. The distance between the portion of the bearing surface 62 including the ends ES1, ES2 of the minor axis AS and the outer peripheral surface 19 of the rotor shaft 14 is relatively narrow.

[0031] The screw compressor 2 includes an oil supply passage 66 that communicates with the oil reservoir 64. In the embodiment shown in FIG. 3, the oil supply passage 66 includes an oil supply hole 68 provided in the sleeve 60. The oil supply passage 66 may include the passage 56 (see FIG. 2) provided in the casing 12. The oil supply passage 66 may also include a groove 70 (see FIGS. 4 and 5) provided circumferentially on the outer circumferential surface of the sleeve 60. Oil from the oil separator 4 (see FIG. 1) is supplied to the oil reservoir 64 via the oil supply line 10 (see FIG. 1) and the oil supply passage 66 (the passage 56, the groove 70, and the oil supply hole 68).

[0032] In the above-described embodiment, the bearing surface 62 of the sleeve 60 has a noncircular profile defined by the major axis AL and the minor axis AS in a cross section perpendicular to the axial direction. Therefore, a relatively large oil reservoir 64 is formed between a portion of the bearing surface 62 including the ends EL1 and EL2 of the major axis AL and the outer circumferential surface 19 of the rotor shaft 14. Therefore, fresh oil (relatively cold oil) supplied to the relatively large oil reservoir 64 via the oil supply passage 66 is easily drawn into the sliding surface as the rotor shaft 14 rotates, improving cooling efficiency. Furthermore, because the bearing surface 62 of the sleeve 60 has the above-described noncircular profile, the circumferential range R1 where the gap between the bearing surface 62 and the outer circumferential surface 19 of the rotor shaft 14 is narrow (i.e., the range where the gap between the portion including the ends ES1 and ES2 of the minor axis AS and the outer circumferential surface 19 of the rotor shaft 14 is narrow; see FIG. 3 ) is relatively small. Therefore, friction loss between the rotor shaft and the sleeve can be reduced. Therefore, according to the above-described embodiment, the rotor shaft 14 can be appropriately supported while reducing the amount of oil supplied to the radial plain bearing 18 or while enabling the radial plain bearing 18 to be made smaller.

[0033] 3 to 5 , in some embodiments, a recess 72 into which the oil supply passage 66 opens is provided in the bearing surface 62 of the sleeve 60. The recess 72 may include a bottom surface 74 into which the oil supply passage 66 opens, and a side wall surface 76 provided to surround the bottom surface 74.

[0034] In the above-described embodiment, the bearing surface 62 of the sleeve 60 is provided with the recess 72 into which the oil supply passage 66 opens, so that the oil supplied from the oil supply passage 66 can be retained in the recess 72. Therefore, oil can be smoothly supplied to the space between the bearing surface 62 and the outer peripheral surface 19 of the rotor shaft 14 via the recess 72.

[0035] 3 to 5, the recess 72 provided in the bearing surface 62 may be surrounded by a dam. That is, when viewed from the radial direction, the recess 72 may be closed by a side wall surface 76 that surrounds the recess 72.

[0036] In conventional screw compressors with a relatively large rotor shaft diameter, in order to supply a large amount of oil to the bearing, it was necessary to provide an oil relief groove (a groove provided in the bearing surface so as to communicate with the recessed portion) to discharge the oil from the recessed portion of the bearing surface where the oil could accumulate. In this regard, in the above-described embodiment, as already mentioned, the amount of oil supplied to the bearing is small, so it is possible to realize a configuration in which the recessed portion 72 is surrounded by a dam and there is no oil relief groove, and thereby it is possible to reduce the amount of oil supplied to the bearing.

[0037] In some embodiments, the axial distance L1 (see Figures 4 and 5) between the axial suction end 72a of the recess 72 and the opening 69 of the oil supply passage 66 on the bearing surface 62 is shorter than the axial distance L2 (see Figures 4 and 5) between the axial discharge end 72b of the recess 72 and the opening 69 of the oil supply passage 66 on the bearing surface 62.

[0038] According to the above-described embodiment, the opening 69 of the oil supply passage 66 is located axially closer to the suction end 72a than to the discharge end 72b of the recess 72. In other words, the opening 69 of the oil supply passage 66 is provided at a position on the relatively high-pressure side of the recess 72, and therefore the oil supplied from the oil supply passage 66 to the recess 72 flows in a balanced manner toward the suction end 72a on the relatively high-pressure side and the discharge end 72b on the relatively low-pressure side, making it easier to appropriately lubricate and cool the radial plain bearing 18.

[0039] Figure 6 is a schematic diagram showing a cross section perpendicular to the axial direction of the rotor shafts 14, 16 of a screw compressor 2 according to one embodiment and the radial plain bearing 18 that supports each of the rotor shafts 14, 16. In Figure 6, reference numerals 15a and 17a indicate the orbits (positions of the outermost circumferences) of the tooth tips of the male rotor 15 and the female rotor 17, respectively.

[0040] 6, when viewed from the axial direction, the discharge port 54 of the screw compressor 2 is located between the axial center O1 of the rotor shaft 14 and the axial center O2 of the rotor shaft 16 in the horizontal direction, and is located offset from the axial center O1 of the rotor shaft 14 and the axial center O2 of the rotor shaft 16 in the vertical direction. In addition, when viewed from the axial direction, the discharge port 54 is formed in a region including an intersection P0 of the orbit 15a of the tooth tips of the male rotor 15 and the orbit 17a of the tooth tips of the female rotor 17.

[0041] The magnitude and direction of the radial loads FA, FB generated on the radial plain bearing 18 are determined by the pressure distribution around the rotor shafts 14, 16. Around the rotor shafts 14, 15, the pressure is highest at the position on the discharge port 54 side and lowest at the opposite position (the suction side position). Due to this pressure difference, the radial loads FA, FB generated on the radial plain bearing 18 are directed diagonally upward, as shown in Figure 6.

[0042] Therefore, in some embodiments, the radial plain bearing 18 is provided so that the minor axis AS of the contour of the bearing surface 62 is aligned along the directions of the radial loads FA and FB so that the radial plain bearing 18 can appropriately bear the above-mentioned diagonally upward radial load. That is, in some embodiments, the radial plain bearing 18 supporting the rotor shaft 14 constituting the male rotor 15 is provided so that the minor axis AS of the contour of the bearing surface 62 is aligned along the direction connecting the discharge port 54 and the axial center O1 of the rotor shaft 14 when viewed from the axial direction. Furthermore, the radial plain bearing 18 supporting the rotor shaft 16 constituting the female rotor 17 is provided so that the minor axis AS of the contour of the bearing surface 62 is aligned along the direction connecting the discharge port 54 and the axial center O2 of the rotor shaft 16 when viewed from the axial direction.

[0043] For example, when viewed from the axial direction, the radial plain bearing 18 may be arranged so that the minor axis AS of the contour of the bearing surface 62 of the radial plain bearing 18 is aligned along the intersection P0 of the orbit 15a of the tooth tips of the male rotor 15 and the orbit 17a of the tooth tips of the female rotor 17, and along the direction of the straight line L3, L4 passing through the axial center O1 of the rotor shaft 14 or the axial center O2 of the rotor shaft 16.

[0044] In one embodiment, the radial plain bearing 18 may be arranged so that, when viewed from the axial direction, the angle θ1 or θ2 (see Figure 6) between the straight line L3 or L4 passing through the above-mentioned intersection point P0 and the axial center O1 or O2 of the rotor shaft 14 or 16 and the straight line L1 or L2 extending in the direction of the minor axis AS of the contour of the bearing surface 62 is 30 degrees or less.

[0045] Alternatively, in one embodiment, the radial plain bearing 18 may be provided so that, when viewed from the axial direction, the minor axis AS of the outline of the bearing surface 62 is located within the region Z1 or Z2 between the above-mentioned line L3 or L4 and the line L5 or L6. Here, the lines L5 and L6 are lines that pass through the point in the opening region of the discharge port 54 that is farthest from the line L0 in the circumferential direction and the axial centers O1 and O2 of the rotor shafts 14 and 16, respectively (see FIG. 6 ).

[0046] Furthermore, for example, the radial plain bearing 18 may be provided so that, when viewed from the axial direction, the angle B (see FIG. 6 ) between a line L0 passing through the axial center O1 or O2 of the pair of rotor shafts 14 or 16 and a line L1 or L2 in the direction of the minor axis AS satisfies the following formula (a): B=(A+C) / 2 (a) where A in the formula (a) represents the angle between the line L0 and the line L5 or L6, and C in the formula (a) represents the angle between the line L0 and the line L3 or L4 (see FIG. 6 ). Note that the angle A is determined by the design volume ratio of the screw compressor 2.

[0047] As described above, in the screw compressor 2, the magnitude and direction of the radial loads FA, FB generated on the radial plain bearing 18 are determined by the pressure distribution around the rotor shafts 14, 16, and the radial loads FA, FB generated on the radial plain bearing 18 are directed obliquely upward as shown in Fig. 6. In this regard, according to the above-described embodiment, the radial plain bearing 18 is provided so that the minor axis AS of the profile of the bearing surface 62 is aligned along the direction connecting the discharge port 54 and the axial centers O1, O2 of the rotor shafts 14, 16. This allows the radial plain bearing 18 to appropriately bear the load of the rotor shafts 14, 16, and, as already described, reduces the amount of oil supplied to the radial plain bearing 18 or makes it possible to reduce the size of the radial plain bearing 18.

[0048] The contents described in each of the above embodiments can be understood, for example, as follows.

[0049] [1] A screw compressor (2) according to at least one embodiment of the present invention comprises: a rotor shaft (14, 16); and a radial plain bearing (18) including a sleeve (60) having a bearing surface (62) on its inner circumference and rotatably supporting the rotor shaft, wherein the bearing surface of the sleeve has a non-circular outline defined by a major axis (AL) and a minor axis (AS) in a cross section perpendicular to the axial direction of the rotor shaft, and comprises an oil supply passage (66) communicating with an oil reservoir (64) formed between a portion of the bearing surface including ends (EL1, EL2) of the major axis and the outer circumferential surface (19) of the rotor shaft.

[0050] In the configuration [1] above, the bearing surface of the sleeve has a noncircular contour defined by the major axis and the minor axis in a cross section perpendicular to the axial direction. Therefore, a relatively large oil reservoir is formed between the portion of the bearing surface including the end of the major axis and the outer circumferential surface of the rotor shaft. Therefore, fresh oil (relatively cold oil) supplied to the relatively large oil reservoir via the oil supply passage is easily drawn into the sliding surface as the rotor shaft rotates, improving cooling efficiency. Furthermore, because the bearing surface of the sleeve has the noncircular contour, the circumferential range where the gap between the bearing surface and the outer circumferential surface of the rotor shaft is narrow is relatively small. Therefore, friction loss between the rotor shaft and the sleeve can be reduced. Therefore, the configuration [1] above allows the rotor shaft to be properly supported while reducing the amount of oil supplied to the bearing or enabling the bearing to be made smaller.

[0051] [2] In some embodiments, in the configuration of [1] above, the screw compressor includes a discharge port (54) for discharging a fluid compressed by a screw rotor (e.g., a male rotor 15 and a female rotor 17) including the rotor shaft, and the radial plain bearing is arranged such that, when viewed from the axial direction, the minor axis of the contour of the bearing surface is aligned along a direction connecting the discharge port and an axial center (O1, O2) of the rotor shaft.

[0052] In a screw compressor, the magnitude and direction of the radial load generated on the radial plain bearing is determined by the pressure distribution around the rotor shaft, and the radial load generated on the radial plain bearing is directed obliquely upward when viewed from the axial direction. In this regard, according to the configuration [2] above, the radial plain bearing is provided so that the minor axis of the outline of the bearing surface is aligned with the direction connecting the discharge port and the axial center of the rotor shaft, so that the load of the rotor shaft can be appropriately borne by the radial bearing, and as described in [1] above, the amount of oil supplied to the bearing can be reduced or the bearing can be made smaller.

[0053] [3] In some embodiments, in the configuration of the above [1] or [2], the screw compressor includes a recess (72) provided in the bearing surface and into which the oil supply passage opens.

[0054] According to the configuration [3] above, the bearing surface of the sleeve is provided with a recess into which the oil supply passage opens, so that the oil supplied from the oil supply passage can be retained in the recess, thereby enabling the oil to be smoothly supplied to the space between the bearing surface and the outer peripheral surface of the rotor shaft via the recess.

[0055] [4] In some embodiments, in the configuration of [3] above, the recess is surrounded by a dam (including, for example, a side wall surface 76).

[0056] In conventional screw compressors with a relatively large rotor shaft diameter, a large amount of oil is supplied to the bearings, and therefore it is necessary to provide an oil relief groove to discharge the oil from the recesses where the oil can accumulate. In this regard, in the configuration of [4] above, as described in [1] above, the amount of oil supplied to the bearings is small, and therefore by using a configuration in which the recesses are surrounded by a dam and there is no oil relief groove, the amount of oil supplied to the bearings can be reduced.

[0057] [5] In some embodiments, in the configuration of [3] or [4] above, the recess has an intake side end (72a) and a discharge side end (72b) which are opposite ends in the axial direction, and the distance (L1) in the axial direction between an opening (69) of the oil supply passage that opens into the recess and the intake side end is shorter than the distance (L2) in the axial direction between the opening and the discharge side end.

[0058] According to the configuration [5] above, the opening of the oil supply passage is located axially closer to the suction end of the recess than to the discharge end of the recess. That is, the opening of the oil supply passage is located on the relatively high-pressure side of the recess, so that oil supplied from the oil supply passage to the recess flows in a balanced manner toward the relatively high-pressure suction end and the relatively low-pressure discharge end, making it easier to properly lubricate and cool the bearing.

[0059] [6] A gas compression facility according to at least one embodiment of the present invention comprises: a screw compressor (2) according to any one of the above [1] to [5] configured to compress gas; and an oil separator (4) for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor, wherein the oil from the oil separator is supplied to the oil reservoir.

[0060] In the configuration [6] above, the bearing surface of the sleeve has a noncircular contour defined by the major axis and the minor axis in a cross section perpendicular to the axial direction, thereby forming a relatively large oil supply passage between a portion of the bearing surface including the end of the major axis and the outer circumferential surface of the rotor shaft. Therefore, fresh oil (relatively cold oil) supplied to the relatively large oil reservoir through the oil supply passage is easily drawn into the sliding surface as the rotor shaft rotates, improving cooling efficiency. Furthermore, because the bearing surface of the sleeve has the noncircular contour, the circumferential range where the gap between the bearing surface and the outer circumferential surface of the rotor shaft is narrow is relatively small. Therefore, friction loss between the rotor shaft and the sleeve can be reduced. Therefore, the configuration [6] above allows the rotor shaft to be properly supported while reducing the amount of oil supplied to the bearing or enabling the bearing to be made smaller.

[0061] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0062] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0063] REFERENCE SIGNS LIST 1 gas compression equipment 2 screw compressor 4 oil separator 6 cooler 8 pump 10 oil supply line 12 casing 14 rotor shaft 15 male rotor 15a raceway 16 rotor shaft 17 female rotor 17a raceway 18 radial plain bearing 18A radial plain bearing 18B radial plain bearing 19 outer circumferential surface 20 thrust bearing 24 shaft seal portion 28 return line 30 balance piston 42 balance piston chamber 45 accommodation space 50 suction space 52 suction port 54 discharge port 56 passage 60 sleeve 60a end face 60b end face 61 flange portion 62 bearing surface 62a suction side end 62b discharge side end 64 oil reservoir portion 66 oil supply passage 68 oil supply hole 69 Opening 70 Groove 72 Recess 72a Suction side end 72b Discharge side end 74 Bottom surface 76 Side wall surface AL Major axis AS Minor axis EL1 End EL2 End ES1 End ES2 End O1 Shaft center O2 Shaft center P0 Intersection Pd Discharge pressure Poil Pressure Ps Suction pressure R1 Circumferential range

Claims

1. A screw compressor comprising: a rotor shaft; and a radial plain bearing including a sleeve having a bearing surface on its inner circumference and rotatably supporting the rotor shaft, wherein the bearing surface of the sleeve has a non-circular contour defined by a major axis and a minor axis in a cross section perpendicular to the axial direction of the rotor shaft, and an oil supply passage communicating with an oil reservoir formed between a portion of the bearing surface including an end of the major axis and the outer peripheral surface of the rotor shaft.

2. A screw compressor as claimed in claim 1, further comprising a discharge port for discharging fluid compressed by a screw rotor including the rotor shaft, and wherein the radial plain bearing is arranged such that, when viewed from the axial direction, the minor axis of the contour of the bearing surface is aligned along a direction connecting the discharge port and the axial center of the rotor shaft.

3. The screw compressor according to claim 1 or 2, further comprising a recess provided on the bearing surface into which the oil supply passage opens.

4. The screw compressor according to claim 3, wherein the recess is surrounded by a dam.

5. A screw compressor as described in claim 3, wherein the recess has a suction end and a discharge end which are opposite ends in the axial direction, and the distance in the axial direction between an opening of the oil supply passage that opens into the recess and the suction end is shorter than the distance in the axial direction between the opening and the discharge end.

6. A gas compression facility comprising: a screw compressor as claimed in claim 1 or 2 configured to compress gas; and an oil separator for separating the oil from a mixture of compressed gas and oil discharged from the screw compressor, wherein the oil from the oil separator is configured to be supplied to the oil reservoir.

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