Screw compressor and gas compression facility

Abstract

This screw compressor comprises: a screw rotor; a radial sliding bearing which includes a sleeve having a bearing surface on an inner periphery and which rotatably supports the screw rotor; an oil supply passage formed in the sleeve to supply oil to the bearing surface; and a recess which is provided to be recessed from the bearing surface and in which the oil supply passage opens. The recess has a first end and a second end that are both ends in an axial direction. The first end is one of the both ends and positioned on an upstream side in a first direction from a suction port toward a discharge port of the screw compressor in the axial direction. A distance in the axial direction between the first end and the opening of the oil supply passage that opens in the recess is shorter than a distance in the axial direction between the opening and the second end.

Description

Screw compressors and gas compression equipment

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

[0002] Plain bearings are used as radial bearings in rotating machinery.

[0003] Patent Document 1 describes a journal bearing (radial sliding bearing) equipped with a bearing metal (bearing sleeve) through which a rotating shaft is inserted. The bearing surface, which is the inner circumferential surface of the bearing metal, is provided with lubrication grooves, and lubricating oil is supplied to the bearing surface through these lubrication grooves.

[0004] Japanese Patent Application Publication No. 2-159411

[0005] Incidentally, in radial sliding bearings installed in screw compressors, there is a pressure difference between both ends of the bearing sleeve (or both ends of the bearing surface) in the axial direction during the operation of the screw compressor. Oil supplied to the recesses (lubrication grooves) provided on the bearing surface of the bearing sleeve flows from the recesses towards each end of the bearing sleeve. If this flow rate difference is large, the bearing sleeve cannot be lubricated and cooled evenly, making it difficult to achieve a uniform bearing temperature.

[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 facilitate uniform lubrication and cooling of radial sliding bearings.

[0007] A screw compressor according to at least one embodiment of the present invention comprises: a screw rotor; a radial sliding bearing that includes a sleeve having a bearing surface on its inner circumference and rotatably supports the screw rotor; an oil supply passage formed in the sleeve for supplying oil to the bearing surface; and a recess provided so as to be recessed from the bearing surface, with the oil supply passage opening into the recess, wherein the recess has a first end and a second end which are both ends in the axial direction, the first end being the upstream end of the two ends in the axial direction from the suction port to the discharge port of the screw compressor, and the axial distance between the opening of the oil supply passage opening into the recess and the first end is shorter than the axial distance between the opening and the second end.

[0008] Furthermore, a gas compression apparatus according to at least one embodiment of the present invention comprises the above-described screw compressor configured to compress gas, and an oil separator for separating 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 recess.

[0009] According to at least one embodiment of the present invention, a screw compressor and gas compression equipment are provided that facilitate uniform lubrication and cooling of radial sliding bearings.

[0010] This is a schematic diagram of a gas compression system including a screw compressor according to one embodiment. This is a schematic cross-sectional view of the screw compressor in plan view according to one embodiment. This is a schematic diagram showing a cross-section perpendicular to the axial direction of the rotor shaft and radial sliding bearing of the screw compressor according to one embodiment. This is a diagram showing the B-B cross-section of the radial sliding bearing shown in Figure 3. This is a diagram showing the B-B cross-section of the radial sliding bearing shown in Figure 3. This is a diagram showing an enlarged view of a part of the B-B cross-section of the radial sliding bearing according to one embodiment. This is a diagram showing an enlarged view of a part of the B-B cross-section of the radial sliding bearing according to one embodiment. This is a schematic diagram showing a cross-section perpendicular to the axial direction of the radial sliding bearing according to one embodiment.

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

[0012] (Configuration of the gas compression equipment) Figure 1 is a schematic diagram of a gas compression equipment including a screw compressor according to several embodiments. As shown in the figure, the gas compression equipment 1 comprises 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 inhaled gas. In the figure, 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 the oil supply line 10 for cooling and lubrication. 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 in general terms, the screw compressor 2 comprises a pair of screw rotors (male rotor 15 and female rotor 17) each containing rotor shafts 14 and 16, and radial sliding bearings 18 for rotatably supporting the rotor shafts 14 and 16, respectively. The radial sliding bearings 18 include a radial sliding bearing 18A located axially toward the intake port 52 (see Figure 2), which will be described later, and a radial sliding bearing 18B located axially toward the discharge port 54 (see Figure 2), which will be described later. Oil is supplied to the radial sliding bearings 18 via an oil supply line 10 for lubrication and cooling.

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

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

[0017] A pair of rotor shafts 14 and 16 are rotatably supported by radial sliding bearings 18A and 18B and a thrust bearing 20, respectively. Each bearing is supplied with oil from a pressure pot 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, along with the casing 12, forms a plurality of tooth groove spaces (chambers) along the axial direction of the rotor shafts 14 and 16.

[0019] The rotor shaft 14 constituting 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, which 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 the female rotor 17 rotate while meshed, the tooth groove space moves axially from the suction side to the discharge side.

[0020] The oil supplied to the bearings is discharged from the casing 12 and returned to the relatively low-pressure space (a space with a pressure slightly higher than the discharge pressure Ps, Ps+β (see Figure 1)) of the screw rotor housing in the casing 12 via the return line 28 (see Figures 1 and 2). Although Figure 2 shows the oil supply lines to each bearing section branching off from the oil supply line 10 and the return lines 28 from each section as external lines, they may also be lines provided inside the casing.

[0021] Gas is drawn into the aforementioned tooth groove space from the intake space 50 formed within the casing 12 via the intake port 52. As the male rotor 15 and female rotor 17 rotate, the tooth groove space moves axially from the end of the screw rotor on the intake port 52 side toward the end on the discharge port 54 side. In this process, once the intake port 52 is closed, the volume of the tooth groove space decreases, compressing the gas within the tooth groove space. When the tooth groove space reaches the discharge port 54 and communicates with the discharge space (not shown) formed in the casing 12, the compressed gas within the tooth groove space is discharged into the discharge space. The discharge port 54 is formed by an opening provided at the discharge end of the casing 12.

[0022] Here, in this specification, the direction from the intake port 52 to the discharge port 54 in the axial direction is defined as the first direction.

[0023] Figure 3 is a schematic diagram showing a cross-section perpendicular to the axial direction of the rotor shaft 14 and radial sliding bearings 18 (18A, 18B) of a screw compressor 2 according to one embodiment. Figures 4 and 5 are diagrams showing the B-B cross-section of the radial sliding bearing shown in Figure 3, respectively. Figure 4 shows the cross-section of the radial sliding bearing 18A on the intake port 52 side, and Figure 5 shows the cross-section of the radial sliding bearing 18B on the discharge port 54 side. Figures 6 and 7 are enlarged views showing a part of the B-B cross-section of the radial sliding bearing according to one embodiment, respectively. Figure 6 is an enlarged view of the cross-section of the radial sliding bearing shown in Figure 3, and Figure 7 is an enlarged view of the cross-section of the radial sliding bearing according to another embodiment.

[0024] In the following description, the radial sliding bearings 18 (18A, 18B) supporting the rotor shaft 14 that constitutes the male rotor 15 will be explained with reference to the figures, but the same explanation can be applied to the radial sliding bearings 18 (18A, 18B) supporting the rotor shaft 16 that constitutes the female rotor 17.

[0025] As shown in Figures 3 to 5, the radial sliding bearing 18 includes a sleeve 60 having a bearing surface 62 on its inner circumference. As shown in Figures 4 and 5, the sleeve 60 has an upstream end face 60a and a downstream end face 60b in the first direction. The bearing surface 62 also has a first upstream end 62a and a second downstream end 62b in the first direction.

[0026] As shown in Figures 4 and 5, the first end 62a and the second end 62b of the bearing surface 62 do not necessarily coincide with the upstream end face 60a and the downstream end face 60b of the sleeve 60. That is, as shown in Figures 4 and 5, the bearing surface 62 may be formed only in a portion of the axial extension range of the sleeve 60. Alternatively, the first end 62a and the second end 62b of the bearing surface 62 may coincide with the upstream end face 60a and the downstream end face 60b of the sleeve 60.

[0027] The sleeve 60 may include a flange 61 for positioning the sleeve 60 in the axial direction. As shown in the figure, the flange 61 of the radial sliding bearing 18A provided on the intake port 52 side in the axial direction may be provided at the upstream end of the radial sliding bearing 18A in the first direction. The flange 61 of the radial sliding bearing 18B provided on the discharge port 54 side in the axial direction may be provided at the downstream end of the radial sliding bearing 18A in the first direction.

[0028] As shown in Figure 3, the bearing surface 62 of the sleeve 60 may have a perfectly circular contour centered on the central axis O in a cross-section perpendicular to the axial direction of the rotor shaft 14. Alternatively, the bearing surface 62 of the sleeve 60 may have a non-circular contour such as a substantially elliptical shape.

[0029] A bearing gap 64 is formed between the bearing surface 62 and the outer circumferential surface 19 of the rotor shaft 14.

[0030] The screw compressor 2 is equipped with an oil supply passage 66 that communicates with the bearing gap 64. In the embodiment shown in Figure 3, the oil supply passage 66 includes an oil supply hole 68 provided in the sleeve 60. The oil supply passage 66 may also include a passage 56 (see Figure 2) provided in the casing 12. Alternatively, the oil supply passage 66 may include a groove 70 (see Figures 4 and 5) provided circumferentially on the outer surface of the sleeve 60. Oil from the oil separator 4 (see Figure 1) is supplied to the bearing gap 64 via the oil supply line 10 (see Figure 1) and the oil supply passage 66 (passage 56, groove 70, and oil supply hole 68).

[0031] As shown in Figures 3 to 7, in some embodiments, the bearing surface 62 of the sleeve 60 is provided with a recess 72 through which an oil supply passage 66 opens. The recess 72 is provided so as to be recessed from the bearing surface 62. The recess 72 may include a bottom surface 74 through which the oil supply passage 66 opens, and a pair of side wall surfaces 76 (see Figures 4 and 5) provided at the axial end of the recess 72. The bottom surface 74 may have a curved surface that curves along the circumferential direction, as shown in Figures 3 to 6, or it may have a flat surface.

[0032] In the exemplary embodiments shown in Figures 3 to 6, the recess 72 includes a bottom surface 74 and a pair of side wall surfaces 76, as well as a pair of side wall surfaces 75 (see Figures 3 and 6) provided at the circumferential end of the recess 72. When the recess 72 is viewed radially, the bottom surface 74 is surrounded by the pair of side wall surfaces 76 and the pair of side wall surfaces 75.

[0033] In the exemplary embodiment shown in Figure 7, the recess 72 includes a bottom surface 74 that curves along an arc with a greater curvature than the bearing surface 62 when viewed from the axial direction, and a pair of side wall surfaces 76 (see Figures 4 and 5) provided at the axial end of the recess 72. When viewed from the axial direction, the intersection 74a of the arc containing the bottom surface 74 and the bearing surface 62 forms the circumferential end of the recess 72.

[0034] As shown in Figures 3 to 7, 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 side wall surfaces 76 located at both ends of the recess 72 (see Figures 3 to 7), and by side wall surfaces 75 (see Figure 6) or circumferential ends (see Figure 7) located at both ends in the circumferential direction of the recess 72.

[0035] The recess 72 has two ends in the axial direction, a first end 72a and a second end 72b. The first end 72a is the upstream end in the first direction described above, and the second end 72b is the downstream end in the first direction described above. In the exemplary embodiments shown in Figures 3 to 7, the pair of side wall surfaces 76 provided at the axial ends of the recess 72 include the first end 72a and the second end 72b of the recess 72.

[0036] In some embodiments, as shown in Figure 3, for example, a pair of recesses are provided on both sides of the central axis O of the radial sliding bearing 18 when viewed from the axial direction.

[0037] In some embodiments, the axial distance L1 between the opening 69 of the oil supply passage 66 opening into the recess 72 and the first end 72a of the recess 72 is shorter than the axial distance L2 between the opening 69 and the second end 72b of the recess 72.

[0038] In the screw compressor 2, of the two ends of the bearing surface 62 of the sleeve 60 of the radial sliding bearing 18, the pressure at the first end 62a, which is located upstream in the first direction, is higher than that at the second end 62b, which is located downstream. This is because, in the case of the radial sliding bearing 18A on the suction port 52 side, the pressure at the first end 62a of the bearing surface 62 is Ps + β (pressure in the return line 28), and the pressure at the second end 62b of the bearing surface 62 is the suction pressure Ps (<(Ps + β)). Also, in the case of the radial sliding bearing 18B on the discharge port 54 side, the pressure at the first end 62a of the bearing surface 62 is the discharge pressure Pd, and the pressure at the second end 62b of the bearing surface 62 is Ps + β (pressure in the return line 28; Pd > (Ps + β)).

[0039] Furthermore, among the two axial ends of the recess 72 provided on the bearing surface 62 of the sleeve 60, the first end 72a located on the upstream side in the first direction has a higher pressure than the second end 72b located on the downstream side.

[0040] According to the above-described embodiment, the opening 69 of the oil supply passage 66 for supplying oil to the recess 72 provided on the bearing surface 62 of the sleeve 60 is located relatively upstream in the first direction in the axial direction (the side closer to the first end 72a of the recess 72). That is, among the first end 72a and the second end 72b of the recess 72, the distance (L2) to the second end 72b, which has a lower pressure and a larger pressure difference from the pressure at the opening 69 of the oil supply passage 66 (a high pressure equal to or higher than the discharge pressure (Pd + α)), is relatively long. Therefore, the amount of oil flowing from the opening 69 toward the second end 72b of the recess 72 in the axial direction can be made larger than the amount of oil flowing from the opening 69 toward the first end 72a of the recess 72 in the axial direction. Accordingly, in the region between the first end 72a and the second end 72b of the recess 72 in the axial direction, oil can be easily supplied uniformly in the axial direction to the bearing gap 64. Therefore, the radial plain bearing 18 can be easily uniformly lubricated and cooled.

[0041] In some embodiments, in a cross section perpendicular to the axial direction, the ratio S / A of the area S of the recess 72 (see FIGS. 6 and 7) to the area A of the bearing gap 64 (see FIGS. 6 and 7) included in the angular range θ in which the recess 72 is present around the central axis O of the radial plain bearing 18 (see FIGS. 6 and 7) is 30 or more and 60 or less.

[0042] The area S of the above-described recess 72 is an area surrounded by the recess 72 and the circle including the bearing surface 62 in a cross section perpendicular to the axial direction. In addition, the area A of the above-described bearing gap 64 is the area of the portion of the bearing gap 64 included in the above-described angular range θ when the central axis of the rotor shaft 14 coincides with the central axis O of the radial plain bearing 18 (that is, when the width of the bearing gap 64 is constant over the entire circumference) in a cross section perpendicular to the axial direction.

[0043] In the above configuration, the ratio S / A is 30 or more, and the area S of the recess 72 is large to a certain extent, so that an appropriate amount of oil can be supplied to the bearing surface 62. In addition, in the above configuration, the ratio S / A is 60 or less, and the area S of the recess 72 is small to a certain extent, so that a pressure gradient corresponding to the flow path length in the axial direction (the length between the opening 69 of the oil supply passage 66 and the first end 72a and the second end 72b of the recess 72) can be formed inside the recess 72. Therefore, as described above, the pressure gradient between the opening 69 and the first end 72a of the recess 72 and the pressure gradient between the opening 69 and the second end 72b of the recess 72 can be made substantially equal, which makes it easy to uniformly supply oil to the bearing gap 64 in the axial direction. Therefore, according to the above embodiment, uniform lubrication and cooling can be easily achieved while supplying an appropriate amount of oil to the radial plain bearing 18.

[0044] Incidentally, when gas is dissolved in oil, the viscosity of the oil decreases. If the viscosity of oil in a plain bearing decreases, a sufficient bearing oil film cannot be formed, which may cause problems such as wear and vibration. In this regard, the recess 72 provided on the bearing surface 62 degasses the gas dissolved in the oil and dams the degassed air bubbles so as not to flow them out into the bearing gap 64, thereby maintaining the viscosity of the oil supplied to the bearing gap 64 and also having the role of suppressing a decrease in the load capacity of the radial plain bearing 18.

[0045] Here, the pressure of the oil supplied to the recess 72 is reduced at the opening 69 of the oil supply passage 66. On the other hand, the pressures at both ends (the first end 62a and the second end 62b) of the bearing surface 62 (Ps+β and Ps, or Pd and Ps+β) are constant. Further, since the recess 72 has a certain cross-sectional area S, the pressure gradient in the axial direction is relatively gentle, while the region outside the recess 72 (the region between the first end 72a / second end 72b of the recess 72 and the first end 62a / second end 62b of the bearing surface 62) forms the bearing gap 64 with a small cross-sectional area A, so the pressure gradient in the axial direction is relatively steep. These pressure gradients and the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 change according to the degree of restriction (S / A) imposed by the bearing gap 64.

[0046] In the above-described embodiment, since the ratio S / A is 30 or more, the degree of restriction by the bearing gap 64 is not too small, so the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 does not become too large, and the amount of gas removed from the oil does not become too large. Therefore, it is possible to suppress the outflow of the removed gas into the bearing gap 64, the resulting decrease in the viscosity of the oil in the bearing gap 64, and the occurrence of a cavitation region in the bearing gap 64. Also, in the above-described embodiment, since the ratio S / A is 60 or less, the degree of restriction by the bearing gap 64 is not too large, so the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 does not become too small, and the gas in the oil is appropriately removed. Therefore, it is possible to suppress the decrease in the viscosity of the oil supplied to the bearing gap 64. Thus, according to the above-described embodiment, it is possible to maintain the viscosity of the oil in the bearing gap 64 within an appropriate range, suppress the decrease in the load capacity of the radial sliding bearing 18, and to make it easier to uniformly lubricate and cool the radial sliding bearing 18 as described above.

[0047] In some embodiments, when L0 is the distance between the first end 62a and the second end 62b of the bearing surface 62 in the axial direction, b1 is the distance between the first end 72a of the recess 72 and the first end 62a of the bearing surface 62 in the axial direction, and b2 is the distance between the second end 72b of the recess 72 and the second end 62b of the bearing surface 62 in the axial direction, the ratio b1 / L0 of distance b1 to distance L0, and the ratio b2 / L0 of distance b2 to distance L0 are 0.1 or more and 0.2 or less (see Figures 4 and 5).

[0048] In the above-described embodiment, the ratios b1 / L0 and b2 / L0 are 0.1 or greater, and the distances b1 and b2 between the ends of the recess 72 (first end 72a and second end 72b) and the ends of the bearing surface 62 (first end 62a and second end 62b) are sufficiently large relative to the length L0 of the bearing surface 62 in the axial direction, so that the degree of constriction by the bearing gap 64 is not too small. As a result, the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 does not become too large, and the amount of degassing from the oil does not become too large. As a result, it is possible to suppress the outflow of degassed gas into the bearing gap 64, the resulting decrease in the viscosity of the oil in the bearing gap 64, and the generation of cavitation regions in the bearing gap 64. Furthermore, in the above-described embodiment, the ratios b1 / L0 and b2 / L0 are 0.2 or less, and the length of the recess 72 in the axial direction (L0 - (b1 + b2) = L1 + L2) is somewhat long compared to the distances b1 and b2 between the end of the recess 72 and the end of the bearing surface 62, so the degree of constriction by the bearing gap 64 is not too great. As a result, the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 is not too small, and gas in the oil is properly degassed. As a result, a decrease in the viscosity of the oil supplied to the bearing gap 64 can be suppressed. Thus, according to the above-described embodiment, it is easier to uniformly lubricate and cool the radial sliding bearing 18 while appropriately supplying oil to it, while suppressing a decrease in the load capacity of the radial sliding bearing 18.

[0049] In some embodiments, the ratio a / D of the circumferential length a of the bearing surface 62 (see Figures 4 to 7) within the angular range θ where the recess 72 exists around the central axis O of the radial sliding bearing 18, to the diameter D of the bearing surface 62 (see Figure 3), is 0.3 or more and 0.4 or less.

[0050] In the above-described embodiment, the ratio a / D is 0.3 or more, the circumferential length a of the recess 72 relative to the diameter D of the bearing surface 62 is relatively long, and the area occupied by the recess 72 in the circumferential direction is relatively wide, so the flow velocity of the oil in the recess 72 can be suppressed, thereby ensuring the residence time of the oil in the recess 72. Therefore, the oil can be properly degassed in the recess 72. Also, in the above-described embodiment, the ratio a / D is 0.4 or less, the circumferential length a of the recess 72 relative to the diameter D of the bearing surface 62 is relatively short, and the area occupied by the recess 72 in the circumferential direction is relatively narrow, so a wide range of loads can be appropriately borne. Therefore, according to the above-described embodiment, it is possible to enable the bearing of a wide range of loads while suppressing a decrease in load capacity, and uniform lubrication and cooling can be easily achieved.

[0051] Figure 8 is a schematic diagram showing cross-sections perpendicular to the axial direction of the rotor shafts 14 and 16 and the radial sliding bearings 18 that support the rotor shafts 14 and 16, respectively, of a screw compressor 2 according to one embodiment. In Figure 8, reference numerals 15a and 17a indicate the tooth tip raceways (outermost positions) of the male rotor 15 and female rotor 17, respectively.

[0052] As shown in Figure 8, when viewed from the axial direction, the discharge port 54 of the screw compressor 2 is located horizontally between the central axis O1 of the rotor shaft 14 and the central axis O2 of the rotor shaft 16, and vertically offset from the central axis O1 of the rotor shaft 14 and the central axis O2 of the rotor shaft 16. Also, when viewed from the axial direction, the discharge port 54 is formed in a region that includes the intersection point P0 of the tooth tip raceway 15a of the male rotor 15 and the tooth tip raceway 17a of the female rotor 17.

[0053] Radial load F generated on the radial sliding bearing 18 Ａ , F Ｂ The magnitude and direction of the radial load F generated on the radial sliding bearing 18 are determined by the pressure distribution around the rotor shafts 14 and 16. Around the rotor shafts 14 and 16, the pressure is highest at the discharge port 54 side and lowest at the opposite side (the suction side). This pressure difference generates a radial load F on the radial sliding bearing 18. Ａ , F Ｂ As shown in Figure 8, it points diagonally upwards.

[0054] Therefore, in some embodiments, the radial sliding bearing 18 is configured to appropriately receive the aforementioned diagonally upward radial load, such that when viewed from the axial direction, a straight line A2 perpendicular to a straight line A1 connecting a pair of recesses 72 provided on either side of the central axis O(O1, O2) of the radial sliding bearing 18 is such that the radial load F Ａ F Ｂ They are provided so as to be aligned in the direction of the radial sliding bearing 18. That is, in some embodiments, when viewed from the axial direction, the straight line A1 connecting the pair of recesses 72 provided on either side of the central axis O(O1, O2) of the radial sliding bearing 18 is provided so as to be aligned in a direction perpendicular to the straight line A2 in the direction connecting the discharge port 54 and the central axis O(O1, O2) of the radial sliding bearing 18.

[0055] For example, the radial sliding bearing 18 may be provided such that, when viewed from the axial direction, the straight line A2 connecting the discharge port 54 and the central axis O(O1, O2) of the radial sliding bearing 18 aligns with the intersection point P0 of the tooth tip raceway 15a of the male rotor 15 and the tooth tip raceway 17a of the female rotor 17, and with the straight lines Lc and Ld passing through the central axis O1 of the rotor shaft 14 or the central axis O2 of the rotor shaft 16.

[0056] In one embodiment, the radial sliding bearing 18 may be provided such that, when viewed from the axial direction, the angle θ1 or θ2 (see Figure 6) between the straight line Lc or Ld passing through the intersection P0 and the central axis O1 or O2 of the rotor shaft 14 or 16 and the straight line La or Lb extending in the direction of the straight line A2 is 30 degrees or less.

[0057] Alternatively, in one embodiment, the radial sliding bearing 18 may be provided such that, when viewed from the axial direction, the aforementioned straight line A2 is located within the region Z1 or Z2 between the aforementioned straight line Lc or Ld and the straight line Le or Lf. Here, the straight lines Le and Lf are the point furthest from the straight line Lx in the circumferential direction in the opening region of the discharge port 54, and the straight line passing through the central axes O1 and O2 of the rotor shafts 14 and 16, respectively (see Figure 8).

[0058] Further, for example, when viewed from the axial direction, an angle B2 (see FIG. 8) between a straight line Lx passing through the central axis O1 or O2 of the pair of rotor shafts 14 or 16 and a straight line La or Lb in the direction of the aforementioned straight line A2 may satisfy the following formula (a), and the radial slide bearing 18 may be provided so as to satisfy this condition. B2=(B1+B3) / 2 ...(a) Here, B1 in the above formula (a) represents the angle between the aforementioned straight line Lx and the aforementioned straight line Le or Lf, and B3 in the above formula (a) represents the angle between the aforementioned straight line Lx and the aforementioned straight line Lc or Ld (see FIG. 8). The aforementioned angle B1 is determined by the design volume ratio of the screw compressor 2.

[0059] As described above, in the screw compressor 2, the radial load F generated in the radial slide bearing 18 Ａ , F Ｂ The magnitude and direction of are determined by the pressure distribution around the rotor shafts 14 and 16, and the radial load F generated in the radial slide bearing 18 Ａ , F Ｂ is directed obliquely upward as shown in FIG. 8. In this regard, according to the above embodiment, the radial slide bearing 18 is provided such that the straight line A1 connecting the pair of recesses 72 to each other extends along a direction orthogonal to the direction connecting the discharge port 54 and the central axis O of the radial slide bearing 18. Therefore, the load of the rotor shafts 14 and 16 can be appropriately borne by the radial slide bearing 18, and as already described, it becomes easy to uniformly lubricate and cool the radial slide bearing 18.

[0060] The contents described in each of the above embodiments can be understood, for example, as follows.

[0061] [1] A screw compressor (2) according to at least one embodiment of the present invention comprises: a screw rotor (15, 17); a radial sliding bearing (18) that rotatably supports the screw rotor, including a sleeve (60) having a bearing surface (62) on its inner circumference; an oil supply passage (66) formed in the sleeve for supplying oil to the bearing surface; and a recess (72) provided so as to be recessed from the bearing surface, with the oil supply passage opening into the recess, wherein the recess has a first end (72a) and a second end (72b) which are both ends in the axial direction, the first end being the one of the two ends located upstream in the axial direction from the suction port (52) to the discharge port (54) of the screw compressor, and the axial distance (L1) between the opening (69) of the oil supply passage opening into the recess and the first end is shorter than the axial distance (L2) between the opening and the second end.

[0062] In a screw compressor, of the two ends of the bearing surface of the sleeve of a radial sliding bearing in the axial direction, the first end, located upstream in the first direction, is at a higher pressure than the second end, located downstream. According to the configuration in [1] above, the opening of the oil supply passage for supplying oil to the recess provided on the bearing surface of the sleeve is located relatively upstream in the first direction in the axial direction (closer to the first end 72a of the recess). That is, of the first and second ends of the recess, the distance to the second end, which is at a lower pressure and has a larger pressure difference with the pressure at the opening of the oil supply passage (high pressure equal to or greater than the discharge pressure (Pd + α)), is relatively long. For this reason, the amount of oil flowing from the opening to the second end of the recess in the axial direction can be increased compared to the amount of oil flowing from the opening to the first end of the recess in the axial direction. For this reason, it becomes easier to supply oil uniformly in the axial direction to the bearing gap in the region between the first and second ends of the recess in the axial direction. Thus, it becomes easier to lubricate and cool the radial sliding bearing uniformly.

[0063] [2] In some embodiments, in the configuration of [1] above, the ratio S / A of the area S of the recess and the area A of the bearing clearance (64) included in the angular range (θ) where the recess exists around the central axis (O) of the radial sliding bearing is 30 or more and 60 or less.

[0064] In the configuration of [2] above, the ratio S / A is 30 or more, and the area S of the recess is relatively large, so an appropriate amount of oil can be supplied to the bearing surface. Also, in the configuration of [2] above, the ratio S / A is 60 or less, and the area S of the recess is relatively small, so a pressure gradient corresponding to the flow path length (the length between the oil supply port and the first and second ends of the recess) can be formed in the axial direction inside the recess. For this reason, as described in [1] above, the pressure gradient between the opening of the oil supply passage and the first end of the recess can be made to be about the same as the pressure gradient between the opening of the oil supply passage and the second end of the recess, making it easier to supply oil uniformly to the bearing gap in the axial direction. Thus, according to the configuration of [2] above, it is easier to lubricate and cool the radial sliding bearing uniformly while supplying an appropriate amount of oil.

[0065] Incidentally, when gas is dissolved in oil, the viscosity of the oil decreases. In sliding bearings, if the viscosity of the oil decreases, the bearing oil film may not form sufficiently, which may lead to problems such as wear and vibration. In this regard, the recess provided on the bearing surface plays a role in maintaining the viscosity of the oil supplied to the bearing gap by degassing the gas dissolved in the oil and preventing the degassed air bubbles from flowing out into the bearing gap, thereby suppressing a decrease in the load capacity of the radial sliding bearing.

[0066] In the configuration of [2] above, since the ratio S / A is 30 or more, the degree of restriction due to the bearing gap is not too small, so the degree of pressure reduction at the opening of the oil supply passage in the recess does not become too large, and the amount of gas removed from the oil does not become too large. Therefore, it is possible to suppress the outflow of the removed gas into the bearing gap, the decrease in the viscosity of the oil in the bearing gap caused by this, and the generation of cavitation regions in the bearing gap. Also, in the configuration of [2] above, since the ratio S / A is 60 or less, the degree of restriction due to the bearing gap is not too large, so the degree of pressure reduction at the opening of the oil supply passage in the recess does not become too small, and the gas in the oil is properly removed. Therefore, it is possible to suppress the decrease in the viscosity of the oil supplied to the bearing gap. Thus, according to the configuration of [2] above, it is possible to maintain the viscosity of the oil in the bearing gap within an appropriate range, suppress the decrease in the load capacity of the radial sliding bearing, and to lubricate and cool the radial sliding bearing uniformly as described above.

[0067] [3] In some embodiments, in the configuration of [1] or [2] above, the bearing surface (62) of the sleeve has a first end (62a) and a second end (62b) which are both ends in the axial direction, the first end of the bearing surface is the one of the two ends of the bearing surface that is located on the upstream side in the first direction, and when the distance between the first end of the bearing surface and the second end of the bearing surface in the axial direction is L0, the distance between the first end of the recess and the first end of the bearing surface in the axial direction is b1, and the distance between the second end of the recess and the second end of the bearing surface in the axial direction is b2, the ratio of distance b1 to distance L0 b1 / L0 and the ratio of distance b2 to distance L0 b2 / L0 are 0.1 or more and 0.2 or less.

[0068] In the configuration of [3] above, the ratios b1 / L0 and b2 / L0 are 0.1 or greater, and the distances b1 and b2 between the end of the recess and the end of the bearing surface are relatively large relative to the length L of the bearing surface in the axial direction, so the degree of constriction by the bearing gap 64 is not too small. As a result, the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 does not become too large, and the amount of degassing from the oil does not become too large. As a result, the outflow of degassed gas into the bearing gap 64, the resulting decrease in the viscosity of the oil in the bearing gap 64, and the generation of a cavitation region in the bearing gap 64 can be suppressed. Furthermore, in the configuration of [3] above, the ratios b1 / L0 and b2 / L0 are 0.2 or less, and the length of the recess in the axial direction (L0 - (b1 + b2)) is relatively long relative to the distances b1 and b2 between the end of the recess and the end of the bearing surface, so the degree of constriction by the bearing gap 64 is not too large. Therefore, the degree of pressure reduction at the opening 69 of the oil supply passage 66 in the recess 72 does not become too small, and gas in the oil is properly degassed. As a result, a decrease in the viscosity of the oil supplied to the bearing gap 64 can be suppressed. Thus, according to the configuration of [3] above, it becomes easier to uniformly lubricate and cool the radial sliding bearing while properly supplying oil to it while suppressing a decrease in load capacity.

[0069] [4] In some embodiments, in any of the configurations [1] to [3] above, the ratio a / D of the circumferential length a of the bearing surface to the diameter D of the bearing surface, which is included in the angular range (θ) where the recess exists around the central axis of the radial sliding bearing, is 0.3 or more and 0.4 or less.

[0070] In the configuration of [4] above, the ratio a / D is 0.3 or more, the circumferential length a of the recess relative to the diameter D of the bearing surface is relatively long, and the area occupied by the recess in the circumferential direction is relatively wide, so the flow velocity of the oil in the recess can be suppressed, thereby ensuring the residence time of the oil in the recess. Therefore, proper degassing of the oil can be performed in the recess. Also, in the configuration of [4] above, the ratio a / D is 0.4 or less, the circumferential length a of the recess relative to the diameter D of the bearing surface is relatively short, and the area occupied by the recess in the circumferential direction is relatively narrow, so a wide range of loads can be appropriately borne. Therefore, according to the configuration of [4] above, uniform lubrication and cooling can be easily achieved while suppressing a decrease in load capacity and enabling the bearing of a wide range of loads.

[0071] [5] In some embodiments, in any of the configurations [1] to [4] above, the recess is surrounded by a dam (including, for example, a side wall surface 75 and / or a side wall surface 76).

[0072] According to the configuration of [5] above, since a recess surrounded by a dam is provided on the bearing surface, as described in [1] above, it is possible to suppress the expansion of the difference in oil flow rate from the recess toward both ends of the bearing surface of the sleeve in the axial direction, making it easier to uniformly lubricate and cool the radial sliding bearing.

[0073] [6] In some embodiments, in any of the configurations [1] to [5] above, the screw compressor comprises a pair of recesses located on both sides of the central axis of the radial sliding bearing when viewed from the axial direction, and a discharge port for discharging the fluid compressed by the screw rotor, and the radial sliding bearing is provided such that, when viewed from the axial direction, the straight line (A1) connecting the pair of recesses is aligned in a direction perpendicular to the direction connecting the discharge port and the central axis of the radial sliding bearing.

[0074] In a screw compressor, the magnitude and direction of the radial load generated on the radial sliding bearing are determined by the pressure distribution around the rotor shaft, and the radial load generated on the radial sliding bearing is obliquely upward when viewed from the axial direction. In this respect, according to the configuration of [6] above, when viewed from the axial direction, the radial sliding bearing is provided such that the straight line connecting the pair of recesses is aligned in a direction perpendicular to the direction connecting the discharge port and the central axis of the radial sliding bearing. This allows the radial bearing to appropriately bear the load of the rotor shaft, and as described in [1] above, it becomes easier to uniformly lubricate and cool the radial sliding bearing.

[0075] [7] A gas compression apparatus (1) according to at least one embodiment of the present invention comprises a screw compressor (2) according to any one of [1] to [6] above, configured to compress gas, and an oil separator (4) for separating 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 recess.

[0076] In a screw compressor, of the two ends of the bearing surface of the sleeve of a radial plain bearing in the axial direction, the first end, which is located upstream in the first direction, is under higher pressure than the second end, which is located downstream. According to the configuration of [7] above, the opening of the oil supply passage for supplying oil to the recess provided in the bearing surface of the sleeve is located relatively upstream in the first direction in the axial direction (closer to the first end of the recess), so that the pressure gradient between the first end of the recess and the first end of the bearing surface and the pressure gradient between the second end of the recess and the second end surface of the bearing surface can be made to be about the same. Therefore, it is possible to suppress the expansion of the difference in the flow rate of oil flowing from the recess to both ends of the bearing surface of the sleeve in the axial direction. Therefore, it becomes easier to lubricate and cool the radial plain bearing uniformly.

[0077] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0078] In this specification, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" shall not only describe such arrangements strictly, but also describe states of relative displacement with tolerances or angles or distances sufficient to achieve the same function. For example, expressions describing things being in an equal state such as "identical," "equal," and "homogeneous" shall not only describe states of being strictly equal, but also describe states where tolerances or differences exist to the extent that the same function is achieved. Furthermore, in this specification, expressions describing shapes such as quadrilaterals or cylindrical shapes shall not only describe geometrically precise quadrilaterals or cylindrical shapes, but also describe shapes including concave and concave parts, chamfered parts, etc., to the extent that the same effect is achieved. In addition, in this specification, expressions such as "equipment," "includes," or "possesses" a component are not exclusive expressions that exclude the existence of other components.

[0079] 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 surface 20 Thrust bearing 24 Shaft seal section 28 Return line 30 Balance piston 42 Balance piston chamber 45 Housing space 50 Suction space 52 Suction port 54 Discharge port 56 Passageway 60 Sleeve 60a End face 60b End face 61 Flange 62 Bearing surface 62a First end 62b Second end 64 Bearing clearance 66 Oil supply passage 68 Oil supply hole 69 Opening 70 Groove 72 Recess 72a First end 72b Second end 74 Bottom surface 74a Circumferential end 75 Side wall surface 76 Side wall surface A Area O Central axis O1 Central axis O2 Central axis P0 Intersection Pd Discharge pressure Poil Pressure Ps Suction pressure S Area θ Angle range

Claims

1. A screw compressor comprising: a screw rotor; a radial sliding bearing including a sleeve having a bearing surface on its inner circumference, which rotatably supports the screw rotor; an oil supply passage formed in the sleeve for supplying oil to the bearing surface; and a recess provided so as to be recessed from the bearing surface, through which the oil supply passage opens, wherein the recess has a first end and a second end which are both ends in the axial direction, the first end being the upstream end of the two ends in the axial direction from the suction port to the discharge port of the screw compressor, and the axial distance between the opening of the oil supply passage opening into the recess and the first end is shorter than the axial distance between the opening and the second end.

2. The screw compressor according to claim 1, wherein, in a cross section perpendicular to the axial direction, the ratio S / A of the area of ​​the recess to the area of ​​the bearing clearance A included in the angular range in which the recess exists around the central axis of the radial sliding bearing is 30 or more and 60 or less.

3. The screw compressor according to claim 1 or 2, wherein the bearing surface of the sleeve has a first end and a second end which are both ends in the axial direction, the first end being the one of the two ends of the bearing surface located on the upstream side in the first direction, and when L0 is the distance between the first end of the bearing surface and the second end of the bearing surface in the axial direction, b1 is the distance between the first end of the recess and the first end of the bearing surface in the axial direction, and b2 is the distance between the second end of the recess and the second end of the bearing surface in the axial direction, the ratio b1 / L0 of distance b1 to distance L0 and the ratio b2 / L0 of distance b2 to distance L0 are 0.1 or more and 0.2 or less.

4. The screw compressor according to claim 1 or 2, wherein the ratio a / D of the diameter D of the bearing surface to the length a in the circumferential direction of the bearing surface included in the angular range in which the recess exists around the central axis of the radial sliding bearing is 0.3 or more and 0.4 or less.

5. The screw compressor according to claim 1 or 2, wherein the recess is surrounded by a dam.

6. The screw compressor according to claim 1 or 2, comprising a pair of recesses provided on both sides of the central axis of the radial sliding bearing when viewed from the axial direction, and a discharge port for discharging the fluid compressed by the screw rotor, wherein the radial sliding bearing is provided such that, when viewed from the axial direction, the straight line connecting the pair of recesses is aligned in a direction perpendicular to the direction connecting the discharge port and the central axis of the radial sliding bearing.

7. A gas compression apparatus comprising: a screw compressor according to claim 1 or 2, configured to compress gas; and an oil separator for separating 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 recess.

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