Oil-flooded screw compressor and method for recovering lubricating oil from the discharge side bearing chamber of the oil-flooded screw compressor

Abstract

The lubricating oil in the discharge side bearing chamber is recovered into the compressor body at a low temperature. [Solution] The discharge-side bearing chamber and gear chamber 71 of the compressor body 10 of the oil-cooled screw compressor 1 are connected via a pressure recovery passage 47, and an oil sump 75 formed at the bottom of the gear chamber 71 is connected via a lubricating oil recovery passage 5 to a recovery space 29, which is a space within the cylinder casing 11 at a lower pressure than the gear chamber 71. The high-temperature lubricating oil recovered from the discharge-side bearing chamber is separated from the compressed gas within the gear chamber 71 and recovered in the oil sump 75 at the bottom of the gear chamber 71, where it is cooled by mixing with the lubricating oil in the oil sump 75. By recovering the lubricating oil recovered in the oil sump 75 in the recovery space 29, the cooled lubricating oil can be recovered in the compressor body 10, preventing a rise in temperature within the recovery space 29 and suppressing an increase in stirring resistance without requiring an increase in the amount of lubricating oil for cooling.

Description

[Technical Field]

[0001] The present invention relates to an oil-cooled screw compressor having a structure for recovering lubricating oil supplied to the discharge side bearing chamber of the compressor body into a lubricating oil circulation system, and a method for recovering lubricating oil from the discharge side bearing chamber of the compressor body, which is performed in the oil-cooled screw compressor. [Background technology]

[0002] An oil-cooled screw compressor has a compressor body that is driven by a driving source such as an engine or motor, and is configured to generate compressed gas by compressing the gas to be compressed together with lubricating oil supplied through an oil supply port by meshing and rotating a pair of male and female screw rotors within a cylinder formed within the casing of the compressor body.

[0003] As such, the compressor body of an oil-cooled screw compressor generates compressed gas as a gas-liquid mixed fluid with lubricating oil. The compressed gas discharged from the compressor body is first introduced into a receiver tank where gas-liquid separation takes place, and the compressed gas from which the lubricating oil has been removed is then supplied to the consumption side. At the same time, the lubricating oil recovered in the receiver tank is re-supplied to the compressor body via the aforementioned oil inlet, etc., thereby forming a lubricating oil circulation system and enabling the lubricating oil to be circulated and used.

[0004] As an example of the configuration of a compressor body provided in such an oil-cooled screw compressor, Patent Document 1, cited below, discloses a multi-stage compressor body 100 shown in FIG.

[0005] This multi-stage compressor body 100 is configured such that the discharge port 125 of the low-pressure stage compressor body 120 is connected to the intake port 136 of the high-pressure stage compressor body 130 via an intermediate stage flow path 140, so that the compressed gas generated in the low-pressure stage compressor body 120 can be introduced into the high-pressure stage compressor body 130 via the intermediate stage flow path 140 and further compressed.

[0006] The configuration shown in Figure 8 includes a cylinder casing 111 in which a low-pressure stage cylinder 122 and a high-pressure stage cylinder 132 are formed in parallel, end covers 151, 152 that cover the discharge side end of the cylinder casing 111, and a gear casing 170 that covers the suction side end of the cylinder casing 111, and a pair of male and female screw rotors 123, 124; 133, 134 (the screw rotors 124, 134 are hidden on the back side of the paper of the screw rotors 123, 133) are meshed with and rotatable in the low-pressure stage cylinder 122 and the high-pressure stage cylinder 132, respectively. The low-pressure stage compressor body 120 and the high-pressure stage compressor body 130 are formed by the discharge side rotor shafts 123a, 124a; 133a, 134a of the screw rotors 123, 124; 133, 134 being housed in the end covers 151, 152 and by the bearings 161, 164 housed in the end covers 151, 152, the discharge side rotor shafts 123a, 124a; 133a, 134a of the screw rotors 123, 124; 133, 134 being rotatably supported, and the suction side rotor shafts 123b, 124b; 133b, 134b of the screw rotors 123, 124; 133, 134 being rotatably supported in bearings 163, 166 provided in shaft holes formed in the suction side end wall 153 of the cylinder casing 111.

[0007] The gear chamber 171 formed in the gear casing 170 accommodates a gear mechanism 180 consisting of driven gears 182, 183 attached to the suction side rotor shafts (in the illustrated example, the suction side rotor shafts 123b, 133b of the male rotors 123, 133) and a drive gear 181 attached to an input shaft 190 that passes through the gear casing 170 and is inserted into the gear chamber 171, and is configured so that when the input shaft 190 is rotated, both the low-pressure stage compressor body 120 and the high-pressure stage compressor body 130 can be rotated via the gear mechanism 180 accommodated in the gear chamber 171.

[0008] In the compressor main body 100 configured as described above, the bearings 161, 163, 164, 166 that support the rotor shafts 123a, 123b, 124a, 124b, 133a, 133b, 134a, 134b of the screw rotors 123, 124, 133, 134 are continuously supplied with oil while the compressor main body 100 is in operation, thereby lubricating and cooling each of the bearings 161, 163, 164, 166.

[0009] Here, the end cover 152 attached to the discharge side end of the high-pressure stage cylinder 132 is formed with a discharge side bearing chamber 152a that houses the bearing 164 that supports the rotor shafts 133a, 134a on the discharge side of the high-pressure stage compressor main body 130, among the bearings 161, 163, 164, 166 mentioned above. Not only is this discharge side bearing chamber 152a continuously supplied with lubricating oil to lubricate and cool the bearing 164 while the compressor main body 100 is in operation, but it is also designed so that high-pressure compressed gas that leaks from the compression action space of the high-pressure stage compressor main body 130 just before discharge flows in, making it easy for the internal pressure to increase.

[0010] If the pressure inside the discharge side bearing chamber 152a increases excessively, the pressure will press the screw rotors 133, 134 toward the suction side, and a large thrust load will be applied to the bearings 164, 166, thereby shortening the life of the bearings 164, 166.

[0011] Therefore, in order to reduce the thrust load on the bearings 164, 166, the oil-cooled screw compressor is configured so that when the lubricating oil is discharged from the discharge side bearing chamber 152a of the compressor main body 100, the compressed gas is also discharged along with the lubricating oil, thereby preventing the internal pressure of the discharge side bearing chamber 152a from rising excessively, and the lubricating oil discharged from the discharge side bearing chamber 152a is returned to the lubricating oil circulation system, allowing the lubricating oil to be recycled.

[0012] As a method for recovering and circulating the lubricating oil in the discharge side bearing chamber 152a, Patent Document 2, cited below, describes recovering the lubricating oil by connecting the discharge side bearing chamber 152a of the high-pressure stage compressor main body 130 to the compression action space (not shown) one pitch after the intake air is trapped in the low-pressure stage compressor main body 120 (Claim 4 of Patent Document 2). [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-110760 [Patent Document 2] Japanese Patent Application Publication No. 9-53583 Summary of the Invention [Problem to be solved by the invention]

[0014] In the compressor body 100 described in the above-mentioned Patent Document 2, the lubricating oil in the discharge side bearing chamber 152a of the high-pressure stage compressor body 130 is recovered together with the compressed gas into the compression action space of the low-pressure stage compressor body 120, so that the lubricating oil after lubricating the bearing 164 in the discharge side bearing chamber 152a can be recycled and reused without being wasted.

[0015] However, since the discharge side bearing chamber 152a of the high-pressure stage compressor main body 130 is connected to the space inside the cylinder 132 of the high-pressure stage compressor main body 130 through a gap that occurs around the axis of the discharge side rotor shafts 133a, 134a, the compressed gas compressed in the compression action space of the high-pressure stage compressor main body 130 just before being discharged flows into the discharge side bearing chamber 152a through this gap.

[0016] Therefore, the lubricating oil discharged from the discharge side bearing chamber 152a of the high-pressure stage compressor main body 130 is not only heated by lubricating and cooling the bearing 164, but also by contact with the high-temperature compressed gas that flows into the discharge side bearing chamber 152a, and therefore becomes very hot.

[0017] When the lubricating oil and compressed gas in the discharge side bearing chamber 152a, which has reached such a high temperature, are introduced into the compression action space one pitch after the intake air is trapped in the low-pressure stage compressor main body 120, the temperature in the compression action space rises. Therefore, in order to achieve the target discharge temperature, it is necessary to increase the amount of lubricating oil supplied from the receiver tank through the oil inlet for cooling, and there is a risk that the power required by the compressor main body 100 will increase in order to stir this increased amount of lubricating oil.

[0018] Therefore, it is desirable to be able to recover the lubricating oil and compressed gas recovered from the discharge side bearing chamber 152a of the high-pressure stage compressor main body 130 into the low-pressure stage compressor main body 120 while keeping them at a low temperature.

[0019] In the above explanation, we have explained the problems that arise when recovering lubricating oil in the discharge side bearing chamber 152a of the high-pressure stage compressor body 130 in a multi-stage compressor body 100 into the compression action space of the low-pressure stage compressor body 120, but similar problems can also arise when recovering lubricating oil in the discharge side bearing chamber of a single-stage compressor body into the suction side space of the same compressor body (for example, the suction space or the compression action space close to the suction side).

[0020] Therefore, the present invention has been made to eliminate the drawbacks of the above-mentioned conventional technology, and aims to provide an oil-cooled screw compressor in which the lubricating oil recovered from the discharge side bearing chamber of the compressor body of the oil-cooled screw compressor can be recovered into the suction side space of the compressor body at a low temperature, and a method for recovering lubricating oil from the discharge side bearing chamber in such an oil-cooled screw compressor. [Means for solving the problem]

[0021] The means for solving the problems are described below together with the reference numerals used in the description of the embodiment of the invention. These reference numerals are intended to clarify the correspondence between the claims and the description of the embodiment of the invention, and needless to say, are not used to restrict the interpretation of the technical scope of the present invention.

[0022] In order to achieve the above object, the oil-flooded screw compressor 1 of the present invention is The cylinder casing 11 includes a cylinder casing 11, male rotors 23, 33 (Fig. 2), 13 (Fig. 7) and female rotors 24, 34 (Fig. 2), 14 (Fig. 7) accommodated in the cylinder casing 11 so as to be able to mesh and rotate, discharge-side bearing chambers 52a (Fig. 2), 52a' (Fig. 7) formed in end covers 52 (Fig. 2), 52' (Fig. 7) attached to the discharge-side end of the cylinder casing 11, and a gear chamber 71 formed in a gear casing 70 attached to the suction-side end of the cylinder casing 11, and discharge-side rotor shafts 33a, 34a (Fig. 2), 13a, 14a (Fig. In the oil-cooled screw compressor 1, a compressor body 10 (Fig. 2), 10' (Fig. 7) is provided which accommodates bearings 64, 65 (Fig. 2), 64' (Fig. 7) for rotatably supporting a rotor shaft 23b, 33b (Fig. 2), 13b (Fig. 7) that penetrates shaft holes 55, 56 (Fig. 2), 55' (Fig. 7) formed in the suction side end walls 53, 54 (Fig. 2), 54' (Fig. 7) of the cylinder casing 11 and protrudes into the gear chamber 71, and a gear mechanism 80 is provided which consists of driven gears 82, 83 (Fig. 2), 84 (Fig. 7) attached to suction side rotor shafts 23b, 33b (Fig. 2), 13b (Fig. 7) that penetrate shaft holes 55, 56 (Fig. 2), 55' (Fig. 7) formed in the suction side end walls 53, 54 (Fig. 2), 54' (Fig. 7) of the cylinder casing 11 and protrudes into the gear chamber 71, and a drive gear 81 attached to an input shaft 90 that penetrates the gear casing 70 and is inserted into the gear chamber 71, a pressure recovery passage 47 that connects the discharge side bearing chambers 52a (FIG. 2), 52a' (FIG. 7) of the compressor main body 10, 10' with the gear chamber 71 and introduces the lubricating oil in the discharge side bearing chambers 52a, 52a' into the gear chamber 71 together with the compressed gas in the discharge side bearing chambers 52a, 52a'; A lubricating oil recovery passage 5 is provided which connects an oil reservoir 75 formed at the bottom of the gear chamber 71 with a recovery space 29, which is a space within the cylinder casing 11 that is at a lower pressure than the gear chamber 71, and recovers the lubricating oil in the oil reservoir 75 into the recovery space 29 (Claim 1).

[0023] The compressor body 10 can be configured as a multi-stage type having a low-pressure stage compressor body 20 formed by rotatably accommodating the male rotors 23, 33 and the female rotors 24, 34 in a low-pressure stage cylinder 22 and a high-pressure stage cylinder 32 provided in the cylinder casing 11, respectively, and a high-pressure stage compressor body 30, and an intermediate stage flow path 40 that communicates the discharge port 25 of the low-pressure stage compressor body 20 with the suction port 36 of the high-pressure stage compressor body 30, In this case, the pressure recovery passage 47 connects the discharge side bearing chamber 52a of the high-pressure stage compressor body 30, which is the discharge side bearing chamber, to the gear chamber 71, The lubricating oil recovery passage 5 allows the space within the low-pressure stage cylinder 22 to communicate with the gear chamber 71 as the recovery space 29 (claim 2; see Figs. 1-5).

[0024] It is preferable to provide oil seals 57, 58 (FIGS. 2, 4, 5), 59 (FIG. 7) to seal the gap between the outer periphery of the suction side rotor shaft 23b, 33b (FIGS. 2, 4, 5), 13b (FIG. 7) and the shaft holes 55, 56 (FIGS. 2, 4, 5), 55' (FIG. 7) (claim 3).

[0025] The lubricating oil recovery passage 5 may be provided as an external pipe attached to the outside of the casing, but it can also be formed as an internal flow passage formed within the thickness of the cylinder casing 11 and gear casing 70 (claim 4; see Figure 3).

[0026] Furthermore, the pressure recovery path 47 may be provided as an external pipe attached to the outside of the casing, or may be configured as an internal flow path formed within the thickness of the cylinder casing 11 (Claim 5; Figures 1-3, 5, 7).

[0027] In a configuration in which the pressure recovery passage 47 is formed within the thickness of the cylinder casing 11, heat dissipation fins 48 may be provided on the cylinder casing 11 in the portion where the pressure recovery passage 47 is formed (claim 6; see Figure 6).

[0028] In addition, the method for recovering lubricating oil from the discharge side bearing chamber in the oil-cooled screw compressor of the present invention is as follows: The cylinder casing 11 includes a cylinder casing 11, male rotors 23, 33 (Fig. 2), 13 (Fig. 7) and female rotors 24, 34 (Fig. 2), 14 (Fig. 7) accommodated in the cylinder casing 11 so as to be able to mesh and rotate, end covers 52 (Fig. 2), 52' (Fig. 7) attached to the discharge side end of the cylinder casing 11 are provided in discharge side bearing chambers 52a (Fig. 2), 52a' (Fig. 7), and a gear chamber 71 formed in a gear casing 70 attached to the suction side end of the cylinder casing 11. The discharge side bearing chambers 52a, 52a' are provided in the discharge side rotor shafts 33a of the male rotors 33, 13 and female rotors 34, 14. In an oil-cooled screw compressor 1 having a compressor body 10 that houses bearings 64, 65 (Fig. 2), 64' (Fig. 7) that rotatably support rotor shafts 23b, 33b (Fig. 2), 13b (Fig. 7) that penetrate shaft holes provided in the suction side end walls 53, 54 (Fig. 2), 54' (Fig. 7) of the cylinder casing 11 and protrude into the gear chamber 71, and a gear mechanism 80 consisting of driven gears 82, 83 (Fig. 2), 84 (Fig. 7) attached to suction side rotor shafts 23b, 33b (Fig. 2), 13b (Fig. 7) that protrude into the gear chamber 71 through shaft holes provided in the suction side end walls 53, 54 (Fig. 2), 54' (Fig. 7) of the cylinder casing 11, and a drive gear 81 attached to an input shaft 90 that penetrates the gear casing 70 and is inserted into the gear chamber 71, The lubricating oil in the discharge side bearing chambers 52a, 52a' is introduced into the gear chamber 71 together with the compressed gas in the discharge side bearing chambers 52a, 52a', and is collected in an oil reservoir 75 formed at the bottom of the gear chamber 71, The lubricating oil collected in the oil reservoir 75 is collected in a collection space 29, which is a space in the cylinder casing 11 that has a lower pressure than the gear chamber 71 (claim 7).

[0029] When the compressor body 10 is configured as a multi-stage type having a low-pressure stage compressor body 20 formed by rotatably accommodating the male rotors 23, 33 and the female rotors 24, 34 in a low-pressure stage cylinder 22 and a high-pressure stage cylinder 32 provided in the cylinder casing 11, and a high-pressure stage compressor body 30, and an intermediate stage flow path 40 connecting the discharge port 25 of the low-pressure stage compressor body 20 and the suction port 36 of the high-pressure stage compressor body 30, The discharge side bearing chamber of the high-pressure stage compressor body 30 is formed as the discharge side bearing chamber 52a, The space inside the low-pressure stage cylinder 22 may be used as the recovery space 29 (claim 8: see FIGS. 1-5).

[0030] The lubricating oil in the oil reservoir 75 may be recovered into the recovery space 29 through a lubricating oil recovery passage 5 formed within the thickness of the cylinder casing 11 and the gear casing 70 (claim 9; see Figure 3).

[0031] In addition, the lubricating oil and compressed gas in the discharge side bearing chambers 52a, 52a' may be introduced into the gear chamber 71 through a pressure recovery passage 47 formed within the thickness of the cylinder casing 11 (Claim 10; see Figures 1-3, 5-7).

[0032] In this case, it is preferable to provide heat dissipation fins 48 on the cylinder casing 11 in the portion where the pressure recovery passage 47 is formed, so that the lubricating oil and compressed gas passing through the pressure recovery passage 47 can be cooled before being introduced into the gear chamber 71 (Claim 11; see Figure 6). [Effects of the Invention]

[0033] With the configuration of the present invention described above, the oil-cooled screw compressor 1 of the present invention can provide the following significant effects.

[0034] A pressure recovery passage 47 is provided that connects the discharge side bearing chambers 52a, 52a' of the compressor body 10, 10' with the gear chamber 71, and the lubricating oil in the discharge side bearing chambers 52a, 52a' is introduced into the gear chamber 71 together with the compressed gas.This allows the lubricating oil to be recovered in an oil reservoir 75 at the bottom of the gear chamber 71 and mixed with the lubricating oil in the oil reservoir 75, thereby lowering the temperature of the high-temperature lubricating oil recovered from the discharge side bearing chambers 52a, 52a'.

[0035] As a result, by recovering the lubricating oil cooled by mixing with the lubricating oil in the oil reservoir 75 into the recovery space 29 together with the lubricating oil in the oil reservoir 75, the increase in discharge temperature that may occur when high-temperature lubricating oil is recovered into the recovery space 29 can be suppressed without cooling due to an increase in the amount of lubricating oil from the oil supply passage 8 supplied through the oil supply port 9, and therefore without increasing the stirring resistance of the lubricating oil caused by the screw rotor.

[0036] In addition, by first introducing the lubricating oil recovered together with the compressed gas from the discharge side bearing chambers 52a, 52a' into the gear chamber 71, gas-liquid separation of the compressed gas and the lubricating oil occurs within the gear chamber 71.Therefore, by recovering the lubricating oil recovered in the oil reservoir 75 at the bottom of the gear chamber 71 by gas-liquid separation into the recovery space 29, it is possible to prevent high-temperature compressed gas from the discharge side bearing chambers 52a, 52a' from being directly introduced into the recovery space 29.

[0037] When the compressor body 10 of the oil-cooled screw compressor of the present invention is a multi-stage compressor body 10 having a configuration in which the low-pressure stage compressor body 20 and the high-pressure stage compressor body 30 are connected via an intermediate stage flow path 40, the lubricating oil in the discharge side bearing chamber 52a of the high-pressure stage compressor body 30 is introduced into the gear chamber 71 together with the compressed gas, and then the lubricating oil recovered in the oil reservoir 75 is recovered in the space within the low-pressure stage compressor body 20, which is the recovery space 29, so that the lubricating oil in the discharge side bearing chamber 52a, which has been heated by contact with the compressed gas, which has become hotter due to the multi-stage compression, can also be sufficiently cooled before being recovered in the recovery space 29.

[0038] In a configuration in which oil seals 57, 58, 59 are provided to seal the gap between the outer periphery of the suction side rotor shaft 23b, 33b, 13b and the shaft holes 55, 56, 55', communication between the gear chamber 71 and the space inside the cylinder casing 11 can be blocked, the pressure inside the gear chamber 71 can be prevented from flowing into the suction side space of the cylinder casing 11, and the pressure inside the gear chamber 71 can be maintained at the pressure required to recover lubricating oil in the recovery space 29.

[0039] In particular, in an oil-cooled screw compressor 1 equipped with a multi-stage compressor body 10, the compressed gas on the suction side of the high-pressure stage compressor body 30 is prevented from flowing into the gear chamber 71, thereby preventing the pressure on the suction side of the high-pressure stage compressor body 30 from being introduced into the suction space 27 of the low-pressure stage compressor body 20 via the gear chamber 71.

[0040] In a configuration in which the lubricating oil recovery passage 5 is formed within the wall thickness of the cylinder casing 11 and the gear casing 70, the lubricating oil recovery passage 5 can be provided simply by assembling the gear casing 70 to the cylinder casing 11 without connecting external piping, etc., making it easy to assemble the oil-cooled screw compressor 1.

[0041] For the same reason, even in the configuration in which the pressure recovery passage 47 is formed within the wall thickness of the cylinder casing 11, the assembly work of the oil-cooled screw compressor 1 can be easily performed.

[0042] Furthermore, compared to when the pressure recovery passage 47 is formed using external piping, when the pressure recovery passage 47 is formed within the thickness of the cylinder casing 11, the lubricating oil and compressed gas passing through the pressure recovery passage 47 are less likely to be cooled.However, when heat dissipation fins 48 are provided on the cylinder casing 11 at the position where the pressure recovery passage 47 is formed, the lubricating oil and compressed gas passing through the pressure recovery passage 47 can be cooled effectively. [Brief explanation of the drawings]

[0043] [Figure 1] FIG. 1 is an explanatory diagram of an oil-cooled screw compressor according to the present invention. [Figure 2]FIG. 2 is a cross-sectional side view of the compressor body (multi-stage type). [Figure 3] FIG. 10 is an explanatory diagram of a modified oil-cooled screw compressor of the present invention. [Figure 4] Cross-sectional view of line IV-IV in Figure 2. [Figure 5] Cross-sectional view of line VV in Figure 2. [Figure 6] FIG. [Figure 7] FIG. 10 is a schematic cross-sectional plan view showing a modified example (single stage type) of the compressor body. [Figure 8] Cross-sectional side view of the compressor body (multi-stage type) (corresponding to Figure 1 of Patent Document 1) DETAILED DESCRIPTION OF THE INVENTION

[0044] The configuration of the oil-cooled screw compressor of the present invention will be described below with reference to the accompanying drawings.

[0045] In Figure 1, the symbol 1 indicates the oil-cooled screw compressor of the present invention, and this oil-cooled screw compressor 1 comprises a compressor main body 10 driven by a driving source such as an engine or motor (not shown), and a receiver tank 7 into which compressed gas discharged by the compressor main body 10 as a gas-liquid mixed fluid with lubricating oil is introduced, and is configured so that the compressed gas from which the lubricating oil has been removed in the receiver tank 7 can be supplied to the consumer side to which an air working machine (not shown) is connected, and the lubricating oil recovered in the receiver tank 7 can be supplied to each part of the compressor main body 10 after passing through an oil cooler 8a and an oil filter 8b provided in the oil supply flow path 8.

[0046] In this embodiment, the aforementioned compressor body 10 is configured as a multi-stage compressor body 10 in which the discharge port 25 of the low-pressure stage compressor body 20 and the suction port 36 of the high-pressure stage compressor body 30 are connected via an intermediate stage flow path 40.

[0047] This multi-stage compressor body 10 has a cylinder casing 11 in which a low-pressure stage cylinder 22 and a high-pressure stage cylinder 32 are formed, as shown in Figure 2, and the low-pressure stage cylinder 22 and high-pressure stage cylinder 32 formed within this cylinder casing 11 respectively house male rotors 23, 33 and female rotors 24, 34 in a meshed and rotatable manner, thereby forming the low-pressure stage compressor body 20 and high-pressure stage compressor body 30.

[0048] In the embodiment shown in Figure 2, a low-pressure stage cylinder casing 21 having a low-pressure stage cylinder 22 formed therein and a high-pressure stage cylinder casing 31 having a high-pressure stage cylinder 32 formed therein are provided separately, and the low-pressure stage cylinder casing 21 and the high-pressure stage cylinder casing 31 are arranged in parallel to form the cylinder casing 11 as a whole, but as explained with reference to Figure 8, a configuration in which both the low-pressure stage cylinder 122 and the high-pressure stage cylinder 132 are provided within a single cylinder casing 111 may also be adopted, and the configuration of the cylinder casing 11 is not limited to the configuration shown in Figure 2.

[0049] As shown in Figures 2 and 4, the low-pressure stage compressor body 20 is composed of the low-pressure stage cylinder casing 21 with the low-pressure stage cylinder 22 formed therein, an end cover 51 covering the discharge end of the low-pressure stage cylinder casing 21, an inlet casing 53 forming an end wall covering the suction end of the low-pressure stage cylinder casing 21, and a male rotor 23 and a female rotor 24 (in Figure 2, the female rotor 24 is hidden behind the male rotor 23) that are housed in the low-pressure stage cylinder 22 so as to be able to mesh and rotate. With the male rotor 23 and female rotor 24 housed in the low-pressure stage cylinder casing 21, an end cover 51 is attached to the discharge side end of the low-pressure stage cylinder casing 21 and an inlet casing 53 is attached to the suction side end, so that the discharge side rotor shafts 23a and 24a of the male rotor 23 and female rotor 24 of the low-pressure stage compressor main body 20 are rotatably supported by bearings 61 and 62 housed in the end cover 51, and the suction side rotor shafts 23b and 24b of the male rotor 23 and female rotor 24 of the low-pressure stage compressor main body 20 are rotatably supported by bearing 63 provided in the inlet casing 53.

[0050] 2 and 5, the high-pressure stage compressor body 30 is composed of a high-pressure stage cylinder casing 31 with a high-pressure stage cylinder 32 formed therein, an end cover 52 covering the discharge side end of the high-pressure stage cylinder casing 31, and a male rotor 33 and a female rotor 34 (in FIG. 2, the female rotor 34 is hidden behind the male rotor 33) that are housed in the high-pressure stage cylinder 32 formed in the high-pressure stage cylinder casing 31 so as to be able to mesh and rotate. By attaching the end cover 52 to the discharge side end of the high-pressure stage cylinder casing 31 with the nozzle 4 housed therein, the discharge side rotor shafts 33a, 34a of the male rotor 33 and female rotor 34 of the high-pressure stage compressor main body 30 are rotatably supported by bearings 64, 65 provided in the discharge side bearing chamber 52a formed in the end cover 52, and the suction side rotor shafts 33b, 34b of the male rotor 33 and female rotor 34 of the high-pressure stage compressor main body 30 are rotatably supported by bearings 66 provided in the end wall 54 that closes the suction side end of the high-pressure stage cylinder casing 31.

[0051] A gear casing 70 is attached to the suction side end of the cylinder casing 11, which in the illustrated embodiment is the suction side end of both the low-pressure stage cylinder casing 21 and the high-pressure stage cylinder casing 31, and a gear chamber 71 is formed within this gear casing 70 to accommodate a gear mechanism 80 for transmitting rotational driving force from a driving source (engine, motor, etc.) not shown to the low-pressure stage compressor main body 20 and the high-pressure stage compressor main body 30.

[0052] Into this gear chamber 71, the suction side rotor shaft of the low-pressure stage compressor main body 20 (in the illustrated example, the suction side rotor shaft 23b of the male rotor 23) protrudes through an axial hole 56 that penetrates the inlet casing 53 of the low-pressure stage compressor main body 20, and the suction side rotor shaft of the high-pressure stage compressor main body 30 (in the illustrated example, the suction side rotor shaft 33b of the male rotor 33) protrudes through an axial hole 55 that penetrates the suction side end wall 54 of the high-pressure stage cylinder casing 31, and driven gears 82, 83 are attached to these two rotor shafts 23b, 33b, respectively. The gap between the outer periphery of the suction side rotor shaft 23b of the male rotor 23 of the low-pressure stage compressor main body 20 and the shaft hole 56 provided in the inlet casing 53 is sealed by an oil seal 58, and the gap between the outer periphery of the suction side rotor shaft 33b of the male rotor 33 of the high-pressure stage compressor main body 30 and the shaft hole 55 formed in the suction side end wall 54 of the high-pressure stage cylinder casing 31 is sealed by an oil seal 57, thereby preventing the compressed gas on the suction side of the high-pressure stage compressor main body 30 from flowing into the suction space 27 of the low-pressure stage compressor main body 20 via the gear chamber 71.

[0053] In addition, an input shaft 90 is inserted into the gear chamber 71, via a shaft hole 72 that penetrates the gear casing 70, and is connected to a drive source such as an engine or motor (not shown). A drive gear 81 that meshes with the driven gears 82 and 83 mentioned above is attached to this input shaft 90, and the gear mechanism 80 consisting of this drive gear 81 and driven gears 82 and 83 is configured so that when the input shaft 90 is rotated, both the low-pressure stage compressor main body 20 and the high-pressure stage compressor main body 30 can be rotated.

[0054] In the illustrated embodiment, the driving gear 81 has a larger diameter than the driven gears 82 and 83, thereby giving the gear mechanism 80 the function of a speed increasing device that increases the rotation from the driving source input via the input shaft 90 and transmits it to the low-pressure stage compressor main body 20 and the high-pressure stage compressor main body 30.

[0055] As shown in Figure 2, an intake port 26 is provided at the top of the low-pressure stage cylinder casing 21 at a midpoint in the longitudinal direction, and an unloader valve 2 is attached to this intake port 26 to control the opening and closing of the intake port 26.

[0056] In addition, within the low-pressure stage compressor body 20, an intake space 27 is formed between the upper outer periphery of the male rotor 23 and female rotor 24 on the intake side and the inner wall of the low-pressure stage cylinder 22, and between the intake side end faces of the male rotor 23 and female rotor 24 and the inlet casing 53, for introducing gas intake from the intake port 26 into the compression action space.

[0057] Therefore, when the rotors 23, 24 of the low-pressure stage compressor main body 20 are rotated with the unloader valve 2 open, the compressed gas sucked in through the unloader valve 2 and the intake port 26 is introduced into the compression action space (not shown) formed by the meshing of the male rotor 23 and the female rotor 24 through the intake space 27 provided in the low-pressure stage compressor main body 20, and is compressed together with the lubricating oil supplied to the compression action space after the intake air is trapped through the oil supply port 9 (see Figure 1).In this way, the compressed gas generated in the low-pressure stage compressor main body 20 as a gas-liquid mixed fluid with the lubricating oil is introduced into the intake port 36 of the high-pressure stage compressor main body 30 through the discharge port 25 and intermediate stage flow path 40 of the low-pressure stage compressor main body 20, and is configured to be compressed in the high-pressure stage compressor main body 30.

[0058] As shown in Figure 1, a portion of the lubricating oil recovered in the receiver tank 7 is introduced into the gear chamber 71 through an oil supply passage 8 to supply oil to the gear mechanism 80 housed in the gear chamber 71.The lubricating oil introduced into the gear chamber 71 in this way lubricates the gear mechanism 80, and then falls to the bottom of the gear chamber 71, forming an oil reservoir 75 at the bottom of the gear chamber 71.

[0059] The lubricating oil accumulated at the bottom of this gear chamber 71 is configured to be able to be recovered into the low-pressure stage compressor main body 20 by a lubricating oil recovery passage 5, one end 5a of which is connected to the bottom of the gear chamber 71 (oil reservoir 75) and the other end 5b of which is connected to the recovery space 29 of the low-pressure stage compressor main body 20.

[0060] The aforementioned recovery space 29 may be located anywhere within the space within the low-pressure stage compressor main body 20 as long as it is at a lower pressure than the gear chamber 71, and the aforementioned recovery space 29 may be any of the suction space 27 formed in communication with the intake port 26 within the low-pressure stage compressor main body 20, the compression action space before the intake air is trapped (not shown), and the compression action space after the intake air is trapped (not shown).

[0061] However, when lubricating oil in the gear chamber 71 is introduced into the intake space 27 or the compression action space before intake air is trapped, the amount of compressed gas introduced into the compression action space decreases in accordance with the amount of lubricating oil introduced, and the compression efficiency decreases. Therefore, it is preferable to use the compression action space after intake air is trapped as the recovery space 29. In this embodiment, the compression action space after intake air is trapped, which is provided on the intake side of the oil fill port 9, is used as the recovery space 29, and the other end 5b of the lubricating oil recovery path 5 is connected to this part.

[0062] This allows the pressure within the gear chamber 71 to be used to recover the lubricating oil within the gear chamber 71 into the low-pressure stage compressor main body 20, and the lubricating oil recovered from the discharge side bearing chamber 52a can be circulated and reused.

[0063] As shown in Figure 1, a portion of the lubricating oil recovered in the receiver tank 7 is pumped into the gear chamber 71 via the oil supply passage 8 by the pressure in the receiver tank 7, and the pressure in the gear chamber 71 is increased by the oil supply via the oil supply passage 8.

[0064] In addition, as described below, compressed gas is introduced into the gear chamber 71 along with lubricating oil from the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30 via the pressure recovery passage 47, which also increases the pressure inside the gear chamber 71.

[0065] As a result, when the oil reservoir 75 formed at the bottom of the gear chamber 71, whose pressure has been increased in this manner, is connected to the recovery space 29 of the low-pressure stage compressor main body 20 via the lubricating oil recovery passage 5, the lubricating oil accumulated in the oil reservoir 75 is pushed out of the gear chamber 71 by the pressure within the gear chamber 71 and introduced into the recovery space 29 within the low-pressure stage compressor main body 20.

[0066] The discharge side bearing chamber 52a formed within the end cover attached to the discharge side end of the high-pressure stage cylinder casing 31 accommodates bearings 64, 65 that rotatably support the discharge side rotor shafts 33a, 34a of the screw rotors 33, 34 of the high-pressure stage compressor main body 30.

[0067] In order to lubricate these bearings 64, 65, an oil supply port (not shown) is connected to the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30, and lubricating oil from, for example, a receiver tank 7 is supplied through this oil supply port via an oil supply flow path 8.

[0068] In addition, since the discharge side bearing chamber 52a is connected to the space inside the cylinder 32 of the high-pressure stage compressor main body 30 through a gap formed around the axis of the discharge side rotor shaft 33a, the compressed gas compressed in the high-pressure stage compressor main body 30 just before being discharged leaks out of the high-pressure stage cylinder 32 and flows into the discharge side bearing chamber 52a.

[0069] Therefore, the pressure in the discharge side bearing chamber 52a increases due to the supply of lubricating oil from the receiver tank 7 and the inflow of compressed gas from the high-pressure stage cylinder 32 side, and if this is left unattended, a large thrust load will be applied to the bearings 64, 65, 66, shortening the life of the bearings 64, 65, 66.Therefore, the discharge side bearing chamber 52a and the gear chamber 71 are connected by a pressure recovery path 47.

[0070] In this way, by connecting the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30 to the gear chamber 71 via the pressure recovery path 47, the lubricating oil in the discharge side bearing chamber 52a is introduced into the gear chamber 71 together with the compressed gas, and the lubricating oil and compressed gas are separated into gas and liquid within the gear chamber 71.

[0071] The lubricating oil separated from the compressed gas falls into an oil reservoir 75 formed at the bottom of the gear chamber 71 and mixes with the lubricating oil that has accumulated in the oil reservoir 75.

[0072] As a result, the lubricating oil in the discharge side bearing chamber 52a, which has become hot due to the cooling of the bearings 64, 65 in the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30 and contact with the high-temperature compressed gas, is cooled by mixing with the lubricating oil that has accumulated in the oil reservoir 75, and by recovering the lubricating oil cooled in this way, together with the lubricating oil that has accumulated in the oil reservoir 75, in the recovery space 29 formed in the low-pressure stage cylinder 22 of the low-pressure stage compressor main body 20, it is possible to prevent the temperature in the recovery space 29 from rising.As a result, there is no need to increase the amount of lubricating oil supplied from the oil supply passage 8 via the oil supply port 9 in order to maintain the discharge temperature, and it is possible to suppress an increase in the stirring resistance when the screw rotor stirs the lubricating oil.

[0073] Furthermore, by connecting the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30 to the gear chamber 71, which has a lower pressure than the discharge side bearing chamber 52a and is a relatively large space, the pressure in the discharge side bearing chamber 52a can be smoothly discharged, reducing the pressure in the discharge side bearing chamber 52a and reducing the thrust load applied to the bearings 64, 65, and 66.In addition, by first introducing the lubricating oil in the discharge side bearing chamber 52a into the gear chamber 71 via the pressure recovery path 47 and then recovering it in the low-pressure stage compressor main body 20 via the lubricating oil recovery path 5, the lubricating oil discharged together with the compressed gas from the discharge side bearing chamber 52a can be separated into gas and liquid in the gear chamber 71, and the lubricating oil separated from the high-temperature compressed gas can be recovered in the low-pressure stage compressor main body 20.

[0074] In the embodiment shown in Figures 1 and 2, an example is shown in which the aforementioned lubricating oil recovery path 5 is constructed by external piping provided outside the gear casing 70, but this lubricating oil recovery path 5 may also be formed as internal piping within the cylinder casing 11 and gear casing 70 as shown in Figure 3.

[0075] In this case, drilled holes formed in the wall thickness of the cylinder casing 11 or the gear casing 70 may be used as the lubricating oil recovery passage 5 .

[0076] As shown in Figures 1 and 2, in a configuration in which the lubricating oil recovery passage 5 is formed as an external pipe, it is possible to easily check for any malfunctions in the lubricating oil recovery passage 5 (for example, the piping of the lubricating oil recovery passage 5 coming loose or lubricating oil leaking from the lubricating oil recovery passage 5) from outside the casing, and since the lubricating oil recovery passage 5 is exposed to the outside air, there is the advantage that the lubricating oil passing through the lubricating oil recovery passage 5 can be cooled before being introduced into the low-pressure stage compressor main body 20.

[0077] However, in a configuration in which the lubricating oil recovery path 5 is an external pipe, the external pipe that serves as the lubricating oil recovery path 5 must be installed in addition to the work of assembling the gear casing 70 to the low-pressure stage cylinder casing 21, which has the disadvantage of increasing the amount of work required during assembly.

[0078] On the other hand, in a configuration in which the lubricating oil recovery passage 5 is formed as a drilled hole or the like within the thickness of the cylinder casing 11 or the gear casing 70, the lubricating oil recovery passage 5 can be formed simply by assembling the gear casing 70 to the cylinder casing 11, which improves workability during assembly, such as eliminating the need to install external piping.However, as mentioned above, this has the disadvantages of making it difficult to check for defects from the outside and making it difficult for the lubricating oil to cool when passing through the lubricating oil recovery passage 5.

[0079] Similarly, the pressure recovery passage 47 connecting the discharge side bearing chamber 52a of the high-pressure stage compressor main body 30 and the gear chamber 71 may be an internal piping formed by a drilled hole or the like formed in the thickness of the high-pressure stage cylinder casing 31, or it may be formed by an external piping provided outside the high-pressure stage cylinder casing 31.

[0080] In addition, when the pressure recovery passage 47 is formed as an internal flow path, as an example, as shown in Figure 6, heat dissipation fins 48 may be provided on the outer wall portion of the high-pressure stage casing 31 at the position where the pressure recovery passage 47 is formed, so that the lubricating oil and compressor gas are cooled by heat exchange with the outside air as they pass through the pressure recovery passage 47.

[0081] By configuring it in this way, it is possible to compensate for the deterioration in heat dissipation caused by configuring the pressure recovery path 47 as an internal pipe.

[0082] In the above-described embodiment described with reference to Figures 1 to 6, the oil-cooled screw compressor 1 of the present invention is described as having a multi-stage compressor body 10 as an example, but the configuration of the oil-cooled screw compressor 1 of the present invention is not limited to this configuration, and can also be adopted as an oil-cooled screw compressor 1 having a single-stage compressor body 10' in which a gear chamber 71 is provided on the suction side to accommodate a gear mechanism 80 such as a speed-up gear or a timing gear, as shown in Figure 7.

[0083] The single-stage compressor body 10 shown in Figure 7 accommodates a pair of male rotors 13 and female rotors 14 in a single cylinder 12 formed in a cylinder casing 11, and the discharge side rotor shafts 13a, 14a of the male rotor 13 and female rotor 14 are rotatably supported by bearings 64' accommodated in a discharge side bearing chamber 52a' formed in an end cover 52' ​​attached to the discharge side end of the cylinder casing 11.

[0084] In addition, a gear chamber 71 is formed in a gear casing 70 attached to the suction side end of the cylinder casing 11, and a gear mechanism 80 (e.g., a speed increasing device) is housed within the gear chamber 71, which is composed of a driven gear 84 attached to the suction side rotor shaft 13b of the male rotor 13 which protrudes through an axial hole 55' provided in the suction side end wall 54' of the cylinder casing 11, and a drive gear 81 provided on an input shaft 90 which passes through the gear casing 70.

[0085] In an oil-cooled screw compressor equipped with such a single-stage compressor body 10', the discharge side bearing chamber 52a' of the compressor body 10' and the gear chamber 71 are connected by a pressure recovery passage 47 so that the lubricating oil and compressed gas in the discharge side bearing chamber 52a can be introduced into the gear chamber 71, and the bottom of the gear chamber 71 is connected via the lubricating oil recovery passage 5 to the recovery space 29, which is a space within the cylinder casing 11 of the compressor body 10 that has a lower pressure than the gear chamber 71.

[0086] The gap between the outer periphery of the suction side rotor shaft 13b of the male rotor 13 and the shaft hole 55' provided in the suction side end wall 54' of the cylinder casing 11 is sealed by an oil seal 59, thereby preventing the pressure in the gear chamber 71, which has increased when compressed gas is introduced along with lubricating oil from the discharge side bearing chamber 52a', from flowing into the suction side of the cylinder casing 11, and by maintaining the pressure in the gear chamber 71, lubricating oil can be introduced into the recovery space 29 using the pressure in the gear chamber 71.

[0087] This allows the high-temperature lubricating oil recovered from the discharge side bearing chamber 52a' to be mixed with the lubricating oil accumulated at the bottom of the gear chamber 71, cooled, and then recovered in the recovery space 29, thereby allowing the lubricating oil at a low temperature to be recovered in the recovery space 29.

[0088] As a result, by suppressing the temperature rise in the recovery space 29, the discharge temperature could be maintained without increasing the amount of lubricating oil from the oil supply passage 8 supplied through the oil supply port 9, and the increase in stirring resistance of the screw rotor due to the increase in the amount of lubricating oil could be suppressed.

[0089] In this way, the configuration of the oil-cooled screw compressor 1 of the present invention is applicable regardless of whether a multi-stage compressor body 10 or a single-stage compressor body 10' is used as the compressor body 10, 10'.

[0090] However, compared to the discharge side bearing chamber 52a' of the single-stage compressor body 10' shown in Figure 7, the discharge side bearing chamber 52a of the high-pressure stage compressor body 30 of the multi-stage compressor body 10 described with reference to Figures 1 to 6 generally has a higher temperature and higher pressure inside.

[0091] Therefore, the configuration of the oil-cooled screw compressor 1 of the present invention can be more effective when it is adopted as the configuration of the oil-cooled screw compressor 1 having a multi-stage compressor body 10. [Explanation of symbols]

[0092] 1. Oil-flooded screw compressor 2 Unloader valve 5 Lubricating oil recovery channel 5a One end (of lubricating oil recovery passage) 5b Other end (of lubricating oil recovery path) 7. Receiver Tank 8 Oil supply passage 8a Oil cooler 8b Oil filter 9 Fuel filler 10,100 Compressor body (multi-stage type) 10' Compressor body (single stage type) 11,111 Cylinder casing 12 cylinders 13 Osrota 13a Discharge side rotor shaft (male rotor) 13b Intake side rotor shaft (male rotor) 14 Mesrota 14a Discharge side rotor shaft (female rotor) 14b Intake side rotor shaft (female rotor) 20,120 Low-pressure stage compressor body 21,121 Low-pressure stage cylinder casing 22,122 Low-pressure stage cylinder 23,123 Osrota 23a, 123a Discharge side rotor shaft (male rotor) 23b, 123b Intake side rotor shaft (male rotor) 24,124 Mesrota 24a, 124a Discharge side rotor shaft (female rotor) 24b, 124b Intake side rotor shaft (female rotor) 25,125 outlet 26 Air intake 27 Inhalation space 29 Recovery Space 30,130 High-pressure stage compressor body 31,131 High-pressure stage cylinder casing 32,132 High-pressure stage cylinder 33,133 Osrota 33a, 133a Discharge side rotor shaft (male rotor) 33b, 133b Intake side rotor shaft (male rotor) 34,134 Mesrotor 34a, 134a Discharge side rotor shaft (female rotor) 34b, 134b Intake side rotor shaft (female rotor) 35 Discharge port 36,136 intake 40,140 Intermediate stage flow path 47 Pressure recovery path 48 Heat dissipation fin 51, 52, 52', 151, 152 End cover 52a,52a',152a Discharge side bearing chamber 53 Inlet casing (end wall) 54,54',153 End wall 55,55',56 shaft hole 57, 58, 59 Oil seal 61,62,63,64,64',65,66,67,161,163,164,166 Bearings 70,170 Gear casing 71,171 Gear room 72 Shaft hole 75 Oil Puddle 80,180 Gear mechanism (speed increasing device) 81,181 Drive gear 82, 83, 84, 182, 183 Driven gear 90,190 Input shaft

Claims

1. an oil-cooled screw compressor having a compressor body comprising: a cylinder casing; a male rotor and a female rotor housed in the cylinder casing so as to be able to mesh and rotate within the cylinder casing; a discharge-side bearing chamber formed in an end cover attached to the discharge-side end of the cylinder casing; and a gear chamber formed in a gear casing attached to the suction-side end of the cylinder casing, wherein the discharge-side bearing chamber houses bearings that rotatably support the discharge-side rotor shafts of the male rotor and female rotor, and the gear chamber houses a gear mechanism comprising a driven gear attached to a suction-side rotor shaft that penetrates a shaft hole provided in the suction-side end wall of the cylinder casing and protrudes into the gear chamber, and a drive gear attached to an input shaft that penetrates the gear casing and is inserted into the gear chamber, a pressure recovery passage that communicates between the discharge side bearing chamber and the gear chamber of the compressor body and introduces lubricating oil in the discharge side bearing chamber into the gear chamber together with compressed gas in the discharge side bearing chamber; The oil-cooled screw compressor is characterized in that a lubricating oil recovery passage is provided that connects an oil reservoir formed at the bottom of the gear chamber with a recovery space, which is a space within the cylinder casing that is at a lower pressure than the gear chamber, and recovers the lubricating oil in the oil reservoir into the recovery space.

2. The compressor body is configured as a multi-stage type including a low-pressure stage compressor body formed by rotatably accommodating the male rotor and the female rotor in a low-pressure stage cylinder and a high-pressure stage cylinder provided in the cylinder casing, respectively, and a high-pressure stage compressor body, and an intermediate stage flow path communicating a discharge port of the low-pressure stage compressor body with a suction port of the high-pressure stage compressor body, The pressure recovery passage communicates the discharge side bearing chamber of the high-pressure stage compressor body, which is the discharge side bearing chamber, with the gear chamber, 2. The oil-cooled screw compressor according to claim 1, wherein the lubricating oil recovery passage communicates the space within the low-pressure stage cylinder as the recovery space with the gear chamber.

3. 3. The oil-cooled screw compressor according to claim 1, further comprising an oil seal for sealing a gap between an outer periphery of the suction side rotor shaft and the shaft hole.

4. 3. An oil-cooled screw compressor according to claim 1, wherein the lubricating oil recovery passage is formed within the wall thickness of the cylinder casing and the gear casing.

5. 3. An oil-cooled screw compressor according to claim 1, wherein the pressure recovery passage is formed within the wall thickness of the cylinder casing.

6. 6. The oil-cooled screw compressor according to claim 5, wherein a heat radiation fin is provided on the cylinder casing at a portion where the pressure recovery passage is formed.

7. an oil-cooled screw compressor having a compressor body comprising: a cylinder casing; a male rotor and a female rotor housed in the cylinder casing so as to be able to mesh and rotate within the cylinder casing; a discharge-side bearing chamber formed in an end cover attached to the discharge-side end of the cylinder casing; and a gear chamber formed in a gear casing attached to the suction-side end of the cylinder casing, wherein the discharge-side bearing chamber houses bearings that rotatably support the discharge-side rotor shafts of the male rotor and female rotor, and the gear chamber houses a gear mechanism comprising a driven gear attached to the suction-side rotor shaft that penetrates the suction-side end wall of the cylinder casing and protrudes into the gear chamber, and a drive gear attached to an input shaft that penetrates the gear casing and is inserted into the gear chamber, The lubricating oil in the discharge side bearing chamber is introduced into the gear chamber together with the compressed gas in the discharge side bearing chamber, and is collected in an oil reservoir formed at the bottom of the gear chamber, A method for recovering lubricating oil from the discharge side bearing chamber in an oil-cooled screw compressor, characterized in that the lubricating oil recovered in the oil reservoir is recovered in a recovery space, which is a space within the cylinder casing that is at a lower pressure than the gear chamber.

8. The compressor body is configured as a multi-stage type including a low-pressure stage compressor body formed by rotatably accommodating the male rotor and the female rotor in a low-pressure stage cylinder and a high-pressure stage cylinder provided in the cylinder casing, respectively, and a high-pressure stage compressor body, and an intermediate stage flow path communicating a discharge port of the low-pressure stage compressor body with a suction port of the high-pressure stage compressor body, The discharge side bearing chamber of the high-pressure stage compressor body is the discharge side bearing chamber, 8. The method for recovering lubricating oil from a discharge-side bearing chamber in an oil-cooled screw compressor according to claim 7, wherein the recovery space is a space within the low-pressure stage cylinder.

9. A method for recovering lubricating oil from the discharge side bearing chamber in an oil-cooled screw compressor according to claim 7 or 8, characterized in that the lubricating oil in the oil reservoir is recovered into the recovery space through a lubricating oil recovery path formed within the wall thickness of the cylinder casing and the gear casing.

10. 9. A method for recovering lubricating oil from a discharge-side bearing chamber in an oil-cooled screw compressor according to claim 7 or 8, characterized in that the lubricating oil and compressed gas in the discharge-side bearing chamber are introduced into the gear chamber through a pressure recovery passage formed within the thickness of the cylinder casing.

11. A method for recovering lubricating oil from the discharge side bearing chamber in an oil-cooled screw compressor as described in claim 10, characterized in that by providing heat dissipation fins on the cylinder casing in the portion where the pressure recovery passage is formed, the lubricating oil and compressed gas passing through the pressure recovery passage are cooled before being introduced into the gear chamber.

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