Screw Compressor

Abstract

To provide a screw compressor in which cooling capacity for the delivery-side shaft portion of a screw rotor can be increased by means of simple structure.SOLUTION: A male rotor 2 of a screw compressor 1 has an axially extending cooling flow path 25 inside a delivery-side shaft portion 22. Groove structure 26 is provided in at least a part of a region between the position of a delivery-side end surface 21b of the male rotor 2 and the mounting position of a delivery-side bearing 6 in the wall surface 25a of the cooling flow path 25. The groove structure 26 is constituted of grooves 27 that have a length-directional component in the circumferential direction of the screw rotor 2 and are present at spaces from each other in the axial direction. A nozzle 15 of a stationary member is disposed with a gap from the wall surface 25a within the cooling flow path 25. The nozzle 15 is disposed in such a way as to overlap with at least a part of the groove structure 26 at an axial position.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a screw compressor, and more particularly to a screw compressor in which a screw rotor is cooled by a cooling fluid. [Background technology]

[0002] A screw compressor includes a rotating screw rotor and a casing that houses the screw rotor. The volume of a plurality of working chambers formed by the screw rotor and the inner wall surface of the casing that surrounds it increases and decreases as the screw rotor rotates, thereby sucking in and compressing gas.

[0003] A typical factor that reduces the performance of a screw compressor is internal leakage of compressed gas. Internal leakage of compressed gas refers to the phenomenon in which compressed gas flows back from a high-pressure space (working chamber) where pressure has increased as compression progresses to a relatively low-pressure space where compression has not yet begun or is not progressing. This internal leakage requires energy for the compressed gas to return to a low-pressure state, resulting in energy loss. Internal gaps that can serve as routes for internal leakage of compressed gas include the gap between the meshing portions of the screw rotor, the gap between the tips of the screw rotor teeth and the inner wall surface (inner peripheral surface) of the casing, and the gap between the discharge-side end face of the screw rotor and the opposing discharge-side inner wall surface of the casing (hereinafter sometimes referred to as the discharge-side end face gap).

[0004] In a screw compressor, the compressed gas becomes hot, causing the casing and screw rotor to heat up and deform. The thermal deformation of the casing and screw rotor tends to increase the internal clearance.

[0005] As a measure to reduce thermal deformation of the screw rotor, a method of cooling the screw rotor by supplying a coolant to cooling passages (holes) provided inside the screw rotor is known. An example of such a method of cooling a screw rotor is the technology described in Patent Document 1. In the rotor of the compressor element described in Patent Document 1, a plurality of inward fins are provided in an internal cooling passage extending in the axial direction at the center of the rotor. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2010-510432 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to improve compressor efficiency, it is necessary to suppress the expansion of the internal gap by further improving the cooling capacity of the screw rotor. It has been revealed that the discharge-side end face gap expands due to thermal deformation in the axial direction of the screw rotor. Therefore, it is necessary to reduce the thermal deformation of the screw rotor, which expands the discharge-side end face gap. In particular, it is expected that thermal deformation of the discharge-side shaft portion of the screw rotor will have a significant impact on the expansion of the discharge-side end face gap.

[0008] One method for improving the cooling capacity of the screw rotor is to lower the temperature of the coolant supplied to the cooling passage of the screw rotor. However, this method requires an enlarged cooler for cooling the coolant, which increases costs. Furthermore, if the cooler is an air-cooled type that uses outside air for cooling, the coolant temperature is limited to a temperature higher than the outside air temperature.

[0009] Another method for improving the cooling capacity is to increase the flow rate of the coolant supplied to the cooling flow passage, but this method requires an enlarged pump for supplying the coolant, which results in an increase in the overall power consumption of the compressor system.

[0010] Therefore, it is necessary to increase the cooling capacity for the screw rotor without changing the temperature or flow rate of the coolant supplied to the cooling flow passage.

[0011] Furthermore, in the technology described in Patent Document 1, the presence of multiple fins in the cooling flow passage increases the heat exchange surface area with the coolant flowing through the cooling flow passage, which is thought to improve the cooling capacity for the screw rotor. However, providing multiple inward-facing fins in the cooling flow passage of the screw rotor makes the structure complex.

[0012] The present invention has been made to solve the above problems, and one of its objects is to provide a screw compressor that can increase the cooling capacity for the discharge side shaft portion of the screw rotor with a simple structure. [Means for solving the problem]

[0013] A preferred example of the present invention includes a screw rotor including a rotor tooth portion having twisted lobes and a discharge-side end face on one side in the axial direction, and a discharge-side shaft portion provided on the one side of the rotor tooth portion in the axial direction, and a discharge-side bearing attached to the discharge-side shaft portion, wherein the screw rotor has a cooling flow passage extending in the axial direction at least inside the discharge-side shaft portion, and a groove structure is provided in at least a part of an area between the position of the discharge-side end face in the axial direction on a wall surface of the cooling flow passage and an attachment position of the discharge-side bearing, the groove structure having a longitudinal component in the circumferential direction of the screw rotor and being constituted by grooves present at intervals in the axial direction, and a nozzle of a stationary member for supplying a cooling fluid is arranged inside the cooling flow passage with a gap from the wall surface, and the nozzle is arranged so as to overlap with at least a part of the groove structure at the axial position. A side hole opening in the radial direction is provided in a region of the nozzle that overlaps with the groove structure. It is a screw compressor. [Effects of the Invention]

[0014] According to a preferred example of the present invention, the relative velocity of the cooling fluid flowing in the vicinity of the wall surface located between the grooves of the groove structure in the cooling flow channel relative to the wall surface is increased by the influence of the cooling fluid flowing in the region of the axially adjacent groove position. Furthermore, the relative velocity of the cooling fluid flowing on the wall surface side of the cooling flow channel relative to the wall surface is increased by the influence of the cooling fluid flowing near the nozzle. This increases the heat transfer coefficient on the wall surface having the groove structure of the cooling flow channel, thereby improving the cooling capacity for the discharge-side shaft portion of the screw rotor. In other words, the cooling capacity for the discharge-side shaft portion of the screw rotor can be increased with a simple structure. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view showing a schematic structure of a screw compressor according to a first embodiment of the present invention, and a system diagram showing an external supply path of a cooling fluid to the screw compressor. [Figure 2] 2 is a cross-sectional view of the screw compressor according to the first embodiment, taken along the line II-II in FIG. 1. [Figure 3] 2 is a cross-sectional view showing the structure of cooling passages and the arrangement of nozzles in a screw rotor (male rotor) in the screw compressor according to the first embodiment shown in FIG. 1. FIG. [Figure 4] FIG. 3 is a diagram showing the analysis results of the distribution of the heat transfer coefficient for the cooling passages of the screw rotor in the screw compressor according to the first embodiment. [Figure 5] FIG. 4 is a diagram showing the analysis results of the distribution of the heat transfer coefficient of the cooling flow passage of the screw rotor of the comparative example (without a groove structure) in comparison with the cooling flow passage of the screw rotor of the screw compressor according to the first embodiment. [Figure 6] FIG. 3 is an explanatory diagram showing the operation of the cooling passage of the screw rotor in the screw compressor according to the first embodiment. [Figure 7] FIG. 4 is a cross-sectional view showing the structure of a cooling passage and the arrangement of nozzles of a screw rotor in a screw compressor according to a modified example of the first embodiment. [Figure 8] FIG. 4 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to a third embodiment of the present invention. [Figure 10] FIG. 10 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to a fourth embodiment of the present invention. [Figure 11] FIG. 10 is a schematic diagram showing the structure of a screw rotor in a screw compressor according to a modified example of the fourth embodiment of the present invention. [Figure 12] 12 is a schematic diagram showing the dimensional relationship between the recesses of the rotor teeth and the discharge-side shaft portion in the screw rotor shown in FIG. 11. FIG. [Figure 13] FIG. 13 is an explanatory view showing a state after joining of a discharge-side shaft portion in a screw rotor of a comparative example to a screw rotor of a screw compressor according to a modified example of the fourth embodiment. [Figure 14] FIG. 10 is an explanatory diagram showing the operation and effect of the screw compressor according to a modified example of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of a screw compressor according to the present invention will be described with reference to the drawings. The embodiment described here shows an example in which the present invention is applied to an oil-free screw compressor.

[0017] [First embodiment] The configuration of a screw compressor according to a first embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 1 is a cross-sectional view showing the schematic structure of a screw compressor according to a first embodiment of the present invention and a system diagram showing an external supply path of a cooling fluid to the screw compressor. Fig. 2 is a cross-sectional view of the screw compressor according to the first embodiment as seen from the arrows II-II shown in Fig. 1. In Fig. 1, the left side is the axial suction side of the screw compressor, and the right side is the axial discharge side. In Fig. 2, the thick arrow indicates the rotation direction of the screw rotor.

[0018] 1 and 2, the screw compressor 1 includes a male rotor 2 (male screw rotor) and a female rotor 3 (female screw rotor) that rotate while meshing with each other, and a casing 4 that rotatably houses the male and female rotors 2 and 3 in their meshed state. The male rotor 2 and the female rotor 3 are arranged so that their central axes A1 and A2 are parallel to each other. The male rotor 2 is rotatably supported on one side (right side in FIG. 1) and the other side (left side in FIG. 1) of its axial direction (left-right direction in FIG. 1) by discharge-side bearings 6 and 7 and a suction-side bearing 8, respectively, and is connected to, for example, a motor 90, which serves as a rotary drive source. The discharge-side bearing 6 is, for example, a bearing for positioning the male rotor 2 in the axial direction. The female rotor 3 is rotatably supported on one side and the other side of its axial direction by a discharge-side bearing and a suction-side bearing (neither of which are shown), respectively. In the oil-free screw compressor 1, the male rotor 2 and the female rotor 3 are arranged to rotate without contacting each other.

[0019] The male rotor 2 is composed of a rotor tooth portion 21 having a plurality of spirally twisted male teeth (lobes) 21a (four in FIG. 2), a discharge-side shaft portion 22 provided on one axial side (right side in FIG. 1) of the rotor tooth portion 21, and a suction-side shaft portion 23 provided on the other axial side (left side in FIG. 1). The male rotor 2 is composed of the rotor tooth portion 21, the discharge-side shaft portion 22, and the suction-side shaft portion 23 integrally formed as a single member (see FIG. 3 described below). The rotor tooth portion 21 has a discharge-side end face 21b and a suction-side end face 21c at one axial end (right end in FIG. 1) and the other axial end (left end in FIG. 1), respectively, which are perpendicular to the axial direction (center axis A1). In the rotor tooth portion 21, the male teeth 21a extend from the discharge-side end face 21b to the suction-side end face 21c, and tooth grooves are formed between the male teeth 21a. A timing gear 10 is attached to the tip of the discharge-side shaft 22. The suction-side shaft 23 extends, for example, outside the casing 4 and is connected to the motor 90 via a gear 11. Note that the suction-side shaft 23 may also be configured to be directly connected to the motor 90 without the gear 11 being interposed therebetween.

[0020] The female rotor 3 is composed of a rotor tooth portion 31 having a plurality of spirally twisted female teeth (lobes) 31a (six in FIG. 2), a discharge-side shaft portion 32 provided on one side of the rotor tooth portion 31 in the axial direction (perpendicular to the plane of FIG. 2 ), and a suction-side shaft portion (not shown) provided on the other side. Like the male rotor 2, the female rotor 3 is also composed as a single member in which the rotor tooth portion 31, discharge-side shaft portion 32, and suction-side shaft portion are integrally formed. The rotor tooth portion 31 has a discharge-side end face and a suction-side end face (neither of which are shown) at one and the other axial ends, respectively, that are perpendicular to the axial direction (center axis A2). In the rotor tooth portion 31, the female teeth 31a extend from the suction-side end face to the discharge-side end face, and tooth grooves are formed between the female teeth 31a. A timing gear (not shown) that meshes with the timing gear 10 on the male rotor 2 side is attached to the tip of the discharge-side shaft portion 32. The rotational force of the male rotor 2 is transmitted to the female rotor 3 by the timing gear 10 on the male rotor 2 side and the timing gear on the female rotor 3 side, and the male rotor 2 and female rotor 3 rotate synchronously without contacting each other.

[0021] The casing 4 comprises a main casing 41, an suction side cover 42 attached to the suction side (left side in Figure 1) of the main casing 41, and an discharge side cover 43 attached to the discharge side (right side in Figure 1) of the main casing 41.

[0022] An accommodation chamber 45 is formed inside the casing 4 to accommodate the rotor tooth portions 21 of the male rotor 2 and the rotor tooth portions 31 of the female rotor 3 in a mutually meshed state. The accommodation chamber 45 is made up of two partially overlapping cylindrical spaces formed inside the casing 4. The wall surfaces (inner wall surfaces of the casing 4) that form the accommodation chamber 45 are composed of a substantially cylindrical male-side inner circumferential surface 46 that covers the radial outside of the rotor tooth portions 21 of the male rotor 2, a substantially cylindrical female-side inner circumferential surface 47 that covers the radial outside of the rotor tooth portions 31 of the female rotor 3, a discharge-side inner wall surface 48 on one axial side (right side in FIG. 1) that faces the discharge-side end faces 21b of the rotor tooth portions 21, 31 of both the male and female rotors 2, 3, and a suction-side inner wall surface 49 on the other axial side (left side in FIG. 1) that faces the suction-side end faces 21c of the rotor tooth portions 21, 31 of both the male and female rotors 2, 3. The rotor teeth 21, 31 of the male and female rotors 2, 3 are arranged with a gap of several tens to several hundreds of μm maintained against the inner wall surface of the casing 4. The rotor teeth 21, 31 of the male and female rotors 2, 3 and the inner wall surface of the casing 4 that surrounds them form multiple working chambers C. The working gas in the working chambers C is compressed as the working chambers C move axially and contract as the male and female rotors 2, 3 rotate.

[0023] 1, the casing 4 is provided with an intake passage 51 for drawing gas into the working chamber C, which is in communication with the other axial side (left side in FIG. 1) of the accommodation chamber 45. The casing 4 is also provided with a discharge passage 52 for guiding the compressed air in the working chamber C to the outside of the casing 4 and discharging it, which is in communication with one axial side (right side in FIG. 1) of the accommodation chamber 45.

[0024] A suction side bearing 8 on the male rotor 2 side and a suction side bearing on the female rotor 3 side are arranged at the end of the main casing 41 on the suction flow path 51 side. In addition, a shaft seal member 12 is arranged on the suction side shaft portion 23 of the male rotor 2, closer to the motor 90 than the suction side bearing 8. A suction side cover 42 is attached to the main casing 41 so as to cover the suction side bearing 8 and the shaft seal member 12. An oil supply passage 53 is provided in the suction side cover 42 to supply lubricating oil to the suction side bearing 8 and the shaft seal member 12.

[0025] Discharge side bearings 6, 7 and timing gear 10 on the male rotor 2 side, and a discharge side bearing and timing gear on the female rotor 3 side are arranged at the end of the main casing 41 on the discharge flow path 52 side. An oil supply passage 53 is provided in the main casing 41 to supply lubricating oil to the discharge side bearings 6, 7 and timing gear 10. A discharge side cover 43 is attached to the main casing 41 so as to cover the discharge side bearings 6, 7 and timing gear 10.

[0026] As shown in Figures 1 and 2, the male rotor 2 (male screw rotor) and the female rotor 3 (female screw rotor) according to this embodiment are provided with cooling passages 25 and 35 for circulating a cooling fluid. The cooling passages 25 and 35 are used to circulate a cooling fluid for cooling the male rotor 2 and the female rotor 3, to which heat generated by gas compression is transferred. The screw compressor 1 according to this embodiment is characterized by the structure of the cooling passage 25 of the male rotor 2. The structure of the cooling passage 25 will be described in detail later.

[0027] As shown in Fig. 1, an external cooling system 70 for circulating a cooling fluid is connected to the cooling passages 25, 35 of the male and female rotors 2, 3 (screw rotors). The external cooling system 70 is configured to use, for example, lubricating oil for lubricating the discharge-side bearings 6, 7 and the suction-side bearing 8 of the male and female rotors 2, 3 as the cooling fluid for cooling the male and female rotors 2, 3. Specifically, the external cooling system 70 includes a pump 71 that sends lubricating oil (cooling fluid) to the discharge-side bearings 6, 7, the suction-side bearing 8, and the cooling passages 25, 35 of the male and female rotors 2, 3, a cooler 72 that cools the lubricating oil (cooling fluid), accessories 73 such as a filter and a check valve, and piping 74 that connects these components. The cooler 72 is, for example, an air-cooled type that uses external air around the cooler 72 for cooling. The piping 74 includes a cooling fluid supply line 74a that supplies lubricating oil as a cooling fluid to the cooling flow paths 25 and 35, and a lubricating oil supply line 74b that supplies lubricating oil to the discharge side bearings 6 and 7 and the suction side bearing 8. In Figure 1, the thick arrows indicate the flow direction of the lubricating oil (cooling fluid).

[0028] In this embodiment, lubricating oil is used as the cooling fluid for both the male and female rotors 2 and 3, and an external cooling system that supplies cooling fluid to the cooling passages 25 and 35 of the male and female rotors 2 and 3 and a lubrication system that supplies lubricating oil to the discharge-side bearings 6 and 7 and the suction-side bearing 8 are integrated into one unit. However, other than lubricating oil, a liquid or gas such as cooling water can also be used as the cooling fluid. In this case, the external cooling system is configured as a separate system from the lubrication system. For example, the external cooling system can be configured to introduce a cooling fluid such as cooling water into both the male and female rotors 2 and 3 and the motor 90.

[0029] Next, the configuration and structure of the cooling passages of the screw rotor (male rotor) in the screw compressor according to the first embodiment will be described with reference to Figures 1 to 3. Figure 3 is a cross-sectional view showing the structure of the cooling passages and the arrangement of nozzles in the screw rotor (male rotor) in the screw compressor according to the first embodiment shown in Figure 1.

[0030] In the screw compressor 1 having the above-described configuration, when the male rotor 2 is driven to rotate by the motor 90 shown in FIG. 1, the male rotor 2 drives to rotate the female rotor 3 shown in FIG. 2 via the timing gear 10. As a result, the working chamber C shown in FIGS. 1 and 2 moves in the axial direction as the male and female rotors 2, 3 rotate. At this time, the working chamber C increases its volume to suck in gas (e.g., air) from outside the casing 4 through the suction passage 51 shown in FIG. 1, and compresses the gas to a predetermined pressure by reducing its volume. When the working chamber C communicates with the discharge passage 52, the compressed gas in the working chamber C passes through the discharge passage 52 and is discharged to the outside of the casing 4.

[0031] Heat generated during the gas compression stroke is transferred to the areas around the discharge passage 52 of the male and female rotors 2 and 3 and to the axial discharge side area of ​​the accommodation chamber 45 of the casing 4, causing temperatures to rise. This heat transfer causes thermal deformation of the male and female rotors 2 and 3. Thermal deformation is particularly significant in the discharge-side shaft portions 22 and 32 of the male and female rotors 2 and 3, which are located around the discharge passage 52 through which high-temperature compressed gas flows. This thermal deformation can increase the relative distance from the mounting position of the discharge-side bearing 6 of the male rotor 2 to the position of the discharge-side end face 21b, and the relative distance from the mounting position of the discharge-side bearing of the female rotor 3 to the position of the discharge-side end face. If this increase in relative distance widens the discharge-side end face gap, which is the gap between the discharge-side end face 21b of the male and female rotors 2 and 3 and the opposing discharge-side inner wall surface 48 of the casing 4, then internal leakage of compressed gas through the discharge-side end face gap increases.

[0032] The screw compressor 1 according to this embodiment is equipped with a cooling system that cools both the male and female rotors 2, 3. The male rotor 2 has a cooling passage 25 that extends in the axial direction along the central axis A1, as shown in Fig. 2 and Fig. 3, for example. Similarly, the female rotor 3 has a cooling passage 35 that extends in the axial direction along the central axis A2, as shown in Fig. 2, for example. The cooling passages 25, 35 are formed by through holes that axially pass through both the male and female rotors 2, 3, as shown in Fig. 3, for example. That is, the cooling passages 25, 35 extend from the tips of the discharge-side shaft portions 22, 32 of both the male and female rotors 2, 3 to the tip of the suction-side shaft portion 23, and are open on both sides.

[0033] In this embodiment, a groove structure 26 is provided on a wall surface 25a (inner peripheral surface of the through hole) that forms the cooling flow passage 25 of the male rotor 2. The groove structure 26 is provided, for example, across the region between the position of the discharge side end face 21b of the male rotor 2 and the mounting position of the discharge side bearing 6. The groove structure 26 is composed of grooves that have a length component in the circumferential direction (rotational direction) of the male rotor 2 and that exist at intervals in the axial direction. The groove structure 26 is composed, for example, of a plurality of annular grooves 27 that are arranged at intervals in the axial direction.

[0034] A nozzle 15 for supplying a cooling fluid is disposed inside the cooling flow passage 25. The nozzle 15 is configured as a stationary member and is disposed with a gap between it and the wall surface 25a of the cooling flow passage 25. That is, the wall surface 25a of the cooling flow passage 25 is displaced circumferentially relative to the outer peripheral surface 15a of the nozzle 15. The nozzle 15 is disposed so as to overlap at least a portion of the groove structure 26 on the wall surface 25a of the cooling flow passage 25 in the axial direction. The nozzle 15 is inserted, for example, from an opening on the discharge-side shaft portion 22 side of the cooling flow passage 25 and extends within the cooling flow passage 25 from a position near the discharge-side end surface 21b of the male rotor 2 to the tip of the discharge-side shaft portion 22. A plurality of side holes 15b are provided at intervals in the axial direction in the nozzle 15 in the area overlapping with the groove structure 26. The side holes 15b are configured as outlets for the cooling fluid into the cooling flow passage 25. The nozzle 15 is connected to a cooling fluid supply line 74a of an external cooling system 70 either directly or via a connecting pipe.

[0035] As described above, in this embodiment, a groove structure 26 is provided in a predetermined region (region between the position of the discharge side end face 21b of the male rotor 2 and the mounting position of the discharge side bearing 6) on the wall surface 25a of the cooling flow passage 25 of the male rotor 2, and the nozzles 15 of the stationary members are arranged inside the cooling flow passage 25 so as to overlap in the axial direction with at least a part of the groove structure 26. The inventors have found that by increasing the coefficient of heat transfer between the wall surface 25a of the cooling flow passage 25 and the cooling fluid using the groove structure 26 on the wall surface 25a of the cooling flow passage 25 and the nozzles 15 of the stationary members inside the cooling flow passage 25, it is possible to improve the cooling capacity for the discharge side shaft portion 22 of the male rotor 2.

[0036] Next, the operation and effect of the cooling system for the screw rotor in the screw compressor according to the first embodiment will be described with reference to Fig. 1 and Fig. 3 to Fig. 6. Fig. 4 is a diagram showing the analysis results of the distribution of the heat transfer coefficient for the cooling flow passages of the screw rotor in the screw compressor according to the first embodiment. Fig. 5 is a diagram showing the analysis results of the distribution of the heat transfer coefficient for the cooling flow passages of a screw rotor of a comparative example (without a groove structure) for the cooling flow passages of the screw rotor of the screw compressor according to the first embodiment.

[0037] In the screw compressor 1 shown in Fig. 1, lubricating oil is supplied as a cooling fluid from an external cooling system 70 to the cooling passage 25 of the male rotor 2. The cooling fluid, whose temperature has increased after cooling the male rotor 2, is sent to a cooler 72 by a pump 71 of the external cooling system 70, and is cooled in the cooler 72. The cooling fluid, whose temperature has been reduced by the cooler 72, is introduced again into the cooling passage 25 of the male rotor 2 via an auxiliary device 73 and a cooling fluid supply line 74a.

[0038] In this embodiment, cooling fluid is supplied from the nozzle 15 to the cooling passage 25 of the male rotor 2 via a cooling fluid supply line 74a of the external cooling system 70. As shown in FIG. 3 , the cooling fluid flows inside the nozzle 15 from the tip of the discharge-side shaft portion 22 toward the rotor tooth portion 21. Most of the cooling fluid flows into the cooling passage 25 from the tip of the nozzle 15, and a portion flows into the cooling passages 25, 35 from the side holes 15b of the nozzle 15. In FIG. 3 , the outline arrows and thick arrows indicate the flow direction of the cooling fluid (lubricating oil). The cooling fluid that flows into the cooling passage 25 from the tip of the nozzle 15 passes through the interior of the rotor tooth portion 21 and the interior of the suction-side shaft portion 23 in this order. The cooling fluid that flows into the cooling passage 25 from the side holes 15b located downstream of the nozzle 15 flows through the gap (annular passage) between the wall surface 25a of the cooling passage 25 and the outer circumferential surface 15a of the nozzle 15 toward the rotor tooth portion 21. On the other hand, the cooling fluid that flows into the cooling flow path 25 from the side hole 15b located upstream in the nozzle 15 flows through the gap (annular flow path) between the wall surface 25a of the cooling flow path 25 and the outer peripheral surface 15a of the nozzle 15 toward the discharge side bearing 6 (in the opposite direction to the flow direction of the cooling fluid in the nozzle 15).

[0039] Incidentally, one possible measure to improve the cooling capacity of the male rotor 2 is to lower the temperature of the cooling fluid supplied to the cooling passage 25. However, in this case, it is necessary to increase the size of the cooler 72 of the external cooling system 70, which increases costs accordingly. In addition, if the cooler 72 is an air-cooled type, the temperature of the cooling fluid is restricted to be equal to or higher than the outside air temperature, making it difficult to improve the cooling capacity by lowering the temperature of the cooling fluid.

[0040] Another method for improving the cooling capacity is to increase the flow rate of the cooling fluid supplied to the cooling flow passage 25. This increases the axial flow velocity of the cooling fluid, improving the heat transfer coefficient near the wall surface 25a of the cooling flow passage 25. However, in this case, it is necessary to increase the size of the pump 71 of the external cooling system 70, which increases the power required for the pump 71. As a result, the overall power required for the compressor system may increase.

[0041] In contrast, in this embodiment, even if the temperature and flow rate of the cooling fluid for the male rotor 2 are set to the same as before, the cooling capacity for the male rotor 2 is improved by providing the above-mentioned groove structure 26 in the above-mentioned predetermined area on the wall surface 25a of the cooling flow path 25 of the male rotor 2 and arranging the nozzle 15 of the stationary member inside the cooling flow path 25 so that it overlaps at least a part of the groove structure 26 in the axial direction.

[0042] 4, the heat transfer coefficient is low in the bottom region of each annular groove 27 of the groove structure 26 on the wall surface 25a of the cooling flow channel 25. In contrast, it can be seen that the heat transfer coefficient is relatively high in the smooth curved surface region Wc that exists between adjacent annular grooves 27 of the groove structure 26 on the wall surface 25a of the cooling flow channel 25.

[0043] 5, the heat transfer coefficient is low on the wall surface 25a without a groove structure (the entire area is a curved area without any irregularities) in the cooling flow path 25P of the screw rotor of the comparative example. It can be seen that the heat transfer coefficient on the wall surface 25a of the cooling flow path 25P without a groove structure of the comparative example is lower than the heat transfer coefficient on the curved area Wc without any irregularities that exists between the annular grooves 27 of the groove structure 26 of the wall surface 25a of the cooling flow path 25 having the groove structure 26 of the present embodiment.

[0044] That is, in this embodiment, the coefficient of heat transfer between the cooling fluid and the wall surface 25a having the groove structure 26 in the cooling flow passage 25 of the male rotor 2 increases, so even if the temperature and flow rate of the cooling fluid are set to the same as before, the amount of heat transferred from the male rotor 2 to the cooling fluid increases. As a result, the temperature rise of the male rotor 2 is suppressed, and the amount of thermal deformation of the male rotor 2 in the axial direction can be reduced. Therefore, the expansion of the gap (discharge side end face gap) between the discharge side end face 21b of the male rotor 2 and the discharge side inner wall surface 48 of the casing 4 is suppressed, reducing the amount of internal leakage of compressed gas, thereby improving the efficiency of the compressor.

[0045] Here, the reason why the heat transfer coefficient of the wall surface increases when a groove structure is provided on the wall surface of the cooling flow channel will be explained using Figure 6. Figure 6 is a diagram showing the distribution of the relative velocity (circumferential velocity) of the cooling fluid with respect to the wall surface of the cooling flow channel of the screw rotor according to the first embodiment. In Figure 6, the two-dot chain line indicates the wall surface of the cooling flow channel. The region below the two-dot chain line is the region where the cooling fluid flows. The white arrow indicates the viscous force acting on the cooling fluid in region D.

[0046] It is generally known that the heat transfer coefficient increases as the relative velocity of the fluid to the solid wall increases.

[0047] In a region D located near a curved region Wc (for example, a cylindrical region) without irregularities that exists between the annular grooves 27 of the groove structure 26 on the wall surface 25a of the cooling flow channel 25 (between grooves that exist at intervals in the axial direction) on the wall surface 25a of the cooling flow channel 25, the relative velocity (circumferential velocity) of the cooling fluid with respect to the wall surface 25a of the cooling flow channel 25 is low. This is because a shear force is generated between the cooling fluid and the wall surface 25a of the cooling flow channel 25, which moves in the rotational direction of the male rotor 2, causing the cooling fluid to move in the same direction (circumferential direction) as the wall surface 25a of the cooling flow channel 25.

[0048] On the other hand, in region E, which is adjacent to region D in the axial direction of the male rotor 2, the distance to the bottom or side surface of the annular groove 27 of the groove structure 26 serving as the wall surface of the cooling flow passage 25 located radially is relatively larger than the distance between region D and the smooth curved surface region Wc. Therefore, the shear force acting on the cooling fluid flowing in region E is relatively smaller than in the case of the cooling fluid flowing in region D, and the relative velocity (circumferential velocity) of the cooling fluid in region E with respect to the wall surface 25a of the cooling flow passage 25 is larger than in the case of the cooling fluid in region D.

[0049] This causes a difference in speed between the cooling fluid in region D and the cooling fluid in region E, and the viscous force acting between the cooling fluid in region D and the cooling fluid in region E acts as a brake on the cooling fluid in region D, reducing the flow velocity (circumferential velocity) in region D. This increases the relative speed of the cooling fluid flowing through region D with respect to wall surface 25a of cooling channel 25, and therefore increases the heat transfer coefficient in region D compared to the case of wall surface 25a of cooling channel 25P without groove structure 26 (see FIG. 5).

[0050] 3, the nozzle 15 of the stationary member is disposed inside the cooling flow channel 25 with a gap between it and the wall surface 25a of the cooling flow channel 25, and is disposed so as to overlap with a part of the groove structure 26 at an axial position of the male rotor 2. Therefore, a shear force is generated between the nozzle 15 of the stationary member and the cooling fluid, and the speed of the cooling fluid flowing near the outer circumferential surface 15a of the nozzle 15 decreases. As a result, the cooling fluid flowing on the side of the wall surface 25a of the rotating cooling flow channel 25 (for example, the cooling fluid in region D and region E shown in FIG. 6) is affected by the cooling fluid near the nozzle 15 whose speed has decreased, and the relative speed of the cooling fluid flowing on the side of the wall surface 25a of the cooling flow channel 25 with respect to the wall surface 25a of the cooling flow channel 25 increases compared to when the nozzle 15 is not present.

[0051] In this way, by providing the groove structure 26 on the wall surface 25a of the cooling flow passage 25, the relative velocity (circumferential velocity) of the cooling fluid with respect to the wall surface 25a of the cooling flow passage 25 increases. Furthermore, by arranging the nozzle 15 of the stationary member inside the cooling flow channel 25 so as to overlap at least a part of the groove structure 26 in the axial direction, the relative velocity (circumferential velocity) of the cooling fluid with respect to the wall surface 25a of the cooling flow channel 25 increases. This makes it possible to increase the heat transfer coefficient between the cooling fluid and the wall surface 25a having the groove structure 26 of the cooling flow channel 25.

[0052] As described above, the screw compressor 1 of this embodiment includes a male rotor 2 (screw rotor) including a rotor tooth portion 21 having twisted lobes 21a and a discharge-side end face 21b on one axial side, and a discharge-side shaft portion 22 provided on the one axial side of the rotor tooth portion 21, and a discharge-side bearing 6 attached to the discharge-side shaft portion 22. The male rotor 2 (screw rotor) has a cooling flow passage 25 extending axially at least inside the discharge-side shaft portion 22. A groove structure 26 is provided in at least a portion of an area on a wall surface 25a of the cooling flow passage 25 between the position of the axial discharge-side end face 21b and the attachment position of the discharge-side bearing 6, and the groove structure 26 has a longitudinal component in the circumferential direction of the male rotor 2 (screw rotor) and is composed of grooves 27 spaced apart in the axial direction. A nozzle 15, a stationary member for supplying a cooling fluid, is disposed inside the cooling flow passage 25 with a gap relative to the wall surface 25a and is positioned so as to overlap at least a portion of the groove structure 26 in the axial direction.

[0053] With this configuration, the relative speed of the cooling fluid flowing in the region D near the wall surface We located between the grooves 27 of the groove structure 26 in the cooling flow passage 25 to the wall surface We is increased by the influence of the cooling fluid flowing in the region E of the axially adjacent groove position. Also, the relative speed of the cooling fluid flowing on the wall surface 25a side of the cooling flow passage 25 to the wall surface 25a is increased by the influence of the cooling fluid flowing near the nozzle 15 of the stationary member. This increases the heat transfer coefficient on the wall surface 25a having the groove structure 26 of the cooling flow passage 25, thereby improving the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2 (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2 (screw rotor) can be increased with a simple structure.

[0054] In this embodiment, the groove structure 26 is formed of a plurality of annular grooves 27 spaced apart in the axial direction. This configuration makes the groove structure 26 simple, and therefore the groove structure 26 can be easily processed.

[0055] Furthermore, in this embodiment, the groove structure 26 is provided over the entire area between the position of the discharge-side end face 21b and the mounting position of the discharge-side bearing 6. This configuration can improve the cooling capacity for the entire area that has a significant impact on the expansion of the discharge-side end face gap in the discharge-side shaft portion 22, and therefore can more effectively reduce the expansion of the discharge-side end face gap due to thermal deformation of the discharge-side shaft portion 22.

[0056] [Modification of the first embodiment] A screw compressor according to a modified example of the first embodiment will be illustrated with reference to Fig. 7. It is a cross-sectional view showing the structure of the cooling passages of the screw rotor and the arrangement of the nozzles in the screw compressor according to the modified example of the first embodiment. In Fig. 7, the same reference numerals as those in Figs. 1 to 6 denote similar parts, and therefore detailed description thereof will be omitted.

[0057] The screw compressor according to the modified example of the first embodiment shown in Figure 7 differs from the first embodiment in that the groove structure 26A of the cooling passage 25 of the male rotor 2A (screw rotor) is different. Specifically, the groove structure 26A of the cooling passage 25 of the male rotor 2A is composed of a single spiral groove 27A extending in the axial direction of the male rotor 2A. The spiral groove 27A has a length component in the rotational direction (circumferential direction) of the male rotor 2A and is a groove that exists at intervals in the axial direction. The winding direction of the spiral groove 27A can be either right-handed or left-handed.

[0058] Even when groove structure 26A of cooling flow channel 25 is configured with spiral grooves 27A, similarly to the first embodiment, a speed difference occurs between the cooling fluid flowing in region D (see FIG. 6) near region Wc (see FIG. 6) located between spiral grooves 27A that exist at intervals in the axial direction of groove structure 26A on wall surface 25a of cooling flow channel 25, and the cooling fluid flowing in region E (see FIG. 6) at a groove position adjacent in the axial direction to region D. Therefore, the relative speed of the cooling fluid flowing in region D with respect to wall surface 25a of cooling flow channel 25 increases, and the heat transfer coefficient in region D increases accordingly compared to the case of wall surface 25a of cooling flow channel 25P without groove structure 26 (see FIG. 5).

[0059] In this way, if the heat transfer coefficient between the cooling fluid and the wall surface 25a having the groove structure 26A in the cooling flow passage 25 of the male rotor 2A is increased, the amount of heat transferred from the male rotor 2A to the cooling fluid increases, even if the temperature and flow rate of the cooling fluid are set to the same as before. As a result, the temperature rise of the male rotor 2A is suppressed, and the amount of thermal deformation in the axial direction of the male rotor 2A can be reduced. Therefore, the expansion of the gap (discharge side end face gap) between the discharge side end face 21b of the male rotor 2A and the inner wall surface 48 of the casing 4 is suppressed, reducing the amount of internal leakage of compressed gas, and improving the efficiency of the compressor.

[0060] In this modified example, the groove structure 26A of the cooling flow path 25 is configured by one spiral groove 27A. However, the groove structure 26A of the cooling flow path 25 may be configured by a plurality of spiral grooves 27A.

[0061] In the above-described modification of the first embodiment, similarly to the first embodiment, by providing a groove structure 26A on the wall surface 25a of the cooling flow passage 25 and arranging the nozzle 15 of the stationary member inside the cooling flow passage 25 so as to overlap at least a part of the groove structure 26A, the heat transfer coefficient on the wall surface 25a having the groove structure 26A of the cooling flow passage 25 is increased, thereby improving the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2A (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2A (screw rotor) can be increased with a simple structure.

[0062] In this modification, groove structure 26A is formed of spiral grooves 27A. With this configuration, spiral grooves 27A as groove structure 26A can be provided over a wide axial range on the wall surface of cooling flow channel 25 by a single cutting process, which makes it possible to reduce the number of manufacturing steps and manufacturing costs compared to the first embodiment.

[0063] [Second embodiment] A screw compressor according to a second embodiment will be illustrated with reference to Fig. 8. Fig. 8 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to a second embodiment of the present invention. In Fig. 8, the outline arrows and thick arrows indicate the direction of flow of a cooling fluid (lubricating oil). In Fig. 8, the same reference numerals as those in Figs. 1 to 7 indicate similar parts, and therefore detailed description thereof will be omitted.

[0064] The screw compressor according to the second embodiment shown in FIG. 8 differs from the modified example of the first embodiment (see FIG. 7) in that sealing members 28 are provided at both axial openings of the through-hole serving as the cooling passage 25 of the male rotor 2B (screw rotor). The sealing members 28 prevent fluids other than the cooling fluid from entering the cooling passage 25. One sealing member 28 is attached, for example, to the tip of the discharge-side shaft portion 22 of the male rotor 2B with the nozzle 15 passing through it so as to close the cooling passage 25. The other sealing member 28 is attached, for example, to the tip of the suction-side shaft portion 23 of the male rotor 2B with a discharge pipe 29 passing through it so as to close the cooling passage 25. The discharge pipe 29 discharges the cooling fluid supplied from the nozzle 15 to the cooling passage 25 to the outside of the male rotor 2B.

[0065] 8, the cooling fluid supplied to the nozzle 15 flows into the cooling flow passage 25 from the tip of the nozzle 15 and also flows into the cooling flow passage 25 from the side holes 15b of the nozzle 15. The cooling fluid that flows into the cooling flow passage 25 from the tip of the nozzle 15 passes through the interior of the rotor tooth portion 21 and the interior of the suction-side shaft portion 23 in that order. The cooling fluid that flows into the cooling flow passage 25 from the side holes 15b of the nozzle 15 flows through the gap (annular flow passage) between the wall surface 25a of the cooling flow passage 25 and the outer circumferential surface 15a of the nozzle 15 only toward the rotor tooth portion 21, because the opening of the cooling flow passage 25 on the discharge-side shaft portion 22 side is closed by the sealing member 28.

[0066] In the aforementioned modified example of the first embodiment (see FIG. 7), both axial ends of the cooling passage 25 of the male rotor 2A are open. Therefore, there is a concern that gas, such as external air, may enter the cooling passage 25 through the openings. When gas enters the cooling passage 25, the cooling fluid with a relatively high density moves toward the wall surface 25a of the cooling passage 25 on the radially outer side of the male rotor 2A due to centrifugal force. On the other hand, the gas with a relatively low density may move toward the outer peripheral surface 15a of the nozzle 15 on the radially inner side of the male rotor 2A and form a layer. When a layer of gas is formed on the outer peripheral surface 15a of the nozzle 15, the contact area between the outer peripheral surface 15a of the nozzle 15 and the cooling fluid decreases, thereby reducing the shear force generated between the nozzle 15 (the stationary member) and the cooling fluid. As a result, the effect of increasing the relative velocity of the cooling fluid with respect to the wall surface 25a of the cooling passage 25 is reduced.

[0067] In contrast, in this embodiment, a sealing member 28 is provided at the opening of cooling flow channel 25, thereby preventing gas from entering the interior of cooling flow channel 25. This allows the interior of cooling flow channel 25 to be filled with the cooling fluid supplied from nozzle 15 to cooling flow channel 25, preventing a decrease in the contact area between outer circumferential surface 15a of nozzle 15 and the cooling fluid. Therefore, the arrangement of a stationary member within cooling flow channel 25 of nozzle 15 can reliably achieve the effect of increasing the relative speed of the cooling fluid with respect to wall surface 25a of cooling flow channel 25.

[0068] In the second embodiment described above, as in the modified example of the first embodiment, by providing a groove structure 26A on the wall surface 25a of the cooling flow passage 25 and arranging the nozzle 15 of the stationary member inside the cooling flow passage 25 so as to overlap at least a part of the groove structure 26A, the heat transfer coefficient on the wall surface 25a of the cooling flow passage 25 having the groove structure 26A is increased, thereby improving the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2B (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2B (screw rotor) can be increased with a simple structure.

[0069] In addition, in this embodiment, the cooling flow path 25 is formed by a through hole that passes through the male rotor 2B (screw rotor) in the axial direction, and a sealing member 28 is provided at the axial opening of the cooling flow path 25 to prevent fluids other than the cooling fluid from entering the cooling flow path 25.

[0070] According to this configuration, the sealing member 28 can prevent fluids other than the cooling fluid from entering the cooling flow passage 25, thereby avoiding a decrease in the contact area between the outer circumferential surface 15a of the nozzle 15 and the cooling fluid due to the invading fluid. This ensures an increase in the relative speed of the cooling fluid with respect to the wall surface 25a of the cooling flow passage 25, thereby increasing the heat transfer coefficient on the wall surface 25a having the groove structure 26A of the cooling flow passage 25 and improving the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2B (screw rotor).

[0071] [Third embodiment] A screw compressor according to a third embodiment will be illustrated with reference to Fig. 9. Fig. 9 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to a third embodiment of the present invention. In Fig. 9, outline arrows and thick arrows indicate the direction of flow of a cooling fluid (lubricating oil). In Fig. 9, the same reference numerals as those in Figs. 1 to 8 indicate similar parts, and therefore detailed description thereof will be omitted.

[0072] The screw compressor according to the third embodiment shown in FIG. 9 differs from the modified example of the first embodiment (see FIG. 7) in that the cooling passage 25C of the male rotor 2C (screw rotor) is configured as a bottomed hole with one side open, rather than a through-hole. The cooling passage 25C is formed, for example, so as to extend from the tip of the discharge-side shaft portion 22 of the male rotor 2C to the position of the discharge-side end face 21b of the rotor tooth portion 21, with an opening at the tip of the discharge-side shaft portion 22 and a bottom 25b at the position of the discharge-side end face 21b. In other words, the male rotor 2C has a hollow discharge-side shaft portion 22 and a solid suction-side shaft portion 23. As in the modified example of the first embodiment, a groove structure 26A on the wall surface 25a of the cooling passage 25C is configured as a spiral groove 27A provided across the region between the position of the discharge-side end face 21b of the rotor tooth portion 21 and the position of the discharge-side bearing 6.

[0073] 9, the cooling fluid that flows into the cooling flow channel 25C from the tip of the nozzle 15 is turned by the bottom 25b of the cooling flow channel 25C and flows through the gap (annular flow channel) between the wall surface 25a of the cooling flow channel 25C and the outer circumferential surface 15a of the nozzle 15 toward the opening on the tip side of the discharge-side shaft portion 22. The cooling fluid that flows into the cooling flow channel 25C from the side hole 15b of the nozzle 15, together with the cooling fluid that is turned by the bottom 25b of the cooling flow channel 25C, flows through the gap (annular flow channel) between the wall surface 25a of the cooling flow channel 25C and the outer circumferential surface 15a of the nozzle 15 toward the opening on the tip side of the discharge-side shaft portion 22. The cooling fluid that flows into the cooling flow channel 25C from the nozzle 15 is discharged from the opening of the cooling flow channel 25C. At this time, the cooling fluid flowing through the cooling flow path 25C pushes out and discharges gas remaining in the cooling flow path 25C to the opening of the cooling flow path 25C, so that the inside of the cooling flow path 25C becomes filled with the cooling fluid.

[0074] In this way, by configuring the cooling flow passage 25C of the male rotor 2C as a bottomed hole that is open on one side, it is possible to prevent outside air from entering the cooling flow passage 25C. Therefore, as in the second embodiment, it is possible to prevent the gas that has entered the cooling flow passage 25C from forming a layer on the outer circumferential surface 15a of the nozzle 15, which would otherwise reduce the contact area between the outer circumferential surface 15a of the nozzle 15 and the cooling fluid. In other words, it is possible to prevent outside air from entering the cooling flow passage 25C, as in the second embodiment, without using the sealing member 28 of the second embodiment.

[0075] In the third embodiment described above, as in the modified example of the first embodiment, by providing a groove structure 26A on the wall surface 25a of the cooling flow path 25C and arranging the nozzle 15 of the stationary member inside the cooling flow path 25C so as to overlap at least a part of the groove structure 26A, the heat transfer coefficient on the wall surface 25a of the cooling flow path 25C having the groove structure 26A is increased, thereby improving the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2C (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22 of the male rotor 2C (screw rotor) can be increased with a simple structure.

[0076] Furthermore, in the present embodiment, cooling flow path 25C is configured as a bottomed hole that opens at the tip end side of discharge-side shaft portion 22. With this configuration, the cooling fluid supplied to cooling flow path 25C turns at bottom 25b of cooling flow path 25C and flows out from the opening of cooling flow path 25C, so that it is possible to prevent fluids other than the cooling fluid from entering cooling flow path 25C without using sealing member 28 as in the second embodiment. Therefore, compared to the second embodiment, it is possible to reduce the number of parts, as well as the number of manufacturing steps and manufacturing costs.

[0077] [Fourth embodiment] A screw compressor according to a fourth embodiment will be illustrated with reference to Fig. 10. Fig. 10 is a cross-sectional view showing the structure of a screw rotor in a screw compressor according to the fourth embodiment of the present invention. In Fig. 10, outline arrows and thick arrows indicate the direction of flow of a cooling fluid (lubricating oil). In Fig. 10, the same reference numerals as those in Figs. 1 to 9 indicate similar parts, and therefore detailed description thereof will be omitted.

[0078] The screw compressor according to the fourth embodiment shown in FIG. 10 differs from the modified example of the first embodiment (see FIG. 7) in that the rotor tooth portion 21 and the discharge-side shaft portion 22D of the male rotor 2D (screw rotor) are not formed as a single, integral member but as separate members. Specifically, the male rotor 2D is formed from the rotor tooth portion 21 and the suction-side shaft portion 23 as a single, integrally formed member, and the discharge-side shaft portion 22D as a separate member from the rotor tooth portion 21 and the suction-side shaft portion 23. The base end of the discharge-side shaft portion 22D is joined to the discharge-side end face 21b of the rotor tooth portion 21. The rotor tooth portion 21 and the discharge-side shaft portion 22D are joined by, for example, friction welding or welding. The groove structure 26A is formed over a region from the end of the cooling channel 25 of the discharge-side shaft portion 22D on the joining side (left side in FIG. 10) to the mounting position of the discharge-side bearing.

[0079] In the male rotor 2D of this embodiment, it is possible to machine the groove structure 26A into the wall surface 25a of the cooling flow passage 25 of the discharge-side shaft portion 22D before joining the discharge-side shaft portion 22D to the rotor tooth portion 21. This makes it possible to insert a processing device for machining the groove structure 26A from the opening of the cooling flow passage 25 on the joining side of the discharge-side shaft portion 22D. This processing method makes it easier to insert the processing device compared to inserting the processing device from the opening on the tip side of the discharge-side shaft portion, and therefore leads to a reduction in the processing time for the groove structure 26A.

[0080] In the fourth embodiment described above, as in the modified example of the first embodiment, by providing a groove structure 26A on the wall surface 25a of the cooling flow passage 25 and arranging the nozzle 15 of the stationary member inside the cooling flow passage 25 so as to overlap at least a part of the groove structure 26A, the heat transfer coefficient on the wall surface 25a having the groove structure 26A of the cooling flow passage 25 is increased, thereby improving the cooling capacity for the discharge-side shaft portion 22D of the male rotor 2D (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22D of the male rotor 2D (screw rotor) can be increased with a simple structure.

[0081] Furthermore, in this embodiment, the discharge-side shaft portion 22D is configured as a separate member from the rotor tooth portion 21, and the cooling flow passage 25 penetrates the discharge-side shaft portion 22D. With this configuration, it is possible to machine the groove structure 26A on the wall surface 25a of the cooling flow passage 25 of the discharge-side shaft portion 22D before joining the discharge-side shaft portion 22D to the rotor tooth portion 21. This makes it easier to position the discharge-side shaft portion 22D relative to a processing device that processes the groove structure 26A and to insert the processing device into the cooling flow passage 25, compared to when the rotor tooth portion 21 and the discharge-side shaft portion 22 are configured as an integrated, single member, making it easier to process the groove structure 26A.

[0082] [Modification of the Fourth Embodiment] A screw compressor according to a modified example of the fourth embodiment will now be described. First, the structure of the screw rotor in the screw compressor according to the modified example of the fourth embodiment will be described with reference to Figs. 11 and 12. Fig. 11 is a schematic diagram showing the structure of the screw rotor in the screw compressor according to the modified example of the fourth embodiment of the present invention. Fig. 12 is a schematic diagram showing the dimensional relationship between the recesses in the rotor teeth and the discharge-side shaft in the screw rotor shown in Fig. 11. In Figs. 11 and 12, the same reference numerals as those in Figs. 1 to 10 denote similar parts, and detailed description thereof will be omitted.

[0083] The screw compressor according to the modified example of the fourth embodiment shown in Figure 11 differs from the fourth embodiment (see Figure 10) in that the cooling flow path 25E of the male rotor 2E is provided only in the discharge side shaft portion 22D, and that a recess 21f is provided in the portion of the rotor tooth portion 21E that joins with the discharge side shaft portion 22D (at the position of the discharge side end face 21b).

[0084] Specifically, the male rotor 2E is composed of a rotor tooth portion 21E and a suction-side shaft portion 23, which are integrally formed as one member, and a discharge-side shaft portion 22D, which is also a single member. A through-hole is formed in the discharge-side shaft portion 22D in the axial direction as a cooling channel 25E. Some members of the rotor tooth portion 21E and the suction-side shaft portion 23 are configured without a cooling channel. That is, the cooling channel 25E is present only in the discharge-side shaft portion 22D. A recess 21f is provided in the end face of the rotor tooth portion 21E (at the position of the discharge-side end face 21b) on the side of the joint with the discharge-side shaft portion 22D. As shown in FIG. 12, the diameter Dl of the recess 21f of the rotor tooth portion 21E is set to be smaller than the outer diameter ds of the discharge-side shaft portion 22D and larger than the diameter dp of the cooling channel 25E (through-hole) of the discharge-side shaft portion 22D. The portion of the rotor tooth portion 21E on the discharge side end surface 21b side and the end surface on the base end side (left side in FIG. 11) of the discharge side shaft portion 22D are joined by friction welding.

[0085] Next, the effects of the screw rotor in a screw compressor according to a modification of the fourth embodiment will be described with reference to Figures 13 and 14, in comparison with a screw rotor of a comparative example. Figure 13 is an explanatory diagram showing the state after joining of the discharge-side shaft portion of the screw rotor of the comparative example to the screw rotor of the screw compressor according to a modification of the fourth embodiment. Figure 14 is an explanatory diagram showing the effects of the screw compressor according to the modification of the fourth embodiment. In Figures 13 and 14, the same reference numerals as those in Figures 1 to 12 indicate similar parts, and detailed description thereof will be omitted.

[0086] Friction welding is a process in which the base materials are rubbed together at high speed, generating frictional heat that softens the base materials, and then pressure is applied to plastically deform them, joining them in a solid state. During friction welding, materials that hinder joining, such as oxide films, are pushed out from the joining surfaces as burrs.

[0087] The screw rotor 102 of the comparative example has a configuration in which a discharge-side shaft portion 122 having a cooling flow passage 125 is joined by friction welding to a flat discharge-side end surface 121b of the rotor tooth portion 121 that has no recesses. That is, the joining surface of the rotor tooth portion 121 of the comparative example is a flat surface, while the joining surface of the discharge-side shaft portion 122 having the cooling flow passage 125 is an annular flat surface. Therefore, when the rotor tooth portion 121 and the discharge-side shaft portion 122 are joined by friction welding, burrs B are generated near the outer circumferential surface of the discharge-side shaft portion 122 and the wall surface 125a of the cooling flow passage 125. There is a concern that the burrs B generated near the wall surface 125a of the cooling flow passage 125 will cover the wall surface 125a of the cooling flow passage 125, thereby reducing the heat transfer area between the wall surface 125a of the cooling flow passage 125 and the cooling fluid.

[0088] 12, a recess 21f is provided at the joining portion of the discharge-side end surface 21b of the rotor tooth portion 21E, and the diameter Dl of the recess 21f is set to be smaller than the outer diameter ds of the discharge-side shaft portion 22D and larger than the diameter dp of the cooling flow passage 25E of the discharge-side shaft portion 22D. As a result, burrs B extruded from the joining surfaces 21j, 22j of the rotor tooth portion 21E and the discharge-side shaft portion 22D during friction welding between the rotor tooth portion 21E and the discharge-side shaft portion 22D are generated on the recess 21f side of the rotor tooth portion 21E, not on the cooling flow passage 25E side of the discharge-side shaft portion 22D. This prevents the burrs B from covering the wall surface 25a of the cooling flow passage 25E, which has the groove structure 26A, of the cooling flow passage 25E, and reducing the heat transfer area between the wall surface 25a of the cooling flow passage 25E and the cooling fluid.

[0089] In the modification of the fourth embodiment described above, similarly to the fourth embodiment, by providing a groove structure 26A on the wall surface 25a of the cooling flow passage 25E and arranging the nozzle 15 of the stationary member inside the cooling flow passage 25E so as to overlap at least a part of the groove structure 26A, the heat transfer coefficient on the wall surface 25a of the cooling flow passage 25E having the groove structure 26A is increased, thereby improving the cooling capacity for the discharge-side shaft portion 22D of the male rotor 2E (screw rotor). In other words, the cooling capacity for the discharge-side shaft portion 22D of the male rotor 2E (screw rotor) can be increased with a simple structure.

[0090] In this modification, the rotor tooth portion 21E has a recess 21f at the portion where the rotor tooth portion 21E is joined to the discharge-side shaft portion 22D. The diameter of the recess 21f is set to be smaller than the outer diameter of the discharge-side shaft portion 22D and larger than the diameter of the cooling flow path 25E.

[0091] With this configuration, when the rotor tooth portion 21E and the discharge-side shaft portion 22D are joined by friction welding, burrs B pushed out from the joining surfaces 21j, 22j are generated in the recesses 21f of the rotor tooth portion 21E rather than inside the cooling flow passage 25E, so that the wall surfaces 25a of the cooling flow passage 25E can be prevented from being covered with burrs B generated by friction welding. Therefore, it is possible to prevent the cooling capacity of the male rotor 2E (screw rotor) for the discharge-side shaft portion 22D from being impaired by friction welding.

[0092] [Other embodiments] The present invention is not limited to the above-described embodiments, but includes various modifications. The above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. That is, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0093] In the above-described first to fourth embodiments and their modified examples, an oil-free screw compressor 1 has been used as an example, but the present invention can also be applied to a liquid-feed screw compressor in which a liquid such as oil or water is supplied to the working chamber C.

[0094] In the above-described embodiment, the twin-screw screw compressor 1 having a pair of screw rotors (male rotor and female rotor 3) has been described as an example. However, the present invention can also be applied to a multi-screw screw compressor having three or more screw rotors. The present invention can also be applied to a single-screw screw compressor having one screw rotor and a pair of gate rotors. Furthermore, in the above-described embodiment, an example has been shown in which the groove structures 26, 26A are provided only on the wall surfaces 25a of the cooling passages 25, 25C, 25E ​​of the male rotor 2. However, it is also possible to provide a groove structure only on the wall surfaces 35a of the cooling passages 35 of the female rotor 3, or to provide a groove structure on both the wall surfaces 25a of the cooling passages 25, 25C, 25E ​​of the male rotor 2 and the wall surfaces 35a of the cooling passages 35 of the female rotor 3.

[0095] In the above-described embodiment, an example of a configuration has been shown in which the groove structures 26, 26A are provided over the entire region between the position of the discharge side end face 21b on the wall surface 25a of the cooling flow passage 25 of the male rotor 2 and the mounting position of the discharge side bearing 6. However, it is also possible to provide the groove structures in a portion of the region between the position of the discharge side end face 21b on the wall surface 25a of the cooling flow passage 25 and the mounting position of the discharge side bearing 6. It is also possible to provide the groove structures beyond the region between the position of the discharge side end face 21b on the wall surface 25a of the cooling flow passage 25 and the mounting position of the discharge side bearing 6. [Explanation of symbols]

[0096] REFERENCE SIGNS LIST 1...Screw compressor, 2, 2A, 2B, 2C, 2D, 2E...Male rotor (screw rotor), 3...Female rotor (screw rotor), 6, 7...Discharge side bearing, 15...Nozzle, 21, 21E...Rotor tooth portion, 21a...Lobe, 21b...Discharge side end face, 21f...Recess, 22, 22D...Discharge side shaft portion, 25, 25C, 25E...Cooling passage, 25a...Wall surface, 26, 26A...Groove structure, 27...Annular groove, 27A...Spiral groove, 28...Sealing member, 31...Rotor tooth portion, 31a...Lobe, 32...Discharge side shaft portion, 35...Cooling passage, 35a...Wall surface

Claims

1. a screw rotor including a rotor tooth portion having twisted lobes and a discharge side end face on one side in the axial direction, and a discharge side shaft portion provided on the one side in the axial direction of the rotor tooth portion; a discharge-side bearing attached to the discharge-side shaft portion, the screw rotor has a cooling flow passage extending in the axial direction at least inside the discharge-side shaft portion, a groove structure is provided in at least a part of a region in a wall surface of the cooling flow path between the position of the discharge-side end surface in the axial direction and a mounting position of the discharge-side bearing, the groove structure is configured by grooves having a longitudinal component in the circumferential direction of the screw rotor and spaced apart in the axial direction, a nozzle of a stationary member for supplying a cooling fluid is disposed inside the cooling channel with a gap from the wall surface; the nozzle is positioned to overlap at least a portion of the groove structure at the axial position; A side hole that opens in the radial direction is provided in a region of the nozzle that overlaps with the groove structure. Screw compressor.

2. a screw rotor including a rotor tooth portion having twisted lobes and a discharge side end face on one side in the axial direction, and a discharge side shaft portion provided on the one side in the axial direction of the rotor tooth portion; a discharge-side bearing attached to the discharge-side shaft portion, the screw rotor has a cooling flow passage extending in the axial direction at least inside the discharge-side shaft portion, a groove structure is provided in at least a part of a region in a wall surface of the cooling flow path between the position of the discharge-side end surface in the axial direction and a mounting position of the discharge-side bearing, the groove structure is configured by grooves having a longitudinal component in the circumferential direction of the screw rotor and spaced apart in the axial direction, a nozzle of a stationary member for supplying a cooling fluid is disposed inside the cooling channel with a gap from the wall surface; the nozzle is disposed so as to overlap at least a portion of the groove structure at a position in the axial direction, and a side hole is provided in a region of the nozzle that overlaps with the groove structure; the cooling flow path is formed by a through hole that penetrates the screw rotor in the axial direction, A sealing member is provided at the axial opening of the cooling flow path to prevent fluids other than the cooling fluid from entering the cooling flow path. Screw compressor.

3. a screw rotor including a rotor tooth portion having twisted lobes and a discharge side end face on one side in the axial direction, and a discharge side shaft portion provided on the one side in the axial direction of the rotor tooth portion; a discharge-side bearing attached to the discharge-side shaft portion, the screw rotor has a cooling flow passage extending in the axial direction at least inside the discharge-side shaft portion, a groove structure is provided in at least a part of a region in a wall surface of the cooling flow path between the position of the discharge-side end surface in the axial direction and a mounting position of the discharge-side bearing, the groove structure is configured by grooves having a longitudinal component in the circumferential direction of the screw rotor and spaced apart in the axial direction, a nozzle of a stationary member for supplying a cooling fluid is disposed inside the cooling channel with a gap from the wall surface; the nozzle is disposed so as to overlap at least a portion of the groove structure at a position in the axial direction, and a side hole is provided in a region of the nozzle that overlaps with the groove structure; the discharge-side shaft portion is configured as a separate member from the rotor teeth portion, The cooling passage passes through the discharge-side shaft portion. Screw compressor.

4. The screw compressor according to any one of claims 1 to 3, The groove structure is composed of a plurality of annular grooves spaced apart in the axial direction. Screw compressor.

5. The screw compressor according to any one of claims 1 to 3, The groove structure is formed by a spiral groove. Screw compressor.

6. 2. The screw compressor according to claim 1, The cooling flow path is formed by a hole with a bottom that opens at the tip end of the discharge-side shaft portion. Screw compressor.

7. The screw compressor according to any one of claims 1 to 3, The groove structure is provided over the entire area between the position of the discharge side end face and the mounting position of the discharge side bearing. Screw compressor.

8. A screw compressor according to claim 3, the rotor tooth portion has a recess at a portion where it joins with the discharge-side shaft portion, The diameter of the recess is set to be smaller than the outer diameter of the discharge-side shaft portion and larger than the diameter of the cooling flow path. Screw compressor.

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