Turbomachine, multistage rotor, and manufacturing method thereof

Abstract

A turbo machine includes a casing and a multistage rotor supported by the casing. The multistage rotor includes: a rotor shaft that is a single object and includes a stepped surface; impellers fitted to the rotor shaft and lined up in an axial direction of the rotor shaft from the stepped surface; and a lock nut fitted to the rotor shaft. The impellers are sandwiched between the stepped surface and the lock nut.

Description

Technical Field

[0001] The present disclosure relates to a multistage rotor of a turbo machine, such as a compressor.Background Art

[0002] A turbo machine continuously performs energy conversion between fluid energy and mechanical energy through an impeller that rotates. The turbo machine may include a multistage rotor including impellers. PTL 1 discloses this type of turbo machine.

[0003] The turbo machine of PTL 1 is a centrifugal compressor and includes a multistage rotor including: a tie bolt; short rotor shafts (i.e., stub shafts) respectively assembled to both ends of the tie bolt; and impellers supported by the tie bolt and lined up in an axial direction. The adjacent impellers are connected to each other by mechanical coupling and are fastened to each other by axial force of the tie bolt.Citation List Patent Literature

[0004] PTL 1: International Publication WO2021 / 230869Summary of Invention Technical Problem

[0005] According to the multistage rotor of PTL 1, since the tie bolt is assembled to a pair of rotor shafts, misalignment between each rotor shaft and the tie bolt may occur. The imbalance of the multistage rotor due to such misalignment is difficult to be removed by a balancing step. Moreover, an increase in a compression rate of the rotor can be realized by an increase in a rotor axial length by an increase in the number of stages and an increase in a rotation peripheral speed of the rotor. However, this increases a risk of the interference of an natural frequency of the tie bolt with an operation rotational frequency. To detune the natural frequency of the tie bolt from the operation rotational frequency, the tie bolt tends to increase in diameter. When the tie bolt increases in diameter, influence of the misalignment between each rotor shaft and the tie bolt on the imbalance of the multistage rotor increases.

[0006] The present disclosure was made under these circumstances, and an object of the present disclosure is to provide a multistage rotor that prevents imbalance caused due to misalignment between a rotor shaft and a tie bolt, and a turbo machine including this multistage rotor.Solution to Problem

[0007] In order to solve the above problems, a multistage rotor according to one aspect of the present disclosure includes: a rotor shaft that is a single object and includes a stepped surface; impellers fitted to the rotor shaft and lined up in an axial direction of the rotor shaft from the stepped surface; and a lock nut fitted to the rotor shaft, wherein the impellers are sandwiched between the stepped surface and the lock nut while being pressurized by axial force of the rotor shaft.

[0008] A turbo machine according to one aspect of the present disclosure includes: a casing; and the multistage rotor supported by the casing.

[0009] A method of manufacturing a multistage rotor according to one aspect of the present disclosure includes: fitting impellers to a rotor shaft that is a single object and includes a stepped surface; and fitting a lock nut to the rotor shaft to sandwich the impellers between the stepped surface and the lock nut in a state where the impellers are pressurized by axial force of the rotor shaft. Advantageous Effects of Invention

[0010] The present disclosure can provide the multistage rotor that prevents the imbalance caused due to the misalignment between the tie bolt and the rotor shaft, and the turbo machine including this multistage rotor.Brief Description of Drawings

[0011] FIG. 1 is a schematic sectional view of a turbo machine according to one aspect of the present disclosure. FIG. 2 is a schematic sectional view of a multistage rotor. FIG. 3 is a schematic sectional view of the multistage rotor having a straight arrangement. FIG. 4 is a sectional view of the multistage rotor which explains an internal passage. FIG. 5 is a sectional view of the multistage rotor which explains a modified example of the internal passage. FIG. 6 is a diagram which explains a method of manufacturing the multistage rotor. FIG. 7 is a diagram showing a balance piston and a lock nut according to Modified Example 1. FIG. 8 is a diagram showing the balance piston and the lock nut according to Modified Example 2. FIG. 9 is a schematic sectional view of the multistage rotor in which impellers are located at both sides of a second section. FIG. 10 is a schematic sectional view showing the multistage rotor according to Modified Example. Description of Embodiments

[0012] FIG. 1 is a schematic sectional view of a turbo machine 1 according to one aspect of the present disclosure. FIG. 1 shows an upper half of the turbo machine 1 which is located at an upper side of a rotor axis A. As one aspect of the turbo machine 1, FIG. 1 shows a centrifugal compressor including a multistage rotor 2. The multistage rotor 2 is a rotor that stepwisely compresses fluid by impellers 4. Moreover, the centrifugal compressor is a compressor which: allows the fluid to flow therethrough, the fluid being to be compressed in a radial direction of the impeller 4 that rotates; and compresses the fluid by centrifugal force generated at that moment. The multistage rotor 2 of the present disclosure is not limited to the centrifugal compressor and is widely applicable to the turbo machine 1.

[0013] The turbo machine 1 includes: a casing 12; the multistage rotor 2 accommodated in the casing 12; and a driver that rotates the multistage rotor 2.

[0014] FIG. 2 is a schematic sectional view of the multistage rotor 2. As shown in FIGS. 1 and 2, the multistage rotor 2 is a rotating body whose center corresponds to the rotor axis A. The multistage rotor 2 includes: a rotor shaft 3 whose center corresponds to the rotor axis A and which extends in parallel with an axial direction X; and the impellers 4 located at a substantially middle portion of the rotor shaft 3 in the axial direction X and lined up in the axial direction X. A combination of the impellers 4 stacked on each other in the axial direction X is called an impeller stack 40, and the multistage rotor 2 is also called a stacked rotor.

[0015] The rotor shaft 3 is a stepped shaft including a stepped surface 36. The rotor shaft 3 includes: a first section 31 located at a middle portion thereof in the axial direction X; a second section 32 located next to the first section 31; a pair of third sections 33 that sandwich the first section 31 and the second section 32 from both sides in the axial direction X; and a pair of end sections 34 located at both end portions thereof in the axial direction X. The rotor shaft 3 is a rigid body that is a single object. The rotor shaft 3 is seamless.

[0016] The first section 31 of the rotor shaft 3 has a first shaft diameter D1 smaller than an impeller bore diameter d1 of each impeller 4. The second section 32 of the rotor shaft 3 has a second shaft diameter D2 larger than the first shaft diameter D1 and the impeller bore diameter d1 of the impeller 4. By the difference between the shaft diameters, the stepped surface 36 facing in the axial direction X exists at a boundary between the second section 32 and the first section 31. A fourth shaft diameter D4 of each end section 34 of the rotor shaft 3 is smaller than the first shaft diameter D1. A third shaft diameter D3 of each third section 33 of the rotor shaft 3 is larger than the fourth shaft diameter D4 of the end section 34 and is smaller than the impeller bore diameter d1 of the impeller 4. The third shaft diameter D3 of the third section 33 may be larger than the first shaft diameter D1 as long as the third shaft diameter D3 of the third section 33 is smaller than the impeller bore diameter d1 of the impeller 4. As above, according to the rotor shaft 3, the impeller 4 can be moved from the end section 34 through the third section 33 to the first section 31.

[0017] The first section 31 of the rotor shaft 3 is in the impeller stack 40. Each impeller 4 has a known structure, and for example, includes: an impeller hub in which the rotor shaft 3 is located; a disc whose center corresponds to the impeller hub; blades located on the disc; and a shroud attached to tips of the blades. The impeller 4 includes a passage which is defined by the disc, the blades, and the shroud and through which the fluid to be compressed flows. The impeller 4 is of a closed type but may be of an open type which does not include the shroud. Both end surfaces of the impeller hub of the impeller 4 in the axial direction X are toothed flanges including circumferential teeth. The impellers 4 located adjacent to each other in the axial direction X are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the impellers 4 can transmit power to each other. The mechanical coupling may be curvic coupling or hearth coupling.

[0018] An increase in a workload given to the fluid by the turbo machine 1 is accompanied by an increase in a peripheral speed of the impeller 4. As the peripheral speed of the impeller 4 increases, a centrifugal stress acting on the impeller 4 increases. To withstand the increase in the centrifugal stress, the impeller 4 is preferably made of an aluminum alloy, and the rotor shaft 3 is preferably made of steel. The specific strength (specific strength = tensile strength / density) of the aluminum alloy is about three to four times the specific strength of the steel. Therefore, the centrifugal stress acting on the impeller 4 made of the aluminum alloy is smaller than the centrifugal stress acting on the impeller 4 made of the steel, and the impeller 4 made of the aluminum alloy has strength that can withstand the increase in the peripheral speed.

[0019] The impeller stack 40 may include at least one balance piston 57. Axial thrust of the multistage rotor 2 that is rotating is autonomously adjusted by the balance piston 57. The impeller stack 40 according to the present embodiment includes the balance piston 57 located at a portion thereof in the axial direction X and has a so-called Back-to-Back arrangement in which the direction of the impeller 4 located at an anti-load side of the balance piston 57 and the direction of the impeller 4 located at a load side of the balance piston 57 are different from each other. However, the arrangement of the impellers 4 of the impeller stack 40 is not limited to this. As shown in FIG. 3, the impeller stack 40 may have a straight arrangement in which the directions of all the impellers 4 lined up are the same as each other. As with the impellers 4, the balance piston 57 is fitted to the rotor shaft 3. Both end surfaces of the balance piston 57 in the axial direction X are toothed flanges including circumferential teeth. The impeller 4 and the balance piston 57 which are located adjacent to each other in the axial direction X are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the impeller 4 and the balance piston 57 can transmit power to each other.

[0020] Referring back to FIG. 2, the impeller 4 located closest to the second section 32 in the impeller stack 40 is called a "leading impeller 4L" for convenience sake. In the present embodiment, the leading impeller 4L is a first-stage impeller 4A that compresses the fluid first among the impellers 4. However, the leading impeller 4L is not limited to the first-stage impeller 4A. The leading impeller 4L is in contact with the stepped surface 36 of the rotor shaft 3. A surface of the leading impeller 4L which faces the stepped surface 36 is a flat surface and has no teeth. The leading impeller 4L and the stepped surface 36 are in surface contact with each other. The leading impeller 4L and the stepped surface 36 are coupled to each other by friction, and power can be transmitted from the rotor shaft 3 to the leading impeller 4L. To give redundancy to the power transmission from the rotor shaft 3 to the leading impeller 4L and perform the alignment between the rotor shaft 3 and the leading impeller 4L, the rotation of the leading impeller 4L relative to the rotor shaft 3 and the movement of the leading impeller 4L in the radial direction relative to the rotor shaft 3 may be restricted by interference fit, spline fitting, or meshing.

[0021] In the present embodiment, the leading impeller 4L is in contact with the stepped surface 36 of the rotor shaft 3. However, at least one cylindrical body may be located between the leading impeller 4L and the stepped surface 36 in the axial direction X. In this case, as in a modified example shown in FIG. 10, a cylindrical body 47 located at the first section 31 of the rotor shaft 3 is located between the leading impeller 4L and the stepped surface 36. Moreover, the stepped surface 36 and the cylindrical body 47 are in contact with each other, and the cylindrical body 47 and the leading impeller 4L are in contact with each other. A surface of the cylindrical body 47 which faces the stepped surface 36 is a flat surface and has no teeth, and the cylindrical body 47 and the stepped surface 36 are in surface contact with each other. The cylindrical body 47 and the stepped surface 36 are coupled to each other by friction, and power can be transmitted from the rotor shaft 3 to the cylindrical body 47. To give redundancy to the power transmission from the rotor shaft 3 to the cylindrical body 47 and perform the alignment between the rotor shaft 3 and the cylindrical body 47, the rotation of the cylindrical body 47 relative to the rotor shaft 3 and the movement of the cylindrical body 47 in the radial direction relative to the rotor shaft 3 may be restricted by interference fit, spline fitting, or meshing. A surface of the cylindrical body 47 which faces the leading impeller 4L and a surface of the leading impeller 4L which faces the cylindrical body 47 are toothed flanges including circumferential teeth. The cylindrical body 47 and the leading impeller 4L are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the cylindrical body 47 and the leading impeller 4L can transmit power to each other.

[0022] Referring back to FIG. 2, the impeller 4 located farthest from the second section 32 in the impeller stack 40 is called a "trailing impeller 4T" for convenience sake. In the present embodiment, the trailing impeller 4T is a fourth-stage impeller and is not a last-stage impeller 4E that compresses the fluid last among the impellers 4. The trailing impeller 4T is in contact with a balance piston 56 fitted to the rotor shaft 3. The balance piston 56 may be fitted to the third section 33 of the rotor shaft 3 or may be fitted to the first section 31 of the rotor shaft 3. The trailing impeller 4T and the balance piston 56 are coupled to each other by the mechanical coupling that is the meshing.

[0023] A lock nut 6 is screwed to the third section 33 of the rotor shaft 3. The lock nut 6 is in contact with the balance piston 56. The impeller stack 40 and the balance piston 56 are located between the stepped surface 36 of the rotor shaft 3 and the lock nut 6 in the axial direction X. The impeller stack 40 and the balance piston 56 are sandwiched between the stepped surface 36 and the lock nut 6 while being pressurized in the axial direction by the axial force of the rotor shaft 3. Thus, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are kept in a tight-contact state in the axial direction X. Moreover, the alignment between the rotor shaft 3 and the impeller stack 40 is performed by the lock nut 6 such that the rotor axis A of the rotor shaft 3 and the center axis of the impeller stack 40 coincide with each other.

[0024] As shown FIG. 1, dry gas seals 54 and 55 that seal between the casing 12 and the rotor shaft 3 are located around the respective third sections 33 of the rotor shaft 3. The dry gas seals 54 and 55 prevent an operating fluid, which has been compressed by the multistage rotor 2 to have high pressure, from leaking to the outside. A seal gas is supplied from the outside to the dry gas seals 54 and 55. The end sections 34 of the rotor shaft 3 are rotatably supported by the casing 12 through journal bearings 51 and 52. Moreover, the end section 34 of the rotor shaft 3 is supported by the casing 12 through a thrust bearing 53.

[0025] Bearing coverings made of white metal are on bearing surfaces of the journal bearings 51 and 52 that support the end sections 34 of the rotor shaft 3. When the peripheral speed of the impeller 4 increases, a sliding speed between the end section 34 of the rotor shaft 3 and the journal bearing 52 increases, and this increases the temperatures of the journal bearings 51 and 52. The bearing covering has an allowable temperature. The fourth shaft diameter D4 of the end section 34 of the rotor shaft 3 needs to be designed such that the temperatures of the journal bearings 51 and 52 fall within a range of the allowable temperature. In the turbo machine 1, when the peripheral speed of the impeller 4 is determined, the workload at the stage of this impeller 4 is determined. The peripheral speed of the impeller 4 is obtained by a product of the diameter of the impeller 4 and the rotational speed (rotational frequency) of the impeller 4. An impeller hub diameter d2 (see FIG. 2) is designed based on a structural strength validity with respect to the peripheral speed of the impeller 4. Moreover, the fourth shaft diameter D4 of the end section 34 of the rotor shaft 3 is designed based on the rotational speed of the impeller 4. A ratio (= impeller hub diameter d2 / fourth shaft diameter D4) of the impeller hub diameter d2 to the fourth shaft diameter D4 in the multistage rotor 2 is preferably 2.0 or more and 2.8 or less, further preferably 2.2 or more and 2.6 or less. The multistage rotor 2 has such ratio of the impeller hub diameter d2 to the fourth shaft diameter D4. Therefore, even when the peripheral speed of the impeller 4 increases to such a degree that the workload that compresses a gas (for example, hydrogen) which is light in molecular weight and large in gas constant is obtained, the temperatures of the journal bearings 51 and 52 can be suppressed to the allowable temperature or less.

[0026] FIG. 1 shows part of the casing 12. The casing 12 includes connection passages 21 each of which connects the adjacent impellers 4. The connection passage 21 is connected to passages of the impellers 4. The fluid compressed by the impeller 4 at a certain stage is discharged to the connection passage 21 and then flows through this connection passage 21 into the passage of the impeller 4 at the next stage. The casing 12 includes: an inlet port 22 through which the fluid to be compressed is introduced to the impeller 4 at a first stage; and an outlet port 23 through which the fluid compressed by the impeller 4 at a last stage is sent to the outside. Moreover, the casing 12 includes: an intermediate outlet port 27 through which the fluid compressed at an intermediate stage is once taken out to the outside; and an intermediate inlet port 28 through which the fluid returns to the inside. As above, the turbo machine 1 according to the present embodiment includes a compression passage W which is defined by the casing 12 and the impellers 4 and in which: the fluid sucked through the inlet port 22 is stepwisely compressed by the impellers 4; the fluid is once taken out to the outside through the intermediate outlet port 27; the fluid returns to the inside through the intermediate inlet port 28; the fluid is further stepwisely compressed through the impellers 4; and the fluid is discharged to the outside through the outlet port 23. The fluid passages of the turbo machine 1 and the number of impellers 4 are merely examples.

[0027] There is a minute gap between an inner peripheral surface of each impeller 4 and an outer peripheral surface of the rotor shaft 3, and an internal passage 7 is defined by this gap. FIG. 4 is a sectional view of the multistage rotor 2 which explains the internal passage 7. As shown in FIG. 4 and FIG. 5 described below, the flow of the fluid flowing through a connection passage 74, the internal passage 7, and a connection passage 73 is shown by a two-dot chain line, and the flow of the fluid flowing through the compression passage W from the inlet port 22 to the outlet port 23 is shown by a dotted line. As shown in FIG. 4, the internal passage 7 through which the fluid flows in the axial direction X is located between the impeller stack 40 and the rotor shaft 3. The internal passage 7 is connected to an extraction position E of the compression passage W by the connection passage 74. Moreover, the internal passage 7 is connected to a return position R of the compression passage W by the connection passage 73. The return position R is located upstream of the extraction position E. Part of the fluid flowing through the extraction position E of the compression passage W is introduced to the internal passage 7 through the connection passage 74, flows through the internal passage 7 in the axial direction, and returns to the return position R of the compression passage W through the connection passage 73. As above, part of the fluid circulates in the compression passage W and the internal passage 7. Therefore, pressure in the radial gap between the rotor shaft 3 and the impeller stack 40 is stabilized, and impurities are prevented from being accumulated in this gap. Moreover, the temperature difference between the impeller stack 40 and the rotor shaft 3 is reduced. A thermal barrier coating is on the inner peripheral surface of the impeller 4 to suppress heat transfer to the internal passage 7 from the fluid flowing through the internal passage 7. The outer peripheral surface of the rotor shaft 3 which is exposed to the internal passage 7 may include a fin that increases a heat transfer area.

[0028] In the present embodiment, the extraction position E of the compression passage W is located in the vicinity of an inlet of the trailing impeller 4T. The connection passage 74 penetrates the balance piston 56 in the radial direction, extends through the rotor shaft 3, and reaches the internal passage 7. However, the connection passage 74 may extend through a gap between meshing surfaces of the mechanical coupling between the trailing impeller 4T and the balance piston 56.

[0029] In the present embodiment, the return position R of the compression passage W is located in the vicinity of an inlet of the leading impeller 4L that is the first-stage impeller 4A. The connection passage 73 extends from the internal passage 7 through the inside of the rotor shaft 3 and reaches the compression passage W. Specifically, a passage that connects the internal passage 7 and the return position R of the compression passage W is located inside the second section 32 of the rotor shaft 3 which is in contact with the leading impeller 4L, and this passage is utilized as the connection passage 73. As above, since the connection passage 73 extends through the inside of the rotor shaft 3, the degree of freedom of the position of the return position R that is an outlet of the connection passage 73 improves, and the return position R can be located at a position away from and upstream of the inlet of the leading impeller 4L. When the return position R is located away from and upstream of the inlet of the first-stage impeller 4A, influence of the returned fluid on the main flow of the compression passage W can be suppressed.

[0030] As shown in FIG. 5, the connection passage 73 may extend between the rotor shaft 3 and the first-stage impeller 4A. The planar stepped surface 36 of the rotor shaft 3 and a planar contact surface 48 of the leading impeller 4L are in contact with each other in the axial direction X. At least one of the stepped surface 36 or the contact surface 48 includes a groove, and this groove is utilized as part of the connection passage 73. A groove located on at least one of the outer peripheral surface of the rotor shaft 3 or the inner peripheral surface of the leading impeller 4L may be utilized as the connection passage 73, or a radial gap between the outer peripheral surface of the rotor shaft 3 and the inner peripheral surface of the leading impeller 4L may be utilized as the connection passage 73.

[0031] Moreover, the return position R of the compression passage W may be located downstream of the inlet of the first-stage impeller 4A. In this case, the connection passage 73 extends through a gap between meshing surfaces of the mechanical coupling between the first-stage impeller 4A and the impeller 4 located adjacent to the first-stage impeller 4A.

[0032] The following will describe a method of assembling the impellers 4 to the rotor shaft 3 in the multistage rotor 2 configured as above.

[0033] First, the impellers 4 are fitted to the rotor shaft 3 through a load-side end portion of the rotor shaft 3 in order from the leading impeller 4L to the trailing impeller 4T. In the present embodiment, the second section 32 of the rotor shaft 3 is located at an anti-load side of a middle of the rotor shaft 3 in the axial direction X, and the impellers 4, the balance pistons 56 and 57, and the lock nut 6 are inserted from the load-side end portion of the rotor shaft 3 toward the stepped surface 36. However, these components may be inserted from an anti-load-side end portion of the rotor shaft 3 in accordance with the arrangement of the second section 32.

[0034] The leading impeller 4L is brought into contact with the stepped surface 36 of the rotor shaft 3. The alignment between the rotor shaft 3 and the leading impeller 4L may be performed in such a manner that the leading impeller 4L is fitted to the first section 31 of the rotor shaft 3 by interference fit. Moreover, the balance piston 57 is located between the impellers 4. As with the impellers 4, the balance piston 57 is externally fitted to the rotor shaft 3.

[0035] Next, the rotor shaft 3 is cooled, and as shown in an upper diagram in FIG. 6, the balance piston 56 is fitted to the rotor shaft 3 which has contracted by the cooling. An inner peripheral surface of the balance piston 56 and the outer peripheral surface of the rotor shaft 3 which has contracted by the cooling are located away from each other in the radial direction. Next, as shown in a middle diagram in FIG. 6, axial force in a pulling direction is applied to the rotor shaft 3 by a tensioner, and the lock nut 6 is fitted to the rotor shaft 3 which has contracted by the cooling. As shown in a lower diagram in FIG. 6, when the application of the axial force in the pulling direction is stopped, and the temperature of the rotor shaft 3 returns to a normal temperature, the rotor shaft 3 contracts in the axial direction X and expands in the radial direction. By the axial force in a compression direction of the rotor shaft 3, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X. Moreover, since the rotor shaft 3 expands in the radial direction, the balance piston 56 tightly contacts the rotor shaft 3 while generating fastening force with respect to the rotor shaft 3, and thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed. To be specific, the balance piston 56 is fitted to the rotor shaft 3 by interference fit. The alignment of the impellers 4 and the balance pistons 56 and 57 is performed by the mechanical coupling. Therefore, the alignment between the rotor shaft 3 and the balance piston 56 is performed, and thus, the alignment between the rotor shaft 3 and the impeller stack 40 is performed. When performing the interference fit of the balance piston 56, the balance piston 56 may be heated instead of cooling the rotor shaft 3.

[0036] As will be described in Modified Examples 1 and 2 below, the alignment between the rotor shaft 3 and the impeller stack 40 can be performed without utilizing the interference fit of the balance piston 56 with respect to the rotor shaft 3.

[0037] In Modified Example 1 shown in FIG. 7, the lock nut 6 includes a head portion 61 having a truncated conical shape whose center corresponds to a center axis of the lock nut 6. An inner diameter of the balance piston 56 is larger an outer diameter of the rotor shaft 3, and an end surface of the balance piston 56 in the axial direction X includes a tapered recess 561 to which the head portion 61 of the lock nut 6 is fitted and whose center corresponds to the center axis of the balance piston 56. Then, the balance piston 56 is loosely fitted to the rotor shaft 3, and then, the lock nut 6 is screwed to the rotor shaft 3. The lock nut 6 is screwed in a state where the head portion 61 of the lock nut 6 is fitted into the recess 561 of the balance piston 56. As above, part of the lock nut 6 is located between the balance piston 56 and the rotor shaft 3 in the radial direction, and the balance piston 56 is pushed outward in the radial direction by the lock nut 6. Thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed, i.e., the alignment between the rotor shaft 3 and the impeller stack 40 is performed. Moreover, the balance piston 56 is pushed in the axial direction X by the lock nut 6. Thus, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X.

[0038] In Modified Example 2 shown in FIG. 8, the inner diameter of the balance piston 56 is larger than the outer diameter of the rotor shaft 3, and the balance piston 56 is loosely fitted to the rotor shaft 3. The end surface of the balance piston 56 in the axial direction X includes a recess 561 having a cylindrical shape whose center corresponds to the center axis of the balance piston 56. Then, the balance piston 56 is loosely fitted to the rotor shaft 3, and then, a compression ring 59 that is an elastic body is fitted into the recess 562 of the balance piston 56. Next, the lock nut 6 is screwed to the rotor shaft 3. Since the lock nut 6 pushes the compression ring 59, the compression ring 59 is compressed in the axial direction X and expands in the radial direction. An inner periphery of the compression ring 59 which has been elastically deformed as above is brought into contact with the rotor shaft 3, and an outer periphery of the compression ring 59 is brought into contact with an inner wall of the recess 562 of the balance piston 56. Since the compression ring 59 stretches between the rotor shaft 3 and the balance piston 56, the balance piston 56 is pushed outward in the radial direction. Thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed, i.e., the alignment between the rotor shaft 3 and the impeller stack 40 is performed. Moreover, since the compression ring 59 is compressed in the axial direction X, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X.Conclusion

[0039] The multistage rotor 2 according to a first aspect of the present disclosure includes: the rotor shaft 3 that is a single object and includes the stepped surface 36; the impellers 4 fitted to the rotor shaft 3 and lined up in the axial direction X of the rotor shaft 3 from the stepped surface 36; and the lock nut 6 fitted to the rotor shaft 3, wherein the impellers 4 are sandwiched between the stepped surface 36 and the lock nut 6.

[0040] In the multistage rotor 2 configured as above, the impellers 4 are supported by the rotor shaft 3 that is directly supported by the bearings 51, 52, and 53. The rotor shaft 3 is a single object and is not a combination of a tie bolt and a stub shaft. Therefore, the imbalance caused due to the misalignment between the conventional rotor shaft and the conventional tie bolt never occurs. Moreover, in the multistage rotor 2 configured as above, as compared to the case of using the combination of the tie bolt and the stub shaft, the shaft diameters of portions of the rotor shaft 3 which are supported by the bearings 51, 52, and 53 and at which the dry gas seals 54 and 55 are located can be reduced. This can contribute to size reductions of the bearings 51, 52, and 53 and the dry gas seals 54 and 55.

[0041] The multistage rotor 2 configured as above is suitably applied to a centrifugal compressor that is directed to a gas, such as hydrogen, which is low in molecular weight (MW) and requires a high compression ratio. To increase the compression rate of the centrifugal compressor, it is effective to increase the number of impellers 4 and the peripheral speed of the multistage rotor 2. When the number of impellers 4 increases, the entire length of the rotor shaft 3 increases. Therefore, it is preferable that to suppress wobbles caused by the rotation, the shaft diameter be large. According to the conventional tie bolt system, since a stepped surface between the stub shaft and the tie bolt is utilized to hold the impeller, the shaft diameter of the tie bolt is smaller than the shaft diameter of the stub shaft. On the other hand, in the multistage rotor 2 according to the present disclosure, the shaft diameter of a portion (i.e., the first section 31) of the rotor shaft 3 which supports the impeller 4 can be made larger than the shaft diameter of the conventional tie bolt. Therefore, in the multistage rotor 2 of the present disclosure, even when the entire length of the rotor shaft 3 is increased in accordance with the increase in the number of impellers 4, dynamic strength of the rotor shaft 3 with respect to the wobbles and the like can be improved by increasing the shaft diameter of the portion supporting the impeller 4. Since the dynamic strength of the rotor shaft 3 is improved, the peripheral speed of the multistage rotor 2 can be increased.

[0042] The multistage rotor 2 according to a second aspect is configured such that in the multistage rotor 2 according to the first aspect, the impellers 4 are sandwiched between the stepped surface 36 and the lock nut 6 while being pressurized by the axial force of the rotor shaft 3.

[0043] The multistage rotor 2 according to a third aspect is configured such that: in the multistage rotor 2 according to the first or second aspect, the rotor shaft 3 includes a pair of end sections 34 located at both end portions of the rotor shaft 3 in the axial direction X and supported by the bearings 51, 52, and 53, the first section 31 located between the pair of end sections 34 in the axial direction X and having the first shaft diameter, and the second section 32 located between the pair of end sections 34 in the axial direction X and having the second shaft diameter larger than the first shaft diameter; the stepped surface 36 is located between the first section 31 and the second section 32; and the impellers 4 are fitted to the first section 31 of the rotor shaft 3.

[0044] In the multistage rotor 2 configured as above, the second section 32 of the rotor shaft 3 can be located at any position between the pair of end sections 34, and the second section 32 can be located at a suitable position in accordance with the configuration of the impeller stack 40.

[0045] For example, as shown in FIG. 9, the second section 32 may be located at a substantially middle portion of the rotor shaft 3 in the axial direction X, and the impellers 4 may be located at both sides of the second section 32, i.e., the anti-load side and the load side. In this case, the impellers 4, the balance piston 56, and the lock nut 6 are fitted to the rotor shaft 3 through the anti-load-side end portion of the rotor shaft 3 in order, and the impellers 4 and the balance piston 56 are sandwiched between the lock nut 6 and the stepped surface 36 facing the anti-load side of the multistage rotor 2. Similarly, the impellers 4, the balance piston 56, and the lock nut 6 are fitted to the rotor shaft 3 through the load-side end portion of the rotor shaft 3 in order, and the impellers 4 and the balance piston 56 are sandwiched between the lock nut 6 and the stepped surface 36 facing the load side of the multistage rotor 2.

[0046] The multistage rotor 2 according to a fourth aspect is configured such that: in the multistage rotor 2 according to any one of the first to third aspects, among the impellers 4, the impellers 4 adjacent to each other in the axial direction X are concentrically coupled to each other by meshing; and among the impellers 4, the first impeller (in the above embodiment, the leading impeller 4L) that is in contact with the stepped surface 36 is coupled to the stepped surface 36 by friction.

[0047] As above, the rotor shaft 3 and the impeller stack 40 including the impellers 4 are coupled to each other so as to be able to transmit power to each other.

[0048] The multistage rotor 2 according to a fifth aspect is configured such that: in the multistage rotor 2 according to the fourth aspect, the inner peripheral surface of the first impeller (in the above embodiment, the leading impeller 4L) and the outer peripheral surface of the rotor shaft 3 are in pressure contact with each other; and thus, the first impeller 4L and the rotor shaft 3 are concentrically located.

[0049] As above, the alignment between the leading impeller 4L and the rotor shaft 3 is performed such that the center axis of the leading impeller 4L and the rotor axis A of the rotor shaft 3 coincide with each other. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0050] The multistage rotor 2 according to a sixth aspect is configured such that: in the multistage rotor 2 according to any one of the first to third aspects, among the impellers 4, the impellers 4 adjacent to each other in the axial direction X are concentrically coupled to each other by meshing; the cylindrical body 47 is located between the stepped surface 36 and the first impeller 4 located closest to the stepped surface 36 among the impellers 4; the stepped surface 36 and the cylindrical body 47 are coupled to each other by friction; and the cylindrical body 47 and the first impeller 4 are concentrically coupled to each other by meshing.

[0051] As above, the rotor shaft 3 and the impeller stack 40 including the impellers 4 are coupled to each other so as to be able to transmit power to each other.

[0052] The multistage rotor 2 according to a seventh aspect is configured such that: the multistage rotor 2 according to any one of the first to sixth aspects further includes the balance piston 56 located between the impellers 4 and the lock nut 6 in the axial direction X and fitted to the rotor shaft 3; and among the impellers 4, the second impeller (in the above embodiment, the trailing impeller 4T) that is in contact with the balance piston 56 is concentrically coupled to the balance piston 56 by meshing.

[0053] As above, since the balance piston 56 is located between the trailing impeller 4T and the lock nut 6, the balance piston 56 can be utilized for the alignment between the rotor shaft 3 and the impellers 4.

[0054] The multistage rotor 2 according to an eighth aspect is configured such that: in the multistage rotor 2 according to the seventh aspect, the inner peripheral surface of the balance piston 56 and the outer peripheral surface of the rotor shaft 3 are in pressure contact with each other; and thus, the balance piston 56 and the rotor shaft 3 are concentrically located.

[0055] As above, the alignment between the impeller stack 40 and the rotor shaft 3 is performed by the alignment between the balance piston 56 and the rotor shaft 3. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0056] The multistage rotor 2 according to a ninth aspect is configured such that: in the multistage rotor 2 according to the seventh aspect, the balance piston 56 is loosely fitted to the rotor shaft 3; the balance piston 56 is pushed outward in the radial direction by the lock nut 6 or the elastic body (in the above embodiment, the compression ring 59) which is located between the balance piston 56 and the rotor shaft 3 in the radial direction; and thus, the balance piston 56 and the rotor shaft 3 are concentrically located.

[0057] As above, the alignment between the impeller stack 40 and the rotor shaft 3 is performed by the alignment between the balance piston 56 and the rotor shaft 3. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0058] The multistage rotor 2 according to a tenth aspect of the present disclosure is configured such that: in the multistage rotor 2 according to any one of the first to ninth aspects, the rotor shaft 3 includes steel; and the impellers 4 include aluminum.

[0059] As above, the impellers 4 are made of aluminum that is higher in specific strength than steel. Thus, as compared to when the impellers 4 are made of steel, the centrifugal stress acting on the impellers 4 can be reduced.

[0060] The multistage rotor 2 according to an eleventh aspect of the present disclosure is configured such that: in the multistage rotor 2 according to any one of the first to tenth aspects, a ratio (= impeller hub diameter d2 / shaft diameter D4) of the impeller hub diameter d2 of the impellers 4 to the shaft diameter D4 of the pair of end sections 34 of the rotor shaft 3 is 2.0 or more and 2.8 or less.

[0061] According to the multistage rotor 2, even when the peripheral speed of the impeller 4 increases to such a degree that the workload that compresses a gas (for example, hydrogen) which is light in molecular weight and large in gas constant is obtained, the temperatures of the journal bearings 51 and 52 can be suppressed to the allowable temperature or less.

[0062] The turbo machine 1 according to a twelfth aspect of the present disclosure includes: the casing 12; and the multistage rotor 2 according to any one of the first to eleventh aspects, which is supported by the casing 12.

[0063] The multistage rotor 2 configured as above is preferable as the rotor of the turbo machine 1, especially the rotor of the centrifugal compressor.

[0064] The turbo machine 1 according to a thirteenth aspect of the present disclosure is configured such that the turbo machine 1 according to the twelfth aspect further includes the compression passage W through which the fluid to be compressed flows from the inlet port 22 to the outlet port 23 through the impellers 4 of the multistage rotor 2 in order, and the internal passage 7 extending in the axial direction X and located between the impellers 4 of the multistage rotor 2 and the rotor shaft 3 of the multistage rotor 2 in the radial direction, wherein the compression passage W and the internal passage 7 are in connection with each other by the connection passages 73 and 74 extending through the rotor shaft 3.

[0065] As above, the connection passages 73 and 74 are formed by utilizing the rotor shaft 3. Therefore, machine work that forms the connection passages 73 and 74 is easy, and bending stiffness of a portion of the rotor shaft 3 which supports the impeller stack 40 is not influenced by the connection passages 73 and 74. Moreover, since the connection passage 73 extends through the rotor shaft 3, a position to which the fluid returns from the internal passage 7 can be located further upstream of the inlet of the first-stage impeller 4A, and influence of the fluid, which has returned to the compression passage W, on the main flow of the compression passage W can be suppressed.

[0066] The turbo machine 1 according to a fourteenth aspect of the present disclosure is configured such that in the turbo machine 1 according to the thirteenth aspect, the connection passage 73 connects the internal passage 7 and a position of the compression passage W which is located upstream of the inlet of the impeller 4 through which the fluid flows first among the impellers 4.

[0067] As above, since the connection passage 73 extends through the rotor shaft 3, the configuration in which the fluid returns from the internal passage 7 to the position of the compression passage W which is located away from and upstream of the inlet of the first-stage impeller 4A can be easily realized. Then, since the fluid returns to the position of the compression passage W which is located away from and upstream of the inlet of the first-stage impeller 4A, influence of the fluid, which has returned to the compression passage W, on the main flow of the compression passage W can be suppressed.

[0068] The turbo machine 1 according to a fifteenth aspect of the present disclosure is configured such that: the turbo machine 1 according to the twelfth aspect (except for the turbo machine 1 including the multistage rotor 2 according to the sixth aspect) includes the compression passage W through which the fluid to be compressed flows from the inlet port 22 to the outlet port 23 through the impellers 4 of the multistage rotor 2 in order, and the internal passage 7 extending in the axial direction X and located between the impellers 4 of the multistage rotor 2 and the rotor shaft 3 of the multistage rotor 2 in the radial direction; the stepped surface 36 of the rotor shaft 3 of the multistage rotor 2 and the planar contact surface 48 of the first impeller 4L among the impellers 4 are in contact with each other in the axial direction X; and the connection passage 21 that connects the compression passage W and the internal passage 7 extends through the groove located on at least one of the stepped surface 36 or the contact surface 48.

[0069] The method of manufacturing the multistage rotor 2 according to a sixteenth aspect of the present disclosure includes: fitting the impellers 4 to the rotor shaft 3 that is a single object and includes the stepped surface 36; and fitting the lock nut 6 to the rotor shaft 3 to sandwich the impellers 4 between the stepped surface 36 and the lock nut 6 in a state where the impellers 4 are pressurized by the axial force of the rotor shaft 3.

[0070] The above method of manufacturing the multistage rotor 2 can manufacture the multistage rotor 2 according to the first aspect.

[0071] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description. The foregoing is not intended to limit the present disclosure to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the present disclosure are grouped together in one embodiment for the purpose of streamlining the disclosure. However, some of the features may be combined with each other. The features of the present disclosure may be combined in alternate embodiments, configurations, or aspects other than those discussed above.

Examples

Embodiment Construction

[0012]FIG. 1 is a schematic sectional view of a turbo machine 1 according to one aspect of the present disclosure. FIG. 1 shows an upper half of the turbo machine 1 which is located at an upper side of a rotor axis A. As one aspect of the turbo machine 1, FIG. 1 shows a centrifugal compressor including a multistage rotor 2. The multistage rotor 2 is a rotor that stepwisely compresses fluid by impellers 4. Moreover, the centrifugal compressor is a compressor which: allows the fluid to flow therethrough, the fluid being to be compressed in a radial direction of the impeller 4 that rotates; and compresses the fluid by centrifugal force generated at that moment. The multistage rotor 2 of the present disclosure is not limited to the centrifugal compressor and is widely applicable to the turbo machine 1.

[0013]The turbo machine 1 includes: a casing 12; the multistage rotor 2 accommodated in the casing 12; and a driver that rotates the multistage rotor 2.

[0014]FIG. 2 is a schematic sectiona...

Technical Field

[0001] The present disclosure relates to a multistage rotor of a turbo machine, such as a compressor.Background Art

[0002] A turbo machine continuously performs energy conversion between fluid energy and mechanical energy through an impeller that rotates. The turbo machine may include a multistage rotor including impellers. PTL 1 discloses this type of turbo machine.

[0003] The turbo machine of PTL 1 is a centrifugal compressor and includes a multistage rotor including: a tie bolt; short rotor shafts (i.e., stub shafts) respectively assembled to both ends of the tie bolt; and impellers supported by the tie bolt and lined up in an axial direction. The adjacent impellers are connected to each other by mechanical coupling and are fastened to each other by axial force of the tie bolt.Citation List Patent Literature

[0004] PTL 1: International Publication WO2021 / 230869Summary of Invention Technical Problem

[0005] According to the multistage rotor of PTL 1, since the tie bolt is assembled to a pair of rotor shafts, misalignment between each rotor shaft and the tie bolt may occur. The imbalance of the multistage rotor due to such misalignment is difficult to be removed by a balancing step. Moreover, an increase in a compression rate of the rotor can be realized by an increase in a rotor axial length by an increase in the number of stages and an increase in a rotation peripheral speed of the rotor. However, this increases a risk of the interference of an natural frequency of the tie bolt with an operation rotational frequency. To detune the natural frequency of the tie bolt from the operation rotational frequency, the tie bolt tends to increase in diameter. When the tie bolt increases in diameter, influence of the misalignment between each rotor shaft and the tie bolt on the imbalance of the multistage rotor increases.

[0006] The present disclosure was made under these circumstances, and an object of the present disclosure is to provide a multistage rotor that prevents imbalance caused due to misalignment between a rotor shaft and a tie bolt, and a turbo machine including this multistage rotor.Solution to Problem

[0007] In order to solve the above problems, a multistage rotor according to one aspect of the present disclosure includes: a rotor shaft that is a single object and includes a stepped surface; impellers fitted to the rotor shaft and lined up in an axial direction of the rotor shaft from the stepped surface; and a lock nut fitted to the rotor shaft, wherein the impellers are sandwiched between the stepped surface and the lock nut while being pressurized by axial force of the rotor shaft.

[0008] A turbo machine according to one aspect of the present disclosure includes: a casing; and the multistage rotor supported by the casing.

[0009] A method of manufacturing a multistage rotor according to one aspect of the present disclosure includes: fitting impellers to a rotor shaft that is a single object and includes a stepped surface; and fitting a lock nut to the rotor shaft to sandwich the impellers between the stepped surface and the lock nut in a state where the impellers are pressurized by axial force of the rotor shaft. Advantageous Effects of Invention

[0010] The present disclosure can provide the multistage rotor that prevents the imbalance caused due to the misalignment between the tie bolt and the rotor shaft, and the turbo machine including this multistage rotor.Brief Description of Drawings

[0011] FIG. 1 is a schematic sectional view of a turbo machine according to one aspect of the present disclosure. FIG. 2 is a schematic sectional view of a multistage rotor. FIG. 3 is a schematic sectional view of the multistage rotor having a straight arrangement. FIG. 4 is a sectional view of the multistage rotor which explains an internal passage. FIG. 5 is a sectional view of the multistage rotor which explains a modified example of the internal passage. FIG. 6 is a diagram which explains a method of manufacturing the multistage rotor. FIG. 7 is a diagram showing a balance piston and a lock nut according to Modified Example 1. FIG. 8 is a diagram showing the balance piston and the lock nut according to Modified Example 2. FIG. 9 is a schematic sectional view of the multistage rotor in which impellers are located at both sides of a second section. FIG. 10 is a schematic sectional view showing the multistage rotor according to Modified Example. Description of Embodiments

[0012] FIG. 1 is a schematic sectional view of a turbo machine 1 according to one aspect of the present disclosure. FIG. 1 shows an upper half of the turbo machine 1 which is located at an upper side of a rotor axis A. As one aspect of the turbo machine 1, FIG. 1 shows a centrifugal compressor including a multistage rotor 2. The multistage rotor 2 is a rotor that stepwisely compresses fluid by impellers 4. Moreover, the centrifugal compressor is a compressor which: allows the fluid to flow therethrough, the fluid being to be compressed in a radial direction of the impeller 4 that rotates; and compresses the fluid by centrifugal force generated at that moment. The multistage rotor 2 of the present disclosure is not limited to the centrifugal compressor and is widely applicable to the turbo machine 1.

[0013] The turbo machine 1 includes: a casing 12; the multistage rotor 2 accommodated in the casing 12; and a driver that rotates the multistage rotor 2.

[0014] FIG. 2 is a schematic sectional view of the multistage rotor 2. As shown in FIGS. 1 and 2, the multistage rotor 2 is a rotating body whose center corresponds to the rotor axis A. The multistage rotor 2 includes: a rotor shaft 3 whose center corresponds to the rotor axis A and which extends in parallel with an axial direction X; and the impellers 4 located at a substantially middle portion of the rotor shaft 3 in the axial direction X and lined up in the axial direction X. A combination of the impellers 4 stacked on each other in the axial direction X is called an impeller stack 40, and the multistage rotor 2 is also called a stacked rotor.

[0015] The rotor shaft 3 is a stepped shaft including a stepped surface 36. The rotor shaft 3 includes: a first section 31 located at a middle portion thereof in the axial direction X; a second section 32 located next to the first section 31; a pair of third sections 33 that sandwich the first section 31 and the second section 32 from both sides in the axial direction X; and a pair of end sections 34 located at both end portions thereof in the axial direction X. The rotor shaft 3 is a rigid body that is a single object. The rotor shaft 3 is seamless.

[0016] The first section 31 of the rotor shaft 3 has a first shaft diameter D1 smaller than an impeller bore diameter d1 of each impeller 4. The second section 32 of the rotor shaft 3 has a second shaft diameter D2 larger than the first shaft diameter D1 and the impeller bore diameter d1 of the impeller 4. By the difference between the shaft diameters, the stepped surface 36 facing in the axial direction X exists at a boundary between the second section 32 and the first section 31. A fourth shaft diameter D4 of each end section 34 of the rotor shaft 3 is smaller than the first shaft diameter D1. A third shaft diameter D3 of each third section 33 of the rotor shaft 3 is larger than the fourth shaft diameter D4 of the end section 34 and is smaller than the impeller bore diameter d1 of the impeller 4. The third shaft diameter D3 of the third section 33 may be larger than the first shaft diameter D1 as long as the third shaft diameter D3 of the third section 33 is smaller than the impeller bore diameter d1 of the impeller 4. As above, according to the rotor shaft 3, the impeller 4 can be moved from the end section 34 through the third section 33 to the first section 31.

[0017] The first section 31 of the rotor shaft 3 is in the impeller stack 40. Each impeller 4 has a known structure, and for example, includes: an impeller hub in which the rotor shaft 3 is located; a disc whose center corresponds to the impeller hub; blades located on the disc; and a shroud attached to tips of the blades. The impeller 4 includes a passage which is defined by the disc, the blades, and the shroud and through which the fluid to be compressed flows. The impeller 4 is of a closed type but may be of an open type which does not include the shroud. Both end surfaces of the impeller hub of the impeller 4 in the axial direction X are toothed flanges including circumferential teeth. The impellers 4 located adjacent to each other in the axial direction X are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the impellers 4 can transmit power to each other. The mechanical coupling may be curvic coupling or hearth coupling.

[0018] An increase in a workload given to the fluid by the turbo machine 1 is accompanied by an increase in a peripheral speed of the impeller 4. As the peripheral speed of the impeller 4 increases, a centrifugal stress acting on the impeller 4 increases. To withstand the increase in the centrifugal stress, the impeller 4 is preferably made of an aluminum alloy, and the rotor shaft 3 is preferably made of steel. The specific strength (specific strength = tensile strength / density) of the aluminum alloy is about three to four times the specific strength of the steel. Therefore, the centrifugal stress acting on the impeller 4 made of the aluminum alloy is smaller than the centrifugal stress acting on the impeller 4 made of the steel, and the impeller 4 made of the aluminum alloy has strength that can withstand the increase in the peripheral speed.

[0019] The impeller stack 40 may include at least one balance piston 57. Axial thrust of the multistage rotor 2 that is rotating is autonomously adjusted by the balance piston 57. The impeller stack 40 according to the present embodiment includes the balance piston 57 located at a portion thereof in the axial direction X and has a so-called Back-to-Back arrangement in which the direction of the impeller 4 located at an anti-load side of the balance piston 57 and the direction of the impeller 4 located at a load side of the balance piston 57 are different from each other. However, the arrangement of the impellers 4 of the impeller stack 40 is not limited to this. As shown in FIG. 3, the impeller stack 40 may have a straight arrangement in which the directions of all the impellers 4 lined up are the same as each other. As with the impellers 4, the balance piston 57 is fitted to the rotor shaft 3. Both end surfaces of the balance piston 57 in the axial direction X are toothed flanges including circumferential teeth. The impeller 4 and the balance piston 57 which are located adjacent to each other in the axial direction X are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the impeller 4 and the balance piston 57 can transmit power to each other.

[0020] Referring back to FIG. 2, the impeller 4 located closest to the second section 32 in the impeller stack 40 is called a "leading impeller 4L" for convenience sake. In the present embodiment, the leading impeller 4L is a first-stage impeller 4A that compresses the fluid first among the impellers 4. However, the leading impeller 4L is not limited to the first-stage impeller 4A. The leading impeller 4L is in contact with the stepped surface 36 of the rotor shaft 3. A surface of the leading impeller 4L which faces the stepped surface 36 is a flat surface and has no teeth. The leading impeller 4L and the stepped surface 36 are in surface contact with each other. The leading impeller 4L and the stepped surface 36 are coupled to each other by friction, and power can be transmitted from the rotor shaft 3 to the leading impeller 4L. To give redundancy to the power transmission from the rotor shaft 3 to the leading impeller 4L and perform the alignment between the rotor shaft 3 and the leading impeller 4L, the rotation of the leading impeller 4L relative to the rotor shaft 3 and the movement of the leading impeller 4L in the radial direction relative to the rotor shaft 3 may be restricted by interference fit, spline fitting, or meshing.

[0021] In the present embodiment, the leading impeller 4L is in contact with the stepped surface 36 of the rotor shaft 3. However, at least one cylindrical body may be located between the leading impeller 4L and the stepped surface 36 in the axial direction X. In this case, as in a modified example shown in FIG. 10, a cylindrical body 47 located at the first section 31 of the rotor shaft 3 is located between the leading impeller 4L and the stepped surface 36. Moreover, the stepped surface 36 and the cylindrical body 47 are in contact with each other, and the cylindrical body 47 and the leading impeller 4L are in contact with each other. A surface of the cylindrical body 47 which faces the stepped surface 36 is a flat surface and has no teeth, and the cylindrical body 47 and the stepped surface 36 are in surface contact with each other. The cylindrical body 47 and the stepped surface 36 are coupled to each other by friction, and power can be transmitted from the rotor shaft 3 to the cylindrical body 47. To give redundancy to the power transmission from the rotor shaft 3 to the cylindrical body 47 and perform the alignment between the rotor shaft 3 and the cylindrical body 47, the rotation of the cylindrical body 47 relative to the rotor shaft 3 and the movement of the cylindrical body 47 in the radial direction relative to the rotor shaft 3 may be restricted by interference fit, spline fitting, or meshing. A surface of the cylindrical body 47 which faces the leading impeller 4L and a surface of the leading impeller 4L which faces the cylindrical body 47 are toothed flanges including circumferential teeth. The cylindrical body 47 and the leading impeller 4L are coupled to each other by mechanical coupling in which the toothed flanges mesh with each other, and therefore, the cylindrical body 47 and the leading impeller 4L can transmit power to each other.

[0022] Referring back to FIG. 2, the impeller 4 located farthest from the second section 32 in the impeller stack 40 is called a "trailing impeller 4T" for convenience sake. In the present embodiment, the trailing impeller 4T is a fourth-stage impeller and is not a last-stage impeller 4E that compresses the fluid last among the impellers 4. The trailing impeller 4T is in contact with a balance piston 56 fitted to the rotor shaft 3. The balance piston 56 may be fitted to the third section 33 of the rotor shaft 3 or may be fitted to the first section 31 of the rotor shaft 3. The trailing impeller 4T and the balance piston 56 are coupled to each other by the mechanical coupling that is the meshing.

[0023] A lock nut 6 is screwed to the third section 33 of the rotor shaft 3. The lock nut 6 is in contact with the balance piston 56. The impeller stack 40 and the balance piston 56 are located between the stepped surface 36 of the rotor shaft 3 and the lock nut 6 in the axial direction X. The impeller stack 40 and the balance piston 56 are sandwiched between the stepped surface 36 and the lock nut 6 while being pressurized in the axial direction by the axial force of the rotor shaft 3. Thus, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are kept in a tight-contact state in the axial direction X. Moreover, the alignment between the rotor shaft 3 and the impeller stack 40 is performed by the lock nut 6 such that the rotor axis A of the rotor shaft 3 and the center axis of the impeller stack 40 coincide with each other.

[0024] As shown FIG. 1, dry gas seals 54 and 55 that seal between the casing 12 and the rotor shaft 3 are located around the respective third sections 33 of the rotor shaft 3. The dry gas seals 54 and 55 prevent an operating fluid, which has been compressed by the multistage rotor 2 to have high pressure, from leaking to the outside. A seal gas is supplied from the outside to the dry gas seals 54 and 55. The end sections 34 of the rotor shaft 3 are rotatably supported by the casing 12 through journal bearings 51 and 52. Moreover, the end section 34 of the rotor shaft 3 is supported by the casing 12 through a thrust bearing 53.

[0025] Bearing coverings made of white metal are on bearing surfaces of the journal bearings 51 and 52 that support the end sections 34 of the rotor shaft 3. When the peripheral speed of the impeller 4 increases, a sliding speed between the end section 34 of the rotor shaft 3 and the journal bearing 52 increases, and this increases the temperatures of the journal bearings 51 and 52. The bearing covering has an allowable temperature. The fourth shaft diameter D4 of the end section 34 of the rotor shaft 3 needs to be designed such that the temperatures of the journal bearings 51 and 52 fall within a range of the allowable temperature. In the turbo machine 1, when the peripheral speed of the impeller 4 is determined, the workload at the stage of this impeller 4 is determined. The peripheral speed of the impeller 4 is obtained by a product of the diameter of the impeller 4 and the rotational speed (rotational frequency) of the impeller 4. An impeller hub diameter d2 (see FIG. 2) is designed based on a structural strength validity with respect to the peripheral speed of the impeller 4. Moreover, the fourth shaft diameter D4 of the end section 34 of the rotor shaft 3 is designed based on the rotational speed of the impeller 4. A ratio (= impeller hub diameter d2 / fourth shaft diameter D4) of the impeller hub diameter d2 to the fourth shaft diameter D4 in the multistage rotor 2 is preferably 2.0 or more and 2.8 or less, further preferably 2.2 or more and 2.6 or less. The multistage rotor 2 has such ratio of the impeller hub diameter d2 to the fourth shaft diameter D4. Therefore, even when the peripheral speed of the impeller 4 increases to such a degree that the workload that compresses a gas (for example, hydrogen) which is light in molecular weight and large in gas constant is obtained, the temperatures of the journal bearings 51 and 52 can be suppressed to the allowable temperature or less.

[0026] FIG. 1 shows part of the casing 12. The casing 12 includes connection passages 21 each of which connects the adjacent impellers 4. The connection passage 21 is connected to passages of the impellers 4. The fluid compressed by the impeller 4 at a certain stage is discharged to the connection passage 21 and then flows through this connection passage 21 into the passage of the impeller 4 at the next stage. The casing 12 includes: an inlet port 22 through which the fluid to be compressed is introduced to the impeller 4 at a first stage; and an outlet port 23 through which the fluid compressed by the impeller 4 at a last stage is sent to the outside. Moreover, the casing 12 includes: an intermediate outlet port 27 through which the fluid compressed at an intermediate stage is once taken out to the outside; and an intermediate inlet port 28 through which the fluid returns to the inside. As above, the turbo machine 1 according to the present embodiment includes a compression passage W which is defined by the casing 12 and the impellers 4 and in which: the fluid sucked through the inlet port 22 is stepwisely compressed by the impellers 4; the fluid is once taken out to the outside through the intermediate outlet port 27; the fluid returns to the inside through the intermediate inlet port 28; the fluid is further stepwisely compressed through the impellers 4; and the fluid is discharged to the outside through the outlet port 23. The fluid passages of the turbo machine 1 and the number of impellers 4 are merely examples.

[0027] There is a minute gap between an inner peripheral surface of each impeller 4 and an outer peripheral surface of the rotor shaft 3, and an internal passage 7 is defined by this gap. FIG. 4 is a sectional view of the multistage rotor 2 which explains the internal passage 7. As shown in FIG. 4 and FIG. 5 described below, the flow of the fluid flowing through a connection passage 74, the internal passage 7, and a connection passage 73 is shown by a two-dot chain line, and the flow of the fluid flowing through the compression passage W from the inlet port 22 to the outlet port 23 is shown by a dotted line. As shown in FIG. 4, the internal passage 7 through which the fluid flows in the axial direction X is located between the impeller stack 40 and the rotor shaft 3. The internal passage 7 is connected to an extraction position E of the compression passage W by the connection passage 74. Moreover, the internal passage 7 is connected to a return position R of the compression passage W by the connection passage 73. The return position R is located upstream of the extraction position E. Part of the fluid flowing through the extraction position E of the compression passage W is introduced to the internal passage 7 through the connection passage 74, flows through the internal passage 7 in the axial direction, and returns to the return position R of the compression passage W through the connection passage 73. As above, part of the fluid circulates in the compression passage W and the internal passage 7. Therefore, pressure in the radial gap between the rotor shaft 3 and the impeller stack 40 is stabilized, and impurities are prevented from being accumulated in this gap. Moreover, the temperature difference between the impeller stack 40 and the rotor shaft 3 is reduced. A thermal barrier coating is on the inner peripheral surface of the impeller 4 to suppress heat transfer to the internal passage 7 from the fluid flowing through the internal passage 7. The outer peripheral surface of the rotor shaft 3 which is exposed to the internal passage 7 may include a fin that increases a heat transfer area.

[0028] In the present embodiment, the extraction position E of the compression passage W is located in the vicinity of an inlet of the trailing impeller 4T. The connection passage 74 penetrates the balance piston 56 in the radial direction, extends through the rotor shaft 3, and reaches the internal passage 7. However, the connection passage 74 may extend through a gap between meshing surfaces of the mechanical coupling between the trailing impeller 4T and the balance piston 56.

[0029] In the present embodiment, the return position R of the compression passage W is located in the vicinity of an inlet of the leading impeller 4L that is the first-stage impeller 4A. The connection passage 73 extends from the internal passage 7 through the inside of the rotor shaft 3 and reaches the compression passage W. Specifically, a passage that connects the internal passage 7 and the return position R of the compression passage W is located inside the second section 32 of the rotor shaft 3 which is in contact with the leading impeller 4L, and this passage is utilized as the connection passage 73. As above, since the connection passage 73 extends through the inside of the rotor shaft 3, the degree of freedom of the position of the return position R that is an outlet of the connection passage 73 improves, and the return position R can be located at a position away from and upstream of the inlet of the leading impeller 4L. When the return position R is located away from and upstream of the inlet of the first-stage impeller 4A, influence of the returned fluid on the main flow of the compression passage W can be suppressed.

[0030] As shown in FIG. 5, the connection passage 73 may extend between the rotor shaft 3 and the first-stage impeller 4A. The planar stepped surface 36 of the rotor shaft 3 and a planar contact surface 48 of the leading impeller 4L are in contact with each other in the axial direction X. At least one of the stepped surface 36 or the contact surface 48 includes a groove, and this groove is utilized as part of the connection passage 73. A groove located on at least one of the outer peripheral surface of the rotor shaft 3 or the inner peripheral surface of the leading impeller 4L may be utilized as the connection passage 73, or a radial gap between the outer peripheral surface of the rotor shaft 3 and the inner peripheral surface of the leading impeller 4L may be utilized as the connection passage 73.

[0031] Moreover, the return position R of the compression passage W may be located downstream of the inlet of the first-stage impeller 4A. In this case, the connection passage 73 extends through a gap between meshing surfaces of the mechanical coupling between the first-stage impeller 4A and the impeller 4 located adjacent to the first-stage impeller 4A.

[0032] The following will describe a method of assembling the impellers 4 to the rotor shaft 3 in the multistage rotor 2 configured as above.

[0033] First, the impellers 4 are fitted to the rotor shaft 3 through a load-side end portion of the rotor shaft 3 in order from the leading impeller 4L to the trailing impeller 4T. In the present embodiment, the second section 32 of the rotor shaft 3 is located at an anti-load side of a middle of the rotor shaft 3 in the axial direction X, and the impellers 4, the balance pistons 56 and 57, and the lock nut 6 are inserted from the load-side end portion of the rotor shaft 3 toward the stepped surface 36. However, these components may be inserted from an anti-load-side end portion of the rotor shaft 3 in accordance with the arrangement of the second section 32.

[0034] The leading impeller 4L is brought into contact with the stepped surface 36 of the rotor shaft 3. The alignment between the rotor shaft 3 and the leading impeller 4L may be performed in such a manner that the leading impeller 4L is fitted to the first section 31 of the rotor shaft 3 by interference fit. Moreover, the balance piston 57 is located between the impellers 4. As with the impellers 4, the balance piston 57 is externally fitted to the rotor shaft 3.

[0035] Next, the rotor shaft 3 is cooled, and as shown in an upper diagram in FIG. 6, the balance piston 56 is fitted to the rotor shaft 3 which has contracted by the cooling. An inner peripheral surface of the balance piston 56 and the outer peripheral surface of the rotor shaft 3 which has contracted by the cooling are located away from each other in the radial direction. Next, as shown in a middle diagram in FIG. 6, axial force in a pulling direction is applied to the rotor shaft 3 by a tensioner, and the lock nut 6 is fitted to the rotor shaft 3 which has contracted by the cooling. As shown in a lower diagram in FIG. 6, when the application of the axial force in the pulling direction is stopped, and the temperature of the rotor shaft 3 returns to a normal temperature, the rotor shaft 3 contracts in the axial direction X and expands in the radial direction. By the axial force in a compression direction of the rotor shaft 3, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X. Moreover, since the rotor shaft 3 expands in the radial direction, the balance piston 56 tightly contacts the rotor shaft 3 while generating fastening force with respect to the rotor shaft 3, and thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed. To be specific, the balance piston 56 is fitted to the rotor shaft 3 by interference fit. The alignment of the impellers 4 and the balance pistons 56 and 57 is performed by the mechanical coupling. Therefore, the alignment between the rotor shaft 3 and the balance piston 56 is performed, and thus, the alignment between the rotor shaft 3 and the impeller stack 40 is performed. When performing the interference fit of the balance piston 56, the balance piston 56 may be heated instead of cooling the rotor shaft 3.

[0036] As will be described in Modified Examples 1 and 2 below, the alignment between the rotor shaft 3 and the impeller stack 40 can be performed without utilizing the interference fit of the balance piston 56 with respect to the rotor shaft 3.

[0037] In Modified Example 1 shown in FIG. 7, the lock nut 6 includes a head portion 61 having a truncated conical shape whose center corresponds to a center axis of the lock nut 6. An inner diameter of the balance piston 56 is larger an outer diameter of the rotor shaft 3, and an end surface of the balance piston 56 in the axial direction X includes a tapered recess 561 to which the head portion 61 of the lock nut 6 is fitted and whose center corresponds to the center axis of the balance piston 56. Then, the balance piston 56 is loosely fitted to the rotor shaft 3, and then, the lock nut 6 is screwed to the rotor shaft 3. The lock nut 6 is screwed in a state where the head portion 61 of the lock nut 6 is fitted into the recess 561 of the balance piston 56. As above, part of the lock nut 6 is located between the balance piston 56 and the rotor shaft 3 in the radial direction, and the balance piston 56 is pushed outward in the radial direction by the lock nut 6. Thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed, i.e., the alignment between the rotor shaft 3 and the impeller stack 40 is performed. Moreover, the balance piston 56 is pushed in the axial direction X by the lock nut 6. Thus, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X.

[0038] In Modified Example 2 shown in FIG. 8, the inner diameter of the balance piston 56 is larger than the outer diameter of the rotor shaft 3, and the balance piston 56 is loosely fitted to the rotor shaft 3. The end surface of the balance piston 56 in the axial direction X includes a recess 561 having a cylindrical shape whose center corresponds to the center axis of the balance piston 56. Then, the balance piston 56 is loosely fitted to the rotor shaft 3, and then, a compression ring 59 that is an elastic body is fitted into the recess 562 of the balance piston 56. Next, the lock nut 6 is screwed to the rotor shaft 3. Since the lock nut 6 pushes the compression ring 59, the compression ring 59 is compressed in the axial direction X and expands in the radial direction. An inner periphery of the compression ring 59 which has been elastically deformed as above is brought into contact with the rotor shaft 3, and an outer periphery of the compression ring 59 is brought into contact with an inner wall of the recess 562 of the balance piston 56. Since the compression ring 59 stretches between the rotor shaft 3 and the balance piston 56, the balance piston 56 is pushed outward in the radial direction. Thus, the alignment between the rotor shaft 3 and the balance piston 56 is performed, i.e., the alignment between the rotor shaft 3 and the impeller stack 40 is performed. Moreover, since the compression ring 59 is compressed in the axial direction X, the stepped surface 36 and the leading impeller 4L, the impellers 4 adjacent to each other, and the trailing impeller 4T and the balance piston 56 are brought into pressure contact with each other in the axial direction X.Conclusion

[0039] The multistage rotor 2 according to a first aspect of the present disclosure includes: the rotor shaft 3 that is a single object and includes the stepped surface 36; the impellers 4 fitted to the rotor shaft 3 and lined up in the axial direction X of the rotor shaft 3 from the stepped surface 36; and the lock nut 6 fitted to the rotor shaft 3, wherein the impellers 4 are sandwiched between the stepped surface 36 and the lock nut 6.

[0040] In the multistage rotor 2 configured as above, the impellers 4 are supported by the rotor shaft 3 that is directly supported by the bearings 51, 52, and 53. The rotor shaft 3 is a single object and is not a combination of a tie bolt and a stub shaft. Therefore, the imbalance caused due to the misalignment between the conventional rotor shaft and the conventional tie bolt never occurs. Moreover, in the multistage rotor 2 configured as above, as compared to the case of using the combination of the tie bolt and the stub shaft, the shaft diameters of portions of the rotor shaft 3 which are supported by the bearings 51, 52, and 53 and at which the dry gas seals 54 and 55 are located can be reduced. This can contribute to size reductions of the bearings 51, 52, and 53 and the dry gas seals 54 and 55.

[0041] The multistage rotor 2 configured as above is suitably applied to a centrifugal compressor that is directed to a gas, such as hydrogen, which is low in molecular weight (MW) and requires a high compression ratio. To increase the compression rate of the centrifugal compressor, it is effective to increase the number of impellers 4 and the peripheral speed of the multistage rotor 2. When the number of impellers 4 increases, the entire length of the rotor shaft 3 increases. Therefore, it is preferable that to suppress wobbles caused by the rotation, the shaft diameter be large. According to the conventional tie bolt system, since a stepped surface between the stub shaft and the tie bolt is utilized to hold the impeller, the shaft diameter of the tie bolt is smaller than the shaft diameter of the stub shaft. On the other hand, in the multistage rotor 2 according to the present disclosure, the shaft diameter of a portion (i.e., the first section 31) of the rotor shaft 3 which supports the impeller 4 can be made larger than the shaft diameter of the conventional tie bolt. Therefore, in the multistage rotor 2 of the present disclosure, even when the entire length of the rotor shaft 3 is increased in accordance with the increase in the number of impellers 4, dynamic strength of the rotor shaft 3 with respect to the wobbles and the like can be improved by increasing the shaft diameter of the portion supporting the impeller 4. Since the dynamic strength of the rotor shaft 3 is improved, the peripheral speed of the multistage rotor 2 can be increased.

[0042] The multistage rotor 2 according to a second aspect is configured such that in the multistage rotor 2 according to the first aspect, the impellers 4 are sandwiched between the stepped surface 36 and the lock nut 6 while being pressurized by the axial force of the rotor shaft 3.

[0043] The multistage rotor 2 according to a third aspect is configured such that: in the multistage rotor 2 according to the first or second aspect, the rotor shaft 3 includes a pair of end sections 34 located at both end portions of the rotor shaft 3 in the axial direction X and supported by the bearings 51, 52, and 53, the first section 31 located between the pair of end sections 34 in the axial direction X and having the first shaft diameter, and the second section 32 located between the pair of end sections 34 in the axial direction X and having the second shaft diameter larger than the first shaft diameter; the stepped surface 36 is located between the first section 31 and the second section 32; and the impellers 4 are fitted to the first section 31 of the rotor shaft 3.

[0044] In the multistage rotor 2 configured as above, the second section 32 of the rotor shaft 3 can be located at any position between the pair of end sections 34, and the second section 32 can be located at a suitable position in accordance with the configuration of the impeller stack 40.

[0045] For example, as shown in FIG. 9, the second section 32 may be located at a substantially middle portion of the rotor shaft 3 in the axial direction X, and the impellers 4 may be located at both sides of the second section 32, i.e., the anti-load side and the load side. In this case, the impellers 4, the balance piston 56, and the lock nut 6 are fitted to the rotor shaft 3 through the anti-load-side end portion of the rotor shaft 3 in order, and the impellers 4 and the balance piston 56 are sandwiched between the lock nut 6 and the stepped surface 36 facing the anti-load side of the multistage rotor 2. Similarly, the impellers 4, the balance piston 56, and the lock nut 6 are fitted to the rotor shaft 3 through the load-side end portion of the rotor shaft 3 in order, and the impellers 4 and the balance piston 56 are sandwiched between the lock nut 6 and the stepped surface 36 facing the load side of the multistage rotor 2.

[0046] The multistage rotor 2 according to a fourth aspect is configured such that: in the multistage rotor 2 according to any one of the first to third aspects, among the impellers 4, the impellers 4 adjacent to each other in the axial direction X are concentrically coupled to each other by meshing; and among the impellers 4, the first impeller (in the above embodiment, the leading impeller 4L) that is in contact with the stepped surface 36 is coupled to the stepped surface 36 by friction.

[0047] As above, the rotor shaft 3 and the impeller stack 40 including the impellers 4 are coupled to each other so as to be able to transmit power to each other.

[0048] The multistage rotor 2 according to a fifth aspect is configured such that: in the multistage rotor 2 according to the fourth aspect, the inner peripheral surface of the first impeller (in the above embodiment, the leading impeller 4L) and the outer peripheral surface of the rotor shaft 3 are in pressure contact with each other; and thus, the first impeller 4L and the rotor shaft 3 are concentrically located.

[0049] As above, the alignment between the leading impeller 4L and the rotor shaft 3 is performed such that the center axis of the leading impeller 4L and the rotor axis A of the rotor shaft 3 coincide with each other. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0050] The multistage rotor 2 according to a sixth aspect is configured such that: in the multistage rotor 2 according to any one of the first to third aspects, among the impellers 4, the impellers 4 adjacent to each other in the axial direction X are concentrically coupled to each other by meshing; the cylindrical body 47 is located between the stepped surface 36 and the first impeller 4 located closest to the stepped surface 36 among the impellers 4; the stepped surface 36 and the cylindrical body 47 are coupled to each other by friction; and the cylindrical body 47 and the first impeller 4 are concentrically coupled to each other by meshing.

[0051] As above, the rotor shaft 3 and the impeller stack 40 including the impellers 4 are coupled to each other so as to be able to transmit power to each other.

[0052] The multistage rotor 2 according to a seventh aspect is configured such that: the multistage rotor 2 according to any one of the first to sixth aspects further includes the balance piston 56 located between the impellers 4 and the lock nut 6 in the axial direction X and fitted to the rotor shaft 3; and among the impellers 4, the second impeller (in the above embodiment, the trailing impeller 4T) that is in contact with the balance piston 56 is concentrically coupled to the balance piston 56 by meshing.

[0053] As above, since the balance piston 56 is located between the trailing impeller 4T and the lock nut 6, the balance piston 56 can be utilized for the alignment between the rotor shaft 3 and the impellers 4.

[0054] The multistage rotor 2 according to an eighth aspect is configured such that: in the multistage rotor 2 according to the seventh aspect, the inner peripheral surface of the balance piston 56 and the outer peripheral surface of the rotor shaft 3 are in pressure contact with each other; and thus, the balance piston 56 and the rotor shaft 3 are concentrically located.

[0055] As above, the alignment between the impeller stack 40 and the rotor shaft 3 is performed by the alignment between the balance piston 56 and the rotor shaft 3. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0056] The multistage rotor 2 according to a ninth aspect is configured such that: in the multistage rotor 2 according to the seventh aspect, the balance piston 56 is loosely fitted to the rotor shaft 3; the balance piston 56 is pushed outward in the radial direction by the lock nut 6 or the elastic body (in the above embodiment, the compression ring 59) which is located between the balance piston 56 and the rotor shaft 3 in the radial direction; and thus, the balance piston 56 and the rotor shaft 3 are concentrically located.

[0057] As above, the alignment between the impeller stack 40 and the rotor shaft 3 is performed by the alignment between the balance piston 56 and the rotor shaft 3. Thus, the imbalance during the rotation of the multistage rotor 2 can be prevented.

[0058] The multistage rotor 2 according to a tenth aspect of the present disclosure is configured such that: in the multistage rotor 2 according to any one of the first to ninth aspects, the rotor shaft 3 includes steel; and the impellers 4 include aluminum.

[0059] As above, the impellers 4 are made of aluminum that is higher in specific strength than steel. Thus, as compared to when the impellers 4 are made of steel, the centrifugal stress acting on the impellers 4 can be reduced.

[0060] The multistage rotor 2 according to an eleventh aspect of the present disclosure is configured such that: in the multistage rotor 2 according to any one of the first to tenth aspects, a ratio (= impeller hub diameter d2 / shaft diameter D4) of the impeller hub diameter d2 of the impellers 4 to the shaft diameter D4 of the pair of end sections 34 of the rotor shaft 3 is 2.0 or more and 2.8 or less.

[0061] According to the multistage rotor 2, even when the peripheral speed of the impeller 4 increases to such a degree that the workload that compresses a gas (for example, hydrogen) which is light in molecular weight and large in gas constant is obtained, the temperatures of the journal bearings 51 and 52 can be suppressed to the allowable temperature or less.

[0062] The turbo machine 1 according to a twelfth aspect of the present disclosure includes: the casing 12; and the multistage rotor 2 according to any one of the first to eleventh aspects, which is supported by the casing 12.

[0063] The multistage rotor 2 configured as above is preferable as the rotor of the turbo machine 1, especially the rotor of the centrifugal compressor.

[0064] The turbo machine 1 according to a thirteenth aspect of the present disclosure is configured such that the turbo machine 1 according to the twelfth aspect further includes the compression passage W through which the fluid to be compressed flows from the inlet port 22 to the outlet port 23 through the impellers 4 of the multistage rotor 2 in order, and the internal passage 7 extending in the axial direction X and located between the impellers 4 of the multistage rotor 2 and the rotor shaft 3 of the multistage rotor 2 in the radial direction, wherein the compression passage W and the internal passage 7 are in connection with each other by the connection passages 73 and 74 extending through the rotor shaft 3.

[0065] As above, the connection passages 73 and 74 are formed by utilizing the rotor shaft 3. Therefore, machine work that forms the connection passages 73 and 74 is easy, and bending stiffness of a portion of the rotor shaft 3 which supports the impeller stack 40 is not influenced by the connection passages 73 and 74. Moreover, since the connection passage 73 extends through the rotor shaft 3, a position to which the fluid returns from the internal passage 7 can be located further upstream of the inlet of the first-stage impeller 4A, and influence of the fluid, which has returned to the compression passage W, on the main flow of the compression passage W can be suppressed.

[0066] The turbo machine 1 according to a fourteenth aspect of the present disclosure is configured such that in the turbo machine 1 according to the thirteenth aspect, the connection passage 73 connects the internal passage 7 and a position of the compression passage W which is located upstream of the inlet of the impeller 4 through which the fluid flows first among the impellers 4.

[0067] As above, since the connection passage 73 extends through the rotor shaft 3, the configuration in which the fluid returns from the internal passage 7 to the position of the compression passage W which is located away from and upstream of the inlet of the first-stage impeller 4A can be easily realized. Then, since the fluid returns to the position of the compression passage W which is located away from and upstream of the inlet of the first-stage impeller 4A, influence of the fluid, which has returned to the compression passage W, on the main flow of the compression passage W can be suppressed.

[0068] The turbo machine 1 according to a fifteenth aspect of the present disclosure is configured such that: the turbo machine 1 according to the twelfth aspect (except for the turbo machine 1 including the multistage rotor 2 according to the sixth aspect) includes the compression passage W through which the fluid to be compressed flows from the inlet port 22 to the outlet port 23 through the impellers 4 of the multistage rotor 2 in order, and the internal passage 7 extending in the axial direction X and located between the impellers 4 of the multistage rotor 2 and the rotor shaft 3 of the multistage rotor 2 in the radial direction; the stepped surface 36 of the rotor shaft 3 of the multistage rotor 2 and the planar contact surface 48 of the first impeller 4L among the impellers 4 are in contact with each other in the axial direction X; and the connection passage 21 that connects the compression passage W and the internal passage 7 extends through the groove located on at least one of the stepped surface 36 or the contact surface 48.

[0069] The method of manufacturing the multistage rotor 2 according to a sixteenth aspect of the present disclosure includes: fitting the impellers 4 to the rotor shaft 3 that is a single object and includes the stepped surface 36; and fitting the lock nut 6 to the rotor shaft 3 to sandwich the impellers 4 between the stepped surface 36 and the lock nut 6 in a state where the impellers 4 are pressurized by the axial force of the rotor shaft 3.

[0070] The above method of manufacturing the multistage rotor 2 can manufacture the multistage rotor 2 according to the first aspect.

[0071] The foregoing discussion of the present disclosure has been presented for purposes of illustration and description. The foregoing is not intended to limit the present disclosure to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the present disclosure are grouped together in one embodiment for the purpose of streamlining the disclosure. However, some of the features may be combined with each other. The features of the present disclosure may be combined in alternate embodiments, configurations, or aspects other than those discussed above.

Examples

Embodiment Construction

[0012]FIG. 1 is a schematic sectional view of a turbo machine 1 according to one aspect of the present disclosure. FIG. 1 shows an upper half of the turbo machine 1 which is located at an upper side of a rotor axis A. As one aspect of the turbo machine 1, FIG. 1 shows a centrifugal compressor including a multistage rotor 2. The multistage rotor 2 is a rotor that stepwisely compresses fluid by impellers 4. Moreover, the centrifugal compressor is a compressor which: allows the fluid to flow therethrough, the fluid being to be compressed in a radial direction of the impeller 4 that rotates; and compresses the fluid by centrifugal force generated at that moment. The multistage rotor 2 of the present disclosure is not limited to the centrifugal compressor and is widely applicable to the turbo machine 1.

[0013]The turbo machine 1 includes: a casing 12; the multistage rotor 2 accommodated in the casing 12; and a driver that rotates the multistage rotor 2.

[0014]FIG. 2 is a schematic sectiona...

Claims

1. A multistage rotor comprising: a rotor shaft that is a single object and includes a stepped surface; impellers fitted to the rotor shaft and lined up in an axial direction of the rotor shaft from the stepped surface; and a lock nut fitted to the rotor shaft, wherein the impellers are sandwiched between the stepped surface and the lock nut.

2. The multistage rotor according to claim 1, wherein the impellers are sandwiched between the stepped surface and the lock nut while being pressurized by axial force of the rotor shaft.

3. The multistage rotor according to claim 1, wherein: the rotor shaft includes a pair of end sections located at both end portions of the rotor shaft in the axial direction and supported by bearings, a first section located between the pair of end sections in the axial direction and having a first shaft diameter, and a second section located between the pair of end sections in the axial direction and having a second shaft diameter larger than the first shaft diameter; the stepped surface is located between the first section and the second section; and the impellers are fitted to the first section of the rotor shaft.

4. The multistage rotor according to any one of claims 1 to 3, wherein: among the impellers, the impellers adjacent to each other in the axial direction are concentrically coupled to each other by meshing; and among the impellers, a first impeller that is in contact with the stepped surface is coupled to the stepped surface by friction.

5. The multistage rotor according to claim 4, wherein: an inner peripheral surface of the first impeller is in pressure contact with an outer peripheral surface of the rotor shaft; and the first impeller and the rotor shaft are concentrically located.

6. The multistage rotor according to any one of claims 1 to 3, wherein: among the impellers, the impellers adjacent to each other in the axial direction are concentrically coupled to each other by meshing; a cylindrical body is located between the stepped surface and a first impeller located closest to the stepped surface among the impellers; the stepped surface and the cylindrical body are coupled to each other by friction; and the cylindrical body and the first impeller are concentrically coupled to each other by meshing.

7. The multistage rotor according to any one of claims 1 to 3, further comprising a balance piston located between the impellers and the lock nut in the axial direction and fitted to the rotor shaft, wherein among the impellers, a second impeller that is in contact with the balance piston is concentrically coupled to the balance piston by meshing.

8. The multistage rotor according to claim 7, wherein: an inner peripheral surface of the balance piston is in pressure contact with an outer peripheral surface of the rotor shaft; and the balance piston and the rotor shaft are concentrically located.

9. The multistage rotor according to claim 7, wherein: the balance piston is loosely fitted to the rotor shaft; the balance piston is pushed outward in a radial direction by the lock nut or an elastic body which is located between the balance piston and the rotor shaft in the radial direction; and thus, the balance piston and the rotor shaft are concentrically located.

10. The multistage rotor according to any one of claims 1 to 3, wherein: the rotor shaft includes steel; and the impellers include an aluminum alloy.

11. The multistage rotor according to claim 3, wherein a ratio of an impeller hub diameter of the impellers to a shaft diameter of the pair of end sections of the rotor shaft is 2.0 or more and 2.8 or less.

12. A turbo machine comprising: a casing; and the multistage rotor according to claim 1, which is supported by the casing.

13. The turbo machine according to claim 12, further comprising: a compression passage through which fluid to be compressed flows from an inlet port to an outlet port through the impellers of the multistage rotor in order; and an internal passage extending in the axial direction and located between the impellers of the multistage rotor and the rotor shaft of the multistage rotor in a radial direction, wherein the compression passage and the internal passage are in connection with each other by a connection passage extending through the rotor shaft.

14. The turbo machine according to claim 13, wherein the connection passage connects the internal passage and a position of the compression passage which is located upstream of an inlet of the impeller through which the fluid flows first among the impellers.

15. The turbo machine according to claim 12, further comprising: a compression passage through which fluid to be compressed flows from an inlet port to an outlet port through the impellers of the multistage rotor in order; and an internal passage extending in the axial direction and located between the impellers of the multistage rotor and the rotor shaft of the multistage rotor in a radial direction, wherein: the stepped surface of the rotor shaft of the multistage rotor and a planar contact surface of a first impeller among the impellers are in contact with each other in the axial direction; and a connection passage that connects the compression passage and the internal passage extends through a groove located on at least one of the stepped surface or the contact surface.

16. A method of manufacturing a multistage rotor, the method comprising: fitting impellers to a rotor shaft that is a single object and includes a stepped surface; and fitting a lock nut to the rotor shaft to sandwich the impellers between the stepped surface and the lock nut in a state where the impellers are pressurized by axial force of the rotor shaft.

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