Patent Publication Number: US-11041504-B2

Title: Rotor of centrifugal compressor, centrifugal compressor, and method for manufacturing rotor of centrifugal compressor

Description:
TECHNICAL FIELD 
     The present invention relates to a rotor of a centrifugal compressor, a centrifugal compressor, and a method of manufacturing a rotor of a centrifugal compressor. 
     BACKGROUND 
     Generally, a rotary machine such as a centrifugal compressor includes a rotor which is rotationally driven and a casing which covers the rotor from an outer circumferential side to form a flow path inside. A rotor includes a rotating shaft extending along a rotation axis and an impeller installed on an outer circumferential surface of the rotating shaft. 
     In installing an impeller on a rotating shaft, it is common to perform tight fitting by shrink fitting or cold fitting as described in Patent Literature 1 below, for example. 
     PATENT LITERATURE 
     
         
         Patent Literature 1
       Japanese Unexamined Utility Model Application, First Publication No. S63-26701   
     
       
    
     Incidentally, in a compressor with a relatively high compression ratio, it is particularly necessary to rotate the rotor at a high speed. When a rotor is rotated at a high speed, a centrifugal force from a radial inner side with respect to a rotating shaft toward the outside is applied to the impeller. Such a centrifugal force may cause the impeller to rise upward from an outer circumferential surface of the rotating shaft toward a radial outer side. 
     Further, a thrust force is also applied to the impeller along the rotating shaft from a high pressure side toward a low pressure side. Such a thrust force also increases in proportion to an increase in compression ratio. 
     In order to resist the thrust force while suppressing the rising up of the impeller, it is also conceivable to increase a tightening margin when performing the tight fitting as described above. However, when the tightening margin is large, slight bending may occur in the rotor due to a high tightening force, which may induce vibrations during operation. In addition, since it takes time and labor for installing and removing the impeller, there is a likelihood of manufacturing costs and maintenance costs increasing. 
     SUMMARY 
     One or more embodiments of the present invention provide a rotor of a centrifugal compressor which can be easily assembled, a method of manufacturing the same, and a centrifugal compressor which can be stably operated under a relatively high compression ratio. 
     A rotor of a centrifugal compressor according to one or more embodiments of the present invention includes a rotor main body extending in an axis direction and having a recessed part formed on an outer circumferential surface thereof, an impeller including a cylinder part having a cylindrical shape extending around the axis and in which an inner circumferential surface having a fitting region tightly fitted to the outer circumferential surface of the rotor main body is formed, an annular disc extending from the cylinder part to a radial outer side with respect to the axis, a plurality of blades provided at intervals in a circumferential direction on a surface facing one side in the axis direction of the annular disc, and a cover covering the plurality of blades from the one side in the axis direction, and a contact member fitted into the recessed part and in which a part protrudes toward a radial outer side from the outer circumferential surface to come in contact with the cylinder part from the axis direction. 
     According to one or more embodiments, a part of the contact member protruding toward a radial outer side from the outer circumferential surface of the rotor main body comes in contact with the cylinder part of the impeller from the axis direction. That is, a thrust force applied to the impeller can be received by the contact member. Further, a size of the fitting region and a magnitude of a tightening margin can be reduced to be small as compared with a case in which the contact member is not provided. Thereby, a likelihood of occurrence of vibration in the centrifugal compressor can be reduced. 
     According to one or more embodiments of the present invention, in the rotor of a centrifugal compressor according to the first aspect, the cylinder part may include a first cylinder part disposed on the one side in the axis direction and a second cylinder part disposed on the other side of the first cylinder part in the axis direction with a clearance therebetween in the axis direction with respect to the first cylinder part, a stepped part recessed to the radial outer side may be formed in a region of the inner circumferential surface of the first cylinder part including an end part on the other side in the axis direction, an end surface on the one side in the axis direction of the stepped part may come in contact with the contact member from the one side in the axis direction, and an end surface on the one side in the axis direction of the second cylinder part may come in contact with the contact member from the other side in the axis direction, and an end part on the radial inner side of the clearance may communicate with a region on the radial inner side of the stepped part. 
     According to one or more embodiments, the thrust force applied to the impeller can be received by the contact member. Further, since the cylinder part is divided into the first cylinder part and the second cylinder part with the clearance formed therebetween, a natural frequency of the impeller can be reduced to a low level. 
     On the other hand, when the above-described clearance is not provided, the natural frequency of the impeller increases due to an influence of the natural frequency of the split ring. Thereby, whirling vibration or the like may be generated in the rotor. 
     However, according to one or more embodiments, since increase in natural frequency can be suppressed by providing a clearance, a possibility of the whirling vibration or the like being generated can be reduced. 
     According to one or more embodiments of the present invention, in the rotor of a centrifugal compressor according to the first aspect, the contact member may come in contact with an end surface on the one side in the axis direction of the cylinder part from the one side in the axis direction. 
     According to one or more embodiments, the contact member comes in contact with the cylinder part from the one side in the axis direction. Thereby, even when a thrust force is applied to the cylinder part from the other side in the axis direction toward the one side, the thrust force can sufficiently be resisted. Further, a size of the fitting region and a magnitude of a tightening margin can be reduced to be small as compared with a case in which the contact member is not provided. Thereby, a likelihood of occurrence of vibration in the centrifugal compressor can be reduced. 
     According to one or more embodiments of the present invention, in the rotor of a centrifugal compressor according to any one of the first to third aspects, the inner circumferential surface of the cylinder part may include a non-fitting region adjacent to the fitting region in the axis direction and having an inner diameter larger than that of the rotor main body. 
     According to one or more embodiments, a fitting region and a non-fitting region are formed on the inner circumferential surface of the cylinder part. Thereby, a tightening force can be reduced to be small as compared with a case in which the fitting region is provided over the entire inner circumferential surface. Therefore, the impeller can be easily installed on and removed from the rotor main body. 
     According to one or more embodiments of the present invention, in the rotor of a centrifugal compressor according to any one of the first to fourth aspects, the contact member may include a plurality of segmented parts arranged in the circumferential direction with respect to the axis. 
     According to one or more embodiments, the contact member can be easily configured by sequentially installing a plurality of segmented parts on a recessed groove of the rotor main body from the outer circumferential side. 
     According to one or more embodiments of the present invention, a centrifugal compressor includes the rotor of a centrifugal compressor according to any one of claims  1  to  5  and a casing which covers the rotor from an outer circumferential side to form a flow path inside. 
     According to one or more embodiments, it is possible to obtain a centrifugal compressor having a high compression ratio and easy assemblability. 
     According to one or more embodiments of the present invention, a method of manufacturing the rotor of a centrifugal compressor according to any one of the first to fifth aspects includes a process of installing the cylinder part of the impeller on the rotor main body from the axis direction and forming the fitting region, and a process of installing the contact member on the recessed part of the rotor main body. 
     According to one or more embodiments, it is possible to easily obtain a rotor of a centrifugal compressor which can be stably operated under a high compression ratio. 
     According to one or more embodiments of the present invention, it is possible to provide a rotor of a centrifugal compressor which can be easily assembled, a method of manufacturing the same, and a centrifugal compressor which can be stably operated under a high compression ratio. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a configuration of a centrifugal compressor according to one or more embodiments of the present invention. 
         FIG. 2  is a view illustrating a configuration of a rotor according to one or more embodiments of the present invention. 
         FIG. 3  is a view illustrating a configuration of a contact member (a split ring) according to one or more embodiments of the present invention. 
         FIG. 4  is a process flow diagram illustrating a method of manufacturing the rotor according to one or more embodiments of the present invention. 
         FIG. 5  is a view illustrating a configuration of a rotor according to one or more embodiments of the present invention. 
         FIG. 6  is a view illustrating a configuration of a centrifugal compressor according to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. As illustrated in  FIG. 1 , a centrifugal compressor  100  (rotary machine) according to one or more embodiments includes a rotor  1  having a plurality (six) of impellers  2  and a casing  4  which covers the rotor  1  from an outer circumferential side to form a flow path  3 . 
     The casing  4  has a cylindrical shape extending substantially along an axis A. The rotor  1  extends to pass through an inside of this casing  4  along the axis A. A journal bearing  5  and a thrust bearing  6  are provided at opposite end parts of the casing  4  in an axis A direction. The rotor  1  is rotatably supported around the axis A by the journal bearing  5  and the thrust bearing  6 . 
     An intake port  7  for taking in a fluid from outside is provided on one side in the axis A direction of the casing  4 . Further, a discharge port  8  through which a fluid compressed inside the casing  4  is discharged is provided on the other side in the axis A direction of the casing  4 . That is, the centrifugal compressor  100  employs a method in which a fluid flows from one side in the axis A direction to the other side (straight type). 
     Inside the casing  4 , an internal space through which the intake port  7  and the discharge port  8  communicate with each other and in which diameter reduction and expansion are repeated is formed. This internal space accommodates the plurality of impellers  2  and forms a part of the flow path  3 . 
     As illustrated in  FIG. 2 , the rotor  1  includes a substantially rod-shaped rotor main body  9  extending in the axis A direction, the plurality of impellers  2  provided at intervals in the axis A direction on an outer circumferential surface  9 A of the rotor main body  9 , and a split ring  10  (a contact member) which is in contact with the rotor main body  9  and each of the impellers  2 . In one or more embodiments, since all of the plurality of impellers  2  provided in the rotor main body  9  have the same configuration, only one impeller  2  will be representatively illustrated and described. 
     An angular groove shaped recessed part  11  recessed from a radial outer side toward an inner side with respect to the axis A is formed on the outer circumferential surface  9 A of the rotor main body  9 . A surface on a radial inner side of the recessed part  11  is a recessed part bottom surface  111 . A surface on one side in the axis A direction of the recessed part  11  is a recessed part first end surface  112  extending in a direction substantially perpendicular to the recessed part bottom surface  111  (that is, a radial direction with respect to the axis A). A surface on the other side in the axis A direction of the recessed part  11  is a recessed part second end surface  113  extending substantially parallel to the recessed part first end surface  112 . 
     The split ring  10  to be described below is installed on this recessed part  11 . On opposite sides in the axis A direction with the recessed part  11  interposed therebetween, outer diameters of the rotor main body  9  are substantially the same as each other. Further, a dimension in the radial direction (depth) of the recessed part  11  is smaller than a dimension in the radial direction of the split ring  10 . Thus, a part of the radial outer side of the split ring  10  protrudes toward the radial outer side from the recessed part  11 . 
     The impeller  2  includes a tubular cylinder part  12  extending around the axis A, an annular disc  13  integrally formed with the cylinder part  12  and extending from the cylinder part  12  toward the radial outer side with respect to the axis A, a plurality of blades  14  provided on a surface on one side in the axis A direction of the annular disc  13 , and a cover  15  covering the blades  14  from one side in the axis A direction. 
     The cylinder part  12  includes a first cylinder part  121  disposed on one side in the axis A direction and a second cylinder part  122  disposed at a distance from the first cylinder part  121  on the other side in the axis A direction. 
     An inner circumferential surface  12 A of the first cylinder part  121  has a circular cross section centered on the axis A when viewed from the axis A direction. Further, only a part of the inner circumferential surface  12 A including an end part on one side in the axis A direction is a fitting region  16  (a first fitting region  161 ) which is fixed to the outer circumferential surface  9 A of the rotor main body  9  from the radial outer side by tight fitting. That is, in a state in which the impeller  2  is installed on the rotor main body  9 , the outer circumferential surface  9 A of the rotor main body  9  and the inner circumferential surface  12 A of the first cylinder part  121  are in contact with each other without a clearance therebetween in the first fitting region  161 . 
     As an example, the fitting region  16  is formed by shrink fitting. That is, at a stage before applying shrink fitting, an outer diameter of the rotor main body  9  is set to be larger than an inner diameter of the cylinder part  12 . A difference between the outer diameter of this rotor main body  9  and the inner diameter of the cylinder part  12  serves as a tightening margin when shrink fitting is applied. In one or more embodiments, a tightening ratio is set to 0.5/1000 or more and 8.0/1000 or less. 
     In one or more embodiments, the tightening ratio is set to 1.0/1000 or more and 5.0/1000 or less. In one or more embodiments, the tightening ratio is set to 1.5/1000 or more and 3.0/1000 or less. 
     The tightening ratio referred to here represents an index indicating a relative magnitude of the tightening margin with respect to a design reference dimension of the rotor main body  9 . Specifically, when a reference dimension of the outer shape of the rotor main body  9  is assumed to be 1000 and a magnitude of the tightening margin is assumed to be X, the tightening ratio is expressed as X/1000. 
     In such a configuration, when the impeller  2  (the cylinder part  12 ) is heated and thermally expands, the inner diameter of the cylinder part  12  is enlarged and becomes larger than the outer diameter of the rotor main body  9 . In a state in which the inner diameter of the cylinder part  12  is enlarged, the rotor main body  9  is inserted inside the cylinder part  12 . Thereafter, when the heat applied to the impeller  2  is removed, the impeller  2  contracts and returns to an initial dimension. That is, in the above-described fitting region  16 , the cylinder part  12  is tightly fitted to the rotor main body  9 . 
     On the inner circumferential surface  12 A of the first cylinder part  121 , a region on the other side in the axis A direction adjacent to the fitting region  16  is a non-fitting region  17  (a first non-fitting region  171 ) which is not subjected to such tight fitting as described above. That is, in the first non-fitting region  171 , the inner diameter of the cylinder part  12  is slightly larger than the outer diameter of the rotor main body  9 . Thus, in a state in which the impeller  2  is installed on the rotor main body  9 , the first cylinder part  121  is fitted to the rotor main body  9  with a clearance therebetween in the first non-fitting region  171 . 
     On a cross section including the axis A, a surface on an outer circumferential side of the first cylinder part  121  gradually curves from the radial inner side with respect to the axis A toward the outer side from one side in the axis A direction toward the other side. In other words, the surface on the outer circumferential side of the first cylinder part  121  is formed in a substantially conical shape. This surface serves as a flow path forming surface  18  which forms a part of the above-described flow path  3 . 
     A stepped part  19  recessed from the radial inner side to the outer side with respect to the axis A is formed in a region of the inner circumferential surface  12 A of the first cylinder part  121  including an end part on the other side in the axis A direction. More specifically, this stepped part  19  has a first end surface  191  which forms a wall surface on one side in the axis A direction and an annular bottom surface  192  substantially perpendicular to the first end surface  191  and extending in a circumferential direction of the axis A formed therein. In a cross-sectional view including the axis A, the first end surface  191  and a second end surface extend in the radial direction with respect to the axis A. The bottom surface  192  extends along the axis A. 
     The second cylinder part  122  is provided at a distance (clearance C) from the above-described first cylinder part  121  on the other side in the axis A direction. This second cylinder part  122  is formed integrally with the annular disc  13  to be described below. An inner circumferential surface  12 B of the second cylinder part  122  is in contact with the outer circumferential surface  9 A of the rotor main body  9  from the radial outer side in a region on the other side in the axis A direction with respect to the above-described recessed part  11  on the rotor main body  9 . An end surface on one side in the axis A direction of the second cylinder part  122  (a second cylinder part end surface  123 ) faces inside the stepped part  19  from the other side in the axis A direction. 
     An end surface on the other side in the axis A direction of the first cylinder part  121  faces the annular disc  13  via the clearance C described above. That is, an outer circumferential side of the cylinder part  12  and a radial inner side region of the stepped part  19  communicate with each other via the clearance C. 
     The inner circumferential surface  12 B of the second cylinder part  122  has a circular cross section centered on the axis A when viewed from the axis A direction. Further, as in the above-described first fitting region  161  and the first non-fitting region  171 , a second fitting region  162  tightly fitted to the outer circumferential surface  9 A of the rotor main body  9  and a second non-fitting region  172  adjacent to the second fitting region  162  are also formed on the inner circumferential surface  12 B of the second cylinder part  122 . Specifically, the second fitting region  162  is formed in a region of the inner circumferential surface  12 B of the second cylinder part  122  including an end part on the other side in the axis A direction. The second non-fitting region  172  is an area on one side with respect to this second fitting region  162  in the axis A direction. As in the first non-fitting region  171 , the second non-fitting region  172  is also fitted to the outer circumferential surface  9 A of the rotor main body  9  with a clearance therebetween. 
     The annular disc  13  has an annular shape extending from the above-described second cylinder part  122  toward the radial outer side with respect to the axis A. The plurality of blades  14  are arranged at intervals in a circumferential direction with respect to the axis A on a surface facing one side in the axis A direction of the annular disc  13  (a first facing surface  13 A). Each of the blades  14  is a wing-shaped member extending from the first facing surface  13 A toward one side in the axis A direction. 
     Although not illustrated in detail, when viewed from the axis A direction, the blade  14  curves from the radial inner side toward the outer side from one side in a circumferential direction toward the other side. A space between a pair of adjacent blades  14  in the circumferential direction forms a part of the flow path  3  (an impeller flow path  21 ). 
     A cover  15  is installed on an end edge on one side in the direction of axis A of these blades  14 . The cover  15  covers the plurality of blades  14  from one side in the axis A direction. Specifically, the cover  15  has an annular shape around the axis A. In opposite surfaces in the axis A direction of the cover  15 , a surface facing the other side in the axis A direction (that is, a surface to which an end edge on one side in the axis A direction of the blade  14  is connected) is a second facing surface  15 A facing the above-described first facing surface  13 A in the axis A direction with the space between the adjacent blades  14  interposed therebetween. 
     On a radial inner side of the cover  15 , a protruding part  20  protruding toward one side in the axis A direction is integrally provided. A surface on a radial inner side of this protruding part  20  is a cover facing surface  20 A facing the flow path forming surface  18  of the first cylinder part  121  from the radial outer side with respect to the axis A. 
     A space through which a fluid flows is formed inside the impeller  2  by the above-described flow path forming surface  18 , the cover facing surface  20 A, the first facing surface  13 A, and the second facing surface  15 A. This space forms the impeller flow path  21  which is a part of the above-described flow path  3 . 
     On one side in the axis A direction of the impeller  2 , a sleeve  22  formed in a cylindrical shape around the axis A is installed. This sleeve  22  is in contact with the first cylinder part  121  from one side in the axis A direction. In one or more embodiments, an inner diameter and outer diameter of the sleeve  22  are substantially uniform throughout in the axis A direction. Further, an outer circumferential surface of the sleeve  22  and an outer circumferential surface of the first cylinder part  121  are continuous in the axis A direction. 
     The split ring  10  is an annular member disposed in a space surrounded by the recessed part  11  formed on the outer circumferential surface  9 A of the rotor main body  9 , the stepped part  19  formed on the inner circumferential surface  12 A of the first cylinder part  121 , and the end surface in the axis A direction of one side of the second cylinder part  122 . In a cross-sectional view including the axis A, a cross-sectional shape of the split ring  10  is substantially rectangular. As illustrated in  FIG. 3 , the split ring  10  according to one or more embodiments is segmented into a plural number (three) in the circumferential direction with respect to the axis A. That is, the split ring  10  is formed of three segmented parts arranged in the circumferential direction. 
     More specifically, the segmented parts include a pair of first segmented parts  101  adjacent to each other in the circumferential direction and a second segmented part  102  surrounded on both circumferential sides by the pair of first segmented parts  101 . The first segmented parts  101  and the second segmented part  102  are formed from an elastically deformable member having a substantially arc shape. Further, in a state before being installed on the rotor main body  9 , each of the first segmented parts  101  and the second segmented part  102  has a larger curvature than that of the outer circumferential surface  9 A of the rotor main body  9 . 
     An end surface  101 B on one side in a circumferential direction of each of the first segmented parts  101  extends substantially parallel to a radial direction with respect to its own central axis. On the other hand, an end surface on the other side in the circumferential direction of each of the first segmented parts  101  (a first inclined surface  101 A) extends to be inclined with respect to the radial direction with respect to its own central axis. More specifically, this first inclined surface  101 A is obliquely cut so as to face a radial inner side. That is, each of the first segmented parts  101  has a shape which is asymmetrical in the circumferential direction with reference to the radial direction with respect to its own central axis. 
     Unlike the first segmented parts  101 , the second segmented part  102  has a shape symmetrical in the circumferential direction. Each of the end surfaces on both circumferential sides of the second segmented part  102  (a second inclined surface  102 A) extends to be inclined with respect to the radial direction with respect to its own central axis. More specifically, the second inclined surface  102 A is obliquely cut so as to face a radial outer side. The second inclined surface  102 A is inclined with respect to the radial direction at substantially the same angle as the above-described first inclined surface  101 A. In other words, in a state in which the first segmented parts  101  and the second segmented part  102  are assembled, the first inclined surface  101 A and the second inclined surface  102 A come into contact with each other substantially parallel to each other. 
     The two first segmented parts  101  and one second segmented part  102  as described above are fitted into the recessed part  11  of the rotor main body  9  from the radial outer side. In a state of being fitted into the recessed part  11 , all of the first segmented parts  101  and the second segmented part  102  are elastically deformed in a direction in which curvatures become small. Further, in this state, the first inclined surface  101 A of the first segmented parts  101  and the second inclined surface  102 A of the second segmented part  102  are in contact with each other without a clearance therebetween. That is, the second inclined surface  102 A facing substantially the radial inner side comes into contact with the first inclined surface  101 A that faces substantially the radial outer side. 
     Here, since the second segmented part  102  is elastically deformed in a direction in which the curvature decreases as described above, a force that restores in a direction in which the curvature increases acts on the second segmented part  102  due to its own elastic restoring force. That is, in a state in which the split ring  10  is assembled, the second inclined surface  102 A of the second segmented part  102  exerts a force to the first inclined surface  101 A of the first segmented parts  101  from the radial outer side. Due to this force, the two first segmented parts  101  are undetachably accommodated in the recessed part  11  while they are elastically deformed in a direction in which the curvatures become smaller. 
     The split ring  10  is surrounded from both sides in the radial direction by the recessed part  11  of the rotor main body  9  and the stepped part  19  of the impeller  2 . Specifically, as illustrated in  FIG. 2 , the recessed part first end surface  112  of the recessed part  11  and the first end surface  191  of the stepped part  19  are in contact with a surface on one side in the axis A direction of the split ring  10 . The recessed part bottom surface  111  of the recessed part  11  is in contact with a surface on a radial inner side of the split ring  10 . The bottom surface  192  of the stepped part  19  is in contact with a surface on the radial outer side of the split ring  10 . The recessed part second end surface  113  of the recessed part  11  and the second cylinder part end surface  123  of the second cylinder part  122  are in contact with a surface on the other side in the axis A direction of the split ring  10 . 
     Next, a method of manufacturing the rotor  1  of the centrifugal compressor  100  will be described with reference to  FIG. 4 . First, the impeller  2  and the rotor main body  9  configured as described above are prepared (process S 1 ). In one or more embodiments, each of these members is integrally formed of a relatively hard metal material, for example, such as stainless steel. 
     Next, the impeller  2  is installed on the rotor main body  9 . In installing the impeller  2  on the rotor main body  9 , as an example, the first cylinder part  121  is first installed by shrink fitting. Through this process, the first fitting region  161  and the first non-fitting region  171  described above are formed (process S 2 ). 
     Next, the split ring  10  (the first segmented parts  101  and the second segmented part  102 ) is installed on the recessed part  11  of the rotor main body  9  (process S 3 ). After the split ring  10  is installed, the second cylinder part  122  is installed on the outer circumferential surface  9 A of the rotor  1  (process S 4 ). Through this process, the second cylinder part  122  and the annular disc  13  integrally formed with the second cylinder part  122  are installed on the rotor main body  9 . Specifically, the surface on one side in the axis A direction of the second cylinder part  122  (that is, the second end surface of the stepped part  19 ) comes into contact with the surface on the other side in the axis A direction of the split ring  10 . 
     Further, at this time, the above-described clearance C is formed between the first cylinder part  121  and the second cylinder part  122  in the axis A direction. Further, through this process, the second fitting region  162  and the second non-fitting region  172  described above are formed. Next, the sleeve  22  is installed on the rotor main body  9  (process S 5 ). As described above, each process of the method of manufacturing the rotor  1  of the centrifugal compressor  100  according to one or more embodiments is thus completed. 
     Next, an operation of the centrifugal compressor  100  according to one or more embodiments will be described. In operating the centrifugal compressor  100 , the rotor  1  is first rotated by a driving source (not illustrated). When the rotor  1  is rotationally driven around the axis A by a driving source (not illustrated), the plurality of impellers  2  provided on the rotor  1  rotate integrally with the rotor  1 . As the impeller  2  rotates, an external fluid is introduced into the flow path  3  in the casing  4  from the intake port  7 . 
     The fluid introduced from one side in the axis A direction through the flow path  3  as described above is compressed through the impeller flow path  21 . More specifically, the fluid flows from one side in the axis A direction toward the other side through a space formed by the cover facing surface  20 A and the flow path forming surface  18 . Next, after a direction of the fluid is changed along a curved shape of the flow path forming surface  18 , the fluid flows into the space formed by the first facing surface  13 A and the second facing surface  15 A from the radial inner side toward the outer side. In the same manner, the fluid is sequentially compressed through a plurality of impeller flow paths  21 . The compressed high-pressure fluid is supplied to various external devices (not illustrated) through the discharge port  8 . 
     Here, during the operation of the centrifugal compressor  100 , a relatively low pressure fluid is flowing through one side in the axis A direction (the intake port  7  side) in the flow path  3  while a relatively high pressure fluid is flowing through the other side in the axis A direction (the discharge port  8  side). Due to this pressure difference, a force (a thrust force) directed from the other side in the axis A direction toward one side is applied to the impeller  2 . 
     In addition, in a compressor with a high compression ratio, since it is particularly necessary to rotate the rotor  1  at a high speed, a centrifugal force from a radial inner side toward an outer side with respect to the rotating shaft is applied to the impeller  2 . Due to such a centrifugal force, there may be a case that the impeller  2  rise upward from the outer circumferential surface  9 A of the rotor main body  9  toward the radial outer side. 
     In order to resist the thrust force while suppressing rising up of the impeller  2 , it is also conceivable to increase the tightening margin when performing the tight fitting as described above. However, when the tightening margin is large, slight bending may occur in the rotor  1  due to a high tightening force, which may induce vibrations during operation. In addition, since it takes time and labor for installing and removing the impeller  2 , there is a likelihood of manufacturing costs and maintenance costs increased. 
     Therefore, in the centrifugal compressor  100  according to one or more embodiments, since some of the thrust force is received by the split ring  10 , a size of the fitting region  16  and a magnitude of a tightening margin are reduced to be relatively small. More specifically, a part of the split ring  10  protruding toward the radial outer side from the outer circumferential surface  9 A of the rotor main body  9  is in contact with the cylinder part  12  of the impeller  2  from the axis A direction. Specifically, the recessed part first end surface  112  of the recessed part  11  and the first end surface  191  of the stepped part  19  are in contact with the surface on one side in the axis A direction of the split ring  10 . The recessed part bottom surface  111  of the recessed part  11  is in contact with the surface on the radial inner side of the split ring  10 . The bottom surface  192  of the stepped part  19  is in contact with the surface on the radial outer side of the split ring  10 . The recessed part second end surface  113  of the recessed part  11  and the second cylinder part end surface  123  of the second cylinder part  122  are in contact with the surface on the other side in the axis A direction of the split ring  10 . 
     In this way, as the split ring  10  is provided on the outer circumferential surface  9 A of the rotor main body  9  and is brought into contact with the impeller  2 , it is possible to receive the thrust force applied to the impeller  2 . That is, it is possible to reduce a force applied to the fitting region  16  by an amount corresponding to the thrust force received by the split ring  10 . As a result, the size of the fitting region  16  can be reduced to be small as compared with a case in which the split ring  10  is not provided. In other words, the non-fitting region  17  can be formed on the outer circumferential surface  9 A of the rotor main body  9 . Further, a magnitude of a tightening margin in the fitting region  16  can also be reduced to be small. Thereby, a likelihood of occurrence of vibration in the centrifugal compressor  100  can be reduced to be small as compared with a case in which tight fitting is applied over the entire outer circumferential surface  9 A of the rotor main body  9 , and the impeller  2  can be easily installed on or removed from the rotor main body  9 . 
     Further, since the cylinder part  12  is divided into the first cylinder part  121  and the second cylinder part  122  with the clearance C formed therebetween, a natural frequency of the impeller  2  can be reduced to a low level. 
     On the other hand, when the above-described clearance is not provided, the natural frequency of the impeller  2  increases due to an influence of the natural frequency of the split ring  10 . Thereby, whirling vibration or the like may be generated in the rotor  1 . 
     However, according to the above configuration, since an increase in natural frequency can be reduced by providing a clearance, a possibility of whirling vibration or the like being generated can be reduced. 
     In addition, according to the above-described configuration, the split ring  10  can be easily configured by sequentially installing the plurality of segmented parts (the first segmented parts  101  and the second segmented part  102 ) on the recessed part  11  of the rotor main body  9  from the outer circumferential side. 
     Next, embodiments of the present invention will be described with reference to  FIG. 5 . Configuration parts the same as those in one or more embodiments described above will be denoted with the same reference signs and detailed description thereof will be omitted. As illustrated in the drawing, in one or more embodiments, a cylinder part  212  of an impeller  202  is integrally formed as one member, which is different from one or more embodiments described above. That is, in one or more embodiments, the above-described clearance C is not formed in the cylinder part  212 . 
     Further, a fitting region  16  similar to the above is formed in a region of an inner circumferential surface  212 A of this cylinder part  212  including an end part on one side in an axis A direction. A non-fitting region  17  is formed on the other side in the axis A direction of the fitting region  16 . 
     A split ring  10  is in contact with an end surface on one side in the axis A direction of the cylinder part  212  formed as described above. As in one or more embodiments described above, a part of a radial outer side of the split ring  10  protrudes from an outer circumferential surface  9 A of a rotor main body  9  to the radial outer side. A step is formed in a radial direction between an outer circumferential surface of the split ring  10  and an outer circumferential surface of the cylinder part  212  (a flow path forming surface  218 ). 
     On one side in the axis A direction of the split ring  10 , a sleeve  222  formed in a cylindrical shape around the axis A is installed. An outer circumferential surface of the sleeve  222  has a substantially uniform outer diameter over the entire region in the axis A direction. On the other hand, an enlarged diameter part  223  which covers the split ring  10  from the radial outer side is formed at an end edge on the other side in the axis A direction in an inner circumferential surface of the sleeve  222 . The enlarged diameter part  223  fills the step between the outer circumferential surface of the split ring  10  and the flow path forming surface  218 . That is, in a state in which the sleeve  222  and the impeller  202  are installed on the rotor main body  9 , the outer circumferential surface of the sleeve  222  and the flow path forming surface  218  are continuous in the axis A direction. 
     According to this configuration, the split ring  10  comes into contact with the end surface on one side in the axis A direction of the cylinder part  212  from one side in the axis A direction. Thereby, even when a thrust force is applied to the cylinder part  212  from the other side in the axis A direction toward the one side, the thrust force can sufficiently be resisted. Further, a size of the fitting region  16  and a magnitude of a tightening margin can be reduced to be small as compared with a case in which the split ring  10  is not provided. Thereby, a likelihood of occurrence of vibration in the centrifugal compressor  100  can be reduced. 
     Next, embodiments of the present invention will be described with reference to  FIG. 6 . Configurations parts the same as those in one or more embodiments described above will be denoted with the same reference signs and detailed description thereof will be omitted. As illustrated in the drawing, a centrifugal compressor  300  according to one or more embodiments described below is a so-called back-to-back type unlike the straight type centrifugal compressor  100  in one or more embodiments described above. 
     The centrifugal compressor  300  includes a rotor  301  which extends around an axis A 2 , a pair of bearing parts  302  which rotatably support the rotor  301  around the axis A 2 , a casing  303  which covers these from an outer circumferential side, and a balance piston  304  installed on the casing  303 . 
     The rotor  301  includes a substantially rod-shaped rotor main body  305 , a plurality of impellers  306  provided at intervals in the axis A 2  direction on this rotor main body  305 , and a split ring  10  (a contact member) interposed between the rotor main body  305  and each of the impellers  306 . 
     In one or more embodiments, six impellers  306  are installed on the rotor main body  305 . Among these impellers  306 , in the three impellers  306  positioned on one side in the axis A 2  direction (a first impeller group G 1 ), blades  307  extend toward one side in the axis A 2  direction. On the other hand, in the three impellers  306  positioned on the other side in the axis A 2  direction (a second impeller group G 2 ), blades  307  extend toward the other side in the axis A 2  direction. 
     All the impellers  306  are fixed to the rotor main body  305  by tight fitting. That is, a fitting region  316  and a non-fitting region  317  as in the above-described embodiments are formed between an outer circumferential surface  305 A of the rotor main body  305  and an inner circumferential surface  312 A of a cylinder part  312  of the impeller  306 . Further, as in the above-described embodiments, the split ring  10  is installed between each of the impellers  306  and the rotor main body  305 . 
     A first intake port  308  and a second intake port  309  for taking a fluid into the casing  303  are provided in the casing  303 . Further, a first discharge port  310  and a second discharge port  311  for discharging a compressed fluid are provided in the casing  303 . 
     A fluid introduced into the casing  303  through the first intake port  308  is compressed by the rotating first impeller group G 1  to a high pressure (intermediate pressure). The fluid compressed by the first impeller group G 1  is introduced into the casing  303  again by the second intake port  309  from the first discharge port  310  via a pipe (not illustrated). The fluid at the intermediate pressure introduced from the second intake port  309  is compressed again by the second impeller group G 2  and reaches a higher pressure (target pressure). The fluid compressed by the second impeller group G 2  is discharged outside through the second discharge port  311 . 
     Here, a fluid having a higher pressure than that of the first impeller group G 1  side is flowing on the second impeller group G 2  side. Thus, there is a possibility of a fluid leaking from the second impeller group G 2  side toward the first impeller group G 1  side. The balance piston  304  is provided for sealing a flow of a fluid between the first impeller group G 1  and the second impeller group G 2 . 
     In the centrifugal compressor  300  configured as described above, as in the centrifugal compressor  100  in the above-described embodiments, a thrust force is applied to each of the impellers  306 . More specifically, a thrust force from the other side in the axis A 2  direction toward one side is applied to the three impellers  306  of the first impeller group G 1 . A thrust force from one side in the axis A 2  direction toward the other side is applied to the three impellers  306  of the second impeller group G 2 . However, it is possible to sufficiently resist such a thrust force by providing the above-described split ring  10 . That is, also with a back-to-back type device such as the centrifugal compressor  300 , by using the split ring  10 , it is possible to reduce a size of the fitting region  316  and a magnitude of a tightening margin. Thereby, a likelihood of occurrence of vibration in the centrifugal compressor  300  can be reduced to be small as compared with a case in which tight fitting is applied over the entire outer circumferential surface  305 A of the rotor main body  305 , and the impellers  306  can be easily installed on or removed from the rotor main body  305 . 
     Embodiments of the present invention have been described with reference to the drawings. Further, each of the above-described configurations is merely an example, and various modifications and changes can be applied thereto. 
     For example, the number of impellers  2  (impellers  306 ) provided in the centrifugal compressor  100  and the centrifugal compressor  300  illustrated in each of the above embodiments is not limited to the above, and may be arbitrarily determined according to design and specifications. 
     Further, in each of the above-described embodiments, an example in which a type of impeller  2  having the cover  15  (closed impeller) is employed as the impeller  2  has been described. However, the type of impeller  2  is not limited thereto, and it is also possible to employ a type not having the cover  15  (open impeller). 
     In addition, in each of the above embodiments, an example in which one split ring  10  is provided corresponding to one impeller  2  has been described. However, it is also possible to provide a plurality (two, or three or more) of split rings  10  for one impeller  2 . According to such a configuration, a thrust force applied to the impeller  2  can be more sufficiently resisted. 
     In addition, in each of the above-described embodiments, an example in which the annular split ring  10  is used as the contact member has been described. However, a form of the contact member is not limited to the split ring  10 . As an example, a plurality of pin-shaped members protruding toward the radial outer side may be arranged at intervals in the circumferential direction on the outer circumferential surface  9 A of the rotor main body  9  to form a contact member. Also with such a configuration, the thrust force applied to the impeller  2  can be sufficiently resisted. 
     INDUSTRIAL APPLICABILITY 
     According to the above configuration, it is possible to provide a rotor of a centrifugal compressor which can be easily assembled, a method of manufacturing the same, and a centrifugal compressor which can be stably operated under a high compression ratio. 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Rotor 
               2  Impeller 
               3  Flow path 
               4  Casing 
               5  Journal bearing 
               6  Thrust bearing 
               7  Intake port 
               8  Discharge port 
               9  Rotor main body 
               10  Split ring 
               11  Recessed part 
               12  Cylinder part 
               13  Annular disc 
               14  Blade 
               15  Cover 
               16 ,  316  Fitting region 
               17 ,  317  Non-fitting region 
               18  Flow path forming surface 
               19  Stepped part 
               20  Protruding part 
               21  Impeller flow path 
               22  Sleeve 
               100  Centrifugal compressor 
               101  First segmented part 
               102  Second segmented part 
               111  Recessed part bottom surface 
               112  Recessed part first end surface 
               113  Recessed part second end surface 
               121  First cylinder part 
               122  Second cylinder part 
               123  Second cylinder part end surface 
               161  First fitting region 
               162  Second fitting region 
               171  First non-fitting region 
               172  Second non-fitting region 
               191  First end surface 
               192  Bottom surface 
               202  Impeller 
               212  Cylinder part 
               212 A Inner circumferential surface 
               218  Flow path forming surface 
               222  Sleeve 
               223  Enlarged diameter part 
               300  Centrifugal compressor 
               301  Rotor 
               302  Bearing part 
               303  Casing 
               304  Balance piston 
               305  Rotor main body 
               306  Impeller 
               307  Blade 
               308  First intake port 
               309  Second intake port 
               310  First discharge port 
               311  Second discharge port 
               9 A Outer circumferential surface 
               12 A,  12 B Inner circumferential surface 
               13 A First facing surface 
               15 A Second facing surface 
               20 A Cover facing surface 
               101 A First inclined surface 
               102 A Second inclined surface 
             A, A 2  Axis 
             C Clearance 
             G 1  First impeller group 
             G 2  Second impeller group 
           
         
       
    
     Although the disclosure has been described with respect to only a limited number of embodiments, those skill in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the invention. Accordingly, the scope of the invention should be limited only by the attached claims.