Patent Publication Number: US-11022135-B2

Title: Impeller and rotating machine

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an impeller and a rotating machine. 
     Priority is claimed on Japanese Patent Application No. 2019-032344, filed on Feb. 26, 2019, the content of which is incorporated herein by reference. 
     Description of Related Art 
     As a rotating machine used for a compressor, a turbo refrigerator, a small gas turbine, and the like, a structure including an impeller in which a plurality of blades are attached to a disk fixed to a rotating shaft is known. The rotating machine gives pressure energy and velocity energy to a fluid flowing inside by rotating the impeller. 
     In such a rotating machine, for example, Japanese Unexamined Patent Application, First Publication No. 2011-85088 discloses a structure including a concave portion that is recessed toward an inlet side of an impeller into which a gas is introduced, on a back surface of a disk. According to such a configuration, it is possible to reduce the weight of the impeller while maintaining a required strength. 
     SUMMARY OF THE INVENTION 
     If an attempt is made to further reduce the weight of the structure of Japanese Unexamined Patent Application, First Publication No. 2011-85088, there is a concern that the strength of the impeller may be insufficient. Therefore, it is desired to further reduce the weight of the impeller while maintaining a required strength. 
     The present invention provides an impeller and a rotating machine capable of further reducing weight while maintaining a required strength. 
     An impeller according to an aspect of the present invention includes: a disk having a disk shape centered on an axis; a plurality of blades provided on a front surface of the disk facing a first side in an axial direction at intervals in a circumferential direction around the axis; and a cover that covers the plurality of blades from the first side and gradually expands in diameter from the first side toward a second side in the axial direction, wherein the cover has a thick portion at a position distant from a first end portion positioned closest to the first side, the thick portion having a thickness greater than the thickness of the first end portion. 
     With such a configuration, in the cover, only the thickness of the thick portion is larger than the thickness of the first end portion. As a result, a weight of the cover is reduced. In addition, in the cover, a centrifugal force when the impeller rotates around the axis acts more as being further distant from the first end portion in the axial direction. Further, a pressure of the working fluid flowing between the disk and the cover increases from the inner side toward the outer side in the radial direction. That is, a more pressure by the working fluid acts as being further distant from the first end portion in the axial direction. On the other hand, in the cover, by making a position distant from the first end portion the thickest thick portion, a sufficient strength of the impeller is secured against the centrifugal force and the pressure of the working fluid. Accordingly, it is possible to further reduce weight while maintaining the required strength of the impeller. 
     In addition, according to a second aspect of the present invention, in the impeller of the first aspect, the thickness of the thick portion may increase from the first side toward the second side. 
     With such a configuration, when the impeller rotates, the thickness of the thick portion can be partially increased in response to an influence of the working fluid of which a pressure gradually increases toward an outlet of the impeller. Therefore, the necessary strength of the impeller can be appropriately maintained without increasing the weight excessively. 
     In addition, according to a third aspect of the present invention, in the impeller of the first or second aspect, the cover may have a transition portion that connects the first end portion and the thick portion with each other and increases in thickness from the first side toward the second side. 
     With such a configuration, the thickness of the cover can be partially increased over a wide region in the axial direction in response to an influence of the working fluid flowing between the disk and the cover. As a result, a shape of the cover can be made an appropriate shape according to the pressure of the working fluid. In addition, since the thickness gradually increases, a locally high stress is hardly generated in the cover. Therefore, the necessary strength of the impeller can be more appropriately maintained. 
     In addition, according to a fourth aspect of the present invention, in the impeller of the any one of the first to third aspects, in the disk, a concave portion may be formed on a back surface facing the second side in the axial direction, the concave portion being recessed toward the first side in the axial direction, and in the axial direction, the thick portion may be formed in a region overlapping with a position of a bottom of the concave portion in the axial direction. 
     In the portion where the concave portion is formed, a rigidity of the disk decreases, and a stress tends to concentrate on a connection portion between the disk and the blade. On the other hand, the thick portion is formed in the axial direction so as to correspond to the position where the bottom portion of the concave portion is formed. As a result, the disk can be reinforced by the cover via the blade. Accordingly, the stress generated at the connection portion between the disk and the blade can be reduced. 
     In addition, a rotating machine according to a fifth aspect of the present invention includes: a rotating shaft that is configured to rotate around an axis; and the impeller according to any one of the first to fourth aspects fixed to the rotating shaft. 
     With such a configuration, it is possible to provide a rotating machine having an impeller capable of further reducing a weight while maintaining a required strength. 
     According to the present invention, it is possible to further reduce weight while maintaining the required strength. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal sectional view of a rotating machine according to an embodiment of the present invention. 
         FIG. 2  is a sectional view showing an upper half of an impeller provided in the rotating machine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, an embodiment for implementing an impeller and a rotating machine according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited only to the embodiment. 
       FIG. 1  is a longitudinal sectional view of a rotating machine according to an embodiment of the present invention. As shown in  FIG. 1 , a centrifugal compressor (rotating machine)  10  according to the present embodiment mainly includes a casing  20 , a rotating shaft  30 , and an impeller  40 . 
     The casing  20  accommodates the rotating shaft  30  and the impeller  40 . The casing  20  has a cylindrical shape extending in a direction in which an axis O of the rotating shaft  30  extends (hereinafter, this direction is referred to as an axial direction Da). The casing  20  is provided with an internal space  24  in which a diameter is repeatedly reduced and increased. The impeller  40  is accommodated in the internal space  24 . 
     A suction port  25  through which a working fluid (process gas) G flows into the casing  20  from an outside is provided at first end portion  20   a  of the casing  20  on a first side (upstream side) Dau in the axial direction Da. In addition, a discharge port  26  through which the working fluid G flows out to the outside of the casing  20  is provided at the second end portion  20   b  of the casing  20  on a second side (downstream side) Dad in the axial direction Da. 
     A casing-side flow path  50  is formed in the casing  20  so as to connect the impellers  40  to each other. The casing-side flow path  50  allows the working fluid G flowing through the impeller  40  to flow from the first side Dau to the second side Dad in the axial direction Da in the casing  20 . 
     The casing-side flow path  50  has a diffuser portion  51 , a return bend portion  52 , and a return flow path  53 . The diffuser portion  51  extends from an outer peripheral portion of the impeller  40  in a radial direction Dr toward an outer side Dro in the radial direction Dr. The return bend portion  52  is turned in a U-shape in cross section from an outer peripheral portion of the diffuser portion  51  in the radial direction Dr, and extends toward an inner side Dri in the radial direction Dr. The return bend portion  52  guides the working fluid G, which flows toward the outer side Dro in the radial direction Dr, by reversing a flow direction of the working fluid G toward the inner side Dri in the radial direction Dr. The return flow path  53  extends from the return bend portion  52  toward the inner side Dri in the radial direction Dr to an end portion of the impeller  40  on the first side Dau in the axial direction Da. 
     The rotating shaft  30  is rotatably supported around the axis O with respect to the casing  20  via journal bearings  28 A and  28 B. The journal bearing  28 A is fixed to a first end portion  20   a  of the casing  20 . The journal bearing  28 B is fixed to a second end portion  20   b  of the casing  20 . In addition, a thrust bearing  29  is further fixed to the first end portion  20   a  of the casing  20 . One end portion of the rotating shaft  30  in the axial direction Da is supported by the thrust bearing  29  in the axial direction Da. 
     A plurality of the impellers  40  are fixed to the rotating shaft  30 , respectively. The impeller  40  compresses the working fluid G using a centrifugal force. The plurality of impellers  40  are accommodated in the internal space  24  inside the casing  20  at intervals in the axial direction Da. Further, although  FIG. 1  shows an example in which six impellers  40  are provided, at least one or more impellers  40  may be provided. 
       FIG. 2  is a sectional view showing an upper half of an impeller provided in the rotating machine. As shown in  FIG. 2 , each impeller  40  is a so-called closed impeller including a disk  41 , a blade  42 , and a cover  43 . 
     The disk  41  is formed in a disk shape centered on the axis O. The disk  41  is formed so as to gradually expand in diameter toward the outer side Dro in the radial direction Dr, from the first side Dau toward the second side Dad in the axial direction Da. 
     A circular through-hole  411  penetrating in the axial direction Da is formed in a center of the disk  41 . The impeller  40  is integrally fixed to the rotating shaft  30  with an inner peripheral surface of the through-hole  411  fitted into an outer peripheral surface of the rotating shaft  30 . 
     A surface of the disk  41  facing the second side Dad in the axial direction Da is a back surface  412  that expands in a direction intersecting with the axis O. A concave portion  47  is formed on the back surface  412 . The concave portion  47  is formed so as to be recessed from the back surface  412  toward the first side Dau in the axial direction Da. When viewed from the radial direction Dr, the concave portion  47  is recessed toward the first side Dau in the axial direction Da from a second end portion  432  of the cover  43  on the second side Dad in the axial direction Da. That is, a position of a bottom  47   b  of the concave portion  47  in the axial direction Da is positioned on the first side Dau in the axial direction Da with respect to the second end portion  432  of the cover  43 . Here, the bottom  47   b  of the concave portion  47  is formed on a most first side Dau in the axial direction Da in the concave portion  47 . The concave portion  47  is formed near a middle in the radial direction Dr, in the back surface  412 . The concave portion  47  is formed at a position distant from the through-hole  411  toward the outer side Dro in the radial direction Dr. The concave portion  47  is formed at a position distant from an end portion of the back surface  412  on the outer side Dro in the radial direction Dr, toward the inner side Dri in the radial direction Dr. By forming such a concave portion  47 , the weight of the disk  41  is reduced. 
     A surface of the disk  41  facing the first side Dau in the axial direction Da is a disk main surface (front surface)  413 . The disk main surface  413  is curved and extends so as to gradually be toward the outer side Dro in the radial direction Dr, from the first side Dau toward the second side Dad in the axial direction Da. A portion of the disk main surface  413  on the first side Dau in the axial direction Da is toward the outer side Dro in the radial direction Dr. A portion of the disk main surface  413  on the second side Dad in the axial direction Da is toward the first side Dau in the axial direction Da. The disk main surface  413  has a concave curved surface shape. 
     A plurality of the blades  42  are provided on the disk main surface  413  at intervals in a circumferential direction of the axis O. Each blade  42  extends from the disk main surface  413  toward the first side Dau in the axial direction Da. 
     The cover  43  covers the plurality of blades  42  from the first side Dau in the axial direction Da. The cover  43  is disposed to face the disk  41  so that the blade  42  is sandwiched between the cover and the disk  41 . That is, an end portion of the blade  42  opposite to an end portion connected to the disk main surface  413  is fixed to the cover  43 . The cover  43  is formed so as to gradually expand in diameter toward the outer side Dro in the radial direction Dr, from the first side Dau toward the second side Dad in the axial direction Da. In the cover  43 , a cover inner surface  430  facing the disk  41  is curved and extends so as to gradually be toward the outer side Dro in the radial direction Dr, from the first side Dau toward the second side Dad in the axial direction Da. The blade  42  is connected to the cover inner surface  430 . The cover inner surface  430  has a convex curved surface shape. 
     The cover  43  has a thin portion  48 , a thick portion  49 , and a transition portion  60 . The thin portion  48  is a region that includes a first end portion  431  positioned on a most first side Dau in the axial direction Da in the cover  43 . The thin portion  48  is a region having a smallest thickness in the cover  43 . Here, the thickness is a thickness in a direction orthogonal to the cover inner surface  430 . The thin portion  48  has a constant thickness in the axial direction Da. 
     The thick portion  49  is a region that includes the second end portion  432  positioned on a most second side Dad in the axial direction Da in the cover  43 . The thick portion  49  is a region having a largest thickness in the cover  43 . That is, a thickness T 2  of the thick portion  49  is larger than a thickness T 1  of the thin portion  48 . A region A in which the thick portion  49  is formed is formed at a position distant from the first end portion  431  in the axial direction Da. The region A is formed at a position overlapping with a position of the bottom  47   b  of the concave portion  47  in the axial direction Da. In the thick portion  49  of the present embodiment, the thickness increases from the first side Dau toward the second side Dad in the axial direction Da. 
     Further, in the present embodiment, the thick portion  49  having a large thickness is, for example, a region in which a thickness is larger than the average value of a thickness of the first end portion  431  and a thickness of the second end portion  432  in the cover  43 . 
     The transition portion  60  is a region that connects the first end portion  431  and the thick portion  49  with each other. That is, the transition portion  60  is a region that connects the thin portion  48  and the thick portion  49  with each other. In the transition portion  60 , the thickness increases from the first side Dau toward the second side Dad in the axial direction Da. The transition portion  60  smoothly connects an outer peripheral surface of the thin portion  48  to an outer peripheral surface of the thick portion  49 . Therefore, a thickness of the cover  43  gradually increases from the thin portion  48  toward the thick portion  49 . That is, the cover  43  is formed to have the smallest thickness at the first end portion  431  and the largest thickness at the second end portion  432 . 
     In the impeller  40 , an impeller flow path  45  is formed between the cover inner surface  430 , the disk main surface  413 , and the blade  42 . The impeller flow path  45  extends while being curved so as to be toward the outer side Dro in the radial direction Dr, from the first side Dau toward the second side Dad in the axial direction Da. The impeller flow path  45  has an inlet  451  and an outlet  452 . The inlet  451  is formed at an end portion of the impeller  40  on the first side Dau in the axial direction Da and on the inner side Dri in the radial direction Dr. The inlet  451  is open toward the first side Dau in the axial direction Da. The outlet  452  is formed at an end portion of the impeller  40  on the second side Dad in the axial direction Da and on the outer side Dro in the radial direction Dr. The outlet  452  is open toward the outer side Dro in the radial direction Dr. 
     As shown in  FIG. 1 , in such a centrifugal compressor  10 , the working fluid G is introduced from the suction port  25  into the casing-side flow path  50 . The working fluid G is compressed by passing through the impeller flow path  45  of the impeller  40  that rotates around the axis O together with the rotating shaft  30 . Specifically, as shown in  FIG. 2 , in the rotating impeller  40 , the working fluid G is introduced into the impeller flow path  45  from the inlet  451 . The working fluid G introduced into the impeller flow path  45  flows from the inner side Dri to the outer side Dro in the radial direction Dr and is pressurized in the impeller flow path  45  from the first side Dau toward the second side Dad in the axial direction Da. The working fluid G pressurized in the impeller flow path  45  is discharged from the outlet  452  to the diffuser portion  51  (see  FIG. 1 ) on the outer side Dro in the radial direction Dr. 
     As shown in  FIG. 1 , the working fluid G discharged to the diffuser portion  51  flows to the outer side Dro in the radial direction Dr, and the flow direction is reversed at the return bend portion  52 . After that, the working fluid G is sent to another impeller  40  disposed at a subsequent stage through the return flow path  53 . In this way, the working fluid G is compressed in multiple stages by passing through the impeller  40  and the casing-side flow path  50  provided in multiple stages from the first end portion  20   a  to the second end portion  20   b  of the casing  20 , and is discharged from the discharge port  26 . 
     According to the impeller  40  and the centrifugal compressor  10  as described above, in the cover  43 , the thickness T 2  of the thick portion  49  formed on the second side Dad in the axial direction Da is larger than the thickness T 1  of the thin portion  48  formed on the first side Dau in the axial direction Da. That is, in the cover  43 , only the thick portion  49  is thicker than other regions. As a result, the weight of the cover  43  is reduced. 
     Further, the second end portion  432  of the cover  43  is positioned closer to the outer side Dro in the radial direction Dr than the first end portion  431 . That is, in the cover  43 , a centrifugal force when the impeller  40  rotates around the axis O acts more as being further distant from the first end portion  431  in the axial direction Da. Further, a pressure of the working fluid G flowing through the impeller flow path  45  increases from the inner side Dri toward the outer side Dro in the radial direction Dr. That is, in the cover  43 , a more pressure by the working fluid G acts as being further distant from the first end portion  431  in the axial direction Da. In particular, in the impeller  40  corresponding to a large flow rate through which a large amount of the working fluid flows, the impeller flow path  45  is largely inclined with respect to the axis O near the outlet  452  as in the present embodiment. As a result, the pressure acted by the working fluid G near the outlet  452  increases. On the other hand, in the cover  43 , by making the region including the second side Dad in the axial direction Da the thickest thick portion  49 , a sufficient strength of the impeller  40  is secured against the centrifugal force and the pressure of the working fluid G. 
     Therefore, even if a large centrifugal force or a large pressure of the working fluid G acts on the second side Dad in the axial direction Da of the cover  43 , the thick portion  49  can secure a sufficient strength. In addition, since the thin portion  48  and the transition portion  60  are formed without forming the entire region of the cover  43  with the thickness T 2  of the thick portion  49 , further reduction in weight can be achieved while maintaining the necessary strength of the impeller  40 . 
     In addition, the thickness of the thick portion  49  increases toward the second side Dad in the axial direction Da, and is thickest at the second end portion  432 . Thus, when the impeller  40  rotates, the thickness T 2  of the thick portion  49  can be partially increased in response to an influence of the working fluid G of which a pressure gradually increases toward the vicinity of the outlet  452 . Therefore, the necessary strength of the impeller  40  can be appropriately maintained without increasing the weight excessively. 
     In addition, in the cover  43 , the outer peripheral surface of the thin portion  48  and the outer peripheral surface of the thick portion  49  are smoothly connected to each other by the transition portion  60 . That is, the thickness of the cover  43  is gradually increased toward the second side Dad in the axial direction Da. Therefore, the cover  43  is thickened over a wide region in the axial direction Da so as to correspond to an increase in pressure of the working fluid G flowing through the impeller flow path  45 . Accordingly, the thickness of the cover  43  can be partially increased in response to the influence of the working fluid G flowing through the impeller flow path  45 . As a result, a shape of the cover  43  can be made an appropriate shape according to the pressure of the working fluid G. In addition, since the thickness gradually increases, a locally high stress is hardly generated in the cover  43 . Therefore, the necessary strength of the impeller  40  can be more appropriately maintained. 
     In addition, in the axial direction Da, a thick portion  49  is formed in the region A overlapping with the position of the bottom  47   b  of the concave portion  47  formed in the disk  41 . In the portion where the concave portion  47  is formed, a rigidity of the disk  41  decreases. As a result, when the impeller  40  rotates, the disk  41  is deformed to collapse toward the first side Dau in the axial direction Da with the bottom  47   b  as a reference point. Accordingly, a high stress is generated in the vicinity of the inlet  451  near the bottom  47   b  even in the connection portion between the disk  41  and the blade  42 . On the other hand, the thick portion  49  is formed in the axial direction Da so as to correspond to the position where the bottom  47   b  of the concave portion  47  is formed. As a result, bending composition of the cover  43  increases, and the deformation of the disk  41  can be suppressed via the blade  42 . That is, the disk  41  can be reinforced by the cover  43  via the blade  42 . Accordingly, the stress generated at the connection portion between the disk  41  and the blade  42  can be reduced. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 
     For example, the shape of the impeller  40  is not limited to the shape of the present embodiment. For example, in the impeller  40 , the concave portion  47  may not be formed in the disk  41 . 
     In addition, the thick portion  49  is not limited to the structure in which the thickness increases from the first side Dau toward the second side Dad in the axial direction Da as in the present embodiment. The thick portion  49  may be formed in the cover  43  so that the thickness is locally increased. In addition, the thick portion  49  is not limited to being connected to the thin portion  48  via the transition portion  60 . The thick portion  49  may be formed distant from the thin portion  48  as long as it is formed at a position distant from the first end portion  431 . 
     Furthermore, although the centrifugal compressor  10  is illustrated as an example of the rotating machine, the present invention is not limited to this, and the same configuration can be applied to other rotating machines such as a pump as long as an impeller is provided. 
     EXPLANATION OF REFERENCES 
     
         
         
           
               10 : centrifugal compressor (rotating machine) 
               20 : casing 
               20   a : first end portion (one end portion) 
               20   b : second end portion (other end portion) 
               24 : internal space 
               25 : suction port 
               26 : discharge port 
               28 A,  28 B: journal bearing 
               29 : thrust bearing 
               30 : rotating shaft 
               40 : impeller 
               41 : disk 
               42 : blade 
               43 : cover 
               45 : impeller flow path 
               47 : concave portion 
               47   b : bottom 
               48 : thin portion 
               49 : thick portion 
               60 : transition portion 
               50 : casing-side flow path 
               51 : diffuser portion 
               52 : return bend portion 
               53 : return flow path 
               411 : through-hole 
               412 : back surface 
               413 : disk main surface (front surface) 
               430 : cover inner surface 
               431 : first end portion 
               432 : second end portion 
               451 : inlet 
               452 : outlet 
             A: region 
             Da: axial direction 
             Dau: first side 
             Dad: second side 
             Dr: radial direction 
             Dri: inner side 
             Dro: outer side 
             G: working fluid (process gas) 
             O: axis 
             T 1 , T 2 : thickness