Patent Publication Number: US-2023160396-A1

Title: Centrifugal compressor and turbocharger

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2021/032537, filed on Sep. 3, 2021, which claims priority to Japanese Patent Application No. 2020-204236 filed on Dec. 9, 2020, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present disclosure relates to a centrifugal compressor and a turbocharger. 
     Patent Literature 1 discloses a centrifugal compressor comprising a compressor housing and a compressor impeller. A diffuser flow path and a scroll flow path are formed in the compressor housing of Patent Literature 1. A radially-inner end located at the radially-innermost position is formed in the scroll flow path. The radially-inner end of the scroll flow path is located on a side closer to the diffuser flow path with respect to the middle point of the maximum flow path width in the rotational axis direction of the compressor impeller. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 6347457 B 
     SUMMARY 
     Technical Problem 
     When the radially-inner end of the scroll flow path is located on the side closer to the diffuser flow path, a cross-sectional shape of a radially-inner side of the scroll flow path has a large curvature. This causes a large change in a flow direction along the scroll flow path wall, and air is likely to separate from an inner surface of the scroll flow path on the inner side closer to the diffuser flow path. 
     The purpose of the present disclosure is to provide a centrifugal compressor and a turbocharger than can curb air separation in the scroll flow path. 
     Solution to Problem 
     To solve the above problem, a centrifugal compressor of the present disclosure includes: a housing accommodating an impeller; a diffuser flow path formed radially outside the impeller in the housing; and a scroll flow path formed in the housing and connected to the diffuser flow path from a radially-outer side, the scroll flow path extending in a rotational axis direction and a rotational direction of the impeller with respect to the diffuser flow path, the scroll flow path including a radially-inner end located at the radially-innermost position, and the radially-inner end being spaced apart from the diffuser flow path with respect to a middle point of the maximum flow path width of the scroll flow path in the rotational axis direction. 
     The scroll flow path may include an radially-inner surface located on a radially-inner side, the radially-inner surface may include a first curvature surface closer to the diffuser flow path with respect to the radially-inner end and a second curvature surface spaced apart from the diffuser flow path with respect to the radially-inner end, and a radius of curvature of the first curvature surface may be equal to a radius of curvature of the second curvature surface. 
     A separation distance in the rotational axis direction between the middle point and the radially-inner end may be larger in an intermediate section than those at a tongue and an end of winding of the scroll flow path, the intermediate section being located between the tongue and the end of winding in a direction of extension of the scroll flow path. 
     The scroll flow path may include an radially-inner surface located on a radially-inner side, the radially-inner surface may include a first curvature surface closer to the diffuser flow path with respect to the radially-inner end and a second curvature surface spaced apart from the diffuser flow path with respect to the radially-inner end, and a radius of curvature of the first curvature surface may be larger than a radius of curvature of the second curvature surface in the intermediate section. 
     To solve the above problem, a turbocharger of the present disclosure includes the centrifugal compressor described above. 
     Effects of Disclosure 
     According to the present disclosure, flow separation along a scroll flow path wall can be curbed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic cross-sectional view of a turbocharger. 
         FIG.  2    is a schematic cross-sectional view of a compressor scroll flow path of an embodiment. 
         FIG.  3    is a view visualizing velocity of air flowing in the compressor scroll flow path. 
         FIG.  4    is a graph indicating a relationship between an azimuth angle from the beginning to the end of winding of the compressor scroll flow path and a distance between a radially-inner end and a middle point in the rotational axis direction. 
         FIG.  5    is a schematic cross-sectional view of the compressor scroll flow path in an intermediate section. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Specific dimensions, materials, and numerical values described in the embodiment are merely examples for a better understanding, and do not limit the present disclosure unless otherwise specified. In this specification and the drawings, duplicate explanations are omitted for elements having substantially the same functions and configurations by assigning the same reference sign. Furthermore, elements not directly related to the present disclosure are omitted from the figures. 
       FIG.  1    is a schematic cross-sectional view of a turbocharger TC. Hereinafter, a direction indicated by an arrow L in  FIG.  1    is described as the left side of the turbocharger TC. A direction indicated by an allow R in  FIG.  1    is described as the right side of the turbocharger TC. As shown in  FIG.  1   , the turbocharger TC comprises a turbocharger body  1 . The turbocharger body  1  includes a bearing housing  3 , a turbine housing  5 , and a compressor housing (housing)  7 . The turbine housing  5  is connected to the left side of the bearing housing  3  by a fastening bolt  9 . The compressor housing  7  is connected to the right side of the bearing housing  3  by a fastening bolt  11 . 
     A bearing hole  3   a  is formed in the bearing housing  3 . The bearing hole  3   a  passes through the bearing housing  3  in the left-to-right direction of the turbocharger TC. The bearing hole  3   a  accommodates a portion of a shaft  13 . The bearing hole  3   a  accommodates a bearing  15 . In this embodiment, the bearing  15  is a full floating bearing. However, the bearing  15  is not limited thereto, and may be any other bearing such as a semi-floating bearing or a rolling bearing. The shaft  13  is rotatably supported by the bearing  15 . The left end of the shaft  13  is provided with a turbine wheel  17 . The turbine wheel  17  is rotatably housed in the turbine housing  5 . A compressor impeller (impeller)  19  is provided at the right end of the shaft  13 . The compressor impeller  19  is rotatably housed in the compressor housing  7 . In the present disclosure, a rotational axis direction, a radial direction, and a rotational direction of the shaft  13 , the turbine wheel  17 , and the compressor impeller  19  may simply be referred to as the rotational axis direction, the radial direction, and the rotational direction, respectively. 
     An inlet  21  is formed in the compressor housing  7 . The inlet  21  opens to the right side of the turbocharger TC. The inlet  21  is connected to an air cleaner (not shown). A diffuser flow path  23  is formed by opposing surfaces of the bearing housing  3  and the compressor housing  7 . The diffuser flow path  23  is formed in an annular shape. The diffuser flow path  23  is formed radially outside the compressor impeller  19  in the compressor housing  7 . The diffuser flow path  23  is connected to the inlet  21  via the compressor impeller  19  at a radially-inner part. Air flowing from the inlet  21  flows in the diffuser flow path  23  through the compressor impeller  19 . The diffuser flow path  23  pressurizes the air. 
     A compressor scroll flow path (scroll flow path)  25  is formed in the compressor housing  7 . The compressor scroll flow path  25  is formed in an annular shape. For example, the compressor scroll flow path  25  is located radially outside the diffuser flow path  23 . The compressor scroll flow path  25  is connected to a radially outer part of the diffuser flow path  23 . The compressor scroll flow path  25  extends in the rotational axis direction and the rotational direction with respect to the diffuser flow path  23 . The compressor scroll flow path  25  is connected to an intake port of an engine (not shown) and the diffuser flow path  23 . When the compressor impeller  19  rotates, air is sucked into the compressor housing  7  from the inlet  21 . The sucked air is pressurized and accelerated while flowing through blades of the compressor impeller  19 . The pressurized and accelerated air is pressurized in the diffuser flow path  23  and the compressor scroll flow path  25 . The pressurized air is directed to the intake port of the engine. 
     A centrifugal compressor CC comprises the above-described compressor housing  7  and the bearing housing  3 . In this embodiment, an example in which the centrifugal compressor CC is mounted in the turbocharger TC is described. However, the centrifugal compressor CC is not limited thereto, and may be incorporated into a device other than the turbocharger TC, or may be a stand-alone unit. 
     An outlet  27  is formed in the turbine housing  5 . The outlet  27  opens to the left side of the turbocharger TC. The outlet  27  is connected to an exhaust gas purifier (not shown). A connecting flow path  29  and a turbine scroll flow path  31  are formed in the turbine housing  5 . The connecting flow path  29  is located radially outside the turbine wheel  17 . The connecting flow path  29  is formed in an annular shape. The connecting flow path  29  connects the outlet  27  to the turbine scroll flow path  31  through the turbine wheel  17 . 
     For example, the turbine scroll flow path  31  is located radially outside the connecting flow path  29 . The turbine scroll flow path  31  is formed in an annular shape. The turbine scroll flow path  31  is connected to a gas inlet (not shown). Exhaust gas discharged from an exhaust manifold of the engine (not shown) is directed to the gas inlet. The exhaust gas passes through the turbine scroll flow path  31  and the connecting flow path  29 , and is directed to the outlet  27  through the turbine wheel  17 . The exhaust gas rotates the turbine wheel  17  while flowing through the turbine wheel  17 . 
     The rotational force of the turbine wheel  17  is transmitted to the compressor impeller  19  via the shaft  13 . As the compressor impeller  19  rotates, air is pressurized as described above. As such, the air is directed to the intake port of the engine. 
       FIG.  2    is a schematic cross-sectional view of the compressor scroll flow path  25  of the embodiment. As shown in  FIG.  2   , the compressor scroll flow path  25  includes lateral ends  25   a  and  25   a  that define the maximum flow path width Th in the rotational axis direction. An inner surface of the compressor scroll flow path  25  includes a radially-outer surface  25   b  and a radially-inner surface  25   c  across the lateral ends  25   a  and  25   a.    
     The radially-outer surface  25   b  is formed radially outside the lateral ends  25   a  and  25   a  in the inner surface of the compressor scroll flow path  25 . The radially-outer surface  25   b  has a curved-surface shape protruding radially outward. The radially-inner surface  25   c  is formed radially inside the lateral ends  25   a  and  25   a  in the inner surface of the compressor scroll flow path  25 . The radially-inner surface  25   c  has a curved-surface shape protruding radially inward. 
     Most of the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  is guided along the radially-outer surface  25   b  from a portion proximate to the diffuser flow path  23  to a portion spaced apart from the diffuser flow path  23 . The air moving along the radially-outer surface  25   b  is guided from the radially-outer surface  25   b  to the radially-inner surface  25   c , and then guided along the radially-inner surface  25   c  from a portion spaced apart from the diffuser flow path  23  to a portion proximate to the diffuser flow path  23 . As such, most of the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  forms a clockwise swirling flow in  FIG.  2    (in a direction indicated by an arrow Ra in the figure) in the compressor scroll flow path  25 . 
     Furthermore, a portion of the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  moves from an exit end surface  23   a  of the diffuser flow path  23  to the right side in  FIG.  2   , and is guided along the radially-inner surface  25   c  from the portion proximate to the diffuser flow path  23  to the portion spaced apart from the diffuse flow path  23 . As such, a portion of the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  forms a counterclockwise swirling flow (in a direction indicated by an arrow Rb in the figure) in the compressor scroll flow path  25  in  FIG.  2   . 
     The clockwise swirling flow and the counterclockwise swirling flow in the compressor scroll flow path  25  in  FIG.  2    collide with each other at a first curvature surface  25   g  (described later) in the radially-inner surface  25   c , and form a stagnation area (separation area). 
     The radially-outer surface  25   b  includes a radially-outer end  25   d  that is located radially-outermost position in the compressor scroll flow path  25 . The radially-inner surface  25   c  includes a radially-inner end  25   e  that is located radially-innermost position in the compressor scroll flow path  25 . 
     In the radial direction, a distance from the lateral ends  25   a  and  25   a  to the radially-outer end  25   d  is shorter than a distance from the lateral ends  25   a  and  25   a  to the radially-inner end  25   e . A cross-sectional area of the flow path  25  on a radially-outer side with respect to the lateral ends  25   a  and  25   a  is smaller than a cross-sectional area of the flow path  25  on a radially-inner side with respect to the lateral ends  25   a  and  25   a.    
     The radially-outer end  25   d  is in the same position as the radially-inner end  25   e  in the rotational axis direction. However, the radially-outer end  25   d  is not limited thereto, and may be at a different position from the radially-inner end  25   e  in the rotational axis direction. The radially-outer end  25   d  is spaced apart from the diffuser flow path  23  with respect to a middle point  25   f  of the maximum flow path width Th in the rotational axis direction. 
     The radially-inner end  25   e  is spaced apart from the diffuser flow path  23  with respect to the middle point  25   f  of the maximum flow path width Th in the rotational axis direction. A width Ei between the lateral end  25   a  closer to the diffuser flow path  23  and the radially-inner end  25   e  is larger than a width Mh between the lateral end  25   a  closer to the diffuser flow path  23  and the middle point  25   f . In other words, a separation distance in the rotational axis direction between the lateral end  25   a  closer to the diffuser flow path  23  and the radially-inner end  25   e  is larger than a separation distance in the rotational axis direction between the lateral end  25   a  closer to the diffuser flow path  23  and the middle point  25   f . The radially-inner end  25   e  is located between the lateral end  25   a  spaced apart from the diffuser flow path  23  and the middle point  25   f  in the rotational axis direction. The radially-inner end  25   e  is closer to the middle point  25   f  with respect to the lateral end  25   a  spaced apart from the diffuser flow path  23 . 
     The radially-inner surface  25   c  includes the first curvature surface  25   g  and a second curvature surface  25   h . The first curvature surface  25   g  is closer to the diffuser flow path  23  with respect to the radially-inner end  25   e  of the radially-inner surface  25   c . The second curvature surface  25   h  is spaced apart from the diffuser flow path  23  with respect to the radially-inner end  25   e  of the radially-inner surface  25   c . A radius of curvature of the first curvature surface  25   g  is equal to a radius of curvature of the second curvature surface  25   h . In the present disclosure, “equal” means including a case where they are completely equal to each other, and a case where they are substantially equal to each other with a manufacturing tolerance or an error. However, the radius of curvature of the first curvature surface  25   g  is not limited thereto, and may be different from the radius of curvature of the second curvature surface  25   h.    
     As mentioned above, in the compressor scroll flow path  25  of this embodiment, a height of the radially-outer side (distance to the radially-outer end  25   d  in the radial direction) is smaller than a height of the radially-inner side (distance to the radially-inner end  25   e  in the radial direction), with respect to the lateral ends  25   a  and  25   a  defining the maximum flow path width Th. Accordingly, the maximum outer diameter of the compressor scroll flow path  25  can be reduced compared to a case where the height of the radially-outer side and the height of the radially-inner side with respect to the lateral ends  25   a  and  25   a  are equal to each other. As a result, the maximum outer diameter of the compressor housing  7  can be reduced. 
     Meanwhile, the compressor scroll flow path  25  of this embodiment has a larger height on the radially-inner side and has a shape protruding radially more inwardly, compared to the case where the height on the radially-outer side and the height on the radially-inner side with respect to the lateral ends  25   a  and  25   a  are equal to each other. As the height of the radially-inner side of the compressor scroll flow path  25  increases, the curvature of the cross-sectional shape of the flow path on the radially-inner side increases. Accordingly, the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  is likely to separate especially at the first curvature surface  25   g , and the separation area is likely to expand. As the separation area expands, the performance of the centrifugal compressor CC decreases. 
     As the radially-inner end  25   e  of the compressor scroll flow path  25  approaches the diffuser flow path  23  with respect to the middle point  25   f , an angle α between the exit end surface  23   a  of the diffuser flow path  23  and the first curvature surface  25   g  increases. As the angle α increases, the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  is likely to separate from the first curvature surface  25   g.    
     Accordingly, in this embodiment, the radially-inner end  25   e  of the compressor scroll flow path  25  is arranged to be spaced apart from the diffuser flow path  23  with respect to the middle point  25   f . This allows the angle α between the exit end surface  23   a  of the diffuser flow path  23  and the first curvature surface  25   g  to be smaller compared to a case where the radially-inner end  25   e  is located closer to the diffuser flow path  23  with respect to the middle point  25   f . As a result, the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  is less likely to separate from the first curvature surface  25   g , and the expansion of the separation area can be curbed. 
     Furthermore, when the radii of curvature of the first curvature surface  25   g  and the second curvature surface  25   h  are equal to each other, the air flowing from the diffuser flow path  23  into the compressor scroll flow path  25  can move smoothly on the first curvature surface  25   g  and the second curvature surface  25   h . As a result, the air is less likely to separate from the first curvature surface  25   g  and the second curvature surface  25   h , and the expansion of the separation area can be curbed. 
       FIG.  3    is a view visualizing velocity of air flowing in the compressor scroll flow path  25 .  FIG.  4    is a graph indicating a relationship between an azimuth angle from the beginning to the end of winding of the compressor scroll flow path  25  and a distance between a radially-inner end  25   e  and the middle point  25   f  in the rotational axis direction. In  FIG.  3   , multiple curves shown in the compressor scroll flow path  25  indicate magnitude of air velocity, with longer curves indicating higher velocity. In  FIG.  4   , the vertical axis indicates a distance in the rotational axis direction with respect to the lateral end  25   a  closer to the diffuser flow path  23 , and the horizontal axis indicates the azimuth angle from the beginning to the end of winding of the compressor scroll flow path  25 . 
     As shown in  FIGS.  3  and  4   , the beginning  25   i  of winding of the compressor scroll flow path  25  is represented by an azimuth angle of 0°, and the end  25   j  of winding by an azimuth angle of 330°. The compressor scroll flow path  25  also includes a tongue  25   k  that divides a upstream portion and a downstream portion of the compressor scroll flow path  25 . The tongue  25   k  of the compressor scroll flow path  25  is represented by an approximate azimuth angle of 15°. The compressor scroll flow path  25  includes an intermediate section  25   m  between the beginning  25   i  (tongue  25   k ) and the end  25   j  of winding in the direction of extension of the compressor scroll flow path  25 . The intermediate section  25   m  has a range represented, for example, by an azimuth angle of 60° to 210°, as shown in  FIG.  4   . However, the range (azimuth angle) of the intermediate section  25   m  is not limited thereto. 
     As shown in  FIG.  4   , a separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  varies along the direction of extension (azimuth angle) of the compressor scroll flow path  25 . The separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  is smallest at the tongue  25   k.    
     The separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  gradually increases from the tongue  25   k  to the intermediate section  25   m  and gradually decreases from the intermediate section  25   m  to the end  25   j  of winding. In other words, the separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  is larger in the intermediate section  25   m  than those at the beginning  25   i  (tongue  25   k ) and the end  25   j  of winding of the compressor scroll flow path  25 . 
       FIG.  5    is a schematic cross-sectional view of the compressor scroll flow path  25  in the intermediate section  25   m . In  FIG.  5   , the cross-sectional shape of the flow path at the end  25   j  of winding is shown as a dashed line, and the cross-sectional shape of the flow path in the intermediate section  25   m  is shown as a solid line. The cross-sectional shape of the flow path at the end  25   j  of winding is the same as the cross-sectional shape of the flow path shown in  FIG.  2   . 
     As shown in  FIG.  5   , the radially-inner end  125   e  of the compressor scroll flow path  25  in the intermediate section  25   m  is more spaced apart from the diffuser flow path  23  compared to the radially-inner end  25   e  of the compressor scroll flow path  25  at the end  25   j  of winding. In other words, the separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  125   e  in the intermediate section  25   m  is larger than the separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  in the end  25   j  of winding. 
     Accordingly, the first curvature surface  125   g  of the compressor scroll flow path  25  in the intermediate section  25   m  has a larger radius of curvature than that of the first curvature surface  25   g  of the compressor scroll flow path  25  at the end  25   j  of winding. 
     The second curvature surface  125   h  of the compressor scroll flow path  25  in the intermediate section  25   m  has a smaller radius of curvature than that of the second curvature surface  25   h  of the compressor scroll flow path  25  at the end  25   j  of winding. As a result, the radius of curvature of the first curvature surface  125   g  is larger than the radius of curvature of the second curvature surface  125   h . In other words, the radius of curvature of the second curvature surface  125   h  is smaller than the radius of curvature of the first curvature surface  125   g.    
     As shown in  FIG.  3   , the plurality of curves shown in the compressor scroll flow path  25  extend longer to the vicinity of the radially-outer end of the compressor scroll flow path  25  in the intermediate section  25   m  (especially in azimuth angles of 60° to 150°). As such, the velocity of the air flowing in the compressor scroll flow path  25  is highest in the intermediate section  25   m  (especially in azimuth angles of 60° to 150°). As the velocity of the air increases, the air is likely to separate from the first curvature surfaces  25   g  and  125   g.    
     Accordingly, in this embodiment, the radius of curvature of the second curvature surface  125   h  is reduced in the intermediate section  25   m  where the velocity of the air is the largest. By reducing the radius of curvature, the clockwise air swirling velocity in  FIG.  5    can be reduced more efficiently compared to a case where the radius of curvature is larger. This reduces the air moving from the second curvature surface  125   h  to the first curvature surface  125   g  separating from the first curvature surface  125   g , and the expansion of the separation area can be curbed. 
     Although the embodiment of the present disclosure has been described above with reference to the accompanying drawings, the present disclosure is not limited thereto. It is obvious that a person skilled in the art can conceive of various examples of variations or modifications within the scope of the claims, which are also understood to belong to the technical scope of the present disclosure. 
     The above embodiment describes an example in which the separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  varies along the direction of extension of the compressor scroll flow path  25 . However, the separation distance in the rotational axis direction between the middle point  25   f  and the radially-inner end  25   e  is not limited thereto, and may be constant along the direction of extension of the compressor scroll flow path  25 .