Patent Publication Number: US-10788045-B2

Title: Discharge section structure for centrifugal compressor

Description:
TECHNICAL FIELD 
     The present disclosure relates to a discharge section structure for a centrifugal compressor. 
     BACKGROUND ART 
     From related art, various structures related to a compressor housing, such as scroll of a centrifugal compressor, have been studied. For example, as described in Patent Literature 1, in a compressor housing of a turbo supercharger, a spiral scroll having a tongue section as a starting point, a cross-sectional area gradually increasing in a clockwise direction, and leading to a discharge tube is known. The tongue section is formed at a branching point between the scroll and the discharge tube. In this structure, the tongue section is defined as a starting point and an ending point of the scroll, and by setting the starting point at 0° to take an angle clockwise and by setting 360° as the ending point, the scroll is ended at this position. The portion subsequent to the ending point of the scroll is a discharge tube. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Publication No. 2005-207337 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the compressor housing of the related art, in many cases, the shape of the discharge section was configured to be straight. In a case where the discharge section is configured in a straight shape, a loss due to collision of flow tends to occur on a side of a larger flow rate than the flow rate producing peak efficiency. As a result, a reduction in efficiency occurs. 
     The present disclosure describes a structure of a discharge section of a centrifugal compressor capable of suppressing reduction in efficiency in a discharge section. 
     Solution to Problem 
     The inventor repeatedly conducted extensive studies on generating factors of the loss due to collision of flow and the remedial measures thereof in a scroll flow passage or a discharge flow passage. As a result, the inventor has found that the aforementioned problem can be solved by devising the shape of the discharge flow passage and the position of the tongue section with respect to the shape of the discharge flow passage. That is, in the conventional discharge section configured in a straight shape, it was found that a loss was generated due to, for example, collision of the flow from the diffuser or the like with the tongue section. 
     An aspect of the present disclosure is a discharge section structure for a centrifugal compressor provided with a scroll flow passage and a discharge flow passage connected to a discharge side of the scroll flow passage. The discharge section structure includes a tongue section provided in a branching section between the scroll flow passage and the discharge flow passage; a first flow passage section having a center of curvature on an origin side of the scroll flow passage; and a second flow passage section communicating with the discharge side of the first flow passage section and having a center of curvature on an outer side of the scroll flow passage. The first flow passage section includes at least a part of the scroll flow passage, the second flow passage section includes at least a part of the discharge flow passage, and the tongue section faces the second flow passage section and is located in the middle of the second flow passage section. 
     Effects of Invention 
     According to an embodiment of the present disclosure, it is possible to suppress the flow of gas from colliding with the tongue section. As a result, it is possible to reduce the loss and to suppress the decrease in efficiency of the discharge section. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a turbocharger including a compressor to which an embodiment of the present disclosure is applied. 
         FIG. 2  is a perspective view of the compressor housing in  FIG. 1 . 
         FIG. 3  is a perspective view illustrating an external form of a compressed gas flow passage. 
         FIG. 4  is a diagram illustrating an external form of a compressed gas flow passage, and is a cross-sectional view taken along a plane orthogonal to a central axis passing through the origin. 
         FIG. 5A  is a diagram illustrating a relation between a winding finish section and the tongue section, and  FIG. 5B  is a cross-sectional view of the flow passage taken along the plane including the central axis. 
         FIG. 6  is a diagram illustrating a flow passage shape from the winding finish section to the discharge flow passage. 
         FIG. 7A  is a diagram illustrating a relation between an angle in the circumferential direction and a distance from the origin to the flow passage center, and  FIG. 7B  is a diagram illustrating a relation between the angle in the circumferential direction and the cross-sectional area of the flow passage. 
         FIG. 8A  is a diagram illustrating a total pressure distribution in the discharge section structure for the present embodiment illustrated in  FIG. 3 , and  FIG. 8B  is a diagram illustrating a total pressure distribution in a discharge section structure of a comparative example illustrated in  FIG. 9 . 
         FIG. 9  is a perspective view illustrating an external form of a compressed gas flow passage according to a comparative example. 
         FIG. 10A  is a diagram illustrating an external form of a compressed gas flow passage according to a modified example, and  FIG. 10B  is a diagram illustrating an external form of a compressed gas flow passage according to another modified example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An aspect of the present disclosure is a discharge section structure for a centrifugal compressor provided with a scroll flow passage and a discharge flow passage connected to a discharge side of the scroll flow passage. The discharge section structure includes a tongue section provided in a branching section between the scroll flow passage and the discharge flow passage, a first flow passage section having a center of curvature on an origin side of the scroll flow passage, and a second flow passage section communicating with the discharge side of the first flow passage section and having a center of curvature on an outer side of the scroll flow passage. The first flow passage section includes at least a part of the scroll flow passage, the second flow passage section includes at least a part of the discharge flow passage, and the tongue section faces the second flow passage section and is located in the middle of the second flow passage section. 
     According to the discharge section structure for the centrifugal compressor, the second flow passage section including at least a part of the discharge flow passage has the center of curvature on the outer side of the scroll flow passage. That is, a curved direction of the second flow passage section is opposite to that of the first flow passage section having the center of curvature on the origin side of the scroll flow passage. The tongue section facing the second flow passage section is located in the middle of the second flow passage section. Since the tongue section is provided in the middle of the second flow passage section that curves outward as described above, the tongue section is located on the outer circumference side of the second flow passage section that forms a curve. Therefore, as compared with a case where the discharge flow passage is straight, the tongue section is located far from the flow, and the flow is hard to collide with the tongue section. Loss can be reduced by the positional relation between the discharge flow passage having such a curved shape and the tongue section. As a result, reduction in efficiency in the discharge section is suppressed. 
     In some embodiments, the tongue section may be located at a central portion of the second flow passage section or on a downstream side of the central portion. According to this configuration, the position of the tongue section becomes farther, and the aforementioned effect can be exhibited more remarkably. 
     In some embodiments, in a cross section orthogonal to the central axis passing through the origin of the scroll flow passage, an angle formed between a wall surface of the tongue section on the scroll flow passage side and a wall surface of the tongue section on the discharge flow passage side may be 50° or more. 
     Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and the repeated description will not be provided. In the present embodiment, in the case of using the terms “upstream” or “downstream”, the terms are based on the flow direction of the gas. 
     A turbocharger  1  to which the discharge section structure for the present embodiment is applied will be described with reference to  FIG. 1 . As illustrated in  FIG. 1 , a turbocharger  1  is applied to, for example, an internal combustion engine of a ship or a vehicle. The turbocharger  1  includes a turbine  2  and a compressor (a centrifugal compressor)  3 . The turbine  2  includes a turbine housing  4 , and a turbine wheel  6  housed in the turbine housing  4 . The turbine housing  4  has a scroll section  4   a  extending in a circumferential direction at an inner circumferential edge portion. The compressor  3  includes a compressor housing  5 , and a compressor wheel  7  housed in the compressor housing  5 . The compressor housing  5  has a scroll section  5   a  extending in the circumferential direction at the inner circumferential edge portion. 
     The turbine wheel  6  is provided at one end of a rotary shaft  14 , and the compressor wheel  7  is provided at the other end of the rotary shaft  14 . The compressor wheel  7  is fixed to the rotary shaft  14  by a nut  16  provided at the other end of the rotary shaft  14 . A bearing housing  13  is provided between the turbine housing  4  and the compressor housing  5 . The rotary shaft  14  is rotatably supported by the bearing housing  13  via a journal bearing  15 . The rotary shaft  14 , the turbine wheel  6 , and the compressor wheel  7  rotate around the rotary axis H as an integral rotating body  12 . 
     An exhaust gas inlet port (not illustrated) and an exhaust gas outlet port  10  is provided in the turbine housing  4 . The exhaust gas (fluid) discharged from an internal combustion engine (not illustrated) flows into the turbine housing  4  through the exhaust gas inlet port, and flows into the turbine wheel  6  through the scroll flow passage  19  in the scroll section  4   a , thereby rotating the turbine wheel  6 . Thereafter, the exhaust gas flows out of the turbine housing  4  through the exhaust gas outlet port  10 . 
     A suction port  9  and a discharge port  11  are provided in the compressor housing  5  (see  FIG. 2 ). When the turbine wheel  6  rotates as described above, the compressor wheel  7  rotates via the rotary shaft  14 . The rotating compressor wheel  7  sucks and compresses outside air through the suction port  9 , and discharges the outside air from the discharge port through the scroll flow passage  21  in the scroll section  5   a . The compressed air discharged from the discharge port  11  is supplied to the aforementioned internal combustion engine. 
     Next, the compressor housing  5  to which the discharge section structure of this embodiment is applied will be described with reference to  FIGS. 2 to 4 . As illustrated in  FIG. 2 , the compressor housing  5  includes a spiral scroll section  5   a , a cylindrical suction tube  5   b  provided at the center of the scroll section  5   a , and a discharge tube  5   c  connected to the scroll section  5   a  and including the aforementioned discharge port  11 . Since the compressor housing  5  includes a novel compressed gas flow passage  20  inside, it is possible to reduce the loss of flow particularly at a large flow rate and to promote an improvement in the efficiency. In particular, in the compressor housing  5 , the shape of the internal flow passage from the scroll section  5   a  to the discharge tube  5   c  is characterized. 
       FIG. 3  is a perspective view illustrating an external form of the compressed gas flow passage  20 .  FIG. 4  is a diagram illustrating the external form of the compressed gas flow passage  20 , and for example, is a cross-sectional view taken along a plane orthogonal to the rotary axis H (central axis) passing through an origin C of the scroll flow passage  21 . As illustrated in  FIG. 3 , the compressed gas flow passage  20  provided in the compressor housing  5  includes a spiral scroll flow passage  21 , and a discharge flow passage  22  connected to the discharge side of the scroll flow passage  21 . Here, the external form of the compressed gas flow passage  20  is, for example, a curve that connects a position (referred to as an outermost circumferential portion) at which the outer wall surface of each flow passage cross section is the maximum in a radial direction and a position (referred to as an innermost circumferential portion) at which the inner wall surface is the minimum in the radial direction. A height (a length from a bottom surface of the compressor housing  5  perpendicular to the rotary axis H) of the outermost circumferential portion and the innermost circumferential portion in the direction of the rotary axis H is not necessarily the same. In this case, for example, even when the height in the direction of the rotary axis H is different, on the plane orthogonal to the rotary axis H passing through the origin C, the outermost circumferential portion and the innermost circumferential portion are projected in the direction of the rotary axis H, and the projected outer circumferential line and the inner circumferential line may be regarded as the external form of the compressed gas flow passage  20 . The air sent by the compressor wheel  7  is collected in the compressed gas flow passage  20  via the diffuser  17  (sec  FIG. 5B ) and discharged from the discharge port  11 . The annular diffuser  17  is a parallel flow passage having a constant height in the direction of the rotary axis H. The diffuser  17  is provided between a space in which the compressor wheel  7  is disposed and the compressed gas flow passage  20  to allow them communicate with each other. An annular diffuser outlet port  21   c  appears on the inner circumferential side of the compressed gas flow passage  20 . The origin C of the scroll flow passage  21  is, for example, a point which serves as a reference of the radial distance from the rotary axis H of the inner wall section  23  or the outer wall section  24  of each flow passage cross section in the scroll flow passage  21 . In this case, the rotary axis H passes through the origin C. The rotary axis H can be determined, for example, on the basis of a structure of the compressor housing  5  or a fitting structure between the compressor housing  5  and the bearing housing  13  (see  FIG. 1 ). The rotary axis H may be an axial center of the inner circumferential surface of the suction tube  5   b  (that is, the suction port  9 ). The rotary axis H may be an axial center of a front end portion on the outer circumferential side of the wall section  5   d  (the wall section facing the scroll flow passage  21 ) of the compressor housing  5  forming the diffuser  17 , that is, the outer circumferential edge  17   a  of the diffuser  17 . The rotary axis H may be an axial center of the fitting section  18  between the compressor housing  5  and the bearing housing  13 . When each of the inner circumferential surface of the suction tube  5   b , the outer circumferential edge  17   a  of the diffuser  17 , and the fitting section  18  has a circular shape, as described above, the rotary axis H can be the axial center (center). When the inner circumferential surface of the suction tube  5   b , the outer circumferential edge  17   a  of the diffuser  17 , and the fitting section  18  do not have a circular shape (when they are not perfect circles), the rotary axis H may be the area center thereof. 
     As illustrated in  FIGS. 2 to 4 , a tongue section  30  is provided at the branching section between the scroll flow passage  21  and the discharge flow passage  22 . A section from a winding start section  21   a  corresponding to the tongue section  30  to a winding finish section  21   b  is the scroll flow passage  21  in the compressed gas flow passage  20 . More specifically, an angle in the circumferential direction from the winding start section  21   a  to the winding finish section  21   b  is, for example, about 300°. The invention is not limited to this aspect, and the angle in the circumferential direction from the winding start section  21   a  to the winding finish section  21   b  may be less than 300° or may be 300° or more. The range of the scroll flow passage  21  can vary depending on the shape of the discharge tube  5   c , the position of the discharge port  11 , the designing method, and the like. The scroll flow passage  21  may be continuous over one cycle (that is, 360°). 
     In the present embodiment, the scroll flow passage  21  starts at the position corresponding to the tongue section  30 , and the scroll flow passage  21  ends at the position of the representative cross section A (see  FIG. 5A ). The flow passage continued to the scroll flow passage  21  is the above-described discharge flow passage  22 . The discharge flow passage  22  may have any shape or size as the position or shape of the discharge port  11  is changed depending on the usage form of the turbocharger  1 . The shapes of the scroll flow passage  21  and the discharge flow passage  22  are determined so that efficiency is enhanced with respect to the predetermined discharge port  11 . 
     As illustrated in  FIG. 4 , the compressed gas flow passage  20  has a second flow passage section F 2  of a shape curved outward within the range of the discharge flow passage  22 . That is, the compressed gas flow passage  20  has a first flow passage section F 1  having a center of curvature on the origin C side (in other words, the inner side), and a second flow passage section F 2  which is provided so as to be continuous with the first flow passage section F 1  and has a center of curvature on the outer side on the scroll flow passage  21 . 
     Here, the curvature of each flow passage section is, for example, determined by the curve which connects the centers of the cross section (center of gravity or centroid, see the center P of  FIG. 5B ), when cutting the compressed gas flow passage  20  on the plane passing through the origin C. The curve connecting the centers is not necessarily positioned on the same plane. For example, the curve connecting the centers may be projected in the axial direction passing through the origin C, and the curvature of each flow passage section may be calculated on the basis of the center line L projected on a plane orthogonal to the axis. 
     The curvature of each flow passage section may be determined on the basis of the portion closest to the origin C of the cross section (see the inner end E of  FIG. 5B ), without being limited to a case where the curvature is determined by the center of the cross section. In contrast, the curvature of each flow passage section may be determined on the basis of the farthest portion from the origin C. 
     The curvature of each flow passage section may vary depending on the location. In the compressed gas flow passage  20 , the first flow passage section F 1  and the second flow passage section F 2  are determined depending on whether the center of the curvature is located inside or outside the scroll flow passage  21 . The above-described center line L includes a first center line L 1  corresponding to the first flow passage section F 1 , and a second center line L 2  corresponding to the second flow passage section F 2 . The center of the curvature of the first center line L 1  is located inside the scroll flow passage  21 , and the center of the curvature of the second center line L 2  is located outside the scroll flow passage  21 . That is, the curvature varies between the first flow passage section F 1  and the second flow passage section F 2  (an inflection point exists). 
     The first flow passage section F 1  includes an inner wall section  23  which roughly constitutes the inner circumferential side of the scroll flow passage  21 , and an outer wall section  24  which roughly constitutes the outer circumferential side of the scroll flow passage  21 . The second flow passage section F 2  includes an outer wall section  25  which roughly constitutes the outer circumferential side of the discharge flow passage  22 , and an inner wall section  26  which roughly constitutes the inner circumferential side of the discharge flow passage  22 . The outer wall section  24  is continuous with the inner wall section  26 . The tongue section  30  is provided between the outer wall section  24  and the outer wall section  25 . 
     The scroll flow passage  21  and the first flow passage section F 1  may be in a coincident range or may be in different ranges. Even when the scroll flow passage  21  and the first flow passage section F 1  are in the different ranges, the scroll flow passage  21  and the first flow passage section F 1  partially overlap each other. The discharge flow passage  22  and the second flow passage section F 2  may be in the coincident range or may be in different ranges. Even when the discharge flow passage  22  and the second flow passage section F 2  are in the different ranges, the discharge flow passage  22  and the second flow passage section F 2  partially overlap each other. In other words, the first flow passage section F 1  includes at least a part of the scroll flow passage  21 . The second flow passage section F 2  includes at least a part of the discharge flow passage  22 . 
     For example, in the example illustrated in  FIG. 4 , one ending points (ending points on the upstream side) of the scroll flow passage  21  and the first flow passage section F 1  coincide with the other, and the other ending points (ending points on the downstream side) do not coincide with each other. Regarding the discharge flow passage  22  and the second flow passage section F 2 , neither one ending point (ending point on the upstream side) nor the other ending point (ending point on the downstream side) coincides with each other. 
     In such a compressed gas flow passage  20 , the tongue section  30  is located in the middle of the second flow passage section F 2  curved outward. The tongue section  30  faces the second flow passage section F 2  (that is, opposite to the second flow passage section F 2 ). In other words, the second flow passage section F 2  includes the position of the tongue section  30 . The discharge flow passage  22  also includes the position of the tongue section  30 . 
     More specifically, the tongue section  30  is located at the central portion of the second flow passage section F 2 . As described above, since the second flow passage section F 2  is curved outward, the outer circumferential portion of the curve is formed by the outer wall section  25 . The inner wall section  23  of the first flow passage section F 1  and the outer wall section  25  of the second flow passage section F 2  are not continuous in the region the tongue section  30  is facing, but there is a space between them. However, it is possible to assume an imaginary surface  27  which smoothly connects the inner wall section  23  and the outer wall section  25 . A convex shaped wall section of the second flow passage section F 2  is formed by the imaginary surface  27  and the outer wall section  25 . Since the end portion on the upstream side of the outer wall section  25  is the front end  30   a  of the tongue section  30 , the imaginary surface  27  passes through the front end  30   a.    
     The tongue section  30  is located at the central portion of the convex shaped wall section. The tongue section  30  may be located on the upstream side of the convex shaped wall section or may be located on the downstream side thereof. At least the tongue section  30  is located on the side closer to the outer circumferential than the imaginary line  28  (in  FIG. 4 , below the imaginary line  28 ) which connects the outer circumferential wall section Wa of the starting point of the second flow passage section F 2  and the outer circumferential wall section Wb of the ending point of the second flow passage section F 2 . In other words, the discharge flow passage  22  exists at a position along the curved shape, but when considering the conventional straight discharge section shape as a standard, the discharge flow passage  22  exists at a more retracted position. The tongue section  30  may be located on the downstream side of the central portion of the second flow passage section F 2 . 
     Further, features of the tongue section  30  will be described from a different point of view. In a cross section orthogonal to the central axis passing through the origin C, an angle formed between the outer wall section  24  which is the wall surface of the tongue section  30  on the side of the scroll flow passage  21 , and the outer wall section  25  which is the wall surface of the tongue section  30  on the discharge flow passage  22  side (the outer wall sections intersect with each other at the front end  30   a ) is 50° or more. The angle of the tongue section  30  may be 30° or more and less than 50°, and may be 50° or more. 
     Further, from another point of view, the compressed gas flow passage  20  can also be explained as follows. Here, a plane perpendicular to the straight line which connects the center of the radius of curvature of the scroll flow passage  21  and the front end  30   a  of the tongue section  30  is assumed. For example, this plane may be considered as a perpendicular bisector between the aforementioned two points. The center of the radius of curvature of the discharge flow passage  22  at the position of the tongue section  30  is located on the opposite side of the center of the radius of curvature of the scroll flow passage  21  across the plane. Such a feature means the same technical matters as the above-described second flow passage section F 2 . 
     Subsequently, features of the compressed gas flow passage  20  based on the representative cross section A will be described with reference to  FIG. 5 . As illustrated in  FIG. 5A , in the compressed gas flow passage  20 , a representative cross section A is taken as a cross section of a position of 360°. The representative cross section A is a cross section that is located at a position shifted upward by several tens of degrees (for example, 30 to 60°) from the tongue section  30  on the basis of the discharge flow passage  22 . The representative cross section A may be a cross section that is located at a position shifted by 50° or 60° to the upstream side of the tongue section  30  on the basis of the discharge flow passage  22 . 
     An example of the representative cross section A will be described. As illustrated in  FIG. 7A , a final region in which the distance R (see  FIG. 5B ) from the origin C to the center P of the compressed gas flow passage  20  increases with a substantially constant inclination, may be the representative cross section A. On the other hand, as illustrated in  FIG. 7B , the final region in which the cross sectional area of the compressed gas flow passage  20  increases with a substantially constant inclination may be the representative cross section A. For example, the representative cross section A may be a cross section at any position in the range of 360 to 390° in the angle in the circumferential direction. The representative cross section A may be a cross section of the position of 360° in the angle in the circumferential direction. 
     In the compressed gas flow passage  20 , the direction which connects the origin C and the representative cross section A is defined as a Y-axis direction, and the direction orthogonal to the plane including the origin C and the representative cross section A is defined as a X-axis direction. In this case, as illustrated in  FIG. 6 , when looking at the change tendency of the value in the Y direction to the X direction after the winding finish section  21   b  corresponding to the representative cross section A, the distance from the X-axis to the center P of the flow passage cross section, and the distance from the X-axis to the inner end E which is a portion closest to the X-axis have a shape protruding downward. 
     According to the discharge section structure of related art, in many cases, the straight flow passage shape was often formed from the winding finish section  21   b  toward the discharge port  11 . That is, as illustrated by a broken line in  FIG. 6 , a linear shape was often obtained. In contrast, in the compressed gas flow passage  20  of the present embodiment, a flow passage has a downward protruding shape. This feature means the same technical matters as the above-described second flow passage section F 2 . 
     The discharge section structure of the compressor housing  5  and the conventional discharge section structure described above were evaluated by fluid analysis, and the following results were obtained.  FIG. 8A  is a diagram illustrating the total pressure distribution in the discharge section structure for the present embodiment, and  FIG. 8B  is a diagram illustrating the total pressure distribution in the discharge section structure of the comparative example illustrated in  FIG. 9 . In this figure, the total pressure in the flow passage is indicated by shading. In other words, the total pressure is higher for areas that are displayed thinner, and the total pressure is lower for areas that are displayed darker. 
     In the compressed gas flow passage  20  according to the present embodiment, it is understood that the reduction in total pressure is suppressed in the second flow passage section F 2 . 
     The conventional compressed gas flow passage  120  illustrated in  FIG. 9  includes a scroll flow passage  121  and a discharge flow passage  122 , and the discharge flow passage  122  has a straight shape. The shape of the flow passage from the winding start section  121   a  to the winding finish section  121   b , the thickness of the diffuser outlet port  121   c , and the like are not largely different from those of the compressed gas flow passage  20  of the present embodiment, but the position and shape of the tongue section  130  are different. That is, the tongue section  130  is located at a high position in the Y direction with respect to the winding finish section  121   b . It is needless to say that the second flow passage section F 2  is not formed in the compressed gas flow passage  120 . 
     As illustrated in  FIG. 8B , in the compressed gas flow passage  120 , the flow from the diffuser outlet port  121   c  collides with the tongue section  130 , and the total pressure lowers in a wide range around the tongue section  130 . As a result, a loss occurs in the discharge port  111 . 
     From the above, the effectiveness of the compressed gas flow passage  20  in the efficiency aspect was checked. 
     According to the discharge section structure of the compressor  3  described above, the second flow passage section F 2  including at least a part of the discharge flow passage  22  has the center of curvature on the outer side of the scroll flow passage  21 . That is, the curved direction of the second flow passage section F 2  is opposite to that of the first flow passage section F 1  having the center of curvature on the origin C side of the scroll flow passage  21 . The tongue section  30  facing the second flow passage section F 2  is located in the middle of the second flow passage section F 2 . Since the tongue section  30  is provided in the middle of the second flow passage section F 2  that curves outward as described above, the tongue section  30  is located on the outer circumference side of the second flow passage section F 2  that forms a curve. Therefore, as compared with a case where the discharge flow passage  22  is straight, the tongue section  30  is located far from the flow, and the flow is hard to collide with the tongue section  30 . Due to the positional relation between the discharge flow passage  22  having such a curved shape and the tongue section  30 , the loss is reduced. As a result, reduction in efficiency at the discharge port  11  is suppressed. This effect is particularly effectively exhibited on the side of the larger flow rate than the flow rate indicating the peak efficiency. In the conventional straight discharge section shape, the efficiency tends to decrease as the flow rate increases. However, in this embodiment, this point is improved. 
     When the tongue section  30  is located at the central portion of the second flow passage section F 2  or on the downstream side of the central portion, the position of the tongue section  30  becomes farther than the representative cross section. A, and the aforementioned effect can be more remarkably exhibited. 
     When the angle formed between the outer wall section  24  which is the wall surface of the tongue section  30  on the side of the scroll flow passage  21  and the outer wall section  25  which is the wall surface of the tongue section  30  on the side of the discharge flow passage  22  is formed to be 50° or more, by smoothly connecting the diffuser flow passage (scroll flow passage) and the discharge flow passage, for example, disturbance of the flow flowing in from the diffuser flow passage is reduced, and the aforementioned effect can be more remarkably exhibited. 
     Although the embodiments of the present disclosure have been described above, the present invention is not limited to the above embodiments. For example, various modified aspects illustrated in  FIG. 10  may be adopted. As illustrated in  FIG. 10A , even when the position of the discharge port  11  is set to be low in the Y direction with respect to the representative cross section A, it is possible to adopt a compressed gas flow passage  40  which includes a scroll flow passage  41  extending from a winding start section  41   a  to a winding finish section  41   b , and a discharge flow passage  42  connected to the scroll flow passage  41 . On the downstream side of the representative cross section A, a gently curved second flow passage section F 2  is formed, and the tongue section  30  facing the second flow passage section F 2  is located in the middle of the second flow passage section F 2 . 
     As illustrated in  FIG. 10B , even when the position of the discharge port  11  is set to be higher than the representative cross section A in the Y direction, it is possible to adopt a compressed gas flow passage  50  which includes a scroll flow passage  51  extending from a winding start section  51   a  to a winding finish section  51   b , and a discharge flow passage  52  connected to the scroll flow passage  51 . A second flow passage section F 2  is formed on the downstream side of the representative cross section A, and the tongue section  30  facing the second flow passage section F 2  is located in the middle of the second flow passage section F 2 . 
     Even with such compressed gas flow passages  40  and  50 , the same operation and effect as illustrated in  FIG. 8A  are exhibited. 
     The first flow passage section F 1  and the second flow passage section F 2  are not limited to a case where they are continuous. A straight flow passage section may be provided over a predetermined length between the first flow passage section F 1  and the second flow passage section F 2 . In this case, there is no inflection point, and the first flow passage section F 1  and the second flow passage section F 2  communicate with each other by the straight flow passage section. 
     The shape of the discharge port is not limited to the case of extending in the substantially circumferential direction of the scroll flow passage. For example, a shape curved in a paper surface direction may be provided. In this case, for example, on the basis of the shape projected on the cross section cut along the plane orthogonal to the central axis passing through the origin C, similarly to the above-described embodiment, it is possible to adopt a scroll flow passage which includes a scroll flow passage extending from the winding start section to the winding finish section, and a discharge flow passage connected to the scroll flow passage. 
     The present invention is not limited to the turbocharger  1 , and can be applied to any centrifugal compressor. Further, as viewed from the suction port  9  of the centrifugal compressor  3 , winding of the scroll flow passage is not limited to the case of being formed from the winding start section to the winding finish section in a clockwise direction. For example, as viewed from the suction port  9 , a spiral of the scroll flow passage may be formed from the winding start section to the winding finish section in a counterclockwise direction. 
     INDUSTRIAL APPLICABILITY 
     According to some aspects of the present disclosure, it is possible to suppress the flow of gas from colliding with the tongue section, and as a result, it is possible to reduce the loss and to suppress the decrease in efficiency in the discharge section. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  turbocharger 
               3  compressor (centrifugal compressor) 
               20  compressed gas flow passage 
               21  scroll flow passage 
               22  discharge flow passage 
               23  inner wall section 
               24  outer wall section 
               25  outer wall section 
               26  inner wall section 
               30  tongue section 
               40  compressed gas flow passage 
               41  scroll flow passage 
               42  discharge flow passage 
               50  compressed gas flow passage 
               51  scroll flow passage 
               52  discharge flow passage 
             C origin 
             F 1  first flow passage section 
             F 2  second flow passage section 
             L center line