Centrifugal compressor casing, centrifugal compressor, and turbocharger

Abstract

This centrifugal compressor casing is provided with a scroll part that forms a scroll flow path in which the volute beginning and the volute end of the scroll flow path merge. The scroll part includes: an outer-side wall surface that demarcates the radially outer side of the scroll flow path; and an inner-side wall surface that demarcates the radially inner side of the scroll flow path. The outer-side wall surface has, in an axially orthogonal cross-section, on the volute-beginning side of the scroll flow path: an outer-side concave arc section constituted in a concave arc form that is recessed toward the radially outer side; an outer-side convex arc section constituted in a convex arc form that protrudes toward the radially inner side on the scroll flow-path upstream side from the outer-side concave arc section, and on the radially outer side; and an outer-side inflection point provided in the location where the outer-side concave arc section and the outer-side convex arc section join.

Description

Centrifugal compressor casing, centrifugal compressor and turbocharger

[0001] This disclosure relates to a casing for a centrifugal compressor, a centrifugal compressor including the casing, and a turbocharger. This application claims priority to Japanese Patent Application No. 2023-202297, filed with the Japan Patent Office on November 30, 2023, the contents of which are incorporated herein by reference.

[0002] A turbocharger includes, for example, a centrifugal compressor provided at one end of a rotating shaft and a turbine provided at the other end of the rotating shaft. The turbocharger is configured to rotate a turbine rotor using the energy of exhaust gas sent from an engine, compress gas with the centrifugal compressor impeller rotating together with the turbine rotor, and supply the compressed gas to the engine. A scroll passage is formed in the casing of the centrifugal compressor to guide the gas compressed by the impeller (see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2012-202323

[0004] Conventionally, as shown in the invention described in Patent Document 1, it has been common to assume a gas flow that flows in the rotation direction of the impeller and determine the flow path shape of the scroll flow path so that the gradient of acceleration and deceleration of this gas flow is appropriate.

[0005] When an unsteady pressure change occurs, such as pressure pulsation generated in equipment located downstream of the scroll passage, such as an engine, the gas in the scroll passage is not limited to flowing in the direction of rotation of the impeller, but a backflow may occur in the opposite direction to the rotation of the impeller. For this reason, conventional technologies may not be able to suppress the pressure loss caused by the backflow in the gas flowing through the scroll passage.

[0006] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a casing for a centrifugal compressor that can suppress pressure loss of compressed gas flowing through a scroll passage of the centrifugal compressor, and a centrifugal compressor and a turbocharger that include the casing.

[0007] A casing of a centrifugal compressor according to at least one embodiment of the present disclosure is a casing of a centrifugal compressor configured to be able to accommodate an impeller, and comprising a scroll section forming a scroll passage through which compressed gas that has passed through the impeller flows in a circumferential direction of the impeller, the scroll section including an outer wall surface that defines the outer side of the scroll passage in a radial direction, and an inner wall surface that defines the inner side of the scroll passage in the radial direction, and the outer wall surface has, in a cross section perpendicular to the axial direction, an outer concave arc section formed in a concave arc shape that is concave outward in the radial direction, an outer convex arc section formed upstream of the scroll passage than the outer concave arc section, and formed in a convex arc shape that is convex inward in the radial direction outside the outer concave arc section, and an outer inflection point provided at a connection position between the outer concave arc section and the outer convex arc section, on the winding start side of the scroll passage.

[0008] A centrifugal compressor according to at least one embodiment of the present disclosure includes: a casing for the centrifugal compressor; and the impeller rotatably housed in the casing of the centrifugal compressor.

[0009] A turbocharger according to at least one embodiment of the present disclosure includes the centrifugal compressor.

[0010] According to at least one embodiment of the present disclosure, there are provided a casing for a centrifugal compressor capable of suppressing pressure loss of compressed gas flowing through a scroll passage of the centrifugal compressor, a centrifugal compressor including the casing, and a turbocharger.

[0011] FIG. 1 is a schematic diagram of an internal combustion engine system including a turbocharger according to an embodiment of the present disclosure; FIG. 2 is a schematic cross-sectional view taken along an axis of the turbocharger according to an embodiment of the present disclosure; FIG. 3 is a schematic perspective view of a scroll section according to an embodiment of the present disclosure; FIG. 4 is a schematic cross-sectional view taken perpendicular to the axial direction of a centrifugal compressor according to a comparative example; FIG. 5 is a schematic cross-sectional view taken perpendicular to the axial direction of a centrifugal compressor according to an embodiment of the present disclosure; FIG. 6 is a schematic cross-sectional view taken perpendicular to the axial direction of a centrifugal compressor according to an embodiment of the present disclosure, showing a compressed gas flow near a confluence of scroll flow passages of the centrifugal compressor shown in FIG. 4; FIG. 7 is a schematic cross-sectional view taken perpendicular to the axial direction of a centrifugal compressor according to an embodiment of the present disclosure, showing a compressed gas flow near a confluence of scroll flow passages of the centrifugal compressor shown in FIG. 5;

[0012] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure.

[0013] In the following embodiments, the centrifugal compressor of the present disclosure will be described as being provided in a turbocharger, but the centrifugal compressor of the present disclosure may also be an electric centrifugal compressor, etc. Furthermore, the gas to be compressed by the centrifugal compressor of the present disclosure does not need to be limited to air. In other words, the centrifugal compressor of the present disclosure may be configured as a single centrifugal compressor or may be configured in combination with mechanisms or devices other than a turbine as long as it is capable of compressing and sending gas. Furthermore, there is no need to limit its use, etc.

[0014] (Centrifugal Compressor, Turbocharger) Fig. 1 is a schematic diagram of an internal combustion engine system 11 including a turbocharger 10 according to an embodiment of the present disclosure. Fig. 2 is a schematic cross-sectional view taken along an axis line LA of the turbocharger 10 according to an embodiment of the present disclosure. As shown in Figs. 1 and 2, a centrifugal compressor 1 according to some embodiments includes an impeller 2 and a casing 3 configured to rotatably house the impeller 2. The centrifugal compressor 1 according to the present disclosure can be mounted on a turbocharger (supercharger) 10 for, for example, an automobile, a marine vehicle, or an industrial application (e.g., for land-based power generation).

[0015] 1 and 2, the turbocharger 10 includes a centrifugal compressor 1 and a turbine 12 configured to drive the centrifugal compressor 1. The turbine 12 includes a turbine rotor 14 that rotates by the energy of exhaust gas discharged from an internal combustion engine 13 (engine, see FIG. 1), and a turbine housing 15 configured to rotatably accommodate the turbine rotor 14.

[0016] The turbocharger 10 further includes a rotating shaft 16 having the impeller 2 connected to one end thereof and the turbine rotor 14 connected to the other end thereof, and a bearing 17 that rotatably supports the rotating shaft 16 between the impeller 2 and the turbine rotor 14. The turbocharger 10 may further include a bearing housing 18 that is disposed between the casing 3 and the turbine housing 15 and is configured to house the rotating shaft 16 and the bearing 17.

[0017] The turbine 12 (turbocharger 10) is configured to rotate a turbine rotor 14 by using the energy of exhaust gas discharged from an internal combustion engine 13. The impeller 2 is coaxially connected to the turbine rotor 14 via a rotating shaft 16, and therefore rotates around an axis LA together with the turbine rotor 14 and the rotating shaft 16. The centrifugal compressor 1 (turbocharger 10) is configured to suck air (gas) into the casing 3, compress the air, and send the compressed air to the internal combustion engine 13 as the impeller 2 rotates around the axis LA.

[0018] The compressed air sent from the centrifugal compressor 1 to the internal combustion engine 13 is used for combustion in the internal combustion engine 13. Exhaust gas generated by the combustion in the internal combustion engine 13 is sent from the internal combustion engine 13 to the turbine 12, causing the turbine rotor 14 to rotate.

[0019] Hereinafter, the direction in which the axis LA of the impeller 2 extends will be referred to as the axial direction of the impeller 2, the direction perpendicular to the axis LA will be referred to as the radial direction of the impeller 2, and the circumferential direction around the axis LA will be referred to as the circumferential direction of the impeller 2. Hereinafter, the axial direction, radial direction, and circumferential direction of the impeller 2 may be abbreviated to simply as the axial direction, radial direction, and circumferential direction.

[0020] 2 , the turbine rotor 14 includes a hub 141 having a substantially truncated cone shape and a plurality of turbine blades 142 provided on the outer peripheral surface of the hub 141. The hub 141 and the plurality of turbine blades 142 are provided to be rotatable integrally with the rotating shaft 16 about the axis LA. The turbine rotor 14 is configured to guide exhaust gas introduced from the outside in the radial direction of the turbine rotor 14 to the front side of the turbine rotor 14 along the axial direction of the turbine rotor 14.

[0021] (Turbine Housing) A turbine scroll passage 151 for guiding exhaust gas discharged from the internal combustion engine 13 to the turbine rotor 14, and an exhaust gas discharge passage 152 for discharging exhaust gas that has passed through the turbine rotor 14 to the outside of the turbine housing 15 are formed inside the turbine housing 15. The turbine scroll passage 151 is provided on the outer periphery of the turbine rotor 14 and consists of a spiral passage extending along the circumferential direction of the turbine rotor 14. The exhaust gas discharge passage 152 extends along the axial direction of the turbine rotor 14.

[0022] Exhaust gas discharged from the internal combustion engine 13 is guided to the turbine rotor 14 via the turbine scroll passage 151, causing the turbine rotor 14 to rotate. The exhaust gas that has passed through the turbine rotor 14 is discharged to the outside of the turbine housing 15 via the exhaust gas discharge passage 152.

[0023] (Impeller) As shown in FIG. 2 , the impeller 2 includes a hub 21 having a generally truncated cone shape and a plurality of impeller vanes 23 provided on an outer peripheral surface 22 of the hub 21. The plurality of impeller vanes 23 are spaced apart from one another in the circumferential direction around the axis LA. The hub 21 is fixed to one end of the rotary shaft 16, so that the hub 21 and the plurality of impeller vanes 23 are rotatable integrally with the rotary shaft 16 about the axis LA of the impeller 2. The impeller 2 is configured to guide air introduced along the axial direction of the impeller 2 to the outside in the radial direction of the impeller 2. As shown in FIG. 3 , a gap (clearance) is formed between the tip ends (tips) 24 of the plurality of impeller vanes 23 and a shroud surface 31 that is convexly curved so as to face the tip ends 24. In other words, the impeller 2 is an open-type impeller that does not include an annular member covering the tip ends 24.

[0024] (Casing) As shown in Fig. 2, the casing 3 includes a scroll section 4 that forms a scroll passage 40. The scroll passage 40 is provided on the outer periphery of the impeller 2 along the circumferential direction of the impeller 2. The scroll passage 40 allows compressed gas that has passed through the impeller 2 to flow. The scroll passage 40 is made up of a spiral passage that extends along the circumferential direction of the impeller 2. The casing 3 has the shroud surface 31 described above. Inside the casing 3, a gas introduction passage 32, a diffuser passage 33, and the scroll passage 40 described above are formed.

[0025] The gas introduction passage 32 is a passage for taking in air from outside the casing 3 and guiding the taken-in air (gas) to the impeller 2. The gas introduction passage 32 is provided on one side (forward side) of the impeller 2 in the axial direction of the impeller 2, and extends along the axial direction of the impeller 2. By rotating the impeller 2, air is taken in from outside the casing 3 into the gas introduction passage 32, and the taken-in air flows through the gas introduction passage 32 toward the other side (rear side) in the axial direction of the impeller 2 and is guided to the impeller 2.

[0026] The diffuser passage 33 is a passage for guiding air that has passed through the impeller 2 and been compressed by the impeller 2 to the scroll passage 40. The diffuser passage 33 is provided between the scroll passage 40 and the impeller 2 in the radial direction of the impeller 2, and extends along the radial direction of the impeller 2. The diffuser passage 33 communicates with the scroll passage 40 at an outlet (communication port) 34 provided at the downstream end (outer peripheral end) of the diffuser passage 33. The compressed air (compressed gas) compressed by the impeller 2 flows into the diffuser passage 33, flows through the diffuser passage 33 toward the outside in the radial direction of the impeller 2, and is guided to the scroll passage 40.

[0027] FIG. 3 is a schematic perspective view of the scroll section 4 in an embodiment of the present disclosure. FIG. 4 is a schematic cross-sectional view perpendicular to the axial direction of a centrifugal compressor 01 according to a comparative example. FIG. 5 is a schematic cross-sectional view perpendicular to the axial direction of the scroll passage 40 of the centrifugal compressor 1 according to an embodiment of the present disclosure, near a confluence portion 403. As shown in FIGS. 3 to 5 , the scroll passage 40 is configured so that the start of the winding 401 and the end of the winding 402 of the scroll passage 40 converge. In other words, the scroll passage 40 has a confluence portion 403 where the start of the winding 401 and the end of the winding 402 converge. The scroll passage 40 extends from the start of the winding 401 to the end of the winding 402 along the rotation direction of the impeller 2 (clockwise in FIGS. 4 and 5 , on one side of the circumferential direction). Hereinafter, the connection position of the beginning of the winding 401 with the confluence 403 is defined as the upstream end, the upstream side in the rotation direction of the impeller 2 is defined as the upstream side of the scroll flow path 40, and the downstream side in the rotation direction of the impeller 2 is defined as the downstream side of the scroll flow path 40.

[0028] FIG. 3 shows a cross section CS1 of the scroll passage 40 perpendicular to the axial direction of the impeller 2, a cross section CS2 along the axial direction of the impeller 2 at the beginning of the winding 401 of the scroll passage 40 (cross section perpendicular to the circumferential direction), and a cross section CS3 along the axial direction of the impeller 2 at the end of the winding 402 of the scroll passage 40 (cross section perpendicular to the circumferential direction).

[0029] 3 to 5 , the scroll section 4 includes, in a cross section perpendicular to the axial direction of the impeller 2, an outer wall surface 5 that defines the radial outside of the scroll passage 40 and an inner wall surface 6 that defines the radial inside of the scroll passage 40. The outer wall surface 5 includes a first outer wall surface 5A that defines the radial outside of the winding start 401 and a second outer wall surface 5B that defines the radial outside of the winding end 402. The inner wall surface 6 includes a first inner wall surface 6A that defines the radial inside of the winding start 401 and a second inner wall surface 6B that defines the radial inside of the winding end 402. As shown in FIG. 3 , the upstream end of the first outer wall surface 5A is connected to the second inner wall surface 6B.

[0030] When an unsteady pressure change occurs, such as pressure pulsation generated in equipment arranged downstream of the scroll passage 40 (downstream of the end of the spiral 402), such as an engine (internal combustion engine 13), the gas in the scroll passage 40 is not limited to flowing in the direction of rotation of the impeller 2, and a backflow may occur in the opposite direction to the rotation direction of the impeller 2, as shown in Figures 4 and 5 . As shown in Figures 4 and 5 , a backflow through the scroll passage 40, i.e., a flow flowing in the opposite direction (counterclockwise) to the rotation direction of the impeller 2, is referred to as FA, and a forward flow through the scroll passage 40, i.e., a flow flowing in the direction of rotation of the impeller 2, is referred to as FB. These flows FA and FB may simultaneously exist in the scroll passage 40. The flow FA is generated on the start of the spiral 401 side of the scroll passage 40.

[0031] 5 , in the casing 3 of the centrifugal compressor 1 according to some embodiments, the outer wall surface 5 has, in a cross section perpendicular to the axial direction, an outer concave arc portion 51, an outer convex arc portion 52, and an outer inflection point 53 on the side of the start of winding 401 of the scroll flow passage 40. In the illustrated embodiment, the first outer wall surface 5A has the outer concave arc portion 51, the outer convex arc portion 52, and the outer inflection point 53.

[0032] (Outer concave arc portion) In the cross section shown in Fig. 5, the outer concave arc portion 51 is formed in a concave arc shape that is concave outward in the radial direction. In the embodiment shown in Fig. 5, the outer concave arc portion 51 is formed in a concave arc shape having a predetermined curvature and curvature radius R1. Note that in some embodiments, the outer concave arc portion 51 may be formed of multiple curves with different curvatures (curvature radii), such as a semi-elliptical shape.

[0033] (Outer Convex Arc Portion) In the cross section shown in Fig. 5 , the outer convex arc portion 52 is formed upstream of the outer concave arc portion 51 in the scroll flow passage 40. The outer convex arc portion 52 is formed in a convex arc shape that is convex radially inward and radially outward of the outer concave arc portion 51. In the embodiment shown in Fig. 5 , the outer convex arc portion 52 is formed in a concave arc shape having a predetermined curvature and curvature radius R2. Note that in some embodiments, the outer convex arc portion 52 may be formed by a plurality of curves with different curvatures (curvature radii), such as a semi-elliptical shape.

[0034] In the illustrated embodiment, the upstream end 50 of the outer convex arc portion 52 is connected to the second inner wall surface 6B, and the downstream end of the outer convex arc portion 52 is connected to the upstream end of the outer concave arc portion 51. The distance of the outer convex arc portion 52 from the scroll center CS in the scroll flow path 40 increases from the downstream end to the upstream end. In the embodiment shown in Fig. 5, the scroll center CS is located on the axis LA.

[0035] (Outer inflection point) The outer inflection point 53 is an inflection point provided at a connection position between the outer concave arc portion 51 and the outer convex arc portion 52. Specifically, the outer inflection point 53 is provided at a connection position between the upstream end of the outer concave arc portion 51 and the downstream end of the outer convex arc portion 52.

[0036] As shown in FIG. 4 , the centrifugal compressor 01 according to the comparative example differs from the centrifugal compressor 1 shown in FIG. 5 in that the outer wall surface 5 does not have the outer convex arc portion 52 and the outer inflection point 53.

[0037] 6 is an explanatory diagram for explaining the flow of compressed gas near the confluence 403 of the scroll passage 40 of the centrifugal compressor 01 shown in FIG. 4. FIG. 7 is an explanatory diagram for explaining the flow of compressed gas near the confluence 403 of the scroll passage 40 of the centrifugal compressor 1 shown in FIG. 5. As shown in FIG. 6, in the scroll passage 40 of the centrifugal compressor 01, a flow FA that flows backward through the beginning of the spiral 401 of the scroll passage 40 and passes through the confluence 403 has a relatively large curvature in the portion including the confluence 403. After passing through the confluence 403, the flow FA is pushed and bent by a flow FB that flows forward through the scroll passage 40. As a result, friction loss occurring between the flow FA and the flow FB becomes a pressure loss of the gas flowing through the scroll passage 40.

[0038] The outer wall surface 5 of the centrifugal compressor 1 shown in Figure 5 has an outer convex arc portion 52 on the side of the beginning of the spiral 401 of the scroll passage 40. This allows the flow path cross-sectional area of ​​the scroll passage 40 (the beginning of the spiral 401) facing the outer convex arc portion 52 to be enlarged, thereby increasing the flow rate of the flow FA flowing backward through the scroll passage 40 and passing through the joining portion 403 of the scroll passage 40. Enlarging the flow path cross-sectional area of ​​the scroll passage 40 (the beginning of the spiral 401) facing the outer convex arc portion 52 allows the flow FA passing through the joining portion 403 to be decelerated. Furthermore, the radius of curvature RF1 (see Figure 5) of the portion including the joining portion 403 of the flow FA of the centrifugal compressor 1 shown in Figure 5 is larger than the radius of curvature RF2 (see Figure 4) of the portion including the joining portion 403 of the flow FA of the centrifugal compressor 01 according to the comparative example. 5, the curvature of the portion of the flow FA including the confluence portion 403 is smaller than that of the centrifugal compressor 01 according to the comparative example. This makes it possible to decelerate the flow FA passing through the confluence portion 403 and to make the curvature relatively small, thereby suppressing friction loss between the flow FB flowing forward through the scroll passage 40 and the flow FA.

[0039] FIG. 8 is an explanatory diagram for explaining the efficiency reduction in the scroll section 4 of the centrifugal compressor 1 according to an embodiment of the present disclosure. The graph shows time T on the horizontal axis and the percentage DE of the efficiency reduction in the scroll section 4, which is the percentage DE of the efficiency reduction in the vicinity of the confluence section 403, on the vertical axis. The period from time T0 to time T1 is the same period as one cycle of the internal combustion engine 13. In FIG. 8, the centrifugal compressor 01 according to the comparative example shown in FIG. 4 is indicated by a solid line, and the centrifugal compressor 1 according to the present embodiment shown in FIG. 5 is indicated by a dotted line. As shown in FIG. 8, in the centrifugal compressor 01 and the centrifugal compressor 1, the percentage DE is maximized during the period when the backflow FA occurs. The centrifugal compressor 1 has a smaller percentage DE than the centrifugal compressor 01. The centrifugal compressor 1 can reduce the pressure loss of the gas flowing through the scroll flow path 40 more than the comparative example and the conventional example described in Patent Document 1.

[0040] According to the above configuration, the outer wall surface 5 has the outer convex arc portion 52 on the side of the start of spiraling 401 of the scroll passage 40, so that the flow path cross-sectional area of ​​the scroll passage 40 facing the outer convex arc portion 52 can be enlarged, and the flow rate of the flow FA flowing backward through the scroll passage 40, passing through the confluence portion 403 of the scroll passage 40, can be increased. As a result, the flow FA passing through the confluence portion 403 can be decelerated and the curvature can be made relatively small, so that friction loss between the flow FA and the flow FB flowing forward through the scroll passage 40 is suppressed, and the pressure loss of the gas flowing through the scroll passage 40 can be reduced more than in the past.

[0041] 5 , the (circumferential) angular position θ around the scroll center CS of the above-described scroll passage 40 is defined as 0° at a confluence 403 of the scroll passage 40, where the winding start 401 and winding end 402 of the scroll passage 40 are located, and the angle gradually increases from the confluence 403 toward the downstream side of the scroll passage 40. Specifically, the position at which the upstream end of the first outer wall surface 5A and the second inner wall surface 6B, which form the outer circumferential end of the confluence 403, are connected is defined as 0°.

[0042] In the centrifugal compressor 1 according to some embodiments, in the cross section shown in Fig. 5, the outer inflection point 53 is located within a range where the angular position θ is from 0 degrees to 30 degrees. It is preferable that the outer inflection point 53 is located within a range where the angular position θ is from 10 degrees to 30 degrees.

[0043] The inventors have found that pressure pulsations occurring in equipment arranged downstream of the scroll passage 40, such as an engine (internal combustion engine 13), cause a flow FA that flows backward through the scroll passage 40 when the angular position θ is between 0 degrees and approximately 30 degrees.

[0044] According to the above configuration, by providing the outer inflection point 53, i.e., the downstream end of the outer convex arc portion 52, within the angular position θ range of 0 to 30 degrees, it is possible to increase the cross-sectional area of ​​the scroll passage 40 through which the flow FA flowing backward through the scroll passage 40 passes, and to appropriately suppress the pressure loss of the compressed gas flowing through the scroll passage 40. Note that the outer inflection point 53 may be provided within a range where the angular position θ exceeds 30 degrees, but in this case, the volume of the scroll passage 40 would be excessively enlarged, which is not preferable from the viewpoint of mountability on the engine (internal combustion engine 13).

[0045] In the centrifugal compressor 1 according to some embodiments, in the cross section shown in FIG. 5 , the radius of curvature R2 of the outer convex arc portion 52 is smaller than the radius of curvature R1 of the outer concave arc portion 51 (R2<R1). In this case, the curve of the outer convex arc portion 52 becomes sharper than when the radius of curvature R2 of the outer convex arc portion 52 is larger than the radius of curvature R1 of the outer concave arc portion 51 (R2>R1), and the flow path cross-sectional area of ​​the scroll flow path 40 facing the outer convex arc portion 52 can be increased. This makes it possible to appropriately suppress pressure loss of the compressed gas flowing through the scroll flow path 40. Note that in some embodiments, the radius of curvature R2 of the outer convex arc portion 52 may be larger than the radius of curvature R1 of the outer concave arc portion 51.

[0046] 9 and 10 are schematic cross-sectional views perpendicular to the axial direction near the confluence portion 403 of the scroll passage 40 of the centrifugal compressor 1 according to one embodiment of the present disclosure. In the casing 3 of the centrifugal compressor 1 according to some embodiments, as shown in Fig. 9 and 10 , the inner wall surface 6 described above has an inner convex arc portion 61, an inner concave arc portion 62, and an inner inflection point 63 on the side of the start of winding 401 of the scroll passage 40 in a cross section perpendicular to the axial direction. In the illustrated embodiment, the first inner wall surface 6A described above has the inner convex arc portion 61, the inner concave arc portion 62, and the inner inflection point 63.

[0047] (Inner convex arc portion) The inner convex arc portion 61 is formed in a convex arc shape that is convex outward in the radial direction in a cross section perpendicular to the axial direction as shown in Figures 9 and 10. In the embodiment shown in Figures 9 and 10, the inner convex arc portion 61 is formed in a convex arc shape having a predetermined curvature and curvature radius R3. Note that in some embodiments, the inner convex arc portion 61 may be formed of multiple curves with different curvatures (curvature radii), such as a semi-elliptical shape.

[0048] (Inner concave arc portion) In the cross section shown in Figures 9 and 10, the inner concave arc portion 62 is formed upstream of the inner convex arc portion 61 in the scroll flow passage 40. The inner concave arc portion 62 is formed in a concave arc shape that is concave radially inward and radially inward of the inner convex arc portion 61. In the embodiment shown in Figures 9 and 10, the inner concave arc portion 62 is formed in a concave arc shape having a predetermined curvature and curvature radius R4. Note that in some embodiments, the inner concave arc portion 62 may be formed by a plurality of curves with different curvatures (curvature radii), such as a semi-elliptical shape.

[0049] In the illustrated embodiment, the upstream end of the inner concave arc portion 62 is connected to the second inner wall surface 6B, and the downstream end of the inner concave arc portion 62 is connected to the upstream end of the inner convex arc portion 61. The inner concave arc portion 62 may be configured such that the distance from the scroll center CS in the scroll flow path 40 decreases from the downstream end to the upstream end. In the embodiment shown in Figures 9 and 10, the scroll center CS is located on the axis LA.

[0050] (Inner inflection point) The inner inflection point 63 is an inflection point provided at the connection position between the inner convex arc portion 61 and the inner concave arc portion 62. Specifically, the inner inflection point 63 is provided at the connection position between the upstream end of the inner convex arc portion 61 and the downstream end of the inner concave arc portion 62.

[0051] According to the above configuration, the inner wall surface 6 has the inner concave arc portion 62 on the side of the start of winding 401 of the scroll passage 40, so that the flow path cross-sectional area of ​​the scroll passage 40 facing the inner concave arc portion 62 can be enlarged, thereby increasing the flow rate of the flow FA flowing backward through the scroll passage 40 and passing through the confluence portion 403 of the scroll passage 40. Enlarging the flow path cross-sectional area of ​​the scroll passage 40 (the start of winding 401) facing the inner concave arc portion 62 can decelerate the flow FA passing through the confluence portion 403. This reduces the friction loss between the flow FB flowing forward through the scroll passage 40 and the flow FA, and reduces the pressure loss of the gas flowing through the scroll passage 40 more than ever before.

[0052] In the casing 3 of the centrifugal compressor 1 according to some embodiments, as shown in FIG. 9 , the inner wall surface 6 has the inner convex arc portion 61, the inner concave arc portion 62, and the inner inflection point 63 on the side of the start of winding 401 of the scroll passage 40 in a cross section perpendicular to the axial direction. The outer wall surface 5 does not have the outer convex arc portion 52 or the outer inflection point 53 in a cross section perpendicular to the axial direction. According to the above configuration, considering the law of conservation of angular momentum, the effect of decelerating the flow FA is smaller than in the embodiment shown in FIG. 5 . However, since the outer wall surface 5 does not have the outer convex arc portion 52, the casing 3 of the centrifugal compressor 1 according to this embodiment does not deteriorate the mountability to the engine (internal combustion engine 13).

[0053] In the casing 3 of the centrifugal compressor 1 according to some embodiments, as shown in FIG. 10 , the inner wall surface 6 has the inner convex arc portion 61, the inner concave arc portion 62, and the inner inflection point 63 on the side of the start of winding 401 of the scroll passage 40 in a cross section perpendicular to the axial direction. The outer wall surface 5 has the outer concave arc portion 51, the outer convex arc portion 52, and the outer inflection point 53 on the side of the start of winding 401 of the scroll passage 40 in a cross section perpendicular to the axial direction. In the illustrated embodiment, the inner inflection point 63 is located upstream of the outer inflection point 53 in the scroll passage 40 (on the side where the angular position θ is closer to 0 degrees). Note that the inner inflection point 63 may also be located downstream of the outer inflection point 53 in the scroll passage 40.

[0054] In the centrifugal compressor 1 according to some embodiments, in the cross section shown in Figures 9 and 10, the inner inflection point 63 is located within the range of the angular position θ from 0 degrees to 30 degrees. It is preferable that the inner inflection point 63 is located within the range of the angular position θ from 10 degrees to 30 degrees.

[0055] The inventors have found that pressure pulsations occurring in equipment arranged downstream of the scroll passage 40, such as an engine (internal combustion engine 13), cause a flow FA that flows backward through the scroll passage 40 when the angular position θ is between 0 degrees and approximately 30 degrees.

[0056] According to the above configuration, by providing the inner inflection point 63, i.e., the downstream end of the inner concave arc portion 62, within the range where the angular position θ is from 0 to 30 degrees, it is possible to increase the cross-sectional area of ​​the scroll passage 40 through which the flow FA flowing backward through the scroll passage 40 passes, and to appropriately suppress the pressure loss of the compressed gas flowing through the scroll passage 40. Note that the inner inflection point 63 may be provided within a range where the angular position θ exceeds 30 degrees. However, in this case, the volume of the scroll passage 40 would be excessively enlarged, which may make it difficult for the flow FB flowing forward through the scroll passage 40, and this is not preferable.

[0057] In the centrifugal compressor 1 according to some embodiments, in the cross section shown in FIG. 9 , the radius of curvature R4 of the inner concave arc portion 62 is smaller than the radius of curvature R3 of the inner convex arc portion 61 (R4<R3). In this case, the inner concave arc portion 62 curves more sharply than when the radius of curvature R4 of the inner concave arc portion 62 is larger than the radius of curvature R3 of the inner convex arc portion 61 (R4>R3). This increases the cross-sectional area of ​​the scroll passage 40 facing the inner concave arc portion 62. This allows the pressure loss of the compressed gas flowing through the scroll passage 40 to be appropriately reduced. Note that in some embodiments, the radius of curvature R4 of the inner concave arc portion 62 may be larger than the radius of curvature R3 of the inner convex arc portion 61.

[0058] As shown in Fig. 2, a centrifugal compressor 1 according to some embodiments includes the above-described casing 3 and the above-described impeller 2 rotatably housed in the casing 3. As shown in Fig. 1, a turbocharger 10 according to some embodiments includes the above-described centrifugal compressor 1. According to the above configuration, the pressure loss of the gas flowing through the scroll passage 40 is reduced, thereby improving the efficiency of the centrifugal compressor 1 and the turbocharger 10 including the centrifugal compressor 1.

[0059] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0060] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0061] The contents of the above-described embodiments can be understood, for example, as follows.

[0062] 1) A casing (3) of a centrifugal compressor (1) according to at least one embodiment of the present disclosure is a casing (3) of a centrifugal compressor (1) configured to be able to accommodate an impeller (2), and includes a scroll section (4) that forms a scroll passage (40) through which a compressed gas that has passed through the impeller (2) flows along the circumferential direction of the impeller (2), the scroll passage (40) being formed at a joining point of a start of winding (401) and an end of winding (402) of the scroll passage (40), the scroll section (4) including: an outer wall surface (5) that defines the outer side of the scroll passage (40) in a radial direction; and an inner wall surface (6) that defines the inner side of the scroll passage (40) in the radial direction, and the outer wall surface (5) has, in a cross section perpendicular to the axial direction, an outer concave arc portion (51) formed in a concave arc shape that is concave outward in the radial direction; The scroll flow path (40) has an outer convex arc portion (52) formed on the upstream side of the scroll flow path (40) relative to the outer concave arc portion (51), the outer convex arc portion (52) being formed in a convex arc shape that is convex toward the inside in the radial direction and on the outside in the radial direction relative to the outer concave arc portion (51); and an outer inflection point (53) provided at a connection position between the outer concave arc portion (51) and the outer convex arc portion (52), on the side of the start of winding (401) of the scroll flow path (40).

[0063] According to the configuration 1), the outer wall surface (5) has an outer convex arc portion (52) on the side of the start of winding (401) of the scroll flow path (40), so that the flow path cross-sectional area of ​​the scroll flow path (40) facing the outer convex arc portion (52) can be enlarged, and the flow rate of the flow (FA) flowing backward through the scroll flow path (40) passing through the confluence portion (403) of the scroll flow path (40) can be increased. As a result, the flow (FA) passing through the confluence portion (403) can be decelerated and the curvature can be made relatively small, so that friction loss between the flow (FB) flowing forward through the scroll flow path (40) and the flow (FA) is suppressed, and the pressure loss of the gas flowing through the scroll flow path (40) can be reduced more than in the past.

[0064] 2) In some embodiments, in the casing (3) of the centrifugal compressor (1) described in 1) above, when the angular position (θ) around the scroll center (CS) in the scroll flow path (40) is defined such that the confluence (403) of the start of winding (401) and the end of winding (402) of the scroll flow path (40) is 0 degree and the angle gradually increases from the confluence (403) toward the downstream side of the scroll flow path (40), the outer inflection point (53) is provided within a range of the angular position (θ) from 0 degree to 30 degrees.

[0065] The present inventors have found that a flow (FA) that flows backward through the scroll flow path (40) occurs when the angular position (θ) is between 0 and 30 degrees due to pressure pulsations generated in equipment, such as an engine, located downstream of the scroll flow path. According to the configuration of 2) above, by providing the outer inflection point (53), i.e., the downstream end of the outer convex arc portion (52), within a range where the angular position (θ) is between 0 and 30 degrees, the cross-sectional area of ​​the scroll flow path (40) through which the flow (FA) that flows backward through the scroll flow path (40) passes can be increased, and pressure loss of the compressed gas flowing through the scroll flow path (40) can be appropriately suppressed. While the outer inflection point (53) may be provided in a range where the angular position (θ) exceeds 30 degrees, this would excessively increase the volume of the scroll flow path (40), which is not suitable from the viewpoint of ease of installation in an engine.

[0066] 3) In some embodiments, in the casing (3) of the centrifugal compressor (1) described in 1) or 2), the radius of curvature (R2) of the outer convex arc portion (52) is smaller than the radius of curvature (R1) of the outer concave arc portion (51).

[0067] According to the configuration 3), the outer convex arc portion (52) bends more sharply than when the radius of curvature (R2) of the outer convex arc portion (52) is larger than the radius of curvature (R1) of the outer concave arc portion (51) (R2>R1), and the flow path cross-sectional area of ​​the scroll flow path (40) facing the outer convex arc portion (52) can be increased. This makes it possible to appropriately suppress pressure loss of the compressed gas flowing through the scroll flow path (40).

[0068] 4) In some embodiments, the casing (3) of the centrifugal compressor (1) according to any one of 1) to 3) above is provided, in which the inner wall surface (6) has, in a cross section perpendicular to the axial direction, an inner convex arc portion (61) formed in a convex arc shape that is convex outward in the radial direction, an inner concave arc portion (62) formed upstream of the scroll flow path (40) from the inner convex arc portion (61), the inner concave arc portion (62) being formed in a concave arc shape that is concave inward in the radial direction and more inward than the inner convex arc portion (61), and an inner inflection point (63) provided at a connection position between the inner convex arc portion (61) and the inner concave arc portion (62), on the side of the start of winding (401) of the scroll flow path (40).

[0069] According to the configuration 4) above, the inner wall surface (6) has the inner concave arc portion (62) on the side of the start of winding (401) of the scroll flow path (40), so that the flow path cross-sectional area of ​​the scroll flow path (40) facing the inner concave arc portion (62) can be enlarged, and the flow rate of the flow (FA) flowing backward through the scroll flow path (40) passing through the confluence portion (403) of the scroll flow path (40) can be increased. As a result, the flow (FA) passing through the confluence portion (403) can be decelerated and the curvature can be made relatively small, so that friction loss between the flow (FB) flowing forward through the scroll flow path (40) and the flow (FA) is suppressed, and the pressure loss of the gas flowing through the scroll flow path (40) can be reduced more than in the past.

[0070] 5) In some embodiments, in the casing (3) of the centrifugal compressor (1) described in 4) above, when the angular position (θ) around the scroll center (CS) in the scroll flow path (40) is defined such that the confluence (403) of the start of winding (401) and the end of winding (402) of the scroll flow path (40) is 0 degrees and the angle gradually increases from the confluence (403) toward the downstream side of the scroll flow path (40), the inner inflection point (63) is provided within a range of the angular position (θ) from 0 degrees to 30 degrees.

[0071] According to the configuration of 5) above, by providing the inner inflection point (63), i.e., the downstream end of the inner concave arc portion (62), within the angular position (θ) range of 0 to 30 degrees, the cross-sectional area of ​​the scroll flow path (40) through which the flow (FA) flowing backward through the scroll flow path (40) passes can be increased, and the pressure loss of the compressed gas flowing through the scroll flow path (40) can be appropriately suppressed. Note that the inner inflection point (63) may be provided within the angular position (θ) range exceeding 30 degrees, but in this case, the volume of the scroll flow path (40) will be excessively increased, which is not preferable from the viewpoint of mountability in an engine.

[0072] 6) In some embodiments, the casing (3) of the centrifugal compressor (1) described in 4) or 5) above, wherein the radius of curvature (R4) of the inner concave arc portion (62) is smaller than the radius of curvature (R3) of the inner convex arc portion (61).

[0073] According to the configuration 6), the curve of the inner concave arc portion (62) becomes sharper than when the radius of curvature (R4) of the inner concave arc portion (62) is larger than the radius of curvature (R3) of the inner convex arc portion (61) (R4>R3), and the flow path cross-sectional area of ​​the scroll flow path (40) facing the inner concave arc portion (62) can be enlarged. This makes it possible to appropriately suppress pressure loss of the compressed gas flowing through the scroll flow path (40).

[0074] 7) A casing (3) of a centrifugal compressor (1) according to at least one embodiment of the present disclosure is a casing (3) of a centrifugal compressor (1) configured to be able to accommodate an impeller (2), and includes a scroll section (4) that forms a scroll passage (40) through which a compressed gas that has passed through the impeller (2) flows along the circumferential direction of the impeller (2), the scroll passage (40) being formed at a joining point of a start of winding (401) and an end of winding (402) of the scroll passage (40), the scroll section (4) including: an outer wall surface (5) that defines the outer side of the scroll passage (40) in a radial direction; and an inner wall surface (6) that defines the inner side of the scroll passage (40) in the radial direction, and the inner wall surface (6) includes, in a cross section perpendicular to the axial direction, an inner convex arc portion (61) formed in a convex arc shape that is convex toward the outer side in the radial direction; an inner concave arc portion (62) formed upstream of the scroll flow path (40) relative to the inner convex arc portion (61), the inner concave arc portion (62) being formed in a concave arc shape that is concave toward the inside in the radial direction and radially inside the inner convex arc portion (61); and an inner inflection point (63) provided at a connection position between the inner convex arc portion (61) and the inner concave arc portion (62) on the side of the start of winding (401) of the scroll flow path (40).

[0075] According to the configuration of 7) above, the inner wall surface (6) has the inner concave arc portion (62) on the side of the start of winding (401) of the scroll flow path (40), so that the flow path cross-sectional area of ​​the scroll flow path (40) facing the inner concave arc portion (62) can be enlarged, and the flow rate of the flow (FA) flowing backward through the scroll flow path (40) passing through the confluence portion (403) of the scroll flow path (40) can be increased. This makes it possible to decelerate the flow (FA) passing through the confluence portion (403), thereby suppressing friction loss between the flow (FB) flowing forward through the scroll flow path (40) and the flow (FA), and thus reducing pressure loss of the gas flowing through the scroll flow path (40) more than in the past.

[0076] 8) In some embodiments, in the casing (3) of the centrifugal compressor (1) described in 7) above, when the angular position (θ) around the scroll center (CS) in the scroll flow path (40) is defined such that the confluence (403) of the start of winding (401) and the end of winding (402) of the scroll flow path (40) is 0 degrees and the angle gradually increases from the confluence (403) toward the downstream side of the scroll flow path (40), the inner inflection point (63) is provided within a range of the angular position (θ) from 0 degrees to 30 degrees.

[0077] According to the configuration of 8) above, by providing the inner inflection point (63), i.e., the downstream end of the inner concave arc portion (62), within an angular position (θ) range from 0 to 30 degrees, the cross-sectional area of ​​the scroll flow path (40) through which the flow (FA) flowing backward through the scroll flow path (40) passes can be increased, and the pressure loss of the compressed gas flowing through the scroll flow path (40) can be appropriately suppressed. Note that, if the inner inflection point (63) is provided within a range where the angular position (θ) exceeds 30 degrees, the volume of the scroll flow path (40) will be excessively increased, which may make it difficult for the flow (FB) flowing forward through the scroll flow path (40).

[0078] 9) In some embodiments, the casing (3) of the centrifugal compressor (1) described in 7) or 8) above, wherein the radius of curvature (R4) of the inner concave arc portion (62) is smaller than the radius of curvature (R3) of the inner convex arc portion (61).

[0079] According to the configuration 9), the curve of the inner concave arc portion (62) becomes sharper than when the radius of curvature (R4) of the inner concave arc portion (62) is larger than the radius of curvature (R3) of the inner convex arc portion (61) (R4>R3), and the flow path cross-sectional area of ​​the scroll flow path (40) facing the inner concave arc portion (62) can be enlarged. This makes it possible to appropriately suppress pressure loss of the compressed gas flowing through the scroll flow path (40).

[0080] 10) A centrifugal compressor (1) according to at least one embodiment of the present disclosure includes: a casing (3) of the centrifugal compressor (1) described in any one of 1) to 9) above; and the impeller (2) rotatably housed in the casing (3) of the centrifugal compressor (1).

[0081] According to the configuration of 10) above, the pressure loss of the gas flowing through the scroll passage (40) can be reduced, thereby improving the efficiency of the centrifugal compressor (1).

[0082] 11) A turbocharger (10) according to at least one embodiment of the present disclosure includes the centrifugal compressor (1) described in 10) above.

[0083] According to the above configuration 11), the pressure loss of the gas flowing through the scroll passage (40) can be reduced, thereby improving the efficiency of the turbocharger (10).

[0084] REFERENCE SIGNS LIST 1 Centrifugal compressor 2 Impeller 3 Casing 4 Scroll section 5 Outer wall surface 5A First outer wall surface 5B Second outer wall surface 6 Inner wall surface 6A First inner wall surface 6B Second inner wall surface 10 Turbocharger 11 Internal combustion engine system 12 Turbine 13 Internal combustion engine 14 Turbine rotor 15 Turbine housing 16 Rotating shaft 17 Bearing 18 Bearing housing 31 Shroud surface 32 Gas introduction passage 33 Diffuser passage 40 Scroll passage 50 Upstream end 51 Outer concave arc portion 52 Outer convex arc portion 53 Outer inflection point 61 Inner convex arc portion 62 Inner concave arc portion 63 Inner inflection point 401 Start of winding 402 End of winding 403 Confluence portion CS Scroll center CS1, CS2, CS3 Cross section LA Axis R1, R2, R3, R4 Radius of curvature T, T0, T1 Time

Claims

1. A casing for a centrifugal compressor configured to be able to accommodate an impeller, comprising a scroll section forming a scroll passage through which compressed gas that has passed through the impeller flows along a circumferential direction of the impeller, the scroll section forming a scroll passage where a start of winding and an end of winding of the scroll passage join together, the scroll section including an outer wall surface that defines the outer side of the scroll passage in a radial direction, and an inner wall surface that defines the inner side of the scroll passage in the radial direction, the outer wall surface having, in a cross section perpendicular to the axial direction, an outer concave arc portion formed in a concave arc shape concave toward the outer side in the radial direction, an outer convex arc portion formed upstream of the scroll passage than the outer concave arc portion, the outer convex arc portion formed in a convex arc shape convex toward the inner side in the radial direction outside the outer concave arc portion, and an outer inflection point provided at a connection position between the outer concave arc portion and the outer convex arc portion, on the start of winding side of the scroll passage.

2. A casing for a centrifugal compressor as described in claim 1, wherein, with respect to an angular position of the scroll passage about a scroll center, when the confluence of the start and end of the scroll passage is defined as 0 degrees and the angle gradually increases from the confluence toward the downstream side of the scroll passage, the outer inflection point is located within a range of angular positions from 0 degrees to 30 degrees.

3. A casing for a centrifugal compressor according to claim 1 or 2, wherein the radius of curvature of the outer convex arc portion is smaller than the radius of curvature of the outer concave arc portion.

4. A casing for a centrifugal compressor as claimed in claim 1 or 2, wherein the inner wall surface, in a cross section perpendicular to the axial direction, has, on the start of winding side of the scroll flow passage, an inner convex arc portion formed in a convex arc shape that convexly extends outward in the radial direction, an inner concave arc portion formed upstream of the scroll flow passage further than the inner convex arc portion, and formed in a concave arc shape that is concave inward in the radial direction and more inward than the inner convex arc portion, and an inner inflection point provided at a connection position between the inner convex arc portion and the inner concave arc portion.

5. A casing for a centrifugal compressor as described in claim 4, wherein, with respect to an angular position of the scroll passage about a scroll center, when the confluence of the start and end of the scroll passage is defined as 0 degrees and the angle gradually increases from the confluence toward the downstream side of the scroll passage, the inner inflection point is provided within a range of angular positions from 0 degrees to 30 degrees.

6. A casing for a centrifugal compressor according to claim 4, wherein the radius of curvature of the inner concave arc portion is smaller than the radius of curvature of the inner convex arc portion.

7. A casing for a centrifugal compressor configured to be able to accommodate an impeller, comprising a scroll section forming a scroll passage through which compressed gas that has passed through the impeller flows along the circumferential direction of the impeller, the scroll section forming a scroll passage where a start of winding and an end of winding of the scroll passage join together, the scroll section including an outer wall surface defining an outer side of the scroll passage in a radial direction, and an inner wall surface defining an inner side of the scroll passage in the radial direction, the inner wall surface having, in a cross section perpendicular to the axial direction, an inner convex arc portion formed in a convex arc shape that convex toward the outer side in the radial direction, an inner concave arc portion formed upstream of the scroll passage relative to the inner convex arc portion, the inner concave arc portion formed in a concave arc shape that is concave toward the inner side in the radial direction and on the radially inner side than the inner convex arc portion, and an inner inflection point provided at a connection position between the inner convex arc portion and the inner concave arc portion, on the start of winding side of the scroll passage.

8. A casing for a centrifugal compressor as described in claim 7, wherein, with respect to an angular position of the scroll passage about a scroll center, when the confluence of the start and end of the scroll passage is defined as 0 degrees and the angle gradually increases from the confluence toward the downstream side of the scroll passage, the inner inflection point is provided within a range of angular positions from 0 degrees to 30 degrees.

9. A casing for a centrifugal compressor according to claim 7 or 8, wherein a radius of curvature of the inner concave arc portion is smaller than a radius of curvature of the inner convex arc portion.

10. A centrifugal compressor comprising: a casing for a centrifugal compressor according to any one of claims 1, 2, 7 and 8; and an impeller rotatably accommodated in the casing of the centrifugal compressor.

11. A turbocharger comprising the centrifugal compressor according to claim 10.

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