Compressor housing and centrifugal compressor

Abstract

When the compressor housing defines the intake port side in the axial direction of the centrifugal compressor as the front side and the opposite side of the intake port side in the axial direction as the rear side, it includes: a shroud, which includes a surface that faces the front end of the impeller blades of the impeller with a predetermined clearance; a front-side inner peripheral surface, which is formed on the front side in the axial direction of the shroud and is located radially outside compared to the front end of the shroud; a plurality of groove portions, which are formed at intervals in the circumferential direction on the front-side inner peripheral surface; each of the plurality of groove portions includes an inclined portion whose depth gradually increases as it faces the rotation direction of the impeller and a segment portion formed at the downstream end in the rotation direction of the inclined portion.

Description

Technical Field

[0001] The present disclosure relates to a compressor housing for rotatably accommodating an impeller of a centrifugal compressor and a centrifugal compressor including the compressor housing. Background Art

[0002] A centrifugal compressor used in a compressor section of a vehicle or marine turbocharger applies kinetic energy to a fluid (e.g., air) by rotation of an impeller, discharges the fluid radially outward, and obtains a pressure rise of the fluid using centrifugal force. In this centrifugal compressor, it is required to achieve a high pressure ratio and high efficiency in a wide operating range, and various efforts have been made for this purpose.

[0003] For example, at low flow rates where the suction flow rate of the centrifugal compressor is small, an unstable phenomenon called surge occurs in which the fluid vibrates violently in the fluid flow direction. If surge occurs, a reverse flow in the direction opposite to the flow of air introduced from the intake port occurs near the shroud surface, and due to this reverse flow, the efficiency of the centrifugal compressor decreases.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-210902 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] Patent Document 1 discloses a technique for suppressing a reverse flow by guiding the reverse flow radially inward and pressurizing the air flowing toward the impeller side by using a recess formed on a wall surface of an inflow passage for guiding air to the impeller.

[0009] In order to achieve high efficiency of a centrifugal compressor, it is necessary to suppress as much as possible the pressure loss of the working fluid flowing in the compressor housing.

[0010] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide a compressor housing capable of improving the efficiency of a centrifugal compressor and a centrifugal compressor including the compressor housing.

[0011] Technical Solution for Solving the Technical Problem

[0012] The compressor housing of the present disclosure is a compressor housing for rotatably accommodating an impeller of a centrifugal compressor.

[0013] In a case where the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes:

[0014] A shroud that includes a surface facing the front end of the impeller blades of the impeller with a specified clearance;

[0015] A front-side inner peripheral surface that is formed on the front side in the axial direction of the shroud and is located radially outside compared to the front end of the shroud;

[0016] A plurality of convex portions that protrude from the front-side inner peripheral surface toward the inside in the radial direction and are formed between adjacent groove portions among a plurality of groove portions formed at intervals in the circumferential direction on the front-side inner peripheral surface;

[0017] Each of the plurality of groove portions includes:

[0018] An inclined portion whose depth gradually increases as it approaches the rotation direction of the impeller;

[0019] A stepped portion that is formed at the downstream end in the rotation direction of the inclined portion.

[0020] The centrifugal compressor of the present disclosure includes the compressor housing.

[0021] Effects of the Invention

[0022] According to at least one embodiment of the present disclosure, it is possible to provide a compressor housing that improves the efficiency of a centrifugal compressor and a centrifugal compressor including the compressor housing. Description of the Drawings

[0023] Figure 1 It is an explanatory diagram for explaining the configuration of a turbocharger including a centrifugal compressor according to one embodiment.

[0024] Figure 2 It is a schematic cross-sectional view showing the compressor side of a turbocharger including a centrifugal compressor according to one embodiment, and is a schematic cross-sectional view including the axis of the centrifugal compressor.

[0025] Figure 3 It is an explanatory diagram for explaining the compressor housing according to the first embodiment.

[0026] Figure 4 It schematically shows Figure 3 a schematic cross-sectional view of the cross-section taken along line A-B in

[0027] Figure 5 It is an explanatory diagram for explaining a modified example of the compressor housing according to the first embodiment.

[0028] Figure 6 It is an explanatory diagram for explaining the compressor according to the second embodiment.

[0029] Figure 7This is an explanatory diagram for explaining the compressor housing of the third embodiment.

[0030] Figure 8 It schematically shows the vicinity of the tightening surface of the compressor housing shown Figure 7 when viewed from the rear side in the axial direction. Specific Embodiments

[0031] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, etc. of the constituent elements described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure thereto, but are merely illustrative examples.

[0032] For example, expressions indicating relative or absolute arrangements such as "a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" do not strictly represent such arrangements, but also represent a state of relative displacement with a tolerance or at an angle or distance that can achieve the same function.

[0033] For example, expressions indicating an equal state of things such as "the same", "equal", and "homogeneous" not only represent a strictly equal state, but also represent a state with a tolerance or a difference that can achieve the same function.

[0034] For example, expressions indicating shapes such as a quadrilateral shape or a cylindrical shape not only represent strictly geometric quadrilateral shapes or cylindrical shapes, etc., but also represent shapes including concavo-convex portions or chamfered portions, etc. within a range where the same effect can be obtained.

[0035] In addition, expressions such as "comprising", "including", and "having" a constituent element are not exclusive expressions excluding the existence of other constituent elements.

[0036] It should be noted that the same constituent elements are denoted by the same reference numerals and the description thereof is omitted.

[0037] (Centrifugal Compressor, Turbocharger)

[0038] Figure 1 This is an explanatory diagram for explaining the configuration of a turbocharger of a centrifugal compressor having one embodiment. Figure 2 It is a schematic cross-sectional view showing the compressor side of a turbocharger of a centrifugal compressor having one embodiment, and is a schematic cross-sectional view including the axis of the centrifugal compressor.

[0039] The centrifugal compressor 1 of several embodiments of the present disclosure is as Figure 1 , Figure 2 shown, and includes an impeller 2 and a compressor housing 3 that rotatably houses the impeller 2.

[0040] The centrifugal compressor 1 can be applied, for example, to turbochargers 10 for motor vehicles, ships, or power generation, or other industrial centrifugal compressors, blowers, etc. In the illustrated embodiment, the centrifugal compressor 1 is mounted on the turbocharger 10. The turbocharger 10 is as Figure 1 shown and includes a centrifugal compressor 1, a turbine 11, and a rotating shaft 12. The turbine 11 has a turbine rotor 13 mechanically connected to the impeller 2 via the rotating shaft 12, and a turbine housing 14 that rotatably houses the turbine rotor 13.

[0041] In the illustrated embodiment, as Figure 1 shown, the turbocharger 10 further includes a bearing 15 that rotatably supports the rotating shaft 12, and a bearing housing 16 configured to house the bearing 15. The bearing housing 16 is disposed between the compressor housing 3 and the turbine housing 14 and is mechanically connected to the compressor housing 3 and the turbine housing 14 by connection members (e.g., connecting bolts, etc.).

[0042] Hereinafter, for example, as Figure 1 shown, the axis CA of the centrifugal compressor 1, that is, the direction in which the axis of the impeller 2 extends, is defined as the axial direction X, and the direction orthogonal to the axis CA is defined as the radial direction Y. In the axial direction X, the upstream side in the suction direction of the centrifugal compressor 1 (the direction in which the main flow is introduced into the impeller 2), that is, the side where the air inlet 31 is located with respect to the impeller 2 (the left side in the drawing), is defined as the front side XF. And, the opposite side to the front side XF in the axial direction X, that is, the downstream side in the suction direction of the centrifugal compressor 1 (the right side in the drawing), is defined as the rear side XR.

[0043] In Figure 1 the illustrated embodiment, an air inlet 31 for introducing fluid (e.g., air) from the outside to the inside of the compressor housing 3 and an outlet 32 for discharging the fluid that has passed through the impeller 2 to the outside of the compressor housing 3 are formed in the compressor housing 3. A turbine-side inlet 141 for introducing a working fluid (e.g., exhaust gas) that rotates the turbine rotor 13 from the outside to the inside of the turbine housing 14 and a turbine-side outlet 142 for discharging the working fluid that has passed through the turbine rotor 13 to the outside of the turbine housing 14 are formed in the turbine housing 14.

[0044] As Figure 1 shown, the rotating shaft 12 has a length direction along the axial direction X. The rotating shaft 12 is mechanically connected to the impeller 2 on one side (front side XF) in its length direction and to the turbine rotor 13 on the other side (rear side XR) in its length direction.

[0045] The turbocharger 10 rotates the turbine rotor 13 by using the working fluid introduced into the interior of the turbine housing 14 through the turbine-side inlet 141. As the above-mentioned working fluid, exhaust gas generated from an exhaust gas generating device (for example, an internal combustion engine such as an engine), which is not shown, can be cited. The impeller 2 is mechanically connected to the turbine rotor 13 via the rotating shaft 12, and thus rotates in conjunction with the rotation of the turbine rotor 13. The turbocharger 10 compresses the fluid introduced into the interior of the compressor housing 3 through the inlet 31 and delivers it to the supply target of the compressed fluid (for example, an internal combustion engine such as an engine) through the outlet 32.

[0046] (Impeller)

[0047] As Figure 2 shown, the impeller 2 includes a hub 21 and a plurality of impeller blades 23 provided on the outer surface 22 of the hub 21. The hub 21 is mechanically fixed to one side of the rotating shaft 12, and thus the hub 21 and the plurality of impeller blades 23 are supported so as to be able to rotate integrally with the rotating shaft 12 about the axis CA of the impeller 2. The impeller 2 is configured to be accommodated in the compressor housing 3 and guide the fluid introduced from the front side XF in the axial direction X to the outside in the radial direction Y.

[0048] In the illustrated embodiment, the outer surface 22 of the hub 21 is formed in a concave curved shape in which the distance from the axis CA of the impeller 2 increases as it goes from the front side XF to the rear side XR. Each of the plurality of impeller blades 23 is arranged at intervals from each other in the circumferential direction around the axis CA. The shroud 4 includes a surface 41 formed in a convex curved shape in which the distance from the axis CA of the impeller 2 increases as it goes from the front side XF to the rear side XR. The front end (tip side end) 24 of the impeller blade 23 is located on the opposite side of the connecting portion (hub side end) with the outer surface 22 of the hub 21. A gap G (void) is formed between the front ends 24 between the surfaces 41 that are convexly curved in a manner facing the front ends 24.

[0049] (Compressor housing)

[0050] In the illustrated embodiment, as Figure 2 shown, the compressor housing 3 includes a shroud portion 33 including the above-mentioned shroud 4, a suction introduction portion 34 forming the suction introduction passage 50 of the centrifugal compressor 1, a diffuser portion 35 forming the diffuser passage 60 of the centrifugal compressor 1, and a scroll portion 36 forming the scroll passage 360 of the centrifugal compressor 1.

[0051] The suction introduction passage 50 is a passage for guiding the suction (for example, a fluid such as air) introduced into the compressor housing 3 through the inlet 31 to the impeller blades 23. The diffuser passage 60 is a passage for guiding the fluid that has passed through the impeller 2 to the scroll-shaped scroll passage 360 provided around the impeller 2. The scroll passage 360 is for guiding the fluid that has passed through the impeller 2 and the diffuser passage 60 through the outlet 32 (refer toFigure 1 )The flow path guided to the outside of the compressor housing 3.

[0052] The suction inlet passage 50 and the vortex flow path 360 are respectively formed inside the compressor housing 3. The suction inlet portion 34 has an inner peripheral surface 5 on the front side that forms the suction inlet passage 50. The inner peripheral surface 5 on the front side is formed on the front side XF in the axial direction of the cover surface 4 and is located outside in the radial direction Y compared to the front end 42 (front side XF end) of the cover surface 4. And, the above-mentioned air inlet 31 is formed at the front end of the suction inlet portion 34.

[0053] The vortex flow path 360 is formed to be located outside the impeller 2 in the radial direction Y so as to surround the periphery of the impeller 2 housed in the compressor housing 3. The vortex portion 36 has a flow path wall surface 361 that forms the vortex flow path 360.

[0054] And, in the illustrated embodiment, as Figure 2 shown, the compressor housing 3 forms the above-mentioned diffuser flow path 60 by being combined with other components (in the illustrated example, the bearing housing 16). The diffuser flow path 60 is formed by the diffuser surface 6 and the surface 161 of the bearing housing 16 that faces the diffuser surface 6. In addition, in some other embodiments, the diffuser flow path 60 can be formed inside the compressor housing 3.

[0055] The above-mentioned cover portion 33 is provided between the suction inlet portion 34 and the diffuser portion 35. The outlet of the suction inlet passage 50 communicates with the inlet of the diffuser flow path 60, and the outlet of the diffuser flow path 60 communicates with the inlet of the vortex flow path 360. The fluid introduced into the inside of the compressor housing 3 through the air inlet 31 flows toward the rear side XR in the suction inlet passage 50 and is then delivered to the impeller 2. The fluid delivered to the impeller 2 flows through the diffuser flow path 60 and the vortex flow path 360 in sequence, and then is discharged to the outside of the compressor housing 3 from the discharge port 32 (refer to Figure 1 ).

[0056] At low flow rates where the suction flow rate of the centrifugal compressor 1 (the flow rate of the main flow MF that flows into the suction inlet passage 50 through the air inlet 31 and flows toward the impeller 2) is small, an unstable phenomenon called surge occurs in which the fluid vibrates violently in the flow direction of the fluid. If surge occurs, a reverse flow RF that flows in the direction opposite to the main flow MF, that is, toward the front side XF in the axial direction X, will be generated near the cover surface 4, and there is a possibility that the efficiency of the centrifugal compressor 1 will decrease.

[0057] Figure 3 It is an explanatory diagram for explaining the compressor housing of the first embodiment. Figure 4 It schematically shows Figure 3 The schematic cross-sectional view of the A - B line section in Figure 3 In , the cross-section along the axis CA of the impeller 2 of the centrifugal compressor 1 is schematically shown.

[0058] As Figure 3 shown, the compressor housing 3 of some embodiments includes: a shroud 4 having a surface 41 that faces the front end 24 of the impeller blades 23 of the impeller 2 with a predetermined gap G; a front-side inner peripheral surface 5 formed on the front side XF in the axial direction of the shroud 4 and located outside in the radial direction Y compared to the front end 42 of the shroud 4; and a plurality of convex portions 7A protruding inward in the radial direction from the front-side inner peripheral surface 5.

[0059] In Figure 4 the cross-sectional view shown, which is viewed from the front side XF in the axial direction of the impeller 2, the plurality of convex portions 7A are respectively formed between adjacent groove portions 7B among the plurality of groove portions 7B formed at intervals in the circumferential direction on the front-side inner peripheral surface 5. Further, in the above cross-sectional view, the plurality of groove portions 7B each include: an inclined portion 71 whose depth gradually increases as it faces the rotation direction RD of the impeller 2; and a stepped portion 73 formed at the downstream end 72 in the rotation direction RD of the inclined portion 71. In the illustrated embodiment, the convex portion 7A is located outside in the radial direction compared to the front end 24A at the leading edge 25 of the impeller 2.

[0060] According to the above configuration, a plurality of groove portions 7B each including an inclined portion 71 and a stepped portion 73 are formed in the compressor housing 3. As described above, at a low flow rate with a small intake flow rate of the centrifugal compressor 1, a reverse flow RF is generated near the shroud 4. The reverse flow RF is given a rotational component in the rotation direction RD of the impeller 2 by the rotation of the impeller 2, and thus has a strong centrifugal force. The inclined portion 71 guides such a reverse flow RF having a strong centrifugal force along the inclined portion 71 in the rotation direction RD, and by colliding with the stepped portion 73 formed at the downstream end 72 in the rotation direction RD of the inclined portion 71, the reverse flow RF can be suppressed. By suppressing the above reverse flow RF, the surge flow rate in the low-flow-rate operating range can be reduced, and thus the efficiency of the centrifugal compressor 1 can be improved.

[0061] Further, according to the above configuration, since the groove portion 7B gradually increases in depth as it faces the rotation direction RD of the impeller 2, the air flow that enters the groove portion 7B from the main flow MF introduced into the impeller 2 is extruded from the groove portion 7B in the opposite direction of the rotation direction RD to the inside in the radial direction. Thus, by imparting rotation in the opposite direction of the rotation direction RD of the impeller 2 to the main flow MF introduced into the impeller 2, rotation can be imparted in advance to increase the relative inflow velocity of the main flow MF when it is introduced into the impeller 2. By increasing the relative inflow velocity of the main flow MF, the surge flow rate in the low-flow-rate operating range can be reduced, and thus the efficiency of the centrifugal compressor 1 can be improved.

[0062] In some embodiments, as Figure 4As shown, the above-mentioned inclined portion 71 includes an arcuate portion 71A that is concavely curved outward in the radial direction. In this case, the reverse-flow RF can be smoothly guided in the rotational direction RD along the arcuate portion 71A, thus promoting the collision of the reverse-flow RF with the segment portion 73. Thereby, the reverse-flow RF can be effectively suppressed. Moreover, the groove portion 7B having the arcuate portion 71A enlarges the space inside the groove portion 7B, so that a large amount of the mainstream MF introduced into the impeller 2 can flow into the groove portion 7B, and can be extruded from the groove portion 7B in a large amount to the inner side in the radial direction in the opposite direction to the rotational direction RD. Thereby, the above-mentioned rotation can be effectively imparted to the mainstream MF introduced into the impeller 2 in advance, and the relative inflow velocity of the mainstream MF when introduced into the impeller 2 can be increased.

[0063] In some embodiments, the above-mentioned segment portion 73 includes Figure 4 a step surface 73A as shown with an angle θ formed with the inclined portion 71 of 120 degrees or less. Preferably, the above-mentioned angle θ is 90 degrees or less. If the angle θ formed between the segment portion 73 and the inclined portion 71 is large, there is a possibility that the reverse-flow RF flowing in the rotational direction RD along the inclined portion 71 of the groove portion 7B directly flows along the step surface 73A (segment portion 73) and the collision of the reverse-flow RF with the step surface 73A is insufficient. According to the above configuration, the segment portion 73 includes a step surface 73A with an angle formed with the inclined portion 71 of 120 degrees or less. In this case, the collision angle of the reverse-flow RF with the step surface 73A is small, so that the reverse-flow RF can sufficiently collide with the step surface 73A, and the reverse-flow RF can be effectively suppressed.

[0064] In some embodiments, as Figure 3 shown, the rear end 74 of the groove portion 7B is configured to be connected to the front end 42 of the shroud surface 4. The groove portion 7B is provided near the leading edge 25 of the impeller 2 in the axial direction X, and the effect of suppressing the reverse-flow RF is higher. According to the above configuration, the rear end 74 of the groove portion 7B is connected to the front end 42 of the shroud surface 4, so that the groove portion 7B is located near the leading edge 25 in the axial direction X, and thus the reverse-flow RF can be effectively suppressed. By suppressing the above-mentioned reverse-flow RF, the surge flow rate in the low-flow-side operating range can be reduced, and further, the efficiency of the centrifugal compressor 1 can be improved.

[0065] In some embodiments, as Figure 3 shown, the inclined portion 71 of the groove portion 7B includes at least a conical surface 75 that expands in diameter from the rear end 74 of the groove portion 7B toward the front side XF. In the illustrated embodiment, the inclined portion 71 of the groove portion 7B further includes a bottom surface 77 that extends along the axial direction X from the front end 76 of the conical surface 75 toward the front side XF. In Figure 3In the illustrated embodiment, the bottom of the groove portion 7B (for example, the bottom surface 77) is formed on the radially inner side compared to the axial surface 53. According to the above configuration, since the inclined portion 71 includes the conical surface 75, it is possible to suppress the sudden contraction loss of the air flow of the main flow MF introduced into the impeller 2. In addition, the inclined portion 71 can smoothly guide the reverse flow RF in the rotational direction RD along the conical surface 75, and thus it is possible to promote the collision of the reverse flow RF with the segment portion 73. Thereby, the reverse flow RF can be effectively suppressed.

[0066] Figure 5 is an explanatory diagram for explaining a modified example of the compressor housing of the first embodiment. In Figure 5 a cross-section along the axis CA of the impeller 2 of the centrifugal compressor 1 is schematically shown.

[0067] In some embodiments, as Figure 3 , Figure 5 shown, the above-mentioned front-side inner peripheral surface 5 includes: a conical surface 51 that expands in diameter toward the front side XF from the front end 42 of the cover surface 4; and an axial surface 53 that extends along the axis X toward the front side XF from the front end 52 of the conical surface 51. As Figure 5 shown, the above-mentioned convex portion 7A is configured to project only from the conical surface 51 on the front-side inner peripheral surface 5. In the illustrated embodiment, the convex portion 7A extends at least throughout the entire axis X of the conical surface 51. In this case, by providing the convex portion 7A or the groove portion 7B on the conical surface 51, the reverse flow RF can be effectively suppressed. In addition, by providing the convex portion 7A only on the conical surface 51 of the front-side inner peripheral surface 5, that is, not on the axial surface 53 of the front-side inner peripheral surface 5, the collision loss of the main flow MF caused by the collision with the convex portion 7A can be suppressed.

[0068] It should be noted that in some other embodiments, as Figure 3 shown, the above-mentioned convex portion 7A may be configured to project from both the conical surface 51 and the axial surface 53.

[0069] Figure 6 is an explanatory diagram for explaining the compressor of the second embodiment. In Figure 6 a state of observing a plurality of convex portions 7A and a plurality of groove portions 7B from the radially inner side of the impeller 2 is schematically shown.

[0070] As Figure 3 , Figure 5 shown, the compressor housing 3 of some embodiments includes: a cover surface 4 that includes a surface 41 that faces the front end 24 of the impeller blade 23 of the impeller 2 with a predetermined gap G; a front-side inner peripheral surface 5 that is formed on the front side XF in the axial direction of the cover surface 4 and is located on the outer side in the radial direction Y compared to the front end 42 of the cover surface 4; and a plurality of convex portions 7A that project from the front-side inner peripheral surface 5 toward the radially inner side.

[0071] InFigure 4 In the cross-sectional view shown and observed from the front side XF in the axial direction of the impeller 2, the plurality of convex portions 7A are respectively formed between adjacent ones of the plurality of groove portions 7B formed at intervals in the circumferential direction on the front-side inner peripheral surface 5. As Figure 6 shown, each of the plurality of groove portions 7B is configured such that the rear end 74 of the groove portion 7B is located on the upstream side in the rotational direction RD of the impeller 2 compared to the front end 78 of the groove portion 7B.

[0072] It should be noted that in the above several embodiments, the groove portion 7B extends along the axial direction X, and the rear end 74 of the groove portion 7B is configured to be located at the same position as the front end 78 of the groove portion 7B in the rotational direction RD of the impeller 2.

[0073] In the illustrated embodiment, the rear end 74 of the groove portion 7B is configured to be connected to the front end 42 of the shroud surface 4. In Figure 6 the view shown and observed from the inner side in the radial direction of the impeller 2, the groove portion 7B is formed linearly from the front end 78 to the rear end 74.

[0074] According to the above configuration, the rear end 74 of the groove portion 7B is configured to be located on the upstream side in the rotational direction RD of the impeller 2 compared to the front end 78 of the groove portion 7B. Therefore, by guiding the main flow MF introduced into the impeller 2 using the groove portion 7B, it is possible to impart rotation to the main flow MF in advance in the direction opposite to the rotational direction RD of the impeller 2. By imparting the above rotation to the main flow MF in advance, it is possible to increase the relative inflow velocity of the main flow MF when it is introduced into the impeller 2. By increasing the relative inflow velocity of the main flow MF, it is possible to reduce the surge flow rate in the low-flow-side operating range, and thus it is possible to improve the efficiency of the centrifugal compressor 1.

[0075] It should be noted that this embodiment can be implemented in combination with the above several embodiments or independently. For example, this embodiment can be applied to the groove portion 7B including the above-mentioned inclined portion 71 and stepped portion 73, or this embodiment can be applied to a concave-shaped groove portion other than the groove portion 7B. Figure 4 shown, or this embodiment can be applied to a concave-shaped groove portion other than the groove portion 7B.

[0076] In some embodiments, as Figure 3 shown, each of the plurality of convex portions 7A among the above-mentioned plurality of convex portions 7A is integrally formed with the above-mentioned front-side inner peripheral surface 5 (for example, the conical surface 51) by cutting or casting.

[0077] According to the above configuration, the convex portion 7A is integrally formed with the front-side inner peripheral surface 5 by cutting or casting. In this case, compared with the case where the convex portion 7A separately manufactured from the front-side inner peripheral surface 5 is fixed to the front-side inner peripheral surface 5 by welding, bolt connection, etc., the surface roughness of the convex portion 7A and the groove portion 7B can be made. By increasing the surface roughness of the convex portion 7A and the groove portion 7B, the pressure loss of the main flow MF introduced into the impeller 2 can be reduced.

[0078] It should be noted that, in some embodiments, as Figure 5 shown, the above convex portion 7A can be separately manufactured from the above front-side inner peripheral surface 5. In Figure 5 the shown embodiment, an annular body 7 having an inner surface formed with a plurality of convex portions 7A and a plurality of groove portions 7B is supported inside the front-side inner peripheral surface 5.

[0079] In the above several embodiments, the above convex portion 7A and the groove portion 7B are provided on the upstream side of the impeller 2, but by providing such a convex portion 7A and a groove portion 7B on the downstream side of the impeller 2, the backflow at the downstream side of the impeller 2 can be suppressed, thereby achieving an improvement in the efficiency of the centrifugal compressor 1.

[0080] Figure 7 is an explanatory drawing for explaining the compressor housing of the third embodiment. Figure 8 is a schematic view showing the vicinity of the tightening surface of the compressor housing shown when viewed from the rear side in the axial direction Figure 7 In Figure 7 it schematically shows a cross-section of the centrifugal compressor 1 along the axis CA of the impeller 2.

[0081] As Figure 7 shown, the compressor housing 3 of some embodiments includes: a shroud surface 4, which includes a surface 41 that faces the front end 24 of the impeller blade 23 of the impeller 2 with a predetermined gap G; a diffuser surface 6, which is located on the back surface 26 side (rear side XR) of the impeller 2 in the axial direction compared to the rear end 43 of the shroud surface 4, and includes a radial surface 61 extending along the radial direction Y and a tightening surface 63 that connects the inner end 62 of the radial surface 61 to the rear end 43 of the shroud surface 4; and a plurality of diffuser-side convex portions 8A, which project from the tightening surface 63 toward the back surface 26 side (rear side XR) of the impeller 2 in the axial direction.

[0082] In Figure 8 the view shown when observing from the rear side XR in the axial direction of the impeller 2, each of the plurality of diffuser-side convex portions 8A is formed between adjacent diffuser-side groove portions 8B formed at intervals in the circumferential direction on the diffuser surface 6.

[0083] According to the above configuration, the compressor housing 3 has a plurality of diffuser side groove portions 8B formed at intervals in the circumferential direction on the tightening surface 63. Through the plurality of diffuser side groove portions 8B, it is possible to suppress the reverse flow RF2 having a rotational direction component pointing in the rotational direction RD of the impeller 2 generated near the tightening surface 63, and it is possible to suppress the rotational pressure loss of the main flow MF at the downstream side compared to the impeller 2.

[0084] On the downstream side of the centrifugal compressor 1 compared to the impeller 2, a non-uniform flow velocity distribution is generated. The plurality of diffuser side convex portions 8A function as vortex simulators to suppress boundary layer separation. Therefore, not only when the rotating stall occurs at the inlet of the diffuser flow path 60, but also at the normal operating point of the centrifugal compressor 1, the efficiency of the centrifugal compressor 1 can be improved.

[0085] In some embodiments, when Figure 8 viewed from the rear side XR in the axial direction of the impeller 2 as shown, each of the plurality of diffuser side groove portions 8B includes: a diffuser side inclined portion 81 whose depth gradually increases as it faces the rotational direction RD of the impeller 2; and a diffuser side stepped portion 83 formed at the downstream end 82 in the rotational direction RD of the diffuser side inclined portion 81.

[0086] According to the above configuration, each of the plurality of diffuser side groove portions 8B includes a diffuser side inclined portion 81 and a diffuser side stepped portion 83. By guiding the reverse flow RF2 having a rotational direction component generated near the tightening surface 63 along the diffuser side inclined portion 81 in the rotational direction RD, and by causing the reverse flow RF2 to collide with the diffuser side stepped portion 83 formed at the downstream end 82 of the diffuser side inclined portion 81, the reverse flow RF2 can be suppressed.

[0087] In some embodiments, as Figure 8 shown, the diffuser side inclined portion 81 includes an arcuate portion 81A that is concave and curved toward the outer side in the radial direction. In this case, the reverse flow RF2 can be smoothly guided along the arcuate portion 81A in the rotational direction RD, so that the collision between the reverse flow RF2 and the diffuser side stepped portion 83 can be promoted. Thereby, the reverse flow RF2 can be effectively suppressed. Moreover, the diffuser side groove portion 8B having the arcuate portion 81A enlarges the space inside the diffuser side groove portion 8B, so that a large amount of the main flow MF introduced into the impeller 2 flows into the diffuser side groove portion 8B, and is extruded from the diffuser side groove portion 8B toward the inner side in the radial direction in the direction opposite to the rotational direction RD. Thereby, the non-uniform flow velocity distribution can be suppressed.

[0088] In some embodiments, as Figure 8As shown, the diffuser side section 83 includes a step surface 83A having an angle θ1 with the diffuser side inclined section 81 of 120 degrees or less. Preferably, the angle θ1 is 90 degrees or less. If the angle θ1 formed between the diffuser side section 83 and the diffuser side inclined section 81 is large, there is a possibility that the reverse flow RF2 flowing along the diffuser side inclined section 81 of the diffuser side groove section 8B in the rotational direction RD directly flows along the step surface 83A and the collision between the reverse flow RF2 and the step surface 83A is insufficient. According to the above configuration, the diffuser side section 83 includes a step surface 83A having an angle of 120 degrees or less with the diffuser side inclined section 81. In this case, the collision angle between the reverse flow RF2 and the step surface 83A is small, so that the reverse flow RF2 can collide with the step surface 83A sufficiently, and the reverse flow RF2 can be effectively suppressed.

[0089] It should be noted that this embodiment can be combined with the above several embodiments or can be implemented independently. For example, the compressor housing 3 can have the above convex portion 7A and the above diffuser side convex portion 8A. In this case, rotational stall at the upstream side and the downstream side of the impeller 2 can be suppressed, and thus, due to the superimposed effect of the convex portion 7A and the diffuser side convex portion 8A, the efficiency of the centrifugal compressor 1 can be effectively improved.

[0090] In some embodiments, as Figure 7 shown, the above diffuser side convex portion 8A can be integrally formed with the above diffuser surface 6 (for example, the tightening surface 63) by cutting or casting.

[0091] According to the above configuration, the diffuser side convex portion 8A is integrally formed with the diffuser surface 6 by cutting or casting. In this case, compared with the case where the diffuser side convex portion 8A separately manufactured from the diffuser surface 6 is fixed to the diffuser surface 6 by welding or bolt connection, etc., the surface roughness of the diffuser side groove portion 8B can be improved. By improving the surface roughness of the diffuser side groove portion 8B, the pressure loss of the main flow MF after passing through the impeller 2 can be reduced.

[0092] It should be noted that in some other embodiments, the above diffuser side convex portion 8A can be separately manufactured from the above diffuser surface 6.

[0093] As Figure 1 、 Figure 2 shown, the centrifugal compressor 1 of some embodiments includes the above compressor housing 3. In this case, the pressure loss of the working fluid flowing in the compressor housing 3 can be effectively suppressed, and thus the efficiency of the centrifugal compressor 1 can be improved.

[0094] The present disclosure is not limited to the above embodiments, and includes embodiments in which deformations are implemented on the basis of the above embodiments and embodiments in which these embodiments are appropriately combined.

[0095] The content described in the above several embodiments can be understood as follows, for example.

[0096] 1) The compressor housing (3) of at least one embodiment of the present disclosure is a compressor housing (3) for rotatably accommodating the impeller (2) of a centrifugal compressor (1).

[0097] When the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes:

[0098] A cover surface (4) including a surface (41) that faces the front end (24) of the impeller blades (23) of the impeller with a predetermined gap (G).

[0099] A front-side inner peripheral surface (5) formed on the front side in the axial direction of the cover surface (4) and located radially outside compared to the front end (42) of the cover surface (4).

[0100] A plurality of convex portions (7A) protruding from the front-side inner peripheral surface (5) toward the inside in the radial direction and formed between adjacent groove portions (7B) formed at intervals in the circumferential direction on the front-side inner peripheral surface (5).

[0101] Each of the plurality of groove portions (7B) includes:

[0102] An inclined portion (71) whose depth gradually increases as it approaches the rotation direction (RD) of the impeller (2).

[0103] A stepped portion (73) formed at the downstream end (72) in the rotation direction (RD) of the inclined portion (71).

[0104] According to the configuration of the above 1), a plurality of groove portions each including an inclined portion and a stepped portion are formed in the compressor housing. At low flow rates where the intake flow rate of the centrifugal compressor is small, a reverse flow is generated near the cover surface. The reverse flow is given a rotational direction component in the rotational direction of the impeller by the rotation of the impeller, and thus has a strong centrifugal force. The inclined portion guides such a reverse flow with a strong centrifugal force along the inclined portion in the rotational direction and can suppress the reverse flow by colliding with the stepped portion formed at the downstream end in the rotational direction of the inclined portion. By suppressing the above reverse flow, the surge flow rate in the low-flow-rate operating range can be reduced, and furthermore, the efficiency of the centrifugal compressor can be improved.

[0105] Moreover, according to the configuration of 1) above, as the groove portion gradually increases in depth along the rotation direction of the impeller, the air flow that enters the groove portion in the main flow introduced into the impeller is squeezed from the groove portion toward the inner side in the radial direction in the direction opposite to the rotation direction. Thus, it is possible to pre-impart rotation to the main flow introduced into the impeller in the direction opposite to the rotation direction of the impeller, and it is possible to increase the relative inflow velocity of the main flow when introduced into the impeller by pre-imparting the above rotation. By increasing the relative inflow velocity of the main flow, it is possible to reduce the surge flow rate in the low-flow-side operating range, and furthermore, it is possible to improve the efficiency of the centrifugal compressor.

[0106] 2) In some embodiments, based on the compressor housing (3) described in 1) above,

[0107] The inclined portion (71) includes an arc-shaped portion (71A) that is concave and curved toward the outer side in the radial direction.

[0108] According to the configuration of 2) above, the inclined portion includes an arc-shaped portion that is concave and curved toward the outer side in the radial direction. In this case, since the reverse flow can be smoothly guided along the arc-shaped portion in the rotation direction, the collision between the reverse flow and the segment portion can be promoted. Thus, the reverse flow can be effectively suppressed. And the groove portion having the above arc-shaped portion enlarges the space inside the groove portion, so that a large amount of the main flow introduced into the impeller flows in, and a large amount can be extruded from the groove portion toward the inner side in the radial direction in the direction opposite to the rotation direction. Thus, the above rotation can be effectively pre-imparted to the main flow introduced into the impeller, and the relative inflow velocity of the main flow when introduced into the impeller can be increased.

[0109] 3) In some embodiments, based on the compressor housing (3) described in 1) or 2) above,

[0110] The segment portion (73) includes a step surface (73A) whose angle (θ) formed with the inclined portion (71) is 120 degrees or less.

[0111] If the angle formed by the segment portion and the inclined portion is large, there is a problem that the reverse flow flowing along the inclined portion of the groove portion in the rotation direction directly flows along the step surface (segment portion), and the collision between the reverse flow and the step surface is insufficient. According to the configuration of 3) above, the segment portion includes a step surface whose angle formed with the inclined portion is 120 degrees or less. In this case, since the collision angle between the reverse flow and the step surface is small, the reverse flow can collide sufficiently with the step surface, and the reverse flow can be effectively suppressed.

[0112] 4) In some embodiments, based on the compressor housing (3) described in any one of 1) to 3) above,

[0113] Each of the plurality of groove portions (7B) is configured such that a rear end (74) of the groove portion is located on an upstream side in a rotation direction (RD) of the impeller (2) compared to a front end (78) of the groove portion.

[0114] According to the configuration of 4) above, the rear end of the groove portion is configured to be on the upstream side in the rotation direction of the impeller compared to the front end of the groove portion. Thus, the main flow introduced into the impeller is guided by the groove portion, and thereby pre-rotation can be imparted to the main flow in a direction opposite to the rotation direction of the impeller in advance. By imparting the above rotation to the main flow in advance, the relative inflow velocity of the main flow when introduced into the impeller can be increased. By increasing the relative inflow velocity of the main flow, the surge flow rate in the low-flow side operating range can be reduced, and furthermore, the efficiency of the centrifugal compressor can be improved. Also, since the groove portion includes the above inclined portion and the above stepped portion, the superimposed effect of the rotation pre-generated by the airflow extruded from the groove portion in a direction opposite to the rotation direction can effectively impart rotation to the main flow introduced into the impeller in advance.

[0115] 5) In some embodiments, based on the compressor housing (3) described in any one of 1) to 4) above,

[0116] Each of the plurality of convex portions (7A) is integrally formed with the front-side inner peripheral surface (5) by machining or casting.

[0117] According to the configuration of 5) above, the convex portion is integrally formed with the front-side inner peripheral surface by machining or casting. In this case, compared with the case where a convex portion separately manufactured on the same front-side inner peripheral surface is fixed to the front-side inner peripheral surface by welding or bolts, etc., the surface roughness of the convex portion and the groove portion can be increased. By increasing the surface roughness of the convex portion and the groove portion, the pressure loss of the main flow introduced into the impeller can be reduced.

[0118] 6) In some embodiments, based on the compressor housing (3) described in any one of 1) to 5) above, further comprising:

[0119] A diffuser surface (6) that is located on the back side (26) of the impeller (2) in the axial direction compared to a rear end (43) of the shroud surface (4), and includes a radial surface (61) extending along the radial direction and a constricting surface (63) connecting an inner end (62) of the radial surface (61) to the rear end (43) of the shroud surface (4);

[0120] A plurality of diffuser-side convex portions (8A) that project from the constricting surface (63) toward the back side of the impeller in the axial direction and are formed between adjacent diffuser-side groove portions (8B) formed at intervals in the circumferential direction on the diffuser surface (6).

[0121] According to the configuration of 6) above, the compressor housing has a plurality of diffuser side groove portions formed on the tightening surface at intervals in the circumferential direction. Through the plurality of diffuser side groove portions, it is possible to suppress the countercurrent having a rotational direction component pointing in the rotational direction of the impeller generated near the tightening surface, and it is possible to suppress the rotational pressure loss of the main flow on the downstream side compared to the impeller.

[0122] At a position downstream of the impeller in the centrifugal compressor, a non-uniform flow velocity distribution is generated. The plurality of diffuser side groove portions function as vortex simulators to suppress boundary layer separation. Therefore, not only when the rotating stall occurs at the inlet of the diffuser flow path, but also at the normal operating point of the centrifugal compressor, the efficiency of the centrifugal compressor can be improved.

[0123] 7) In some embodiments, based on the compressor housing (3) described in 6) above,

[0124] Each of the plurality of diffuser side groove portions (8B) includes:

[0125] A diffuser side inclined portion (81) whose depth gradually increases in the rotational direction of the impeller;

[0126] A diffuser side segment portion (83) formed at the downstream end (82) in the rotational direction of the diffuser side inclined portion (81).

[0127] According to the configuration of 7) above, each of the plurality of diffuser side groove portions includes a diffuser side inclined portion and a diffuser side segment portion. By guiding the countercurrent (RF2) having a rotational direction component generated near the tightening surface along the diffuser side inclined portion in the rotational direction and causing the countercurrent to collide with the diffuser side segment portion formed at the downstream end of the diffuser side inclined portion, the above-mentioned countercurrent can be suppressed.

[0128] 8) In some embodiments, based on the compressor housing (3) described in 6) or 7) above,

[0129] The plurality of diffuser side convex portions (8A) are integrally formed with the diffuser surface (6) by machining or casting.

[0130] According to the configuration of 8) above, the diffuser side convex portions are integrally formed with the diffuser surface by machining or casting. In this case, compared with the case where the diffuser side convex portions separately manufactured from the diffuser surface are fixed to the diffuser surface by welding or bolt connection, etc., the surface roughness of the diffuser side groove portions can be improved. By improving the surface roughness of the diffuser side groove portions, the pressure loss of the main flow after passing through the impeller can be reduced.

[0131] 9) The compressor housing (3) of at least one embodiment of the present disclosure is for rotatably accommodating the impeller (2) of the centrifugal compressor (1), and is characterized in that

[0132] In a case where the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes:

[0133] A shroud surface (4) including a surface (41) that faces the front end (24) of the impeller blades (23) of the impeller with a predetermined gap (G);

[0134] A front side inner peripheral surface (5) formed on the front side in the axial direction of the shroud surface (4) and located radially outside compared to the front end (42) of the shroud surface (4);

[0135] A plurality of convex portions (7A) protruding from the front side inner peripheral surface (5) toward the inner side in the radial direction and formed between adjacent groove portions (7B) formed at intervals in the circumferential direction on the front side inner peripheral surface (5);

[0136] Each of the plurality of groove portions (7B) is configured such that:

[0137] The rear end (74) of the groove portion is located on the upstream side in the rotation direction (RD) of the impeller compared to the front end (78) of the groove portion.

[0138] According to the configuration in 9) above, the rear end of the groove portion is configured to be located on the upstream side in the rotation direction of the impeller compared to the front end of the groove portion. Therefore, the main flow introduced into the impeller can be guided through the groove portion, and thus the main flow can be pre-rotated in the direction opposite to the rotation direction of the impeller. By pre-rotating the main flow, the relative inflow velocity of the main flow when introduced into the impeller can be increased. By increasing the relative inflow velocity of the main flow, the surge flow rate in the low flow rate side operating range can be reduced, and furthermore, the efficiency of the centrifugal compressor can be improved.

[0139] 10) The compressor housing (3) of at least one embodiment of the present disclosure is for rotatably accommodating the impeller (2) of the centrifugal compressor (1), and is characterized in that:

[0140] In a case where the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes:

[0141] A shroud surface (4) including a surface (41) that faces the front end (24) of the impeller blades (23) of the impeller with a predetermined gap (G);

[0142] A diffuser surface (6) which is located on the back (26) side of the impeller (2) in the axial direction compared to the rear end (43) of the shroud surface (4), and includes a radial surface (61) extending along the radial direction and a tightening surface (63) connecting the inner end (62) of the radial surface (61) and the rear end (43) of the shroud surface (4);

[0143] A plurality of diffuser side convex portions (8A) which protrude from the tightening surface (63) toward the back side of the impeller in the axial direction and are formed between adjacent diffuser side groove portions (8B) formed at intervals in the circumferential direction on the diffuser surface (6);

[0144] Each of the plurality of diffuser side groove portions (8B) includes:

[0145] A diffuser side inclined portion (81) whose depth gradually increases as it faces the rotation direction of the impeller;

[0146] A diffuser side section portion (83) which is formed at the downstream end (82) in the rotation direction of the diffuser side inclined portion (81).

[0147] According to the configuration of the above 10), the compressor housing has a plurality of diffuser side groove portions formed at intervals in the circumferential direction on the tightening surface. Each diffuser side groove portion among the plurality of diffuser side groove portions includes a diffuser side inclined portion and a diffuser side section portion. By guiding the countercurrent having a rotational direction component pointing to the rotation direction of the impeller generated near the tightening surface along the diffuser side inclined portion toward the rotation direction and causing the countercurrent to collide with the diffuser side section portion formed at the downstream end of the diffuser side inclined portion, the above countercurrent can be suppressed. Thereby, the rotational pressure loss of the main flow at the downstream side compared to the impeller can be suppressed. Therefore, according to the configuration of the above 10), the rotational stall at the inlet of the diffuser flow path in the low flow rate side operating range can be suppressed, and furthermore, the efficiency of the centrifugal compressor can be improved.

[0148] At a position downstream of the impeller in the centrifugal compressor, a non-uniform flow velocity distribution is generated. The plurality of diffuser side groove portions act as vortex simulators to suppress boundary layer separation. Therefore, not only when the rotational stall occurs at the inlet of the diffuser flow path, but also at the normal operating point of the centrifugal compressor, the efficiency of the centrifugal compressor can be improved.

[0149] 11) The centrifugal compressor (1) according to at least one embodiment of the present disclosure includes the compressor housing (3) described in any one of the above 1) to 10).

[0150] According to the configuration of the above 11), since the pressure loss of the fluid flowing in the compressor housing (3) can be effectively suppressed, the efficiency of the centrifugal compressor (1) can be improved.

[0151] Explanation of reference numerals

[0152] 1 Centrifugal compressor;

[0153] 2 Impeller;

[0154] 21 Hub;

[0155] 22 Outer surface;

[0156] 23 Impeller blade;

[0157] 24 Front end;

[0158] 25 Leading edge;

[0159] 26 Back surface;

[0160] 3 Compressor housing;

[0161] 31 Inlet port;

[0162] 32 Outlet port;

[0163] 33 Cover part;

[0164] 34 Suction introduction part;

[0165] 35 Diffuser part;

[0166] 36 Vortex part;

[0167] 360 Vortex flow path;

[0168] 361 Flow path wall surface;

[0169] 4 Cover surface;

[0170] 41 Surface;

[0171] 42 Front end;

[0172] 43 Rear end;

[0173] 5 Front side inner peripheral surface;

[0174] 50 Suction introduction path;

[0175] 51 Conical surface;

[0176] 52 Front end;

[0177] 53 Axial surface;

[0178] 6 Diffuser surface;

[0179] 60 Diffuser flow path;

[0180] 61 Radial surface;

[0181] 62 Inner end;

[0182] 63 Tightening surface;

[0183] 7 Annular body;

[0184] 7A Protrusion;

[0185] 7B Groove;

[0186] 71 Inclined part;

[0187] 71A Arc-shaped part;

[0188] 72 Downstream end;

[0189] 73 Step part;

[0190] 73A Step surface;

[0191] 74 Rear end;

[0192] 75 Tapered surface;

[0193] 76, 78 Front end;

[0194] 77 Bottom surface;

[0195] 8A Diffuser side protrusion;

[0196] 8B Diffuser side groove;

[0197] 81 Diffuser side inclined part;

[0198] 81A Arc-shaped part;

[0199] 82 Downstream end;

[0200] 83 Diffuser side step part;

[0201] 83A Step surface;

[0202] 10 Turbocharger;

[0203] 11 Turbine;

[0204] 12 Rotating shaft;

[0205] 13 Turbine rotor;

[0206] 14 Turbine housing;

[0207] 141 Turbine side inlet;

[0208] 142 Turbine side outlet;

[0209] 15 Bearing;

[0210] 16 Bearing housing;

[0211] CA Axis;

[0212] G Gap;

[0213] MF Main flow;

[0214] RD rotation direction;

[0215] RF, RF2 countercurrent flow;

[0216] X-axis direction;

[0217] XF (axial) front side;

[0218] XR (axial) rear side;

[0219] Y radial direction.

Claims

1. A compressor housing for rotatably accommodating an impeller of a centrifugal compressor, characterized in that: when the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes: a cover surface including a surface that faces the front ends of the impeller blades of the impeller with a predetermined clearance; a front-side inner peripheral surface formed on the front side in the axial direction of the cover surface and located radially outside compared to the front end of the cover surface; a plurality of convex portions protruding from the front-side inner peripheral surface toward the inside in the radial direction and formed between adjacent groove portions formed at intervals in the circumferential direction on the front-side inner peripheral surface; each of the plurality of groove portions includes: an inclined portion whose depth gradually increases as it goes toward the rotation direction of the impeller; a stepped portion formed at the downstream end in the rotation direction of the inclined portion and including a stepped surface extending along the radial direction from the downstream end of the inclined portion toward the inside in the radial direction.

2. The compressor housing according to claim 1, wherein the inclined portion includes an arcuate portion that is concave and curved toward the outside in the radial direction.

3. The compressor housing according to claim 1, wherein the stepped portion includes a stepped surface that forms an angle of 120 degrees or less with the inclined portion.

4. The compressor housing according to claim 1, wherein each of the plurality of groove portions is configured such that the rear end of the groove portion is located on the upstream side in the rotation direction of the impeller compared to the front end of the groove portion.

5. The compressor housing according to claim 1, wherein each of the plurality of convex portions is integrally formed with the front-side inner peripheral surface by cutting or casting.

6. The compressor housing according to claim 1, further including: a diffuser surface located on the back side of the impeller in the axial direction compared to the rear end of the cover surface and including a radial surface extending along the radial direction and a tightening surface connecting the inner end of the radial surface and the rear end of the cover surface; a plurality of diffuser-side convex portions protruding from the tightening surface toward the back side of the impeller in the axial direction and formed between adjacent diffuser-side groove portions formed at intervals in the circumferential direction on the diffuser surface.

7. The compressor housing according to claim 6, wherein each of the plurality of diffuser-side groove portions includes: a diffuser-side inclined portion whose depth gradually increases as it goes toward the rotation direction of the impeller; a diffuser-side stepped portion formed at the downstream end in the rotation direction of the diffuser-side inclined portion.

8. The compressor housing according to claim 6 or 7, wherein each of the plurality of diffuser-side convex portions is integrally formed with the diffuser surface by cutting or casting.

9. A compressor housing for rotatably accommodating an impeller of a centrifugal compressor, characterized in that: when the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes: A shroud, which includes a surface that faces the front end of the impeller blades of the impeller with a predetermined clearance; A front-side inner peripheral surface, which is formed on the front side in the axial direction of the shroud and is located radially outside compared to the front end of the shroud; A plurality of convex portions, which project from the front-side inner peripheral surface toward the inside in the radial direction and are formed between adjacent ones of a plurality of groove portions formed at intervals in the circumferential direction on the front-side inner peripheral surface; Each of the plurality of groove portions is configured such that the rear end of the groove portion is located on the upstream side in the rotational direction of the impeller compared to the front end of the groove portion.

10. A compressor housing for rotatably accommodating an impeller of a centrifugal compressor, characterized in that when the intake port side in the axial direction of the centrifugal compressor is defined as the front side and the opposite side of the intake port side in the axial direction is defined as the rear side, it includes: A shroud, which includes a surface that faces the front end of the impeller blades of the impeller with a predetermined clearance; A diffuser surface, which is located on the back side of the impeller in the axial direction compared to the rear end of the shroud and includes a radial surface extending in the radial direction and a constricting surface connecting the inner end of the radial surface to the rear end of the shroud; A plurality of diffuser-side convex portions, which project from the constricting surface toward the back side of the impeller in the axial direction and are formed between adjacent ones of a plurality of diffuser-side groove portions formed at intervals in the circumferential direction on the diffuser surface; Each of the plurality of diffuser-side groove portions includes: A diffuser-side inclined portion, the depth of which gradually increases as it faces the rotational direction of the impeller; A diffuser-side stepped portion, which is formed at the downstream end in the rotational direction of the diffuser-side inclined portion.

11. A centrifugal compressor, including the compressor housing according to any one of claims 1 to 10.

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