Compressor cover, centrifugal compressor, turbocharger, compressor cover manufacturing method, and centrifugal compressor diffuser

Abstract

Provided is an annular compressor cover forming a passage wall of a diffuser passage in a centrifugal compressor, wherein, when the end-of-winding position of a scroll passage of the centrifugal compressor is defined as the 360° position of the compressor cover in the circumferential direction, the direction in which a fluid flows through the scroll passage in the circumferential direction is defined as the positive direction of positions in the circumferential direction, and the distance between outlets of the diffuser passage at each position in the circumferential direction and the central axis of the inner circumferential surface of the compressor cover is defined as the diffuser radius, the average value of the diffuser radius in a range up to 180° from the position of a tongue section of the scroll passage in the circumferential direction is smaller than the average value of the diffuser radius in a range from 180° to 360° in the circumferential direction.

Description

[Technical Field]

[0001] The present disclosure relates to a compressor cover, a centrifugal compressor, a turbocharger, a method for manufacturing a compressor cover, and a diffuser for a centrifugal compressor. [Background technology]

[0002] For example, as described in Patent Document 1, a centrifugal compressor includes an impeller, a scroll passage formed on the outer periphery of the impeller, and a diffuser passage that guides fluid that has passed through the impeller to the scroll passage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2016-108994 Summary of the Invention [Problem to be solved by the invention]

[0004] In a centrifugal compressor, the scroll passage on the outer periphery of the impeller has a circumferentially asymmetric shape, which can cause localized low-speed regions in the scroll passage and result in backflow in the diffuser passage, as shown in Fig. 11. To address this phenomenon, for example, if the diffuser radius, which is the distance between the outlet of the diffuser passage and the rotation axis of the impeller, is reduced, the load on the diffuser passage is reduced, thereby suppressing the occurrence of the localized low-speed regions and the occurrence of backflow in the diffuser passage.

[0005] However, if the diffuser radius is reduced, it is possible to expand the operating range of the centrifugal compressor to the low flow rate side by suppressing the occurrence of local low-speed regions in the scroll passage and the occurrence of backflow in the diffuser passage, but it also suppresses pressure recovery in the diffuser passage, resulting in a decrease in compressor efficiency.

[0006] In view of the above circumstances, at least one embodiment of the present disclosure has an object to provide a compressor cover, a centrifugal compressor, a turbocharger, a method for manufacturing a compressor cover, and a diffuser for a centrifugal compressor, which are capable of realizing a highly efficient centrifugal compressor that can operate over a wide operating range. [Means for solving the problem]

[0007] In order to achieve the above object, a compressor cover according to at least one embodiment of the present disclosure comprises: An annular compressor cover that forms a flow path wall of a diffuser flow path in a centrifugal compressor, When the position of the end of the scroll passage of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as a positive direction of the position in the circumferential direction, and the distance between the outlet of the diffuser passage and the central axis of the inner circumferential surface of the compressor cover at each position in the circumferential direction is defined as a diffuser radius, The average value of the diffuser radius in the range from the position of the tongue of the scroll passage to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0008] To achieve the above object, a centrifugal compressor according to at least one embodiment of the present disclosure includes an impeller and the above compressor cover.

[0009] To achieve the above object, a turbocharger according to at least one embodiment of the present disclosure includes the above centrifugal compressor.

[0010] In order to achieve the above object, a method for manufacturing a compressor cover according to at least one embodiment of the present disclosure includes: A method for manufacturing a compressor cover that forms a flow path wall of a diffuser flow path in a centrifugal compressor, comprising: manufacturing an intermediate molded product of the compressor cover; and cutting an edge portion of the intermediate compressor cover molded product that defines an outlet of the diffuser flow path while rotating the intermediate compressor cover molded product around a rotation axis that is eccentric from the central axis of the inner circumferential surface of the compressor cover.

[0011] In order to achieve the above object, a diffuser for a centrifugal compressor according to at least one embodiment of the present disclosure comprises: a shroud side wall portion; a hub sidewall portion facing the shroud sidewall portion and forming an annular diffuser flow passage between the shroud sidewall portion and the hub sidewall portion, When the position of the end of the spiral of the diffuser of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as the positive direction of the position in the circumferential direction, and the distance between the outlet of the diffuser passage and the rotation axis of the impeller of the centrifugal compressor at each position in the circumferential direction is defined as a diffuser radius R, The average value of the diffuser radius in the range from the position of the tongue of the scroll passage to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 180° to 360° in the circumferential direction. [Effects of the Invention]

[0012] According to at least one embodiment of the present disclosure, there are provided a compressor cover, a centrifugal compressor, a turbocharger, a method for manufacturing a compressor cover, and a diffuser for a centrifugal compressor, which are capable of realizing a highly efficient centrifugal compressor that can operate over a wide operating range. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a partial cross-sectional view showing a schematic configuration of a turbocharger including a centrifugal compressor according to an embodiment. [Figure 2] FIG. 10 is a diagram for explaining the definition of a circumferential position. [Figure 3]FIG. 1 is a diagram showing a change in the flow passage cross section (axial cross section of the scroll flow passage and the diffuser flow passage) downstream of the impeller at intervals of 60° from 0° to 360° in the circumferential direction for one example of the centrifugal compressor. [Figure 4] FIG. 1 is a diagram showing the change in the flow passage cross section (the cross section along the axial direction of the scroll flow passage and the diffuser flow passage) at the position of the impeller at every 60° from 0° to 360° in the circumferential direction for a centrifugal compressor according to a comparative example. [Figure 5] 1 is a graph showing the relationship between the circumferential position and the diffuser radius in each of the centrifugal compressor according to the embodiment and the centrifugal compressor according to the comparative example. [Figure 6] 10 is a graph showing the relationship between the circumferential position and the diffuser radius in a centrifugal compressor according to another embodiment. [Figure 7] 10 is a graph showing the relationship between the circumferential position and the diffuser radius in a centrifugal compressor according to yet another embodiment. [Figure 8] FIG. 2 is a diagram showing the position of an outlet of a diffuser flow passage of a centrifugal compressor (the position of the outer circumferential edge of a shroud side wall portion) as viewed in the axial direction. [Figure 9] 1 is a flowchart illustrating an example of a method for manufacturing a compressor cover of a centrifugal compressor. [Figure 10] 10A and 10B are views seen in the axial direction showing the positions of the outer peripheral edge of the shroud side wall portion of the compressor cover before and after the cutting process in S13 of FIG. 9. [Figure 11] FIG. 10 is a diagram showing a radial flow velocity near a hub-side wall surface downstream of an impeller of a conventional centrifugal compressor. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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 invention. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, 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 such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0015] (Outline of turbocharger configuration) FIG. 1 is a partial cross-sectional view showing a schematic configuration of a turbocharger 2 including a centrifugal compressor 4 according to one embodiment. 1, the turbocharger 2 includes a centrifugal compressor 4 and a turbine (not shown) connected to the centrifugal compressor 4 via a rotary shaft 8. The centrifugal compressor 4 includes an impeller 6 and a casing 14 that houses the impeller 6.

[0016] Hereinafter, unless otherwise specified, "axial direction" means the axial direction of the impeller 6, "radial direction" means the radial direction of the impeller 6, and "circumferential direction" means the circumferential direction of the impeller 6, unless otherwise specified. In addition, the side of the air inlet 13 of the centrifugal compressor 4 in the axial direction will be referred to as the "front side," and the side opposite to the front side in the axial direction will be referred to as the "rear side."

[0017] The casing 14 includes a cylindrical portion 16 that guides air to the impeller 6 and forms an impeller accommodating space 15 that accommodates the impeller 6, a scroll portion 20 that forms a scroll passage 18 on the outer periphery of the impeller 6, and a diffuser portion 24 (diffuser) that forms an annular diffuser passage 22 that connects the impeller accommodating space 15 and the scroll passage 18.

[0018] The diffuser portion 24 includes a shroud sidewall portion 26 formed on the outer periphery of the impeller 6 along a plane perpendicular to the axial direction, and a hub sidewall portion 28 located rearward of the shroud sidewall portion 26 and formed on the outer periphery of the impeller 6 along a plane perpendicular to the axial direction so as to face the shroud sidewall portion 26. The diffuser flow path 22 is formed between the shroud sidewall portion 26 and the hub sidewall portion 28. That is, the diffuser flow path 22 is defined by the shroud sidewall portion 26 and the hub sidewall portion 28.

[0019] In the illustrated exemplary embodiment, the casing 14 includes an annular compressor cover 30 and an annular bearing casing 32. The cylindrical portion 16, a shroud side wall portion 26 of the diffuser portion 24, and a portion of the scroll portion 20 are integrally molded to form the compressor cover 30. The hub side wall portion 28 is formed by a portion of the bearing casing 32 that houses a bearing (not shown) that supports the rotating shaft 8. The compressor cover 30 and the bearing casing 32 are fastened together by fasteners such as bolts (not shown).

[0020] Furthermore, as will be described in detail later, in the centrifugal compressor 4, the distance R between the outlet 22a of the diffuser passage 22 and the central axis O1 of the inner circumferential surface 30a of the compressor cover changes depending on the position in the circumferential direction. Hereinafter, for each position in the circumferential direction, the distance R between the outlet 22a of the diffuser passage 22 and the central axis O1 of the inner circumferential surface 30a of the compressor cover 30 will be referred to as the "diffuser radius R."

[0021] The central axis O1 of the inner peripheral surface 30a of the annular compressor cover 30 coincides with the rotational axis O1 of the impeller 6, the axial direction of the compressor cover 30 coincides with the axial direction of the impeller 6 and the axial direction of the diffuser section 24, the radial direction of the compressor cover 30 coincides with the radial direction of the impeller 6 and the radial direction of the diffuser section 24, and the circumferential direction of the compressor cover 30 coincides with the circumferential direction of the impeller 6 and the circumferential direction of the diffuser section 24. At each position in the circumferential direction, the diffuser radius R corresponds to the distance between the outlet 22a of the diffuser passage 22 and the rotational axis O1 of the impeller 6. The outlet 22a of the diffuser passage 22 refers to the boundary between the diffuser passage 22 and the scroll passage 18, and more specifically refers to the open end formed in the diffuser passage 22 at the radially outer end 26a of the shroud side wall 26 (hereinafter, may be referred to as the outer peripheral edge 26a of the shroud side wall 26). The diffuser radius R corresponds to the radial distance between the radially outer end 26a of the shroud side wall 26 and the central axis O1.

[0022] (Example of diffuser passage and scroll passage configuration) Hereinafter, several examples of the configuration of the scroll passage 18 and the diffuser passage 22 will be described. FIG. 2 is a diagram for explaining the definition of the circumferential position (angular position). As shown in FIG. 2, in the following description, the position of the end of the spiral 18e of the scroll passage 18 is defined as a 360° (i.e., 0°) position in the circumferential direction, and the direction in which the exhaust gas (fluid) flows through the scroll passage 18 in the circumferential direction is defined as the positive direction of the position in the circumferential direction. The position of the tongue 18t of the scroll passage 18 in the circumferential direction may be approximately 60° (e.g., a position between 45° and 75°). As is well known to those skilled in the art, the position of the tongue 18t of the scroll passage 18 refers to the position of the tip of a tongue-like protrusion formed at the position where the beginning of the spiral 18a and the discharge portion 18b of the scroll passage 18 connect. The direction in which the exhaust gas flows through the scroll passage 18 in the circumferential direction coincides with the rotation direction of the impeller 6 (see FIG. 1).

[0023] FIG. 3 is a diagram showing a change in the flow passage cross section (the cross section along the axial direction of the scroll flow passage 18 and the diffuser flow passage 22) downstream of the impeller 6 at intervals of 60° from 60° to 360° in the circumferential direction for a centrifugal compressor 4A, which is an example of the centrifugal compressor 4.

[0024] 3, in the centrifugal compressor 4A, the flow path cross-sectional area of ​​the scroll flow path 18 gradually increases from 60° to 360° in the circumferential direction. In addition, the position of the outlet 22a of the diffuser flow path 22 changes according to the position in the circumferential direction, and the position of the outlet 22a changes from the inner side to the outer side in the radial direction in the order of 60°, 120°, 180°, 240°, and 360° (0°).

[0025] FIG. 4 is a diagram showing the change in the flow passage cross section (the cross section along the axial direction of the scroll flow passage 18 and the diffuser flow passage 22) downstream of the impeller 6 at intervals of 60° from 60° to 360° in the circumferential direction for a centrifugal compressor 04 according to a comparative example.

[0026] 4, in the centrifugal compressor 04 as well, the flow path cross-sectional area of ​​the scroll flow path 18 gradually increases from 60° to 360° in the circumferential direction. Moreover, in the centrifugal compressor 04, the radial position of the outlet 22a of the diffuser flow path 22 is constant regardless of the circumferential position. That is, in the centrifugal compressor 04, the outlet 22a of the diffuser flow path 22 is circular when viewed in the axial direction, in other words, the outer peripheral edge 26a of the shroud side wall portion 26 is circular.

[0027] Fig. 5 is a graph showing the relationship between the circumferential position and the diffuser radius R in each of the centrifugal compressor 4A and the centrifugal compressor 04. In the graph shown in Fig. 5, the horizontal axis represents the circumferential position, and the vertical axis represents the diffuser radius R.

[0028] As shown in Fig. 5, in the centrifugal compressor 04 according to the comparative example, the diffuser radius R is constant regardless of the position in the circumferential direction. In contrast, in the centrifugal compressor 4A, the diffuser radius R changes depending on the position in the circumferential direction. In the exemplary centrifugal compressor 4A shown in Fig. 5, the diffuser radius R decreases linearly from 0° to position A1 in the circumferential direction, is a constant value (=Rmin1) from position A1 to position A2, and increases linearly from position A2 to 360°. In the illustrated example, position A1 is a position between 0° and 60° in the circumferential direction, and position A2 is a position between 90° and 120° in the circumferential direction.

[0029] In the example shown in Fig. 5, the diffuser radius R varies depending on the position in the circumferential direction and has a minimum value R1min in at least a portion of the range from 0° to 180° in the circumferential direction. The diffuser radius R may also have a minimum value R1min in at least a portion of the range from 45° to 180° in the circumferential direction. The diffuser radius R may also have a minimum value R1min in at least a portion of the range from 60° to 180° in the circumferential direction. The diffuser radius R may also have a minimum value R1min in at least a portion of the range from 90° to 180° in the circumferential direction.

[0030] 5, if the range from 90° to 180° in the circumferential direction is defined as a first range S1, in the centrifugal compressor 4A, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the range excluding the first range S1 in the circumferential direction. Note that the range excluding the first range S1 in the circumferential direction means the range from 0° to 360° in the circumferential direction excluding the range from 90° to 180°, in other words, the range from 0° to 90° and the range from 180° to 360° in the circumferential direction excluding the 90° position and the 180° position.

[0031] 5, in the centrifugal compressor 4A, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range excluding the first range S1 in the circumferential direction. In addition, in the centrifugal compressor 4A, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the average value R0ave (not shown) of the diffuser radius R in the range excluding the first range S1 in the circumferential direction.

[0032] In the centrifugal compressor 4A, the average value of the diffuser radius R in the range from the position of the tongue 18t of the scroll passage 18 to 180° in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value of the diffuser radius R in the range from 180° to 360° in the circumferential direction excluding the 180° position. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The minimum value R1min of the diffuser radius R in the circumferential direction range from 90° to 180° is smaller than the minimum value R1max of the diffuser radius R in the circumferential direction range from 180° to 360°.

[0033] Furthermore, if the range from 270° to 360° in the circumferential direction is defined as a second range S2, in the centrifugal compressor 4A, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the second range S2 in the circumferential direction. Furthermore, in the centrifugal compressor 4A, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, in the centrifugal compressor 4A, the minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, in the centrifugal compressor 4A, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2ave (not shown) of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. The diffuser radius R in at least a part of the first range S1 in the circumferential direction is the minimum value R1min of the diffuser radius R in the range from 0° to 360° in the circumferential direction. That is, the diffuser radius R is minimum in at least a part of the first range S1 in the circumferential direction.

[0034] In the centrifugal compressor 4A, the average value of the diffuser radius R in a range of 180° from the position of the tongue 18t of the scroll passage 18 in the circumferential direction is smaller than the average value of the diffuser radius R in a second range S2 in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. The minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction.

[0035] In the centrifugal compressor 4A, the diffuser radius R decreases as the angle advances in the positive circumferential direction in at least a part of the circumferential range from 0° to 90°, and the diffuser radius R increases as the angle advances in the positive circumferential direction in at least a part of the circumferential range from 180° to 270°.

[0036] The effects achieved by the centrifugal compressor 4A will be described below. Generally, in a centrifugal compressor, the scroll passage on the outer periphery of the impeller has an asymmetric shape in the circumferential direction, which can cause a localized low-speed region (stall region) in the scroll passage, resulting in backflow in the diffuser passage. As a result of extensive research by the present inventors into this phenomenon, it has become clear that backflow is particularly likely to occur in the diffuser passage in the circumferential range of 90° to 180° (the first range S1 described above), as shown in Fig. 11. It has also become clear that backflow is less likely to occur in the diffuser passage in the circumferential range of 270° to 360° (the second range S2 described above).

[0037] Therefore, in the centrifugal compressor 4A, as described above, the average value of the diffuser radius R in the circumferential range from the tongue 18t of the scroll passage 18 to 180° is smaller than the average value of the diffuser radius R in the circumferential range from 180° to 360°. This makes it possible to make the load on the diffuser passage 22 in the range from the tongue 18t to 180°, which includes a location in the circumferential direction where a stall region is likely to occur (the range from 90° to 180°), smaller than the load on the diffuser passage 22 in the circumferential range from 180° to 360°. This suppresses the occurrence of local low-speed regions and backflow in the diffuser passage 22, thereby expanding the operating range of the centrifugal compressor 4A to the low flow rate side. Furthermore, compared to a case in which the diffuser radius R is uniformly small from 0° to 360°, it is possible to promote pressure recovery in the diffuser passage 22 in the circumferential range from 180° to 360°, thereby suppressing a decrease in compressor efficiency. Therefore, it is possible to realize a highly efficient centrifugal compressor 4A that can be operated in a wide operating range.

[0038] As described above, the centrifugal compressor 4A is configured such that the average value of the diffuser radius R in the first range S1 from 90° to 180° in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. This makes it possible to reduce the load on the diffuser passage 22 in the first range S1 from 90° to 180°, where a stall region is likely to occur, compared to the load on the diffuser passage 22 in the range from 180° to 360° in the circumferential direction. This suppresses the occurrence of local low-speed regions and backflow in the diffuser passage 22, thereby expanding the operating range of the centrifugal compressor 4A to the low flow rate side. Furthermore, compared to a case in which the diffuser radius R is uniformly reduced from 0° to 360°, this configuration promotes pressure recovery in the diffuser passage 22 in at least a part of the range excluding the first range S1 in the circumferential direction, thereby suppressing a decrease in compressor efficiency. Therefore, it is possible to realize a highly efficient centrifugal compressor 4A that can be operated in a wide operating range.

[0039] Furthermore, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the average value R1ave of the diffuser radius R in a first range S1 from 90° to 180° in the circumferential direction is smaller than the average value R0ave of the diffuser radius R in a range excluding the first range S1 in the circumferential direction. Therefore, the load on the diffuser passage 22 in the first range S1 from 90° to 180°, where a stall region is likely to occur in the circumferential direction, can be made smaller than the load on the diffuser passage 22 in a range excluding the first range in the circumferential direction. Therefore, it is possible to enhance the effect of expanding the operating range of the centrifugal compressor 4A to the low flow rate side and the effect of suppressing a decrease in compressor efficiency.

[0040] In addition, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the maximum value R1max of the diffuser radius R in a first range S1 from 90° to 180° in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in a range excluding the first range S1 in the circumferential direction. This enhances the effect of expanding the operating range of the centrifugal compressor 4A to the low flow rate side and the effect of suppressing a decrease in compressor efficiency.

[0041] Furthermore, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the diffuser radius R in at least a part of a first range S1 from 90° to 180° in the circumferential direction is smaller than the diffuser radius R in at least a part of a second range S2 from 270° to 360° in the circumferential direction. This makes it possible to make the load on the diffuser passage 22 in at least a part of the first range S1 from 90° to 180°, where a stall region is likely to occur, smaller than the load on the diffuser passage 22 in at least a part of the second range S2 from 270° to 360°, where a stall region is unlikely to occur (a region where the flow is normal). This makes it possible to suppress the occurrence of local low-speed regions and backflow in the diffuser passage 22, and to expand the operating range of the centrifugal compressor 4A to the low flow rate side. Furthermore, compared to when the diffuser radius R is uniformly reduced over the range from 0° to 360°, the pressure recovery in the diffuser passage 22 in the second range S2 from 270° to 360° in the circumferential direction can be promoted, thereby suppressing a decrease in compressor efficiency. Therefore, a highly efficient centrifugal compressor 4A that can be operated over a wide operating range can be realized.

[0042] Furthermore, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the average value R1ave of the diffuser radius R in a first range S1 from 90° to 180° in the circumferential direction is smaller than the average value R2ave of the diffuser radius R in a second range S2 from 270° to 360° in the circumferential direction. Therefore, the load on the diffuser passage 22 in the first range S1 from 90° to 180°, where a stall region is likely to occur in the circumferential direction, can be made smaller than the load on the diffuser passage 22 in the second range S2 from 270° to 360°, where a stall region is unlikely to occur in the circumferential direction (a region where the flow is normal). This can enhance the effects of expanding the operating range of the centrifugal compressor 4A to the low flow rate side and suppressing a decrease in compressor efficiency.

[0043] In addition, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the maximum value R1max of the diffuser radius R in a first range S1 from 90° to 180° in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in a second range S1 from 270° to 360° in the circumferential direction. This can enhance the effect of expanding the operating range of the centrifugal compressor 4A to the low flow rate side and the effect of suppressing a decrease in compressor efficiency.

[0044] In addition, in the centrifugal compressor 4A, the compressor cover 30 is configured so that the minimum value R1min of the diffuser radius R in a first range S1 from 90° to 180° in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in a second range S1 from 270° to 360° in the circumferential direction. This enhances the effect of expanding the operating range of the centrifugal compressor 4A to the low flow rate side and the effect of suppressing a decrease in compressor efficiency.

[0045] Fig. 6 is a graph showing the relationship between the circumferential position and the diffuser radius R in a centrifugal compressor 4B according to another embodiment. In the graph shown in Fig. 6, the horizontal axis represents the circumferential position, and the vertical axis represents the diffuser radius R.

[0046] In the exemplary centrifugal compressor 4B shown in FIG. 6, the diffuser radius R decreases linearly in the circumferential direction from 0° to 60°, remains constant from 60° to 180° (=Rmax1, Rmin1), increases linearly from 180° to 270°, and remains constant from 270° to 360° (=Rmax2, Rmin2).

[0047] In the centrifugal compressor 4B shown in Fig. 6, the diffuser radius R also varies depending on the position in the circumferential direction, and takes on a minimum value R1min in at least a portion of the range from 0° to 180° in the circumferential direction. Alternatively, the diffuser radius R may take on a minimum value R1min in at least a portion of the range from 45° to 180° in the circumferential direction. Alternatively, the diffuser radius R may take on a minimum value R1min in at least a portion of the range from 60° to 180° in the circumferential direction. Alternatively, the diffuser radius R may take on a minimum value R1min in at least a portion of the range from 90° to 180° in the circumferential direction.

[0048] In the centrifugal compressor 4B shown in FIG. 6, if a range from 90° to 180° in the circumferential direction is defined as a first range S1, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the range excluding the first range S1 in the circumferential direction.

[0049] Also in the centrifugal compressor 4B, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range excluding the first range S1 in the circumferential direction. Also, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the average value R0ave (not shown) of the diffuser radius R in the range excluding the first range S1 in the circumferential direction.

[0050] In the centrifugal compressor 4B, too, the average value of the diffuser radius R in the range from the position of the tongue 18t of the scroll passage 18 to 180° in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value of the diffuser radius R in the range from 180° to 360° in the circumferential direction excluding the 180° position. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The minimum value R1min of the diffuser radius R in the circumferential direction range from 90° to 180° is smaller than the minimum value R1max of the diffuser radius R in the circumferential direction range from 180° to 360°.

[0051] Also in the centrifugal compressor 4B, if the range from 270° to 360° in the circumferential direction is defined as a second range S2, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the second range S2 in the circumferential direction. Furthermore, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2ave (not shown) of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is the minimum value R1min of the diffuser radius R in the circumferential range from 0° to 360°. Furthermore, in at least a part of the circumferential range from 0° to 90°, the diffuser radius R decreases as the angle advances in the positive circumferential direction, and in at least a part of the circumferential range from 180° to 270°, the diffuser radius R increases as the angle advances in the positive circumferential direction.

[0052] In the centrifugal compressor 4B, too, the average value of the diffuser radius R in a range of 180° from the position of the tongue 18t of the scroll passage 18 in the circumferential direction is smaller than the average value of the diffuser radius R in a second range S2 in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. The minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction.

[0053] According to the centrifugal compressor 4B, similarly to the centrifugal compressor 4A, a highly efficient centrifugal compressor that can be operated in a wide operating range can be realized.

[0054] Fig. 7 is a graph showing the relationship between the circumferential position and the diffuser radius R in a centrifugal compressor 4C according to yet another embodiment. In the graph shown in Fig. 7, the horizontal axis represents the circumferential position, and the vertical axis represents the diffuser radius R.

[0055] In the exemplary centrifugal compressor 4C shown in Fig. 7, the diffuser radius R decreases in the circumferential direction from 0° to position A3, increases from position A3 to position A4, and decreases from position A4 to 360°. In the illustrated example, position A3 is a position between 90° and 180° in the circumferential direction (more specifically, a position between 120° and 180°), and position A4 is a position between 270° and 360° in the circumferential direction (more specifically, a position between 300° and 360°). The graph shown in Fig. 7 is composed of smooth curves.

[0056] In the centrifugal compressor 4C shown in Fig. 7, the diffuser radius R also varies depending on the position in the circumferential direction and has a minimum value R1min in at least a portion of the range from 0° to 180° in the circumferential direction. Alternatively, the diffuser radius R may have a minimum value R1min in at least a portion of the range from 45° to 180° in the circumferential direction. Alternatively, the diffuser radius R may have a minimum value R1min in at least a portion of the range from 60° to 180° in the circumferential direction. Alternatively, the diffuser radius R may have a minimum value R1min in at least a portion of the range from 90° to 180° in the circumferential direction.

[0057] In the centrifugal compressor 4C shown in FIG. 7, if a range from 90° to 180° in the circumferential direction is defined as a first range S1, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the range excluding the first range S1 in the circumferential direction.

[0058] In the centrifugal compressor 4C, the minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the range excluding the first range S1 in the circumferential direction. Also, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range excluding the first range S1 in the circumferential direction. Also, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the average value R0ave (not shown) of the diffuser radius R in the range excluding the first range S1 in the circumferential direction.

[0059] In the centrifugal compressor 4C, the average value of the diffuser radius R in the range from the position of the tongue 18t of the scroll passage 18 to 180° in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value of the diffuser radius R in the range from 180° to 360° in the circumferential direction excluding the 180° position. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the range from 180° to 360° in the circumferential direction. The minimum value R1min of the diffuser radius R in the circumferential direction range from 90° to 180° is smaller than the minimum value R1max of the diffuser radius R in the circumferential direction range from 180° to 360°.

[0060] Also in the centrifugal compressor 4C, if the range from 270° to 360° in the circumferential direction is defined as a second range S2, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is smaller than the diffuser radius R in at least a part of the second range S2 in the circumferential direction. Furthermore, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the average value R1ave (not shown) of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2ave (not shown) of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. Furthermore, the diffuser radius R in at least a part of the first range S1 in the circumferential direction is the minimum value R1min of the diffuser radius R in the circumferential range from 0° to 360°. Furthermore, in at least a part of the circumferential range from 0° to 90°, the diffuser radius R decreases as the angle advances in the positive circumferential direction, and in at least a part of the circumferential range from 180° to 270°, the diffuser radius R increases as the angle advances in the positive circumferential direction.

[0061] In the centrifugal compressor 4C, too, the average value of the diffuser radius R in a range of 180° from the position of the tongue 18t of the scroll passage 18 in the circumferential direction is smaller than the average value of the diffuser radius R in a second range S2 in the circumferential direction. The average value of the diffuser radius R in a first range S1 in the circumferential direction is smaller than the average value of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction. The maximum value R1max of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the maximum value R2max of the diffuser radius R in the second range S2 in the circumferential direction. The minimum value R1min of the diffuser radius R in the first range S1 in the circumferential direction is smaller than the minimum value R2min of the diffuser radius R in the second range S2 in the circumferential direction.

[0062] 8 is a diagram showing the position of the outlet 22a of the diffuser passage 22 of the centrifugal compressor 4C (the position of the outer peripheral edge 26a of the shroud side wall portion 26) as viewed in the axial direction. In Fig. 8, the position of the outlet 22a of the diffuser passage 22 of the centrifugal compressor 4C is indicated by a solid-line circle, and two circles C1 and C2 centered on the central axis O1 (the rotation axis of the impeller 6) of the inner circumferential surface 30a of the compressor cover 30 are indicated by a dashed-dotted circle and a broken-line circle, respectively, for reference. In Fig. 8, the central axis O1 is set as the origin, and the direction from the origin toward the position at 0° in the circumferential direction is set as the positive direction of the X coordinate, and the direction from the origin toward the position at 90° is set as the positive direction of the Y coordinate, showing the position of the outlet 22a of the diffuser passage 22.

[0063] 8, the outlet 22a of the diffuser passage 22 is circular when viewed in the axial direction, and the center O2 of the circle defining the outlet 22a of the diffuser passage 22 is eccentric from the central axis O1 (the rotation axis of the impeller 6) of the inner circumferential surface 30a of the compressor cover 30 so as to be located within a range of 270° to 360° in the circumferential direction. Such a compressor cover 30 of the centrifugal compressor 4C can be easily manufactured by eccentric processing, which will be described below.

[0064] Fig. 9 is a flowchart showing an example of a manufacturing method for the compressor cover 30 of the centrifugal compressor 4C. Fig. 10 is an axial view showing the position of the outer peripheral edge 26a of the shroud side wall portion 26 of the compressor cover 30 before and after the cutting process in S13 of Fig. 9.

[0065] 9, in S11, an intermediate molded product of the compressor cover 30 is manufactured by, for example, casting. Here, the intermediate molded product of the compressor cover 30 is manufactured so that the outer peripheral edge 26a of the shroud side wall portion 26 has a cutting allowance (excess material) for the cutting process performed in S12, as shown by the dashed-dotted circle in FIG.

[0066] In S12, as shown in FIG. 10, the intermediate molded product of the compressor cover 30 is fixed (axially supported) by a jig (not shown) so as to rotate about a rotation axis O2 eccentric from the central axis O1.

[0067] In S13, while the intermediate product of the compressor cover 30 is rotated about a rotation axis O2 eccentric from the central axis O1, a cutting tool (not shown) is applied to the outer peripheral edge 26a (see the dot-dash circle in FIG. 10 ) of the shroud side wall portion 26 in the intermediate product of the compressor cover 30 to perform cutting (eccentric cutting) to remove the excess material. This results in the production of a finished compressor cover 30. In the finished compressor cover 30 produced in this manner, the outer peripheral edge 26a of the shroud side wall portion 26 is circular when viewed in the axial direction, as shown by the solid circle in FIG. 10 , and the center O2 of the circle defining the outer peripheral edge 26a is eccentric from the central axis O1 so as to be located within a range of 270° to 360° in the circumferential direction. That is, in the compressor cover 30 after execution of S13, the outlet 22a of the diffuser passage 22 is circular when viewed in the axial direction, and the center O2 of the circle defining the outlet 22a of the diffuser passage 22 is eccentric from the central axis O1 so as to be located within a range of 270° to 360° in the circumferential direction.

[0068] The centrifugal compressor 4C having the compressor cover 30 manufactured by the above manufacturing method can realize a highly efficient centrifugal compressor that can operate in a wide operating range, similar to the centrifugal compressor 4A. In addition, the compressor cover 30 can be easily manufactured by eccentric machining.

[0069] 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.

[0070] For example, the graph shown in FIG. 6 shows an example in which the diffuser radius R linearly decreases and increases with changes in circumferential position, but the diffuser radius R may also change smoothly, for example, in the range of 60° to 180°, taking a lower value than in other ranges.

[0071] In addition, in some of the above-described embodiments, the compressor cover 30 includes the cylindrical portion 16, the shroud side wall portion 26 of the diffuser portion 24, and a part of the scroll portion 20. However, a compressor cover to which the present disclosure is applicable may include at least the shroud side wall portion of the diffuser portion, and may include, for example, only the shroud side wall portion of the diffuser portion. In this case, the central axis of the inner circumferential surface of the compressor cover may be the central axis of the inner circumferential surface of the annular shroud side wall portion, and coincides with the rotational axis of the impeller.

[0072] Furthermore, in the centrifugal compressors 4A to 4C described above, the flow path area of ​​the scroll flow path 18 basically increases in the forward circumferential direction, but the flow path area of ​​the scroll flow path 18 may locally decrease in the forward circumferential direction in a partial range in the circumferential direction. In this case, by locally decreasing the flow path area of ​​the scroll flow path 18 in the forward circumferential direction in a range where local backflow occurs in the circumferential direction (for example, at least a part of the range from 90° to 180°), a synergistic effect can be obtained with the effect of suppressing the backflow described above.

[0073] The contents described in each of the above embodiments can be understood, for example, as follows.

[0074] (1) A compressor cover according to at least one embodiment of the present disclosure (e.g., the compressor cover 30 described above) An annular compressor cover that forms a flow path wall (for example, the shroud side wall portion 26) of a diffuser flow path (for example, the diffuser flow path 22) in a centrifugal compressor (for example, the centrifugal compressors 4 (4A to 4C) described above), If the position of the end of the spiral (e.g., the above-mentioned end of the spiral 18) of a scroll passage (e.g., the above-mentioned scroll passage 18) of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as the positive direction of the position in the circumferential direction, and the distance between the outlet of the diffuser passage (e.g., the above-mentioned outlet 22a) and the central axis of the inner circumferential surface of the compressor cover (e.g., the above-mentioned central axis O1) for each position in the circumferential direction is defined as a diffuser radius (e.g., the above-mentioned diffuser radius R), then: The average value of the diffuser radius in the range from the position of the tongue of the scroll passage to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0075] According to the compressor cover described in (1) above, the load on the diffuser passage in the range from the tongue position to 180°, which includes the area in the circumferential direction where stall regions are likely to occur (the range from 90° to 180°), can be made smaller than the load on the diffuser passage in other ranges. This suppresses the occurrence of local low-speed regions and backflow in the diffuser passage, and enables the operating range of the centrifugal compressor to be expanded to the low flow rate side. Furthermore, compared to a case in which the diffuser radius R is uniformly reduced from 0° to 360°, it is possible to promote pressure recovery in the diffuser passage in the circumferential range from 180° to 360°, thereby suppressing a decrease in compressor efficiency. Therefore, a highly efficient centrifugal compressor that can be operated over a wide operating range can be realized.

[0076] (2) In some embodiments, in the compressor cover described in (1) above, The average value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0077] According to the compressor cover described in (2) above, the load on the diffuser passage in the circumferential range from 90° to 180°, where a stall region is likely to occur, can be made smaller than the load on the diffuser passage in the circumferential range from 180° to 360°. This makes it possible to suppress the occurrence of localized low-speed regions and backflow in the diffuser passage, thereby expanding the operating range of the centrifugal compressor to the low flow rate side. Furthermore, compared to a case where the diffuser radius R is uniformly reduced from 0° to 360°, this promotes pressure recovery in the diffuser passage in at least a part of the circumferential range excluding the first range, thereby suppressing a decrease in compressor efficiency. This makes it possible to realize a highly efficient centrifugal compressor that can operate over a wide operating range.

[0078] (3) In some embodiments, in the compressor cover described in (1) or (2) above, (For example, the above-mentioned maximum value R1max) The maximum value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the minimum value of the diffuser radius in the range from 180° to 360° in the circumferential direction excluding the 180° position.

[0079] According to the compressor cover described in (3) above, it is possible to enhance the above-mentioned effects of expanding the operating range of the centrifugal compressor to the low flow rate side and suppressing the decrease in compressor efficiency.

[0080] (4) In some embodiments, in the compressor cover according to any one of (1) to (3) above, The maximum value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the maximum value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0081] According to the compressor cover described in (4) above, it is possible to enhance the above-mentioned effect of expanding the operating range of the centrifugal compressor to the low flow rate side and the above-mentioned effect of suppressing a decrease in compressor efficiency.

[0082] (5) In some embodiments, in the compressor cover described in any one of (1) to (4), The minimum value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the minimum value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0083] According to the compressor cover described in (5) above, it is possible to enhance the above-mentioned effects of expanding the operating range of the centrifugal compressor to the low flow rate side and suppressing the decrease in compressor efficiency.

[0084] (6) In some embodiments, in the compressor cover according to any one of (1) to (5) above, The average value of the diffuser radius in the range of 180° from the position of the tongue of the scroll passage in the circumferential direction is smaller than the average value of the diffuser radius in the range of 270° to 360° in the circumferential direction.

[0085] According to the compressor cover described in (6) above, the load on the diffuser passage in the range from the tongue position to 180°, which includes the area where a stall region is likely to occur in the circumferential direction (the range from 90° to 180°), can be made smaller than the load on the diffuser passage in the range from 270° to 360°, which is the area where a stall region is unlikely to occur in the circumferential direction (the area where the flow is normal). This suppresses the occurrence of localized low-speed areas and backflow in the diffuser passage, thereby expanding the operating range of the centrifugal compressor to the low flow rate side. Furthermore, compared to a case where the diffuser radius R is uniformly reduced from 0° to 360°, this promotes pressure recovery in the diffuser passage in the circumferential range from 270° to 360°, thereby suppressing a decrease in compressor efficiency. This makes it possible to realize a highly efficient centrifugal compressor that can operate over a wide operating range.

[0086] (7) In some embodiments, in the compressor cover according to any one of (1) to (6) above, The average value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 270° to 360° in the circumferential direction.

[0087] According to the compressor cover described in (7) above, the load on the diffuser passage in the circumferential direction between 90° and 180°, where a stall region is likely to occur, can be made smaller than the load on the diffuser passage in the circumferential direction between 270° and 360°, where a stall region is unlikely to occur (a region where the flow is normal). This suppresses the occurrence of localized low-speed regions and backflow in the diffuser passage, thereby expanding the operating range of the centrifugal compressor to the low flow rate side. Furthermore, compared with a case where the diffuser radius R is uniformly reduced from 0° to 360°, this promotes pressure recovery in the diffuser passage in the circumferential direction between 270° and 360°, thereby suppressing a decrease in compressor efficiency. This makes it possible to realize a highly efficient centrifugal compressor that can operate over a wide operating range.

[0088] (8) In some embodiments, in the compressor cover according to any one of (1) to (7) above, The maximum value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than the minimum value of the diffuser radius in the range of 270° to 360° in the circumferential direction.

[0089] According to the compressor cover described in (8) above, it is possible to enhance the above-mentioned effect of expanding the operating range of the centrifugal compressor to the low flow rate side and the above-mentioned effect of suppressing a decrease in compressor efficiency.

[0090] (9) In some embodiments, in the compressor cover according to any one of (1) to (8) above, The maximum value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the maximum value of the diffuser radius in the range from 270° to 360° in the circumferential direction.

[0091] According to the compressor cover described in (9) above, it is possible to enhance the above-mentioned effect of expanding the operating range of the centrifugal compressor to the low flow rate side and the above-mentioned effect of suppressing a decrease in compressor efficiency.

[0092] (10) In some embodiments, in the compressor cover according to any one of (1) to (9) above, The minimum value of the diffuser radius in the range from 90° to 180° in the circumferential direction is smaller than the minimum value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0093] According to the compressor cover described in (10) above, it is possible to enhance the above-mentioned effect of expanding the operating range of the centrifugal compressor to the low flow rate side and the above-mentioned effect of suppressing a decrease in compressor efficiency.

[0094] (11) In some embodiments, in the compressor cover according to any one of (1) to (10) above, In a graph with the circumferential position on the horizontal axis and the diffuser radius on the vertical axis, the diffuser radius decreases as the angle progresses in the positive circumferential direction in at least a part of the range from 0° to 60° in the circumferential direction.

[0095] According to the compressor cover described in (11) above, the load on the diffuser passage can be reduced in at least a part of the range from 0° to 60° in the circumferential direction as it approaches the first range from 90° to 180°, where a stall region is likely to occur in the circumferential direction, thereby enhancing the effect of expanding the operating range of the centrifugal compressor to the low flow rate side.

[0096] (12) In some embodiments, in the compressor cover according to any one of (1) to (11) above, In a graph with the circumferential position on the horizontal axis and the diffuser radius on the vertical axis, the diffuser radius increases as the angle progresses in the positive circumferential direction in at least a part of the range from 180° to 270° in the circumferential direction.

[0097] According to the compressor cover described in (12) above, in at least a part of the circumferential range from 180° to 270°, the load on the diffuser passage can be increased as the angle approaches the range from 270° to 360° (as the angle moves in the positive direction in the circumferential direction), where a stall region is unlikely to occur in the circumferential direction, thereby enhancing the pressure recovery function. Furthermore, in at least a part of the circumferential range from 180° to 270°, the load on the diffuser passage can be decreased as the angle approaches the range from 90° to 180° (as the angle moves in the negative direction in the circumferential direction), where a stall region is likely to occur in the circumferential direction. Therefore, the effect of expanding the operating range of the centrifugal compressor to the low flow rate side and the effect of suppressing a decrease in compressor efficiency can be enhanced.

[0098] (13) In some embodiments, in the compressor cover according to any one of (1) to (12) above, When viewed in the axial direction of the compressor cover, the outlet of the diffuser flow path is circular, The center of the circle defining the outlet of the diffuser flow path (for example, the above-mentioned center O2) is eccentric from the central axis (for example, the above-mentioned central axis O1) so as to be located within a range of 270° to 360° in the circumferential direction.

[0099] According to the compressor cover described in (13) above, the effect described in (1) above can be obtained with a simple configuration in which the shape of the outlet of the diffuser flow path as viewed in the axial direction is defined by a circle. Therefore, a compressor cover that can obtain the effect described in (1) above can be easily formed by eccentric machining.

[0100] (14) A centrifugal compressor according to at least one embodiment of the present disclosure (for example, the centrifugal compressor 4 (4A to 4C) described above) has the following features: an impeller (e.g., impeller 6 described above); A compressor cover according to any one of (1) to (13) above (for example, the compressor cover 30 described above), Equipped with.

[0101] According to the centrifugal compressor described in (14) above, since it is equipped with the compressor cover described in any one of (1) to (13) above, it is possible to realize a highly efficient centrifugal compressor that can be operated in a wide operating range.

[0102] (15) A turbocharger according to at least one embodiment of the present disclosure includes: The centrifugal compressor (for example, the centrifugal compressor 4 (4A to 4C)) described above in (14) is provided.

[0103] According to the turbocharger described in (15) above, since it is equipped with the centrifugal compressor described in (1) above, it is possible to realize a highly efficient turbocharger that can be operated in a wide operating range.

[0104] (16) A method for manufacturing a compressor cover according to at least one embodiment of the present disclosure includes: A method for manufacturing a compressor cover (e.g., the above-mentioned compressor cover 30) that forms a flow path wall (e.g., the above-mentioned shroud side wall portion 26) of a diffuser flow path (e.g., the above-mentioned diffuser flow path 22) in a centrifugal compressor (e.g., the above-mentioned centrifugal compressor 4 (4A to 4C)), comprising: manufacturing an intermediate molded product of the compressor cover; and cutting an edge portion (for example, the aforementioned outer peripheral edge 26a) that defines the outlet of the diffuser flow path in the intermediate molded product of the compressor cover while rotating the intermediate molded product of the compressor cover around a rotation axis (for example, the aforementioned rotation axis O2) that is eccentric from a central axis of the inner peripheral surface of the compressor cover (for example, the aforementioned central axis O1).

[0105] According to the manufacturing method of the compressor cover described in (16) above, the shape of the outlet of the diffuser passage when viewed in the axial direction of the compressor cover can be made circular, and the compressor cover can be manufactured so that the center of the circle is eccentric from the central axis of the inner circumferential surface of the compressor cover. Therefore, by setting the direction in which the center of the circle is eccentric from the central axis of the inner circumferential surface of the compressor cover in consideration of the location in the diffuser passage where backflow is likely to occur, it is possible to easily manufacture a compressor cover that realizes a highly efficient centrifugal compressor that can operate over a wide operating range.

[0106] (17) In some embodiments, in the method for manufacturing a compressor cover described in (16) above, If the position of the end of the scroll (for example, the above-mentioned end of the scroll 18e) of the scroll passage (for example, the above-mentioned scroll passage 18) of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, and the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as the positive direction of the position in the circumferential direction, In the step of cutting the edge portion, the edge portion is cut while rotating the intermediate molded product of the compressor cover around a rotation axis (for example, the above-mentioned rotation axis O2) located within a range of 270° to 360° in the circumferential direction.

[0107] According to the compressor cover manufacturing method described in (17) above, a compressor cover having the following effects can be easily manufactured by, for example, lathe machining. With a compressor cover manufactured by the compressor cover manufacturing method described in (14) above, the load on the diffuser passage in the circumferential direction between 90° and 180°, where a stall region is likely to occur, can be made smaller than the load on the diffuser passage in the circumferential direction between 270° and 360°, where a stall region is unlikely to occur (a region where the flow is normal). This suppresses the occurrence of localized low-speed regions and backflow in the diffuser passage, thereby expanding the operating range of the centrifugal compressor to the low flow rate side. Furthermore, compared to a case where the diffuser radius R is uniformly reduced from 0° to 360°, this promotes pressure recovery in the diffuser passage in the circumferential direction between 270° and 360°, thereby suppressing a decrease in compressor efficiency. Therefore, a compressor cover capable of realizing a highly efficient centrifugal compressor that can operate over a wide operating range can be provided.

[0108] (18) A diffuser for a centrifugal compressor according to at least one embodiment of the present disclosure (e.g., the diffuser section 24 described above) may include: a shroud sidewall (e.g., shroud sidewall 26); a hub sidewall portion (e.g., the above-mentioned hub sidewall portion 28) facing the shroud sidewall portion and forming an annular diffuser flow passage (e.g., the above-mentioned diffuser flow passage 22) between the shroud sidewall portion and the hub sidewall portion, If the position of the end of the spiral (for example, the above-mentioned end of the spiral 18e) of a scroll passage (for example, the above-mentioned scroll passage 18) of the centrifugal compressor is defined as a 360° position in the circumferential direction of the diffuser, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as the positive direction of a position in the circumferential direction, and the distance between the outlet of the diffuser passage (for example, the above-mentioned outlet 22a) and the rotation axis (for example, the above-mentioned rotation axis O1) of the impeller (for example, the above-mentioned impeller 6) of the centrifugal compressor for each position in the circumferential direction is defined as a diffuser radius (for example, the above-mentioned diffuser radius R), then: The average value of the diffuser radius in the range from the position of the tongue of the scroll passage to 180° in the circumferential direction is smaller than the average value of the diffuser radius in the range from 180° to 360° in the circumferential direction.

[0109] According to the diffuser for a centrifugal compressor described in (18) above, the load on the diffuser passage in the range from the tongue position to 180°, which includes the area in the circumferential direction where a stall region is likely to occur (the range from 90° to 180°), can be made smaller than the load on the diffuser passage in other ranges. This suppresses the occurrence of local low-speed regions and backflow in the diffuser passage, and enables the operating range of the centrifugal compressor to be expanded to the low flow rate side. Furthermore, compared to a case in which the diffuser radius R is uniformly reduced from 0° to 360°, it is possible to promote pressure recovery in the diffuser passage in the circumferential range from 180° to 360°, thereby suppressing a decrease in compressor efficiency. Therefore, it is possible to provide a diffuser for a centrifugal compressor that can realize a highly efficient centrifugal compressor that can operate over a wide operating range. [Explanation of symbols]

[0110] 2 turbochargers 4(4A, 4B, 4C) Centrifugal compressor 6 impeller 8 Rotation Axis 10 Turbine Wheel 12 Turbine 13 Air inlet 14 Casing 15 Impeller housing space 16 Cylindrical part 18 Scroll flow passage 18a Beginning of winding 18b Discharge part 18e End of roll 18t tongue 20 Scroll section 22 Diffuser passage 22a exit 24 Diffuser section 26 Shroud side wall 26a Outer periphery (outer edge in the radial direction) 28 Hub side wall 30 Compressor cover 30a Inner surface 32 Bearing casing

Claims

1. An annular compressor cover that forms a flow path wall of a diffuser flow path in a centrifugal compressor, When the position of the end of the scroll passage of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as a positive direction of the position in the circumferential direction, and the distance between the outlet of the diffuser passage and the central axis of the inner circumferential surface of the compressor cover at each position in the circumferential direction is defined as a diffuser radius, an average value of the diffuser radius in a range of 180° from a position of a tongue of the scroll passage in the circumferential direction is smaller than an average value of the diffuser radius in a range of 180° to 360° in the circumferential direction, When viewed in the axial direction of the compressor cover, the outlet of the diffuser flow path has a perfect circular shape, a center of the perfect circle defining the outlet of the diffuser flow path is eccentric from the central axis so as to be positioned within a range of 270° to 360° in the circumferential direction; Compressor cover.

2. 2. The compressor cover of claim 1, wherein an average value of the diffuser radius in the circumferential direction range from 90° to 180° is smaller than an average value of the diffuser radius in the circumferential direction range from 180° to 360°.

3. 3. The compressor cover according to claim 1, wherein a maximum value of the diffuser radius within a range from 90° to 180° in the circumferential direction is smaller than a minimum value of the diffuser radius within a range from 180° to 360° in the circumferential direction excluding 180°.

4. 4. The compressor cover according to claim 1, wherein a maximum value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than a maximum value of the diffuser radius in the range of 180° to 360° in the circumferential direction.

5. 5. The compressor cover according to claim 1, wherein a minimum value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than a minimum value of the diffuser radius in the range of 180° to 360° in the circumferential direction.

6. 6. The compressor cover according to claim 1, wherein an average value of the diffuser radius in a range of 180° from the position of the tongue portion of the scroll passage in the circumferential direction is smaller than an average value of the diffuser radius in a range of 270° to 360° in the circumferential direction.

7. 7. The compressor cover according to claim 1, wherein an average value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than an average value of the diffuser radius in the range of 270° to 360° in the circumferential direction.

8. 8. The compressor cover according to claim 1, wherein a maximum value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than a minimum value of the diffuser radius in the range of 270° to 360° in the circumferential direction.

9. 9. The compressor cover according to claim 1, wherein a maximum value of the diffuser radius in the range of 90° to 180° in the circumferential direction is smaller than a maximum value of the diffuser radius in the range of 270° to 360° in the circumferential direction.

10. 10. The compressor cover according to claim 1, wherein, in a graph having a horizontal axis representing position in the circumferential direction and a vertical axis representing the diffuser radius, the diffuser radius decreases as the angle progresses in the positive circumferential direction in at least a part of a range from 0° to 60° in the circumferential direction.

11. 11. The compressor cover according to claim 1, wherein, in a graph having a horizontal axis representing position in the circumferential direction and a vertical axis representing the diffuser radius, the diffuser radius increases as the circumferential direction progresses in the positive direction in at least a part of a range from 180° to 270° in the circumferential direction.

12. The impeller and A compressor cover according to any one of claims 1 to 11; A centrifugal compressor comprising:

13. A turbocharger comprising the centrifugal compressor of claim 12.

14. A method for manufacturing a compressor cover according to any one of claims 1 to 11, manufacturing an intermediate molded product of the compressor cover; cutting an edge portion of the intermediate compressor cover product that defines an outlet of the diffuser flow path while rotating the intermediate compressor cover product around a rotation axis that is eccentric from a central axis of an inner circumferential surface of the compressor cover; A method for manufacturing a compressor cover, comprising:

15. When the position of the end of the scroll flow passage of the centrifugal compressor is defined as a 360° position in the circumferential direction of the compressor cover, and the direction in which the fluid flows in the scroll flow passage in the circumferential direction is defined as a positive direction of the position in the circumferential direction, 15. The method for manufacturing a compressor cover according to claim 14, wherein in the step of cutting the edge portion, the edge portion is cut while rotating the intermediate molded product of the compressor cover around a rotation axis positioned within a range of 270° to 360° in the circumferential direction.

16. 1. A diffuser for a centrifugal compressor, comprising: a shroud side wall portion; a hub sidewall portion facing the shroud sidewall portion and forming an annular diffuser flow passage between the shroud sidewall portion and the hub sidewall portion, When the position of the end of the scroll passage of the centrifugal compressor is defined as a 360° position in the circumferential direction of the diffuser, the direction in which the fluid flows in the scroll passage in the circumferential direction is defined as the positive direction of the position in the circumferential direction, and the distance between the outlet of the diffuser passage and the rotation axis of the impeller of the centrifugal compressor at each position in the circumferential direction is defined as a diffuser radius, an average value of the diffuser radius within a range of 180° from a position of a tongue of the scroll passage in the circumferential direction is smaller than an average value of the diffuser radius within a range of 180° to 360° in the circumferential direction; When viewed in the axial direction of the diffuser, the outlet of the diffuser flow path has a perfect circular shape, a center of the perfect circle defining the outlet of the diffuser flow path is eccentric from the rotation axis so as to be positioned within a range of 270° to 360° in the circumferential direction; Diffuser for centrifugal compressor.

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