Centrifugal compressor

Abstract

A circulation flow path (73) of the centrifugal compressor includes a downstream slit (76), an upstream slit (77), and an intermediate flow path (78) connecting the downstream slit (76) and the upstream slit (77). The intermediate flow path (78) expands at least at a portion continuous with the downstream slit (76) as the intermediate flow path (78) moves from the downstream slit (76) toward the upstream slit (77), and the outer peripheral surface (78a) of the intermediate flow path (78) inclines radially outward at least at a portion continuous with the downstream slit (76) as the intermediate flow path (78) moves from the downstream slit (76) toward the upstream slit (77). The inner peripheral surface (78b) is inclined radially inward at least at a portion continuous with the downstream slit (76) as the inner peripheral surface (78b) moves from the downstream slit (76) toward the upstream slit (77). The angle (alpha2) of the inner peripheral surface (78b) with respect to a straight line (X) that passes through the intermediate flow path (78) and is parallel to the central axis is larger than the angle (alpha1) of the outer peripheral surface (78a) with respect to the straight line (X).

Description

Technical Field

[0001] This invention relates to centrifugal compressors. This application claims the benefit of priority to Japanese Patent Application No. 2023-153480, filed September 20, 2023, the contents of which are incorporated herein by reference. Background Technology

[0002] To suppress surge, centrifugal compressors sometimes have a circulating flow path located radially outside the main flow path (e.g., Patent Documents 1 and 2).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 6598388

[0006] Patent Document 2: Japanese Patent No. 7123029 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The inventors have discovered that even when a centrifugal compressor can suppress surge as expected in a single-unit test, it sometimes fails to suppress surge when the centrifugal compressor is connected to an engine.

[0009] The purpose of this invention is to provide a centrifugal compressor capable of suppressing surge.

[0010] Methods for solving problems

[0011] To address the aforementioned issues, one aspect of the present invention provides a centrifugal compressor comprising a compressor impeller and a compressor housing housing the compressor impeller. The compressor housing includes: a main flow path housing the compressor impeller; and a circulating flow path radially outside the main flow path and connected to the main flow path, the circulating flow path including: a downstream slit radially connected to the main flow path opposite the compressor impeller; an upstream slit connected to the main flow path upstream of the downstream slit; and an intermediate flow path extending along the axial direction of the compressor impeller. The downstream slit is connected to the upstream slit. The intermediate flow path expands at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit. The outer circumferential surface of the intermediate flow path tilts radially outward at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit. The inner circumferential surface of the intermediate flow path tilts radially inward at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit. The angle of the inner circumferential surface relative to a straight line passing through the intermediate flow path and parallel to the central axis of the compressor impeller is larger than the angle of the outer circumferential surface relative to the straight line.

[0012] The extension angle 2θ shown in equation (3) below can be greater than 20°.

[0013] [Mathematical Expression 1]

[0014]

[0015] Among them, A ds : The cross-sectional area of ​​the intermediate flow path at the first end connected to the downstream slit.

[0016] A us : The cross-sectional area of ​​the intermediate flow path at the second end connected to the upstream slit.

[0017] D ds The equivalent diameter of the intermediate flow path at the first end.

[0018] D us The equivalent diameter of the intermediate flow path at the second end.

[0019] L: The distance between the first end and the second end in the axial direction.

[0020] The extension angle 2θ can also be greater than 30°.

[0021] Invention Effects

[0022] According to the present invention, surge can be suppressed. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of the booster of a centrifugal compressor with an implementation method.

[0024] Figure 2 It is shown Figure 1 A simplified enlarged sectional view of part A in the diagram.

[0025] Figure 3 It is a graph showing the relationship between the flow coefficient and the airflow rate in the circulating flow path.

[0026] Figure 4 This is a schematic enlarged cross-sectional view of a centrifugal compressor according to other embodiments.

[0027] Figure 5 This is a schematic enlarged cross-sectional view of a centrifugal compressor according to yet another embodiment.

[0028] Figure 6 This is a schematic enlarged cross-sectional view of a centrifugal compressor according to yet another embodiment. Detailed Implementation

[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and specific values ​​shown in the embodiments are merely illustrative for ease of understanding and are not intended to limit the present invention, unless specifically stated otherwise. It should be noted that in this specification and the accompanying drawings, elements having substantially the same function and structure are omitted from repeated description by using the same reference numerals. Furthermore, elements not directly related to the present invention are omitted from their illustrations.

[0030] Figure 1 This is a schematic cross-sectional view of the booster TC of a centrifugal compressor C with an embodiment. Figure 1 A cross-section is shown that is parallel to and passes through the central axis of the compressor impeller 4 of the centrifugal compressor C. In this embodiment, the centrifugal compressor C is assembled into the booster TC. In other embodiments, the centrifugal compressor C may be assembled into other devices or may be a standalone device.

[0031] The turbocharger TC has a housing 1, a shaft 2, a turbine impeller 3, and a compressor impeller 4.

[0032] As described below, the turbine impeller 3 and the compressor impeller 4 rotate integrally with the shaft 2. Therefore, in this invention, unless otherwise specified, the axial direction, radial direction, and circumferential direction of the shaft 2, turbine impeller 3, and compressor impeller 4 can be simply referred to as "axial direction," "radial direction," and "circumferential direction," respectively. Furthermore, in this invention, unless otherwise specified, the central axis of the shaft 2, turbine impeller 3, and compressor impeller 4 can be simply referred to as "central axis."

[0033] Housing 1 includes a bearing housing 5, a turbine housing 6, and a compressor housing 7. In the axial direction, one end of the bearing housing 5 is connected to the turbine housing 6 by bolts or other fasteners. In the axial direction, the other end of the bearing housing 5 is connected to the compressor housing 7 by bolts or other fasteners.

[0034] The bearing housing 5 includes a bearing bore 5a. The bearing bore 5a extends axially within the bearing housing 5. The bearing bore 5a houses a bearing B. The bearing B supports the shaft 2 for rotation. In this embodiment, a pair of fully floating bearings are used as bearing B. In other embodiments, other radial bearings such as semi-floating bearings or rolling bearings may also be used as bearing B.

[0035] A turbine impeller 3 is provided at the first end of the shaft 2 along the axial direction. The turbine impeller 3 rotates integrally with the shaft 2. The turbine housing 6 houses the turbine impeller 3 so that it can rotate. A compressor impeller 4 is provided at the second end of the shaft 2 on the side opposite to the first end along the axial direction. The compressor impeller 4 rotates integrally with the shaft 2. The compressor housing 7 houses the compressor impeller 4 so that it can rotate.

[0036] The compressor housing 7 includes an air inlet 71 at its end on the side opposite to the bearing housing 5 in the axial direction. The air inlet 71 is connected to an air filter (not shown).

[0037] The compressor housing 7 includes a main flow path 72. The main flow path 72 is connected to the air inlet 71. A compressor impeller 4 is disposed in the main flow path 72. The main flow path 72 extends along the axial direction. The main flow path 72 has a circular cross-sectional shape perpendicular to the axial direction.

[0038] The compressor housing 7 includes a circulation path 73. The circulation path 73 is located radially outside the main flow path 72. The circulation path 73 is connected to the main flow path 72. The circulation path 73 will be described in detail later.

[0039] A diffuser flow path 74 is defined between the bearing housing 5 and the compressor housing 7. The diffuser flow path 74 has an annular shape. The diffuser flow path 74 is located radially outward relative to the compressor impeller 4. The diffuser flow path 74 is in fluid communication with the main flow path 72 and the air inlet 71.

[0040] The compressor housing 7 includes a compressor scroll flow path 75. The compressor scroll flow path 75 is located radially outward relative to the diffuser flow path 74. The compressor scroll flow path 75 is connected to the diffuser flow path 74. In addition, the compressor scroll flow path 75 is in fluid communication with the intake manifold of an engine (not shown).

[0041] When the compressor impeller 4 rotates, air is drawn from the intake port 71 to the main flow path 72. During its passage through the compressor impeller 4, the air is accelerated and pressurized by centrifugal force. As it passes through the diffuser flow path 74 and the compressor vortex flow path 75, the air is further pressurized. The pressurized air flows out of the outlet (not shown) and is guided to the engine's intake manifold. In the supercharger TC, the portion including the compressor impeller 4 and the compressor housing 7 functions as a centrifugal compressor C.

[0042] The turbine housing 6 includes an outlet 61 at its end in the axial direction on the side opposite to the bearing housing 5. The outlet 61 is connected to an exhaust gas purification device (not shown).

[0043] The turbine housing 6 includes a connecting flow path 62. The connecting flow path 62 has an annular shape. The connecting flow path 62 is located radially outward relative to the turbine impeller 3. The connecting flow path 62 is in fluid communication with the outlet 61.

[0044] The turbine housing 6 includes a turbine vortex flow path 63. The turbine vortex flow path 63 is located radially outward relative to the connecting flow path 62. The turbine vortex flow path 63 is connected to the connecting flow path 62. Additionally, the turbine vortex flow path 63 is connected to a gas inlet (not shown). The gas inlet receives exhaust gas exiting from the engine's exhaust manifold.

[0045] Exhaust gas is guided from the gas inlet to the turbine vortex flow path 63, and then through the connecting flow path 62 and the turbine impeller 3 to the outlet 61. The exhaust gas causes the turbine impeller 3 to rotate during its passage. The rotational force of the turbine impeller 3 is transmitted to the compressor impeller 4 via the shaft 2. As the compressor impeller 4 rotates, the air is pressurized as described above. This pressurized air is then guided to the engine's intake manifold. In the turbocharger TC, the portion including the turbine impeller 3 and the turbine housing 6 functions as the turbine T.

[0046] Next, the circulating flow path 73 will be explained.

[0047] Figure 2 It is shown Figure 1 A schematic enlarged cross-sectional view of part A in the diagram. As described above, the circulating flow path 73 is located radially outside the main flow path 72. The circulating flow path 73 includes a downstream slit 76, an upstream slit 77, and an intermediate flow path 78.

[0048] The downstream slit 76 is located radially opposite the compressor impeller 4 and connects to the main flow path 72. The downstream slit 76 has a generally annular shape and extends radially from the inner side to the outer side.

[0049] The upstream slit 77 is located upstream of the downstream slit 76 in the main flow path 72 and connects to the main flow path 72. The upstream slit 77 is separated from the downstream slit 76 in the axial direction. The upstream slit 77 is not radially opposed to the compressor impeller 4. The upstream slit 77 has a generally annular shape and extends radially from the inner side to the outer side.

[0050] An intermediate flow path 78 extends along the axial direction. The intermediate flow path 78 has an annular cross-sectional shape perpendicular to the axial direction. The intermediate flow path 78 includes a first end 78c and a second end 78d in the axial direction. For example, in this invention, the intermediate flow path 78 may refer to a space radially surrounded by both an outer peripheral surface 78a and an inner peripheral surface 78b. In the axial direction, the inner peripheral surface 78b is shorter than the outer peripheral surface 78a. Therefore, the first end 78c and the second end 78d correspond to the two ends of the inner peripheral surface 78b in the axial direction. The first end 78c connects to the downstream slit 76. The second end 78d connects to the upstream slit 77. The intermediate flow path 78 connects the downstream slit 76 and the upstream slit 77.

[0051] Regarding the formation of the circulating flow path 73 as described above, for example, the compressor housing 7 of this embodiment includes a main body 8, a first ring 9, and a second ring 10.

[0052] The main body 8 includes the outer peripheral surface 78a of the circulation flow path 73.

[0053] The first ring 9 is disposed radially inside the body 8. The radial gap between the body 8 and the first ring 9 corresponds to the intermediate flow path 78. That is, the outer circumferential surface of the first ring 9 corresponds to the inner circumferential surface 78b of the circulation flow path 73. The axial gap between the body 8 and the first end 78c on the first ring 9 corresponds to the downstream slit 76. For example, the first ring 9 is fixed to the body 8 by a plurality of blades 11. The plurality of blades 11 connect the inner circumferential surface 78b to the outer circumferential surface 78a.

[0054] Reference Figure 1 The second ring 10 is fitted inside the main body 8. The second ring 10 includes the aforementioned air intake 71. (See reference...) Figure 2 The axial gap between the second end 78d on the first ring 9 and the second ring 10 corresponds to the upstream slit 77.

[0055] In this embodiment, the intermediate flow path 78 expands as it moves from the downstream slit 76 toward the upstream slit 77. In this embodiment, the intermediate flow path 78 expands along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77.

[0056] Specifically, in Figure 2 In the cross-section, the outer peripheral surface 78a of the intermediate flow path 78 slopes radially outward as it moves along the axial direction from the downstream slit 76 toward the upstream slit 77. In other words, the radius of the outer peripheral surface 78a increases as it moves along the axial direction from the downstream slit 76 toward the upstream slit 77. In this embodiment, the outer peripheral surface 78a slopes radially outward along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77. The outer peripheral surface 78a has a truncated conical shape that tapers at the front end from the upstream slit 77 toward the downstream slit 76. In this embodiment, in Figure 2 In the cross-section, the outer peripheral surface 78a has a straight line shape. In other embodiments, in Figure 2 In the cross section, the outer peripheral surface 78a can also have a curved shape.

[0057] exist Figure 2 In the cross-section, the inner circumferential surface 78b of the intermediate flow path 78 slopes radially inward as it moves from the downstream slit 76 toward the upstream slit 77. In other words, the radius of the inner circumferential surface 78b decreases as it moves along the axial direction from the downstream slit 76 toward the upstream slit 77. In this embodiment, the inner circumferential surface 78b slopes radially inward along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77. The inner circumferential surface 78b has a truncated conical shape that tapers at the front end from the downstream slit 76 toward the upstream slit 77. In this embodiment, in Figure 2 In the cross-section, the inner circumferential surface 78b has a straight line shape. In other embodiments, in Figure 2 In the cross section, the inner circumferential surface 78b can also have a curved shape.

[0058] exist Figure 2 In the cross section, X represents a straight line (imaginary line) that is parallel to the central axis and passes through the intermediate flow path 78.

[0059] exist Figure 2 In the cross-section, the angle of the outer peripheral surface 78a relative to the line X is indicated by the reference numeral α1. For example, in Figure 2 In the cross section, when the outer peripheral surface 78a has a curved shape, the angle α1 can also be defined as the angle between the straight line connecting the point on the first end 78c of the outer peripheral surface 78a and the point on the second end 78d and the straight line X.

[0060] exist Figure 2 In the cross-section, the angle of the inner circumferential surface 78b relative to the line X is indicated by the reference numeral α2. For example, in Figure 2 In the cross section, when the inner circumferential surface 78b has a curved shape, the angle α2 can also be defined as the angle between the straight line connecting the point on the first end 78c of the inner circumferential surface 78b and the straight line X.

[0061] The angle α2 of the inner circumferential surface 78b relative to the line X is greater than the angle α1 of the outer circumferential surface 78a relative to the line X. In other words, the absolute value of the decrease in radius of the inner circumferential surface 78b from the first end 78c to the second end 78d is greater than the absolute value of the increase in radius of the outer circumferential surface 78a from the first end 78c to the second end 78d. Furthermore, the absolute value of the increase in radius of the outer circumferential surface 78a from the first end 78c to the second end 78d is less than the absolute value of the increase in radius of the inner circumferential surface 78b from the first end 78c to the second end 78d. Because the increase in radius of the outer circumferential surface 78a is smaller, the outer circumferential surface 78a can be positioned more radially outward. Therefore, the cross-sectional area of ​​the intermediate flow path 78 can be increased, and the airflow rate within the circulating flow path 73 can be increased. In this case, there is less room for the intermediate flow path 78 to expand radially outward from the downstream slit 76 towards the upstream slit 77. However, due to the large increase in the radius of the inner circumferential surface 78b, the intermediate flow path 78 is prone to expand radially inward from the downstream slit 76 toward the upstream slit 77.

[0062] In this embodiment, the expansion angle 2θ shown in the following equation (3) is used as an indicator of the extent to which the intermediate flow path 78 is expanded.

[0063] [Mathematical Expression 2]

[0064]

[0065] Among them, A dsCross-sectional area of ​​the intermediate flow path 78 at the first end 78c connected to the downstream slit 76

[0066] A us Cross-sectional area of ​​the intermediate flow path 78 at the second end 78d connected to the upstream slit 77

[0067] D ds The equivalent diameter of the intermediate flow path 78 at the first end 78c

[0068] D us The equivalent diameter of the intermediate flow path 78 at the second end 78d

[0069] L: The distance between the first end 78c and the second end 78d along the axial direction.

[0070] In this embodiment, the expansion angle 2θ is greater than 20°. Alternatively, in this embodiment, the expansion angle 2θ can also be greater than 30°.

[0071] Next, the operation of the centrifugal compressor C in this embodiment will be explained.

[0072] In the centrifugal compressor C, when the airflow in the main flow path 72 decreases, a portion of the air flows backward near the blade tips of the compressor impeller 4. This backward-flowing air flows into the recirculation path 73 through the downstream slit 76. The air then flows from the first end 78c to the second end 78d in the intermediate flow path 78 and returns to the main flow path 72 through the upstream slit 77. This reduces the impact of the backward flow on the compressor impeller 4 and suppresses surge.

[0073] However, the inventors have discovered that even when the centrifugal compressor suppresses surge as expected in individual tests, it sometimes fails to suppress surge when the centrifugal compressor is connected to an engine. Specifically, when the centrifugal compressor is connected to an engine, the airflow rate in the main flow path varies. Consequently, the airflow rate in the recirculation flow path also varies. The inventors have found that if the airflow rate in the recirculation flow path varies significantly, surge cannot be suppressed as expected.

[0074] In this embodiment, the intermediate flow path 78 expands from the downstream slit 76 towards the upstream slit 77, thus easily separating airflow from the outer peripheral surface 78a and the inner peripheral surface 78b. In other words, in this embodiment, the intermediate flow path 78 expands from the downstream slit 76 towards the upstream slit 77 to separate airflow from the outer peripheral surface 78a and the inner peripheral surface 78b. Therefore, airflow within the intermediate flow path 78 is prone to turbulence, and energy loss is likely. Therefore, even if the pressure of air being forced from the main flow path 72 into the circulating flow path 73 is increased, the airflow rate within the intermediate flow path 78 is difficult to increase. In other words, even if the airflow rate within the main flow path 72 changes, the airflow rate within the circulating flow path 73 is difficult to change. Therefore, the circulating flow path 73 easily performs actions close to the intended purpose. As a result, when the centrifugal compressor C is connected to the engine, surge can be suppressed.

[0075] In particular, in this embodiment, as described above, the angle α2 of the inner peripheral surface 78b relative to the straight line X is greater than the angle α1 of the outer peripheral surface 78a relative to the straight line X. According to this structure, as described above, the intermediate flow path 78 can easily expand radially inward from the downstream slit 76 towards the upstream slit 77. Therefore, airflow is easily separated from the outer peripheral surface 78a and the inner peripheral surface 78b, and the airflow rate within the circulating flow path 73 is less prone to variation. As a result, surge can be suppressed when the centrifugal compressor C is connected to the engine.

[0076] Furthermore, in this embodiment, the expansion angle 2θ is greater than 20°. The inventors have discovered that if the expansion angle 2θ is greater than 20°, airflow is easily separated from the outer peripheral surface 78a and the inner peripheral surface 78b, making it difficult for the airflow rate within the circulation path 73 to change. Moreover, in this embodiment, the expansion angle 2θ can also be greater than 30°. In this case, airflow is even more easily separated from the outer peripheral surface 78a and the inner peripheral surface 78b, making it even more difficult for the airflow rate within the circulation path 73 to change.

[0077] Figure 3 It is a graph showing the relationship between the flow coefficient and the airflow rate within the circulation path 73. Figure 3 The analysis results of the implementation method (plotting of triangles) and the analysis results of the comparative example (plotting of quadrilaterals) are shown. Figure 3 In the analysis, the rotational speed of compressor impeller 4 is set to constant. Figure 3In the diagram, the horizontal axis represents the flow coefficient. The flow coefficient is related to the pressure that forces air into the circulation path 73, i.e., the pressure in the downstream slit 76 and the pressure in the upstream slit 77. Specifically, the compressor impeller 4 rotates at a constant speed, meaning the energy supplied to the air is constant. Therefore, as the flow coefficient increases (shifts to the right), the pressure that forces air into the circulation path 73 decreases, and as the flow coefficient decreases (shifts to the left), the pressure that forces air into the circulation path 73 increases. In other words, a change in the flow coefficient corresponds to a change in the pressure that forces air into the circulation path 73. The vertical axis represents the airflow rate within the circulation path 73. This flow rate is expressed as a percentage (%) relative to the airflow rate within the main flow path 72.

[0078] In the centrifugal compressor C of the embodiment (diagram), as described above, the circulation path 73 expands from the downstream slit 76 toward the upstream slit 77. In contrast, in the centrifugal compressor C of the comparative example (quadrilateral), the circulation path does not expand from the downstream slit toward the upstream slit.

[0079] like Figure 3 As shown, the overall air flow rate in the circulation path 73 of the embodiment is lower than that of the comparative example. However, the slope of the air flow rate in the circulation path 73 of the embodiment is smaller than that of the comparative example. This means that, in the centrifugal compressor C of the embodiment, compared with the comparative example, even if the flow coefficient changes, that is, even if the pressure of the air being forced into the circulation path 73 changes, the air flow rate in the circulation path 73 is difficult to change. Based on this analysis, it can also be seen that in the centrifugal compressor C of the embodiment, the air flow rate in the circulation path 73 is difficult to change.

[0080] The centrifugal compressor C of this embodiment includes a compressor impeller 4 and a compressor housing 7 that houses the compressor impeller 4. The compressor housing 7 includes a main flow path 72 that houses the compressor impeller 4 and a circulation flow path 73 that is radially located outside the main flow path 72 and connected to the main flow path 72. The circulation flow path 73 includes: a downstream slit 76 that is radially connected to the main flow path 72 at a position opposite to the compressor impeller 4; an upstream slit 77 that is connected to the main flow path 72 at a position upstream of the downstream slit 76; and an intermediate flow path 78 that extends along the axial direction and connects the downstream slit 76 and the upstream slit 77. The intermediate flow path 78 expands as it moves from the downstream slit 76 toward the upstream slit 77. The outer peripheral surface 78a of the intermediate flow path 78 is inclined radially outward as it moves from the downstream slit 76 toward the upstream slit 77, and the inner peripheral surface 78b of the intermediate flow path 78 is inclined radially inward as it moves from the downstream slit 76 toward the upstream slit 77. The angle α2 of the inner circumferential surface 78b relative to the straight line X passing through the intermediate flow path 78 and parallel to the central axis is greater than the angle α1 of the outer circumferential surface 78a relative to the straight line X. Based on this structure, as described above, the intermediate flow path 78 can easily expand radially inward from the downstream slit 76 towards the upstream slit 77. Therefore, airflow is easily separated from the outer circumferential surface 78a and the inner circumferential surface 78b, and the airflow rate within the circulating flow path 73 is less prone to variation. As a result, surge can be suppressed when the centrifugal compressor C is connected to the engine.

[0081] Furthermore, in the centrifugal compressor C, the expansion angle 2θ is greater than 20°. In this case, the airflow is easily separated from the outer peripheral surface 78a and the inner peripheral surface 78b, and the airflow rate within the circulation path 73 is difficult to change.

[0082] Furthermore, in the centrifugal compressor C, the expansion angle 2θ can also be greater than 30°. In this case, the airflow is more easily separated from the outer peripheral surface 78a and the inner peripheral surface 78b, and the airflow rate within the circulation path 73 is more difficult to change.

[0083] The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to these embodiments. Those skilled in the art will readily conceive of various modifications or alterations within the scope of the claims, and these modifications or alterations naturally fall within the technical scope of this disclosure.

[0084] For example, in the above embodiment, the intermediate flow path 78 expands along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77, the outer peripheral surface 78a of the intermediate flow path 78 slopes radially outward along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77, and the inner peripheral surface 78b slopes radially inward along its entire length in the axial direction as it moves from the downstream slit 76 toward the upstream slit 77. In other embodiments, the intermediate flow path 78 may also expand at least in a portion continuous with the downstream slit 76 as it moves from the downstream slit 76 toward the upstream slit 77, the outer peripheral surface 78a of the intermediate flow path 78 may also slope radially outward at least in a portion continuous with the downstream slit 76 as it moves from the downstream slit 76 toward the upstream slit 77, and the inner peripheral surface 78b of the intermediate flow path 78 may also slope radially inward at least in a portion continuous with the downstream slit 76 as it moves from the downstream slit 76 toward the upstream slit 77.

[0085] Figure 4 This is a schematic enlarged cross-sectional view of a centrifugal compressor according to other embodiments. For example, in Figure 4 In this embodiment, the outer peripheral surface 78a of the intermediate flow path 78 is parallel to the straight line X near the second end 78d connected to the upstream slit 77. That is, the outer peripheral surface 78a may also, except for a portion that is continuous with the downstream slit 76, move from the downstream slit 76 toward the upstream slit 77 without tilting radially outward. In this case, the angle α1 can also be defined as the angle between the straight line connecting the point on the first end 78c of the outer peripheral surface 78a and the point on the second end 78d, and the straight line X.

[0086] Figure 5 This is a schematic enlarged cross-sectional view of yet another embodiment of a centrifugal compressor. For example, in Figure 5 In this embodiment, besides the outer peripheral surface 78a, the inner peripheral surface 78b is also parallel to the straight line X near the second end 78d connected to the upstream slit 77. That is, the inner peripheral surface 78b may also, except for a portion continuous with the downstream slit 76, move from the downstream slit 76 toward the upstream slit 77 without tilting radially inward. In this case, the angle α2 can also be defined as the angle between the straight line connecting the point on the first end 78c of the inner peripheral surface 78b and the point on the second end 78d, and the straight line X. It should be noted that in Figure 5 In some embodiments, the outer peripheral surface 78a may also exclude the portion parallel to the line X.

[0087] Figure 6 This is a schematic enlarged cross-sectional view of yet another embodiment of a centrifugal compressor. For example, in Figure 6In one embodiment, the outer peripheral surface 78a includes a stepped portion near the second end 78d connected to the upstream slit 77, between a portion parallel to and inclined relative to line X and a parallel portion. In this case, angle α1 can also be defined as the angle between the line connecting a point on the first end 78c of the outer peripheral surface 78a and a point on the second end 78d, and line X. Similarly, the inner peripheral surface 78b includes a stepped portion near the second end 78d connected to the upstream slit 77, between a portion parallel to and inclined relative to line X and a parallel portion. In this case, angle α2 can also be defined as the angle between the line connecting a point on the first end 78c of the inner peripheral surface 78b and a point on the second end 78d, and line X. It should be noted that in Figure 6 In some embodiments, one of the outer peripheral surface 78a and the inner peripheral surface 78b may not include the stepped portion.

[0088] Explanation of reference numerals in the attached figures

[0089] 4 Compressor Impeller

[0090] 7 Compressor Housing

[0091] 72 Main Roads

[0092] 73 Circulating Flow Path

[0093] 76 Downstream Slit

[0094] 77 Upstream Slit

[0095] 78 intermediate flow path

[0096] 78a outer periphery

[0097] 78b inner circumferential surface

[0098] 78c first end

[0099] 78d second end

[0100] C centrifugal compressor

[0101] X is a straight line passing through the intermediate flow path and parallel to the central axis of the compressor impeller.

[0102] α1 Angle of the outer circumference relative to the line

[0103] α2 Angle of the inner circumferential surface relative to the line

Claims

1. A centrifugal compressor, characterized in that, have: Compressor impeller; as well as A compressor housing that houses the compressor impeller, and the compressor housing includes: a main flow path that houses the compressor impeller; and a circulating flow path that is radially located outside the main flow path and connected to the main flow path of the compressor impeller. The circulating flow path includes: a downstream slit connected to the main flow path in the radial direction opposite to the compressor impeller; an upstream slit connected to the main flow path upstream of the downstream slit; and an intermediate flow path extending along the axial direction of the compressor impeller and connecting the downstream slit and the upstream slit. The intermediate flow path widens at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit. The outer peripheral surface of the intermediate flow path slopes radially outward at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit, and the inner peripheral surface of the intermediate flow path slopes radially inward at least in a portion continuous with the downstream slit as it moves from the downstream slit toward the upstream slit. The angle of the inner circumferential surface relative to a straight line passing through the intermediate flow path and parallel to the central axis of the compressor impeller is greater than the angle of the outer circumferential surface relative to the straight line.

2. The centrifugal compressor according to claim 1, characterized in that, The extension angle 2θ, as expressed by the following equation (3), is greater than 20°. [Mathematical Expression 3] Among them, A ds The cross-sectional area of ​​the intermediate flow path at the first end connected to the downstream slit. A us The cross-sectional area of ​​the intermediate flow path at the second end connected to the upstream slit. D ds The equivalent diameter of the intermediate flow path at the first end. D us The equivalent diameter of the intermediate flow path at the second end. L: The distance between the first end and the second end in the axial direction.

3. The centrifugal compressor according to claim 2, characterized in that, The extension angle 2θ is greater than 30°.

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