CENTRIFUGAL COMPRESSOR

Abstract

A centrifugal compressor 100 has an impeller 3 and a housing 6 that contains the impeller 3. The housing 6 has a primary flow path 20 that contains the impeller 3, and a secondary flow path 30 that surrounds the primary flow path 20 in a cross-section perpendicular to an axial direction of the impeller 3. The secondary flow path 30 has a first end 30A that opens to the primary flow path 20 when positioned upstream of the impeller 3 in a flow of air in the primary flow path 20, and a second end 30B that opens to the primary flow path 20 when positioned downstream of the first end 30A. The first end 30A opens to the primary flow path 20 in a direction opposite to the impeller 3 in the axial direction of the impeller 3. The secondary flow path 30 has a throttle 30C, which is continuous with the first end 30A and narrows towards the first end 30A.

Description

Technical area

[0001] The present disclosure relates to a centrifugal compressor. This application claims the benefit of priority based on Japanese Patent Application No. 2022-70654, filed on April 22, 2022, the contents of which are incorporated herein by reference. Technical background

[0002] In a centrifugal compressor, a secondary flow path may be formed in addition to a primary flow path (see, for example, Patent Literatures 1 to 5). A compressor impeller is arranged in the primary flow path. A first end of the secondary flow path is connected to the primary flow path at a position upstream of the compressor impeller. A second end of the secondary flow path is connected to the primary flow path at a position downstream of the first end. In a low flow rate region, part of the air pressurized by the compressor impeller may flow backward in the primary flow path. This is called surge and limits an operating range of the centrifugal compressor in the low flow rate region.However, in the centrifugal compressor with the secondary flow path, a portion of the air enters the secondary flow path from the second end and returns to the primary flow path from the first end. According to such a design, the effect of surge can be reduced and the operating range in the low flow rate region can be expanded. Citation listPatent literature Patent Literature 1: US 2009 / 0263234 A Patent Literature 2: JP 6865604 B Patent Literature 3: JP 2014-202103 A Patent literature 4: WO 2019 / 004386 A Patent Literature 5: JP 2021-95882 A Technical problem

[0003] In a centrifugal compressor, it is desirable to further improve efficiency in a low flow rate range.

[0004] It is the purpose of the present disclosure to provide a centrifugal compressor that can improve efficiency in a low flow rate range. Solution to the problem

[0005] To solve the above problem, a centrifugal compressor according to one aspect of the present disclosure includes an impeller and a casing accommodating the impeller, the casing having a primary flow path accommodating the impeller and a secondary flow path surrounding the primary flow path in a cross section perpendicular to an axial direction of the impeller, the secondary flow path having a first end opening to the primary flow path at a position upstream of the impeller in a flow of air in the primary flow path and a second end opening to the primary flow path at a position downstream of the first end, the first end opening to the primary flow path in a direction opposite to the impeller in the axial direction of the impeller, and the secondary flow path having a throttle continuous with the first end and narrowing toward the first end.

[0006] The secondary flow path may have a plurality of ribs or vanes arranged along a circumferential direction of the impeller.

[0007] The plurality of vanes may be provided in the throttle of the secondary flow path.

[0008] Each of the plurality of vanes may be inclined with respect to a central axis of the impeller, as viewed in a radial direction of the impeller.

[0009] Each of the plurality of vanes may be inclined in the same direction as leading edges of blades of the impeller, as viewed in the radial direction. Effects of revelation

[0010] According to the present disclosure, efficiency in a low flow rate range can be improved. Short description of the drawings Fig. 1 is a schematic cross-sectional view of a turbocharger with a centrifugal compressor according to an embodiment. Fig. 2 is an enlarged cross-sectional view of an area Z in Fig. 1. Fig. 3 is a side view of a second insert as viewed in a radial direction. Fig. 4 is an enlarged cross-sectional view of a first comparative example. Fig. 5 is an enlarged cross-sectional view of a second comparative example. Fig. 6 is an enlarged cross-sectional view of a third comparative example. Fig. Figure 7 shows results of pressure ratio analyses in a low flow rate range. Fig. Figure 8 shows results of analyses of efficiency in the low flow rate range. Fig. Figure 9 shows results of pressure ratio analyses in a high flow rate range. Fig. Figure 10 shows results of efficiency analyses in the high flow rate range. Description of the embodiments

[0011] An embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Specific dimensions, materials, and numerical values ​​described in the embodiment are merely examples for better understanding and do not limit the present disclosure unless otherwise specified. In this description and the drawings, duplicate explanations for elements having substantially the same functions and configurations are omitted by assigning the same reference numerals. Furthermore, elements not directly related to the present disclosure are omitted from the figures.

[0012] Fig. 1 is a schematic cross-sectional view of a turbocharger TC with a centrifugal compressor 100 according to one embodiment. In the present embodiment, the centrifugal compressor 100 is included in the turbocharger TC. In another embodiment, the centrifugal compressor 100 may be included in a device other than the turbocharger TC or may be a stand-alone device.

[0013] The turbocharger TC includes a shaft 1, a turbine impeller 2, and a compressor impeller (runner) 3. As described later, the shaft 1, the turbine impeller 2, and the compressor impeller 3 rotate integrally. As such, in the present disclosure, an "axial direction," a "radial direction," and a "circumferential direction" of the shaft 1, the turbine impeller 2, and the compressor impeller 3 may be simply referred to as the "axial direction," the "radial direction," and the "circumferential direction," respectively.

[0014] The turbocharger TC has a bearing housing 4, a turbine housing 5 and a compressor housing (casing) 6. In the axial direction, the turbine housing 5 is connected to a first end surface of the bearing housing 4 (a left end surface in Fig. 1) by fastening bolts B1. In the axial direction, the compressor housing 6 is connected to a second end face of the bearing housing 4 (a right end face in Fig. 2) connected by fastening bolts B2.

[0015] The bearing housing 4 has a bearing hole 4a. The bearing hole 4a extends in the axial direction within the bearing housing 4. The bearing hole 4a accommodates a bearing 7. In the present embodiment, a fully floating bearing is shown as an example of the bearing 7. In another embodiment, the bearing 7 may be another radial bearing, such as a semi-floating bearing or a rolling bearing. The bearing 7 rotatably supports the shaft 1.

[0016] In the axial direction, a first end of the shaft 1 (a left end in Fig. 1) is provided with the turbine runner 2. The turbine runner 2 rotates integrally with the shaft 1. The turbine runner 2 is rotatably housed in the turbine casing 5. In the axial direction, a second end of the shaft 1 (a right end in Fig. 1) is provided with the compressor impeller 3. The compressor impeller 3 rotates integrally with the shaft 1. The compressor impeller 3 is rotatably mounted in the compressor housing 6.

[0017] The compressor housing 6 has an inlet 6a at an end opposite the bearing housing 4 in the axial direction. The inlet 6a is connected to an air filter (not shown). The compressor housing 6 also has a primary flow path 20 and a secondary flow path 30. The primary flow path 20 and the secondary flow path 30 are described in detail below. The compressor impeller 3 is arranged in the primary flow path 20.

[0018] The bearing housing 4 and the compressor housing 6 define a diffuser flow path 8 between them. The diffuser flow path 8 extends from an inner side to an outer side in the radial direction. The diffuser flow path 8 has an annular shape. The diffuser flow path 8 is connected to the inlet 6a via the compressor impeller 3.

[0019] The compressor housing 6 has a compressor scroll flow path 9. The compressor scroll flow path 9 is located at a radially outer side with respect to the diffuser flow path 8. The compressor scroll flow path 9 communicates with the diffuser flow path 8. The compressor scroll flow path 9 also communicates with an inlet port of a charge air cooler (not shown).

[0020] In the compressor housing 6, as described above, when the compressor impeller 3 rotates, air is drawn into the primary flow path 20 from the inlet 6a. The drawn-in air is accelerated and pressurized by centrifugal force as it passes through the blades of the compressor impeller 3. The air is further pressurized in the diffuser flow path 8 and the compressor scroll flow path 9. The pressurized air flows out from an outlet (not shown) and is guided to the intake port of the intercooler. In the turbocharger TC, a section including the compressor impeller 3 and the compressor housing 6 functions as the centrifugal compressor 100.

[0021] In the present disclosure, with reference to the centrifugal compressor 100 and its components, an upstream side in the flow of the sucked air in the primary flow path 20 may be simply referred to as the “upstream side,” and a downstream side in the flow of the sucked air in the primary flow path 20 may be simply referred to as the “downstream side.”

[0022] The turbine housing 5 has an outlet 5a at an end opposite the bearing housing 4 in the axial direction. The outlet 5a is connected to an exhaust filter (not shown). The turbine housing 5 has a connecting flow path 10. The connecting flow path 10 extends from an inner side to an outer side in the radial direction. The connecting flow path 10 has an annular shape. The connecting flow path 10 is connected to the outlet 5a via the turbine runner 2.

[0023] The turbine housing 5 has a turbine scroll flow path 11. The turbine scroll flow path 11 is located on a radially outer side with respect to the connecting flow path 10. The turbine scroll flow path 11 communicates with the connecting flow path 10. The turbine scroll flow path 11 is also connected to a gas inlet (not shown). The gas inlet receives exhaust gas discharged from an exhaust manifold of an engine (not shown).

[0024] In the turbine housing 5, as described above, the exhaust gas is guided from the gas inlet to the turbine scroll flow path 11 and is further guided to the outlet 5a via the connecting flow path 10 and the turbine runner 2. The exhaust gas rotates the turbine runner 2 while passing through blades of the turbine runner 2. A rotational force of the turbine runner 2 is transmitted to the compressor impeller 3 via the shaft 1. As the compressor impeller 3 rotates, the air is sucked into the inlet 6a and is accelerated and pressurized by the compressor impeller 3, as described above. In the turbocharger TC, a portion including the turbine runner 2 and the turbine housing 5 functions as a turbine 200.

[0025] Next, the primary flow path 20 and the secondary flow path 30 of the compressor housing 6 are described.

[0026] Fig. 2 is an enlarged cross-sectional view of an area Z in Fig. 1. The compressor housing 6 has a main body 60 and an insert 70.

[0027] The main body 60 has a first cylindrical portion 61 and a second cylindrical portion 62. Each of the first cylindrical portion 61 and the second cylindrical portion 62 has a substantially cylindrical shape.

[0028] A center axis of the first cylindrical portion 61 corresponds to the center axis of the compressor impeller 3. An inner diameter of the first cylindrical portion 61 is constant along the axial direction.

[0029] The second cylindrical portion 62 is formed in and coaxial with the first cylindrical portion 61. The first cylindrical portion 61 and the second cylindrical portion 62 are formed integrally. Upstream ends (right ends in Fig. 1) of the first cylindrical portion 61 and the second cylindrical portion 62 are open. Downstream ends (left ends in Fig. 1) The first cylindrical portion 61 and the second cylindrical portion 62 are connected to each other. In the axial direction, the second cylindrical portion 62 is shorter than the first cylindrical portion 61, and the upstream end of the second cylindrical portion 62 is located within the first cylindrical portion 61.

[0030] The outer diameter of the second cylindrical portion 62 is constant along the axial direction and is smaller than the inner diameter of the first cylindrical portion 61. Accordingly, a gap is formed between the first cylindrical portion 61 and the second cylindrical portion 62 in the radial direction. An inner surface of the second cylindrical portion 62 includes a tapered portion 62a that tapers from the upstream side to the downstream side.

[0031] The second cylindrical portion 62 has a slit 63. The slit 63 passes through the second cylindrical portion 62 in the radial direction. For example, the slit 63 may extend in the circumferential direction and may be discontinuous in the circumferential direction. A material of this discontinuous part (rib) connects portions on both sides of the slit 63 along the axial direction. Further, for example, the slit 63 may extend in the circumferential direction and may be continuous in the circumferential direction (ie, continuous over the entire circumference). In this case, in order to connect the first cylindrical portion 61 and the second cylindrical portion 62, a material (rib) that is a discontinuous portion in the circumferential direction is provided in a radial gap between the first cylindrical portion 61 and the second cylindrical portion 62.

[0032] The insert 70 is arranged in the first cylindrical portion 61. In the present embodiment, the insert 70 comprises a first insert 71 and a second insert 72.

[0033] The first insert 71 has a cylindrical shape. The first insert 71 is coaxially fitted into the first cylindrical portion 61. The first cylindrical portion 61 has a counterbore 61a into which the first insert 71 is fitted. In the radial direction, an inner wall of the first insert 71 is formed to be flush with an inner wall of the first cylindrical portion 61. An inner diameter of the first insert 71 is constant along the axial direction. The first insert 71 is flush with an end surface of the first cylindrical portion 61 in the axial direction and defines the inlet 6a. In another embodiment, the first insert 71 may be recessed or protruded relative to the end surface of the first cylindrical portion 61 in the axial direction.

[0034] The second insert 72 has a body 73 and a plurality of wings 74.

[0035] The body 73 is coaxially disposed in the first cylindrical portion 61. An outer surface of the body 73 has a tapered portion 73a that tapers from the upstream side to the downstream side. For example, in the present embodiment, the body 73 has a substantially hollow truncated cone shape. A downstream end of the body 73 (left end in Fig. 2) has a smaller diameter and contacts one end of the second cylindrical portion 62. An upstream end of the body 73 (right end in Fig. 2) has a larger diameter and is located in the first insert 71. An outer diameter of the body 73 is smaller than the inner diameters of the first cylindrical portion 61 and the first insert 71. Accordingly, a gap is formed in the radial direction between the first cylindrical portion 61 and the first insert 71 and the body 73.

[0036] The gap between the first cylindrical portion 61 and the first insert 71 and the body 73, the gap between the first cylindrical portion 61 and the second cylindrical portion 62, and the slit 63 as described above serve as the secondary flow path 30.

[0037] In the first cylindrical portion 61, a space other than the secondary flow path 30 functions as the primary flow path 20. Specifically, a space from the inlet 6a to the upstream end of the body 73 in the first insert 71, a space in the second insert 72, and a space in the second cylindrical portion 62 function as the primary flow path 20. The primary flow path 20 extends from the inlet 6a to a radially inner end of the diffuser flow path 8. The secondary flow path 30 is located outside of the primary flow path 20 in the radial direction in a cross section perpendicular to the axial direction.

[0038] A radial gap between the upstream end of the body 73 and the first insert 71 serves as a first end 30A of the secondary flow path 30. With reference to Fig. 1, the first end 30A opens to the primary flow path 20 at a position upstream of the compressor impeller 3. Furthermore, in the axial direction, the first end 30A opens to the primary flow path 20 in a direction opposite to the compressor impeller 3.

[0039] With reference to Fig. 2, a radially inner end of the slot 63 serves as a second end 30B of the secondary flow path 30. The second end 30B opens to the primary flow path 20 at a position downstream of the first end 30A. In the present embodiment, the second end 30B opens to the primary flow path 20 inward in the radial direction. In the present embodiment, the second end 30B faces the compressor impeller 3 in the radial direction.

[0040] The secondary flow path 30 has a throttle 30C that is continuous with the first end 30A and narrows toward the first end 30A. Specifically, as described above, in the present embodiment, the inner diameters of the first cylindrical portion 61 and the first insert 71 are constant along the axial direction, and the outer surface of the body 73 has a tapered portion 73a that tapers from the upstream side to the downstream side. Accordingly, a space radially outward from the tapered portion 73a functions as the throttle 30C.

[0041] Fig. 3 is a side view of the second insert 72 as viewed in the radial direction. The plurality of ribs or vanes 74 are arranged along the circumferential direction. The vanes 74 protrude radially outward from the outer surface of the body 73. The vanes 74 are inclined with respect to the center axis X of the compressor impeller 3 as viewed in the radial direction. An angle between the vane 74 and the center axis X is defined as α. In the present embodiment, the vanes 74 are inclined in the same direction as leading edges of the compressor impeller 3 as viewed in the radial direction.

[0042] With reference to Fig. 2, radially outer ends of the wings 74 contact the inner surface of the first insert 71. The second insert 72 is fitted to the inner surface of the first insert 71 by the wings 74. The wings 74 fix the second insert 72 to the first insert 71.

[0043] Regarding assembly of the first insert 71 and the second insert 72, the first insert 71 is first fitted into the counterbore 61a. Then, the wings 74 of the second insert 72 are fitted into the inner surface of the first insert 71. This sequence allows the first insert 71 and the second insert 72 to be assembled into the main body 60.

[0044] Next, an operation of the centrifugal compressor 100 will be described.

[0045] First, an operation in a low flow rate range is described.

[0046] As described above, when the compressor impeller 3 rotates, air is sucked from the inlet 6a into the primary flow path 20. The sucked air is pressurized by centrifugal force while passing through the blades of the compressor impeller 3.

[0047] In the low-flow rate range, when a pressure at an inlet of the compressor impeller 3 is lower than a pressure at an outlet of the compressor impeller 3, a portion of the pressurized air is forced back from the outlet of the compressor impeller 3 to the inlet of the compressor impeller 3 due to a reverse pressure gradient. This air flows backward in the primary flow path 20. However, since the centrifugal compressor 100 has the secondary flow path 30, the air flowing backward in the primary flow path 20 enters the secondary flow path 30 from the second end 30B. This inhibits the effect of surge and expands an operating range of the centrifugal compressor 100 in the low-flow rate range.

[0048] The air entering the secondary flow path 30 returns from the first end 30A to the primary flow path 20. However, in the present embodiment, the secondary flow path 30 has the throttle 30C and the vanes 74 continuous with the first end 30A. The throttle 30C and the vanes 74 impede the flow in the secondary flow path 30. Accordingly, the throttle 30C and the vanes 74 can reduce the flow rate of air returning to the primary flow path 20. Thus, in the present embodiment, the secondary flow path 30 functions as a buffer region for temporarily storing air. This is the opposite of the conventional design where air in the secondary flow path is actively returned to the primary flow path.

[0049] Furthermore, in the present embodiment, the first end 30A opens to the primary flow path 20 in the direction opposite to the compressor impeller 3 in the axial direction. Consequently, the secondary flow path 30 is elongated in the axial direction compared to, for example, the case where the first end 30A opens to the primary flow path 20 in the radial direction. Thus, the secondary flow path 30 can store air for a longer time.

[0050] According to the above configuration, the air pressurized by the compressor impeller 3 is stored in the secondary flow path 30 for a longer time. Therefore, the air cools and its pressure decreases while the air is stored in the secondary flow path 30. Thus, when the air returns to the primary flow path 20, the pressure and temperature of the air in the secondary flow path 30 approach the pressure and temperature of the air flowing in the primary flow path 20. According to such a configuration, a loss of flow in the primary flow path 20 can be reduced when the air in the secondary flow path 30 returns to the primary flow path 20. Thus, efficiency in the low flow rate range can be improved.

[0051] Furthermore, in the present embodiment, the vanes 74 are inclined in the same direction as the leading edges of the compressor impeller 3, as viewed in the radial direction. The air flowing in the primary flow path 20 is entrained by rotation of the compressor impeller 3 and is swirled in the same direction as the rotation of the compressor impeller 3. In the present embodiment, since the vanes 74 are inclined in the same direction as the leading edges of the compressor impeller 3, the air returning from the first end 30A to the primary flow path 20 is also swirled in the same direction as the rotation of the compressor impeller 3. Consequently, the air returning to the primary flow path 20 from the first end 30A does not obstruct the flow in the primary flow path 20.Thus, a loss of flow in the primary flow path 20 can be reduced when the air in the secondary flow path 30 returns to the primary flow path 20. Thus, the efficiency in the low flow rate range can be further improved.

[0052] Next, an operation in a high flow rate range is described.

[0053] In the high flow rate region, unlike the low flow rate region, a portion of the air flowing in the primary flow path 20 enters the secondary flow path 30 from the first end 30A. However, in the present embodiment, the secondary flow path 30 has the throttle 30C and the vanes 74 continuous with the first end 30A. The throttle 30C and the vanes 74 can reduce the flow rate of air entering the secondary flow path 30 from the first end 30A. The air entering the secondary flow path 30 returns to the primary flow path 20 from the second end 30B. In the present embodiment, a difference between a pressure of the air at the first end 30A and a pressure of the air at the second end 30B is relatively small because the flow rate of the air entering the secondary flow path 30 from the first end 30A is reduced as described above.According to such a configuration, when the air in the secondary flow path 30 returns to the primary flow path 20 from the second end 30B, a flow loss in the primary flow path 20 can be reduced. Accordingly, efficiency in the high flow rate range can also be improved. Note that, although in the present embodiment, the air returns to a position between the blades of the compressor 3 when the air in the secondary flow path 30 returns to the primary flow path 20 from the second end 30B, the air may return to a position upstream of the compressor impeller 3 as long as the air returns to the primary flow path 20.

[0054] Next, results of analyses of the centrifugal compressor 100 are described.

[0055] Fig. 4, Fig. 5 and Fig. 6 are enlarged cross-sectional views of a first, second and third comparative example, respectively.

[0056] With reference to Fig. 4, a centrifugal compressor 500 for the first comparative example differs from the centrifugal compressor 100 described above in that the centrifugal compressor 500 does not have a secondary flow path. The centrifugal compressor 500 may be substantially similar to the centrifugal compressor 100 in other respects.

[0057] With reference to Fig. 5, a centrifugal compressor 600 for the second comparative example differs from the centrifugal compressor 100 described above in the configuration of the secondary flow path 30D. Specifically, the centrifugal compressor 600 has no insert. The secondary flow path 30D has no throttle, and the first end 30A opens wider to the primary flow path 20 than in the centrifugal compressor 100. The centrifugal compressor 600 may be substantially the same as the centrifugal compressor 100 in other respects.

[0058] With reference to Fig. 6, a centrifugal compressor 700 for the third comparative example differs from the centrifugal compressor 100 described above in the configuration of the secondary flow path 30E. Specifically, in the centrifugal compressor 700, the first end 30A opens to the primary flow path 20 in the radial direction. Accordingly, the secondary flow path 30E is shorter in the axial direction than the secondary flow path 30 of the centrifugal compressor 100 described above. The insert 70 is formed by a single component. The centrifugal compressor 700 may be substantially similar to the centrifugal compressor 100 in other respects.

[0059] Fig. 7 and Fig. 8 show results of analyses of a pressure ratio and an efficiency in a low flow rate range, respectively. Fig. 9 and Fig. 10 show results of pressure ratio and efficiency analyses in a high flow rate range. Fig. 7 to 10, the horizontal axis indicates the flow rate ratio. The vertical axis indicates the pressure ratio in Fig. 7 and Fig. 9 and the efficiency in Fig. 8 and Fig. 10.

[0060] The “pressure ratio” in Fig. 7 and Fig. 9 is calculated by the following equation (1), where the pressure ratio P (tot)ratio is the pressure at the outlet of the compressor (total pressure) P (tot)out and the pressure at the inlet of the compressor (total pressure) P (tot)in is. P(tot)ratio=P(tot)out / P(tot)in

[0061] The “efficiency” in Fig. 8 and Fig. 10 is calculated by the following equation (2), where the efficiency η (tot) is the pressure ratio P (tot)ratiois the specific heat ratio of air γ air is the temperature at the outlet of the compressor (total temperature) T (tot)out and the temperature at the inlet of the compressor (total temperature) T (tot)in is. η(tot)=(P(tot)ratio(γair−1 / γair)−1)−(T(tot)out / T(tot)in−1)

[0062] For example, the “flow rate ratio” in Fig. 7, Fig. 8, Fig. 9 and Fig. 10 is calculated as follows. Flow rates at all rotation rates used in the analyses are calculated for each of the example and the comparative examples. From all calculated flow rates including both the example and the comparative examples, the maximum flow rate at each rotation rate is selected. By calculating a ratio between the selected maximum flow rate and each flow rate at the same rotation rate, the "flow rate ratio" is calculated for each of the example and the comparative examples at each rotation rate.

[0063] Characteristics of the centrifugal compressor 100 of the embodiment shown in Fig. 2, and the centrifugal compressors 500, 600 and 700 of the first, second and third comparative examples shown in Fig. 4 to 6 were analyzed using a fluid analysis tool. Specifically, the pressure ratios and efficiencies were calculated for each condition when air flows from the inlet 6a to the compressor impeller 3 at a variety of flow rates.

[0064] In Fig. 7 to 10, a line A-1 and a line A-2 show results of analyses of Embodiments 1 and 2 of the present disclosure, respectively corresponding to the centrifugal compressor 100 shown in Fig. 2. Embodiment 2 differs from Embodiment 1 in the angle α of the wings 74 and an area of ​​the opening of the first end 30A.

[0065] A line B shows results of analyses of a comparative example 1, which is similar to the centrifugal compressor 500 in Fig. 4 without a secondary flow path. It should be noted that in Fig. 7 and Fig. 8 a line B could not be analyzed at lower flow rates compared to the other conditions.

[0066] A line C shows results of analyses of a comparative example 2, which is similar to the centrifugal compressor 600 of Fig. 5, where the first end 30A of the secondary flow path 30D has a wide opening to the primary flow path 20.

[0067] Lines D-1, D-2 and E show results of analyses of Comparative Examples 3, 4 and 5, respectively, which are assigned to the centrifugal compressor 700 of Fig. 6, where the first end 30A of the secondary flow path 30E opens in the radial direction. Comparative Example 4 differs from Comparative Example 3 in the radius from the central axis X to the first end 30A. In Comparative Examples 3 and 4, the vanes 74 are oriented such that the air returning from the first end 30A to the primary flow path 20 is parallel to the axial direction (which may also be referred to as a non-vortex). In Comparative Example 5, the vanes 74 are oriented such that the air returning from the secondary flow path 30 to the primary flow path 20 is swirled in a direction opposite to the rotation of the compressor impeller 3 (which may also be referred to as a counter-vortex).

[0068] With reference to Fig. 7, in the low flow rate range, the pressure ratios of Embodiments 1 and 2 (lines A-1 and A-2) further increase as the flow rate decreases, compared to those of Comparative Examples 1 to 5 (lines B, C, D-1, D-2, and E). This means that a higher pressure ratio can be maintained in the low flow rate range, and therefore, the pressure at the inlet of the compressor impeller 3, which decreases as the flow rate decreases, can be maintained at a higher pressure. In other words, a critical flow rate range can be expanded to a lower flow rate side (surge limit), and therefore, the working range of the centrifugal compressor can be further expanded to a lower flow rate side compared to conventionally known structures.

[0069] With reference to Fig. 8, in the low flow rate range, the efficiencies of Embodiments 1 and 2 (lines A-1 and A-2) are higher than those of Comparative Examples 2 to 5 (lines C, D-1, D-2, and E), except for Comparative Example 1 (line B). Thus, according to Embodiments 1 and 2, the efficiency in the low flow rate range can be improved.

[0070] With reference to Fig. 9, in the high flow rate region, the pressure ratios of Embodiments 1 and 2 (lines A-1 and A-2) are higher than those of Comparative Examples 1 to 5 (lines B, C, D-1, D-2, and E). This means that the pressure ratio can be maintained higher in the high flow rate region, and therefore, the pressure at the inlet of the compressor impeller 3, which decreases as the flow rate increases, can be maintained at a higher pressure with respect to an exhaust pressure resistance at a side downstream of the compressor impeller 3. In other words, a critical flow rate region can be expanded to a higher flow rate side (stall limit), and therefore, the working range of the centrifugal compressor can be further expanded to a higher flow rate side compared with the conventionally known structure.

[0071] With reference to Fig.10, in the high flow rate range, the efficiencies of Embodiments 1 and 2 (lines A-1 and A-2) are higher than those of Comparative Examples 1 to 5 (lines B, C, D-1, D-2, and E). Thus, according to Embodiments 1 and 2, the efficiency in the high flow rate range can be improved.

[0072] The centrifugal compressor 100 of the present embodiment, as described above, includes the compressor impeller 3 and the compressor housing 6 that houses the compressor impeller 3. The compressor housing 6 has the primary flow path 30 that houses the compressor impeller 3, and the secondary flow path 30 that surrounds the primary flow path 20 in the cross section perpendicular to the axial direction of the compressor impeller 3. The secondary flow path 30 has the first end 30A that opens to the primary flow path 20 at the position upstream of the compressor impeller 3 in the flow of air into the primary flow path 20, and the second end 30B that opens to the primary flow path 20 at the position downstream of the first end 30A.The first end 30A opens to the primary flow path 20 in the direction opposite to the compressor impeller 3 in the axial direction, and the secondary flow path 30 has the throttle 30C, which is continuous with the first end 30A and narrows toward the first end 30A. According to such a configuration, in the low flow rate region, the air flowing backward in the primary flow path 20 enters the secondary flow path 30 from the second end 30B and returns to the primary flow path 20 from the first end 30A. However, the throttle 30C can reduce the flow rate of the air returning from the first end 30A to the primary flow path 20. Accordingly, the secondary flow path 30 functions as the buffer region for temporarily storing air. Furthermore, according to the above configuration, the first end 30A opens to the primary flow path 20 in the direction opposite to the compressor impeller 3 in the axial direction.Accordingly, the secondary flow path 30 is elongated in the axial direction compared to, for example, a case where the first end 30A opens to the primary flow path 20 in the radial direction. Thus, the secondary flow path 30 can store air for a longer time. The air pressurized by the compressor impeller 3 is cooled as its pressure decreases while stored in the secondary flow path 30. Consequently, when the air returns to the primary flow path 20, the pressure and temperature of the air in the secondary flow path 30 approach the pressure and temperature of the air flowing in the primary flow path 20. According to such a configuration, a flow loss in the primary flow path 20 can be reduced when the air in the secondary flow path 30 returns to the primary flow path 20 from the first end 30A. Thus, efficiency in the low flow rate range can be improved.

[0073] In the high-flow-rate region, a portion of the air flowing in the primary flow path 20 enters the secondary flow path 30 from the first end 30A, unlike in the low-flow-rate region. However, the throttle 30C can reduce the flow rate of the air entering the secondary flow path 30 from the first end 30A. According to such a configuration, the difference between the pressure of the air at the first end 30A and the pressure of the air at the second end 30B is relatively smaller. Therefore, when the air in the secondary flow path 30 returns to the primary flow path 20 from the second end 30B, a loss of flow in the primary flow path 20 can be reduced. Thus, the efficiency in the high-flow-rate region can also be improved.

[0074] Furthermore, in the centrifugal compressor 100, the secondary flow path 30 has a plurality of vanes 74 arranged along the circumferential direction. The vanes 74 can obstruct the flow of air in the secondary flow path 30, thereby allowing the air to be stored longer in the secondary flow path 30. Consequently, efficiency in the low flow rate range can be further improved.

[0075] Furthermore, in the centrifugal compressor 100, the plurality of vanes 74 are provided in the throttle 30C of the secondary flow path 30. According to such a configuration, the vanes 74 can reduce the flow rate of air entering the secondary flow path 30 from the first end 30A in the high flow rate region. Consequently, the efficiency in the high flow rate region can be further improved.

[0076] Furthermore, in the centrifugal compressor 100, each of the plurality of vanes 74 is inclined relative to the center axis X of the compressor impeller 3, as viewed in the radial direction. According to such a configuration, the vanes 74 can more strongly impede the flow of air in the secondary flow path 30 and can retain the air in the secondary flow path 30 for a longer period. Consequently, efficiency in the low flow rate range can be further improved.

[0077] Furthermore, in the centrifugal compressor 100, each of the plurality of vanes 74 is inclined in the same direction as the leading edges of the blades of the compressor impeller 3, as viewed in the radial direction. According to such a configuration, the air returning to the primary flow path 20 from the first end 30A is swirled in the same direction as the rotation of the compressor impeller 3, that is, in the direction in which the air flowing in the primary flow path 20 is swirled. Consequently, the air returning to the primary flow path 20 from the first end 30A does not obstruct the flow in the primary flow path 20. Therefore, a flow loss in the primary flow path 20 can be reduced when the air in the secondary flow path 30 returns to the primary flow path 20. Thus, the efficiency in the low flow rate range can be further improved.

[0078] Although the embodiment of the present disclosure has been described above with reference to the accompanying drawings, the present disclosure is not limited thereto. It is obvious that a person skilled in the art can devise various examples of variations or modifications within the scope of the claims, which are also to be understood as belonging to the technical scope of the present disclosure. List of reference symbols 3 Compressor impeller (impeller) 6 Compressor housing (casing) 20 Primary flow path 30 Secondary flow path 30A first end of the secondary flow path 30B second end of the secondary flow path 30C throttle 74 wings 100 centrifugal compressor X center axis QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2022-70654

[0001] US 2009 / 0263234 A

[0002] JP 6865604

[0002] JP 2014-202103 A

[0002] WO 2019 / 004386 A

[0002] JP 2021-95882 A

[0002]

Claims

[1] Centrifugal compressor with: a wheel; and a housing that houses the impeller, the housing having: a primary flow path that houses the impeller; and a secondary flow path surrounding the primary flow path in a cross-section perpendicular to an axial direction of the impeller, where the secondary flow path has the following: a first end opening to the primary flow path at a position upstream of the impeller in a flow of air in the primary flow path; and a second end opening to the primary flow path at a position downstream of the first end, wherein the first end opens to the primary flow path in a direction opposite to the impeller in the axial direction of the impeller, wherein the secondary flow path has a throttle that is continuous with the first end and that narrows toward the first end. [2] The centrifugal compressor according to claim 1, wherein the secondary flow path has a plurality of vanes arranged along a circumferential direction of the impeller. [3] A centrifugal compressor according to claim 2, wherein the plurality of vanes are provided in the throttle of the secondary flow path. [4] The centrifugal compressor according to claim 2, wherein each of the plurality of vanes is inclined with respect to a center axis of the impeller as viewed in a radial direction of the impeller. [5] A centrifugal compressor according to claim 4, wherein each of the plurality of vanes is inclined in the same direction as leading edges of blades of the impeller, as viewed in the radial direction.

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