CN107407291A - Centrifugal compressor and supercharger including the centrifugal compressor - Google Patents

Abstract

The present invention provides a kind of centrifugal compressor, on housing (40) formed with：Impeller side access (51) from blade wheel chamber (45) towards the direction extension comprising radial outside (Dro) composition, the circulation stream (52) from impeller side access (51) towards the direction extension comprising axial front side Daf compositions, the suction side access (55) connected with the suction passage (41) and circulation stream (52) to blade wheel chamber (45) guiding gas.The size (Ri) of radial direction untill axis (Ar) is into circulation stream (52) with the communicating position of suction side access (55), the size (Ro) than the radial direction untill axis (Ar) is into circulation stream (52) with the communicating position of impeller side access (51) are big.It is bigger than the flow path area (Ai) with the circulation stream (52) at the communicating position of impeller side access (51) with the flow path area (Ao) of the circulation stream (52) at the communicating position of suction side access (55).

Description

Centrifugal compressor and supercharger including the centrifugal compressor

technical field

The present invention relates to a centrifugal compressor and a supercharger provided with the centrifugal compressor.

Background technique

The centrifugal compressor includes a rotating shaft, an impeller attached to the outer periphery of the rotating shaft, and a casing covering the impeller. The impeller of the centrifugal compressor guides the gas flowing in from the axial front side radially outward. The housing is formed with a suction flow path that guides the gas to the axial front side of the impeller, an impeller chamber that communicates with the suction flow path and accommodates the impeller, and a discharge port that communicates with the impeller chamber and allows the gas sent radially outward from the impeller to flow in. flow path.

In such a centrifugal compressor, when the flow rate of the gas flowing in the housing decreases, a phenomenon called surge occurs in which the gas vibrates violently in the direction of the gas flow. Therefore, in centrifugal compressors, various methods of suppressing the surge are being studied.

For example, Patent Document 1 below discloses a centrifugal compressor in which an operating range is expanded by shifting a surge limit at which surge occurs to a smaller flow rate side. The casing of this centrifugal compressor is formed with a chamber that communicates the impeller chamber of the casing with the suction flow path, or a chamber that connects the impeller chamber of the casing with a suction pipe connected to the suction flow path side of the casing. . If the chamber is formed on the casing in this way, even if the flow rate of gas flowing from the suction flow path to the discharge flow path through the impeller chamber is small, since part of the gas in the impeller chamber returns to the impeller chamber through the chamber and the suction flow path, the impeller The gas flow rate in the upstream side portion of the chamber is increased, so that surge can be suppressed.

prior art literature

patent documents

Patent Document 1 Patent No. 3006215

Contents of the invention

The problem to be solved by the invention

The technology described in the above-mentioned Patent Document 1 can expand the working area of the centrifugal compressor. However, for centrifugal compressors, it is desirable to further expand the working area.

Therefore, an object of the present invention is to provide a centrifugal compressor capable of expanding an operating area, and a supercharger including the centrifugal compressor.

Technical solutions for solving problems

A centrifugal compressor according to an aspect of the invention for achieving the above object includes: a rotating shaft rotating about an axis, an impeller attached to the outer periphery of the rotating shaft, and a casing covering the impeller. It has a hub and blades, the hub is installed on the rotating shaft, and a plurality of blades are arranged on the hub at intervals in the circumferential direction centered on the axis, and rotate integrally with the hub, The gas flowing in from one side of the axial direction extending from the axis, that is, the axial front side, is guided to the radially outer side relative to the axis, and the housing is formed with: A suction passage for leading gas on the front side, an impeller chamber communicating with the suction passage and accommodating the impeller, and a discharge passage communicating with the impeller chamber and allowing the gas sent from the impeller to the radially outer side to flow in. The flow path communicates with the impeller chamber and extends from the impeller chamber toward a direction including the radially outer component, and communicates with the impeller side communication passage and extends from the impeller side communication passage toward The circulation flow path extending in the direction of the axial front side component, the suction side communication path communicating with the circulation flow path and the suction flow path, the suction side diameter dimension is from the axis to the circulation flow path The radial dimension of the communication position with the suction side communication passage, the impeller side diameter dimension is the radial dimension from the axis to the communication position of the impeller side communication passage in the circulation flow path, the The suction side diameter dimension is larger than the impeller side diameter dimension, and the flow channel area of the circulation flow path at the communicating position with the suction side communicating path is larger than the flow path area at the communicating position with the impeller side communicating path. The flow path area of the above-mentioned circulation flow path is large.

In the centrifugal compressor, when the flow rate of gas flowing into the suction flow path is low, the pressure in the impeller chamber becomes higher than the pressure in the suction flow path. Therefore, if a circulation flow path or the like is formed in the compressor housing as in the centrifugal compressor, part of the gas in the impeller chamber returns to the suction flow path through the circulation flow path or the like. As a result, in the impeller chamber, the flow rate in the axially front side portion becomes larger than that in the impeller side communicating passage. Therefore, surge can be suppressed in this centrifugal compressor. That is, in this centrifugal compressor, the surge limit line can be shifted to the small flow rate side, thereby expanding the operating range.

The flow direction component of the gas flowing from the impeller chamber through the impeller side communication passage into the circulation flow path includes a component that revolves around the axis and in the same direction as the impeller. Assuming that the gas having this swirl component as a flow component returns to the impeller chamber through the circulation flow path, the suction side communication path, and the suction flow path, the angle of attack of the blade becomes small. Therefore, the discharge pressure becomes smaller, in other words, the pressure ratio becomes smaller.

In this centrifugal compressor, the suction side diameter of the circulation flow path is larger than the impeller side diameter of the circulation flow path. Therefore, in this centrifugal compressor, the flow velocity of the gas swirling component at the position communicating with the suction side communication path in the circulation flow path can be made higher than the flow rate of the gas swirling component at the position communicating with the impeller side communication path in the circulation flow path. The flow rate is small.

In addition, in this centrifugal compressor, the flow area of the circulation flow path at the position communicating with the suction side communication path is larger than the flow area of the circulation flow path at the position communicating with the impeller side communication path. Therefore, in this centrifugal compressor, not only the flow velocity of the gas axial component but also the flow velocity of the swirling component can be reduced at a position communicating with the suction side communication passage in the circulation flow path.

As described above, in this centrifugal compressor, the flow velocity of the swirling component of the air flowing into the impeller chamber can be reduced. As a result, in this centrifugal compressor, the angle of attack of the blades increases, and the pressure ratio can be increased. Therefore, in this centrifugal compressor, the surge limit line can be shifted to the high pressure ratio side. Therefore, in this centrifugal compressor, the operating range can be further expanded.

Here, in the centrifugal compressor, the casing may be formed with a plurality of the circulation channels arranged in a circumferential direction centering on the axis, and may be formed with A partition that separates the circumferentially adjacent circulation channels from each other.

In this centrifugal compressor, the flow velocity of the swirling component of the gas in the circulation flow path can be suppressed due to the presence of the partition.

In the centrifugal compressor according to any one of the above aspects, the suction flow path may have a reduced-diameter portion, and the reduced-diameter portion has a shape rotationally symmetrical about the axis, and the flow path area increases with the gradually becomes smaller toward the other side of the axial direction, that is, the rear side of the axial direction, and the communication port of the suction side communication path to the suction flow path is formed in the demarcated flow path in the diameter-reduced portion. face.

In this centrifugal compressor, since the suction flow path has a diameter-reduced portion in which the area of the flow path gradually decreases toward the axial rear side, air can easily flow into the impeller chamber from the outside through the suction flow path. Furthermore, in this centrifugal compressor, since the communication port of the suction-side communication passage is formed on the surface defining the flow passage in the reduced-diameter portion, the suction-side communication passage can be closed due to the static pressure reduction effect on this surface. The gas inside is efficiently guided into the suction flow path.

As a result, in this centrifugal compressor, the flow rate of gas flowing into the impeller chamber through the suction flow path can be increased. Therefore, in this centrifugal compressor, the surge limit line can be further shifted to the small flow rate side, and the operating range can be further expanded.

In addition, in the centrifugal compressor having the diameter-reduced portion, the surface defining the flow path in the diameter-reduced portion may be a curved surface that protrudes toward a side closer to the axis.

In this centrifugal compressor, since a part of the surface defining the suction flow path is formed as a curved surface protruding toward the side closer to the axis, that is, as a bell mouth surface, gas easily flows into the impeller chamber from the outside through the suction flow path. Furthermore, in this centrifugal compressor, since the communication port of the suction side communication passage is formed on the bell mouth surface, the gas in the suction side communication passage can be efficiently guided by the static pressure reduction effect on the bell mouth surface. into the suction flow path.

In addition, in any of the centrifugal compressors having the reduced-diameter portion, the distance from the axis line to the axial front side edge of the communication port of the suction side communication passage may be The radial dimension is smaller than the suction side diameter and larger than the impeller side diameter.

In addition, in any one of the centrifugal compressors described above, the suction-side communication passage may be folded back from the boundary between the circulation flow passage and the suction-side communication passage, The radial inner side extends toward the other axial side, that is, the axial rear side, and communicates with the suction flow path.

In this centrifugal compressor, the length of the gas flow path until a part of the gas in the impeller chamber returns to the suction flow path through the impeller side communication path, the circulation flow path, and the suction side communication path can be increased without lengthening the axial dimension of the casing. . When the length of the flow path in the axial direction becomes longer, the gas tends to follow the wall surface of the flow path extending in the axial direction, and the swirl component of the gas decreases. Therefore, in this centrifugal compressor, the angle of attack of the blades becomes large, and the pressure ratio can be increased. Therefore, in this centrifugal compressor, the operating range can be further expanded.

In addition, in any one of the above centrifugal compressors, L may be defined as a position from a position communicating with the suction side communication channel in the circulation flow channel to a position in the circulation flow channel that is connected to the suction side communication channel. The axial dimension of the communication position of the impeller side communication channel, let do be the equivalent diameter related to the flow path area of the circulation flow channel at the communication position with the suction side communication channel, and let di be the equivalent diameter related to the flow area of the impeller side communication channel. The equivalent diameter related to the channel area of the circulation channel at the communication position of the side communication channel, at this time, the expansion angle 2θ specified by the following formula is smaller than 20°.

2θ＝2×tan((do－di)/2L)

The rapid deceleration of the flow velocity in the circulation flow path leads to the development of the boundary layer on the wall surface defining the circulation flow path. Therefore, the pressure loss of the gas passing through the circulation flow path increases, and the flow rate of the gas flowing through the circulation flow path decreases. Therefore, in this centrifugal compressor, the expansion angle 2θ is made smaller than 20° to suppress a decrease in the flow rate of the gas flowing through the circulation flow path.

In addition, in any one of the centrifugal compressors described above, from a communication position of the circulation flow path with the suction side communication path to a position of the circulation flow path connected to the impeller side may be The axial dimension up to the communication position of the passage is 0.25 times or more the maximum outer diameter of the impeller, that is, the outer diameter of the impeller.

When the length of the flow path in the axial direction becomes longer, the gas tends to follow the wall surface of the flow path extending in the axial direction, and the swirl component of the gas decreases. Therefore, in this centrifugal compressor, the axial dimension from the communication position of the circulation flow path with the suction side communication path to the communication position of the impeller side communication path in the circulation flow path is lengthened, and the swirl of the gas is reduced. Element.

A supercharger according to an aspect of the invention for achieving the above object includes the centrifugal compressor described in any one of the above, and a turbine having: a turbine rotating shaft rotating around the axis; The turbine impeller on the outer periphery of the turbine rotating shaft, and the turbine housing covering the turbine impeller, the turbine rotating shaft and the rotating shaft of the centrifugal compressor are located on the same axis and are connected to each other to rotate integrally. Form the supercharger rotation axis.

Invention effect

According to one aspect of the present invention, it is possible to expand the operating range of the centrifugal compressor.

Description of drawings

Fig. 1 is a schematic cross-sectional view of main parts of a centrifugal compressor according to a first embodiment of the present invention.

Fig. 2 is an overall sectional view of a supercharger according to a first embodiment of the present invention.

FIG. 3 is an explanatory diagram for explaining a spread angle.

4 is a schematic cross-sectional view of main parts of a centrifugal compressor of Comparative Example 2. FIG.

Fig. 5 is a graph showing characteristics of each centrifugal compressor.

6 is a schematic cross-sectional view of main parts of a centrifugal compressor according to a second embodiment of the present invention.

7 is a schematic cross-sectional view of main parts of a centrifugal compressor according to a third embodiment of the present invention.

Fig. 8 is a schematic cross-sectional view of main parts of a centrifugal compressor according to a fourth embodiment of the present invention.

detailed description

Hereinafter, various embodiments of the present invention will be described using the drawings.

"First Embodiment of Centrifugal Compressor and Supercharger"

A first embodiment of a centrifugal compressor and a supercharger will be described using FIGS. 1 to 5 .

As shown in FIG. 2 , the supercharger of this embodiment includes a turbine 10 driven by exhaust gas EX from the engine, a centrifugal compressor 30 that compresses air A and sends it to the engine, and a compressor that connects the centrifugal compressor 30 and the turbine 10 . Connecting part 20.

The turbine 10 has a cylindrical turbine rotating shaft 11 rotating around an axis Ar, a turbine wheel 12 attached to the outer periphery of the turbine rotating shaft 11 , and a turbine casing 19 covering the turbine wheel 12 .

The centrifugal compressor 30 has a cylindrical compressor rotating shaft 31 rotating around an axis Ar, a compressor impeller 32 attached to the outer periphery of the compressor rotating shaft 31 , and a compressor housing 40 covering the compressor impeller 32 .

The connecting portion 20 has a cylindrical connecting rotating shaft 21 that rotates around the axis Ar, a center case 29 covering the connecting rotating shaft 21 , and a bearing 28 that rotatably supports the connecting rotating shaft 21 . The bearing 28 is fixed to the inner peripheral side of the center case 29 .

The axis Ar of the compressor rotating shaft 31 , the axis Ar of the connecting rotating shaft 21 , and the axis Ar of the turbine rotating shaft 11 are located on the same axis Ar and connected to each other in this order to rotate integrally, constituting the turbocharger rotating shaft. In addition, the compressor housing 40, the center housing 29, and the turbine housing 19 are connected to each other to form a supercharger housing.

Here, the direction in which the axis line Ar extends is referred to as an axial direction Da, one side of the axial direction Da is referred to as an axial front side Daf, and the other side of the axial direction Da is referred to as an axial rear side Dab. In the present embodiment, the centrifugal compressor 30 is provided on the axial front side Daf with respect to the connection portion 20 , and the turbine 10 is provided on the axial rear side Dab with respect to the connection portion 20 . In addition, the radial direction relative to the axis Ar is simply referred to as the radial direction Dr, the side farther from the axis Ar in the radial direction Dr is defined as the radially outer side Dro, and the side closer to the axis Ar in the radial direction Dr is defined as the radial direction. Inwardly DRi. In addition, the circumferential direction around the axis Ar is simply referred to as the circumferential direction Dc.

The compressor impeller 32 is an open impeller. The compressor impeller 32 has a hub 33 attached to the outer periphery of the compressor rotating shaft 31 and a plurality of blades 35 provided on the hub 33 at intervals in the circumferential direction Dc.

Seen from the axial direction Da, the hub 33 has a circular shape centered on the axis Ar, and its outer diameter gradually increases from the axial front side Daf toward the axial rear side Dab. Furthermore, the shape of the hub 33 is such that the tangent line at each position on the boundary line between the surface of the radially outer side Dro, that is, the hub surface 34 and the meridian cross section moves from the axial front side Daf to the axial rear side Dab. The substantially parallel direction of Ar gradually moves toward the radial direction Dr.

A plurality of blades 35 are all disposed on the hub surface 34 . The blades 35 protrude in a direction including a direction component perpendicular to the hub surface 34 , along the edge of the hub surface 34 extending from the axial front side Daf of the hub surface 34 to the axial rear side Dab of the hub surface 34 . The edge of the blade 35 on the axially front side Daf forms a leading edge 36 and the edge on the axially rear side Dab of the blade 35 opposite the radially outer Dro forms a trailing edge 37 . In addition, a tip 38 is formed on the tip of the blade 35 with respect to the protruding direction of the hub surface 34 . The tip 38 of the vane 35 faces the inner peripheral surface of the compressor housing 40 .

The compressor housing 40 is formed with: a suction flow path 41 that guides the air A on the axial front side Daf of the compressor impeller 32 , an impeller chamber 45 that communicates with the suction flow path 41 and accommodates the compressor impeller 32 , and an impeller chamber. 45 communicates with the discharge flow path 46 into which the gas sent from the compressor impeller 32 to the radially outer side Dro flows. The suction flow path 41 has a rotationally symmetrical shape about the axis Ar. The air A from the suction flow path 41 flows from between the leading edges 36 of the plurality of blades 35 of the compressor impeller 32 into between the plurality of blades 35 . The discharge flow path 46 has a diverging portion 47 extending radially outward Dro from the trailing edge 37 of the plurality of blades 35 and a scroll portion 48 extending in the circumferential direction Dc from the edge of the radially outer Dro of the diverging portion 47 . The air A from the exhaust flow path 46 flows from the intake manifold of the engine into the cylinders of the engine.

Further, the compressor housing 40 is formed with: an impeller side communication passage 51 communicating with the impeller chamber 45 and extending from the impeller chamber 45 in a direction including the radially outer Dro component; 51 is directed toward a plurality of circulation channels 52 extending in the direction including the axial front side Daf component, and a suction-side communication channel 55 communicating with the plurality of circulation channels 52 and the suction flow channel 41 .

The impeller-side communicating passage 51 opens to the impeller chamber surface 45ip of the compressor housing 40 that defines the impeller chamber 45 . The opening is formed on the inner surface 45ip of the impeller chamber, at a position axially rearward Dab of the front edge 36 of the compressor impeller 32 , and at an axial front side of the rear edge 37 of the compressor impeller 32 . Daf's location. In the present embodiment, the impeller-side communicating passage 51 is formed in a ring shape centering on the axis Ar. That is, the impeller-side communication passage 51 extends from the impeller chamber 45 in a direction including the radially outer Dro component, and expands over 360° in the circumferential direction Dc centered on the axis Ar. Therefore, the opening formed in the impeller chamber surface 45ip of the compressor impeller 32 side passage opens at 360° in the circumferential direction Dc centering on the axis Ar.

Each of the plurality of circulation channels 52 extends from the radially outer Dro end of the impeller side communication channel 51 in a direction including the axially front side Daf component, and expands in the circumferential direction Dc. The plurality of circulation channels 52 are arranged in the circumferential direction Dc centered on the axis Ar. The adjacent circulation channels 52 in the circumferential direction Dc are partitioned by support rods (partitions) 62 of the compressor housing 40 .

The suction side communication passage 55 extends from the axially front Daf end of each of the plurality of circulation flow passages 52 in a direction having a radially inner DRi component, and communicates with the suction flow passage 41 . Like the impeller side communication passage 51 , the suction side communication passage 55 is also formed in a ring shape centering on the axis Ar in this embodiment.

In the compressor housing 40 , a portion of the plurality of circulation channels 52 radially inner DRi and the suction channel 41 radially outer Dro forms a disposal cylinder 63 . The treatment cylinder 63 is formed in a cylindrical shape centering on the axis Ar. The edge of the disposal cylinder 63 on the axial front side Daf forms the edge of the suction side communication passage 55 on the axial rear side Dab. In addition, the edge of the disposal cylinder 63 on the axial rear side Dab forms the edge of the impeller side communicating passage 51 on the axial front side Daf. The disposal cylinder 63 is connected to the casing main body 61 of the compressor casing 40 at the radial outer side Dro of the plurality of circulation channels 52 via a plurality of support rods (partitions) 62 .

Next, the dimension of each part of the compressor casing 40 of this embodiment is demonstrated using FIG. 1. FIG.

Here, let the communication position of the circulation flow path 52 with the impeller side communication path 51 be the inlet 53 of the circulation flow path 52 , and let the communication position of the circulation flow path 52 with the suction side communication path 55 be the opening of the circulation flow path 52 . Exit 54. In this embodiment, the dimension from the axis Ar to the edge of the radially inner side DRi of the outlet 54 of the circulation flow path 52, that is, the suction side diameter dimension (hereinafter referred to as the outlet inner diameter) Ro is larger than The dimension from the axis Ar to the edge of the radially inner side DRi of the outlet 54 of the circulation channel 52 is the impeller side diameter dimension (hereinafter referred to as an inlet inner diameter) Ri.

Ro＞Ri·············(1)

In the present embodiment, as shown in the following formula (2), the flow path area (hereinafter referred to as the outlet flow path area) Ao at the outlet 54 of the circulation flow path 52 is larger than that at the inlet 53 of the circulation flow path 52. The flow path area (as the inlet flow path area) Ai.

Ao＞Ai·············(2)

In this embodiment, the dimension Da in the axial direction from the inlet 53 to the outlet 54 in the circulation flow path 52, that is, the flow path length L of the circulation flow path 52, is the maximum diameter of the compressor impeller 32 as shown in the following formula (3). That is, more than 0.25 times the outer diameter of the impeller D2.

L≧0.25×D2········(3)

In addition, in the present embodiment, the expansion angle 2θ of the circulation channel 52 is expressed by the following formula (4) to be less than 20°.

2θ＝2×tan((do－di)/2L)＜20°··(4)

In addition, L in Formula (4) is the flow path length of the circulation flow path 52 in the axial direction Da as mentioned above. In addition, as shown in FIG. 3 , do is an equivalent diameter whose area is related to the outlet flow path area Ao, and di is an equivalent diameter whose area is related to the inlet flow path area Ai. That is, the divergence angle 2θ is the angle formed by the axis of the cone and the line segment connecting the edge of the inlet position of the flow channel and the edge of the outlet position of the flow channel in a simple diffuser in which the imaginary flow path is conical. 2 times the angle of θ. In addition, the so-called equivalent diameter related to the flow path area is the circle diameter of the flow path area.

Next, comparative examples 1 and 2 of the centrifugal compressor will be described in order to describe the effect of the present embodiment.

In the compressor housing of the centrifugal compressor of Comparative Example 1, similarly to the compressor housing 40 of the centrifugal compressor 30 of the present embodiment, a suction flow path, an impeller chamber, and a discharge flow path are formed. However, the impeller-side communication passage 51 , the circulation flow passage 52 , and the suction-side communication passage 55 of the compressor housing 40 of the centrifugal compressor 30 of the present embodiment are not formed in the compressor housing of the centrifugal compressor of Comparative Example 1.

In addition, as shown in FIG. 4 , in the compressor housing 40x of the centrifugal compressor 30x of Comparative Example 2, similarly to the compressor housing 40 of the centrifugal compressor 30 of the present embodiment, the suction flow path 41 , The impeller chamber 45 and the discharge flow path 46 are further formed with an impeller side communication path 51 , a circulation flow path 52x, and a suction side communication path 55 .

However, in Comparative Example 2, the outlet inner diameter Ro of the circulation flow path 52x is equal to the impeller side diameter Ri of the circulation flow path 52x. In Comparative Example 2, the outlet channel area Ao of the circulation channel 52x is equal to the inlet channel area Ai of the circulation channel 52x.

In the centrifugal compressor, if the flow rate of gas flowing into the suction flow path is small, the pressure in the suction flow path becomes lower than the pressure in the impeller chamber. Therefore, if the circulation channels 52, 52x, etc. are formed in the compressor casings 40, 40x like the present embodiment or Comparative Example 2, part of the gas in the impeller chamber 45 passes through the circulation channels 52, 52x. etc. to return to the suction flow path 41. As a result, in the impeller chamber 45 , the flow rate increases in the portion closer to the axially front side Daf than the impeller side communicating passage 51 .

In the present embodiment or Comparative Example 2, if the flow rate of gas flowing into the suction flow path 41 is small, the flow rate of gas flowing through the discharge flow path 46 will also be small. However, the flow rate of the portion on the front side Daf becomes larger than the flow rate of gas flowing into the suction flow path 41 , so that surge can be suppressed. Therefore, as shown in FIG. 5 , in Examples 1 to 4 or Comparative Example 2 which are various aspects of the present embodiment, the surge limit lines S1 to S4 and Sx2 are similar to the surge limit line Sx1 in Comparative Example 1. than move towards the small flow side. Therefore, in Examples 1 to 4 or Comparative Example 2 which are various aspects of this embodiment, it is possible to expand the operating range of the centrifugal compressor 30 compared with Comparative Example 1. In addition, the centrifugal compressors of Examples 1 to 4 satisfy the preceding expressions (1) to (4). However, as will be described later, the flow path length L of the circulation flow path in the centrifugal compressors of Examples 1 to 4 is different from each other. In addition, in FIG. 5 , a plurality of curves drawn by solid lines are characteristic curves showing the relationship between the flow rate and the pressure ratio at different rotational speeds.

However, the flow of air A flowing from the impeller chamber 45 through the impeller side communicating passage 51 into the circulation passages 52 and 52x includes a component that swirls around the axis Ar and in the same direction as the compressor impeller 32 rotates. Assuming that in Comparative Example 2, when the air A having the swirling component as the airflow component returns to the impeller chamber 45 through the circulation flow path 52x, the suction side communication path 55, and the suction flow path 41, since the angle of attack of the blade 35 becomes small, the The discharge pressure becomes smaller, in other words, the pressure ratio becomes smaller.

When no external force is applied to the gas swirling around the axis Ar, the following formula (5) holds.

ci×Ri＝co×Ro·······(5)

In addition, in formula (5), ci represents the flow rate of the swirling component of the air A at the inlet 53 of the circulation flow path, and co represents the flow rate of the swirling component of the air A at the outlet 54 of the circulation flow path. In addition, in the formula (5), Ri represents the inner diameter of the inlet of the swirl flow path, and Ro represents the inner diameter of the outlet of the circulation flow path 52 .

Therefore, if the inner diameter Ro of the outlet of the circulation flow path 52 is larger than the inner diameter Ri of the inlet of the circulation flow path 52 as in the present embodiment, the flow velocity co of the swirling component of the air A at the outlet 54 of the circulation flow path 52 becomes smaller. The flow velocity ci of the swirling component of the air A in the inlet 53 of the circulation flow path 52 is smaller.

In addition, in the present embodiment, the outlet flow path area Ao of the circulation flow path 52 is larger than the inlet flow path area Ai of the circulation flow path 52 . Therefore, in the present embodiment, the swirling component flow velocity co of the air A at the outlet 54 of the circulation flow path 52 is further smaller than the swirling component flow velocity ci of the air A at the inlet 53 of the circulation flow path 52 .

Therefore, in the centrifugal compressor 30 of the present embodiment, compared with the centrifugal compressor 30x of Comparative Example 2, the flow velocity of the swirling component of the air A flowing into the impeller chamber 45 can be reduced.

Among Examples 1 to 4 which are various forms of this embodiment, Example 1 is the centrifugal compressor 30 in which the flow path length L of the circulation flow path 52 is 0.25×D. Example 2 is the centrifugal compressor 30 in which the flow path length L of the circulation flow path 52 is 0.50×D. Example 3 is a centrifugal compressor 30 in which the flow path length L of the circulation flow path 52 is 0.64×D. Example 4 is a centrifugal compressor 30 in which the flow path length L of the circulation flow path 52 is 0.89×D. That is, among Examples 1 to 4, the channel length L of Example 1 is the shortest, and the channel length L becomes longer as it changes to Example 2, Example 3, and Example 4.

As shown in Fig. 5, among Examples 1 to 4, the surge limit line S1 of Example 1 is closest to the large flow rate side, and as it changes to Example 2, Example 3, and Example 4, the surge limit line moves toward Move on the light traffic side. That is, as the flow path length L of the circulation flow path 52 becomes longer, the surge limit line changes to the lower flow rate side, thereby expanding the operating range of the centrifugal compressor 30 . This is because, due to the influence of friction between the circulation flow path 52 and the air A, as the flow path length L of the circulation flow path 52 becomes longer, in the flow of the air A, not only the velocity component in the axial direction Da becomes smaller. , the cyclotron component will also become smaller. Therefore, in the present embodiment, the flow path length L of the circulation flow path 52 is set to be 0.25×D or more.

However, in the present embodiment, as described above, by making the outlet flow path area Ao of the circulation flow path 52 larger than the inlet flow path area Ai of the circulation flow path 52, the density of the air A in the circulation flow path 52 is reduced. flow rate. However, rapid deceleration in the circulation flow path 52 leads to the development of a boundary layer on the wall surface defining the circulation flow path 52 . Therefore, the pressure loss of the gas passing through the circulation flow path 52 increases, and the flow rate of the gas flowing through the circulation flow path 52 decreases. Therefore, in the present embodiment, the spread angle 2θ is made smaller than 20° as described above by using the expression (5), and the decrease in the flow rate of the air A flowing through the circulation flow path 52 is suppressed. It can also be understood from this formula (5) that in order to reduce the spread angle 2θ, it is preferable that the flow path length of the circulation flow path 52 be long.

That is, the flow path length L of the circulation flow path 52 is preferably long for both the reduction of the swirl component and the reduction of the spread angle 2θ. From this point of view, the flow path length of the circulation flow path 52 is 0.25×D or more, preferably 0.50×D or more if possible. However, if the flow path length L of the circulation flow path 52 becomes longer, the compressor housing 40 will become longer in the axial direction Da. Therefore, it is preferable to determine the flow path length L of the circulation flow path 52 in a trade-off between reducing the swirl component, reducing the spread angle, and lengthening the compressor casing 40 .

"Second Embodiment of Centrifugal Compressor"

A second embodiment of the centrifugal compressor will be described using FIG. 6 .

The centrifugal compressor 30a of this embodiment also has the compressor impeller 32 and the compressor housing 40a similarly to the centrifugal compressor 30 of 1st Embodiment. The configuration of the compressor impeller 32 is the same as that of the first embodiment.

Also in the compressor housing 40a of the present embodiment, similar to the compressor housing 40 of the centrifugal compressor 30 of the first embodiment, a suction flow path 41a, an impeller chamber 45, a discharge flow path 46, and an impeller side are formed. The communication passage 51, the plurality of circulation flow passages 52, and the suction side communication passage 55a. However, the shape of the suction flow path 41a and the suction-side communication path 55a in the compressor housing 40a of this embodiment is different from that of the first embodiment.

The suction flow path 41a of the present embodiment has a rotationally symmetrical shape about the axis Ar, and has a diameter-reduced portion 42 whose flow path area gradually decreases from the axial front side Daf toward the axial rear side Dab. The reduced-diameter portion 42 has a flared shape centered on the axis Ar. Therefore, a smooth convex flared surface 42f is formed on the surface defining the flow path in the narrowed diameter portion 42 toward the side closer to the axis Ar, that is, the radially inner side DRi.

The communication port 55o of the suction side communication passage 55a with respect to the suction flow passage 41a is formed on the bell mouth surface 42f defining the flow passage in the reduced diameter portion 42 . In this suction-side communication passage 55a, the portion on the rear side Dab in the axial direction with the suction-side communication passage 55a as a reference is formed by the disposal cylinder 63a similarly to the first embodiment. In addition, in this suction side communication passage 55 a , a portion on the axial front side Daf with respect to the suction side communication passage 55 a is formed by the case main body 61 and the bell cap 65 .

The inner peripheral surface of the treatment cylinder 63a in the present embodiment forms a portion on the rear side Dab in the axial direction of the bell mouth surface 42f. Therefore, the area of the flow path defined by the inner peripheral surface of the disposal cylinder 63 a gradually decreases from the axially front side Daf toward the axially rear side Dab.

The flared cap 65 has a rotationally symmetrical shape about the axis Ar. The flared cap 65 is fixed to the axially front side Daf of the case body 61 and to the radially inner side DRi of the case body 61 . The flared cap 65 is fixed to the case main body 61 at a distance from the treatment cylinder 63 a toward the axial front side Daf. The suction-side communication path 55a is formed between the disposal cylinder 63a and the bell mouth cap 65 . The inner peripheral surface of the treatment cylinder 63a forms a portion on the axial front side Daf of the bell mouth surface 42f. Therefore, the area of the flow path defined by the inner peripheral surface of the flared cap 65 gradually decreases from the axial front side Daf toward the axial rear side Dab.

The compressor housing 40 a of the present embodiment also satisfies the relationships shown in the formulas (1) to (4) as in the compressor housing 40 of the first embodiment. Furthermore, in this embodiment, the dimension from the axis Ar to the edge of the axial front side Daf in the communication port 55o of the suction side communication passage 55a, in other words, the dimension from the axis Ar to the radial inner side DRi of the bell mouth cap 65 and The dimension Rc to the edge of the axial front side Daf is smaller than the outlet inner diameter Ro and larger than the inlet inner diameter Ri as shown in the following formula (6).

Ro＞Rc＞Ri·········(6)

Since the present embodiment satisfies the above formula (6), the flow path defined by the bell mouth surface 42f around the communication port 55o of the suction side communication path 55a is smoothly reduced in diameter toward the axial rear side Dab.

The compressor housing 40a of the present embodiment also satisfies the relationships shown in formulas (1) to (4) similarly to the compressor housing 40 of the first embodiment, so that the amount of air A flowing into the impeller chamber 45 can be reduced. The swirling component flow rate can expand the working range of the centrifugal compressor 30a.

In addition, in this embodiment, a part of the surface defining the suction flow path 41a constitutes the bell mouth surface 42f, and the air A easily flows into the impeller chamber 45 from the outside through the suction flow path 41a. Furthermore, in the present embodiment, since the communication port 55o between the suction side communication passage 55a and the suction flow passage 41a is formed on the bell mouth surface 42f, the suction side communication passage can be connected by utilizing the static pressure reduction effect on the bell mouth surface 42f. The air A in 55a is efficiently guided into the suction flow path 41a.

As a result, in this embodiment, the flow rate of the air A flowing into the impeller chamber 45 through the suction flow path 41 a can be increased compared to the first embodiment. Therefore, in this embodiment, compared with the first embodiment, the surge limit line can be further moved to the small flow rate side, and the operating range of the centrifugal compressor 30a can be further expanded.

"The Third Embodiment of Centrifugal Compressor"

A third embodiment of the centrifugal compressor will be described using FIG. 7 .

The centrifugal compressor 30b of this embodiment also has the compressor impeller 32 and the compressor housing 40b similarly to the centrifugal compressors 30 and 30a of the first and second embodiments. The configuration of the compressor impeller 32 is the same as that of the first and second embodiments.

Like the compressor housings 40, 40a of the centrifugal compressors 30, 30a of the first and second embodiments, the compressor housing 40b of this embodiment is formed with a suction flow path 41b, an impeller chamber 45, and a discharge flow path 46. , the impeller side communication passage 51, a plurality of circulation flow passages 52, and the suction side communication passage 55b. However, the shape of the suction flow path 41b and the suction-side communication path 55b in the compressor housing 40b of this embodiment is different from that of the first embodiment.

The suction flow path 41b of the present embodiment has a reduced-diameter portion 42b and a straight body portion 43b that are rotationally symmetrical about the axis Ar. The flow path area of the reduced-diameter portion 42b gradually decreases from the axial front side Daf toward the axial rear side Dab. The reduced-diameter portion 42b has a flared shape centered on the axis Ar. Therefore, the surface defining the flow path in the reduced-diameter portion 42b forms a smooth and convex flared surface 42bf toward the side closer to the axis Ar, that is, the radially inner side DRi. The straight body portion 43b has the same flow path area at each position in the axial direction Da. Therefore, the surface defining the flow path in the straight body portion 43b forms a cylindrical inner peripheral surface 43bg centered on the axis Ar.

The communication port 55o to the suction flow path 41b in the suction side communication path 55b is formed on the cylindrical inner peripheral surface 43bg defining the flow path in the straight body portion 43b. In this suction-side communication passage 55b, a part on the rear side Dab in the axial direction based on the suction-side communication passage 55b is formed by the disposal cylinder 63b similarly to the first and second embodiments. In addition, in this suction-side communication passage 55b, a portion on the axial front side Daf with respect to the suction-side communication passage 55b is formed by the case main body 61 and the bell cap 65b. The bell cap 65b is fixed to the axial front side Daf of the case body 61 and to the radially inner side DRi of the case body 61 as in the second embodiment. The flared cap 65b is also fixed to the case main body 61 at a distance from the treatment cylinder 63b toward the axial front side Daf. The suction-side communicating path 55b is formed between the disposal cylinder 63b and the bell mouth cap 65b.

The suction side communication passage 55b is folded back from the boundary between the circulation flow passage 52 and the suction side communication passage 55b, extends toward the axial rear side Dab while going radially inward DRi with respect to the axis Ar, and communicates with the suction flow passage 41b.

In the treatment cylinder 63b of this embodiment, a reduced-diameter inner peripheral surface 63bf whose inner diameter gradually decreases toward the axial rear Dab and a cylindrical inner peripheral surface 63bg whose inner diameter is constant in the axial direction Da are formed. The cylindrical inner peripheral surface 63bg is formed from the edge of the diameter-reduced inner peripheral surface 63bf on the rear side Dab in the axial direction. The flared cap 65b is formed with a flared surface 65bf whose inner diameter gradually decreases toward the axial rear side Dab, and a cylindrical inner peripheral surface 65bg whose inner diameter is constant in the axial direction Da. The cylindrical inner peripheral surface 65bg is formed from the edge of the flared surface 65bf on the rear side Dab in the axial direction. Furthermore, a reduced-diameter outer peripheral surface 65bh whose outer diameter gradually decreases toward the axial rear side Dab is formed on the flared cap 65b.

The suction-side communication passage 55b is formed between the reduced-diameter inner peripheral surface 63bf of the disposal cylinder 63b and the reduced-diameter outer peripheral surface 65bh of the flared cap 65b. The cylindrical inner peripheral surface 43bg defining the flow path in the straight body portion 43b is formed by the cylindrical inner peripheral surface 63bg of the disposal cylinder 63b and the cylindrical inner peripheral surface 65bg of the flared cap 65b.

The compressor housing 40b of the present embodiment also satisfies the relationships shown in the formulas (1) to (4) similarly to the compressor housings 40 and 40a in the above-described embodiments. Therefore, the compressor housing 40b of the present embodiment can also reduce the flow velocity of the swirling component of the air A flowing into the impeller chamber 45 similarly to the compressor housing 40 of the first embodiment, thereby expanding the operating range of the centrifugal compressor 30b. .

In addition, in the present embodiment, the suction side communication passage 55b is folded back from the boundary between the circulation flow passage 52 and the suction side communication passage 55b, then extends toward the axial rear side Dab, and communicates with the suction flow passage 41b. Therefore, the inside of the impeller chamber 45 The length of the flow path until a part of the air A returns to the suction flow path 41b becomes longer. Therefore, similarly to the case where the flow path length L of the circulation flow path 52 is increased, the swirling component flow velocity of the air A flowing into the impeller chamber 45 can be reduced. In addition, in the present embodiment, since the suction side communication passage 55b extends toward the axial rear side Dab after turning back from the boundary between the circulation flow passage 52 and the suction side communication passage 55b, it is possible to suppress the displacement of the compressor housing 40b in the axial direction Da. It is longer, and the length of the flow path until a part of the air A in the impeller chamber 45 returns to the suction flow path 41 b can be increased.

"Fourth Embodiment of Centrifugal Compressor"

A fourth embodiment of the centrifugal compressor will be described using FIG. 8 .

The centrifugal compressor 30c of the present embodiment is a centrifugal compressor in which the configuration of the centrifugal compressor 30a of the second embodiment and the configuration of the centrifugal compressor 30b of the third embodiment are combined. That is, in the present embodiment, while adopting the configuration of the suction side communication passage of the third embodiment, like the second embodiment, the communication between the suction side communication passage and the suction flow passage is formed on the bell mouth surface of the suction side passage. mouth.

The suction flow path 41c of the present embodiment also has a reduced-diameter portion 42c and a straight body portion 43c that are rotationally symmetrical about the axis Ar, as in the third embodiment. The flow path area of the reduced-diameter portion 42c gradually decreases from the axial front side Daf to the axial rear side Dab. The reduced-diameter portion 42c has a flared shape centered on the axis Ar. Therefore, the surface defining the flow path in the reduced-diameter portion 42c forms a smooth convex flared surface 42cf toward the radially inner side DRi. The flow path area of each position in the axial direction Da of the straight body part 43c is the same. Therefore, the surface defining the flow path in the straight body portion 43c forms a cylindrical inner peripheral surface 43cg centered on the axis Ar.

A communication port 55o to the suction flow path 41c in the suction side communication path 55c is formed on the bell mouth surface 42cf of the reduced diameter portion 42c. In this suction-side communication passage 55c, the portion on the rear side Dab in the axial direction with the suction-side communication passage 55c as a reference is formed by the treatment cylinder 63c as in each of the above-mentioned embodiments. In addition, in this suction-side communication passage 55c, a portion on the axial front side Daf with respect to the suction-side communication passage 55c is formed by the case main body 61 and the bell cap 65c. Similar to the second and third embodiments, the flared cap 65c is fixed to the axially front side Daf of the case body 61 and to the radially inner side DRi of the case body 61 . The flared cap 65c is also fixed to the case main body 61 at a distance from the treatment cylinder 63c toward the axial front side Daf. The suction-side communicating path 55c is formed between the disposal cylinder 63c and the flared cap 65c.

Similar to the third embodiment, after the suction side communication passage 55c is folded back from the boundary between the circulation flow passage 52 and the suction side communication passage 55c, it is also directed toward the radially inner side DRi with respect to the axis Ar and at the same time toward the axial rear side Dab. It extends and communicates with the suction flow path 41c.

The treatment cylinder 63c of the present embodiment is formed with a reduced-diameter inner peripheral surface 63cf whose inner diameter gradually decreases toward the axial rear Dab, and a cylindrical inner peripheral surface 63cg whose inner diameter is constant in the axial direction Da. The cylindrical inner peripheral surface 63cg is formed from the edge of the diameter-reduced inner peripheral surface 63cf on the axially rear side Dab. A flared surface 65cf whose inner diameter gradually decreases toward the axial rear side Dab is formed on the flared cap 65c. Furthermore, a reduced-diameter outer peripheral surface 65ch whose outer diameter gradually decreases toward the axial rear side Dab is formed on the flared cap 65c. A portion of the axially rear side Dab within the reduced-diameter inner peripheral surface 63cf of the treatment cylinder 63c forms a flared surface 63cff. The flared surface 63cff of the treatment cylinder 63c is located on a virtual flared surface extending the flared surface 65cf of the flared cap 65c toward the axial rear side Dab.

The suction-side communication passage 55c is formed between the reduced-diameter inner peripheral surface 63cf of the disposal cylinder 63c except the flared surface 63cff and the reduced-diameter outer peripheral surface 65ch of the flared cap 65c. The flared surface 42cf in the reduced-diameter portion 42c of the suction channel 41c is formed by the flared surface 65cf of the flared cap 65c and the flared surface 63cff of the disposal cylinder 63c.

The compressor housing 40c of the present embodiment also satisfies the relationships shown in the formulas (1) to (4) similarly to the compressor housings 40 , 40a , and 40b in the above-described embodiments. Furthermore, in the present embodiment, as in the second embodiment, the dimension Rc from the axis Ar to the radial inner side DRi of the bell mouth cap 65c and the edge of the axial front side Daf is smaller than the inner diameter Ro of the outlet and smaller than the inner diameter Ro of the inlet. The inner diameter is large.

Similar to the third embodiment, the suction side communication passage 55c of this embodiment folds back from the boundary between the circulation flow passage 52 and the suction side communication passage 55c, extends toward the axial rear side Dab, and communicates with the suction flow passage 41c. Therefore, in this embodiment, similarly to the third embodiment, the elongation of the compressor housing 40c in the axial direction Da can be suppressed, and the air A in the impeller chamber 45 can be elongated until a part of the air A returns to the suction flow path 41c. the length of the flow path.

In addition, as in the second embodiment, the communication port 55o to the suction flow path 41c in the suction side communication path 55c of the present embodiment is formed on the bell mouth surface 42cf of the reduced diameter portion 42c. Therefore, in this embodiment, as in the second embodiment, not only can the air A be easily flowed into the impeller chamber 45 from the outside through the suction flow path 41c, but also the static pressure reduction effect on the bell mouth surface 42cf can be used to turn the air into the impeller chamber 45. The air A in the suction side communication path 55c is efficiently guided into the suction flow path 41c.

In addition, the above-mentioned third embodiment and the compressor casings 40b and 40c of this embodiment all satisfy the relationship represented by the formula (3). However, in the above-mentioned third embodiment and the compressor housings 40b and 40c of the present embodiment, the relationship shown in the formula (3) may not be satisfied.

In addition, although the centrifugal compressors in the above embodiments are centrifugal compressors installed on the supercharger, the centrifugal compressor of the present invention may not be installed on the supercharger.

Industrial availability

According to one aspect of the present invention, the operating range of the centrifugal compressor can be expanded.

Explanation of reference signs

10: Turbine, 11: Turbine rotation shaft, 12: Turbine impeller, 19: Turbine casing, 20: Connection part, 21: Connection rotation shaft, 29: Center casing, 30, 30a, 30b, 30c, 30x: Centrifugal compression machine, 31: compressor rotating shaft, 32: compressor impeller, 33: hub, 35: blades, 40, 40a, 40b, 40c, 40x: compressor housing, 41, 41a, 41b, 41c: suction flow path, 42, 42b, 42c: reduced diameter portion, 42f, 42bf, 42cf: bell mouth surface, 43b, 43c: straight body portion, 43bg: inner peripheral surface of cylinder, 45: impeller chamber, 46: discharge flow path, 51: impeller Side communication path, 52: Circulation flow path, 55, 55a, 55b, 55c: Suction side communication path, 55o: Communication port, 61: Housing main body, 62: Support rod (partition part), 63, 63a, 63b, 63c : Disposal barrel, 65, 65b, 65c: Flare cap, Ar: Axial, Da: Axial, Dab: Axial rear, Daf: Axial front, Dc: Circumferential, Dr: Radial, DRi: Diameter Inwardly, Dro: radially outwardly, 65b, 65c: flared cap, Ar: axially, Da: axially, Dab: axially rearwardly, Daf: axially forwardly, Dc: circumferentially, Dr: radially, DRi: radially inner, Dro: radially outer.

Claims (9)

1. A centrifugal compressor, characterized in that, possesses: A rotary shaft that rotates around the axis, an impeller attached to the outer periphery of the rotating shaft, the casing covering the impeller, The impeller has a hub and blades, the hub is installed on the rotating shaft, and a plurality of blades are arranged on the hub at intervals in the circumferential direction centered on the axis. It rotates integrally, and guides the gas flowing in from the axial front side, that is, the axial front side extending from the axis, to the radially outer side relative to the axis, Formed on the casing are: a suction flow path that guides gas on the axially front side of the impeller, an impeller chamber that communicates with the suction flow path and accommodates the impeller, and communicates with the impeller chamber. and a discharge passage through which the gas sent from the impeller to the radially outer side flows in; an impeller side communicating passage which communicates with the impeller chamber and extends from the impeller chamber in a direction including the radially outer portion; A circulation flow path communicating with the impeller-side communication path and extending from the impeller-side communication path toward a direction including the axially front side component, a suction side connection communicating with the circulation flow path and the suction flow path. path, The size of the suction side diameter is the radial dimension from the axis to the communication position in the circulation flow path with the suction side communication path, and the size of the impeller side diameter is the distance from the axis to the circulation flow path and The radial dimension of the communication position of the impeller side communication passage, the suction side diameter dimension is larger than the impeller side diameter dimension, and the flow of the circulation flow passage at the communication position of the suction side communication passage The passage area is larger than the flow passage area of the circulation flow passage at a position communicating with the impeller side communication passage. 2. The centrifugal compressor of claim 1, wherein: On the housing, a plurality of circulation flow paths arranged in a circumferential direction centering on the axis are formed, and a plurality of circulation flow paths adjacent to each other in the circumferential direction are formed to separate each other. of the partition. 3. The centrifugal compressor according to claim 1 or 2, characterized in that, The suction flow path has a reduced-diameter portion, the reduced-diameter portion forms a shape that is rotationally symmetrical about the axis, and the area of the flow path gradually decreases toward the other side of the axial direction, that is, the axial rear side. , A communication port of the suction-side communication path to the suction flow path is formed on a surface defining the flow path in the diameter-reduced portion. 4. The centrifugal compressor of claim 3, wherein: A surface defining the flow path in the reduced-diameter portion forms a curved surface that protrudes toward a side closer to the axis. 5. The centrifugal compressor according to claim 3 or 4, characterized in that, A radial dimension from the axis to the axially front edge of the communication port of the suction side communication passage is smaller than the suction side diameter and larger than the impeller side diameter. 6. The centrifugal compressor according to any one of claims 1 to 5, wherein: The suction-side communication path is turned back from the boundary of the circulation flow path and the suction-side communication path, and then toward the other side in the axial direction, that is, axially rearward, while facing radially inward with respect to the axis. The side extends and communicates with the suction flow path. 7. The centrifugal compressor according to any one of claims 1 to 6, wherein: Let L be an axial dimension from a communication position of the circulation flow path with the suction side communication path to a communication position of the circulation flow path with the impeller side communication path, Let do be an equivalent diameter related to the flow path area of the circulation flow path at a communication position with the suction side communication path, Let di be an equivalent diameter related to the flow path area of the circulation flow path at a communication position with the impeller side communication path, At this time, the spread angle 2θ specified by the following formula is less than 20° 2θ=2×tan((do-di)/2L). 8. The centrifugal compressor according to any one of claims 1 to 7, wherein: The axial dimension from the communication position of the circulation flow path with the suction side communication path to the communication position of the circulation flow path with the impeller side communication path is the maximum outer diameter of the impeller That is, more than 0.25 times the outer diameter of the impeller. 9. A supercharger, characterized in that it has: The centrifugal compressor according to any one of claims 1 to 8, turbine, The turbine has: a turbine rotating shaft rotating around the axis, a turbine impeller attached to the outer periphery of the turbine rotating shaft, a turbine casing covering the turbine wheel, The turbine rotation shaft and the rotation shaft of the centrifugal compressor are positioned on the same axis and are connected to each other to rotate integrally, thereby forming a supercharger rotation shaft.