JP2019007425A - Centrifugal compressor and turbocharger - Google Patents

Abstract

A centrifugal compressor and a turbocharger that suppress surging without impairing the performance of the centrifugal compressor with a simple configuration. When the flow rate of the compressed air in the centrifugal compressor is reduced, the compressed air flows backward from the space between the impeller and the facing portion of the inflow passage. The flow of the backflow air is suppressed by the step portion 56 provided in the inflow channel 46, and the flow is changed radially inward. Thereby, the flow of air flowing into the impeller 44 from the inflow passage 46 is collected radially inward. As a result, the pressure ratio between the inlet side and the outlet side of the centrifugal compressor 14 is reduced, and the backflow of compressed air is suppressed. That is, the occurrence of surging is suppressed. [Selection] Figure 1

Description

  The present invention relates to a centrifugal compressor and a turbocharger.

  In a centrifugal compressor for a turbocharger, when the flow rate of inflow air is reduced at the same rotation speed, the ratio of the downstream outlet pressure to the upstream inlet pressure of the centrifugal compressor increases. As a result, a part of the compressed air flows backward from the impeller outlet through the shroud side gap to the impeller inlet. This reverse flow becomes a spiral flow swirling in the rotation direction and flows out along the outer peripheral surface of the inlet of the centrifugal compressor. This reverse flow gives a swirl speed to the main flow flowing toward the centrifugal compressor, and the inlet flow becomes a swirl flow. As the flow rate of air flowing back increases, the angle of the spiral swirl flow decreases. As a result, the mainstream pre-turn is strengthened, the work of supercharging the impeller is reduced, and the pressure ratio is also lowered. If the flow angle of the main flow becomes small, the angle of attack at the impeller inlet becomes large, separation occurs in the flow flowing into the impeller, and surge is likely to occur.

  In order to prevent this surging, it has been proposed to suppress the surging by providing a throttle at the inlet of the impeller to increase the flow velocity of the incoming air and reduce the inflow angle with respect to the impeller.

  However, when a throttle is provided to suppress surging, there arises a problem that the performance of the centrifugal compressor deteriorates due to an increase in flow path resistance under conditions where surging does not occur. Therefore, only when the inflowing intake air amount is low, the inner peripheral resistor protrudes toward the hub side of the blade to restrict the intake flow path and suppress surging, while the inner peripheral resistor does not protrude at normal flow (high flow). Therefore, a compressor that can exhibit a predetermined performance has been proposed. (See Patent Document 1).

JP 2017-20514 A

  In the case of the technique described in Patent Document 1, a mechanism for moving the throttle (inner peripheral resistor) must be provided in the centrifugal compressor. There is room for improvement in terms of suppressing surging without impairing the performance of the centrifugal compressor with a simple configuration without providing such a movable diaphragm mechanism.

  The subject of this invention is providing the centrifugal compressor and turbocharger which suppress a surging by a simple structure, without impairing the performance of a centrifugal compressor.

  The centrifugal compressor according to claim 1 of the present invention includes a rotating blade that rotates around an axis, compresses air flowing in from the axial direction and flows the air in a radial direction, and an inflow channel that guides air to the rotating blade. A step portion that expands toward the downstream side in the axial direction on the upstream side in the axial direction of the rotor blade is formed on the wall surface of the inflow passage. , The height in the radial direction of the stepped portion is h, the radial distance between the upstream edge of the rotor blade and the wall surface of the inflow channel is d, the axis between the radially inner end of the stepped portion and the rotor blade When the directional distance is s, 0 <h / d <10 and 0 <s / d <10.

  According to the above configuration, the rotating rotor blades compress the air flowing in from the inflow passage formed in the introduction portion and extending in the axial direction, and flow in the radial direction.

  Here, when the flow rate of air flowing into the centrifugal compressor is small, the pressure difference between the upstream side and the downstream side of the rotor blades increases. Thereby, a part of the air compressed in the radial direction and compressed by the rotating rotor blades is folded in the reverse direction and flows (reverses) to the inflow channel side. When the flow rate of the reverse flow is large, surging occurs and the compressor does not operate normally.

  This compressor is provided with a stepped portion that increases in diameter toward the downstream side in the axial direction on the upstream side in the axial direction of the rotor blade on the wall surface of the inflow passage. Therefore, the air that has flowed back to the upstream side of the rotor blade along the wall surface of the inflow channel changes direction at the stepped portion and flows radially inward (axial center side of the rotor blade).

  As a result, the air flowing from the inflow passage toward the rotor blade is pushed (approached) to the rotation (shaft) center side of the rotor blade, and the pressure of the air flowing toward the rotor blade increases. That is, the pressure difference between the upstream side and the downstream side of the rotor blade is suppressed. As a result, the backflow of the air compressed by the rotating rotor blade and flowing in the radial direction is suppressed. Thereby, generation | occurrence | production of surging can be suppressed.

  On the other hand, the higher the height in the radial direction of the stepped portion, the higher the effect of suppressing surging.

  Therefore, the radial height of the step portion is h, the radial distance between the upstream edge of the rotor blade and the wall surface of the inflow channel is d, and the axial distance between the radially inner vertex of the step portion and the rotor blade is s. In this case, 0 <h / d <10 and 0 <s / d <10, so when the inflow flow rate to the centrifugal compressor is small, surging is reliably suppressed and the inflow flow rate to the centrifugal compressor is large. In addition, a predetermined compressor performance can be ensured.

  A centrifugal compressor according to a second aspect of the present invention is the centrifugal compressor according to the first aspect, wherein an inclination angle formed by the stepped portion and the axial direction of the inflow channel located on the upstream side of the stepped portion. The wall surface is larger than the inclination angle formed with the axial direction.

  According to the above configuration, in the inflow channel, the inclination angle formed with the axial direction of the stepped portion is set to be larger than the angle formed with the wall surface of the inflow channel positioned on the upstream side of the stepped portion with the axial direction. The wall surface on the upstream side of the step portion of the inflow channel is configured to be reduced in diameter toward the downstream side or parallel to the axial direction. When the inclination angle between the wall surface and the axial direction is large, if the inflow flow rate to the centrifugal compressor is large, the compressor may not exhibit predetermined performance due to an increase in flow path resistance. On the other hand, the stepped portion has a diameter that increases toward the downstream side, but as the inclination angle increases, the backflow of air from the downstream side to the upstream side of the rotor blade is effectively suppressed.

  In this configuration, by setting the inclination angle formed by the stepped portion in the axial direction to be larger than the inclination angle formed by the inflow channel wall upstream of the stepped portion in the axial direction, surging (backflow) is effectively suppressed. The predetermined compressor performance can be ensured.

  A turbocharger according to a third aspect of the present invention is a turbine unit having a turbine rotor that is rotated by a force through which exhaust gas discharged from an engine flows, and the rotational force is transmitted from the turbine rotor to the rotor blades and supplied to the engine. And a centrifugal compressor according to claim 1 or 2 for compressing air to be compressed.

  According to the said structure, generation | occurrence | production of the surging in a centrifugal compressor is suppressed, and compressed air can be efficiently supplied to an engine.

  According to the present invention, the occurrence of surging can be suppressed with a simple configuration without impairing the performance of the centrifugal compressor.

It is sectional drawing which showed the turbocharger which concerns on embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on embodiment of this invention. It is explanatory drawing explaining the dimension prescription | regulation in the centrifugal compressor which concerns on embodiment of this invention. It is explanatory drawing explaining the dimension prescription | regulation in the centrifugal compressor which concerns on embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on a comparative example. In the case of s / d = 3, the calculation (analysis) result which shows the relationship between h / d and the pressure fluctuation amount ratio of the centrifugal compressor which concerns on a comparative example, and the centrifugal compressor which concerns on embodiment of this invention is shown. It is a figure. In the case of h / d = 3, the calculation (analysis) result showing the relationship between s / d and the pressure fluctuation ratio between the centrifugal compressor according to the comparative example and the centrifugal compressor according to the embodiment of the present invention is shown. It is a figure. It is principal part sectional drawing of the centrifugal compressor which concerns on the variation of embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on the variation of embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on the variation of embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on the variation of embodiment of this invention. It is principal part sectional drawing of the centrifugal compressor which concerns on the variation of embodiment of this invention.

  A centrifugal compressor and a turbocharger according to an embodiment of the present invention will be described with reference to FIGS.

(overall structure)
As shown in FIG. 1, the turbocharger 10 according to the present embodiment includes a turbine unit 12, a centrifugal compressor 14, and a connecting unit 16 that connects the turbine unit 12 and the centrifugal compressor 14. The turbine unit 12 is disposed in the middle of an exhaust passage 18 of an automobile engine (not shown), and the centrifugal compressor 14 is disposed in the middle of an intake passage 20 of the engine.

  The turbine unit 12 and the centrifugal compressor 14 each include a housing 22 and a housing 24, and the connection unit 16 includes a housing 26 that connects the housing 22 and the housing 24. The housing 22, the housing 26, and the housing 24 are fixed to each other with a fixing tool (not shown).

  Further, the turbocharger 10 includes a housing 22, a housing 26, and a rotation shaft 28 that is rotatably disposed inside the housing 24. Hereinafter, the axial direction of the rotary shaft 28 (refer to the arrow E direction in FIG. 1) is referred to as “axial direction”. Further, the radial direction centered on the axis of the rotating shaft 28 (refer to the direction of arrow D in FIG. 1) is hereinafter referred to as “radial direction”.

[Turbine unit]
As shown in FIG. 1, the turbine unit 12 includes a housing 22 and a turbine rotor 30.

  Inside the housing 22, there are a discharge passage 36 extending in the axial direction and having one end in the axial direction (see the direction of arrow E1 in FIG. 1) opened, and the other end in the axial direction of the discharge passage 36 (see FIG. 1, A spiral flow path 38 formed in a spiral shape is formed radially outward from the arrow E2 direction). The spiral flow path 38 allows exhaust gas flowing through the exhaust passage 18 to flow into the housing 22, and the discharge flow path 36 discharges exhaust gas to the outside of the housing 22 (exhaust passage 18).

  The turbine rotor 30 is disposed inside the housing 22 (discharge channel 36). The turbine rotor 30 includes a rotor shaft portion 32 fixed to one end side in the axial direction of the rotating shaft 28 and a plurality of turbine blades 34 extending from the rotor shaft portion 32.

  That is, exhaust gas (an example of fluid) that has flowed into the housing 22 from the spiral flow path 38 flows between adjacent turbine blades 34 and pushes the plurality of turbine blades 34 to rotate the turbine rotor 30. is there. The exhaust gas that has rotated the turbine rotor 30 is discharged from the discharge passage 36 to the exhaust passage 18. That is, the turbine rotor 30 is a so-called radial turbine rotor.

[Connecting unit]
As shown in FIG. 1, the connection unit 16 includes a housing 26. The housing 26 is formed with a hole 40 through which the rotary shaft 28 is inserted, penetrating in the axial direction. In addition, at two locations in the axial direction of the hole 40 (inner peripheral wall), there are support portions 42 that are formed so as to protrude radially inward and support the rotary shaft 28 rotatably.

  Further, the housing 26 circulates an inlet (not shown) through which engine oil supplied to the support portion 42 is circulated and flows into the housing 26, and an outlet (not shown) through which the engine oil is discharged from the inside of the housing 26. And have.

  In this configuration, the engine oil that has flowed into the housing 26 is supplied to the support portion 42, and the rotating shaft 28 can be smoothly rotated in the circumferential direction.

(Centrifuge compressor)
As shown in FIG. 1, the centrifugal compressor 14 includes a housing 24 and an impeller 44 as an example of a rotor blade.

  Inside the housing 24, there are an inflow channel 46 extending in the axial direction and opened at the other end side in the axial direction, a diffusion channel 47 extending radially outward from one axial end side of the inflow channel 46, A spiral channel 48 (so-called scroll channel) formed in a spiral shape on the outer side in the radial direction of the diffusion channel 47 is formed in communication with the diffusion channel 47. The inflow passage 46 allows air flowing through the intake passage 20 to flow into the housing 24, and the spiral passage 48 discharges air out of the housing 24 and outflows into the intake passage 20.

  An impeller 44 is disposed inside the housing 24 (inflow channel 46). The impeller 44 includes a rotation shaft portion 50 fixed to the other axial end of the rotation shaft 28 and a plurality of impeller blades 52 extending from the rotation shaft portion 50.

  Details of the centrifugal compressor 14 will be described later.

(Operation of the overall configuration)
Next, the operation of the turbocharger 10 will be described.

  The turbine blade 34 is pushed by the exhaust gas flowing into the housing 22 from the spiral flow path 38. Thereby, the turbine rotor 30 rotates. As a result, the rotational force of the turbine rotor 30 is transmitted to the impeller 44 through the rotating shaft 28. The exhaust gas that has rotated the turbine rotor 30 inside the housing 22 flows out from the discharge passage 36.

  The impeller 44 rotates when the rotational force of the turbine rotor 30 is transmitted via the rotary shaft 28. The rotating impeller 44 compresses the air that flows into the housing 24 from the inflow channel 46. Further, the compressed air (compressed air) flows out from the spiral flow path 48 to the intake passage 20 and is supplied to the engine as compressed air for combustion.

(Main part configuration)
Next, the centrifugal compressor 14 will be described.
As illustrated in FIG. 1, the centrifugal compressor 14 includes a housing 24 that is an example of an introduction portion, and an impeller 44 that is disposed inside the housing 24.

[Impeller]
As described above, the impeller 44 includes the rotary shaft portion 50 fixed to the other axial end of the rotary shaft 28 and the plurality of impeller blades 52 extending from the rotary shaft portion 50.

  The rotating shaft portion 50 is gradually narrowed toward the other end in the axial direction. Further, as shown in FIG. 1, each impeller blade 52 extends outward in the radial direction while being curved from the rotary shaft portion 50 when viewed from the axial direction. As shown in FIG. 1, each impeller blade 52 is connected to a distal end edge 52 </ b> A that extends in the radial direction on the other end side in the axial direction and a radially outer end portion of the front end edge 52 </ b> A and is curved toward one end side in the axial direction. The curved edge 52B extends. Further, each impeller blade 52 has a base end edge 52C connected to the end of the curved edge 52B and extending in the axial direction.

  In this configuration, the rotating impeller 44 compresses the air flowing from the tip edge 52A of the impeller blade 52, and flows the compressed air (compressed air) from the base end edge 52C of the impeller blade 52 to the outside in the radial direction. ing.

〔housing〕
In the housing 24, an inflow passage 46 that guides air flowing through the intake passage 20 to the impeller 44, a diffusion passage 47 (so-called diffuser passage) through which compressed air compressed by the impeller 44 flows, and compressed air in the intake passage 20 And a spiral flow path 48 for discharging the water.

  The inflow channel 46 extends in the axial direction inside the housing 24, and has an inflow portion 54 that is reduced in diameter from the other axial end side toward the one axial end side, and the shaft of the inflow portion 54. A stepped portion 56 having a diameter expanded radially outward at one end in the direction, and a facing portion extending from the radially outer end of the stepped portion 56 to one end in the axial direction and facing the curved edge 52B of the impeller 44 58 is formed.

  The step portion 56 is formed on one end side in the axial direction of the impeller blade 52. The “one axial end side of the impeller blade 52” includes a case where a part of the stepped portion 56 is located on the radially outer side of the impeller blade 52.

  As shown in FIG. 2, the inclination angle θ1 (θ1 ≦ 90 °) that the inflow portion 54 makes with the axial direction is smaller than the inclination angle θ2 that the step portion 56 makes with the axial direction (θ1 <θ2). Is set. As shown in FIG. 3, the inclination angle θ <b> 1 is an angle formed between the inflow portion 54 and the axial line extending upstream from the point Q <b> 3 on the innermost radial direction of the stepped portion 56. As shown in FIG. 3, the inclination angle θ <b> 2 is an angle formed by the stepped portion 56 and a line in the axial direction from the point Q <b> 3 on the innermost radial direction of the stepped portion 56 toward the downstream side. In addition, when the inflow part 54 and the level | step-difference part 56 are not one linear shape in FIG. 3, for example, in the case of the combination of a curve, a some straight line, etc., let an average angle be inclination-angle (theta) 1 and (theta) 2.

As shown in FIG. 3, the positional relationship between the stepped portion 56 and the impeller 44 is such that the radial height of the stepped portion 56 is h, the axial distance between the stepped portion 56 and the impeller 44 is s, and the impeller 44 is opposed. If the radial distance from the portion 58 is d,
0 <h / d <10
And,
0 <s / d <10
It is set to become. In this embodiment, for example, h / d = 3 and s / d = 3.

  Here, as shown in FIG. 3, the radial distance d is a point Q1 that is the radially outermost point on the upstream edge (tip edge 52A) of the impeller blade 52 and a facing part that is located radially outward of the point Q1. 58 means a radial distance from the point Q2 on 58.

  Further, the radial height h means a radial distance between the point Q3 and the point Q2 on the innermost radial side (of the stepped portion 56) when the inflow channel 46 is viewed in the axial direction from one axial end side. As shown in FIG. 3, in the present embodiment, the radial position h is equal to the point Q3 because the point Q2 of the facing part 58 and the point Q4 of the radially outer end part of the step part 56 are the same in the radial direction. It also coincides with the radial distance from the point Q4.

  However, as shown in FIG. 4, when the facing portion 58 is formed so as to increase in diameter toward one end in the axial direction, the radially outer end of the stepped portion 56 is not always clear. Therefore, the radial height h of the stepped portion 56 is defined by the radial distance between the point Q2 and the point Q3.

  Further, the axial distance s means an axial distance between a point Q3 located on the innermost radial direction in the stepped portion 56 and the tip edge 52A of the impeller blade 52, as shown in FIGS.

(Function)
Next, the operation of the centrifugal compressor 14 according to the present embodiment will be described in comparison with the centrifugal compressor 114 according to the comparative example. In the centrifugal compressor 114 according to the comparative example, the same components as those of the centrifugal compressor 14 are denoted by the same reference numerals as the reference numerals of the centrifugal compressor 14 plus 100, and detailed description thereof will be given. Is omitted.

  As shown in FIG. 5, the stepped portion corresponding to the stepped portion 56 of the present embodiment is not formed in the centrifugal compressor 114 according to the comparative example. Other configurations of the centrifugal compressor 114 are the same as those of the centrifugal compressor 14.

  In this configuration, first, a case where the flow rate of air flowing into the centrifugal compressor 114 is small will be described. The rotating impeller 144 flows in the inflow passage 146 along the axial direction toward the impeller 144 and compresses the air (see arrow L1) flowing in from the leading edge 152A of the impeller blade 152, from the base end edge 152C of the impeller blade 152. It flows to the diffusion channel 147 on the radially outer side. Here, when the flow rate of air flowing into the centrifugal compressor 114 is small, the pressure ratio of the centrifugal compressor 114 (the ratio P2 / P1 between the outlet pressure P2 and the inlet pressure P1 of the centrifugal compressor 114) is the centrifugal compressor. It increases compared with the case where the flow rate of air flowing into 114 is large.

  For this reason, the air flowing from the base end edge 152C of the impeller blade 152 to the radially outer diffusion flow path 147 is folded back in the opposite direction to the air flowing toward the spiral flow path 148 (see arrow L2) and the impeller blade 152 It is separated (peeled) into air (see arrow L3) that flows to the inflow channel 46 side through the gap 160 with the housing 124.

  Further, as shown in FIG. 5, the air that has flowed back to the inflow channel 146 flows spirally around the inner peripheral surface of the inflow channel 146 in the rotational direction of the impeller 144, and from the gap 160 in the axial direction. It flows out to the end side (see arrow L4). When the flow rate of the air flow (back flow) flowing upstream along the inner peripheral surface of the inflow channel 146 increases, surging occurs in the centrifugal compressor 114.

  In addition, when the air flow rate flowing into the centrifugal compressor 114 is large, the pressure ratio of the centrifugal compressor 114 is reduced as compared with the case where the air flow rate flowing into the centrifugal compressor 114 is small. For this reason, the backflow of the air which flowed from the base end edge 152C of the impeller blades 152 to the diffusion channel 147 on the radially outer side is suppressed.

  Next, in the centrifugal compressor 14 of the present embodiment, a case where the flow rate of air flowing into the centrifugal compressor 14 is small will be described. As shown in FIG. 2, the rotating impeller 44 flows in the inflow passage 46 along the axial direction toward the impeller 44 and compresses the air (see arrow M <b> 1) flowing in from the tip edge 52 </ b> A of the impeller blade 52. The gas flows from the base end edge 52 </ b> C of 52 to the diffusion channel 47 on the radially outer side. Here, when the flow rate of air flowing into the centrifugal compressor 14 is small, the pressure ratio of the centrifugal compressor 14 (exit pressure P4 / inlet pressure P3) is compared to when the flow rate of air flowing into the centrifugal compressor 14 is large. ) Will increase.

  For this reason, the air that has flowed from the base end edge 52C of the impeller blade 52 to the radially outer diffusion flow path 47 returns to the spiral flow path 48 side (see arrow M2) and is folded in the opposite direction to the impeller blade 52 It is separated (peeled) into air (see arrow M3) that flows to the inflow channel 46 side through the gap 60 with the housing 24.

  Further, the air that has flowed back to the inflow channel 46 side (hereinafter referred to as “backflow air”) flows in a spiral manner while rotating through the inflow channel 46 in the rotation direction of the impeller 44, as shown in FIG. 2.

  The backflow air that has moved to the other axial end along the inner peripheral surface of the facing portion 58 of the inflow channel 46 changes its flow radially inward by hitting the stepped portion 56, and the radial direction of the inflow channel 46. Inward (see arrow M4).

  Thereby, the air (arrow M1) flowing in from the inflow channel 46 and flowing toward the impeller 44 is pushed (approached) to the rotation center side of the impeller 44 when viewed from the axial direction. For this reason, the pressure of the air flowing to the impeller 44 side becomes relatively higher than the case where the centrifugal compressor 114 is used, and the occurrence of surging can be suppressed.

  Moreover, when the backflow air reaches the upstream side in the axial direction along the inflow portion 54 of the inflow passage 46, the inflow air is strongly swirled and surging is likely to occur. However, in the centrifugal compressor 14, the backflow air is prevented or suppressed from reaching the upstream side of the stepped portion 56 by the stepped portion 56, and the occurrence of surging is suppressed.

  When the air flow rate flowing into the centrifugal compressor 14 is large, the pressure ratio of the centrifugal compressor 14 is smaller than when the air flow rate flowing into the centrifugal compressor 14 is small. For this reason, the air that has flowed from the base end edge 52C of the impeller blade 52 to the radially outer diffusion flow path 47 does not return in the reverse direction.

  Subsequently, numerical analysis was performed on the relationship between the size of the stepped portion 56 of the centrifugal compressor 14 and the amount of pressure fluctuation of the centrifugal compressors 14 and 114. This will be described with reference to FIGS.

  In the numerical analysis, the radial height h of the stepped portion 56 of the centrifugal compressor 14 is 1 mm, the radial distance d between the impeller 44 and the facing portion 58 is 0.33 mm, and the axial direction between the stepped portion 56 and the impeller 44. The distance s is 1 mm. The diameter of the inflow channel 46 at the point Q2 is 36.6 mm, the inlet diameter of the impeller 44 is 36 mm, and the outlet diameter is 48 mm.

  First, the graph shown in FIG. 6 will be described. The vertical axis of the graph shown in FIG. 6 indicates the ratio of the pressure fluctuation amount of the centrifugal compressor 14 to the pressure fluctuation amount when surging occurs in the centrifugal compressor 114, and the horizontal axis represents the radial height h in the centrifugal compressor 14. The ratio with the radial distance d is shown.

  The plot in the graph shown in FIG. 6 shows that when the surging occurs when the rotational speed of the impeller 144 is constant in the centrifugal compressor 114 and the air flow rate flowing into the centrifugal compressor 114 is changed (hereinafter, this case). The amount of pressure fluctuation on the outlet side of the centrifugal compressor 114 in the case of “the flow rate of inflow air” is referred to as “surging generation flow rate” is 1. As for surging, it is determined that surging occurs when the amplitude of the housing 124 reaches a predetermined threshold.

  FIG. 6 shows a step when the ratio (s / d) between the axial distance s between the stepped portion 56 and the impeller 44 and the radial distance d between the impeller 44 and the facing portion 58 in the centrifugal compressor 14 is 3. When the ratio (h / d) between the radial height h of the portion 56 and the radial distance d between the impeller 44 and the facing portion 58 is changed, the inflow air flow rate of the centrifugal compressor 14 is set as the surge generation flow rate. The amount of pressure fluctuation on the outlet side of the centrifugal compressor 14 was calculated. The graph is plotted as a ratio with respect to the pressure fluctuation amount of the centrifugal compressor 114.

  Next, the graph shown in FIG. 7 will be described. The vertical axis of the graph shown in FIG. 7 indicates the ratio of the pressure fluctuation amount of the centrifugal compressor 14 to the pressure fluctuation amount when surging occurs in the centrifugal compressor 114, and the horizontal axis represents the radial height h in the centrifugal compressor 14. The ratio with the axial distance s is shown.

  FIG. 7 shows that when the ratio (h / d) between the radial height h of the step portion 56 and the radial distance d between the impeller 44 and the facing portion 58 is 3, the axial distance s and the impeller 44 By changing the ratio (s / d) with the radial distance d to the facing portion 58, the pressure fluctuation amount on the outlet side of the centrifugal compressor 14 when the inflow air flow rate of the centrifugal compressor 14 is set as the surge generation flow rate. Calculated. The graph is plotted as a ratio with respect to the pressure fluctuation amount of the centrifugal compressor 114.

  As shown in FIG. 6, in the case of s / d = 3, it was confirmed that the amount of pressure fluctuation was suppressed as compared with the comparative example as h / d increased. Specifically, when h / d is 3, the pressure fluctuation amount is suppressed to about 0.3 of the comparative example, and when h / d exceeds 10, the pressure fluctuation amount is substantially constant (about 0.25 of the comparative example). It turns out that it becomes. On the other hand, generally, when the radial height h of the stepped portion 56 increases, the performance of the centrifugal compressor 14 decreases due to an increase in flow path resistance when the flow rate of air flowing into the centrifugal compressor 14 is large. Therefore, if 0 <h / d <10, the backflow air when the inflow air flow rate of the centrifugal compressor 14 is small is suppressed without greatly reducing the performance of the centrifugal compressor 14 when the inflow air flow rate is large. Therefore, it is considered that the occurrence of surging can be suppressed.

  Further, as shown in FIG. 7, in the case of h / d = 3, the pressure fluctuation amount compared with the comparative example is decreased as s / d increases to 3, and when s / d exceeds 3, it is compared with 10. It was confirmed to be suppressed to about 0.5 of the example. On the other hand, it is generally considered that as the stepped portion 56 is separated from the impeller 44, the effect of suppressing the backflow decreases. Therefore, if 0 <s / d <10, the flow rate of air flowing into the centrifugal compressor 14 is small without greatly degrading the performance of the centrifugal compressor 14 when the flow rate of air flowing into the centrifugal compressor 14 is large. In this case, it is considered that the occurrence of surging can be suppressed by suppressing the backflow air.

  In addition, although this numerical calculation result calculated | required the pressure fluctuation amount ratio in the case of s / d = 3 and h / d = 3, respectively, s / d and h / d are 10 or less, and are different numerical values. Even in this case, it is considered that the same numerical calculation result is obtained.

  That is, in the centrifugal compressor 14, the stepped portion 56, the facing portion 58 and the impeller 44 are arranged so that 0 <h / d <10 and 0 <s / d <10, so that a fixed mechanism without a variable mechanism can be obtained. The generation of surging can be suppressed without greatly reducing the performance of the centrifugal compressor 14 at the stepped portion 56.

  In addition, the inflow portion 54 is tapered so as to reduce in diameter toward the other end side (downstream side) in the axial direction. The inclination angle θ1 that the inflow portion 54 forms in the axial direction is a stepped portion 56. Is set to be smaller than the inclination angle θ2 formed with the axial direction. This has the effect of suppressing surging by increasing the inflow speed of inflow air by tapering the inflow portion 54 (providing a throttle). However, if the inclination angle θ1 is too large, the flow resistance increases. It will reduce the compressor performance. On the other hand, the backflow suppression effect increases as the inclination angle θ2 of the step portion 56 increases. Therefore, by setting the inclination angle θ2 of the stepped portion larger than the inclination angle θ1 of the inflow portion 54, surging is more effectively suppressed while suppressing a decrease in compressor performance.

  Further, in the turbocharger 10, by suppressing the occurrence of surging in the centrifugal compressor 14, compressed air can be efficiently supplied to the engine.

[Others]
The shape of the inflow channel 46 of the housing 24 is not limited to this embodiment. For example, as shown in FIG. 8, the inflow portion 54 may have a shape that curves and protrudes inward in the radial direction only immediately before the stepped portion 56. Further, as shown in FIG. 9, the inflow portion 54 has a shape that is reduced in diameter toward one end in the axial direction (impeller 44 side), but has a cylindrical shape (a constant cross-sectional shape perpendicular to the axial direction) Also good. Furthermore, as shown in FIG. 10, the inclination angle θ1 with respect to the axial direction of the inflow portion 54 may be further increased.

  On the other hand, in the present embodiment (see FIG. 3), the stepped portion 56 is a surface extending radially outward, but as shown in FIG. 11, the stepped portion 56 extends from the radially outer side to the one axial end side. An inclined surface inclined toward the surface may be used. Alternatively, as shown in FIG. 12, the stepped portion 56 may be an R-shaped surface in which the radially inner end portion is continuous with the inflow portion 54. In this case, in the stepped portion 56, a portion (point Q3) that protrudes most radially inward in the R shape is a radially inner end portion.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments can be taken within the scope of the present invention. This will be apparent to those skilled in the art.

  Moreover, in the said embodiment, although the centrifugal compressor 14 was used for the turbocharger 10, you may use for another air conditioning apparatus etc.

  Furthermore, in the centrifugal compressor 14, the inclination angle θ1 of the inflow portion 54 is not limited to be smaller than the inclination angle θ2 of the step portion 56.

10 Turbocharger 12 Turbine unit 14 Centrifugal compressor 24 Housing (introduction part)
30 Turbine rotor 44 impeller (rotary blade)
46 Inflow channel 56 Stepped portion d Radial distance h between impeller and opposing portion Radial height s of stepped portion Axial distance between stepped portion and impeller

Claims (3)

A rotating blade that rotates around an axis and compresses air flowing in from the axial direction to flow in the radial direction;
An inflow channel for guiding air to the rotor blade is formed extending in the axial direction, and
On the wall surface of the inflow channel, a stepped portion is formed on the upstream side in the axial direction of the rotor blade and the diameter of the stepped portion is increased toward the downstream side in the axial direction. When the radial distance between the upstream edge of the inlet and the wall surface of the inflow channel is d, and the axial distance between the radially inner end of the stepped portion and the rotor blade is s,
0 <h / d <10
And,
0 <s / d <10
Is a centrifugal compressor.   2. The centrifugal compressor according to claim 1, wherein an inclination angle formed by the step portion with respect to the axial direction is larger than an inclination angle formed by a wall surface of the inflow channel located upstream of the step portion with respect to the axial direction. A turbine unit having a turbine rotor that is rotated by a force through which exhaust gas discharged from the engine flows;
The centrifugal compressor according to claim 1 or 2, wherein a rotational force is transmitted from the turbine rotor to the rotor blades to compress the air supplied to the engine;
Turbocharger with