Turbine and supercharger

Abstract

In the present invention, a turbine comprises: a turbine impeller; an exhaust gas flow path formation part that forms an exhaust gas flow path for guiding exhaust gas from a scroll flow path formed on the outer peripheral side of the turbine impeller to the turbine impeller, the exhaust gas flow path formation part including a hub-side flow path surface and a shroud-side flow path surface that define the exhaust gas flow path; and at least one nozzle vane that is disposed in the exhaust gas flow path and is fixed to at least one of the hub-side flow path surface or the shroud-side flow path surface. The blade height W1, which is the axial-direction length of the at least one nozzle vane of the turbine impeller, is less than the flow path width WO, which is the axial-direction length of the exhaust gas flow path at a blade leading edge position in the turbine impeller.

Description

Technical Field

[0001] The present disclosure relates to a turbine and a turbocharger including the turbine.Background Art

[0002] There are turbines of turbochargers that include turbine blades and a plurality of nozzle vanes provided upstream of the turbine blades in an engine exhaust passage. The plurality of nozzle vanes are disposed radially outward of the turbine blades. The above-described turbine is configured to improve energy recovery efficiency by causing the nozzle vanes to expand and accelerate exhaust gas to be guided to the turbine blades (refer to, for example, PTL 1).Citation ListPatent Literature

[0003] [PTL 1] Japanese Unexamined Patent Application Publication No. 2021-124020Summary of InventionTechnical Problem

[0004] Exhaust gas flowing through an engine exhaust passage may contain vaporized fuel, lubricant, and the like, and carbon (particulate matter) tends to deposit on portions exposed to the exhaust gas, such as nozzle vanes. Carbon deposition on the vane surfaces of the nozzle vanes reduces the nozzle throat area and may lead to surge. As a countermeasure against carbon deposition, early maintenance and cleaning of the nozzle vanes are required; therefore, there is a problem that continuous operation of a turbocharger and of an engine in which the turbocharger is mounted becomes difficult. Accordingly, improvement in robustness of a turbine (specifically, the nozzle vanes) against carbon deposition has been demanded.

[0005] In view of the circumstances described above, an object of at least one embodiment of the present invention is to provide a turbine capable of improving robustness, and a turbocharger including the turbine.Solution to Problem

[0006] According to at least one embodiment of the present invention, there is provided a turbine including: a turbine impeller; an exhaust gas passage forming portion that forms an exhaust gas passage for guiding exhaust gas from a scroll passage formed on an outer peripheral side of the turbine impeller to the turbine impeller, the exhaust gas passage forming portion including a hub-side flow passage surface and a shroud-side flow passage surface that define the exhaust gas passage; and at least one nozzle vane disposed in the exhaust gas passage and fixed to at least one of the hub-side flow passage surface or the shroud-side flow passage surface, in which a vane height W1, which is a length of the at least one nozzle vane in an axial direction of the turbine impeller, is smaller than a flow passage width WO, which is a length of the exhaust gas passage in the axial direction at a blade leading-edge position of the turbine impeller.

[0007] According to at least one embodiment of the present invention, there is provided a turbocharger including: the turbine; and a centrifugal compressor configured to be driven by the turbine. Advantageous Effects of Invention

[0008] According to at least one embodiment of the present invention, a turbine capable of improving robustness and a turbocharger including the turbine are provided.Brief Description of Drawings

[0009] FIG. 1 is a schematic cross-sectional view showing a cross-section taken along an axis of a turbine according to one embodiment. FIG. 2 is a schematic cross-sectional view showing a cross-section taken along an axis located on one side relative to the axis of the turbine according to one embodiment. FIG. 3 is a schematic view showing a state in which a hub-side flow passage surface and a plurality of nozzle vanes of the turbine according to one embodiment are viewed from a shroud side. FIG. 4 is a schematic cross-sectional view showing a cross-section taken along an axis located on one side relative to an axis of a turbine according to a comparative example. FIG. 5 is a schematic view showing a state in which a hub-side flow passage surface and a plurality of nozzle vanes of the turbine according to the comparative example are viewed from a shroud side. FIG. 6 is a diagram illustrating an amount of carbon deposition corresponding to a nozzle throat shape of the turbine. FIG. 7 is a graph illustrating a change in an effective nozzle throat area due to carbon deposition in the turbine according to one embodiment. FIG. 8 is a schematic view of a turbocharger according to one embodiment. Description of Embodiments

[0010] Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, dimensions, materials, shapes, relative dispositions, and the like of components that are described as embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples.(Basic Configuration of Turbine)

[0011] FIG. 1 is a schematic cross-sectional view showing a cross-section taken along an axis of a turbine according to one embodiment. As shown in FIG. 1, a turbine 1 according to some embodiments includes a turbine impeller 2 (hereinafter, an impeller), and a casing 3 configured to rotatably accommodate the impeller 2. The turbine 1 according to the present disclosure is mountable, for example, in a turbocharger 10 and the like for automotive use, marine use, or industrial use (for example, for land-based power generation).

[0012] The impeller 2 is configured to rotate about an axis LA of the impeller 2 by being supported by a bearing (not shown) accommodated in the casing 3. Hereinafter, a direction in which the axis LA of the impeller 2 extends is defined as an axial direction of the impeller 2 (turbine 1), and a direction orthogonal to the axis LA is defined as a radial direction of the impeller 2 (turbine 1). The impeller 2 is configured to guide exhaust gas, which is introduced from a radially outer side of the impeller 2, to an outlet side of the turbine 1 (the right side in FIG. 1) along the axial direction of the impeller 2.

[0013] Hereinafter, the outlet side of the turbine 1 in the axial direction described above is referred to as a shroud side, and a side opposite to the shroud side is defined as a hub side. In the following description, when simply referred to as "upstream", it denotes an upstream side along a principal flow direction of a fluid in a part or region related to a description of direction. Similarly, in the following description, when simply referred to as "downstream", it denotes a downstream side along the principal flow direction of the fluid in the part or region related to the description of direction.

[0014] The impeller 2 includes a hub 21 and a plurality of impeller blades 23 erected on an outer surface 22 of the hub 21. Each of the plurality of impeller blades 23 is disposed at intervals from each other in a circumferential direction of the impeller 2. A tip 24 of each of the plurality of impeller blades 23 is disposed with a predetermined gap with respect to a shroud surface 31, which is an inner surface of the casing 3.(Casing)

[0015] As shown in FIG. 1, the casing 3 includes a shroud portion 32 including the above-described shroud surface 31, a scroll passage forming portion 34 that forms a scroll passage 33 on an outer peripheral side of the impeller 2, and an exhaust gas passage forming portion 36 that forms an exhaust gas passage 35 for guiding exhaust gas from the scroll passage 33 to the impeller 2. The scroll passage 33 and the exhaust gas passage 35 are each formed inside the casing 3.

[0016] The scroll passage 33 is formed by a volute-shaped passage provided on the outer peripheral side of the impeller 2. This volute-shaped passage extends along the circumferential direction of the impeller 2 so as to surround the outer peripheral side (radially outer side) of the impeller 2. The exhaust gas passage 35 is provided between the scroll passage 33 and the impeller 2 in the radial direction of the impeller 2 so as to surround the outer peripheral side (radially outer side) of the impeller 2.

[0017] In the illustrated embodiment, the exhaust gas passage 35 is formed in an annular shape so as to extend along the circumferential direction of the impeller 2, and an upstream end (outer peripheral end) of the exhaust gas passage 35 is in communication with the scroll passage 33. As shown in FIG. 1, in a cross-section taken along the axial direction of the impeller 2, the exhaust gas passage 35 extends along the radial direction of the impeller 2. Exhaust gas introduced into the interior of the casing 3 passes through the scroll passage 33, then passes through the exhaust gas passage 35, and is guided to the impeller 2 to rotate the impeller 2.

[0018] The exhaust gas passage forming portion 36 includes a hub-side flow passage surface 4 and a shroud-side flow passage surface 5 that define the exhaust gas passage 35. The shroud-side flow passage surface 5 is provided on the shroud side relative to the hub-side flow passage surface 4 and faces the hub-side flow passage surface 4 with the exhaust gas passage 35 interposed therebetween. The hub-side flow passage surface 4 defines a hub side (the left side in FIG. 1) of the exhaust gas passage 35, and the shroud-side flow passage surface 5 defines a shroud side (the right side in FIG. 1) of the exhaust gas passage 35. In the illustrated embodiment, each of the hub-side flow passage surface 4 and the shroud-side flow passage surface 5 is formed in an annular shape on the outer peripheral side of the impeller 2 so as to extend along the circumferential direction of the impeller 2.(Nozzle Vane)

[0019] FIG. 2 is a schematic cross-sectional view showing a cross-section taken along an axis located on one side relative to the axis of the turbine according to one embodiment. FIG. 3 is a schematic view showing a state in which the hub-side flow passage surface and the plurality of nozzle vanes of the turbine according to one embodiment are viewed from the shroud side.

[0020] As shown in FIGS. 2 and 3, the above-described turbine 1 further includes at least one nozzle vane 6 disposed in the exhaust gas passage 35 and fixed to at least one of the hub-side flow passage surface 4 or the shroud-side flow passage surface 5. In the illustrated embodiment, the above-described at least one nozzle vane 6 includes a plurality of nozzle vanes 6 disposed at intervals from each other in the circumferential direction of the impeller 2.

[0021] In the illustrated embodiment, the exhaust gas passage forming portion 36 includes an annular member 40 including the hub-side flow passage surface 4. Each of the plurality of nozzle vanes 6 is formed integrally with the annular member 40, and a hub-side end face in the axial direction is connected to the hub-side flow passage surface 4. As a result, each of the plurality of nozzle vanes 6 is fixed to the hub-side flow passage surface 4.

[0022] As shown in FIG. 3, each of the plurality of nozzle vanes 6 includes a leading edge 61 provided at one end in an extending direction of a vane thickness centerline CL that passes through a vane thickness center of the nozzle vane 6, a trailing edge 62 provided at the other end in the extending direction of the vane thickness centerline CL of the nozzle vane 6, and an inner vane surface 63 and an outer vane surface 64 that respectively extend from the leading edge 61 to the trailing edge 62. Each of the plurality of nozzle vanes 6 is provided such that the trailing edge 62 is located radially inward of the leading edge 61 in the radial direction of the impeller 2. Each of the plurality of nozzle vanes 6 is provided such that the inner vane surface 63 is located on a side opposite to the outer vane surface 64 with the vane thickness centerline CL interposed therebetween and is located radially inward of the outer vane surface 64. The leading edge 61, the trailing edge 62, the inner vane surface 63, and the outer vane surface 64 of the nozzle vane 6 constitute vane surfaces that face the exhaust gas passage 35.(Throat)

[0023] As shown in FIG. 3, a position at which a flow passage area between a pair of nozzle vanes 6 and 6 that are adjacent to each other along the circumferential direction of the impeller 2 is minimum is defined as a throat T. The flow passage area between the pair of nozzle vanes 6 and 6 at the throat T is defined as a nozzle throat area, a length of the exhaust gas passage 35 in the axial direction at the throat T is defined as a nozzle throat height, and a length between the pair of nozzle vanes 6 and 6 at the throat T is defined as a nozzle throat width.(Relationship Between Vane Height W1 and Flow passage Width W0)

[0024] As shown in FIG. 2, the turbine 1 according to some embodiments includes the exhaust gas passage forming portion 36 including the above-described hub-side flow passage surface 4 and shroud-side flow passage surface 5, and the above-described at least one nozzle vane 6. A vane height W1, which is a length of the at least one nozzle vane 6 in the axial direction of the impeller 2, is smaller than a flow passage width WO, which is a length of the exhaust gas passage 35 in the axial direction at a blade leading-edge position of the impeller 2. The blade leading-edge position of the impeller 2 is a position on the casing 3 at which a leading edge 25 of the impeller 2 is disposed when the impeller 2 is disposed inside the casing 3.

[0025] In the embodiments shown in FIGS. 2 and 3, the hub-side flow passage surface 4 includes a step 42 that protrudes to the shroud side beyond a hub-side end 26 of the leading edge 25 of the impeller 2. Consequently, each of the plurality of nozzle vanes 6 has the vane height W1 that is smaller than the flow passage width WO. Instead of providing the step 42 on the hub-side flow passage surface 4, by providing a step that protrudes to the hub side on the shroud-side flow passage surface 5, the vane height W1 may be made smaller than the flow passage width WO.(Turbine According to Comparative Example)

[0026] FIG. 4 is a schematic cross-sectional view showing a cross-section taken along an axis located on one side relative to an axis of a turbine according to a comparative example. FIG. 5 is a schematic view showing a state in which a hub-side flow passage surface and a plurality of nozzle vanes of the turbine according to the comparative example are viewed from the shroud side. As shown in FIGS. 4 and 5, a turbine 1A according to the comparative example does not include a step that protrudes to the shroud side from a hub-side flow passage surface 4A of an annular member 40A, nor a step that protrudes to the hub side from the shroud-side flow passage surface 5. The hub-side flow passage surface 4A is provided, in the axial direction of the impeller 2, at the same position as the hub-side end 26 of the leading edge 25 of the impeller 2. A vane height W2, which is a length of each of a plurality of nozzle vanes 6A in the axial direction of the impeller 2, is the same length as the flow passage width WO, which is the length of the exhaust gas passage 35 in the axial direction at the blade leading-edge position of the impeller 2. The vane height W1 of each of the plurality of nozzle vanes 6 in the present embodiment is smaller than the vane height W2 of each of the plurality of nozzle vanes 6A.(Amount of Carbon Deposition Corresponding to Nozzle Throat Shape)

[0027] FIG. 6 is a diagram illustrating an amount of carbon deposition corresponding to a nozzle throat shape of the turbine. In FIG. 6, a nozzle throat height (vane height of the nozzle vane 6) TH of the turbine 1 according to the present embodiment is smaller than a nozzle throat height (vane height of the nozzle vane 6A) TH1 of the turbine 1A according to the comparative example. In FIG. 6, a nozzle throat width TW of the turbine 1 is made larger than a nozzle throat width TW1 of the turbine 1A, so that a nozzle throat area TA of the turbine 1 and a nozzle throat area TA of the turbine 1A are the same. As shown in FIG. 6, the larger the nozzle throat height (the vane height of the nozzle vane) is, the larger the area of the vane surfaces (such as inner vane surfaces 63 and 63A and outer vane surfaces 64 and 64A) of the nozzle vanes 6 and 6A is, and an amount of carbon deposition on the vane surfaces of the nozzle vane 6 increases. The hub-side flow passage surface 4 and the shroud-side flow passage surface 5 tend to have a smaller amount of carbon deposition than the vane surface of the nozzle vane 6.(Change in Effective Nozzle Throat Area)

[0028] FIG. 7 is a graph illustrating a change in an effective nozzle throat area due to carbon deposition in the turbine according to one embodiment. In FIG. 7, a graph is shown in which an operation period WT of the turbine is represented on a horizontal axis, and an effective nozzle throat area ETA, which is obtained by subtracting a blockage area from the nozzle throat area TA, is represented on a vertical axis. In FIG. 7, SL denotes a surge limit, and when the effective nozzle throat area ETA becomes equal to or less than the surge limit SL, there is a high likelihood of surge. In FIG. 7, L1 denotes an approximate straight line indicating a change in the effective nozzle throat area ETA corresponding to the operation period WT of the turbine 1A shown in FIG. 6, and the effective nozzle throat area ETA reaches the surge limit SL in a period WT1. In FIG. 7, L2 denotes an approximate straight line indicating a change in the effective nozzle throat area ETA corresponding to the operation period WT of the turbine 1 shown in FIG. 6, and the effective nozzle throat area ETA reaches the surge limit SL in a period WT2. As shown in FIG. 7, the period WT2 is greater than the period WT1. That is, the turbine 1 can lengthen an operation period until the surge limit SL is reached, as compared with the turbine 1A.

[0029] In the present embodiment, by making the vane height W1 of the at least one nozzle vane 6 smaller than the flow passage width WO of the exhaust gas passage 35 at the blade leading-edge position of the impeller 2, the area of the vane surface of the nozzle vane 6 is smaller than in a case where the vane height W1 is the same length as the flow passage width WO, so that the amount of carbon deposition can be reduced. Consequently, an area that blocks the nozzle throat area TA (blockage area) due to carbon deposited on the vane surface of the nozzle vane 6 can be reduced. By reducing the blockage area, a maintenance frequency of the turbine 1 can be reduced, and an operating time of the turbine 1 and of the turbocharger 10 including the turbine 1 can be increased. With such a turbine 1, adverse effects due to carbon deposition on the nozzle throat area TA can be reduced, thereby improving robustness of the turbine 1.

[0030] In some embodiments, for each of the plurality of nozzle vanes 6 described above, a distance D1 (refer to FIG. 3) from the axis LA of the impeller 2 to the trailing edge 62 of the nozzle vane 6 is determined so as to obtain a desired nozzle throat width TW.

[0031] According to the above-described configuration, when the vane height W1 is merely made smaller than the flow passage width WO, the nozzle throat area is smaller than in a case where the vane height W1 is the same length as the flow passage width WO. In a case where the vane height W1 is made smaller than the flow passage width WO, in order to secure the nozzle throat area TA similar to a case where the vane height W1 is the same length as the flow passage width WO, it is necessary to make the nozzle throat width TW longer than in a case where the vane height W1 is the same length as the flow passage width WO (refer to FIG. 6).

[0032] In the turbine 1 shown in FIG. 3, the distance D1 from the axis LA of the impeller 2 to the trailing edge 62 of the nozzle vane 6 is greater than a distance D2 from the axis LA of the impeller 2 to the trailing edge 62A of the nozzle vane 6A in the turbine 1A shown in FIG. 5. In this way, in a case where the vane height W1 is made smaller than the flow passage width WO, by increasing the distance D1 from the axis LA of the impeller 2 to the trailing edge 62 of the nozzle vane 6 as compared with a case where the vane height W1 is the same length as the flow passage width WO, the nozzle throat width TW can be widened. For each of the plurality of nozzle vanes 6, by adjusting the distance D1 from the axis LA of the impeller 2 to the trailing edge 62 of the nozzle vane 6, a desired nozzle throat width TW and a desired nozzle throat area TA can be secured, and consequently performance of the turbine 1 and of the turbocharger 10 including the turbine 1 can also be ensured.

[0033] In some embodiments, for each of the plurality of nozzle vanes 6 described above, in a case where an angle formed between a tangent line TL1, at the trailing edge 62, to a virtual circle VC that passes through the trailing edge 62 of the nozzle vane 6 about the axis LA of the impeller 2, and a tangent line TL2, at the trailing edge 62, to the vane surface (inner vane surface 63) of the nozzle vane 6 on an impeller 2 side is defined as a stagger angle θ, the stagger angle θ is determined so as to obtain a desired nozzle throat width TW.

[0034] According to the above-described configuration, when the vane height W1 is merely made smaller than the flow passage width WO, the nozzle throat area is smaller than in a case where the vane height W1 is the same length as the flow passage width WO. In a case where the vane height W1 is made smaller than the flow passage width WO, in order to secure the nozzle throat area TA similar to a case where the vane height W1 is the same length as the flow passage width WO, it is necessary to make the nozzle throat width TW longer than in a case where the vane height W1 is the same length as the flow passage width WO (refer to FIG. 6).

[0035] As shown in FIG. 5, an angle corresponding to the above-described stagger angle θ of the turbine 1A according to the comparative example is defined as a stagger angle θ1. The stagger angle θ1 is an angle formed between the tangent line to the virtual circle VC at the trailing edge 62A and the tangent line to the inner vane surface 63A of the nozzle vane 6A at the trailing edge 62A. The stagger angle θ of the turbine 1 shown in FIG. 3 is greater than the stagger angle θ1 of the turbine 1A shown in FIG. 5. In this way, in a case where the vane height W1 is made smaller than the flow passage width WO, by increasing the stagger angle θ as compared with a case where the vane height W1 is the same length as the flow passage width WO, the nozzle throat width TW can be widened. For each of the plurality of nozzle vanes 6, by adjusting the stagger angle θ, a desired nozzle throat width TW and a desired nozzle throat area TA can be secured, and consequently performance of the turbine 1 and of the turbocharger 10 including the turbine 1 can also be ensured.(Step)

[0036] In some embodiments, as shown in FIGS. 2 and 3, the above-described hub-side flow passage surface 4 includes the flat surface 41 formed in a region in which at least one nozzle vane 6 is interposed between the hub-side flow passage surface 4 and the shroud-side flow passage surface 5. The flat surface 41 is located on the shroud side in the axial direction of the impeller 2 relative to the hub-side end 26 of the leading edge 25 of the impeller 2 and extends along the radial direction of the impeller 2. In the illustrated embodiment, the flat surface 41 is formed by an annular surface that extends along the circumferential direction of the impeller 2.

[0037] According to the above-described configuration, by providing, on the hub-side flow passage surface 4, the step 42 including the flat surface 41 as a top surface that protrudes to the shroud side beyond the hub-side end 26 of the leading edge 25 of the impeller 2, the vane height W1 can be made smaller than the flow passage width WO. By providing the step 42 on the hub-side flow passage surface 4, as compared with a case of providing the step 42 on the shroud-side flow passage surface 5, a flow passage loss in the exhaust gas passage 35 can be reduced, and performance degradation of the turbine 1 can be suppressed.(Inner Inclined Surface of Step)

[0038] In some embodiments, as shown in FIGS. 2 and 3, the above-described hub-side flow passage surface 4 further includes an inner inclined surface 43 that is located radially inward of the flat surface 41 in the radial direction of the impeller 2 and that is inclined toward the hub side while extending radially inward.

[0039] In the illustrated embodiment, the inner inclined surface 43 is formed by an annular surface that extends along the circumferential direction of the impeller 2. An outer peripheral edge of the inner inclined surface 43 is continuous with an inner peripheral edge of the flat surface 41. Additionally, an inner peripheral edge of the inner inclined surface 43 constitutes an inner peripheral edge of the hub-side flow passage surface 4 of the annular member 40. Preferably, a length (flow passage width) of the exhaust gas passage 35 in the axial direction at a position of the inner peripheral edge of the inner inclined surface 43 is the same length as the flow passage width WO.

[0040] According to the above-described configuration, since the step 42 provided on the hub-side flow passage surface 4 includes the inner inclined surface 43, a flow passage cross-sectional area of the exhaust gas passage 35 can be gradually increased at a location downstream of at least one nozzle vane 6 (on a radially inner side) in the exhaust gas passage 35. Consequently, since a part of the exhaust gas flowing through the exhaust gas passage 35 can be guided along the inner inclined surface 43 to the hub side of the leading edge 25 of the impeller 2, performance degradation of the turbine 1 due to the step 42 can be suppressed. If the step 42 does not include the inner inclined surface 43, a region to which exhaust gas is not supplied may occur in an axial region of the leading edge 25 of the impeller 2, and an effective area of the impeller 2 may decrease. In addition, in a case where the step 42 does not include the inner inclined surface 43, vortices and separation of an exhaust gas flow may occur downstream of the step 42 in a flow direction of the exhaust gas.(Outer Inclined Surface of Step)

[0041] In some embodiments, as shown in FIGS. 2 and 3, the above-described hub-side flow passage surface 4 further includes an outer inclined surface 44 that is located radially outward of the flat surface 41 in the radial direction of the impeller 2 and that is inclined toward the hub side while extending radially outward. In the illustrated embodiment, the outer inclined surface 44 is formed by an annular surface that extends along the circumferential direction of the impeller 2.

[0042] In the illustrated embodiment, the outer inclined surface 44 is formed by an annular surface that extends along the circumferential direction of the impeller 2. An inner peripheral edge of the outer inclined surface 44 is continuous with an outer peripheral edge of the flat surface 41. Additionally, an outer peripheral edge of the outer inclined surface 44 constitutes an outer peripheral edge of the hub-side flow passage surface 4 of the annular member 40. A length (flow passage width) of the exhaust gas passage 35 in the axial direction at a position of the outer peripheral edge of the outer inclined surface 44 may be the same length as the flow passage width WO.

[0043] According to the above-described configuration, since the step 42 provided on the hub-side flow passage surface 4 includes the outer inclined surface 44, a flow passage cross-sectional area of the exhaust gas passage 35 can be gradually decreased at a location upstream of at least one nozzle vane 6 (on a radially outer side) in the exhaust gas passage 35. As a result, a flow passage loss in the exhaust gas passage 35 due to the step 42 can be reduced, thereby suppressing performance degradation of the turbine 1 due to the step 42.(Inclination Angles of Outer Inclined Surface and Inner Inclined Surface)

[0044] In some embodiments, as shown in FIG. 2, the above-described hub-side flow passage surface 4 is configured such that an inclination angle α of the outer inclined surface 44 is smaller than an inclination angle β of the inner inclined surface 43. The inclination angle α of the outer inclined surface 44 is an angle formed between a virtual extension plane VL obtained by extending the flat surface 41 and the outer inclined surface 44. The inclination angle β of the inner inclined surface 43 is an angle formed between the virtual extension plane VL and the inner inclined surface 43.

[0045] According to the above-described configuration, by making the inclination angle α of the outer inclined surface 44 smaller than the inclination angle β of the inner inclined surface 43, the flow passage cross-sectional area of the exhaust gas passage 35 can be gently decreased at a location upstream of at least one nozzle vane 6 (on a radially outer side) in the exhaust gas passage 35. As a result, a flow passage loss in the exhaust gas passage 35 due to the step 42 can be effectively reduced.(Turbocharger)

[0046] FIG. 8 is a schematic view of the turbocharger according to one embodiment. In some embodiments, the turbocharger 10 includes the turbine 1 having improved robustness as described above and a centrifugal compressor 11 configured to be driven by the turbine 1. The centrifugal compressor 11 includes a compressor impeller 12, and the turbocharger 10 further includes a rotating shaft 13 to which the impeller 2 is coupled on one end side and the compressor impeller 12 is coupled on the other end side. The impeller 2 is rotationally driven by exhaust gas from an engine 14. The compressor impeller 12 is rotationally driven in conjunction with rotational driving of the impeller 2 and compresses a fluid (for example, air or the like) delivered to the engine 14.

[0047] Some embodiments of the present disclosure are also applicable to a method of modifying a turbine, by which the turbine 1A according to the comparative example is modified into the turbine 1. By removing the annular member 40A, to which the plurality of nozzle vanes 6A are fixed, from the casing 3 of the turbine 1A and newly attaching to the casing 3 the annular member 40 to which the plurality of nozzle vanes 6 are fixed, the turbine 1A can be modified into the turbine 1.

[0048] In the present specification, expressions representing relative or absolute dispositions such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" are intended not only to strictly represent such dispositions but also to encompass states in which, within tolerances or to an extent that the same function can be obtained, there is relative displacement in angle or distance.

[0049] For example, expressions representing that things are equal, such as "same", "equal", and "uniform", are intended not only to strictly represent equality but also to encompass states in which differences are present within tolerances or to an extent that the same function can be obtained.

[0050] In addition, in the present specification, expressions representing shapes such as a rectangular shape or a cylindrical shape are intended not only to strictly represent geometrically exact rectangular or cylindrical shapes but also to encompass shapes including uneven portions, chamfered portions, and the like within a range in which the same effect can be obtained.

[0051] Moreover, in the present specification, expressions such as that one component "comprises", "includes", or "has" another component are non-exclusive and do not exclude the presence of other components.

[0052] The present disclosure is not limited to the embodiments described above, and also includes forms obtained by modifying the above-described embodiments and forms obtained by combining these forms as appropriate.

[0053] The matters described in some embodiments described above can be understood, for example, as follows. 1) A turbine (1) according to at least one embodiment of the present disclosure includes: a turbine impeller (2); an exhaust gas passage forming portion (36) that forms an exhaust gas passage (35) for guiding exhaust gas from a scroll passage (33) formed on an outer peripheral side of the turbine impeller (2) to the turbine impeller (2), the exhaust gas passage forming portion (36) including a hub-side flow passage surface (4) and a shroud-side flow passage surface (5) that define the exhaust gas passage (35); and at least one nozzle vane (6) disposed in the exhaust gas passage (35) and fixed to at least one of the hub-side flow passage surface (4) or the shroud-side flow passage surface (5), in which a vane height W1, which is a length of the at least one nozzle vane (6) in an axial direction of the turbine impeller (2), is smaller than a flow passage width WO, which is a length of the exhaust gas passage (35) in the axial direction at a blade leading-edge position of the turbine impeller (2).

[0054] According to the configuration of 1), by making the vane height W1 of at least one nozzle vane smaller than the flow passage width WO of the exhaust gas passage (35) at the blade leading-edge position of the turbine impeller (2), the area of the vane surface of the nozzle vane (6) is smaller than in a case where the vane height W1 is the same length as the flow passage width WO, so that the amount of carbon deposition can be reduced. Consequently, an area that blocks the nozzle throat area (blockage area) due to carbon deposited on the vane surface of the nozzle vane (6) can be reduced. By reducing the blockage area, a maintenance frequency of the turbine (1) can be reduced, and an operating time of the turbine (1) and of the turbocharger (10) including the turbine (1) can be increased. With such a turbine (1), adverse effects due to carbon deposition on the nozzle throat area can be reduced, thereby improving robustness of the turbine (1).

[0055] 2) In some embodiments, the turbine (1) according to 1), in which the at least one nozzle vane (6) includes a plurality of nozzle vanes (6) disposed at intervals from each other in a circumferential direction of the turbine impeller (2), and for each of the plurality of nozzle vanes (6), a distance (D1) from an axis (LA) of the turbine impeller (2) to a trailing edge (62) of the nozzle vane (6) is determined so as to obtain a desired nozzle throat width.

[0056] According to the configuration of 2), when the vane height W1 is merely made smaller than the flow passage width WO, the nozzle throat area is smaller than in a case where the vane height W1 is the same length as the flow passage width WO. In a case where the vane height W1 is made smaller than the flow passage width WO, in order to secure the nozzle throat area similar to a case where the vane height W1 is the same length as the flow passage width WO, it is necessary to make the nozzle throat width longer than in a case where the vane height W1 is the same length as the flow passage width WO. In a case where the vane height W1 is made smaller than the flow passage width WO, by increasing the distance (D1) from the axis (LA) of the turbine impeller (2) to the trailing edge (62) of the nozzle vane (6) as compared with a case where the vane height W1 is the same length as the flow passage width WO, the nozzle throat width can be widened. For each of the plurality of nozzle vanes (6), by adjusting the distance (D1) from the axis (LA) of the turbine impeller (2) to the trailing edge (62) of the nozzle vane (6), a desired nozzle throat width and a desired nozzle throat area can be secured, and consequently performance of the turbine (1) and of the turbocharger (10) including the turbine (1) can also be ensured.

[0057] 3) In some embodiments, the turbine (1) according to 1) or 2), in which the at least one nozzle vane (6) includes a plurality of nozzle vanes (6) disposed at intervals from each other in a circumferential direction of the turbine impeller (2), and for each of the plurality of nozzle vanes (6), in a case where an angle formed between a tangent line (TL1), at a trailing edge (62) of the nozzle vane (6), to a virtual circle (VC) that passes through the trailing edge (62) about an axis (LA) of the turbine impeller (2), and a tangent line (TL2), at the trailing edge (62), to a vane surface (inner vane surface 63) of the nozzle vane (6) on a turbine impeller (2) side is defined as a stagger angle θ, the stagger angle θ is determined so as to obtain a desired nozzle throat width.

[0058] According to the configuration of 3), in a case where the vane height W1 is made smaller than the flow passage width WO, by increasing the stagger angle θ as compared with a case where the vane height W1 is the same length as the flow passage width WO, the nozzle throat width can be widened. For each of the plurality of nozzle vanes (6), by adjusting the stagger angle θ, a desired nozzle throat width and a desired nozzle throat area can be secured, and consequently performance of the turbine (1) and of the turbocharger (10) including the turbine (1) can also be ensured.

[0059] 4) In some embodiments, the turbine (1) according to any one of 1) to 3), in which the hub-side flow passage surface (4) includes a flat surface (41) formed in a region in which the at least one nozzle vane (6) is interposed between the hub-side flow passage surface (4) and the shroud-side flow passage surface (5), the flat surface (41) being located on a shroud side in the axial direction relative to a hub-side end (26) of a leading edge (25) of the turbine impeller (2) and extending along a radial direction of the turbine impeller (2).

[0060] According to the configuration of 4), by providing, on the hub-side flow passage surface (4), the step (42) including the flat surface (41) as a top surface that protrudes to the shroud side beyond the hub-side end (26) of the leading edge (25) of the turbine impeller (2), the vane height W1 can be made smaller than the flow passage width WO. By providing the step (42) on the hub-side flow passage surface (4), as compared with a case of providing the step (42) on the shroud-side flow passage surface (5), a flow passage loss in the exhaust gas passage (35) can be reduced, and performance degradation of the turbine (1) can be suppressed.

[0061] 5) In some embodiments, the turbine (1) according to 4), in which the hub-side flow passage surface (4) further includes an inner inclined surface (43) that is located radially inward of the flat surface (41) in the radial direction of the turbine impeller (2) and that is inclined toward a hub side while extending radially inward.

[0062] According to the configuration of 5), since the step (42) provided on the hub-side flow passage surface (4) includes the inner inclined surface (43), a flow passage cross-sectional area of the exhaust gas passage (35) can be gradually increased at a location downstream of at least one nozzle vane (6) in the exhaust gas passage (35). As a result, since a part of the exhaust gas flowing through the exhaust gas passage (35) can be guided along the inner inclined surface (43) to the hub side of the leading edge (25) of the turbine impeller (2), performance degradation of the turbine (1) due to the step (42) can be suppressed.

[0063] 6) In some embodiments, the turbine (1) according to 4) or 5), in which the hub-side flow passage surface (4) further includes an outer inclined surface (44) that is located radially outward of the flat surface (41) in the radial direction of the turbine impeller (2) and that is inclined toward a hub side while extending radially outward.

[0064] According to the configuration of 6), since the step (42) provided on the hub-side flow passage surface (4) includes the outer inclined surface (44), a flow passage cross-sectional area of the exhaust gas passage (35) can be gradually decreased at a location upstream of at least one nozzle vane (6) in the exhaust gas passage (35). As a result, since a flow passage loss in the exhaust gas passage (35) due to the step (42) can be reduced, performance degradation of the turbine (1) due to the step (42) can be suppressed.

[0065] 7) A turbocharger (10) according to at least one embodiment of the present disclosure includes: the turbine (1) according to any one of 1) to 6); and a centrifugal compressor (11) configured to be driven by the turbine (1).

[0066] According to the configuration of 7), the turbocharger (10) includes the turbine (1) having improved robustness.Reference Signs List

[0067] 1, 1A: turbine 2: impeller (turbine impeller) 3: casing 4, 4A: hub-side flow passage surface 5: shroud-side flow passage surface 6: nozzle vane 10: turbocharger 11: centrifugal compressor 12: compressor impeller 13: rotating shaft 14: engine 21: hub 22: outer surface 23: impeller blade 24: tip 25: leading edge 26: hub-side end 31: shroud surface 32: shroud portion 33: scroll passage 34: scroll passage forming portion 35: exhaust gas passage 36: exhaust gas passage forming portion 40, 40A: annular member 41: flat surface 42: step 43: inner inclined surface 44: outer inclined surface 61: leading edge 62, 62A: trailing edge 63, 63A: inner vane surface 64, 64A: outer vane surface CL: vane thickness centerline D1, D2: distance ETA: effective nozzle throat area LA: axis SL: surge limit T: throat TL1, TL2: tangent line VC: virtual circle VL: virtual extension plane WO: flow passage width W1: vane height

Claims

1. A turbine comprising: a turbine impeller; an exhaust gas passage forming portion that forms an exhaust gas passage for guiding exhaust gas from a scroll passage formed on an outer peripheral side of the turbine impeller to the turbine impeller, the exhaust gas passage forming portion including a hub-side flow passage surface and a shroud-side flow passage surface that define the exhaust gas passage; and at least one nozzle vane disposed in the exhaust gas passage and fixed to at least one of the hub-side flow passage surface or the shroud-side flow passage surface, wherein a vane height W1, which is a length of the at least one nozzle vane in an axial direction of the turbine impeller, is smaller than a flow passage width W0, which is a length of the exhaust gas passage in the axial direction at a blade leading-edge position of the turbine impeller.

2. The turbine according to Claim 1, wherein the at least one nozzle vane includes a plurality of nozzle vanes disposed at intervals from each other in a circumferential direction of the turbine impeller, and for each of the plurality of nozzle vanes, a distance from an axis of the turbine impeller to a trailing edge of the nozzle vane is determined so as to obtain a desired nozzle throat width.

3. The turbine according to Claim 1 or 2, wherein the at least one nozzle vane includes a plurality of nozzle vanes disposed at intervals from each other in a circumferential direction of the turbine impeller, and for each of the plurality of nozzle vanes, in a case where an angle formed between a tangent line, at a trailing edge of the nozzle vane, to a virtual circle that passes through the trailing edge about an axis of the turbine impeller, and a tangent line, at the trailing edge, to a vane surface of the nozzle vane on a turbine impeller side is defined as a stagger angle θ, the stagger angle θ is determined so as to obtain a desired nozzle throat width.

4. The turbine according to Claim 1, wherein the hub-side flow passage surface includes a flat surface formed in a region in which the at least one nozzle vane is interposed between the hub-side flow passage surface and the shroud-side flow passage surface, the flat surface being located on a shroud side in the axial direction relative to a hub-side end of a leading edge of the turbine impeller and extending along a radial direction of the turbine impeller.

5. The turbine according to Claim 4, wherein the hub-side flow passage surface further includes an inner inclined surface that is located radially inward of the flat surface in the radial direction of the turbine impeller and that is inclined toward a hub side while extending radially inward.

6. The turbine according to Claim 4 or 5, wherein the hub-side flow passage surface further includes an outer inclined surface that is located radially outward of the flat surface in the radial direction of the turbine impeller and that is inclined toward a hub side while extending radially outward.

7. A turbocharger comprising: the turbine according to Claim 1; and a centrifugal compressor configured to be driven by the turbine.

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