Mixed flow turbines and turbochargers

Abstract

This diagonal flow turbine is provided with a turbine wheel comprising a hub and vanes provided at intervals in a circumferential direction of the hub on an outer peripheral surface of the hub. The tip ends of the front edges of the vanes are positioned on an outer side in the radial direction of the turbine wheel than the base ends of the front edges. When a distance between the downstream end of the outer peripheral surface of the hub and a rotational axis line of the turbine wheel is Dh and the average of distances between respective positions from the base ends to the tip ends at the front edges and the rotational axis line is Eave, Dh / Eave > 0.4 is satisfied.

Description

[Technical Field]

[0001] The present disclosure relates to mixed flow turbines and turbochargers. [Background technology]

[0002] Patent Document 1 discloses a turbine for suppressing performance degradation due to exhaust pulsation of an engine. This turbine has a turbine wheel and a turbine housing with a scroll section extending circumferentially around the turbine wheel. The scroll section is configured so that, in a graph where A denotes the flow passage area of ​​the scroll section, R denotes the distance from the flow passage center of the scroll section to the axis of the turbine wheel, the horizontal axis represents the circumferential position around the axis of the turbine wheel, and the vertical axis represents A / R, which is the ratio of the flow passage area A to the distance R, A / R has a concave distribution in at least a portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5870083 Summary of the Invention [Problem to be solved by the invention]

[0004] However, because flow separation on the surface of the turbine wheel reduces turbine efficiency, it is important to suppress flow separation on the surface of the turbine wheel in order to improve turbine efficiency. In this regard, Patent Document 1 does not disclose any knowledge about suppressing flow separation on the surface of the turbine wheel.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a mixed-flow turbine and a turbocharger that can suppress flow separation on the surface of a turbine wheel and achieve high turbine efficiency. [Means for solving the problem]

[0006] In order to achieve the above object, a mixed flow turbine according to at least one embodiment of the present disclosure comprises: Hub and blades provided on the outer peripheral surface of the hub at intervals in the circumferential direction of the hub; a turbine wheel including a tip end of a leading edge of the blade is located outward in a radial direction of the turbine wheel relative to a base end of the leading edge, If the distance between the downstream end of the outer peripheral surface of the hub and the rotation axis of the turbine wheel is Dh, and the average value of the distance between each position on the leading edge from the base end to the tip end and the rotation axis is Eave, then Dh / Eave > 0.4 is satisfied.

[0007] In order to achieve the above object, a turbocharger according to at least one embodiment of the present disclosure comprises: The mixed flow turbine is provided. [Effects of the Invention]

[0008] According to at least one embodiment of the present disclosure, a mixed flow turbine and a turbocharger are provided that can suppress flow separation on the surface of a turbine wheel and achieve high turbine efficiency. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view including a rotation axis of a turbine wheel in a mixed flow turbine according to an embodiment. [Figure 2] 2 is a schematic diagram showing the arrangement of the leading edge of the blade shown in FIG. 1, with the horizontal axis being the circumferential direction and the vertical axis being the axial direction. FIG. [Figure 3] 2 is an enlarged schematic cross-sectional view of a portion of the mixed flow turbine shown in FIG. 1. [Figure 4A] 10 is an example of a flow analysis result showing a flow line distribution in the vicinity of a turbine wheel in a radial turbine according to a comparative example. [Figure 4B]10 is an example of a flow analysis result showing a streamline distribution in the vicinity of a turbine wheel in the mixed flow turbine described above. [Figure 5] FIG. 2 is a diagram showing an example of the configuration of a partition wall, and schematically shows a cross section perpendicular to the axial direction of a mixed flow turbine. [Figure 6] FIG. 10 is a diagram showing another example of the configuration of the partition wall, and schematically shows a cross section perpendicular to the axial direction of the mixed flow turbine. [Figure 7] 2 is an enlarged schematic cross-sectional view of a portion of the mixed flow turbine shown in FIG. 1. [Figure 8] 2 is an enlarged schematic cross-sectional view of a portion of the mixed flow turbine shown in FIG. 1. [Figure 9] FIG. 7 is a diagram showing the relationship between A / R and the circumferential position of each of the front scroll passage, the rear scroll passage, and the front and rear confluence portions in the configuration shown in FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the invention. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0011] 1 is a schematic cross-sectional view including a rotation axis O of a turbine wheel 8 in a mixed-flow turbine 4 according to one embodiment. The following description will be given taking as an example a case where the mixed-flow turbine 4 is a turbine of a turbocharger 2. The mixed-flow turbine 4 is connected to a compressor (not shown) via a rotating shaft 6, and is driven by exhaust gas from an engine (not shown).

[0012] 1, the mixed flow turbine 4 includes a turbine wheel 8 and a casing 10 that houses the turbine wheel 8. The turbine wheel 8 includes a hub 12 and a plurality of blades 14 that are provided on an outer peripheral surface 18 of the hub 12 at intervals in the circumferential direction of the hub 12. A distance D between the outer peripheral surface 18 of the hub 12 and the rotation axis O of the turbine wheel 8 decreases along the axial direction of the turbine wheel 8 toward the downstream side of the fluid flow.

[0013] Hereinafter, unless otherwise specified, "circumferential direction" means the circumferential direction of the turbine wheel 8, i.e., the circumferential direction of the hub 12, "radial direction" means the radial direction of the turbine wheel 8, i.e., the radial direction of the hub 12, and "axial direction" means the axial direction of the turbine wheel 8, i.e., the axial direction of the hub 12, unless otherwise specified. In addition, "front side" means the downstream side of the fluid flow along the turbine wheel 8 in the axial direction, and "rear side" means the upstream side of the fluid flow along the turbine wheel 8 in the axial direction.

[0014] In the mixed-flow turbine 4, the tip 16t of the leading edge 16 of the blade 14 is located radially outward of the base end 16h of the leading edge 16. If the distance between the downstream end 18d of the outer peripheral surface 18 of the hub 12 and the rotation axis O of the turbine wheel 8 is Dh and the average value of the distances E between each position on the leading edge 16 from the base end 16h to the tip 16t and the rotation axis O of the turbine wheel 8 is Eave, the turbine wheel 8 is configured to satisfy Dh / Eave > 0.4. Note that the average value Eave may simply be the sum of the distance between the base end 16h of the leading edge 16 and the rotation axis O and the distance between the tip 16t of the leading edge 16 and the rotation axis O, divided by 2.

[0015] In some embodiments, as shown in FIG. 1, the casing 10 includes a shroud wall 20, a scroll outer peripheral wall 22, and a partition wall 24 (partition plate).

[0016] The shroud wall 20 is configured in a cylindrical shape to accommodate the turbine wheel 8. The central axis of the shroud wall 20 coincides with the rotational axis O of the turbine wheel 8 (the rotational axis of the hub 12), and the above-mentioned circumferential direction, radial direction, and axial direction respectively coincide with the circumferential direction, radial direction, and axial direction of the shroud wall 20. Between the shroud wall 20 and the hub 12 of the turbine wheel 8, a working flow passage 21 is formed, through which engine exhaust gas flows.

[0017] The scroll outer peripheral wall 22 is connected to one end side of the shroud wall 20 (the upstream side in the fluid flow direction of the working flow passage 21) and extends along the circumferential direction.

[0018] The partition wall 24 is provided inside the scroll outer peripheral wall 22 and extends circumferentially so as to divide the interior of the scroll outer peripheral wall 22 into a front scroll passage 26 and a rear scroll passage 28. The front scroll passage 26 and the rear scroll passage 28 are aligned in the axial direction, with the front scroll passage 26 located forward of the rear scroll passage 28. In this manner, the mixed-flow turbine 4 shown in FIG. 1 is a so-called twin-scroll turbine. Exhaust gas is supplied to each of the front scroll passage 26 and the rear scroll passage 28 from an engine (not shown).

[0019] FIG. 2 is a schematic diagram showing the position of the leading edge 16 of the blade 14 shown in FIG. 1, expanded in the circumferential direction. In some embodiments, as shown in FIG. 2, for example, a tip 16t of the leading edge 16 of the blade 14 is located downstream of a base end 16h of the leading edge 16 in the rotation direction of the turbine wheel 8.

[0020] FIG. 3 is a schematic cross-sectional view showing an enlarged portion of the mixed flow turbine 4 shown in FIG. In some embodiments, as shown in FIG. 3 , for example, in a cross section including the rotation axis O of the turbine wheel 8 in the mixed-flow turbine 4, the angle α formed between an extension line Le of the tip 30 of the partition wall 24 and the rotation axis O toward the back surface 8b of the turbine wheel 8 is less than 90 degrees. Here, in the cross section including the rotation axis O of the turbine wheel 8, the extension line Le of the tip 30 of the partition wall 24 refers to a straight line extending from the position of the tip 30 of the partition wall 24 to the center line L in the direction of inclination of the center line L at the position of the tip 30, when the locus of the center of the partition wall 24 in the thickness direction from the base end side of the partition wall 24 to the tip 30 is defined as the center line L of the partition wall 24. In addition, the back surface 8b of the turbine wheel 8 is the surface of the hub 12 facing rearward and is the surface that determines the maximum value of the outer diameter of the hub 12.

[0021] The effects achieved by the mixed flow turbine 4 will be described below. Fig. 4A is an example of a flow analysis result showing the flow line distribution near the turbine wheel 08 in a radial turbine according to a comparative embodiment. Fig. 4B is an example of a flow analysis result showing the flow line distribution near the turbine wheel 8 in the mixed flow turbine 4 described above. In the radial turbine shown in Fig. 4A, the ratio Dh / Eave described above is smaller than 0.4, and the leading edges 016 of the blades 014 of the turbine wheel 08 are formed parallel to the axial direction.

[0022] 4A, it can be seen that tornado-shaped separation occurs on the hub 012 side of the turbine wheel 08 in the radial turbine according to the comparative embodiment. Generally, centrifugal force and Coriolis force act on the fluid flowing along the turbine wheel. The resultant force of this centrifugal force and Coriolis force has a component that is opposite to the normal flow direction along the turbine wheel 08, and this acts on the fluid as an adverse pressure gradient (a pressure gradient that acts in the opposite direction to the normal flow direction along the turbine wheel), which is thought to cause tornado-shaped separation on the hub 012 side.

[0023] In contrast, as shown in FIG. 4B, in the mixed-flow turbine 4 according to the embodiment, tornado-shaped separation on the hub 12 side of the turbine wheel 8 is suppressed compared to the comparative example shown in FIG. 4A. As described above, the resultant force of centrifugal force and Coriolis force acting on the fluid flowing along the turbine wheel 8 has a component opposite to the flow direction. However, the magnitude of this component can be reduced by increasing the distance Dh (the inner diameter of the hub 12) between the downstream end 18d of the outer circumferential surface 18 of the hub 12 and the rotation axis O of the hub 12. Therefore, by satisfying Dh / Eave > 0.4 as described above, the opposite component can be reduced, suppressing the adverse pressure gradient and suppressing the occurrence of tornado-shaped separation. Therefore, the mixed-flow turbine 4 can achieve high turbine efficiency.

[0024] Furthermore, under exhaust pulsation from the engine, exhaust gas flows into the leading edges of the turbine wheel blades from a direction inclined relative to the axial direction. In the radial turbine of the comparative example, the leading edges 016 of the blades 014 of the turbine wheel 08 are formed parallel to the axial direction (i.e., the tip and base ends of the leading edges 016 are located at the same position in the rotational direction of the turbine wheel). This causes the inflow direction of the flow into the blades 014 to misalign with the angle of the leading edges 016 of the blades 014, resulting in a large incidence angle and making separation more likely to occur. In contrast, in the mixed-flow turbine 4, the tip 16t of the leading edge 16 of the blade 14 is located downstream of the base end 16h of the leading edge 16 in the rotational direction of the turbine wheel 8. This causes the flow to follow the blades 14, making separation less likely to occur, thereby achieving high turbine efficiency.

[0025] 3 , in a cross section including the rotation axis O of the turbine wheel 8 of the mixed-flow turbine 4, the angle α formed by the extension line Le of the tip 30 of the partition wall 24 and the rotation axis O toward the back surface 8b of the turbine wheel 8 is smaller than 90 degrees. Therefore, compared to when the angle α is 90 degrees or more, it is possible to suppress the flow from turning midway from each of the front scroll passage 26 and the rear scroll passage 28 to the turbine wheel 8, and to smoothly guide the flow from each of the front scroll passage 26 and the rear scroll passage 28 to the turbine wheel 8. This makes it possible to suppress separation at the turbine wheel 8.

[0026] Fig. 5 is a diagram showing an example of the configuration of the partition wall 24, and schematically shows a cross section perpendicular to the axial direction of the mixed-flow turbine 4. Fig. 6 is a diagram showing another example of the configuration of the partition wall 24, and schematically shows a cross section perpendicular to the axial direction of the mixed-flow turbine 4.

[0027] 3, for example, the distance between the tip 30 of the partition wall 24 and the hub 12 of the turbine wheel 8 (the shortest distance between the tip 30 of the partition wall 24 and the outer peripheral surface 18 of the hub 12) is defined as distance d. Also, as shown in FIG. 5, for example, the position of the tongue portion 32 of the scroll outer peripheral wall 22 is defined as the 0° position in the circumferential direction, and the rotation direction K of the turbine wheel 8 is defined as the positive direction of the position in the circumferential direction. Note that, as is well known to those skilled in the art, the position of the tongue portion 32 refers to the position of the tip of a tongue-like protrusion formed at the position where the winding start 22a and the winding end 22b of the scroll outer peripheral wall 22 connect.

[0028] In some embodiments, for example as shown in Figures 5 and 6, the distance d over at least a portion of the circumferential range from 180° to 360° is greater than the distance d over at least a portion of the circumferential range from 0° to 180°.

[0029] In the example shown in FIG. 5 , the distance d is constant regardless of the circumferential position within the circumferential range from 0° to 180°. The partition wall 24 includes a notch 34 formed by cutting out the tip 30 of the partition wall 24 in the range downstream of 180° in the circumferential direction. The distance d increases in the positive circumferential direction within the circumferential range from 180° to 270°. Therefore, the distance d at each position within the circumferential range from 180° to 270° is greater than the distance d at each position within the circumferential range from 0° to 180° (excluding 180°). The height of the partition wall 24 is zero within the circumferential range from 270° to 360°. In other words, the partition wall 24 is not provided within the circumferential range from 270° to 360°. The notch 34 is not necessarily formed by machining, but may be formed by casting or the like so that the distance d is partially increased.

[0030] 6, the distance d is constant regardless of the position in the circumferential direction within the range from 0° to 270°. The partition wall 24 includes a notch 34 formed by cutting out the tip 30 side of the partition wall 24 in the range from 270° to the downstream side in the circumferential direction. In the illustrated example, the notch 34 is formed over the range from 270° to 360° in the circumferential direction. Therefore, the distance d at each position in the range from 270° to 360° in the circumferential direction is greater than the distance d at each position in the range from 0° to 180° in the circumferential direction.

[0031] The effects achieved by the configurations shown in FIGS. 5 and 6 will be described below. In each of the front scroll passage 26 and the rear scroll passage 28, the flow of air to the turbine wheel 8 is less likely to flow smoothly in the circumferential range of 180° to 360° than in the circumferential range of 0° to 180°, which is a relatively upstream range. For this reason, in each of the configurations shown in FIGS. 5 and 6 , the distance d in at least a portion of the circumferential range of 180° to 360° is set to be greater than the distance d in at least a portion of the circumferential range of 0° to 180°. This reduces friction loss on the surface of the partition wall 24 in the 180° to 360° range where the flow of air to the turbine wheel 8 is less likely to flow smoothly, thereby promoting the flow to the turbine wheel 8 and reducing circumferential variation in the flow inflow angle to the blades 14 of the turbine wheel 8. As a result, variation in the torque applied to each blade 14 of the turbine wheel 8 can be reduced, thereby improving turbine output.

[0032] Here, the A / R of each of the front scroll passage 26 and the rear scroll passage 28 of the mixed flow turbine 4 will be described using the configuration shown in FIG. 6 as an example. First, as shown in FIG. 7 , in a cross section including the rotation axis O of the mixed-flow turbine 4 (a cross section perpendicular to the circumferential direction), the area of ​​the region defined between the partition wall 24 and the scroll outer peripheral wall 22 on the front side of the partition wall 24 is defined as the flow path area A of the front scroll passage 26. Also, the area of ​​the region defined between the partition wall 24 and the scroll outer peripheral wall 22 on the rear side of the partition wall 24 is defined as the flow path area A of the rear scroll passage 28. Also, in a cross section including the rotation axis O of the mixed-flow turbine 4, the distance between the center C1 of the flow path cross section of the front scroll passage 26 (the centroid of the flow path cross section of the front scroll passage 26) and the rotation axis O is defined as the distance R of the front scroll passage 26. Also, the distance between the center C2 of the flow path cross section of the rear scroll passage 28 (the centroid of the flow path cross section of the rear scroll passage 28) and the rotation axis O is defined as the distance R of the rear scroll passage 28.

[0033] 6, the entire flow path defined by the inner surface 22a of the outer circumferential wall 22 of the scroll in the range downstream of the 270° position in the circumferential direction is defined as the front and rear confluence 36, as shown in FIG. 8. In addition, in a cross section including the rotation axis O of the mixed-flow turbine 4, the distance between the center C3 of the flow path cross section of the front and rear confluence 36 and the rotation axis O is defined as the distance R of the front and rear confluence 36. In addition, in a cross section including the rotation axis O of the mixed-flow turbine 4, the area of ​​the region defined by the inner surface 22a of the outer circumferential wall 22 of the scroll is defined as the flow path area A of the front and rear confluence 36.

[0034] Fig. 9 is a diagram showing the relationship between the A / R of each of the front scroll passage 26, the rear scroll passage 28, and the front and rear junction 36 and the circumferential position in the configuration shown in Fig. 6. In Fig. 9, the distribution of A / R of the front scroll passage 26 with respect to the circumferential position is defined as the front A / R distribution, the distribution of A / R of the rear scroll passage 28 with respect to the circumferential position is defined as the rear A / R distribution, and the distribution of A / R of the front and rear junction 36 with respect to the circumferential position is defined as the junction A / R distribution, and each distribution is plotted. In addition, the sum of the A / R of the front scroll passage 26 and the A / R of the rear scroll passage 28 for each circumferential position is defined as the total A / R, and the distribution of the total A / R with respect to the circumferential position is defined as the total A / R distribution and plotted.

[0035] As shown in Fig. 9, the slope of the total A / R distribution at a 270° position, which is the position of one end of the cutout 34 of the partition wall 24 (see Fig. 6) in the circumferential direction (the position of the start of the section where the cutout 34 is formed in the circumferential direction), is preferably 95% to 105% of the slope of the confluence A / R distribution at the 270° position.More preferably, the slope of the total A / R distribution at the 270° position, which is the position of one end of the cutout 34 of the partition wall 24 in the circumferential direction, is preferably the same as the slope of the confluence A / R distribution at the 270° position.

[0036] This makes it possible to suppress fluctuations in fluid flow velocity and pressure caused by the provision of the notches 34, and reduce variations in the circumferential direction of the inflow angle of the fluid onto the blades 14 of the turbine wheel 8. As a result, variations in the torque applied to each blade 14 of the turbine wheel 8 can be reduced, and turbine output can be improved.

[0037] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0038] For example, the present disclosure is not limited to the above-described twin-scroll turbine, and may be, for example, a so-called single-scroll turbine having only one scroll passage, or a so-called double-scroll turbine having a scroll passage divided in the circumferential direction. In these cases, high turbine efficiency can be achieved by configuring the turbine so that Dh / Eave > 0.4 is satisfied.

[0039] In some embodiments, the mixed flow turbine 4 shown in Figure 1 may not have the cutout 34, and the distance d between the tip 30 of the partition wall 24 and the hub 12 of the turbine wheel 8 may be constant regardless of the circumferential position over a circumferential range from 0° to 360°.

[0040] In addition, for example, in the mixed flow turbine 4 shown in Figures 1 to 3, the value obtained by dividing the distance R of the front scroll passage at a 180° position in the circumferential direction by the distance between the tongue portion 32 of the scroll outer peripheral wall 22 and the rotation axis O is 1.28 or less, and the value obtained by dividing the distance R of the front scroll passage by the A / R of the front scroll passage at a 180° position in the circumferential direction (R 2 / A) may be 5.7 or less. This reduces the circumferential variation in the inflow angle of the flow to the blades 14 of the turbine wheel 8. According to studies by the present inventors, a parameter Φ, which is defined by the following formula (a) and indicates the non-uniformity of the inflow angle α of the flow to the blades 14 of the turbine wheel 8, is Φ=0.57 in the front scroll passage 26, whereas conventionally Φ=0.70. This value of parameter Φ also indicates the effect of reducing the circumferential variation in the inflow angle of the flow to the blades 14 of the turbine wheel 8. This reduces the variation in the torque applied to each blade 14 of the turbine wheel 8, thereby improving turbine output. TIFF0007779998000001.tif12170In the above formula (a), α is the inflow angle of the flow relative to the blade 14, and α average is the average value of α in the range from 0° to 360° in the circumferential direction, and θ is the position in the circumferential direction.

[0041] The contents described in each of the above embodiments can be understood, for example, as follows.

[0042] (1) A mixed-flow turbine according to at least one embodiment of the present disclosure (e.g., the mixed-flow turbine 4 described above) has the following features: a hub (e.g., hub 12 above) blades (e.g., the blades 14 described above) provided on the outer peripheral surface of the hub at intervals in the circumferential direction of the hub; a turbine wheel (e.g., the turbine wheel 8 described above) including a tip (e.g., the tip 16t) of a leading edge of the blade (e.g., the leading edge 16) is located radially outward of a base end (e.g., the base end 16h) of the leading edge, If the distance between the downstream end of the outer peripheral surface of the hub (for example, the downstream end 18d mentioned above) and the rotation axis of the turbine wheel (for example, the rotation axis O mentioned above) is Dh, and the average value of the distance between each position on the leading edge from the base end to the tip end and the rotation axis (for example, the distance E mentioned above) is Eave, then Dh / Eave > 0.4 is satisfied.

[0043] Generally, centrifugal force and Coriolis force act on the fluid flowing along the turbine wheel. The resultant force of these centrifugal force and Coriolis force has a component in the opposite direction to the flow direction, which acts on the fluid as an adverse pressure gradient (a gradient that causes a flow in the opposite direction to the normal flow), which can cause tornado-shaped separation on the hub side. In contrast, the mixed-flow turbine described in (1) above is configured to satisfy Dh / Eave > 0.4. As described above, the resultant force of the centrifugal force and Coriolis force acting on the fluid flowing along the turbine wheel has a component opposite to the flow direction. However, the magnitude of this component can be reduced by increasing the distance Dh between the downstream end of the outer circumferential surface of the hub and the rotational axis of the hub. Therefore, by satisfying Dh / Eave > 0.4 as described in (1) above, the opposite component can be reduced, suppressing the adverse pressure gradient and preventing the occurrence of the tornado-like separation. This makes it possible to achieve high turbine efficiency.

[0044] (2) In some embodiments, in the mixed flow turbine described in (1), The tip of the leading edge of the turbine wheel is located downstream of the base end of the leading edge in the rotation direction of the turbine wheel.

[0045] Under engine exhaust pulsation, exhaust gas flows into the leading edges of the turbine wheel blades from a direction inclined relative to the axial direction. In conventional radial turbines, the leading edges of the turbine wheel blades are formed parallel to the axial direction, which means that the direction of flow into the blades does not match the angle of the leading edges of the blades, resulting in a large incidence angle and making separation more likely to occur. In contrast, in the mixed-flow turbine described above in (2), the tip of the leading edge of the blade is located downstream of the base end of the leading edge in the direction of rotation of the turbine wheel, so the flow follows the blades, making separation less likely to occur, and achieving high turbine efficiency.

[0046] (3) In some embodiments, in the mixed flow turbine described in (1) or (2), a casing (for example, the casing 10 described above) that houses the turbine wheel; The casing comprises: a cylindrical shroud wall (e.g., the shroud wall 20 described above) that houses the turbine wheel; a scroll outer peripheral wall (for example, the above-mentioned scroll outer peripheral wall 22) connected to one end side of the shroud wall and extending along the circumferential direction; a partition wall (e.g., the above-mentioned partition wall 24) provided inside the scroll outer peripheral wall and dividing the interior of the scroll outer peripheral wall into a front scroll flow path (e.g., the above-mentioned front scroll flow path 26) and a rear scroll flow path (e.g., the above-mentioned rear scroll flow path 28) aligned in the axial direction of the turbine wheel; Includes:

[0047] According to the mixed flow turbine described in (3) above, when used in a turbocharger, it is possible to improve the boost pressure in the low rotation speed range of the engine.

[0048] (4) In some embodiments, in the mixed flow turbine described in (3), In a cross section including the rotation axis, the angle formed between an extension line of the tip of the partition wall (for example, the above-mentioned extension line Le) and the rotation axis on the back surface of the turbine wheel (for example, the above-mentioned back surface 8b) is less than 90 degrees.

[0049] The mixed-flow turbine described in (4) above can suppress the flow from turning midway from the front scroll passage and the rear scroll passage to the turbine wheel, and can smoothly guide the flow from each of the front scroll passage and the rear scroll passage to the turbine wheel, compared to when the angle formed by the extension line of the partition wall tip and the rotation axis on the back side of the turbine wheel is 90 degrees or more. This makes it possible to suppress separation at the turbine wheel.

[0050] (5) In some embodiments, in the mixed flow turbine described in (3) or (4), If the position of the tongue portion of the outer circumferential wall of the scroll (for example, the position of the tongue portion 32) is defined as the 0° position in the circumferential direction, the rotation direction of the turbine wheel is defined as the positive direction of the position in the circumferential direction, and the distance between the tip of the partition wall and the hub at each position in the circumferential direction is defined as d, then: The distance d in at least a portion of the range from 180° to 360° in the circumferential direction is greater than the distance d in at least a portion of the range from 0° to 180° in the circumferential direction.

[0051] In each of the front scroll passage and the rear scroll passage, the flow to the turbine wheel is less likely to flow smoothly in the relatively downstream circumferential range of 180° to 360° than in the relatively upstream circumferential range of 0° to 180°. Therefore, in the mixed-flow turbine described in (5) above, the distance d in at least a portion of the circumferential range of 180° to 360° is set to be greater than the distance d in at least a portion of the circumferential range of 0° to 180°. This increases the throat area of ​​the scroll formed at the tip of the partition wall in the 180° to 360° range where the flow to the turbine wheel is less likely to flow smoothly, promoting the flow to the turbine wheel and reducing circumferential variation in the flow inflow angle to the turbine wheel. As a result, variation in the torque applied to each turbine wheel blade can be reduced, thereby improving turbine output.

[0052] (6) In some embodiments, in the mixed flow turbine described above in (5), The distance d is constant within a range from 0° to 180° in the circumferential direction.

[0053] According to the mixed flow turbine described in (6) above, the variation in torque applied to each blade of the turbine wheel can be reduced, thereby improving the turbine output.

[0054] (7) In some embodiments, in the mixed flow turbine described in any one of (3) to (6), The distance d at each position downstream from a first position that is a position of 180° or more in the circumferential direction (for example, the 180° position in Figure 5 or the 270° position in Figure 6) of the partition wall is greater than the distance d at each position in the range from 0° to 180° in the circumferential direction.

[0055] According to the mixed flow turbine described in (7) above, the variation in torque applied to each blade of the turbine wheel can be reduced, thereby improving the turbine output.

[0056] (8) In some embodiments, in the mixed flow turbine described in (7), The sum of the A / R of the front scroll flow passage and the A / R of the rear scroll flow passage for each circumferential position is defined as a total A / R, the distribution of the total A / R with respect to the circumferential position is defined as a total A / R distribution, the entire flow passage defined by the inner surface of the outer circumferential wall of the scroll is defined as a front-rear junction (for example, the above-mentioned front-rear junction 36), and the distribution of the A / R of the front-rear junction with respect to the circumferential position is defined as a junction A / R distribution, The slope of the total A / R distribution at the first position is 95% or more and 105% or less of the slope of the confluence A / R distribution at the first position.

[0057] According to the mixed flow turbine described in (8) above, by increasing the distance d from the first position, which is a position at or above 180° in the circumferential direction, to the downstream side, it is possible to reduce friction loss on the surface of the partition wall in that range, suppress fluctuations in the fluid flow velocity and pressure, and reduce circumferential variation in the inflow angle of the flow into the turbine wheel. As a result, it is possible to reduce variation in the torque applied to each blade of the turbine wheel and improve turbine output.

[0058] (9) In some embodiments, in the mixed flow turbine described in any one of (3) to (7), a value obtained by dividing the distance between the center of the flow passage cross section of the front scroll flow passage at a position of 180° in the circumferential direction and the rotation axis (for example, the distance R of the front scroll flow passage 26 described above) by the distance between the tongue portion of the scroll outer peripheral wall and the rotation axis (for example, the distance R of the front scroll flow passage 26 described above) is 1.28 or less, At a position of 180° in the circumferential direction, the value obtained by dividing the distance between the center of the flow path cross section of the front scroll flow path and the rotation axis (e.g., the distance R of the front scroll flow path 26 described above) by the A / R of the front scroll flow path (e.g., the A / R of the front scroll flow path 26 described above) is 5.7 or less.

[0059] The mixed flow turbine described in (9) above can reduce the circumferential variation in the inflow angle of the flow into the turbine wheel, thereby reducing the variation in torque applied to each blade of the turbine wheel and improving the turbine output.

[0060] (10) A turbocharger according to at least one embodiment of the present disclosure (for example, the turbocharger 2 described above) includes the mixed flow turbine described in any one of (1) to (9) above.

[0061] According to the mixed flow turbine described in (10) above, since the mixed flow turbine described in any one of (1) to (9) above is included, high turbine efficiency can be achieved. [Explanation of symbols]

[0062] 2 turbochargers 4. Mixed flow turbine 6 Rotation Axis 14 wings 8 Turbine Wheel 8b Back 10 Casing 12 Hub 16 leading edge 16h proximal end 16t tip 18 Outer surface 18d downstream end 20 Shroud Wall 21 Working flow path 22 Scroll outer wall 22a Inner surface 24 Partition Wall 26 Front scroll passage 28 Rear scroll passage 30 Tip 32 Tongue 34 Notch 36 Front and back junction

Claims

1. Hub and Wings provided on the outer peripheral surface of the hub at intervals in the circumferential direction of the hub; a turbine wheel including a tip end of a leading edge of the blade is located outward in a radial direction of the turbine wheel relative to a base end of the leading edge, When a distance between a downstream end of the outer peripheral surface of the hub and the rotation axis of the turbine wheel is Dh, and an average value of distances between each position on the leading edge from the base end to the tip end and the rotation axis is Eave, Dh / Eave > 0.4 is satisfied, and a casing that houses the turbine wheel; The casing comprises: a cylindrical shroud wall that houses the turbine wheel; a scroll outer peripheral wall connected to one end side of the shroud wall and extending along the circumferential direction; a partition wall provided inside the outer circumferential wall of the scroll, the partition wall dividing the interior of the outer circumferential wall of the scroll into a front scroll flow passage and a rear scroll flow passage aligned in the axial direction of the turbine wheel; Including, In a cross section including the rotation axis, an angle formed between an extension line of a tip of the partition wall and the rotation axis on a back side of the turbine wheel is smaller than 90 degrees, In a cross section including the rotation axis, the extension line intersects with the leading edge on a radially inner side of a half position on the leading edge in the radial direction, and a value obtained by dividing a distance between a center of a flow passage cross section of the front scroll flow passage at a 180° position in the circumferential direction and the rotation axis by a distance between a tongue portion of the scroll outer peripheral wall and the rotation axis is 1.28 or less, a value obtained by dividing a distance between a center of a flow passage cross section of the front scroll flow passage and the rotation axis by A / R of the front scroll flow passage at a position of 180° in the circumferential direction is 5.7 or less; Mixed flow turbine.

2. The mixed flow turbine according to claim 1 , wherein the tip of the leading edge of the turbine wheel is located downstream of the base end of the leading edge in the rotation direction of the turbine wheel.

3. The leading edge slopes at a uniform angle from the base end to the tip end. The mixed flow turbine according to claim 2 .

4. When the position of the tongue portion of the outer circumferential wall of the scroll is defined as a 0° position in the circumferential direction, the rotation direction of the turbine wheel is defined as a positive direction of the position in the circumferential direction, and the distance between the tip of the partition wall and the hub at each position in the circumferential direction is defined as d, 4. A mixed flow turbine according to claim 1, wherein the distance d in at least a portion of the range from 180° to 360° in the circumferential direction is greater than the distance d in at least a portion of the range from 0° to 180° in the circumferential direction.

5. 5. The mixed flow turbine according to claim 4, wherein the distance d is constant in a range from 0° to 180° in the circumferential direction.

6. 6. A mixed-flow turbine as described in claim 4 or 5, wherein the distance d at each position downstream from a first position that is a position equal to or greater than 180° in the circumferential direction is greater than the distance d at each position in the range from 0° to 180° in the circumferential direction.

7. The sum of the A / R of the front scroll flow passage and the A / R of the rear scroll flow passage for each position in the circumferential direction is defined as a total A / R, the distribution of the total A / R with respect to the position in the circumferential direction is defined as a total A / R distribution, the entire flow passage defined by the inner surface of the outer circumferential wall of the scroll is defined as a front-rear confluence portion, and the distribution of A / R of the front-rear confluence portion with respect to the position in the circumferential direction is defined as a confluence portion A / R distribution, 7. The mixed flow turbine according to claim 6, wherein the slope of the total A / R distribution at the first position is equal to or greater than 95% and equal to or less than 105% of the slope of the confluence A / R distribution at the first position.

8. A turbocharger comprising the mixed flow turbine according to any one of claims 1 to 7.

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