Axial turbine

Abstract

This axial turbine comprises a turbine shaft, a turbine rotor vane cascade, and a turbine housing that has an exhaust chamber on the downstream side of the turbine rotor vane cascade. The turbine housing includes a flow guide section having an inner peripheral side wall surface that forms, between the inner peripheral side wall surface and an inner wall of the exhaust chamber, a diffuser flow passage for guiding a working fluid, which has passed through the turbine rotor vane cascade, toward the outside in the radial direction. Treating the shortest distance between a trailing edge end and a negative pressure surface of another turbine rotor vane adjacent thereto as the throat s, treating the pitch of the plurality of turbine rotor vanes as t, treating the vane height location of the vane roots as 0%, and treating the vane height location of the vane tips as 100%, in the distribution of the throat / pitch ratio in the vane height direction, the throat / pitch ratio at the 25% vane height location is smaller than a line segment connecting a vane root section and a center section in the vane height direction, and the throat / pitch ratio at the 75% vane height location is smaller than a line segment connecting the center section and a vane tip section.

Description

Axial flow turbine

[0001] This application claims priority to Japanese Patent Application No. 2023-210277, filed on December 13, 2023, with the Japan Patent Office, the contents of which are incorporated herein by reference.

[0002] In order to save space, some axial flow turbines are provided with a diffuser passage for guiding exhaust gas that has passed through the turbine rotor blades outward in the radial direction (see Patent Document 1).

[0003] JP 2016-84730 A

[0004] Generally, turbine rotor blades of axial flow turbines are designed with the aim of improving the efficiency of the turbine rotor blades. However, this design idea does not necessarily improve the efficiency of the entire axial flow turbine.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure has an object to provide an axial turbine that can improve the efficiency of the entire axial turbine.

[0006] an axial flow turbine according to at least one embodiment of the present disclosure, comprising: a turbine shaft; a turbine blade cascade attached to the turbine shaft and arranged in a row in the circumferential direction of the turbine shaft; and a turbine housing rotatably accommodating the turbine blade cascade and having an exhaust chamber downstream of the turbine blade cascade, wherein the turbine housing includes a flow guide portion having an inner peripheral wall surface that forms a diffuser flow path between itself and an inner wall of the exhaust chamber to guide the working fluid that has passed through the turbine blade cascade radially outward, wherein the shortest distance between the trailing edge of a turbine blade and a suction surface of another turbine blade adjacent to the turbine blade is defined as a throat s, the pitch of the plurality of turbine blades arranged in a row is defined as t, and the blade height position of the root of the turbine blade in a blade height direction from the root to the tip of the turbine blade is defined as 0% and the blade height position of the tip of the blade is defined as 100%, the distribution of the throat-pitch ratio s / t in the blade height direction of the turbine blade is The throat pitch ratio s / t at a 25% blade height position is smaller than a line segment connecting the throat pitch ratio s / t of a blade root portion including the blade root and the throat pitch ratio s / t of a central portion in the blade height direction of the turbine rotor blade, and the throat pitch ratio s / t at a 75% blade height position is smaller than a line segment connecting the throat pitch ratio s / t of the central portion and the throat pitch ratio s / t of the blade tip portion including the blade tip.

[0007] In accordance with at least one embodiment of the present disclosure, an axial turbine is provided that can improve the overall efficiency of the axial turbine.

[0008] FIG. 1 is a schematic half sectional view along the axial direction of an axial turbine according to an embodiment of the present disclosure. FIG. 2 is a schematic sectional view of a turbine rotor blade according to an embodiment of the present disclosure. FIG. 3 is an explanatory view for explaining the distribution of the throat pitch ratio of the turbine rotor blade with respect to the blade height position according to an embodiment of the present disclosure. FIG. 4 is an explanatory view for explaining the distribution of the throat pitch ratio of the turbine rotor blade with respect to the blade height position according to an embodiment of the present disclosure. FIG. 5 is a schematic half sectional view along the axial direction of an axial turbine according to a comparative example. FIG. 6 is a schematic sectional view along the axial direction of an axial turbine according to an embodiment of the present disclosure. FIG. 7 is a schematic sectional view perpendicular to the axial direction of an axial turbine according to an embodiment of the present disclosure. FIG. 8 is an explanatory view for explaining the distribution of the axial length of a flow guide portion with respect to the circumferential position according to an embodiment of the present disclosure. FIG. 9 is a schematic sectional view along the axial direction of an axial turbine according to an embodiment of the present disclosure. FIG. 10 is an explanatory view for explaining the distribution of the inclination angle of a trailing edge of a flow guide portion with respect to the axial direction with respect to the circumferential position according to an embodiment of the present disclosure. FIG. 11 is a schematic sectional view along the axial direction of a turbocharger including an axial turbine according to an embodiment of the present disclosure.

[0009] 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 present disclosure.

[0010] (Axial Turbine) Fig. 1 is a schematic half-sectional view along the axial direction of an axial turbine according to an embodiment of the present disclosure. As shown in Fig. 1, an axial turbine 1 according to some embodiments includes a turbine shaft 2 extending along a central rotation axis LA, a turbine rotor blade row 3, and a turbine housing 4.

[0011] Hereinafter, the direction in which the central axis of rotation LA of the turbine shaft 2 extends (the left-right direction in FIG. 1 ) is defined as the axial direction of the turbine shaft 2 (axial flow turbine 1), the direction perpendicular to the central axis of rotation LA is defined as the radial direction of the turbine shaft 2 (axial flow turbine 1), and the circumferential direction around the central axis of rotation LA is defined as the circumferential direction of the turbine shaft 2 (axial flow turbine 1). In this disclosure, the axial direction, radial direction, and circumferential direction of the turbine shaft 2 may be simply referred to as the axial direction, radial direction, and circumferential direction, respectively. Note that, in this disclosure, "along a certain direction" includes not only a certain direction but also a direction inclined within a range of ±15° relative to the certain direction.

[0012] (Turbine Rotor Blade Row) The turbine rotor blade row 3 is attached to the turbine shaft 2 and is composed of a plurality of turbine rotor blades 30 arranged in a row in the circumferential direction of the turbine shaft 2. In the illustrated embodiment, the turbine shaft 2 has a disk portion 22 that protrudes radially outward from the outer circumferential surface 21 of the turbine shaft 2. Each of the plurality of turbine rotor blades 30 has a blade root portion 31 including a blade root 311 connected to the outer circumferential surface 23 of the disk portion 22 of the turbine shaft 2, and a blade tip portion 32 including a blade tip (tip end) 321 that is spaced radially outward of the blade root 311 with respect to the central rotation axis LA. The turbine rotor blade row 3 may be formed integrally with the turbine shaft 2, or may be a separate body from the turbine shaft 2 and fixed to the turbine shaft 2 by welding or the like.

[0013] Figure 2 is a schematic cross-sectional view of a turbine rotor blade 30 according to an embodiment of the present disclosure. As shown in Figure 2, each of the multiple turbine rotor blades 30 has a leading edge 301, a trailing edge 302, a pressure surface 303, and a suction surface 304. The pressure surface 303 has a concavely curved surface on one circumferential side of the turbine shaft 2, one end of which is connected to the leading edge 301 and the other end of which is connected to the trailing edge 302. The suction surface 304 has a convexly curved surface on the other circumferential side of the turbine shaft 2, one end of which is connected to the leading edge 301 and the other end of which is connected to the trailing edge 302. The pressure surface 303 of each of the multiple turbine rotor blades 30 faces, via a circumferential gap, the suction surface 304 of the turbine rotor blade 30A (30) that is arranged adjacent to the one circumferential side of the turbine shaft 2.

[0014] (Turbine Housing) The turbine housing 4 is configured to rotatably accommodate the turbine shaft 2 and the turbine rotor blade row 3. The turbine housing 4 includes an inner annular portion 41 that covers the outer peripheral side (radial outer side) of the outer peripheral surface 21 of the turbine shaft 2 via a radial gap, and an outer annular portion 42 that covers the outer peripheral side (radial outer side) of the outer peripheral surface 411 of the inner annular portion 41 via a radial gap.

[0015] An annular flow passage 43 extending along the axial direction of the turbine shaft 2 is formed between the outer peripheral surface 411 of the inner annular portion 41 and the inner peripheral surface 421 of the outer annular portion 42. The annular flow passage 43 is a flow passage for guiding the working fluid from one axial side (left side in FIG. 1 ) to the other axial side (right side in FIG. 1 ) of the turbine shaft 2. The turbine rotor blade row 3 is arranged in the annular flow passage 43. The blade tip 321 of each of the multiple turbine rotor blades 30 faces the inner peripheral surface 421 of the outer annular portion 42 via a radial gap.

[0016] The axial flow turbine 1 may include a turbine stator vane row 5 arranged upstream of the turbine rotor blade row 3 in the flow direction of the working fluid in the annular flow path 43, i.e., on the one side in the axial direction. The turbine stator vane row 5 is composed of a plurality of turbine stator vanes 50 arranged in a row in the circumferential direction of the turbine shaft 2. In the illustrated embodiment, the outer peripheral end of each of the plurality of turbine stator vanes 50 is connected to the inner peripheral surface 421 of the outer annular portion 42, and the inner peripheral end is connected to the outer peripheral surface 411 of the inner annular portion 41.

[0017] (Exhaust Chamber) As shown in FIG. 1 , the turbine housing 4 has an exhaust chamber 6 downstream of the turbine blade row 3 in the flow direction of the working fluid. The exhaust chamber 6 (turbine housing 4) includes an inner wall 61, a first side wall surface 62, and an second side wall surface 63. The inner wall 61 has at least a convex curved portion that is convex radially inward such that the distance (radial distance) from the rotation center axis LA increases toward the second side in the axial direction of the turbine shaft 2. The first side wall surface 62 and the second side wall surface 63 each extend along the radial direction of the turbine shaft 2. The second side wall surface 63 is located on the second side in the axial direction of the turbine shaft 2 relative to the first side wall surface 62 and faces the first side wall surface 62 with an axial gap therebetween. An exhaust chamber flow path 64 is formed between the first side wall surface 62 and the second side wall surface 63 to guide the working fluid radially outward. The exhaust chamber 6 is formed with an outlet (outlet opening) 65 for discharging the working fluid from an exhaust chamber flow path 64 formed in the exhaust chamber 6. An outer peripheral end 611 of the inner wall 61 is connected to the other side wall surface 63.

[0018] (Flow Guide Portion) As shown in FIG. 1 , the turbine housing 4 includes a flow guide portion 7. The flow guide portion 7 has an inner circumferential wall surface 71 that forms a diffuser passage 70 between itself and the inner wall 61 of the exhaust chamber 6 for guiding the working fluid that has passed through the turbine rotor blade row 3 radially outward. The flow guide portion 7 is disposed inside the exhaust chamber 6. The flow guide portion 7 is an annular body that covers the outer circumferential side (radial outer side) of the inner wall 61 via the diffuser passage 70, and the inner circumferential wall surface 71 faces the inner wall 61 via the diffuser passage 70. The inner circumferential wall surface 71 has at least a convex curved portion that is convex radially inward such that the distance (radial distance) from the rotation center axis LA increases toward the other axial side of the turbine shaft 2.

[0019] An outlet (outlet opening) 73 of the diffuser passage 70 is formed by the trailing edge 72 of the flow guide portion 7 and the portion of the inner wall 61 that is closest to the trailing edge 72. The diffuser passage 70 communicates with the exhaust chamber passage 64 downstream of the diffuser passage 70 via the outlet 73.

[0020] 2 , the throat s is defined as the shortest distance between the trailing edge 302 of a turbine rotor blade 30 and the suction surface 304 of another turbine rotor blade 30A adjacent to that turbine rotor blade 30, and the pitch of the multiple turbine rotor blades 30, 30A arranged in a row is defined as t. The throat pitch ratio s / t is found by dividing the throat s by the pitch t.

[0021] Each of Figures 3 to 5 is an explanatory diagram illustrating the distribution of the throat pitch ratio s / t of the turbine rotor blades 30 with respect to the blade height position in an embodiment of the present disclosure. Figure 6 is a schematic half-sectional view taken along the axial direction of an axial turbine 01 according to a comparative example. As shown in Figure 6, the axial turbine 01 according to the comparative example has the same configuration as the axial turbine 1 according to the present disclosure, except for the turbine rotor blades 30. Figures 3 to 5 show graphs with the blade height position on the horizontal axis and the throat pitch ratio s / t on the vertical axis. Figures 3 to 5 show broken lines L1, L2, and L3 showing the distribution of the throat pitch ratio s / t with respect to the blade height position of two specific examples of the axial turbine 1 according to the present disclosure, and a straight line L4 showing the distribution of the throat pitch ratio s / t with respect to the blade height position of the axial turbine 01 according to the comparative example.

[0022] The direction from the blade root portion 31 (blade root 311) of the turbine rotor blade 30 to the blade tip portion 32 (blade tip 321) is defined as the blade height direction, and the blade height position of the blade root 311 in the blade height direction is defined as 0%, and the blade height position of the blade tip 321 in the blade height direction is defined as 100%. In one embodiment, the blade root portion 31 has a blade height position in the range of 0% to 10%, and the blade tip portion 32 has a blade height position in the range of 90% to 100%. The central portion 33 of the turbine rotor blade 30 in the blade height direction has a blade height position in the range of 40% to 60%.

[0023] 3 to 5 show a line segment LS1 connecting the throat pitch ratio s / t at the blade root portion 31 (0% blade height position, blade root 311 in the illustrated example) and the throat pitch ratio s / t at the central portion 33 (50% blade height position in the illustrated example), and a line segment LS2 connecting the throat pitch ratio s / t at the central portion 33 (50% blade height position in the illustrated example) and the throat pitch ratio s / t at the blade tip portion 32 (100% blade height position, blade tip 321 in the illustrated example).

[0024] In the axial flow turbine 01 according to the comparative example, the throat pitch ratio s / t monotonically decreases toward the blade tip 321 in the blade height direction, as shown by the straight line L4 in Figures 3 to 5. In this case, as shown in Figure 6, separation of the flow of the working fluid from the inner wall 61 that forms the diffuser passage 70 may occur, resulting in a pressure loss in the diffuser passage 70.

[0025] In the axial flow turbine 1 according to some embodiments, as shown in FIGS. 3 to 5 , the distribution of the throat pitch ratios s / t in the blade height direction of the turbine rotor blades 30 described above is configured so that the throat pitch ratio s / t at the 25% blade height position is smaller than the line segment LS1 connecting the throat pitch ratio s / t of the blade root portion 31 and the throat pitch ratio s / t of the central portion 33, and the throat pitch ratio s / t at the 75% blade height position is smaller than the line segment LS2 connecting the throat pitch ratio s / t of the central portion 33 and the throat pitch ratio s / t of the blade tip portion 32.

[0026] The throat pitch ratio s / t distribution in the blade height direction of the turbine rotor blades 30 is shaped so that it is smaller than the line segments LS1 and LS2 at the 25% blade height position and the 75% blade height position, respectively, and the throat pitch ratios s / t of the blade root portion 31 and the blade tip portion 32 of the turbine rotor blades 30 are made relatively large, thereby increasing the flow velocity on each of the inner wall 61 side and the inner peripheral wall surface 71 side in the diffuser passage 70. This makes it possible to suppress separation of the flow of the working fluid from each of the inner wall 61 and the inner peripheral wall surface 71 that form the diffuser passage 70, and ultimately to suppress a decrease in the efficiency of the axial flow turbine 1 as a whole. Furthermore, by making the throat-pitch ratio s / t of the central portion 33 of the turbine rotor blade 30 in the blade height direction relatively large, the flow velocity distribution from the inner wall 61 side to the inner peripheral wall surface 71 side at the outlet 73 of the diffuser passage 70 can be made relatively uniform (see FIG. 1 ), thereby improving the pressure recovery performance of the exhaust chamber 6 and the efficiency of the entire axial flow turbine 1.

[0027] In the axial flow turbine 1 according to some embodiments, as shown by the broken lines L1 and L2 in FIGS. 3 and 4 , the turbine rotor blades 30 described above are configured so that the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blades 30 has a maximum value E1 formed between the blade root portion 31 and the blade tip portion 32, a blade root-side minimum value E2 formed between the blade root portion 31 and the maximum value E1, and a blade tip-side minimum value E3 formed between the maximum value E1 and the blade tip portion 32.

[0028] 3 and 4, the throat pitch ratio s / t of the blade root portion 31 is larger than the blade root side minimum value E2, and the throat pitch ratio s / t gradually decreases from the blade root 311 toward the blade root side minimum value E2 in the blade height direction. The throat pitch ratio s / t gradually increases from the blade root side minimum value E2 toward the blade root side maximum value E1 in the blade height direction.

[0029] In the embodiment shown in Figures 3 and 4, the throat pitch ratio s / t gradually decreases from the maximum value E1 to the tip-side minimum value E3 in the blade height direction. The throat pitch ratio s / t of the blade tip 32 is larger than the tip-side minimum value E3, and the throat pitch ratio s / t gradually increases from the tip-side minimum value E3 to the blade tip 321 in the blade height direction. The blade root-side minimum value E2 may be larger than the tip-side minimum value E3, smaller than the tip-side minimum value E3, or the same as the tip-side minimum value E3. The throat pitch ratio s / t of the maximum value E1 may be larger or smaller than those of the blade root 31 and the blade tip 32.

[0030] The distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blades 30 is shaped to have a maximum value E1, a root-side minimum value E2, and a tip-side minimum value E3, and the throat pitch ratios s / t of the root portion 31, the tip portion 32, and the central portion 33 of the turbine rotor blades 30 are made relatively large, thereby making it possible to make the flow velocity distribution from the inner wall 61 side to the inner circumferential wall surface 71 side at the outlet 73 of the diffuser flow passage 70 relatively uniform, thereby improving the pressure recovery performance of the exhaust chamber 6 and the efficiency of the axial flow turbine 1 as a whole.

[0031] 3 and 4, the above-described turbine rotor blades 30 are formed so that the maximum value E1 of the throat pitch ratio s / t is within a blade height position range of 40% to 60%. By maximizing the throat pitch ratio s / t at the center portion (range of 40% to 60%) in the blade height direction of the turbine rotor blades 30, the flow velocity distribution from the inner wall 61 side to the inner circumferential wall surface 71 side at the outlet 73 of the diffuser passage 70 can be made more uniform, and the pressure recovery performance of the exhaust chamber 6 and the efficiency of the entire axial flow turbine 1 can be more effectively improved.

[0032] 3 and 4, the minimum value E2 of the throat pitch ratio s / t at the blade root side is preferably formed within a blade height range of 20% to 30%. The minimum value E3 of the throat pitch ratio s / t at the blade tip side is preferably formed within a blade height range of 70% to 80%.

[0033] In some embodiments, the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade 30 may be configured not to have the maximum value E1, the root-side minimum value E2, and the tip-side minimum value E3. For example, in the embodiment shown in Fig. 5, the throat pitch ratio s / t at the 25% blade height position is larger than the throat pitch ratio s / t at the central portion 33 (specifically, the 50% blade height position).

[0034] In some embodiments, the above-described turbine rotor blade 30 is configured so that the throat pitch ratio s / t has a maximum value at the blade root portion 31 (the blade root 311 in the illustrated example), as shown in Figures 3 to 5. Note that the throat pitch ratio s / t may also have a maximum value at a blade height position in the blade root portion 31 other than the blade root 311. Because the axial flow turbine 1 is structured to direct the working fluid radially outward, separation of the flow of the working fluid is likely to occur from the inner wall 61 that forms the blade root 31 side of the diffuser passage 70. By maximizing the throat pitch ratio s / t at the blade root 31, separation of the flow of the working fluid from the inner wall 61 that forms the blade root 31 side of the diffuser passage 70 can be more reliably suppressed.

[0035] FIG. 7 is a schematic cross-sectional view taken along the axial direction of an axial flow turbine 1 according to an embodiment of the present disclosure. FIG. 8 is a schematic cross-sectional view perpendicular to the axial direction of the axial flow turbine 1 according to an embodiment of the present disclosure. FIG. 8 schematically illustrates a cross section taken along line A-B shown in FIG. 7. As shown in FIG. 8, the turbine housing 4 has an outlet 65 of the exhaust chamber 6 formed in a portion of its circumferential direction for discharging the working fluid from the exhaust chamber 6. As shown in FIG. 8, in the circumferential direction, with respect to a reference line LB that passes through the rotation center C of the turbine shaft 2 and is parallel to the outlet 65 of the exhaust chamber 6, the side on which the outlet 65 of the exhaust chamber 6 is located (the upper side in the drawing) is defined as the exhaust side, and the side away from the outlet 65 of the exhaust chamber 6 with respect to the reference line LB (the lower side in the drawing) is defined as the anti-exhaust side.

[0036] In the illustrated embodiment, the outlet 65 of the exhaust chamber 6 is formed above in the vertical direction relative to the center of rotation C of the turbine shaft 2, with the side above the center of rotation C being the exhaust side and the side below the center of rotation C being the anti-exhaust side. In the cross-sectional view shown in Fig. 8 , the reference line LB is perpendicular to the axis LC of the outlet 65 of the exhaust chamber 6. In the cross-sectional view shown in Fig. 8 , the exhaust chamber 6 includes an anti-exhaust side wall surface 66 formed in an arc shape on the anti-exhaust side, and an exhaust side wall surface 67 formed along the axis LC on the exhaust side.

[0037] Hereinafter, the circumferential angle positions of the two intersections of the reference line LB with the wall surface of the exhaust chamber 6 are defined as 90° and 270°, respectively, and the range of 90° to 270° is defined as the circumferential angle α (see FIG. 8 ) on the exhaust side.

[0038] In some embodiments, as shown in Fig. 7 , the flow guide section 7 is configured so that the outlet area AU of the diffuser passage 70 in at least a portion on the exhaust side is larger than the outlet area AL of the diffuser passage 70 on the opposite side to the exhaust side. As shown in Fig. 7 , the opening area at the trailing edge 312 of the root 311 of the turbine rotor blade 30 is defined as the inlet area A1 of the diffuser passage 70. The opening area of ​​the diffuser passage 70 increases toward the downstream side of the diffuser passage 70.

[0039] Because the diffuser passage 70 is a deceleration passage for decelerating the working fluid, increasing the area ratio, which is the ratio of the outlet area to the inlet area of ​​the diffuser passage 70, within a range in which separation of the working fluid from the wall surfaces forming the diffuser passage 70 does not occur, can reduce the discharge speed of the working fluid from the diffuser passage 70 and reduce the exhaust loss of the axial flow turbine 1. By increasing the flow velocities on the inner wall 61 side and the inner peripheral wall surface 71 side at the outlet 73 of the diffuser passage 70, separation of the working fluid from the wall surfaces forming the diffuser passage 70 occurs on the side with a higher area ratio, effectively reducing the exhaust loss of the axial flow turbine 1. Furthermore, the area ratio can be made larger on the exhaust side, which has a higher separation tolerance, than on the opposite side to the exhaust side, thereby more effectively reducing the exhaust loss of the axial flow turbine 1.

[0040] In some embodiments, as shown in FIG. 7 , the axial length LFU of the flow guide portion 7 on at least a portion of the exhaust side is smaller than the axial length LFL of the flow guide portion 7 on the opposite side to the exhaust side.

[0041] FIG. 9 is an explanatory diagram illustrating the distribution of the axial length LF of the flow guide portion 7 with respect to the circumferential position in one embodiment of the present disclosure. The curve L6 shown in FIG. 9 indicates the distribution of the axial length LF of the flow guide portion 7 with respect to the circumferential position in the embodiment shown in FIG. 7 . The straight line L7 shown in FIG. 9 indicates the flow guide portion 7 with a constant axial length LF. As shown in FIG. 9 , the axial length LF (LFU) is smallest at the center on the exhaust side (where the circumferential angle α is in the range of 160° to 200°) and is largest at the center on the opposite side (where the circumferential angle α is in the range of 0° to 20° or 340° to 360°). The axial length LF gradually increases from the center on the exhaust side toward the center on the opposite side. In the embodiment shown in FIG. 9 , the axial length LF (LFU) is smallest when the circumferential angle α is 180° and is largest when the circumferential angle α is 0°. In one embodiment, the minimum length of the axial length LF is shorter than the maximum length by up to 5%. Also, in one embodiment, when the axial length from the trailing edge 312 of the blade root 311 of the turbine rotor blade 30 to the one side wall surface 62 is defined as L5, the axial length LF of the flow guide portion 7 is 50% to 70% of L5 around the entire circumference.

[0042] By making the axial length LFU of the flow guide portion 7 on the exhaust side smaller than the axial length LFL on the opposite side to the exhaust side, the area ratio on the exhaust side can be made larger than that on the opposite side to the exhaust side, thereby more effectively reducing the exhaust loss of the axial flow turbine 1.

[0043] 10 is a schematic cross-sectional view along the axial direction of an axial flow turbine 1 according to an embodiment of the present disclosure. In some embodiments, as shown in Fig. 10, the above-mentioned flow guide portion 7 has an inclination angle θU of the trailing edge 72 of the flow guide portion 7 with respect to the axial direction in at least a part of the exhaust side that is larger than an inclination angle θL of the trailing edge 72 of the flow guide portion 7 with respect to the axial direction in the opposite side to the exhaust side.

[0044] FIG. 11 is an explanatory diagram illustrating the distribution of the inclination angle θ of the trailing edge 72 of the flow guide portion 7 relative to the axial direction with respect to the circumferential position in one embodiment of the present disclosure. The curve L8 shown in FIG. 11 illustrates the distribution of the inclination angle θ of the trailing edge 72 of the flow guide portion 7 relative to the axial direction with respect to the circumferential position in the embodiment shown in FIG. 10. The straight line L9 shown in FIG. 11 illustrates a case where the inclination angle θ is constant. As shown in FIG. 11, the inclination angle θ (θU) is maximum at the center on the exhaust side (where the circumferential angle α is in the range of 160° to 200° or in the range of 340° to 360°), and the inclination angle θ (θL) is minimum at the center on the opposite side (where the circumferential angle α is in the range of 0° to 20° or in the range of 340° to 360°). The inclination angle θ gradually decreases from the center on the exhaust side toward the center on the opposite side. 11, the inclination angle θ (θU) is maximum when the circumferential angle α is 180°, and the axial length inclination angle θ (θL) is minimum when the circumferential angle α is 0°. In one embodiment, the maximum angle of the inclination angle θ is 5° or more greater than the minimum angle.

[0045] By making the inclination angle θU on the exhaust side of the flow guide portion 7 larger than the inclination angle θL on the opposite side to the exhaust side, the area ratio on the exhaust side can be made larger than that on the opposite side to the exhaust side, which makes it possible to more effectively reduce exhaust loss in the axial flow turbine 1. Note that in some embodiments, the axial length LFU of the exhaust side of the flow guide portion 7 may be made smaller than the axial length LFL of the opposite side to the exhaust side, and the inclination angle θU of the exhaust side of the flow guide portion 7 may be made larger than the inclination angle θL on the opposite side to the exhaust side.

[0046] In an axial turbine 1 according to some embodiments, as shown in Figures 1, 7, and 10, the turbine rotor blade row 3 included in the axial turbine 1 is a single stage. In the embodiments shown in Figures 1, 7, and 10, the turbine stator vane row 5 included in the axial turbine 1 is also a single stage. When the turbine rotor blade row 3 included in the axial turbine 1 is a single stage, improvements in the efficiency of the diffuser passage 70 and the exhaust chamber 6 have a greater impact on improving the efficiency of the entire axial turbine 1 than improvements in the efficiency of the turbine rotor blade row 3. The distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blades 30 may be shaped to be smaller than the line segments LS1 and LS2 at the 25% blade height position and the 75% blade height position, respectively, or may be shaped to have a maximum value E1, a blade root-side minimum value E2, and a blade tip-side minimum value E3, thereby improving the efficiency of the diffuser passage 70 and the exhaust chamber 6, and thereby effectively improving the efficiency of the entire axial turbine 1.

[0047] Fig. 12 is a schematic cross-sectional view along the axial direction of a turbocharger 100 including an axial turbine 1 according to an embodiment of the present disclosure. In some embodiments, as shown in Fig. 12, the above-mentioned axial turbine 1 is mounted on the turbocharger 100. The turbocharger 100 includes the axial turbine 1 and a centrifugal compressor 101 attached to a turbine shaft 2 of the axial turbine 1. The centrifugal compressor 101 is configured to be driven in conjunction with rotation of the turbine shaft 2 of the axial turbine 1, which is driven by exhaust gas (working fluid) discharged from an internal combustion engine (not shown), and to compress charge air guided to the internal combustion engine.

[0048] Since there is a demand for a compact size of the axial turbine 1 mounted on the turbocharger 100, the axial turbine 1 has a diffuser passage 70 for guiding the exhaust gas, which is the working fluid, outward in the radial direction. By using the axial turbine 1 having such a diffuser passage 70 as the axial turbine 1 according to some of the above-described embodiments, the efficiency of the entire axial turbine 1 can be improved.

[0049] In this specification, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, 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 expressing that things are in an equal state, such as "identical," "equal," and "homogeneous," not only express a state in which there is a strict equivalence, but also express a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions expressing shapes such as a rectangular shape or a cylindrical shape not only express shapes such as a rectangular shape or a cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0050] 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.

[0051] The contents of the above-described embodiments can be understood, for example, as follows.

[0052] 1) An axial flow turbine (1) according to at least one embodiment of the present disclosure comprises: a turbine shaft (2); a turbine rotor blade row (3) attached to the turbine shaft (2) and configured with a plurality of turbine rotor blades (30) arranged in a row in the circumferential direction of the turbine shaft (2); and a turbine housing (4) rotatably accommodating the turbine rotor blade row (3) and having an exhaust chamber (6) downstream of the turbine rotor blade row (3), wherein the turbine housing (4) includes a flow guide portion (7) having an inner peripheral wall surface (71) that forms a diffuser flow path (70) between the inner wall (61) of the exhaust chamber (6) and the flow guide portion (7) for guiding a working fluid that has passed through the turbine rotor blade row (3) radially outward; When the shortest distance between the trailing edge (302) of the turbine rotor blade (30) and the suction surface (304) of another turbine rotor blade (30A) adjacent to the turbine rotor blade (30) is defined as a throat s, the pitch of the plurality of turbine rotor blades (30, 30A) arranged in a row is defined as t, and the blade height position of the blade root (311) in the blade height direction from the blade root (311) to the blade tip (321) of the turbine rotor blade (30) is defined as 0% and the blade height position of the blade tip (321) is defined as 100%, the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade (30) is The throat pitch ratio s / t at a 25% blade height position is smaller than a line segment (LS1) connecting the throat pitch ratio s / t of a blade root portion (31) including the blade root (311) and the throat pitch ratio s / t of a central portion (33) in the blade height direction of the turbine rotor blade (30), and the throat pitch ratio s / t at a 75% blade height position is smaller than a line segment (LS2) connecting the throat pitch ratio s / t of the central portion (33) and the throat pitch ratio s / t of a blade tip portion (32) including the blade tip (321).

[0053] According to the configuration 1), the throat pitch ratio s / t distribution in the blade height direction of the turbine rotor blade (30) is shaped so that it is smaller than the line segments (LS1, LS2) at the 25% blade height position and the 75% blade height position, and the throat pitch ratios s / t of the blade root portion (31) and the blade tip portion (32) of the turbine rotor blade (30) are made relatively large, thereby making it possible to increase the flow velocities on the inner wall (61) side and the inner circumferential wall surface (71) side in the diffuser flow passage (70). This makes it possible to suppress separation of the flow of the working fluid from the inner wall (61) and the inner circumferential wall surface (71) that form the diffuser flow passage (70), and ultimately to suppress a decrease in the efficiency of the axial flow turbine (1) as a whole. Furthermore, by making the throat pitch ratio s / t of the central portion (33) in the blade height direction of the turbine rotor blade (30) relatively large, the flow velocity distribution from the inner wall (61) side to the inner circumferential wall surface (71) side at the outlet (73) of the diffuser flow passage (70) can be made relatively uniform, thereby improving the pressure recovery performance of the exhaust chamber (6) and the efficiency of the entire axial flow turbine (1).

[0054] 2) In some embodiments, in the axial flow turbine (1) described in 1), the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade (30) is configured to have a maximum value (E1) formed between the blade root portion (31) and the blade tip portion (32), a blade root side minimum value (E2) formed between the blade root portion (31) and the maximum value (E1), and a blade tip side minimum value (E3) formed between the maximum value (E1) and the blade tip portion (32).

[0055] According to the configuration 2), the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade (30) is shaped to have a maximum value (E1), a root-side minimum value (E2), and a tip-side minimum value (E3), and the throat pitch ratios s / t of the root portion (31), the tip portion (32), and the central portion (33) of the turbine rotor blade (30) are made relatively large, thereby making it possible to make the flow velocity distribution from the inner wall (61) side to the inner circumferential wall surface (71) side at the outlet (73) of the diffuser flow path (70) relatively uniform, thereby improving the pressure recovery performance of the exhaust chamber (6) and the efficiency of the entire axial-flow turbine (1).

[0056] 3) In some embodiments, in the axial flow turbine (1) described in 1) or 2) above, the turbine rotor blade (30) is configured so that the throat pitch ratio s / t has a maximum value at the blade root portion (31).

[0057] According to the configuration 3), the axial flow turbine (1) is structured to guide the working fluid radially outward, and therefore separation of the flow of the working fluid from the wall surface (inner wall 61) forming the blade root portion (31) side of the diffuser flow passage (70) is likely to occur. By maximizing the throat pitch ratio s / t at the blade root portion (31), separation of the flow of the working fluid from the wall surface (inner wall 61) forming the blade root portion (31) side of the diffuser flow passage (70) can be more reliably suppressed.

[0058] 4) In some embodiments, in the axial flow turbine (1) described in 2), the turbine rotor blade (30) is formed such that the maximum value (E1) of the throat pitch ratio s / t is formed within a range of the blade height position of 40% or more and 60% or less.

[0059] According to the configuration of 4), the throat pitch ratio s / t is maximized in the central portion (in the range of 40% to 60%) of the turbine rotor blades in the blade height direction, thereby making it possible to make the flow velocity distribution from the inner wall (61) side to the inner circumferential wall surface (71) side at the outlet (73) of the diffuser flow passage (70) more uniform, thereby more effectively improving the pressure recovery performance of the exhaust chamber (6) and the efficiency of the entire axial flow turbine (1).

[0060] 5) In some embodiments, in the axial flow turbine (1) according to any one of 1) to 4) above, the turbine housing (4) is formed with an outlet (65) of the exhaust chamber (6) for discharging the working fluid from the exhaust chamber (6) at a part in the circumferential direction, and in the circumferential direction, when a side where the outlet (65) of the exhaust chamber (6) is located with respect to a reference line (LB) that passes through a rotation center (C) of the turbine shaft (2) and is parallel to the outlet (65) of the exhaust chamber (6) is defined as an exhaust side, and a side away from the outlet (65) of the exhaust chamber (6) with respect to the reference line (LB) is defined as a counter-exhaust side, the flow guide portion (7) is configured so that an outlet area (AU) of the diffuser flow path (70) in at least a part of the exhaust side is larger than an outlet area (AL) of the diffuser flow path (70) on the counter-exhaust side.

[0061] According to the configuration of 5) above, the diffuser passage (70) is a deceleration passage for decelerating the working fluid. Therefore, by increasing the area ratio, which is the ratio of the outlet area of ​​the diffuser passage (70) to the inlet area, within a range in which separation of the flow of the working fluid from the wall surfaces forming the diffuser passage (70) does not occur, the discharge speed of the working fluid from the diffuser passage (70) can be reduced, thereby reducing the exhaust loss of the axial-flow turbine (1). By increasing the flow velocities on the inner wall (61) side and the inner peripheral wall surface (71) side at the outlet of the diffuser passage (70), separation of the flow of the working fluid from the wall surfaces forming the diffuser passage (70) occurs on the side with a higher area ratio, thereby effectively reducing the exhaust loss of the axial-flow turbine (1). Furthermore, the area ratio can be made larger on the exhaust side, which has a higher separation margin, than on the opposite side to the exhaust side, thereby more effectively reducing the exhaust loss of the axial-flow turbine (1).

[0062] 6) In some embodiments, in the axial flow turbine (1) described in 5) above, the flow guide portion (7) has an axial length (LFU) of the inner wall surface (71) on at least a portion of the exhaust side that is smaller than the axial length (LFL) of the inner wall surface (71) on the opposite exhaust side.

[0063] According to the configuration 6) above, the axial length (LFU) of the flow guide portion (7) on the exhaust side is made smaller than the axial length (LFL) on the opposite side to the exhaust side, so that the area ratio on the exhaust side can be made larger than that on the opposite side to the exhaust side, thereby more effectively reducing the exhaust loss of the axial flow turbine (1).

[0064] 7) In some embodiments, in the axial turbine (1) described in 5) or 6) above, the flow guide portion (7) has an inclination angle (θU) of the trailing edge end (72) of the flow guide portion (7) with respect to the axial direction in at least a portion of the exhaust side that is greater than an inclination angle (θL) of the trailing edge end of the flow guide portion (7) with respect to the axial direction on the opposite exhaust side.

[0065] According to the configuration of 7) above, by making the inclination angle (θU) on the exhaust side of the flow guide portion (7) larger than the inclination angle (θL) on the opposite side to the exhaust side, the area ratio on the exhaust side can be made larger than that on the opposite side to the exhaust side, thereby more effectively reducing the exhaust loss of the axial flow turbine (1).

[0066] 8) In some embodiments, the axial turbine (1) according to any one of 1) to 7) above, wherein the turbine rotor blade row (3) included in the axial turbine (1) is a single stage.

[0067] According to the configuration of 8) above, when the axial turbine (1) has a single stage of turbine blade row (3), the improvement in efficiency in the diffuser passage (70) and the exhaust chamber (6) has a greater impact on the improvement in the efficiency of the entire axial turbine (1) than the improvement in efficiency in the turbine blade row (3). The distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade (30) is shaped so that the 25% blade height position and the 75% blade height position are smaller than the line segments (LS1, LS2), or is shaped so as to have a maximum value (E1), a blade root side minimum value (E2), and a blade tip side minimum value (E3), thereby improving the efficiency of the diffuser passage (70) and the exhaust chamber (6), and thereby effectively improving the efficiency of the entire axial turbine (1).

[0068] 9) In some embodiments, the axial turbine (1) according to any one of 1) to 8) above, wherein the axial turbine (1) is mounted on a turbocharger (100).

[0069] According to the configuration of 9) above, the axial turbine (1) mounted on the turbocharger (100) has a diffuser passage (70) for guiding the working fluid radially outward, since there is a demand for a compact size. The axial turbine (1) having such a diffuser passage (70) can improve the efficiency of the entire axial turbine (1) by being provided with any of the configurations of 1) to 7) above.

[0070] REFERENCE SIGNS LIST 1, 01 axial flow turbine 2 turbine shaft 3 turbine rotor blade row 4 turbine housing 5 turbine stator blade row 6 exhaust chamber 7 flow guide section 30, 30A turbine rotor blade 31 blade root section 32 blade tip section 33 center section 41 inner annular section 42 outer annular section 43 annular flow passage 50 turbine stator blade 61 inner wall 64 exhaust chamber flow passage 65 outlet 70 diffuser flow passage 71 inner peripheral side wall surface 72 trailing edge 73 outlet 100 turbocharger 101 centrifugal compressor 311 blade root 312 blade tip E1 maximum value E2 blade root side minimum value E3 blade tip side minimum value

Claims

1. A turbine shaft, a turbine blade cascade attached to the turbine shaft and arranged in a row in the circumferential direction of the turbine shaft, and a turbine housing rotatably housing the turbine blade cascade and having an exhaust chamber downstream of the turbine blade cascade, wherein the turbine housing includes a flow guide portion having an inner circumferential wall surface which forms a diffuser flow passage between an inner wall of the exhaust chamber and the inner wall of the flow guide portion for guiding a working fluid which has passed through the turbine blade cascade to the radially outward side, wherein the shortest distance between the trailing edge of the turbine blade and the suction surface of another turbine blade adjacent to the turbine blade is defined as a throat s, the pitch of the plurality of turbine blades arranged in a row is defined as t, the blade height position of the blade root in the blade height direction from the blade root to the blade tip of the turbine blade is defined as 0%, and the blade height position of the blade tip is defined as 100%, the distribution of the throat pitch ratio s / t in the blade height direction of the turbine blade is An axial flow turbine configured such that the throat pitch ratio s / t at a 25% blade height position is smaller than a line segment connecting the throat pitch ratio s / t of a blade root portion including the blade root and the throat pitch ratio s / t of a central portion in the blade height direction of the turbine blade, and the throat pitch ratio s / t at a 75% blade height position is smaller than a line segment connecting the throat pitch ratio s / t of the central portion and the throat pitch ratio s / t of a blade tip portion including the blade tip.

2. An axial flow turbine as claimed in claim 1, wherein the distribution of the throat pitch ratio s / t in the blade height direction of the turbine rotor blade is configured to have a maximum value formed between the blade root and the blade tip, a blade root side minimum value formed between the blade root and the maximum value, and a blade tip side minimum value formed between the maximum value and the blade tip.

3. An axial flow turbine according to claim 1 or 2, wherein the turbine rotor blade is configured so that the throat pitch ratio s / t has a maximum value at the blade root portion.

4. An axial flow turbine according to claim 2, wherein the turbine rotor blade has the maximum value of the throat pitch ratio s / t formed within a range of the blade height position of 40% or more and 60% or less.

5. An axial flow turbine as claimed in claim 1 or 2, wherein the turbine housing has an exhaust chamber outlet formed at a part in the circumferential direction for discharging the working fluid from the exhaust chamber, and in the circumferential direction, when a side on which the exhaust chamber outlet is located is defined as an exhaust side with respect to a reference line passing through the center of rotation of the turbine shaft and parallel to the exhaust chamber outlet, and a side away from the exhaust chamber outlet with respect to the reference line is defined as a counter-exhaust side, the flow guide portion is configured such that an outlet area of ​​the diffuser flow passage in at least a part of the exhaust side is larger than an outlet area of ​​the diffuser flow passage on the counter-exhaust side.

6. An axial flow turbine according to claim 5, wherein the axial length of the flow guide portion in at least a portion of the exhaust side is smaller than the axial length of the flow guide portion in the opposite exhaust side.

7. An axial flow turbine as described in claim 5, wherein the inclination angle of the trailing edge of the flow guide portion with respect to the axial direction in at least a portion of the exhaust side is greater than the inclination angle of the trailing edge of the flow guide portion with respect to the axial direction on the anti-exhaust side.

8. An axial flow turbine according to claim 1 or 2, wherein the turbine rotor blade row included in the axial flow turbine is a single stage.

9. The axial flow turbine according to claim 1 or 2, wherein the axial flow turbine is mounted on a turbocharger.

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