TURBINE AND TURBOCHARGER

Abstract

Turbine (2), comprising: a turbine wheel (3) configured to rotate about an axis; a turbine housing (5) that accommodates the turbine wheel (3) and defines an annular nozzle passage (4) on an outer circumferential side of the turbine wheel (3); and a plurality of nozzle blades (6, 6a, 6b) with a small chord ratio, which are arranged in an interval in a circumferential direction in the nozzle passage (4), wherein circumferentially adjacent nozzle blades (6, 6a, 6b) do not overlap, wherein circumferentially adjacent nozzle blades (6, 6a, 6b) with small chord ratio are arranged at different radial positions in a connection position of each of the nozzle blades (6, 6a, 6b) with small chord ratio with a hub-side wall surface (5a) and a casing-side wall surface (5b) that define the nozzle passage (4).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a turbine and a turbocharger. BACKGROUND

[0002] Radial turbines and mixed-flow turbines equipped with a flow rate adjustment mechanism for exhaust gas to be introduced into the turbine are widely used as small gas turbines or expansion turbines used in power generation engines or turbochargers mounted on automobile engines due to advantages such as variable turbine speed and variable turbine power or ensuring high responsiveness to changes in engine power.

[0003] A turbocharger equipped with the radial turbine or the mixed flow turbine is configured to, for example, rotate the turbine by exhaust gas from the engine, in turn rotate a compressor coaxially connected to the turbine to compress intake air and supply the compressed air to the engine.

[0004] On the other hand, the exhaust gas flow rate adjusting mechanism is configured by arranging nozzle vanes in the circumferential direction in an annular nozzle passage defined by a turbine casing on the outer peripheral side of the turbine wheel.

[0005] Some exhaust gas flow rate adjusting mechanisms are provided with a plurality of variable nozzle vanes rotated by driving an actuator so that, in the closing operation, the leading edge of one of the adjacent nozzle vanes overlaps the trailing edge of the other nozzle vane to close the passage, and are configured to freely adjust the size of the exhaust gas passage, that is, the flow rate of exhaust gas according to the rotation amount of each variable nozzle vane.

[0006] Furthermore, some exhaust gas flow rate adjusting mechanisms are provided with a plurality of small chord ratio nozzle vanes fixedly arranged at an interval (gap serving as the passage) in the circumferential direction, and are configured to automatically adjust the flow rate of exhaust gas according to the magnitude of the exhaust gas pressure (see, for example, Patent Document 1). Citation listPatent literature

[0007] Patent Document 1: JP2018-123802A

[0008] DE 11 2012 003 648 T5 discloses a radial gas expander provided with a rotary shaft, a vane fixed to the rotary shaft, and a housing by which the rotary shaft is rotatably supported and in which an introduction channel is formed which introduces a fluid to the vane.

[0009] DE 694 05 806 T2 relates to a centrifugal compressor having a centrifugal impeller and a guide vane diffuser arranged downstream of the impeller, which has a pair of diffuser plates and a plurality of guide vanes arranged between the pair of diffuser plates in the form of a circular cascade.

[0010] DE 11 2009 004 260 T5 relates to a simplified, low-cost variable nozzle for controlling the exhaust gas flow to a turbine wheel in a variable flow turbocharger.

[0011] US 5 178 516 A discloses a centrifugal compressor having diffusers that convert a high-velocity, low-pressure liquid stream flowing from an impeller into a high-velocity, high-pressure stream through the action of a plurality of stator vanes arranged near the outer periphery of the impeller. SUMMARYProblems to be solved

[0012] On the other hand, the turbocharger is operated under exhaust gas pulsation of the engine, and the exhaust pressure at the inlet of the turbine fluctuates greatly.

[0013] Therefore, the turbine can often be operated at an operating point that differs significantly from the design point (design power). In such a case, the turbine efficiency is reduced.

[0014] Conventional measures to control turbine power reduction include controlling the throat area according to the turbine flow rate by applying variable nozzle blades or reducing changes in the relative flow angle of the blade in response to the pressure fluctuation by applying small chord ratio nozzle blades.

[0015] However, the application of variable nozzle vanes complicates the turbocharger structure, and the use of only small chord ratio nozzle vanes does not significantly improve the incidence characteristics of the vanes.

[0016] The present disclosure has been made in view of the above problems, and an object thereof is to provide a turbine and a turbocharger incorporating the same, whereby it is possible to improve the blade incidence characteristics more than heretofore by using only small chord ratio nozzle blades without using variable nozzle blades having a complicated structure when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, and it is possible to improve the turbine efficiency. Solution to the problems

[0017] A turbine according to one aspect of the present disclosure is provided with: a turbine wheel configured to rotate about an axis; a turbine casing that houses the turbine wheel and defines an annular nozzle passage on an outer peripheral side of the turbine wheel; and a plurality of small-chord ratio nozzle blades arranged in the nozzle passage at an interval in a circumferential direction. Circumferentially adjacent nozzle blades do not overlap. Furthermore, circumferentially adjacent small-chord ratio nozzle blades are arranged at different radial positions in a connecting position of each of the small-chord ratio nozzle blades with a hub-side wall surface and a shroud-side wall surface defining the nozzle passage.

[0018] Further, according to one aspect of the present disclosure, a turbine is provided, including: a turbine wheel configured to rotate about an axis; a turbine casing that houses the turbine wheel and defines an annular nozzle passage on an outer peripheral side of the turbine wheel; and a plurality of small-chord ratio nozzle blades arranged in the nozzle passage at an interval in a circumferential direction. Circumferentially adjacent small-chord ratio nozzle blades have different chord lengths at a connecting position of each of the small-chord ratio nozzle blades with a hub-side wall surface, the hub-side wall surface, and a shroud-side wall surface defining the nozzle passage.

[0019] Further, according to one aspect of the present disclosure, a turbine is provided, comprising: a turbine wheel configured to rotate about an axis; a turbine housing that houses the turbine wheel and defines an annular nozzle passage on an outer peripheral side of the turbine wheel; and a plurality of low-pitch nozzle blades arranged in the nozzle passage at an interval in a circumferential direction. Each of the plurality of low-pitch nozzle blades is configured such that a trailing edge blade height is greater than a leading edge blade height.

[0020] A turbocharger according to one aspect of the present disclosure is provided with the turbine described above. Beneficial effects

[0021] With a turbine and a turbocharger incorporating the same according to one aspect of the present disclosure, when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, it is possible to greatly improve the blade incidence characteristics by using only small chord ratio nozzles without using variable nozzles having a complicated structure, and it is possible to improve the turbine efficiency more than heretofore. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a turbine according to one aspect. Fig. 2 is a diagram showing a nozzle passage and a flow rate adjusting mechanism of a turbine according to one aspect. Fig. 3 is a diagram showing a flow rate adjusting mechanism of a turbine according to the first embodiment and showing the arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes). Fig. Fig. 4 is a diagram showing the turbine according to the first embodiment and the flow rate adjusting mechanism of the turbine and S-section in Fig. 1 shows. Fig. 5 is a diagram showing a flow rate adjusting mechanism of a turbine according to the second embodiment, and showing the arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes) viewed from the shroud side. Fig. 6 is a diagram showing a flow rate adjusting mechanism of a turbine according to the second embodiment, and showing the arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes) viewed from the shroud side. Fig. Fig. 7 is a diagram showing the turbine according to the second embodiment and the flow rate adjusting mechanism of the turbine, and showing the S-section in Fig. 1 shows. Fig. 8 is a diagram showing a flow rate adjusting mechanism of a turbine according to the third embodiment, and showing the shape and arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes). Fig. 9 is a diagram showing the turbine according to the third embodiment and the nozzle vanes (first nozzle vanes and second nozzle vanes) of the flow rate adjusting mechanism of the turbine. Fig. 10 is a diagram showing a flow rate adjusting mechanism of a turbine according to the fourth embodiment, and showing the shape and arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes). Fig. 11 is a diagram showing the turbine according to the fourth embodiment and the flow rate adjusting mechanism of the turbine, and showing the S section in Fig. 1 shows. Fig. 12 is a diagram showing a modified example of the flow rate adjusting mechanism of the turbine according to the fourth embodiment, and showing the shape and arrangement of nozzle vanes (first nozzle vanes and second nozzle vanes). Fig. 13 is a diagram showing a modified example of the turbine according to the fourth embodiment and the flow rate adjusting mechanism of the turbine, and showing the S section in Fig. 1 shows. Fig. 14 is a diagram showing a flow rate adjusting mechanism of a turbine according to the fifth embodiment, and showing the shape and arrangement of nozzle vanes. Fig. 15 is a diagram showing the turbine according to the fifth embodiment and the flow rate adjusting mechanism of the turbine, and showing the S-section in Fig. 1 shows. Fig. 16 is a diagram showing the shape of nozzle vanes of a flow rate adjusting mechanism of a turbine according to the sixth embodiment. Fig. 17 is a diagram showing a modified example that combines the configurations of the plurality of nozzle vanes (first nozzle vanes and second nozzle vanes) according to the above-described embodiments. Fig. 18 is a diagram showing a modified example that combines the configurations of the plurality of nozzle vanes (first nozzle vanes and second nozzle vanes) according to the above-described embodiments. Fig. 19 is a diagram showing a modified example that combines the configurations of the plurality of nozzle vanes (first nozzle vanes and second nozzle vanes) according to the above-described embodiments. DETAILED DESCRIPTION (First Embodiment)

[0022] In the following, a turbine and a turbocharger according to the first embodiment will be described with reference to Fig. 1 to Fig. 4 described. (turbocharger)

[0023] The turbocharger according to the present embodiment is a turbocharging device that improves engine performance by utilizing energy from exhaust gas discharged from the engine. This turbocharger rotates a turbine using exhaust gas discharged from the engine, thereby rotating a compressor coaxially connected to the turbine to compress intake air and supply the compressed air to the engine.

[0024] In particular, as in Fig. 1, the turbocharger 1 of the present embodiment includes a radial turbine 2 or a mixed flow turbine (hereinafter, turbine). (Turbine)

[0025] As in Fig. 1, Fig. 2 and Fig. 3, the turbine 2 includes a turbine wheel 3 configured to rotate around an axis O1 of the turbocharger 1, a turbine housing 5 that houses the turbine wheel 3 and forms an annular nozzle passage 4 on the outer peripheral side of the turbine wheel 3 around the axis O1, and a flow rate adjusting mechanism (flow rate adjusting mechanism for exhaust gas G) 7 composed of a plurality of nozzle vanes 6 arranged radially outside the turbine wheel 3 in the nozzle passage 4 at a predetermined interval in the circumferential direction of the turbine wheel 3.

[0026] The turbine wheel 3 includes a truncated cone and a substantially conical turbine hub 12 integrally formed at one end of a rotary shaft 11 rotatably supported by journal bearings 9 and 10 housed in a bearing housing 8 with their axes O1 coaxial, and a plurality of turbine blades 13 arranged on the circumferential surface of the turbine hub 12 at a predetermined interval in the circumferential direction centered on the axis O1.

[0027] At the other end of the rotary shaft 11, a truncated cone and a substantially conical compressor hub 14 is integrally formed, with a plurality of compressor blades 15 arranged on the peripheral surface of the compressor hub 14 at a predetermined interval in the circumferential direction.

[0028] The compressor hub 14 and the compressor blades 15 form a compressor wheel 16. The compressor wheel 16 is accommodated in a compressor housing 17 in a rotatable manner about the axis O1.

[0029] In the present embodiment, a spiral passage 18 communicating with the nozzle passage 4 and allowing the exhaust gas G introduced from outside the turbine housing 5 to flow into the nozzle passage 4, and a discharge passage 19 communicating with the nozzle passage 4 and allowing the exhaust gas G that has driven the turbine wheel 3 to flow out of the turbine housing 5 are provided in the turbine housing 5.

[0030] The spiral passage 18 is a substantially spiral flow passage formed on the outer peripheral side of the nozzle passage 4, and the discharge passage is a tubular flow passage extending along the axis O1.

[0031] The exhaust gas G from the spiral passage 18 flows through the nozzle passage 4 in the radial direction and enters the turbine wheel 3 to rotate the turbine wheel 3 about the axis O1. The exhaust gas G used to rotate the turbine wheel 3 is discharged from the turbine housing 5 through the discharge passage 19.

[0032] On the other hand, for example, each of the nozzle vanes 6 of the flow rate adjusting mechanism 7 is configured to satisfy Lv < Lc / Nv, where Lv is the length (vane length) of a straight line connecting a leading edge 6c and a trailing edge 6d, Lc is the circumference of a trailing edge inscribed circle C1 passing through the trailing edge 6d, and Nv is the number of nozzle vanes.

[0033] That is, the nozzle vanes 6 of the flow rate adjusting mechanism 7 according to the present embodiment are nozzle vanes with a small chord ratio and are arranged so that circumferentially adjacent nozzle vanes 6 do not overlap, and a throat th is formed between the leading edge 6c of one of the adjacent nozzle vanes 6 and the trailing edge 6d of the other nozzle vane 6 (see Fig. 2 and Fig. 3).

[0034] The throat th indicates a section with a minimum width between adjacent nozzle vanes 6.

[0035] Here, the present inventors found that when the throat th is provided to eliminate nozzle overlap, and a difference (θ2-θ1) between the geometric nozzle exit angle θ1 (angle between the central axis connecting the leading edge 6c and the trailing edge 6d of the nozzle vane 6 and the flow direction of the exhaust gas G2 flowing along the nozzle vane 6 prevailing at a low exhaust pressure (low pressure)) and the exit angle θ2 defined by the minimum nozzle throat th (approximate angle between the central axis connecting the leading edge 6c and the trailing edge 6d of the nozzle vane 6 and the flow direction of the exhaust gas G1 flowing directly through the throat th prevailing at a high exhaust pressure (high pressure)) is increased, it is possible to suppress the nozzle exit angle fluctuation due to the pressure fluctuation of the exhaust gas G.

[0036] Based on this knowledge, as in Fig. 3 and Fig. 4, the flow rate adjusting mechanism 7 according to the present embodiment is configured such that, in a connecting position of each nozzle vane 6 with a hub-side wall surface 5a of the hub-side wall surface 5a and a shroud-side wall surface 5b defining the nozzle passage 4, a nozzle vane 6 and its circumferentially adjacent nozzle vane 6 are placed at different distances from the axis O1 in the radial direction.

[0037] Thus, when circumferentially adjacent nozzle vanes 6 (6a, 6b) are arranged at different radial positions in the connecting position with the hub-side wall surface 5a, the exit angle θ2 defined by the minimum nozzle throat th can be increased to guide the exhaust gas G1 radially inward, and the exit angle fluctuation due to the pressure fluctuation can be increased.

[0038] Therefore, with the turbocharger 1 and the turbine 2 according to the present embodiment, it is possible to improve the blade incidence characteristics more than before by using only nozzles 6 with a small chord ratio without using variable nozzles with a complicated structure when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, and it is possible to improve the turbine efficiency.

[0039] Furthermore, in the present embodiment, the plurality of nozzle vanes 6 includes first nozzle vanes (first nozzle vanes with a small chord ratio) 6a and second nozzle vanes (second nozzle vanes with a small chord ratio) 6b arranged alternately in the circumferential direction. The plurality of first nozzle vanes 6a and the plurality of second nozzle vanes 6b are arranged concentrically, and the second nozzle vanes 6b are arranged radially inward of the first nozzle vanes 6a at a predetermined pitch.

[0040] In other words, in the flow rate adjusting mechanism 7 according to the present embodiment, the adjacent first nozzle vane 6a and second nozzle vane 6b are arranged so that the trailing edge 6d of the second nozzle vane 6b is located radially inward of the trailing edge 6d of the first nozzle vane 6a in the connecting position with the hub-side wall surface 5a.

[0041] With this configuration, the outlet angle fluctuation due to pressure fluctuation can be increased more appropriately. Thus, it is possible to improve the blade incidence characteristics more than before and improve turbine efficiency.

[0042] Furthermore, the adjacent first nozzle vane 6a and second nozzle vane 6b may be arranged such that the trailing edge 6d of the second nozzle vane 6b is arranged radially inward of the trailing edge 6d of the first nozzle vane 6a in the connecting position with the hub-side wall surface 5a, while the trailing edge 6d of each of the first nozzle vanes 6a is arranged radially inward of the trailing edge 6d of each of the second nozzle vanes 6b in the connecting position with the shroud-side wall surface 5b.

[0043] With this configuration, the outlet angle is prevented from varying in the circumferential direction due to pressure fluctuation at the nozzle outlet, and the outlet angle fluctuation can be made uniform in the circumferential direction. Accordingly, the outlet angle fluctuation due to pressure fluctuation can be increased more appropriately. Thus, it is possible to improve the blade incidence characteristics more than before and improve turbine efficiency.

[0044] The second nozzle vane 6b arranged on the radially inner side may be arranged radially outward from the extension line R of the exit angle θ1 of the adjacent first nozzle vane 6a.

[0045] With this configuration, since the second nozzle vane 6b is arranged radially outward from the extension line R of the exit angle θ1 of the adjacent first nozzle vane 6a, it is possible to suppress a large decrease in aerodynamic performance, and it is possible to obtain the effect of increasing the exit angle fluctuation. (Second embodiment)

[0046] Next, the turbocharger and the turbine according to the second embodiment will be described with reference to Fig. 5 to Fig. 7 ( Fig. 1, Fig. 2 and Fig. 3). The turbocharger and turbine according to the present embodiment differ from the turbocharger and turbine according to the first embodiment in the shape and arrangement of the nozzle vanes of the flow rate adjustment mechanism, and the other configurations are the same. Therefore, in the present embodiment, the same configurations (e.g., configuration of the flow rate adjustment mechanism) as those in the first embodiment are assigned the same reference numerals and will therefore not be described in detail again.

[0047] The flow rate adjusting mechanism 7 of the turbocharger 1 and the turbine 2 according to the present embodiment is configured such that the first nozzle vanes 6a and the second nozzle vanes 6b, which are alternately arranged adjacent to each other in the circumferential direction, are arranged at different radial positions, as in the first embodiment.

[0048] Here, when the plurality of first nozzle vanes 6a and the plurality of second nozzle vanes 6b are arranged concentrically, and the second nozzle vanes 6b are arranged radially inside the first nozzle vanes 6a with a predetermined pitch as in the first embodiment, as shown in Fig. 3, in particular, the exit angle θ2 (exit angle θ2 at the nozzle outlet) of the exhaust gas G1 flowing through the respective throats may have a distribution due to the pressure fluctuation, ie, variation in size.

[0049] In contrast, in the flow rate adjusting mechanism 7 according to the present embodiment, as shown in Fig. 5, Fig. 6 and Fig. 7 (see Fig. 1 and Fig. 2), in addition to the configuration in which the first nozzle vanes 6a and the second nozzle vanes 6b, which are arranged alternately adjacent to each other in the circumferential direction, are arranged at different radial positions, the first nozzle vanes 6a are arranged radially inward of the second nozzle vanes 6b on the shroud side, and conversely, the second nozzle vanes 6b are arranged radially inward of the first nozzle vanes 6a on the hub side in order to make the exit angle θ2 uniform.

[0050] In the turbocharger 1 and the turbine 2 according to the present embodiment having this configuration, the discharge angle in the circumferential direction is prevented from varying due to the pressure fluctuation at the nozzle outlet, compared with the first embodiment.

[0051] In other words, by changing the nozzle radial position in the nozzle height direction, the exit angle fluctuation at the nozzle inlet can be made uniform in the circumferential direction.

[0052] Thus, with the turbocharger 1 and turbine 2 according to the present embodiment, in addition to the effect of the first embodiment, the outlet angle fluctuation at the nozzle inlet can be made uniform in the circumferential direction, and further, the pressure fluctuation at the turbine inlet can be reduced. Therefore, it is possible to greatly improve the blade incidence characteristics by using only small-chord nozzles without using variable nozzles with a complicated structure, and it is possible to further improve the turbine efficiency than before.

[0053] Here, as in Fig. 7, for example, the first nozzle vane 6a may be arranged with the shroud side upstream and the hub side downstream in the exhaust gas flow direction, and in the opposite manner to the first nozzle vane 6a, the second nozzle vane 6b may be arranged with the shroud side downstream and the hub side upstream in the exhaust gas flow direction, so that the adjacent first nozzle vane 6a and second nozzle vane 6b are arranged in an X-shape as viewed from the direction perpendicular to the exhaust gas flow direction.

[0054] In this case, the discharge angle in the circumferential direction is more effectively prevented from varying due to the pressure fluctuation at the nozzle outlet, and the discharge angle fluctuation at the nozzle outlet can be made uniform in the circumferential direction.

[0055] Incidentally, in the present embodiment, the trailing edge 6c of each of the first nozzle vanes 6a is arranged radially inward of the trailing edge 6c of each of the second nozzle vanes 6b in the connecting position with the shroud-side wall surface 5b.

[0056] Furthermore, the radial position of the trailing edge 6c of each of the first nozzle vanes 6a in the connecting position with the hub-side wall surface 5a is the same as the radial position of the trailing edge 6c of each of the second nozzle vanes 6b in the connecting position with the shroud-side wall surface 5b.

[0057] Furthermore, the radial position of the trailing edge 6c of each first nozzle vane 6a in the connecting position with the shroud-side wall surface 5b is the same as the radial position of the trailing edge 6c of each second nozzle vane 6b in the connecting position with the hub-side wall surface 5a. (Third embodiment)

[0058] Next, the turbocharger and the turbine according to the third embodiment will be described with reference to Fig. 8 and Fig. 9 ( Fig. 1, Fig. 2 and Fig. 3). The turbocharger and turbine according to the present embodiment differ from the first and second embodiments in the shape of the nozzle vanes of the flow rate adjustment mechanism, and the other configurations are the same. Therefore, in the present embodiment, the same configurations (e.g., configuration of the flow rate adjustment mechanism) as those in the first and second embodiments are assigned the same reference numerals and will therefore not be described in detail again.

[0059] In the turbocharger 1 and the turbine 2 according to the present embodiment, the flow rate adjusting mechanism 7 includes the first nozzle vanes 6a and the second nozzle vanes 6b arranged at different radial positions, as in the first and second embodiments.

[0060] On the other hand, as in Fig. 8 and Fig. 9, in the flow rate adjusting mechanism 7 according to the present embodiment, in the connecting position with the hub-side wall surface 5a, each of the second nozzle vanes 6b has a larger leading edge portion diameter than that of each of the first nozzle vanes 6a.

[0061] Furthermore, in the present embodiment, each nozzle vane 6 is formed to satisfy a relationship of D2 ≤ 3 × D1, where D1 is the leading edge portion diameter of each of the first nozzle vanes 6a and D2 is the leading edge portion diameter of each of the second nozzle vanes 6b. That is, the leading edge portion diameter D2 of the second nozzle vane 6b on the radially inner side is set large within a range of 3 times the leading edge portion diameter D1 of the first nozzle vane 6a on the radially outer side. Preferably, the leading edge portion diameter D2 of the second nozzle vane 6b is 1.5 times or more the leading edge portion diameter D1 of the first nozzle vane 6a.

[0062] Here, the leading edge portion diameter D1 of the first nozzle blade 6a is defined as the diameter of a virtual circle having the maximum thickness dimension D1 in the leading edge portion of the first nozzle blade 6a. Furthermore, the leading edge portion diameter D2 of the second nozzle blade 6b is defined as the diameter of a virtual circle having the maximum thickness dimension D2 in the leading edge portion of the second nozzle blade 6b.

[0063] Furthermore, the “leading edge portion” in the present disclosure refers to a portion in the range of 0 to 20% along the chord length of the nozzle blade 6 when the leading edge 6c of the nozzle blade 6 is defined as a 0% position and the trailing edge 6d of the nozzle blade 6 is defined as a 100% position.

[0064] Since the leading edge portion of the second nozzle vane 6b located on the radially inner side is larger than the leading edge portion of the first nozzle vane 6a located on the radially outer side, in the turbocharger 1 and the turbine 2 according to the present embodiment with this configuration, the exit angle θ2 defined by the minimum nozzle throat th can be directed radially inward, so that the exit angle fluctuation due to the pressure fluctuation can be increased.

[0065] Further, by setting the leading edge portion diameter D2 of the second nozzle vane 6b on the radially inner side to be large within the range of 3 times the leading edge portion diameter D1 of the first nozzle vane 6a on the radially outer side, it is possible to obtain the effect of increasing the exit angle fluctuation while suppressing the increase in the aerodynamic loss.

[0066] The effect by setting the leading edge portion diameter D2 of the second nozzle vane 6b on the radially inner side within 3 times the leading edge portion diameter D1 of the first nozzle vane 6a on the radially outer side has been confirmed by careful research.

[0067] Therefore, with the turbocharger 1 and turbine 2 according to the present embodiment, the pressure fluctuation at the turbine inlet can be reduced compared to the first embodiment. Thus, it is possible to greatly improve the blade incidence characteristics by using only small chord ratio 6 nozzles without using variable nozzles with a complicated structure, and it is possible to further improve the turbine efficiency. (Fourth embodiment)

[0068] Next, the turbocharger and the turbine according to the fourth embodiment will be described with reference to Fig. 10 and Fig. 11 ( Fig. 1 and Fig. 2). The turbocharger and turbine according to the present embodiment differ from the turbocharger and turbine according to the first embodiment in the shape and arrangement of the nozzle vanes of the flow rate adjustment mechanism, and the other configurations are the same. Therefore, in the present embodiment, the same configurations (e.g., configuration of the flow rate adjustment mechanism) as those in the first embodiment are assigned the same reference numerals and will therefore not be described in detail again.

[0069] As in Fig. 10 and Fig. 11, the flow rate adjusting mechanism 7 of the turbocharger 1 and the turbine 2 according to the present embodiment is configured with the first nozzle vanes 6a and the second nozzle vanes 6b arranged alternately adjacent to each other in the circumferential direction, as in the first embodiment.

[0070] On the other hand, in the flow rate adjusting mechanism 7 according to the present embodiment, the second nozzle vane 6 is formed so that its chord length L2 is smaller than the chord length L1 of the first nozzle vane 6a.

[0071] In other words, in the connecting position with the hub-side wall surface 5a, each of the first nozzle blades 6a has a shorter chord length than that of each of the second nozzle blades 6a with a small chord ratio.

[0072] Further, in the present embodiment, the plurality of nozzle vanes 6 including the first nozzle vanes 6a and the second nozzle vanes 6b having different sizes are arranged so that the trailing edges are placed on concentric circles.

[0073] Since the chord length L2 of the second nozzle vane 6b is shorter than the chord length L1 of the first nozzle vane 6a, in the turbocharger 1 and the turbine 2 according to the present embodiment having this configuration, in addition to the effects of the first and second embodiments (the effects by alternately arranging the first nozzle vanes 6a and the second nozzle vanes 6b having a shorter chord length L2), the exit angle θ2 defined by the minimum nozzle throat th can be directed radially inward.

[0074] Thus, the exit angle θ2 defined by the minimum nozzle throat th can be increased to guide the exhaust gas G1 radially inward, and the exit angle fluctuation due to the pressure fluctuation can be increased.

[0075] Therefore, with the turbocharger 1 and the turbine 2 according to the present embodiment, when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, it is possible to greatly improve the blade incidence characteristics more than before by using only small chord ratio 6 nozzles without using variable nozzles having a complicated structure, and it is possible to improve the turbine efficiency.

[0076] Further, in the present embodiment, the chord length L2 of the second nozzle blade 6b is 80% or less of the chord length L1 of the first nozzle blade 6a.

[0077] With this configuration, the exit angle θ2 defined by the minimum nozzle throat th can be directed radially inward, and the exit angle θ2 defined by the minimum nozzle throat th can be increased to direct the exhaust gas G1 radially inward, and the exit angle fluctuation due to the pressure fluctuation can be increased more effectively.

[0078] Here, for example, as in Fig. 12 and Fig. 13, the nozzle blade 6 may be formed such that the chord length L on the shroud side differs from the chord length L on the hub side. In this case, it is preferable to arrange the plurality of nozzle blades 6 in the circumferential direction such that the chord lengths L on the shroud side and the hub side alternately decrease and increase.

[0079] Similarly, in this configuration, the exit angle θ2 defined by the minimum nozzle throat th can be directed radially inward to direct the exhaust gas G1 radially inward, and the exit angle variation due to the pressure variation can be increased.

[0080] Therefore, when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, it is possible to greatly improve the blade incidence characteristics than before by using only nozzles with a small chord ratio 6 without using variable nozzles with a complicated structure, and it is possible to improve the turbine efficiency. (Fifth embodiment)

[0081] Next, the turbocharger and the turbine according to the fifth embodiment will be described with reference to Fig. 14 and Fig. 15 ( Fig. 1, Fig. 2 and Fig. 3). The turbocharger and turbine according to the present embodiment differ from the turbocharger and turbine according to the first to fourth embodiments in the shape and arrangement of the nozzle vanes of the flow rate adjustment mechanism, and the other configurations are the same. Therefore, in the present embodiment, the same configurations (e.g., configuration of the flow rate adjustment mechanism) as those in the first to fourth embodiments are assigned the same reference numerals and will therefore not be described in detail again.

[0082] The flow rate adjusting mechanism 7 of the turbocharger 1 and the turbine 2 according to the present embodiment is configured with a plurality of nozzle vanes 6 arranged at an interval in the circumferential direction as shown in Fig. 14 and Fig. 15 (see Fig. 1 and Fig. 2) is shown.

[0083] On the other hand, in the flow rate adjusting mechanism 7 according to the present embodiment, each nozzle vane 6 is formed so that the vane height H1 of the leading edge is smaller than the vane height H2 of the trailing edge.

[0084] In the present embodiment, the shroud-side end portion (the connection position with the shroud-side wall surface) of the nozzle blade 6 is obliquely cut, so that the blade height H1 of the leading edge 6c is reduced. When the nozzle blade 6 is formed in this manner, as shown in Fig. 15, the nozzle passage 4 is formed according to the shape of the nozzle vane 6.

[0085] Furthermore, in the present embodiment, the nozzle vanes 6 are arranged so that the trailing edges 6d are placed on concentric circles.

[0086] In the turbocharger 1 and the turbine 2 according to the present embodiment having this configuration, since each nozzle vane (small chord ratio nozzle vane) 6 is formed to have a smaller vane height H1 at the leading edge 6c so that the nozzle inlet height is larger than the nozzle outlet, that is, the minimum nozzle area is at the nozzle inlet side, the exit angle θ2 defined by the minimum nozzle throat th can be guided radially inward, and the exit angle fluctuation due to the pressure fluctuation can be increased (see Fig. 3).

[0087] Therefore, with the turbocharger 1 and the turbine 2 according to the present embodiment, when the pressure at the turbine inlet fluctuates greatly due to the exhaust pulsation of the engine, it is possible to greatly improve the blade incidence characteristics more than before by using only small chord ratio 6 nozzles without using variable nozzles with a complicated structure, and it is possible to improve the turbine efficiency.

[0088] Furthermore, when the nozzle blade 6 is formed such that the blade height H1 of the leading edge 6c is 80% or less of the blade height H2 of the trailing edge 6d (H1 ≤ 0.8 × H2), the effects described above can be obtained more reliably and appropriately. (Sixth Embodiment)

[0089] Next, the turbocharger and the turbine according to the sixth embodiment will be described with reference to Fig. 16 ( Fig. 1, Fig. 2 and Fig. 3). The turbocharger and turbine according to the present embodiment differ from the turbocharger and turbine according to the first to fifth embodiments in the shape of the nozzle vanes of the flow rate adjustment mechanism. Therefore, in the present embodiment, the same configurations (configuration of the flow rate adjustment mechanism) as those in the first to fifth embodiments are assigned the same reference numerals and will therefore not be described in detail again.

[0090] As in Fig. As shown in Fig. 16, in the flow rate adjustment mechanism 7 according to the present embodiment, the trailing edge portion of the nozzle vane 6 is curved in the circumferential direction. Furthermore, in the present embodiment, the curved portion (trailing edge curved portion) 6e of the nozzle vane 6 is formed with an angular difference of at most 20° with respect to the nozzle metal angle (leading edge metal angle) θ3.

[0091] Specifically, the nozzle metal angle θ3 in the present embodiment refers to an intersection angle θ3 between a tangent M1 at an intersection point P1 between the leading edge 6c of the nozzle vane 6 and a concentric circle R1 passing through the leading edges 6c of the plurality of nozzle vanes 6, and a straight line (center axis of the nozzle vane 6) connecting the intersection point P1 and the center of an inscribed circle Q1 in contact with the front surface on the pressure side and the rear surface on the suction side of the nozzle vane 6.

[0092] The curvature angle θ4 of the curved portion 6e at the trailing edge 6c of the nozzle vane 6 refers to an intersection angle θ4 between an extension of a straight line T1 connecting the intersection point P1 and the center of the inscribed circle Q1 of the nozzle vane 6 and a center axis T2 of the nozzle vane 6 at the curved portion 6e (or a straight line T2 connecting the trailing edge of the nozzle vane 6 having the curved portion 6e (trailing edge of the curved portion 6e) and an intersection point P2 between a concentric circle R2 passing through the trailing edges of a plurality of nozzle vanes 6' not having the curved portion 6e and the trailing edge of this nozzle vane 6').

[0093] As described above, to increase the nozzle exit angle variation due to the pressure variation, it is necessary to eliminate the nozzle overlap and increase the difference between the geometric nozzle exit angle θ1 and the exit angle θ2 defined by the minimum nozzle throat th.

[0094] In contrast, in the flow rate adjusting mechanism 7 according to the present embodiment, as described above, the trailing edge 6d is curved in the circumferential direction to form the nozzle vane 6.

[0095] With this configuration, the curved portion 6e of the nozzle vane 6 extending in the circumferential direction reduces the geometric nozzle exit angle θ1, that is, increases the difference between the geometric nozzle exit angle θ1 and the exit angle θ2 defined by the minimum nozzle throat th, so that the exit angle fluctuation due to the pressure fluctuation can be increased.

[0096] Thus, with the turbocharger 1 and the turbine 2 according to the present embodiment, the pressure fluctuation at the turbine inlet can be reduced. Therefore, it is possible to greatly improve the blade incidence characteristics by using only small-chord nozzles without using variable nozzles with a complicated structure, and it is possible to further improve the turbine efficiency more than before.

[0097] Furthermore, in the present embodiment, the curvature angle θ4 of the curved portion 6e of the nozzle blade 6 is set to satisfy the nozzle metal angle θ3 < θ4 ≤ θ3 + 20°. Preferably, the curvature angle θ4 satisfies θ3 + 10° ≤ θ4 ≤ θ4 ≤ θ3 + 20°.

[0098] Thus, when the curved portion 6e of the trailing edge of the nozzle vane 6 is formed with an angle difference of at most 20° (20° or less) with respect to the nozzle metal angle θ3, the discharge angle fluctuation due to the pressure change can be increased more effectively.

[0099] The first to sixth embodiments of the turbocharger and the turbine have been described above, but the present disclosure is not limited to the first to sixth embodiments, and the configurations and modifications of these embodiments can be appropriately combined without departing from the spirit of the present disclosure.

[0100] Further improvement of the blade incidence characteristics and turbine efficiency can be achieved synergistically by selectively combining the configurations and modifications of the first to sixth embodiments as needed.

[0101] For example, as in Fig. 17, the radial positions of the first nozzle vanes 6a and the second nozzle vanes 6b can be changed, and the nozzle metal angle θ3 can be changed.

[0102] In this case, in addition to the effect of changing the radial positions of the first nozzle vanes 6a and the second nozzle vanes 6b, by changing the nozzle metal angle θ3, the angle of the minimum nozzle throat can be reduced (the minimum nozzle throat is laid down) and the throat area can be increased. Thus, the exit angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and improve the turbine efficiency.

[0103] Furthermore, for example, as in Fig. 18, the chord lengths L of the first nozzle vanes 6a and the second nozzle vanes 6b can be changed, and the nozzle metal angle θ3 can be changed.

[0104] In this case, in addition to the effect of changing the chord lengths L of the first nozzle blades 6a and the second nozzle blades 6b, by changing the nozzle metal angle θ3, the angle of the minimum nozzle throat can be reduced and the throat area can be increased. Thus, the exit angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is similarly possible to greatly improve the blade incidence characteristics and improve the turbine efficiency.

[0105] Furthermore, for example, as in Fig. 19, the blade heights of the leading edges 6c of the first nozzle blades 6a and the second nozzle blades 6b can be changed, and the nozzle metal angle θ3 can be changed.

[0106] In this case, in addition to the effect of changing the blade heights of the leading edges 6c of the first nozzle blades 6a and the second nozzle blades 6b, by changing the nozzle metal angle θ3, the angle of the minimum nozzle throat can be reduced and the throat area can be increased. Thus, the exit angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is similarly possible to greatly improve the blade incidence characteristics and improve the turbine efficiency.

[0107] In other words, further improvement of the blade incidence characteristics and turbine efficiency can be achieved by selectively combining the configurations and modifications of the first to sixth embodiments as needed.

[0108] In particular, the contents described in the above embodiments would be understood, for example, as follows.

[0109] (1) A turbine according to an aspect of the present disclosure (turbine 2 according to the first embodiment) is provided with: a turbine wheel (turbine wheel 14 according to the first embodiment: Fig. 1) configured to rotate about an axis; a turbine housing (turbine housing 5 according to the first embodiment: Fig. 1) which accommodates the turbine wheel and an annular nozzle passage (nozzle passage 4 according to the first embodiment: Fig.1) defined on an outer peripheral side of the turbine wheel; and a plurality of small-chord ratio nozzle blades (nozzle blades 6, first nozzle blades 6a, second nozzle blades 6b according to the first, second, and third embodiments) arranged in the nozzle passage at an interval in a circumferential direction. Circumferentially adjacent small-chord ratio nozzle blades are arranged at different radial positions in a connecting position of each of the small-chord ratio nozzle blades with a hub-side wall surface (hub-side wall surface 5a according to the first embodiment) of the hub-side wall surface and a shroud-side wall surface (shroud-side wall surface 5b according to the first embodiment) defining the nozzle passage.

[0110] According to the turbine of the present disclosure, since circumferentially adjacent small-chord ratio nozzle blades are arranged at different radial positions in the connection position with the hub-side wall surface, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Therefore, when the pressure at the turbine inlet fluctuates greatly due to the engine's exhaust pulsation, it is possible to greatly improve the blade incidence characteristics than before by using only small-chord ratio nozzles without using variable nozzles with a complicated structure, and it is possible to improve the turbine efficiency.

[0111] (2) A turbine according to another aspect is the turbine described in (1), in which the plurality of small-chord ratio nozzle blades includes: a plurality of small-chord ratio first nozzle blades; and a plurality of small-chord ratio second nozzle blades, each of which has a trailing edge (trailing edge 6d according to the first embodiment) located radially inward of a trailing edge of each of the plurality of small-chord ratio first nozzle blades in the connection position with the hub-side wall surface. The plurality of small-chord ratio first nozzle blades and the plurality of small-chord ratio second nozzle blades are arranged to be alternately adjacent to each other in the circumferential direction.

[0112] With this configuration, since the plurality of small-pitch first nozzle blades and the plurality of small-pitch second nozzle blades are arranged to be alternately adjacent to each other in the circumferential direction, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be appropriately increased. Therefore, when the pressure at the turbine inlet fluctuates greatly due to exhaust gas pulsation of the engine, it is possible to greatly improve the blade incidence characteristics than before by using only small-pitch nozzles without using variable nozzles with a complicated structure, and it is possible to more appropriately improve the turbine efficiency.

[0113] (3) A turbine according to another aspect is the turbine described in (2), in which the trailing edge of each of the plurality of first small chord ratio nozzle blades is arranged radially inward of the trailing edge of each of the plurality of second small chord ratio nozzle blades in a connecting position with the shroud-side wall surface.

[0114] With this configuration, since the trailing edge of each of the plurality of small-chord ratio first nozzle blades is arranged radially inward of the trailing edge of each of the plurality of small-chord ratio second nozzle blades in the connecting position with the shroud-side wall surface, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be more appropriately increased. Therefore, when the pressure at the turbine inlet fluctuates greatly due to exhaust gas pulsation of the engine, it is possible to greatly improve the blade incidence characteristics than before by using only small-chord ratio nozzles without using variable nozzles with a complicated structure, and it is possible to more appropriately improve the turbine efficiency.

[0115] (4) A turbine according to another aspect is the turbine described in (2) or (3), in which each of the plurality of first small chord ratio nozzle blades has a shorter chord length (chord length L1, L2 according to the fourth embodiment) than that of each of the plurality of second small chord ratio nozzle blades in the connection position with the hub-side wall surface.

[0116] With this configuration, since each of the plurality of small-chord ratio first nozzle blades has a shorter chord length than that of each of the plurality of small-chord ratio second nozzle blades in the connection position with the hub-side wall surface, the exit angle defined by the minimum nozzle throat can be directed radially inward. Thus, the exit angle defined by the minimum nozzle throat can be increased to direct the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and to more significantly improve the turbine efficiency.

[0117] (5) A turbine according to another aspect is the turbine described in (3), in which each of the plurality of small chord ratio second nozzle blades has a shorter chord length than that of each of the plurality of small chord ratio first nozzle blades in the connecting position with the shroud-side wall surface.

[0118] With this configuration, since each of the plurality of small-chord ratio second nozzle blades has a shorter chord length than that of each of the plurality of small-chord ratio first nozzle blades in the connection position with the shroud-side wall surface, the exit angle defined by the minimum nozzle throat can be directed radially inward. Thus, the exit angle defined by the minimum nozzle throat can be increased to direct the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and to more significantly improve the turbine efficiency.

[0119] (6) A turbine according to another aspect is the turbine described in any one of (2) to (5), in which each of the plurality of small-chord ratio second nozzle blades has a larger leading edge portion diameter (leading edge portion diameter D1, D2 according to the third embodiment) than that of each of the plurality of small-chord ratio first nozzle blades in the connecting position with the hub-side wall surface.

[0120] With this configuration, since each of the plurality of small-chord second nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord first nozzle blades in the connection position with the hub-side wall surface, the exit angle fluctuation can be effectively increased. Thus, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and to more significantly improve the turbine efficiency.

[0121] (7) A turbine according to another aspect is the turbine described in (6), in which a relationship of D2 ≤ 3 × D1 is satisfied, where D1 is the leading edge portion diameter of each of the plurality of small chord ratio first nozzle blades and D2 is the leading edge portion diameter of each of the plurality of small chord ratio second nozzle blades.

[0122] With this configuration, the outlet angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the outlet angle fluctuation due to pressure fluctuation can be appropriately increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0123] (8) A turbine according to another aspect is the turbine described in (3), wherein each of the plurality of small-chord ratio second nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord ratio first nozzle blades in the connecting position with the hub-side wall surface, and each of the plurality of small-chord ratio first nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord ratio second nozzle blades in the connecting position with the shroud-side wall surface.

[0124] With this configuration, the exit angle fluctuation can be increased more effectively. Thus, the exit angle defined by the minimum nozzle throat can be increased to direct the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0125] (9) A turbine according to another aspect is the turbine described in any one of (2) to (8), in which each of the plurality of second small chord ratio nozzle blades has a larger leading edge metal angle (nozzle metal angle θ3 according to the sixth embodiment) than that of the plurality of first small chord ratio nozzle blades.

[0126] With this configuration, since each of the plurality of low-chord second nozzle blades has a larger leading edge metal angle than that of the plurality of low-chord first nozzle blades, the minimum nozzle throat angle can be reduced (the minimum nozzle throat is laid down) and the throat area can be increased. Thus, the exit angle fluctuation can be effectively reduced while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve the turbine efficiency.

[0127] (10) A turbine according to another aspect is the turbine described in any one of (1) to (9), in which each of the plurality of small chord ratio nozzle blades is configured so that a blade height (blade height H2 according to the fifth embodiment) of a trailing edge is greater than a blade height (blade height H1 according to the fifth embodiment) of a leading edge (leading edge 6c according to the first embodiment).

[0128] With this configuration, the height of the nozzle inlet is greater than that of the nozzle outlet, so the minimum nozzle area is at the nozzle inlet side. Thus, the exit angle defined by the minimum nozzle throat area can be directed radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0129] (11) A turbine according to one aspect of the present disclosure is provided with: a turbine wheel configured to rotate about an axis; a turbine casing that houses the turbine wheel and defines an annular nozzle passage on an outer peripheral side of the turbine wheel; and a plurality of small chord ratio nozzle blades arranged in the nozzle passage at an interval in a circumferential direction. Circumferentially adjacent small chord ratio nozzle blades have different chord lengths in a connecting position of each of the small chord ratio nozzle blades with a hub-side wall surface, the hub-side wall surface and a shroud-side wall surface defining the nozzle passage.

[0130] With this configuration, since each of the plurality of small-chord ratio first nozzle blades has a shorter chord length than that of each of the plurality of small-chord ratio second nozzle blades in the connection position with the hub-side wall surface, the exit angle defined by the minimum nozzle throat can be directed radially inward. Thus, the exit angle defined by the minimum nozzle throat can be increased to direct the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be reduced. Accordingly, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0131] (12) A turbine according to another aspect is the turbine described in (11), in which the plurality of small-chord ratio nozzle blades includes: a plurality of small-chord ratio first nozzle blades; and a plurality of small-chord ratio second nozzle blades, each of which has a shorter chord length than that of each of the plurality of small-chord ratio first nozzle blades in the connection position with the hub-side wall surface. The plurality of small-chord ratio first nozzle blades and the plurality of small-chord ratio second nozzle blades are arranged to be alternately adjacent to each other in the circumferential direction.

[0132] With this configuration, in addition to the effect of (11), the exit angle defined by the minimum nozzle throat can be increased to direct the exhaust gas radially inward, and the exit angle fluctuation due to pressure fluctuation can be significantly increased. Therefore, when the pressure at the turbine inlet fluctuates greatly due to engine exhaust pulsation, it is possible to greatly improve the blade incidence characteristics by using only small-chord ratio nozzles without using variable nozzles with a complicated structure, and it is possible to more appropriately improve the turbine efficiency.

[0133] (13) A turbine according to another aspect is the turbine described in (12), in which a relationship of L2 ≤ 0.8 × L1 is satisfied, where L1 is the chord length of each of the plurality of small chord ratio first nozzle blades and L2 is the chord length of each of the plurality of small chord ratio second nozzle blades.

[0134] With this configuration, since a relationship of L2 ≤ 0.8 × L1 is satisfied, the exit angle defined by the minimum nozzle throat can be effectively directed radially inward. Thus, the exit angle fluctuation due to pressure fluctuation can be more appropriately increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0135] (14) A turbine according to another aspect is the turbine described in (12) or (13), in which each of the plurality of small chord ratio first nozzle blades has a shorter chord length than that of each of the plurality of small chord ratio second nozzle blades in the connecting position with the shroud-side wall surface.

[0136] With this configuration, since a relationship of L2 ≤ 0.8 × L1 is satisfied, the exit angle defined by the minimum nozzle throat can be directed radially inward more effectively. Thus, the exit angle fluctuation due to pressure fluctuation can be significantly increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0137] (15) A turbine according to another aspect is the turbine described in (13) or (14), wherein each of the plurality of second small chord ratio nozzle blades has a larger leading edge portion diameter than that of each of the plurality of first small chord ratio nozzle blades in the connecting position with the hub-side wall surface.

[0138] With this configuration, in addition to the effect of (13) or (14), since each of the plurality of small-chord ratio second nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord ratio first nozzle blades in the connection position with the hub-side wall surface, the exit angle fluctuation can be effectively increased. Thus, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to the pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics, and it is possible to more significantly improve the turbine efficiency.

[0139] (16) A turbine according to another aspect is the turbine described in (15), in which a relationship of D2 ≤ 3 × D1 is satisfied, where D1 is the leading edge portion diameter of each of the plurality of small chord ratio first nozzle blades and D2 is the leading edge portion diameter of each of the plurality of small chord ratio second nozzle blades.

[0140] With this configuration, in addition to the effect of (13) or (14), the outlet angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the outlet angle fluctuation due to pressure fluctuation can be appropriately increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve the turbine efficiency.

[0141] (17) A turbine according to another aspect is the turbine described in (14), wherein each of the plurality of small-chord second nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord first nozzle blades in the connecting position with the hub-side wall surface, and each of the plurality of small-chord first nozzle blades has a larger leading edge portion diameter than that of each of the plurality of small-chord second nozzle blades in the connecting position with the shroud-side wall surface.

[0142] With this configuration, in addition to the effect of (14), the outlet angle is prevented from varying in the circumferential direction due to pressure fluctuation at the nozzle outlet, and the outlet angle fluctuation can be made uniform in the circumferential direction. Accordingly, the outlet angle fluctuation due to pressure fluctuation can be increased more appropriately. Thus, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0143] (18) A turbine according to another aspect is the turbine described in any one of (11) to (17), wherein each of the plurality of second low chord ratio nozzle blades has a larger leading edge metal angle than that of the plurality of first low chord ratio nozzle blades.

[0144] With this configuration, in addition to the effect of any of (11) to (17), the minimum nozzle throat angle can be reduced (the minimum nozzle throat is lowered) and the throat area can be increased. Thus, the exit angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0145] (19) A turbine according to another aspect is the turbine described in any one of (11) to (18), in which each of the plurality of small chord ratio nozzle blades is configured such that a blade height of a trailing edge is greater than a blade height of a leading edge.

[0146] With this configuration, in addition to the effect of any one of (11) to (18), the height of the nozzle inlet is larger than that of the nozzle outlet, so that the minimum nozzle area is at the nozzle inlet side. Thus, the exit angle defined by the minimum nozzle throat area can be directed radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0147] (20) A turbine according to one aspect of the present disclosure is provided with: a turbine wheel configured to rotate about an axis; a turbine casing that houses the turbine wheel and defines an annular nozzle passage on an outer peripheral side of the turbine wheel; and a plurality of small-pitch nozzle blades arranged in the nozzle passage at an interval in a circumferential direction. Each of the plurality of small-pitch nozzle blades is configured such that a blade height of a trailing edge is greater than a blade height of a leading edge.

[0148] With this configuration, since each of the plurality of small-chord nozzle blades is configured such that the trailing edge blade height is greater than the leading edge blade height, the nozzle inlet height is greater than that of the nozzle outlet, so that the minimum nozzle area is at the nozzle inlet side. Thus, the exit angle defined by the minimum nozzle throat area can be directed radially inward, and the exit angle fluctuation due to pressure fluctuation can be increased. Accordingly, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0149] (21) A turbine according to another aspect is the turbine described in (20), in which a relationship of H1 ≤ 0.8 × H2 is satisfied, where H1 is the blade height at the leading edge of each of the plurality of small chord ratio nozzle blades and H2 is the blade height at the trailing edge of each of the plurality of small chord ratio nozzle blades.

[0150] With this configuration, since a relationship of H1 ≤ 0.8 × H2 is satisfied, the height of the nozzle inlet is larger than that of the nozzle outlet, so the minimum nozzle area is at the nozzle inlet side. Furthermore, the exit angle defined by the minimum nozzle throat area can be directed radially inward, and the exit angle fluctuation due to pressure fluctuation can be effectively reduced. Accordingly, it is possible to greatly improve the blade incidence characteristics and significantly improve turbine efficiency.

[0151] (22) A turbine according to another aspect is the turbine described in (20) or (21), in which the plurality of small-chord ratio nozzle blades includes: a plurality of small-chord ratio first nozzle blades; and a plurality of small-chord ratio second nozzle blades, each of which has a larger leading edge metal angle than that of the plurality of small-chord ratio first nozzle blades in a connecting position with a hub-side wall surface of the hub-side wall surface and a shroud-side wall surface defining the nozzle passage. The plurality of small-chord ratio first nozzle blades and the plurality of small-chord ratio second nozzle blades are arranged to be alternately adjacent to each other in the circumferential direction.

[0152] With this configuration, since each of the plurality of low-chord ratio second nozzle blades has a larger leading edge metal angle than that of the plurality of low-chord ratio first nozzle blades in the connection position with the hub-side wall surface, the minimum nozzle throat angle can be reduced and the throat area can be increased. Thus, the exit angle fluctuation can be effectively increased while suppressing the increase in aerodynamic loss, and the exit angle fluctuation due to pressure fluctuation can be reduced.

[0153] Furthermore, since the plurality of small chord ratio first nozzle blades and the plurality of small chord ratio second nozzle blades are arranged to be alternately adjacent to each other in the circumferential direction, the exit angle defined by the minimum nozzle throat can be increased to guide the exhaust gas radially inward, and the exit angle fluctuation due to the pressure fluctuation can be appropriately increased.

[0154] Accordingly, it is possible to greatly improve the blade incidence characteristics, and it is possible to more significantly improve the turbine efficiency.

[0155] (23) A turbine according to another aspect is the turbine described in (22), in which each of the plurality of first small chord ratio nozzle blades has a larger leading edge metal angle than that of each of the plurality of second small chord ratio nozzle blades in a connecting position with the shroud-side wall surface.

[0156] With this configuration, since each of the plurality of small-chord ratio first nozzle blades has a larger leading edge metal angle than that of each of the plurality of small-chord ratio second nozzle blades in the connection position with the shroud-side wall surface, the minimum nozzle throat angle can be further reduced and the throat area can be increased. In addition, the exit angle is prevented from varying in the circumferential direction due to pressure fluctuation at the nozzle outlet, and the exit angle fluctuation can be made uniform in the circumferential direction. Accordingly, the exit angle fluctuation due to pressure fluctuation can be more appropriately increased. Thus, it is possible to improve the blade incidence characteristics more than before, and it is possible to improve turbine efficiency.

[0157] (24) A turbine according to another aspect is the turbine described in (23), in which the leading edge metal angle of each of the plurality of small-chord ratio first nozzle blades in the connecting position with the hub-side wall surface is equal to the leading edge metal angle of each of the plurality of small-chord ratio second nozzle blades in the connecting position with the shroud-side wall surface, and the leading edge metal angle of each of the plurality of small-chord ratio first nozzle blades in the connecting position with the shroud-side wall surface is equal to the leading edge metal angle of each of the plurality of small-chord ratio second nozzle blades in the connecting position with the hub-side wall surface.

[0158] With this configuration, in addition to the effect of (23), the outlet angle is prevented from varying in the circumferential direction due to pressure fluctuation at the nozzle outlet, and the outlet angle fluctuation can be more effectively made uniform in the circumferential direction. Accordingly, the outlet angle fluctuation due to pressure fluctuation can be significantly reduced. Thus, it is possible to greatly improve the blade incidence characteristics and improve turbine efficiency.

[0159] (25) A turbine according to another aspect is the turbine described in any one of (1) to (24), in which each of the plurality of small chord ratio nozzle blades has a curved trailing edge portion (curved portion 6e according to the sixth embodiment) where a trailing edge is curved toward an outer peripheral side.

[0160] With this configuration, in addition to the effect of any one of (1) to (24), since each of the plurality of small-chord ratio nozzle blades has the curved trailing edge portion where the trailing edge is curved toward the outer peripheral side, the geometric nozzle exit angle can be reduced, that is, the difference between the geometric nozzle exit angle and the exit angle defined by the minimum nozzle throat can be increased, so that the exit angle fluctuation due to the pressure fluctuation can be increased. Therefore, the pressure fluctuation at the turbine inlet can be reduced. Thus, it is possible to greatly improve the blade incidence characteristics by using only small-chord ratio nozzles, and it is possible to significantly improve the turbine efficiency more than before.

[0161] (26) A turbine according to another aspect is the turbine described in (25), wherein each of the plurality of small chord ratio nozzle blades has a difference of 20° or less between a curvature angle of the curved trailing edge portion and a nozzle metal angle of a leading edge.

[0162] With this configuration, in addition to the effect of (25), the difference between the geometric nozzle exit angle and the exit angle defined by the minimum nozzle throat can be effectively increased, so that the exit angle fluctuation due to pressure fluctuation can be increased. Therefore, the pressure fluctuation at the turbine inlet can be reduced. Thus, it is possible to greatly improve the blade incidence characteristics by using only small-chord ratio nozzles, and it is possible to significantly improve turbine efficiency.

[0163] (27) A turbocharger according to one aspect (turbocharger 1 according to the first embodiment) is provided with the turbine described in any one of (1) to (26).

[0164] With this configuration it is possible to achieve the turbocharger having the effect of one of (1) to (26).

[0165] For example, when the configurations and modifications of the first to sixth embodiments are appropriately and selectively combined, the nozzle height position adjusting mechanism for adjusting the radial positions of the first nozzle vanes 6a and the second nozzle vanes 6b may be provided to be able to adjust the height and thus the throat.

[0166] Furthermore, if it is possible to improve the blade incidence characteristics by using only the nozzles 6 with small chord ratio more than before, it does not necessarily have to change the radial positions of the nozzle blades 6 alternately, in other words, arrange the adjacent nozzle blades 6 at different radial positions. List of reference symbols 1 turbocharger 2 turbines 3 Turbine wheel 4 nozzle passage 5 Turbine housing 5a Hub-side wall surface 5b Sheathing-side wall surface 6 nozzle vanes (nozzle vanes with small chord ratio) 6a First nozzle vane (first nozzle with small chord ratio) 6b Second nozzle vane (second nozzle with small chord ratio) 6c Leading edge (leading edge section) 6d trailing edge (trailing edge section) 6e Curved section (curved trailing edge section) 7 Flow rate adjustment mechanism 18 Spiral passage 19 delivery round G exhaust O1 axis th neck

Claims

[1] Turbine (2), comprising: a turbine wheel (3) configured to rotate about an axis; a turbine housing (5) which houses the turbine wheel (3) and defines an annular nozzle passage (4) on an outer peripheral side of the turbine wheel (3); and a plurality of nozzle blades (6, 6a, 6b) with a small chord ratio arranged in the nozzle passage (4) at an interval in a circumferential direction, wherein circumferentially adjacent nozzle blades (6, 6a, 6b) do not overlap, wherein circumferentially adjacent small chord ratio nozzle blades (6, 6a, 6b) are arranged at different radial positions in a connecting position of each of the small chord ratio nozzle blades (6, 6a, 6b) with a hub-side wall surface (5a) and a shroud-side wall surface (5b) defining the nozzle passage (4). [2] Turbine (2) according to claim 1, wherein the plurality of small chord ratio nozzle blades (6, 6a, 6b) include: a plurality of first nozzle vanes (6a) with a small chord ratio; and a plurality of small-chord ratio second nozzle vanes (6b), each having a trailing edge disposed radially inward of a trailing edge of each of the plurality of small-chord ratio first nozzle vanes (6a) in the connecting position with the hub-side wall surface (5a), and wherein the plurality of first nozzle blades (6a) with a small chord ratio and the plurality of second nozzle blades (6b) with a small chord ratio are arranged so as to be alternately adjacent to each other in the circumferential direction. [3] The turbine (2) according to claim 2, wherein the trailing edge of each of the plurality of small chord ratio first nozzle blades (6a) is disposed radially inward of the trailing edge of each of the plurality of small chord ratio second nozzle blades (6b) in a connecting position with the shroud-side wall surface (5b). [4] A turbine (2) according to claim 2 or 3, wherein each of the plurality of small chord ratio first nozzle blades (6a) has a shorter chord length than that of each of the plurality of small chord ratio second nozzle blades (6b) in the connecting position with the hub-side wall surface (5a). [5] The turbine (2) according to claim 3, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a shorter chord length than that of each of the plurality of small chord ratio first nozzle blades (6a) in the connecting position with the shroud-side wall surface (5b). [6] A turbine (2) according to any one of claims 2 to 5, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a larger leading edge portion diameter than that of each of the plurality of small chord ratio first nozzle blades (6a) in the connecting position with the hub-side wall surface (5a). [7] The turbine (2) according to claim 6, wherein a relationship of D2 ≤ 3 × D1 is satisfied, where D1 is the leading edge portion diameter of each of the plurality of small chord ratio first nozzle blades (6a) and D2 is the leading edge portion diameter of each of the plurality of small chord ratio second nozzle blades (6b). [8] The turbine (2) according to claim 3, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a larger leading edge portion diameter than that of each of the plurality of small chord ratio first nozzle blades (6a) in the connecting position with the hub-side wall surface (5a), and wherein each of the plurality of small chord ratio first nozzle blades (6a) has a larger leading edge portion diameter than that of each of the plurality of small chord ratio second nozzle blades (6b) in the connecting position with the shroud-side wall surface (5b). [9] A turbine (2) according to any one of claims 2 to 8, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a larger leading edge metal angle than that of the plurality of small chord ratio first nozzle blades (6a). [10] Turbine (2) according to one of claims 1 to 9, wherein each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) is configured such that a blade height of a trailing edge is greater than a blade height of a leading edge. [11] Turbine (2), comprising: a turbine wheel (3) configured to rotate about an axis; a turbine housing (5) which houses the turbine wheel (3) and defines an annular nozzle passage (4) on an outer peripheral side of the turbine wheel (3); and a plurality of nozzle blades (6, 6a, 6b) with a small chord ratio arranged in the nozzle passage (4) at an interval in a circumferential direction, wherein circumferentially adjacent nozzle blades (6, 6a, 6b) do not overlap, wherein circumferentially adjacent small chord ratio nozzle blades (6, 6a, 6b) have different chord lengths in a connecting position of each of the small chord ratio nozzle blades (6, 6a, 6b) with a hub-side wall surface (5a) and a shroud-side wall surface (5b) defining the nozzle passage (4). [12] Turbine (2) according to claim 11, wherein the plurality of nozzle blades (6, 6a, 6b) with a small chord ratio includes: a plurality of first nozzle vanes (6a) with a small chord ratio; and a plurality of small chord ratio second nozzle blades (6b), each having a shorter chord length than that of each of the plurality of small chord ratio first nozzle blades (6a) in the connecting position with the hub-side wall surface (5a), and wherein the plurality of small chord ratio first nozzle blades (6a) and the plurality of small chord ratio second nozzle blades (6b) are arranged to be alternately adjacent to each other in the circumferential direction. [13] Turbine (2) according to claim 12, wherein a relationship of L2 ≤ 0.8 x L1 is satisfied, where L1 is the chord length of each of the plurality of first nozzle blades (6a) with a small chord ratio and L2 is the chord length of each of the plurality of second nozzle blades (6b) with a small chord ratio. [14] A turbine (2) according to claim 12 or 13, wherein each of the plurality of small chord ratio first nozzle blades (6a) has a shorter chord length than that of each of the plurality of small chord ratio second nozzle blades (6b) in the connecting position with the shroud-side wall surface (5b). [15] A turbine (2) according to claim 13 or 14, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a larger leading edge portion diameter than that of each of the plurality of small chord ratio first nozzle blades (6a) in the connecting position with the hub-side wall surface (5a). [16] The turbine (2) according to claim 15, wherein a relationship of D2 ≤ 3 × D1 is satisfied, where D1 is the leading edge portion diameter of each of the plurality of small chord ratio first nozzle blades (6a) and D2 is the leading edge portion diameter of each of the plurality of small chord ratio second nozzle blades (6b). [17] Turbine (2) according to claim 14, wherein each of the plurality of second nozzle blades (6b) with a small chord ratio has a larger leading edge portion diameter than that of each of the plurality of first nozzle blades (6a) with a small chord ratio in the connecting position with the hub-side wall surface (5a), and wherein each of the plurality of first small chord ratio nozzle blades (6a) has a larger leading edge portion diameter than that of each of the plurality of second small chord ratio nozzle blades (6b) in the connecting position with the shroud-side wall surface (5b). [18] A turbine (2) according to any one of claims 11 to 17, wherein each of the plurality of small chord ratio second nozzle blades (6b) has a larger leading edge metal angle than that of the plurality of small chord ratio first nozzle blades (6a). [19] Turbine (2) according to one of claims 11 to 18, wherein each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) is configured such that a blade height of a trailing edge is greater than a blade height of a leading edge. [20] Turbine (2), comprising: a turbine wheel (3) configured to rotate about an axis; a turbine housing (5) which houses the turbine wheel (3) and defines an annular nozzle passage (4) on an outer peripheral side of the turbine wheel (3); and a plurality of nozzle blades (6, 6a, 6b) with a small chord ratio arranged in the nozzle passage (4) at an interval in a circumferential direction, wherein circumferentially adjacent nozzle blades (6, 6a, 6b) do not overlap, wherein each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) is configured such that a trailing edge blade height is greater than a leading edge blade height. [21] Turbine (2) according to claim 20, wherein a relationship of H1 ≤ 0.8 × H2 is satisfied, where H1 is the blade height at the leading edge of each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) and H2 is the blade height at the trailing edge of each of the plurality of small chord ratio nozzle blades (6, 6a, 6b). [22] Turbine (2) according to claim 20 or 21, wherein the plurality of small chord ratio nozzle blades (6, 6a, 6b) include: a plurality of first nozzle vanes (6a) with a small chord ratio; and a plurality of second nozzle blades (6b) with a small chord ratio, each of which has a larger leading edge metal angle than that of the plurality of first nozzle blades (6a) with a small chord ratio in a connecting position with a hub-side wall surface (5a) and a shroud-side wall surface (5b) defining the nozzle passage (4), and wherein the plurality of first nozzle blades (6a) with a small chord ratio and the plurality of second nozzle blades (6b) with a small chord ratio are arranged so as to be alternately adjacent to each other in the circumferential direction. [23] The turbine (2) according to claim 22, wherein each of the plurality of small chord ratio first nozzle blades (6a) has a larger leading edge metal angle than that of each of the plurality of small chord ratio second nozzle blades (6b) in a connecting position with the shroud-side wall surface (5b). [24] Turbine (2) according to claim 23, wherein the leading edge metal angle of each of the plurality of first nozzle blades (6a) with a small chord ratio in the connecting position with the hub-side wall surface (5a) is equal to the leading edge metal angle of each of the plurality of second nozzle blades (6b) with a small chord ratio in the connecting position with the shroud-side wall surface (5b), and wherein the leading edge metal angle of each of the plurality of small chord ratio first nozzle vanes (6a) in the connecting position with the shroud-side wall surface (5b) is equal to the leading edge metal angle of each of the plurality of small chord ratio second nozzle vanes (6b) in the connecting position with the hub-side wall surface (5a). [25] A turbine (2) according to any one of claims 1 to 24, wherein each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) has a curved trailing edge portion where a trailing edge is curved toward an outer peripheral side. [26] The turbine (2) according to claim 25, wherein each of the plurality of small chord ratio nozzle blades (6, 6a, 6b) has a difference of 20° or less between a curvature angle of the curved trailing edge portion and a nozzle metal angle of a leading edge. [27] Turbocharger comprising the turbine (2) according to one of claims 1 to 26.

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