Turbine and method for manufacturing turbine

Abstract

A turbine T comprises: a turbine blade wheel; a plurality of nozzle vanes which are disposed apart from each other in the circumferential direction of the turbine blade wheel on the outer side in the radial direction of the turbine blade wheel, and which are provided so as to be rotatable around a rotation shaft along the axial direction of the turbine blade wheel; an annular member (drive ring 107) which extends in the circumferential direction and is provided so as to be rotatable in conjunction with the plurality of nozzle vanes; and an engagement part 107c which includes a pair of sliding surfaces 107d that are provided on the annular member and face each other in the circumferential direction, and in which a drive member (link plate 111) rotationally driven by the actuator is slidably engaged with the pair of sliding surfaces 107d, and which has a thickness greater than the thickness of a peripheral portion of the annular member.

Description

Turbine and method for manufacturing turbine

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2023-175446, filed on October 10, 2023, the contents of which are incorporated herein by reference.

[0002] Turbines used in turbochargers and the like are sometimes provided with nozzle vanes for adjusting the flow velocity of exhaust gas. For example, as disclosed in Patent Document 1, multiple nozzle vanes are arranged radially outward of the turbine wheel and spaced apart in the circumferential direction of the turbine wheel. As each nozzle vane rotates, the cross-sectional area of ​​the flow passage formed between adjacent nozzle vanes changes, thereby changing the flow velocity of exhaust gas flowing between adjacent nozzle vanes.

[0003] Japanese Patent Application Laid-Open No. 2004-116313

[0004] Each nozzle vane rotates in conjunction with a circular member that is rotated by an actuator. The circular member is provided with an engagement portion that includes a pair of sliding surfaces. A drive member that is driven to rotate by the actuator slidably engages with the pair of sliding surfaces of the engagement portion. As the drive member slides, wear occurs in the engagement portion or the drive member.

[0005] An object of the present disclosure is to provide a turbine and a method for manufacturing the turbine that can reduce wear.

[0006] In order to solve the above problems, the turbine of the present disclosure comprises a turbine wheel, a plurality of nozzle vanes arranged radially outward of the turbine wheel and spaced apart in the circumferential direction of the turbine wheel and rotatable about a rotation axis along the axial direction of the turbine wheel, a circular member extending in the circumferential direction and rotatable in conjunction with the plurality of nozzle vanes, and an engaging portion having a thickness greater than the thickness of the surrounding portion of the circular member, the engaging portion including a pair of sliding surfaces arranged circumferentially opposite each other on the circular member, wherein a drive member rotated by an actuator slidably engages with the pair of sliding surfaces.

[0007] The annular member corresponds to the portion of the annular member excluding the engagement portion, is separate from the engagement portion, and includes a main body portion extending circumferentially, and the engagement portion may be joined to the main body portion via at least one weld.

[0008] The main body portion includes a recessed portion formed by recessing from the circumferential surface of the main body portion and having a circumferential width that decreases as it approaches the bottom, and the engagement portion may be joined to each of the circumferential side surfaces of the recessed portion via a weld.

[0009] The engaging portion may include a first engaging portion joined to one circumferential side surface of the recessed portion via a weld, and a second engaging portion joined to the other circumferential side surface of the recessed portion via a weld and circumferentially spaced apart from the first engaging portion, and the pair of sliding surfaces may include a first opposing surface of the first engaging portion that faces the second engaging portion, and a second opposing surface of the second engaging portion that faces the first engaging portion.

[0010] A first gap may be formed between the bottom and the first engagement portion, and a second gap may be formed between the bottom and the second engagement portion.

[0011] A first groove portion recessed in a direction away from the bottom may be provided on the second engagement portion side of the first engagement portion in the portion facing the bottom, and a second groove portion recessed in a direction away from the bottom may be provided on the first engagement portion side of the second engagement portion in the portion facing the bottom.

[0012] In order to solve the above problem, the method of manufacturing a turbine according to the present disclosure includes: preparing a turbine wheel; arranging a plurality of nozzle vanes radially outward of the turbine wheel and spaced apart circumferentially of the turbine wheel, and arranging them so as to be rotatable about a rotation axis along the axial direction of the turbine wheel; providing a circular member extending in the circumferential direction so as to be rotatable in conjunction with the plurality of nozzle vanes; and providing an engaging portion on the circular member, the engaging portion including a pair of sliding surfaces facing each other in the circumferential direction, a drive member driven to rotate by an actuator slidably engaging with the pair of sliding surfaces, and having a thickness greater than the thickness of a surrounding portion of the circular member.

[0013] Providing an engaging portion on the annular member may include preparing a main body portion that corresponds to the portion of the annular member excluding the engaging portion, is separate from the engaging portion, and extends circumferentially, and joining the engaging portion to the main body portion by welding.

[0014] Preparing the main body portion may include providing an engaging portion on the annular member, forming a recessed portion recessed from the circumferential surface of the main body portion, the recessed portion having a circumferential width that decreases as it approaches the bottom, and joining the engaging portion to the main body portion may include joining the engaging portion to each of the circumferential side surfaces of the recessed portion by welding.

[0015] Joining the engaging portion to the main body portion may include joining a thick-walled member having a thickness greater than that of the main body portion by welding to each of the circumferential side surfaces of the recessed portion, and cutting the thick-walled member to form a first engaging portion joined by welding to one circumferential side surface of the recessed portion and a second engaging portion joined by welding to the other circumferential side surface of the recessed portion and spaced circumferentially from the first engaging portion as engaging portions, and forming a first opposing surface of the first engaging portion that faces the second engaging portion and a second opposing surface of the second engaging portion that faces the first engaging portion as a pair of sliding surfaces.

[0016] Joining the engagement portion to the main body portion may include joining a thick member to each of the circumferentially opposite side surfaces of the recess portion by welding so that a first gap is formed between the bottom and the first engagement portion and a second gap is formed between the bottom and the second engagement portion.

[0017] Joining the engaging portion to the main body portion may include cutting the thick member so that a first groove portion recessed in a direction away from the bottom is provided on the second engaging portion side of the first engaging portion in a portion facing the bottom, and a second groove portion recessed in a direction away from the bottom is provided on the first engaging portion side of the second engaging portion in a portion facing the bottom.

[0018] According to the present disclosure, wear can be suppressed.

[0019] FIG. 1 is a schematic cross-sectional view of a turbocharger according to this embodiment. FIG. 2 is a view in which a first region of FIG. 1 is extracted. FIG. 3 is a view of a drive ring according to this embodiment, as viewed from the bearing housing side. FIG. 4 is a view in which a second region of FIG. 1 is extracted. FIG. 5 is a view in which a third region of FIG. 3 is extracted. FIG. 6 is a cross-sectional view showing a cross section A-A of FIG. 5. FIG. 7 is a view for explaining a first step in the manufacturing process of a drive ring according to this embodiment. FIG. 8 is a view for explaining a second step in the manufacturing process of a drive ring according to this embodiment. FIG. 9 is a view for explaining a third step in the manufacturing process of a drive ring according to this embodiment.

[0020] An embodiment of the present disclosure will be described below with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiment are merely examples for ease of understanding and do not limit the present disclosure unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present disclosure are not shown.

[0021] Fig. 1 is a schematic cross-sectional view of a turbocharger TC according to this embodiment. In the following description, the direction of arrow L shown in Fig. 1 will be referred to as the left side of the turbocharger TC. The direction of arrow R shown in Fig. 1 will be referred to as the right side of the turbocharger TC. As shown in Fig. 1, the turbocharger TC includes a turbocharger main body 1. The turbocharger main body 1 includes a bearing housing 3, a turbine housing 5, and a compressor housing 7.

[0022] A turbine housing 5 is connected to the left side of the bearing housing 3 by a fastening bolt 9. A compressor housing 7 is connected to the right side of the bearing housing 3 by a fastening bolt 11. The turbocharger TC includes a turbine T and a centrifugal compressor C. The turbine T includes a bearing housing 3 and a turbine housing 5. The centrifugal compressor C includes the bearing housing 3 and a compressor housing 7.

[0023] A bearing hole 3a is formed in the bearing housing 3. The bearing hole 3a penetrates the bearing housing 3 in the left-right direction of the turbocharger TC. A bearing 13 is disposed in the bearing hole 3a. In FIG. 1 , a semi-floating bearing is shown as an example of the bearing 13. However, the bearing 13 may be another type of bearing, such as a full-floating bearing or a rolling bearing. The bearing 13 rotatably supports a shaft 15. A turbine wheel 17 is provided at the left end of the shaft 15. The turbine wheel 17 is rotatably housed in the turbine housing 5. A compressor wheel 19 is provided at the right end of the shaft 15. The compressor wheel 19 is rotatably housed in the compressor housing 7. The turbine wheel 17 and the compressor wheel 19 rotate integrally with the shaft 15.

[0024] Hereinafter, the axial direction, radial direction, and circumferential direction of the turbocharger TC will also be simply referred to as the axial direction, radial direction, and circumferential direction, respectively. The axial direction of the turbocharger TC coincides with the axial direction of the shaft 15, the axial direction of the turbine wheel 17, and the axial direction of the compressor wheel 19. The radial direction of the turbocharger TC coincides with the radial direction of the shaft 15, the radial direction of the turbine wheel 17, and the radial direction of the compressor wheel 19. The circumferential direction of the turbocharger TC coincides with the circumferential direction of the shaft 15, the circumferential direction of the turbine wheel 17, and the circumferential direction of the compressor wheel 19.

[0025] An intake port 21 is formed in the compressor housing 7. The intake port 21 opens to the right side of the turbocharger TC. The intake port 21 is connected to an air cleaner (not shown). A diffuser passage 23 is formed between the bearing housing 3 and the compressor housing 7. The diffuser passage 23 pressurizes the air. The diffuser passage 23 extends in the circumferential direction and is formed in an annular shape. The diffuser passage 23 communicates with the intake port 21 on the radially inner side via a space in which the compressor impeller 19 is disposed.

[0026] A compressor scroll passage 25 is formed in the compressor housing 7. The compressor scroll passage 25 extends in the circumferential direction and is formed in an annular shape. The compressor scroll passage 25 is located, for example, radially outward of the compressor impeller 19. The compressor scroll passage 25 communicates with an intake port of the engine (not shown) and the diffuser passage 23.

[0027] When the compressor impeller 19 rotates, air is drawn into the compressor housing 7 through the intake port 21. The drawn air is pressurized and accelerated as it flows between the blades of the compressor impeller 19. The compressed and accelerated air is then pressurized in the diffuser passage 23 and the compressor scroll passage 25. The pressurized air flows out from a discharge port (not shown) and is led to the intake port of the engine.

[0028] An exhaust port 27 is formed in the turbine housing 5. The exhaust port 27 opens to the left side of the turbocharger TC. The exhaust port 27 is connected to an exhaust gas purification device (not shown). A gap 29 is formed between the bearing housing 3 and the turbine housing 5. A flow passage 31 through which exhaust gas flows is formed in the gap 29. The flow passage 31 extends in the circumferential direction and is formed in an annular shape.

[0029] A turbine scroll passage 33 is formed in the turbine housing 5. The turbine scroll passage 33 is located, for example, radially outward of the turbine wheel 17. The flow passage 31 is located between the turbine wheel 17 and the turbine scroll passage 33. The flow passage 31 communicates the turbine scroll passage 33 with the exhaust port 27 via the space in which the turbine wheel 17 is disposed.

[0030] The turbine scroll passage 33 communicates with a gas inlet (not shown). Exhaust gas discharged from an exhaust manifold (not shown) of the engine is introduced to the gas inlet. The exhaust gas introduced from the gas inlet to the turbine scroll passage 33 is introduced to the exhaust port 27 via the flow passage 31 and between the blades of the turbine wheel 17. The exhaust gas introduced to the exhaust port 27 rotates the turbine wheel 17 during its flow process.

[0031] The rotational force of the turbine wheel 17 is transmitted to the compressor impeller 19 via the shaft 15. As described above, the air is pressurized by the rotational force of the compressor impeller 19 and is led to the intake port of the engine.

[0032] When the flow rate of exhaust gas introduced into the turbine housing 5 decreases, the rotation amount of the turbine wheel 17 decreases. When the rotation amount of the turbine wheel 17 decreases, the rotation amount of the compressor wheel 19 also decreases. When the rotation amount of the compressor wheel 19 decreases, it may not be possible to sufficiently increase the pressure of the air supplied to the intake port of the engine.

[0033] A variable capacity mechanism 100 is provided in the gap 29 in the turbine housing 5. The variable capacity mechanism 100 changes the flow path cross-sectional area of ​​the flow path 31 in accordance with the flow rate of the exhaust gas. For example, when the engine speed is low and the flow rate of the exhaust gas is small, the variable capacity mechanism 100 reduces the flow path cross-sectional area of ​​the flow path 31.

[0034] When the flow path cross-sectional area of ​​the flow path 31 is reduced, the flow velocity of the exhaust gas passing through the flow path 31 becomes faster compared to when the flow path cross-sectional area of ​​the flow path 31 is large. When the flow velocity of the exhaust gas increases, the amount of rotation of the turbine wheel 17 increases. When the amount of rotation of the turbine wheel 17 increases, the amount of rotation of the compressor wheel 19 also increases. When the amount of rotation of the compressor wheel 19 increases, the pressure of the air supplied to the intake port of the engine can be sufficiently increased. In this way, the variable capacity mechanism 100 can increase the amount of rotation of the turbine wheel 17 and the compressor wheel 19 when the flow rate of the exhaust gas is small. The variable capacity mechanism 100 will be described in detail below.

[0035] The variable displacement mechanism 100 includes a shroud ring 101 , a nozzle ring 103 , a retaining member 105 , a drive ring 107 , a transmission link 109 , a link plate 111 , a plurality of nozzle vanes 113 , a drive mechanism 115 , and an actuator 117 .

[0036] The shroud ring 101 is disposed in the gap 29 on the side farther from the bearing housing 3. The nozzle ring 103 is disposed in the gap 29 on the side closer to the bearing housing 3. The shroud ring 101 is disposed opposite the nozzle ring 103 in the axial direction. The shroud ring 101 is disposed spaced apart from the nozzle ring 103 in the axial direction. A flow passage 31 is formed between the shroud ring 101 and the nozzle ring 103.

[0037] The shroud ring 101 has an annular shape extending in the circumferential direction. The shroud ring 101 is disposed coaxially with the turbine wheel 17. The shroud ring 101 has a thin ring-shaped main body portion 101a. The nozzle ring 103 has an annular shape extending in the circumferential direction. The nozzle ring 103 is disposed coaxially with the turbine wheel 17. The nozzle ring 103 has a thin ring-shaped main body portion 103a.

[0038] The outer diameter of the main body 103a of the nozzle ring 103 is approximately equal to the outer diameter of the main body 101a of the shroud ring 101. However, the outer diameter of the main body 103a of the nozzle ring 103 may be larger or smaller than the outer diameter of the main body 101a of the shroud ring 101. The inner diameter of the main body 103a of the nozzle ring 103 is larger than the inner diameter of the main body 101a of the shroud ring 101. However, the inner diameter of the main body 103a of the nozzle ring 103 may be equal to the inner diameter of the main body 101a of the shroud ring 101 or may be smaller than the inner diameter of the main body 101a of the shroud ring 101.

[0039] Fig. 2 is a diagram illustrating the first region R1 of Fig. 1. As shown in Fig. 2, a plurality of pin shaft holes 101b are formed in the main body portion 101a of the shroud ring 101. Each pin shaft hole 101b passes through the main body portion 101a in the axial direction. The plurality of pin shaft holes 101b are arranged spaced apart from one another in the circumferential direction. For example, the plurality of pin shaft holes 101b are arranged at equal intervals in the circumferential direction. However, the plurality of pin shaft holes 101b may also be arranged at unequal intervals in the circumferential direction.

[0040] A plurality of pin shaft holes 103b are formed in the main body portion 103a of the nozzle ring 103. Each pin shaft hole 103b passes through the main body portion 103a in the axial direction. The plurality of pin shaft holes 103b are arranged spaced apart from one another in the circumferential direction. For example, the plurality of pin shaft holes 103b are arranged at equal intervals in the circumferential direction. However, the plurality of pin shaft holes 103b may also be arranged at unequal intervals in the circumferential direction.

[0041] The number of pin shaft holes 101b matches the number of pin shaft holes 103b. Each pin shaft hole 101b faces each pin shaft hole 103b in the axial direction. That is, each pin shaft hole 101b is arranged coaxially with each pin shaft hole 103b. Connecting pins 119 are inserted through the pin shaft holes 101b and 103b. The shroud ring 101 is connected to the nozzle ring 103 by the connecting pins 119. The distance between the shroud ring 101 and the nozzle ring 103 is kept constant by the connecting pins 119.

[0042] The holding member 105 is disposed between the nozzle ring 103 and the bearing housing 3. The holding member 105 is connected to the nozzle ring 103 by a connecting pin 119. In the example shown in Fig. 2, the holding member 105 is made up of two ring-shaped thin plates joined together. However, the holding member 105 may be made up of a single ring-shaped thin plate, or may be made up of three or more ring-shaped thin plates joined together.

[0043] The outer peripheral edge of the retaining member 105 is clamped between the turbine housing 5 and the bearing housing 3. The retaining member 105 is held non-rotatably between the turbine housing 5 and the bearing housing 3. The retaining member 105 holds the shroud ring 101 and the nozzle ring 103 non-rotatably. A drive ring 107 is disposed between the nozzle ring 103 and the bearing housing 3. The retaining member 105 holds the drive ring 107 so that it can rotate relative to the nozzle ring 103.

[0044] The drive ring 107 has a circular ring shape extending in the circumferential direction. The drive ring 107 is arranged coaxially with the turbine wheel 17. The drive ring 107 is provided on the opposite side of the nozzle ring 103 to the plurality of nozzle vanes 113. As will be described later, the drive ring 107 is provided to be rotatable in conjunction with the plurality of nozzle vanes 113. The drive ring 107 corresponds to an example of a circular member provided to be rotatable in conjunction with the plurality of nozzle vanes 113.

[0045] Figure 3 is a view of the drive ring 107 as seen from the bearing housing 3 side. As shown in Figure 3, the drive ring 107 has a thin ring-shaped main body portion 107a. The main body portion 107a has an annular shape extending in the circumferential direction. The main body portion 107a is disposed coaxially with the turbine impeller 17. The inner peripheral surface of the main body portion 107a engages with the engaging claws 105a of the holding member 105, thereby holding the main body portion 107a so that it can rotate freely relative to the holding member 105. The drive ring 107 is formed with a plurality of transmission link engaging portions 107b and link plate engaging portions 107c.

[0046] The transmission link engaging portions 107b are portions of the main body 107a that are cut out radially outward from the inner circumferential surface of the main body 107a. The multiple transmission link engaging portions 107b are arranged at equal intervals in the circumferential direction of the main body 107a. An engaging end 109a of the transmission link 109 engages with the transmission link engaging portions 107b.

[0047] The link plate engaging portion 107c is provided on the inner periphery of the drive ring 107 and includes a pair of sliding surfaces 107d. The link plate engaging portion 107c is provided at one specific circumferential position on the drive ring 107. The link plate engaging portion 107c is provided between two circumferentially adjacent transfer link engaging portions 107b. An engaging end 111a of the link plate 111 engages with the pair of sliding surfaces 107d of the link plate engaging portion 107c. As will be described later, the link plate 111 corresponds to an example of a driving member that is rotationally driven by the actuator 117. The link plate engaging portion 107c corresponds to an example of an engaging portion with which a driving member engages.

[0048] An insertion hole 109b is formed in the transmission link 109. The insertion hole 109b is formed on the side of the transmission link 109 opposite the engagement end 109a. As shown in FIG. 3 and FIG. 4 described below, a blade shaft 113a of a nozzle vane 113 is inserted into the insertion hole 109b. The transmission link 109 is crimped with the blade shaft 113a of the nozzle vane 113 inserted into the insertion hole 109b. The transmission link 109 and the nozzle vane 113 rotate integrally with the blade shaft 113a.

[0049] An insertion hole 111b is formed in the link plate 111. The insertion hole 111b is formed on the side of the link plate 111 opposite the engagement end 111a. As shown in FIGS. 2 and 3 , a rotation shaft RA of the drive mechanism 115 is inserted into the insertion hole 111b. The link plate 111 is crimped with the rotation shaft RA of the drive mechanism 115 inserted into the insertion hole 111b. The link plate 111 rotates integrally with the rotation shaft RA of the drive mechanism 115. However, the rotation shaft RA of the drive mechanism 115 may be welded to the insertion hole 111b of the link plate 111.

[0050] Fig. 4 is a diagram illustrating the second region R2 of Fig. 1 . As shown in Fig. 4 , a plurality of blade shaft holes 101c are formed in the main body portion 101a of the shroud ring 101. Each blade shaft hole 101c is disposed radially inward of the pin shaft hole 101b in the main body portion 101a. Each blade shaft hole 101c penetrates the main body portion 101a in the axial direction. The plurality of blade shaft holes 101c are disposed circumferentially spaced apart from one another. Specifically, the plurality of blade shaft holes 101c are disposed at equal intervals in the circumferential direction.

[0051] A plurality of blade shaft holes 103c are formed in the main body portion 103a of the nozzle ring 103. Each blade shaft hole 103c is arranged radially inward of the pin shaft hole 103b in the main body portion 103a. Each blade shaft hole 103c penetrates the main body portion 103a in the axial direction. The plurality of blade shaft holes 103c are arranged spaced apart from one another in the circumferential direction. Specifically, the plurality of blade shaft holes 103c are arranged at equal intervals in the circumferential direction.

[0052] The number of blade shaft holes 103c matches the number of blade shaft holes 101c. Each blade shaft hole 103c faces each blade shaft hole 101c in the axial direction. That is, each blade shaft hole 103c is arranged coaxially with each blade shaft hole 101c. Blade shafts 113a protrude in the axial direction from both axially opposite surfaces of each nozzle vane 113. Each blade shaft 113a is inserted through the blade shaft hole 101c and the blade shaft hole 103c, respectively. Each blade shaft 113a is rotatably supported by the blade shaft hole 101c and the blade shaft hole 103c, respectively.

[0053] The multiple nozzle vanes 113 are arranged in the flow passage 31 at intervals from one another in the circumferential direction. That is, the multiple nozzle vanes 113 are arranged radially outward of the turbine wheel 17 at intervals from one another in the circumferential direction. Specifically, the multiple nozzle vanes 113 are arranged at equal intervals in the circumferential direction. Each nozzle vane 113 is provided integrally with the blade shaft 113a so as to be rotatable about the central axis of the blade shaft 113a. That is, each nozzle vane 113 is provided so as to be rotatable about a rotation axis that extends along the axial direction of the turbine wheel 17.

[0054] 1, the actuator 117 is disposed outside the turbine housing 5, the bearing housing 3, and the compressor housing 7. The actuator 117 is, for example, a solenoid. The actuator 117 is connected to a drive mechanism 115. The drive mechanism 115 converts the linear motion of the actuator 117 into rotational motion about a rotation axis RA.

[0055] When the actuator 117 is driven, the rotation axis RA of the drive mechanism 115 rotates. When the rotation axis RA rotates, the link plate 111 rotates integrally with the rotation axis RA around the central axis of the rotation axis RA. When the link plate 111 rotates, the link plate engaging portion 107c is pressed in the circumferential direction of the link plate 111, causing the drive ring 107 to rotate around the central axis of the drive ring 107. When the drive ring 107 rotates, the transfer link 109 is pressed in the circumferential direction by the transfer link engaging portion 107b, causing the transfer link 109 to rotate around the central axis of the insertion hole 109b. When the transfer link 109 rotates, the blade shaft 113a rotates integrally with the transfer link 109. When the blade shaft 113a rotates, the nozzle vane 113 rotates integrally with the blade shaft 113a.

[0056] When each nozzle vane 113 rotates, the distance between two circumferentially adjacent nozzle vanes 113 changes. When the distance between two circumferentially adjacent nozzle vanes 113 changes, the flow path cross-sectional area of ​​the flow passage 31 changes. When the flow path cross-sectional area of ​​the flow passage 31 changes, the flow velocity of the exhaust gas flowing through the flow passage 31 changes.

[0057] The variable displacement mechanism 100 rotates the multiple nozzle vanes 113 in accordance with the flow rate of exhaust gas, thereby changing the distance between two circumferentially adjacent nozzle vanes 113. This changes the opening degree of the nozzle vanes 113. The closer the extension direction of the nozzle vanes 113 is to the circumferential direction of the turbine wheel 17, the narrower the distance between two circumferentially adjacent nozzle vanes 113, and the smaller the opening degree of the nozzle vanes 113. On the other hand, the larger the angle formed between the extension direction of the nozzle vanes 113 and the circumferential direction of the turbine wheel 17, the wider the distance between two circumferentially adjacent nozzle vanes 113, and the larger the opening degree of the nozzle vanes 113.

[0058] The opening degree of the nozzle vanes 113 is adjustable within a range having upper and lower limits. When the nozzle vanes 113 are fully closed, the extension direction of the nozzle vanes 113 is closest to the circumferential direction of the turbine wheel 17, and the opening degree of the nozzle vanes 113 is minimum. On the other hand, when the nozzle vanes 113 are fully open, the angle formed between the extension direction of the nozzle vanes 113 and the circumferential direction of the turbine wheel 17 is maximum, and the opening degree of the nozzle vanes 113 is maximum. The smaller the opening degree of the nozzle vanes 113, the smaller the flow path cross-sectional area of ​​the flow passage 31.

[0059] For example, when the flow rate of exhaust gas is small, the variable capacity mechanism 100 reduces the opening of the nozzle vanes 113 to increase the flow velocity of the exhaust gas. This allows the variable capacity mechanism 100 to increase the rotation amount of the turbine wheel 17 even when the flow rate of exhaust gas is small. As a result, the variable capacity mechanism 100 can increase the rotation amount of the compressor impeller 19 even when the flow rate of exhaust gas is small.

[0060] As described above, each nozzle vane 113 rotates in conjunction with the drive ring 107, which is a circular member rotated by the actuator 117. The drive ring 107 is provided with a link plate engaging portion 107c including a pair of sliding surfaces 107d. The link plate 111, which is a driving member rotated by the actuator 117, is slidably engaged with the pair of sliding surfaces 107d of the link plate engaging portion 107c. As the link plate 111 slides, wear occurs in the link plate engaging portion 107c or the link plate 111. In this embodiment, the drive ring 107 is designed to suppress such wear. Details of the drive ring 107 will be described below with reference to FIGS. 5 and 6.

[0061] FIG. 5 is a diagram illustrating the third region R3 of FIG. 3 . As shown in FIG. 5 , the link plate engaging portion 107c of the drive ring 107 includes a first engaging portion 107c1 and a second engaging portion 107c2. The first engaging portion 107c1 and the second engaging portion 107c2 are spaced apart from each other in the circumferential direction. The pair of sliding surfaces 107d includes a first opposing surface 107d1 of the first engaging portion 107c1 that faces the second engaging portion 107c2, and a second opposing surface 107d2 of the second engaging portion 107c2 that faces the first engaging portion 107c1. The engaging end 111a of the link plate 111 is slidably engaged with the first opposing surface 107d1 and the second opposing surface 107d2.

[0062] A recess 107e is provided in the main body 107a of the drive ring 107. The main body 107a corresponds to the portion of the drive ring 107 excluding the link plate engaging portion 107c, and is separate from the link plate engaging portion 107c. The recess 107e is formed by being recessed radially from the inner peripheral surface of the main body 107a. The circumferential width of the recess 107e decreases as it approaches the bottom 107e1. In the example of FIG. 5 , the recess 107e has a trapezoidal shape when viewed axially. The bottom 107e1 corresponds to the upper base of the trapezoid. The circumferential side surfaces 107e2 and 107e3 of the recess 107e correspond to the oblique sides of the trapezoid. In the recess 107e, the circumferential distance between the side surfaces 107e2 and 107e3 decreases as it approaches the bottom 107e1.

[0063] The first engaging portion 107c1 is joined to the side surface 107e2 of the recessed portion 107e by welding. Therefore, the first engaging portion 107c1 is joined to the side surface 107e2 of the recessed portion 107e via a welded portion W. The second engaging portion 107c2 is joined to the side surface 107e3 of the recessed portion 107e by welding. Therefore, the second engaging portion 107c2 is joined to the side surface 107e3 of the recessed portion 107e via a welded portion W.

[0064] The first opposing surface 107d1 of the first engaging portion 107c1 and the second opposing surface 107d2 of the second engaging portion 107c2 face each other in the circumferential direction. The first opposing surface 107d1 and the second opposing surface 107d2 extend on a plane that intersects with the circumferential direction. The first opposing surface 107d1 and the second opposing surface 107d2 are, for example, parallel to each other.

[0065] Although the first engagement portion 107c1 is joined to the side surface 107e2 of the recessed portion 107e, it is not joined to the bottom portion 107e1 and is radially spaced apart from the bottom portion 107e1. Therefore, a first gap 107f is formed between the bottom portion 107e1 and the first engagement portion 107c1. The radially outer portion of the first engagement portion 107c1 faces the bottom portion 107e1. In other words, the first gap 107f is the gap between the radially outer portion of the first engagement portion 107c1 and the bottom portion 107e1. The first gap 107f is formed due to the manufacturing process of the drive ring 107, which will be described later.

[0066] Although the second engagement portion 107c2 is joined to the side surface 107e3 of the recessed portion 107e, it is not joined to the bottom portion 107e1 and is radially spaced apart from the bottom portion 107e1. Therefore, a second gap 107g is formed between the bottom portion 107e1 and the second engagement portion 107c2. The radially outer portion of the second engagement portion 107c2 faces the bottom portion 107e1. In other words, the second gap 107g is the gap between the radially outer portion of the second engagement portion 107c2 and the bottom portion 107e1. The second gap 107g is formed due to the manufacturing process of the drive ring 107, which will be described later.

[0067] A first groove 107h is provided on the second engagement portion 107c2 side of the portion of the first engagement portion 107c1 facing the bottom portion 107e1. The first groove 107h is recessed in a direction away from the bottom portion 107e1. In other words, the first groove 107h is provided on the opposite side of the side surface 107e2 in the radially outer portion of the first engagement portion 107c1, and is recessed radially inward. The first groove 107h is formed during the manufacturing process of the drive ring 107, which will be described later.

[0068] A second groove 107i is provided on the first engagement portion 107c1 side of the second engagement portion 107c2, facing the bottom 107e1, and recessed in a direction away from the bottom 107e1. In other words, the second groove 107i is provided on the opposite side of the side surface 107e3 in the radially outer portion of the second engagement portion 107c2, and recessed radially inward. The second groove 107i is formed during the manufacturing process of the drive ring 107, which will be described later.

[0069] Figure 6 is a cross-sectional view showing the A-A cross section in Figure 5. The A-A cross section passes through the engaging end 111a of the link plate 111 and is perpendicular to the circumferential direction. Of the first engaging portion 107c1 and the second engaging portion 107c2, only the second engaging portion 107c2 is shown in Figure 6. However, the shape of the first engaging portion 107c1 and the shape of the second engaging portion 107c2 are symmetrical with respect to the A-A cross section. Hereinafter, the thickness of a member refers to the length in the axial direction.

[0070] As shown in FIG. 6 , the thickness D1 of the second engagement portion 107c2 is thicker than the thickness D2 of the main body portion 107a. In the example of FIG. 6 , the axial position of the right end of the second engagement portion 107c2 coincides with the axial position of the right end of the main body portion 107a. Meanwhile, the left end of the second engagement portion 107c2 is located to the left of the left end of the main body portion 107a. The thickness of the first engagement portion 107c1 coincides with the thickness D1 of the second engagement portion 107c2. Therefore, the thickness D1 of the link plate engagement portion 107c is thicker than the thickness D2 of the surrounding portion of the drive ring 107.

[0071] The thickness D3 of the engaging end 111a of the link plate 111 is thicker than the thickness D4 of the portion of the link plate 111 excluding the engaging end 111a. In the example of Fig. 6, the axial position of the right end of the engaging end 111a coincides with the axial position of the right end of the portion of the link plate 111 excluding the engaging end 111a. On the other hand, the left end of the engaging end 111a is located to the left of the left end of the portion of the link plate 111 excluding the engaging end 111a.

[0072] The thickness D4 of the link plate 111 excluding the engaging end 111 a is greater than the thickness D2 of the main body 107 a. In the example of Fig. 6, the right end of the link plate 111 excluding the engaging end 111 a is located to the right of the right end of the main body 107 a. The left end of the link plate 111 excluding the engaging end 111 a is located to the left of the left end of the main body 107 a.

[0073] The thickness D3 of the engaging end 111a is greater than the thickness D1 of the link plate engaging portion 107c. In the example of Fig. 6, the right end of the engaging end 111a is located to the right of the right end of the second engaging portion 107c2. The left end of the engaging end 111a is located to the left of the left end of the second engaging portion 107c2.

[0074] The manufacturing process of the drive ring 107 according to this embodiment will be described below with reference to FIGS.

[0075] The manufacturing process of the drive ring 107 involves the following steps, which are carried out in this order: a first step of preparing the main body portion 107a; a second step of joining a thick member (see thick member 121 in Figure 8 described later) to the recessed portion 107e of the main body portion 107a by welding; and a third step of forming the first engagement portion 107c1 and the second engagement portion 107c2 by cutting the thick member.

[0076] FIG. 7 is a diagram illustrating the first step in the manufacturing process of the drive ring 107 according to this embodiment. In the first step, a main body portion 107a is prepared. The main body portion 107a corresponds to the portion of the drive ring 107 excluding the link plate engaging portion 107c, and is separate from the link plate engaging portion 107c. In particular, as shown in FIG. 7 , in the first step, a recessed portion 107e, whose circumferential width decreases as it approaches the bottom portion 107e1, is recessed from the inner circumferential surface of the main body portion 107a. For example, the main body portion 107a is formed by punching a thin plate material. In this case, the recessed portion 107e is formed by, for example, the punching process described above.

[0077] 8 is a diagram illustrating a second step in the manufacturing process of the drive ring 107 according to this embodiment. The second step is performed after the first step. In the second step, a thick member 121 having a thickness D1 greater than the thickness D2 of the main body portion 107a is joined to the recessed portion 107e by welding. The thick member 121 corresponds to the material of the first engaging portion 107c1 and the second engaging portion 107c2. The thick member 121 has the same thickness D1 as the thickness D1 of the first engaging portion 107c1 and the second engaging portion 107c2.

[0078] 8 , in the second step, the thick member 121 is joined by welding to the side surfaces 107e2 and 107e3 of the recess 107e on both sides in the circumferential direction. Thus, the thick member 121 is joined to the side surface 107e2 of the recess 107e via the weld W, and is also joined to the side surface 107e3 of the recess 107e via the weld W.

[0079] Although the thick member 121 is joined to the side surfaces 107e2 and 107e3 of the recess 107e, it is not joined to the bottom 107e1 and is spaced apart from the bottom 107e1 in the radial direction. Therefore, a gap 121a is formed between the bottom 107e1 and the thick member 121. As a result of the gap 121a being formed in the second step, a first gap 107f is formed between the bottom 107e1 and the first engaging portion 107c1, and a second gap 107g is formed between the bottom 107e1 and the second engaging portion 107c2 in the third step, as will be described later.

[0080] A groove 121b recessed in a direction away from the bottom 107e1 is provided on the circumferential center side of the portion of the thick member 121 facing the bottom 107e1. By providing the groove 121b in the thick member 121, a first groove 107h of the first engaging portion 107c1 and a second groove 107i of the second engaging portion 107c2 are formed in the third step, as will be described later.

[0081] 9 is a diagram for explaining the third step in the manufacturing process of the drive ring 107 according to this embodiment. The third step is performed after the second step. In the third step, the first engaging portion 107c1 and the second engaging portion 107c2 are formed by cutting the thick member 121.

[0082] The thick-walled member 121 is cut and removed in region R4 shown in FIG. 9 . As shown in FIG. 9 , region R4 is a region of the thick-walled member 121 excluding both circumferential sides. For example, the thick-walled member 121 is cut using a cutting tool such as an end mill. As a result, the first engaging portion 107c1 and the second engaging portion 107c2 are formed as the link plate engaging portion 107c. The first engaging portion 107c1 is a portion of the thick-walled member 121 that remains after region R4 is removed and is joined to side surface 107e2. The second engaging portion 107c2 is a portion of the thick-walled member 121 that remains after region R4 is removed and is joined to side surface 107e3.

[0083] By cutting the thick member 121 as described above, the first opposing surface 107d1 of the first engaging portion 107c1 and the second opposing surface 107d2 of the second engaging portion 107c2 are formed as a pair of sliding surfaces 107d.

[0084] By forming gap 121a in the second step, a first gap 107f is formed between bottom portion 107e1 and first engaging portion 107c1, and a second gap 107g is formed between bottom portion 107e1 and second engaging portion 107c2 after cutting thick member 121 in the third step. In other words, in the manufacturing process of drive ring 107, thick member 121 is welded to recessed portion 107e so that first gap 107f is formed between bottom portion 107e1 and first engaging portion 107c1, and second gap 107g is formed between bottom portion 107e1 and second engaging portion 107c2.

[0085] As described above, by providing groove 121b in thick member 121, first groove 107h of first engaging portion 107c1 and second groove 107i of second engaging portion 107c2 are formed after cutting thick member 121 in the third step. In other words, in the manufacturing process of drive ring 107, thick member 121 is cut so as to form first groove 107h of first engaging portion 107c1 and second groove 107i of second engaging portion 107c2.

[0086] As described above, in the turbine T according to this embodiment, the link plate engaging portion 107c, which is an engaging portion including a pair of sliding surfaces 107d facing each other in the circumferential direction, is provided on the drive ring 107, which is a circular member provided so as to be rotatable in conjunction with the plurality of nozzle vanes 113. The link plate 111, which is a driving member that is driven to rotate by the actuator 117, is slidably engaged with the pair of sliding surfaces 107d. The link plate engaging portion 107c has a thickness D1 that is thicker than a thickness D2 of the surrounding portion of the drive ring 107.

[0087] Furthermore, the manufacturing method of the turbine T according to this embodiment includes preparing a turbine wheel 17, arranging a plurality of nozzle vanes 113 radially outward of the turbine wheel 17 and spaced apart in the circumferential direction of the turbine wheel 17, and arranging them so that they can rotate freely around a rotation axis along the axial direction of the turbine wheel 17, providing a drive ring 107, which is a circular member extending in the circumferential direction, so that it can rotate freely in conjunction with the plurality of nozzle vanes 113, and providing, on the drive ring 107, a link plate engaging portion 107 c, which includes a pair of sliding surfaces 107 d facing each other in the circumferential direction and is an engaging portion in which a link plate 111, which is a driving member driven to rotate by an actuator 117, is slidably engaged with the pair of sliding surfaces 107 d, and which has a thickness D1 that is thicker than a thickness D2 of a surrounding portion of the drive ring 107.

[0088] According to the above-described turbine T and manufacturing method for the turbine T, it is possible to increase the contact area between the link plate engaging portion 107c and the engaging end 111a of the link plate 111. This reduces the surface pressure generated between the link plate engaging portion 107c and the engaging end 111a of the link plate 111. This reduces wear of the link plate engaging portion 107c or the link plate 111 due to sliding of the link plate 111.

[0089] Examples of the thicknesses of the drive ring 107 and the link plates 111 have been described above with reference to Figure 6. However, the thicknesses of the drive ring 107 and the link plates 111 are not limited to the above example. For example, the thickness D2 of the main body 107a of the drive ring 107 may be constant or may vary depending on the position. For example, the thickness D4 of the portion of the link plate 111 excluding the engaging end 111a may be the same as the thickness D3 of the engaging end 111a of the link plate 111, or may be thicker than the thickness D3.

[0090] In particular, in the manufacturing method of the turbine T according to this embodiment, providing the link plate engaging portion 107c on the drive ring 107 includes preparing a main body portion 107a that corresponds to the portion of the drive ring 107 excluding the link plate engaging portion 107c, is separate from the link plate engaging portion 107c, and extends in the circumferential direction, and joining the link plate engaging portion 107c to the main body portion 107a by welding. As a result, in the turbine T according to this embodiment, the drive ring 107 includes the main body portion 107a that corresponds to the portion of the drive ring 107 excluding the link plate engaging portion 107c, is separate from the link plate engaging portion 107c, and extends in the circumferential direction, and the link plate engaging portion 107c is joined to the main body portion 107a via at least one weld W.

[0091] The above-described turbine T and manufacturing method for the turbine T can reduce processing costs compared to when the link plate engaging portion 107c and the main body portion 107a are integrally formed by machining or the like. Furthermore, unlike when the link plate engaging portion 107c is press-fitted into the main body portion 107a, stress caused by press-fitting can be suppressed, and cracking of the members can be suppressed. However, the link plate engaging portion 107c and the main body portion 107a may also be integrally formed by machining or the like. The link plate engaging portion 107c may also be press-fitted into the main body portion 107a.

[0092] In particular, in the manufacturing method of the turbine T according to this embodiment, preparing the main body portion 107a includes forming a recess 107e, the recess 107e having a circumferential width that decreases toward the bottom 107e1, recessed from the circumferential surface of the main body portion 107a, and joining the link plate engaging portion 107c to the main body portion 107a includes joining the link plate engaging portion 107c to each of the side surfaces 107e2, 107e3 on both circumferential sides of the recess 107e by welding. As a result, in the turbine T according to this embodiment, the main body 107a includes the recess 107e, the recess 107e being recessed from the circumferential surface of the main body portion 107a and the recess 107e having a circumferential width that decreases toward the bottom 107e1, and the link plate engaging portion 107c is joined to each of the side surfaces 107e2, 107e3 on both circumferential sides of the recess 107e via welds W.

[0093] According to the turbine T and the manufacturing method for the turbine T described above, the circumferential width of the recess 107e decreases toward the bottom 107e1, which allows the link plate engaging portion 107c to be appropriately welded to each of the side surfaces 107e2 and 107e3 of the recess 107e. This allows the link plate engaging portion 107c to be joined to the main body portion 107a by welding rather than press-fitting, and then appropriately positioned. However, the shape and position of the recess 107e are not limited to the above example. For example, the circumferential width of the recess 107e may be constant regardless of the radial position. For example, the recess 107e may be recessed from the outer circumferential surface of the main body portion 107a.

[0094] In particular, in the manufacturing method of the turbine T according to this embodiment, joining the link plate engaging portion 107c to the main body portion 107a involves joining a thick member 121 having a thickness D1 that is thicker than the thickness D2 of the main body portion 107a to each of the side surfaces 107e2, 107e3 on both sides of the recessed portion 107e in the circumferential direction by welding, and cutting the thick member 121 to remove the first engaging portion 107e joined to the side surface 107e2 on one side of the recessed portion 107e in the circumferential direction by welding. c1 and a second engaging portion 107c2 that is joined by welding to the other circumferential side surface 107e3 of the recess portion 107e and is spaced apart from the first engaging portion 107c1 in the circumferential direction, are formed as the link plate engaging portion 107c, and a first opposing surface 107d1 of the first engaging portion 107c1 that faces the second engaging portion 107c2, and a second opposing surface 107d2 of the second engaging portion 107c2 that faces the first engaging portion 107c1 are formed as the pair of sliding surfaces 107d. As a result, in the turbine T of this embodiment, the link plate engagement portion 107c includes a first engagement portion 107c1 joined to one circumferential side surface 107e2 of the recessed portion 107e via a weld W, and a second engagement portion 107c2 joined to the other circumferential side surface 107e3 of the recessed portion 107e via a weld W and circumferentially spaced apart from the first engagement portion 107c1, and the pair of sliding surfaces 107d include a first opposing surface 107d1 of the first engagement portion 107c1 that faces the second engagement portion 107c2, and a second opposing surface 107d2 of the second engagement portion 107c2 that faces the first engagement portion 107c1.

[0095] According to the turbine T and the manufacturing method of the turbine T described above, the first engaging portion 107c1 and the second engaging portion 107c2 and the first opposing surface 107d1 and the second opposing surface 107d2 can be formed by the simple process of welding the thick member 121 to the recessed portion 107e and then cutting the thick member 121. However, the link plate engaging portion 107c may be an integrally formed member rather than a plurality of separated members. For example, unlike the example shown in FIG. 9 , the cut region R4 of the thick member 121 may not reach the groove portion 121b, and the first engaging portion 107c1 and the second engaging portion 107c2 may be connected without being separated.

[0096] In particular, in the manufacturing method of the turbine T according to this embodiment, joining the link plate engaging portion 107c to the main body portion 107a includes joining the thick-walled member 121 by welding to each of the side surfaces 107e2, 107e3 on both circumferential sides of the recessed portion 107e so that a first gap 107f is formed between the bottom portion 107e1 and the first engaging portion 107c1 and a second gap 107g is formed between the bottom portion 107e1 and the second engaging portion 107c2. As a result, in the turbine T according to this embodiment, the first gap 107f is formed between the bottom portion 107e1 and the first engaging portion 107c1 and the second gap 107g is formed between the bottom portion 107e1 and the second engaging portion 107c2.

[0097] According to the turbine T and the manufacturing method of the turbine T described above, the bottom portion 107e1 and the first engaging portion 107c1 are not welded, and the bottom portion 107e1 and the second engaging portion 107c2 are not welded. This prevents an increase in thermal stress due to an increase in the welding area. Therefore, cracks in the members due to thermal stress can be prevented. However, the bottom portion 107e1 and the first engaging portion 107c1 may be welded, or the bottom portion 107e1 and the second engaging portion 107c2 may be welded. For example, the thick member 121 may be welded to the bottom portion 107e1 at the stage when the thick member 121 is welded to the recessed portion 107e.

[0098] In particular, in the manufacturing method of the turbine T according to this embodiment, joining the link plate engagement portion 107c to the main body portion 107a includes cutting the thick member 121 so that a first groove portion 107h recessed in a direction away from the bottom portion 107e1 is provided on the second engagement portion 107c2 side of the portion of the first engagement portion 107c1 facing the bottom portion 107e1, and a second groove portion 107i recessed in a direction away from the bottom portion 107e1 is provided on the first engagement portion 107c1 side of the portion of the second engagement portion 107c2 facing the bottom portion 107e1. As a result, in the turbine T of this embodiment, a first groove portion 107h recessed in a direction away from the bottom portion 107e1 is provided on the second engagement portion 107c2 side of the first engagement portion 107c1 in the portion facing the bottom portion 107e1, and a second groove portion 107i recessed in a direction away from the bottom portion 107e1 is provided on the first engagement portion 107c1 side of the second engagement portion 107c2 in the portion facing the bottom portion 107e1.

[0099] The turbine T and the manufacturing method of the turbine T described above can prevent burrs or chips generated during cutting of the thick member 121 from remaining between the bottom portion 107e1 and the first engagement portion 107c1 or between the bottom portion 107e1 and the second engagement portion 107c2. For example, burrs or chips generated near the first engagement portion 107c1 during cutting of the thick member 121 are guided by the first groove portion 107h, making them less likely to invade the side surface 107e2 side of the first gap 107f than the first groove portion 107h. For example, burrs or chips generated near the second engagement portion 107c2 during cutting of the thick member 121 are guided by the second groove portion 107i, making them less likely to invade the side surface 107e3 side of the second gap 107g than the second groove portion 107i. However, the first engaging portion 107c1 does not necessarily have to be provided with the first groove portion 107h, and the second engaging portion 107c2 does not necessarily have to be provided with the second groove portion 107i.

[0100] Although the embodiments of the present disclosure have been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to such embodiments. It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present disclosure.

[0101] In the above description, an example has been described in which the turbine T is mounted on the turbocharger TC. However, the device on which the turbine T is mounted may be a device other than the turbocharger TC.

[0102] 17: Turbine impeller 107: Drive ring (annular member) 107a: Main body 107c: Link plate engaging portion (engaging portion) 107c1: First engaging portion 107c2: Second engaging portion 107d: Sliding surface 107d1: First opposing surface 107d2: Second opposing surface 107e: Recessed portion 107e1: Bottom 107e2: Side surface 107e3: Side surface 107f: First gap 107g: Second gap 107h: First groove portion 107i: Second groove portion 111: Link plate (driving member) 113: Nozzle vane 117: Actuator 121: Thick member T: Turbine W: Welded portion

Claims

1. A turbine comprising: a turbine wheel; a plurality of nozzle vanes arranged radially outwardly of the turbine wheel and spaced apart in the circumferential direction of the turbine wheel and rotatable about a rotation axis along the axial direction of the turbine wheel; a circular ring member extending in the circumferential direction and rotatable in conjunction with the plurality of nozzle vanes; and an engagement portion provided on the circular member and including a pair of sliding surfaces facing each other in the circumferential direction, a drive member driven to rotate by an actuator slidably engaging with the pair of sliding surfaces, the engagement portion having a thickness greater than a thickness of a surrounding portion of the circular member.

2. The turbine described in claim 1, wherein the annular member corresponds to a portion of the annular member excluding the engaging portion, is separate from the engaging portion, and includes a main body portion extending in the circumferential direction, and the engaging portion is joined to the main body portion via at least one weld.

3. The turbine according to claim 2, wherein the main body portion includes a recessed portion formed by being recessed from the circumferential surface of the main body portion and the circumferential width becomes shorter as it approaches a bottom portion, and the engagement portion is joined to each of the circumferentially opposite side surfaces of the recessed portion via the welded portion.

4. The turbine described in claim 3, wherein the engagement portion includes a first engagement portion joined to one circumferential side surface of the recessed portion via the welded portion, and a second engagement portion joined to the other circumferential side surface of the recessed portion via the welded portion and spaced apart in the circumferential direction from the first engagement portion, and the pair of sliding surfaces include a first opposing surface of the first engagement portion that faces the second engagement portion, and a second opposing surface of the second engagement portion that faces the first engagement portion.

5. The turbine according to claim 4, wherein a first gap is formed between the bottom and the first engagement portion, and a second gap is formed between the bottom and the second engagement portion.

6. A turbine as described in claim 5, wherein a first groove portion recessed in a direction away from the bottom is provided on the second engagement portion side of the first engagement portion in a portion facing the bottom, and a second groove portion recessed in a direction away from the bottom is provided on the first engagement portion side of the second engagement portion in a portion facing the bottom.

7. A method for manufacturing a turbine comprising: preparing a turbine wheel; arranging a plurality of nozzle vanes radially outward of the turbine wheel and spaced apart in the circumferential direction of the turbine wheel, and rotatably rotatable about a rotation axis along the axial direction of the turbine wheel; providing a circular ring member extending in the circumferential direction so as to be rotatable in conjunction with the plurality of nozzle vanes; and providing an engaging portion on the circular ring member, the engaging portion including a pair of sliding surfaces facing each other in the circumferential direction, a driving member driven to rotate by an actuator slidably engaging with the pair of sliding surfaces, the engaging portion having a thickness greater than a thickness of a surrounding portion of the circular ring member.

8. A method for manufacturing a turbine as described in claim 7, wherein providing the engaging portion on the circular member includes: preparing a main body portion that corresponds to a portion of the circular member excluding the engaging portion, is separate from the engaging portion, and extends in the circumferential direction; and joining the engaging portion to the main body portion by welding.

9. A method for manufacturing a turbine as described in claim 8, wherein preparing the main body portion includes forming a recess portion recessed from the circumferential surface of the main body portion, the circumferential width of which decreases as it approaches a bottom portion, and joining the engagement portion to the main body portion includes joining the engagement portion to each of the circumferentially opposite side surfaces of the recess portion by welding.

10. A method for manufacturing a turbine as claimed in claim 9, wherein joining the engaging portion to the main body portion includes: joining a thick-walled member having a thickness greater than that of the main body portion by welding to each of the circumferentially opposite side surfaces of the recessed portion; and cutting the thick-walled member to form, as the engaging portion, a first engaging portion joined by welding to the circumferentially opposite side surface of the recessed portion on one side, and a second engaging portion joined by welding to the circumferentially opposite side surface of the recessed portion on the other side, the first engaging portion and the second engaging portion being spaced apart in the circumferential direction, and forming, as the pair of sliding surfaces, a first opposing surface of the first engaging portion opposing the second engaging portion, and a second opposing surface of the second engaging portion opposing the first engaging portion.

11. A method for manufacturing a turbine as described in claim 10, wherein joining the engagement portion to the main body portion includes joining the thick-walled member to each of the circumferentially opposite side surfaces of the recessed portion by welding so that a first gap is formed between the bottom and the first engagement portion, and a second gap is formed between the bottom and the second engagement portion.

12. A method for manufacturing a turbine as described in claim 11, wherein joining the engagement portion to the main body portion includes cutting the thick-walled member so that a first groove portion recessed in a direction away from the bottom is provided on the second engagement portion side of the first engagement portion in a portion facing the bottom, and a second groove portion recessed in a direction away from the bottom is provided on the first engagement portion side of the portion facing the bottom.