TURBOCHARGER WITH VARIABLE GEOMETRY

Abstract

Turbocharger (10) with variable geometry, comprising: a rotating shaft (12); a turbine wheel (14) which is arranged at one end of the rotating shaft (12); a compressor wheel (16) which is arranged at another end of the rotating shaft (12); a bearing housing (24) for receiving a bearing part (18) for rotatably supporting the rotating shaft (12); a variable nozzle structure (26) for controlling a flow rate of an exhaust gas flowing into the turbine wheel (14), wherein the variable nozzle structure (26) comprises a nozzle plate (28) and a nozzle holder (30) that define an exhaust gas flow passage (32) to allow the exhaust gas to flow into the turbine wheel (14), a nozzle vane (34) which is rotatably arranged about a bearing shaft (36) in the exhaust gas flow passage (32), and a drive element (38) for rotating the nozzle blade (34), wherein the drive element (38) is arranged in an interior space defined between the bearing housing (24) and the nozzle holder (30); and a cooling gas passage (42) for extracting compressed gas that is compressed by the compressor wheel (16) and introducing the compressed gas into the interior, where: a) the cooling gas passage (42) has an outlet side opening (44) which communicates with the interior, and wherein the variable geometry turbocharger (10) comprises a perforated plate which divides the interior along an axial direction of the rotating shaft (12), the perforated plate being arranged in the interior such that the drive part (38) is arranged in a side space formed on one side of the perforated plate, and the outlet side opening (44) communicates with another side space formed on another side of the perforated plate; or b) wherein the turbine wheel (14) has a third through-hole which causes a rear surface of the turbine wheel (14) to be connected to an exhaust gas outlet flow passage which is formed downstream of the turbine wheel (14).

Description

TECHNICAL AREA

[0001] The present disclosure relates to a variable geometry turbocharger. BACKGROUND

[0002] An exhaust gas turbocharger uses the energy from the exhaust gases emitted by the engine to increase the speed of air supplied to the engine. The turbocharger can be of a variable geometry type, equipped with a variable nozzle structure. In this structure, a number of nozzle blades are rotatably mounted between a nozzle holder and a nozzle plate, and the blade angle of each blade can be adjusted. By changing the blade angle, it is possible to vary the flow range of the exhaust gas supplied to the turbine wheel. This allows for the adjustment of the flow velocity or the amount of exhaust gas supplied to the turbine wheel, as well as the regulation of the boost pressure of the air supplied to the engine.

[0003] The exhaust gas temperature fed to the turbine housing of an exhaust gas turbocharger is approximately 800°C for a diesel engine and approximately 1,000°C for a gasoline engine, and the durability of the components against the increasing exhaust gas temperature is a concern. An exhaust gas turbocharger disclosed in Patent Document 1 aims to improve the thermal cycle efficiency by increasing the exhaust gas temperature at an inlet of the turbine housing to no less than 1,000°C. In Patent Document 1, a cooling hole is provided in the turbine wheel, and compressed air on one side of the compressor is fed into the cooling hole to cool the turbine wheel, thus mitigating the effects of the high-temperature environment. List of citations from patent literature

[0004] Patent Document 1: JP2004-232622A

[0005] JP S61-19602 U discloses a turbocharger in which a nozzle blade is arranged in a gas flow channel from a turbine inlet chamber to a turbine wheel, wherein one end of a blade shaft attached to the nozzle blade protrudes from the turbocharger housing, and the blade shaft is rotatably mounted in a bushing attached to a housing. JP S59-97238 U discloses a variable nozzle vane compressor in which a turbine wheel and a compressor wheel are connected by a rotating shaft, the turbine wheel is housed in a compressor casing, and a nozzle vane is arranged in the turbine casing. The turbine casing is provided with a pressure chamber that is separated from the turbine casing by a partition. JP S59-168 534 U discloses a turbine housing with a pair of left and right support walls, each of which holds a storage chamber on an opposite wall surface and has a support shaft through-bore in an axial core part, and an exhaust inlet and an outlet connected to the inlet, and a supercharger housing with an outside air inlet and a charge air inlet connected to the inlet. US 2018 / 0149078A1 discloses an inner circumferential edge of a first annular element comprising a plurality of first inner edge sections belonging to an angular region in which support holes are present in the circumferential direction of a turbine rotor, and a plurality of second inner edge sections belonging to an angular region in which no support holes are present in the circumferential direction of the turbine rotor. SUMMARY Technical Problem

[0006] In a variable geometry turbocharger, there is a problem where, for example, thermal deformation in a nozzle holder due to an increasing temperature of an exhaust gas causes a nozzle shaft to stick to the nozzle holder, which disables rotation of the nozzle blade or promotes wear of a drive ring, lever plate or the like that form a variable nozzle structure at high temperature.

[0007] The present disclosure was made with regard to the above problem, and one objective of the present disclosure is to solve the above-described problem concerning the variable geometry turbocharger component caused by the increasing temperature of the exhaust gas. Solution to the problem

[0008] To solve the above problem, a variable geometry turbocharger according to the present disclosure comprises a rotating shaft; a turbine wheel arranged at one end of the rotating shaft; a compressor wheel arranged at another end of the rotating shaft; a bearing housing for receiving a bearing part for rotatably supporting the rotating shaft; a variable nozzle structure for controlling a flow rate of an exhaust gas flowing into the turbine wheel, wherein the variable nozzle structure comprises a nozzle plate and a nozzle holder defining an exhaust gas flow channel to allow the exhaust gas to flow into the turbine wheel, a nozzle blade rotatably arranged about a support shaft in the exhaust gas flow channel, and a drive part for rotating the nozzle blade, wherein the drive part is arranged in an interior space defined between the bearing housing and the nozzle holder;and a cooling gas channel for extracting compressed gas that is compressed by the compressor wheel and introducing the compressed gas into the interior.; Beneficial effects

[0009] With a variable geometry turbocharger according to the present disclosure, it is possible, even if the temperature of an exhaust gas increases, to suppress thermal deformation, high-temperature wear, or the like in the configuration of a variable nozzle structure, which includes, for example, a nozzle holder, a drive ring, a lever plate, and the like, under a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a longitudinal sectional view of a variable geometry turbocharger according to one embodiment. Fig. 2 is a view from direction A in Fig. 1. Fig. Figure 3 is an enlarged explanatory view of a part of Fig. 1. Fig. Figure 4 is a longitudinal sectional view of a variable geometry turbocharger according to one embodiment. Fig. Figure 5 is a longitudinal sectional view of a variable geometry turbocharger according to one embodiment. Fig. Figure 6 is a front view of a perforated plate according to one embodiment. Fig. Figure 7 is a longitudinal sectional view of a variable geometry turbocharger according to one embodiment. DETAILED DESCRIPTION

[0010] Fig. 1 to Fig. Figure 7 shows variable geometry turbochargers 10 (10A, 10B, 10C, 10D) according to some embodiments. In each of these variable geometry turbochargers 10, a rotating shaft 12 is arranged laterally in the center of a housing, a turbine wheel 14 is arranged at one end of the rotating shaft 12, and a compressor wheel 16 is arranged at the other end of the rotating shaft 12. A housing for accommodating these elements consists of a turbine housing 20 for housing the turbine wheel 14, a compressor cover 22 for housing the compressor wheel 16, and a bearing housing 24, which is arranged between the turbine housing 20 and the compressor cover 22 to accommodate bearing elements 18 for rotatably supporting the rotating shaft 12.

[0011] Furthermore, the turbine housing 20 internally includes a variable nozzle structure 26 for controlling the flow rate of an exhaust gas e flowing into the turbine wheel 14. The variable nozzle structure 26 comprises a nozzle plate 28 and a nozzle holder 30, and the nozzle plate 28 and the nozzle holder 30 define an exhaust gas flow passage 32 to allow the exhaust gas e to flow into the turbine wheel 14. A nozzle blade 34 is rotatably arranged about a bearing shaft 36 in the exhaust gas flow passage 32. An interior space Si is defined between the bearing housing 24 and the nozzle holder 30, and a drive element 38 for rotating the nozzle blade 34 is arranged in the interior space Si. Additionally, a cooling gas passage 42 (42a, 42b) is provided for extracting compressed gas g (for example, compressed air) which is compressed by the compressor wheel 16, and introducing the compressed gas g into the interior Si.

[0012] With such a configuration, the elements forming the variable nozzle structure 26 can be cooled by supplying the compressed gas g, which is compressed by the compressor wheel 16, to the interior Si through the cooling gas passage 42, thereby making it possible to suppress thermal deformation or wear of these elements in the turbine housing 20, into which the high-temperature exhaust gas e is introduced.

[0013] Fig. 2 is a view from one direction of an arrow A in Fig. 1. In one embodiment, as in Fig. As shown in Figure 2, the drive element 38 of the variable nozzle structure 26, which is located in the interior Si, comprises a drive ring 45 and a lever plate 46 as components. A plurality of lever plates 46 each have one end connected to the drive ring 45 and another end coupled to the bearing shaft 36 of the nozzle blade 34, and are arranged along the circumferential direction of the drive ring 45. The drive ring 45 rotates about an axis of the rotating shaft 12 in the direction of arrow b, thereby rotating the nozzle blade 34 about the bearing shaft 36. This makes it possible to adjust the flow velocity or the quantity of exhaust gas e flowing through the exhaust gas flow passage 32 and to regulate the boost pressure of air supplied to an engine.The drive element 38, located inside Si, is coupled to an actuator 40, which is located outside the bearing housing 24 via a connecting element 39, and is actuated by the actuator 40. The connecting element 39 penetrates the bearing housing 24 and extends to the outside of the bearing housing 24.

[0014] In one embodiment, a nozzle holder 48 is positioned between the nozzle plate 28 and the nozzle bracket 30 to fix the nozzle plate 28 and the nozzle bracket 30, which define the exhaust gas flow passage 32, at predetermined positions. A plurality of nozzle holders 48 are discretely arranged in the circumferential direction of the nozzle bracket 30.

[0015] In one embodiment as in Fig. As shown in Figure 1, a spiral flow passage 51 is formed in the compressor cover 22. A diffuser flow passage 50 is formed on an outlet side of the compressor wheel 16, and the kinetic energy of the compressed gas g discharged from the compressor wheel 16 is converted into pressure energy in the diffuser flow passage 50. The cooling gas passage 42 has an inlet side opening 43 that communicates with an outlet side region of the diffuser flow passage 50, in which the compressor wheel 16 is housed. The cooling gas passage 42 is configured such that the inlet side opening 43 opens to the outlet side region of the diffuser flow passage 50, and the compressed gas g is extracted from the outlet side region of the diffuser flow passage 50 and introduced into the interior Si. Thus, it is possible to supply the compressed gas g, which is increased in pressure through the diffuser flow passage 50, to the interior Si.With a pressure difference between the inlet side and the outlet side of the cooling gas passage 42, it is possible to easily supply the compressed gas g to the interior Si without requiring any other power.

[0016] Fig. Figure 3 is an enlarged view showing the diffuser flow passage 50. As in Fig. Figure 3 shows, assuming that an inlet of the diffuser flow passage 50 is 0% and an outlet is 100%, the “outlet side region of the diffuser flow passage 50”, to which reference is made in this description, a 50% to 100% region in which the pressure of the compressed gas g is high, and a region facing the spiral flow passage 51, and the inlet side opening 43 preferably opens to this region. Preferably, the inlet side opening 43 opens to an 80% to 100% outlet side region of the diffuser flow passage 50 or the region facing the spiral flow passage 51. However, since the long cooling gas passage 42 must be formed in a region of the spiral flow passage 51 that is away from the outlet of the diffuser flow passage 50, the cooling gas passage 42 preferably opens to a region near the outlet of the diffuser flow passage 50.

[0017] In some embodiments, such as in Fig. 1, Fig. 5 and Fig. As shown in Figure 7, the bearing housing 24 has a through-hole 52 (first through-hole) extending along the axial direction of the rotating shaft 12, and the through-hole 52 forms part of the cooling gas passage 42 (42a). In the present embodiment, the compressed gas g, extracted in the outlet side region of the diffuser flow passage 50, is configured to flow through the through-hole 52 and reach the interior Si. Since part of the cooling gas passage 42 (42a) can thus be formed within the bearing housing 24, no space is required for the cooling gas passage outside the bearing housing 24.

[0018] In one embodiment as in Fig. As shown in Figure 4, an external pipe 54 is erected between the compressor cover 22 and the bearing housing 24, and the external pipe 54 forms part of the cooling gas passage 42 (42b). In the present embodiment, the cooling gas passage 42 (42b) is formed by a flow passage 56, which is formed at a partition of the compressor cover 22, the external pipe 54, and a flow passage 58, which is formed at a partition of the bearing housing 24. According to the present embodiment, since part of the cooling gas passage 42 (42b) can be formed outside the bearing housing 24 by the external pipe 54, the cooling gas passage 42 is formed relatively easily.

[0019] In one embodiment, the external tube 54 can be provided with a check valve 60 to prevent the compressed gas g from flowing back from the interior Si to the side of the compressor cover 22. Furthermore, although not shown, a check valve with the same function can be provided in the through-hole 52.

[0020] In one embodiment as in Fig. As shown in Figure 1, the cooling gas passage 42 (42a) has an outlet side opening 44 which is connected to the interior Si. Furthermore, as shown in Figure 1, the cooling gas passage 42 (42a) has an outlet side opening 44 which is connected to the interior Si. Fig. 5 to Fig. Figure 7 shows a perforated plate 62 provided in the interior Si. The interior Si is divided into two spaces S1 and S2 along the axial direction of the rotating shaft 12 by the perforated plate 62, which extends in a direction orthogonal to the rotating shaft 12. The drive ring 45, the lever plate 46, and the like, which form the drive part 38, are arranged in space S1 (one side space), which is subdivided on the side of the exhaust gas flow passage 32 by the perforated plate 62. The outlet side opening 44 is connected to space S2 (the other side space), which is formed on the side of the compressor cover 22 by the perforated plate 62.

[0021] According to the present embodiment, the compressed gas g, which is supplied from the outlet side opening 44 to the chamber S2 of the interior Si, is dispersed in a jet stream from a plurality of perforated plates 62 as it passes through the through-holes of the perforated plates 62, and is also oriented and accelerated. The jets collide with the drive ring 45, the lever plate 46, the nozzle holder 30, and the like, which are arranged as jets in chamber S2, and perform so-called jet cooling (impact cooling). Thus, it is possible to improve the cooling effect on these elements.

[0022] In one embodiment, the perforated plate 62 is configured such that the opening ratio of a radially inner region is greater than the opening ratio of a radially outer region. Of the nozzle holder 30, the drive ring 45, and the lever plate 46, it is necessary to preferably cool the nozzle holder 30, which is closest to the exhaust gas flow passage 32 and is most easily heated. From the A-direction in Fig. 1 seen as in Fig. As shown in Figure 2, a region of the nozzle holder 30 visible on the radially inner side of the drive ring 45 is larger than a region of the nozzle holder 30 visible on the radially outer side of the drive ring 45. Furthermore, a region near an outer circumferential end of the nozzle holder 30 is in contact with the bearing housing 24 and is therefore not facing the interior Si. Thus, by adjusting the opening ratio of the radially inner region of the perforated plate 62 so that it is larger than the opening ratio of the radially outer region, it is possible to increase the flow rate of the compressed gas g that collides with the nozzle holder 30, which makes it possible to improve the cooling effect on the nozzle holder 30.

[0023] Fig. Figure 6 is a front view of the perforated plate 62 according to one embodiment. A plurality of through holes 64 formed in the perforated plate 62 are configured such that an opening ratio X2 of a radially inner region R2 is greater than an opening ratio X1 of a radially outer region R1. Herein, the opening ratios X1 and X2 are defined by: Opening ratio X1 = Total area of ​​through holes 64 in area R1 / Total areas of area R1 (1); and Opening ratio X2 = Total area of ​​through holes 64 in area R2 / Total areas of area R2 (2). The shape, size, number of through holes 64, the spacing between the through holes 62, and the like can be suitably adjusted. For example, the through hole 64 can have a slot-like shape extending in the circumferential or radial direction.

[0024] In Fig. 6. The setting of an inner circumferential edge of the perforated plate is 62 0% and an outer circumferential surface is 100%, a boundary B between the area R1 and the area R2 is preferably set, for example, to 30% to 70% (preferably 40% to 60%) area.

[0025] In one embodiment, the surface of the perforated plate 62 facing space S2 is configured to have a higher emissivity than the surface of the nozzle holder 30. Here, “emissivity” is an emissivity of thermal radiation of an entire electromagnetic wave, including infrared rays, and is defined as: Emissivity = radiation emitted by object / radiation emitted by black body at the same temperature (3).

[0026] The temperature increases when the perforated plate 62 absorbs thermal radiation, and the temperature decreases when the perforated plate 62 emits thermal radiation. Since the surface of the perforated plate 62 facing the outlet side opening 44, where the cooling gas passage 42 communicates with the interior Si, has a higher emissivity than the surface of the nozzle holder 30, this surface has a lower temperature than the surface of the nozzle holder 30 facing the interior Si. As described above, because the surface of the perforated plate 62 facing the outlet side opening 44 has the lower temperature, it is possible to improve the cooling effect on the nozzle holder 30, the drive ring 45, the lever plate 46, and the like. Thus, it is possible to suppress thermal deformation or thermal burn-out in these components.

[0027] As a means of increasing the emissivity of the surface of the perforated plate 62, there is a means, for example a surface treatment, such as applying a black color to the surface, which gives the surface unevenness, roughens the surface or the like.

[0028] In one embodiment as in Fig. 5 and Fig. As shown in Figure 7, a cooling water passage 66, to which cooling water is supplied, is formed in the bearing housing 24. It is possible to cool the bearing housing 24 by circulating cooling water in the cooling water passage 66. By combining the coolant for the bearing housing 24 and the coolant described above for the surface of the perforated plate 62 facing the outlet side opening 44, it is possible to further improve the cooling effect on the nozzle holder 30, the drive ring 45, the lever plate 46, and the like.

[0029] In one embodiment as in Fig. As shown in Figure 5, a through-hole 68 (second through-hole) is formed in the nozzle holder 30, which causes the interior space Si to be connected to the exhaust gas flow passage 32, and the compressed gas g, which is introduced into the interior space Si, is configured such that it is introduced through the through-hole 68 into the exhaust gas flow passage 32. According to the present embodiment, since the compressed gas g is introduced through the through-hole 68 into the exhaust gas flow passage 32, it is possible to cool the exhaust gas e flowing through the exhaust gas flow passage 32, which makes it possible to cool the nozzle holder 30, the drive ring 45, the lever plate 46 and the like. Furthermore, the compressed gas g, which flows through the through-hole 68, is added to the exhaust gas e, which flows through the exhaust gas flow passage 32, increasing the flow rate of the exhaust gas that is supplied to the turbine wheel 14.Thus, it is possible to increase the output of turbine wheel 14.

[0030] In one embodiment, an outlet opening of the through-hole 68 is arranged on the circumference of the nozzle blade 34, for example in the exhaust gas flow passage 32 on the upstream or downstream side. In particular, if the outlet opening of the through-hole 68 is arranged such that the compressed gas g, which flows from the outlet opening of the through-hole 68 to the exhaust gas flow passage 32, flows through the nozzle blade 34, it is possible to improve the cooling effect on the nozzle blade 34.

[0031] In one embodiment, the turbine wheel 14 is designed with a through-hole 70 (third through-hole) which causes a rear surface of the turbine wheel 14 to be connected to an exhaust gas outlet flow passage 72, which is formed downstream of the turbine wheel 14. In the present embodiment, the compressed gas g, which is introduced into the interior Si, flows out through the through-hole 68 to the exhaust gas outlet flow passage 72. Thus, it is possible to cool the turbine wheel 14.

[0032] The contents described in the above embodiments would be understood, for example, as follows.

[0033] (1) A variable geometry turbocharger according to one aspect comprises a rotating shaft; a turbine wheel arranged at one end of the rotating shaft; a compressor wheel arranged at another end of the rotating shaft; a bearing housing for receiving a bearing element for rotatably supporting the rotating shaft; a variable nozzle structure (such as that described in Fig. 1 variable nozzle structure 26) shown for controlling a flow rate of an exhaust gas flowing into the turbine wheel, wherein the variable nozzle structure (such as the one shown in Fig. 1 variable nozzle structure shown 26) comprises a nozzle plate and a nozzle holder which includes an exhaust gas flow channel (such as the one shown in Fig. 1 exhaust gas flow channel 32) to allow the exhaust gas to flow into the turbine wheel, a nozzle blade rotatably arranged around a bearing shaft in the exhaust gas flow channel, and a drive element (such as the one shown in 1) Fig. 1 drive part 38) shown for rotating the nozzle blade, wherein the drive part is located in an interior space (such as the one shown in Fig. 1 interior Si) is arranged, which is defined between the bearing housing and the nozzle holder; and a cooling gas channel (such as the one shown in ). Fig. 1 shown cooling gas channel 42 (42a) and the one in Fig. 4 shown cooling gas channel 42 (42b)) for extracting compressed gas that is compressed by the compressor wheel and introducing the compressed gas into the interior.

[0034] With such a configuration, the nozzle holder or drive ring, lever plate or the like, which form the drive part of the variable nozzle structure, can be cooled by supplying the compressed gas, which is compressed by the compressor wheel, to the interior space defined between the bearing housing and the nozzle holder via the cooling gas passage described above, thereby making it possible to suppress thermal deformation or wear of these elements.

[0035] (2) In one embodiment, the cooling gas passage in the variable geometry turbocharger, as defined in (1), has an inlet side opening (as in Fig. 1 inlet side opening 43) shown, which is connected to an outlet side area of ​​a diffuser flow passage (such as the one in Fig. 1 diffuser flow passage 50) shown, in which the compressor wheel is housed.

[0036] With this configuration, since the inlet side of the cooling gas passage opens towards the outlet side of the diffuser flow passage, the compressed gas, which is now at a higher pressure, can be fed through the diffuser flow passage to the interior described above. The pressure difference between the inlet and outlet sides of the cooling gas passage allows the compressed gas to be fed to the outlet side interior without requiring any other power.

[0037] (3) In one embodiment, the bearing housing in the variable geometry turbocharger, as defined in (1) or (2), has a first through-hole (as in Fig. 1 through hole 52) shown, which runs along an axial direction of the rotating shaft, and the first through hole forms part of the cooling gas passage.

[0038] With such a configuration, since part of the cooling gas passage can be formed inside the bearing housing, no space is required for the cooling gas passage outside the bearing housing.

[0039] (4) In one embodiment, the variable geometry turbocharger, as defined in (1) or (2), further comprises a compressor cover for housing the compressor wheel and an external pipe (as in Fig. 4 external pipe 54), which is located between the compressor cover and the bearing housing. The external pipe forms part of the refrigerant passage.

[0040] With such a configuration, since part of the cooling gas passage can be formed through the external pipe described above, the cooling gas passage is formed relatively easily.

[0041] (5) In one embodiment, the cooling gas passage in the variable geometry turbocharger, as defined in any one of (1) to (4), has an outlet side opening (as in Fig. 1 outlet side opening 44) shown, which is connected to the interior, and the variable geometry turbocharger further comprises a perforated plate (as shown in Fig. 5 perforated plate 62), which divides the interior along an axial direction of the rotating shaft, wherein the perforated plate is arranged in the interior such that the drive part is arranged in a side space formed on one side of the perforated plate and the outlet side opening is connected to another side space formed on another side of the perforated plate.

[0042] With this configuration, the compressed gas supplied to the interior space described above is dispersed and oriented as it passes through the opening in the perforated plate described above, and is also accelerated. It then collides as a jet with the component of the variable nozzle structure located in a side chamber of the interior space described above, thus performing jet cooling (impact cooling). This improves the cooling effect on these components.

[0043] In one embodiment, the perforated plate in the variable geometry turbocharger, as defined in (5), is configured such that an opening ratio of a radially inner region (as defined in (5)) is achieved. Fig. 6 radial inner region R2) larger than an opening ratio of a radial outer region (such as the one shown in Fig. 6 shown radial outer area R1).

[0044] With this configuration, the exposed area of ​​the nozzle holder, viewed upstream of the compressed gas flow, is wider in the radially inner region than in the radially outer region. Therefore, it is possible to increase the flow rate of the compressed gas colliding with the nozzle holder by making the opening ratio of the radially outer region larger than that of the radially inner region of the perforated plate. This, in turn, improves the cooling effect on the nozzle holder.

[0045] In one embodiment, in the variable geometry turbocharger as defined in (5) or (6), a surface of the perforated plate facing the other side space is configured to have a higher emissivity than a surface of the nozzle holder.

[0046] The perforated plate increases its temperature when it absorbs thermal radiation and decreases its temperature when it emits thermal radiation. With the configuration described above, since the surface of the perforated plate facing the outlet side opening, where the cooling gas passage connects with the interior, has a higher emissivity than the surface of the nozzle holder, this surface exhibits a lower temperature than the nozzle holder. Because this surface has a lower temperature than the nozzle holder, it is possible to suppress thermal deformation or thermal burn-out in the nozzle holder or the element that forms the drive component of the variable nozzle structure.

[0047] In one embodiment, the nozzle holder in the variable geometry turbocharger, as defined in one of (1) to (7), has a second through-hole (as in Fig. 5 through-hole 68) shown, which causes the interior to be connected to the exhaust gas flow passage, the second through-hole being configured to allow the compressed gas introduced into the interior to flow.

[0048] With this configuration, since the compressed gas is introduced into the exhaust gas flow passage through the second through-hole described above, it is possible to cool the exhaust gas flowing through the exhaust gas flow passage. This allows for cooling of the nozzle holder facing the exhaust gas flow passage, the nozzle plate, the nozzle blade, and the like. Furthermore, the compressed gas flowing through the second through-hole is added to the exhaust gas flowing through the exhaust gas flow passage, increasing the flow rate of the exhaust gas supplied to the turbine wheel. Thus, it is possible to increase the turbine wheel output.

[0049] In one embodiment, the turbine wheel in the variable geometry turbocharger, as defined in paragraphs (1) to (8), has a third through-hole (as in Fig. 7 through hole 70 shown) which causes a rear surface side of the turbine wheel to be connected to an exhaust gas outlet flow passage which is formed downstream of the turbine wheel.

[0050] With such a configuration, it is possible to cool the turbine wheel, since the compressed gas introduced into the interior flows through the third through-hole described above. Reference symbol list 10 (10A, 10B, 10C, 10D) Variable geometry turbochargers 12 Rotary shaft 14 Turbine wheel 16 compressor wheel 18 Bearing part 20 turbine housings 22 Compressor cover 24 bearing housings 26 Variable nozzle structure 28 nozzle plate 30 nozzle holders 32 Exhaust gas flow passage 34 nozzle blade 36 Bearing shaft 38 Drive part 39 Connecting part 40 actuator 42 (42a, 42b) cooling gas passage 43 Inlet side opening 44 Outlet side opening 45 Drive ring 46 Lever plate 48 nozzle holders 50 Diffuser flow passage 51 Spiral flow passage 52 Through hole (first through hole) 54 External pipe 56, 58 Flow passage 60 Check valve 62 Perforated plates 64 Through hole 66 Cooling water passage 68 Through hole (second through hole) 70 Through hole (third through hole) 72 Exhaust gas outlet flow passage B border R1 Radial outer area R2 Radial inner area S1 Room (one side room) S2 room (another side room) Si interior e exhaust gas g Compressed gas

Claims

[1] Variable geometry turbocharger (10), comprising: a rotating shaft (12); a turbine wheel (14) arranged on one end side of the rotary shaft (12); a compressor wheel (16) arranged on another end side of the rotary shaft (12); a bearing housing (24) for receiving a bearing part (18) for rotatably supporting the rotary shaft (12); a variable nozzle structure (26) for controlling a flow rate of an exhaust gas flowing into the turbine wheel (14), the variable nozzle structure (26) comprising a nozzle plate (28) and a nozzle holder (30) defining an exhaust flow passage (32) to allow the exhaust gas to flow into the turbine wheel (14), a nozzle vane (34) rotatably disposed about a bearing shaft (36) in the exhaust gas flow passage (32), and a drive part (38) for rotating the nozzle vane (34), the drive part (38) being arranged in an interior space defined between the bearing housing (24) and the nozzle holder (30); and a cooling gas passage (42) for extracting compressed gas compressed by the compressor wheel (16) and introducing the compressed gas into the interior, where: a) the cooling gas passage (42) has an outlet side opening (44) communicating with the interior space, and wherein the variable geometry turbocharger (10) comprises a perforated plate dividing the interior space along an axial direction of the rotary shaft (12), wherein the perforated plate is arranged in the interior space such that the drive part (38) is arranged in a side space formed on one side of the perforated plate, and the outlet side opening (44) communicates with another side space formed on another side of the perforated plate; or b) wherein the turbine wheel (14) has a third through-hole that causes a rear surface side of the turbine wheel (14) to communicate with an exhaust gas outlet flow passage formed downstream of the turbine wheel (14). [2] The variable geometry turbocharger (10) of claim 1, wherein the cooling gas passage (42) has an inlet side opening communicating with an outlet side portion of a diffuser flow passage in which the compressor wheel (16) is housed. [3] Variable geometry turbocharger (10) according to claim 1 or 2, wherein the bearing housing (24) has a first through hole extending along an axial direction of the rotary shaft (12), and wherein the first through-hole forms part of the cooling gas passage (42). [4] A variable geometry turbocharger (10) according to claim 1 or 2, comprising: a compressor cover for accommodating the compressor wheel (16); and an external pipe arranged between the compressor cover and the bearing housing (24), wherein the external tube forms part of the cooling gas passage (42). [5] A variable geometry turbocharger (10) according to any one of claims 1 to 4, wherein the perforated plate is configured such that an opening ratio of a radially inner region is greater than an opening ratio of a radially outer region. [6] A variable geometry turbocharger (10) according to any one of claims 1 to 5, wherein a surface of the perforated plate facing the other side space is configured to have a higher emissivity than a surface of the nozzle holder (30). [7] The variable geometry turbocharger (10) according to any one of claims 1 to 6, wherein the nozzle holder (30) has a second through-hole that causes the interior space to communicate with the exhaust gas flow passage (32), the second through-hole being configured to allow the compressed gas introduced into the interior space to flow.

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