TURBINE SHAFT AND TURBOCHARGER

Abstract

Turbine shaft (20) with: an impeller (9) having a projecting section (24) provided on a rear surface (21b) of a main body section (21) thereof and a welded surface (23) provided on the rear surface of the main body section (21) on a radially outer side of the projecting section (24) extending in a radial direction; and a wave (8) an end bore (25) provided on an end surface thereof, wherein the projecting section (24) is inserted into the end bore (25), a weld surface (26) provided in a radially outer side of the end bore (25) and welded to the welded surface (23) and extending in a radial direction, wherein a weld seam extends from an outer circumferential end of the weld surface (26) over an outer circumferential surface (24b) of the projecting section (24) in the direction of an axis of rotation of the turbine shaft, a sealing groove (28) which is provided on another end side with reference to the weld surface (26), and a section (29) of increased diameter formed between the weld surface (26) and the sealing groove (28), wherein a diameter of the section (29) of increased diameter gradually extends radially outwards from the side of the weld surface (26) to the side of the sealing groove (28).

Description

[0001] The present disclosure relates to a turbine shaft comprising a shaft and an impeller and a turbocharger.

[0002] In the prior art, turbochargers are known in which a shaft is pivotally mounted in a bearing housing in a freely rotatable manner. One end of the shaft is equipped with a turbine impeller. The other end of the shaft is equipped with a compressor impeller. Such a turbocharger is connected to an engine. The turbine impeller rotates due to exhaust gases emitted by the engine. The rotation of the turbine impeller causes the compressor impeller to rotate on the shaft. In this way, the turbocharger compresses the air together with the rotation of the compressor impeller and supplies the air to the engine.

[0003] Publication JP 2013-194 528 A describes a welded structure between an impeller and a shaft. Specifically, an insertion section formed at the front end of a shaft is inserted into a recessed section formed on a rear surface of the impeller. On a base end face of the insertion section of the shaft, its weld surface is formed on a section projecting radially from the recessed section. The weld surface of the shaft abuts the rear surface of the impeller in the axial direction. The weld surface is welded using an electron beam. Such an arrangement is described in the Fig. 5 to 7 are visible.

[0004] Document US 2012 / 0076639A1 discloses a turbine shaft with an impeller having a projecting section provided on a rear surface of a main body section and a welded surface provided on the rear surface of the main body section on a radially outer side of the projecting section, and a shaft inserted into a bore provided in the impeller. The shaft is welded to the impeller at a weld surface located in the region of a sealing groove. Another sealing groove is provided on a circumference of the shaft. A section of increased diameter is formed between the weld surface located in the first sealing groove and the second sealing groove.

[0005] A sealing groove is formed on the outer circumferential surface of a shaft. A sealing ring is provided in the sealing groove. The dimensional accuracy required for the sealing groove is high. To suppress thermal deformation due to heat during welding of the shaft and impeller, a technique is desired to suppress heat transfer from the welded section to the sealing groove.

[0006] The publication JP 2009 - 144 633 A describes a turbine heat shielding device. This device is intended to prevent heat transfer from a turbine in a turbine housing to an impeller in a compressor housing by limiting the transfer of heat from the turbine to the shaft supporting it.

[0007] To achieve this, a mating surface on an axial projection of the turbine and a mating surface on the shaft are joined and welded along their circumference. Due to the small radial extent of this weld, heat transfer from the turbine to the shaft is reduced, and the insulating cavity between the end face of the shaft and the turbine projection can be made larger.

[0008] According to one embodiment, chamfering the joining surfaces further reduces the cross-section available for heat transfer, since the chamfers lead to an indentation of the shaft.

[0009] The object of the present invention is to provide a turbine shaft and a turbocharger, each of which is capable of suppressing heat transfer from a welded section between a shaft and an impeller to a sealing groove.

[0010] The object of the invention is achieved by a turbine shaft according to claim 1. Advantageous embodiments are the subject of the dependent claims.

[0011] To solve the problem described above, a turbine shaft according to one aspect of the present disclosure has: an impeller having a projecting section provided on a rear surface of a main body section thereof, and a welded surface provided on the rear surface of the main body section in a radially outer side of the projecting section;and a shaft having an end bore provided on one end surface thereof, and the projecting section being inserted into the end bore, a weld surface provided on a radially outer side of the end bore and welded to the welded surface, a sealing groove provided on another end side with respect to the weld surface, and a section of enlarged diameter formed between the weld surface and the sealing groove, wherein a diameter of the section of enlarged diameter extends gradually radially outward from the side of the weld surface to the side of the sealing groove.

[0012] A bottom surface of the sealing groove can be positioned on a radially outer side of the weld surface.

[0013] The sealing groove can be located closer to a different end face than the end bore.

[0014] It may also include a central bore provided on a bottom surface of the end bore of the shaft and recessed in an axial direction, and a curved section provided on an inner circumferential surface of the central bore and having a curved cross-sectional shape with an axial center.

[0015] To solve the problem described above, a turbocharger, according to one aspect of the present disclosure, has the turbine shaft described above. Effects of Revelation

[0016] According to the present disclosure, it is possible to suppress heat transfer from a welded section between a shaft and an impeller to a sealing groove. Brief description of the drawings Fig. Figure 1 is a schematic cross-sectional view of a turbocharger. Fig. Figure 2 is an explanatory drawing to illustrate a turbine shaft. Fig. Figure 3 is an explanatory drawing to illustrate a welded structure of the turbine shaft. Fig. Figure 4 is an enlarged view of a part marked with a dashed line, which is taken from the Fig. 3 is removed. Fig. Figure 5 is a first drawing to illustrate a first comparative example. Fig. Figure 6 is a second drawing to illustrate the first comparative example. Fig. Figure 7 is a view to explain a second comparative example. Description of the embodiment

[0017] One embodiment of the present disclosure is described below with reference to the Fig. Figures 1 to 4 are described in detail. Dimensions, materials, other specific numerical values, and the like shown in such an embodiment are merely examples to facilitate understanding, and the present disclosure is not limited to them, except where specifically stated. It should be noted that in this description and the drawings, elements having essentially the same function and structure are designated by the same symbol, and repeated explanations are omitted. Components not directly related to this disclosure are not shown.

[0018] The Fig. Figure 1 is a schematic cross-sectional view of a turbocharger C. The following descriptions assume that one direction of a [missing information] in the Fig. In Figure 1, the left side of the turbocharger C is shown as the part L. Descriptions are given assuming that the direction of an arrow R is the right side of the turbocharger C. As shown in the Fig. As shown in Figure 1, the turbocharger C has a turbocharger main body 1. The turbocharger main body 1 has a bearing housing 2. A turbine housing 4 is attached to the end surface of the bearing housing 2 by a fastening screw. A compressor housing 6 is attached to the right end surface of the bearing housing 2 by a fastening screw 5.

[0019] A bearing bore 2a is formed in a bearing housing 2. The bearing bore 2a extends horizontally through the turbocharger C. A bearing 7 is provided in the bearing bore 2a. A shaft 8 is pivotally mounted by the bearing 7 in a freely rotatable manner. A turbine impeller 9 is provided at the left end section of the shaft 8. The turbine impeller 9 is mounted in the turbine housing 4 in a freely rotatable manner. Furthermore, a compressor impeller 10 is provided at the right end section of the shaft 8. The compressor impeller 10 is mounted in the compressor housing 6 in a freely rotatable manner.

[0020] An inlet section 11 is formed in the compressor housing 6. The inlet section 11 opens to the right side of the turbocharger C. The inlet port 11 is connected to an air filter (not shown). Furthermore, in a state where the bearing housing 2 and the compressor housing 6 are connected by the fastening screw 5, a diffuser flow passage 12 is formed. The diffuser flow passage 12 is formed by opposing surfaces of the bearing housing 2 and the compressor housing 6. The diffuser flow passage 12 pressurizes the air. The diffuser flow passage 12 is annular and extends radially from an inner side of the shaft 8. The diffuser flow passage 12 is connected to the inlet port 11 via the compressor impeller 10 on the aforementioned inner side in the radial direction.

[0021] Furthermore, the compressor housing 6 has a compressor screw flow passage 13. The compressor screw flow passage 13 is annular. The compressor screw flow passage 13 is positioned radially to the shaft 8 on the outer side of the diffuser flow passage 12. The compressor screw flow passage 13 is connected to an inlet port of a machine (not shown). The compressor screw flow passage 13 is also connected to the diffuser flow passage 12. Therefore, air is drawn from the inlet port 11 into the compressor housing 6 when the compressor impeller 10 rotates. The drawn-in air is accelerated by centrifugal force as it flows through the blades of the compressor impeller 10. The accelerated air is pressurized through the diffuser flow passage 12 and the compressor screw flow passage 13.The pressurized air is directed to the machine's inlet port.

[0022] A discharge port 14 is formed in a turbine housing 4. The discharge port 14 opens towards the left side of the turbocharger C. The discharge port 14 is connected to an exhaust gas cleaning device (not shown). A flow passage 15 and a turbine screw flow passage 16 are provided in the turbine housing 4. The turbine screw flow passage 16 is annular. The turbine screw flow passage 16 is positioned, for example, on an outer side of the flow passage 15 in the radial direction of the turbine impeller 9. The turbine screw flow passage 16 is connected to a gas inlet port (not shown). Exhaust gas discharged from an exhaust manifold of the machine (not shown) is routed to the turbine screw flow passage 16. The turbine screw flow passage 16 is also connected to the flow passage 15.Therefore, the exhaust gas, which is guided from the gas inlet port to the turbine screw flow passage 16, flows through the flow passage 15 and between the blades of the turbine impeller 9 (and at several blades 22) to the discharge port 14. The exhaust gas leading to the discharge port 14 rotates the turbine impeller 9 as it flows through it.

[0023] The rotational force of the turbine impeller 9 is then transmitted to the compressor impeller 10 via the shaft 8. As described above, the air is pressurized by the rotational force of the compressor impeller 10 and directed to the inlet port of the machine.

[0024] The Fig. Figure 2 is an explanatory drawing to illustrate a turbine shaft 20. As in the Fig. As shown in Figure 2, the turbine shaft 20 has the shaft 8 and the turbine impeller 9, for example, of a radial type. The diameter of a main body section of the turbine impeller 9 widens from the left side (one side) to the right side (the other side) in the Fig. 2 in the axial direction of the turbine shaft 20 (hereinafter referred to simply as the axial direction).

[0025] An outer circumferential surface 21a of the main body section 21 is exposed on one side in the axial direction. A rear surface 21b of the main body section 21 is exposed on the other side in the axial direction. The outer shapes of the outer circumferential surface 21a and the rear surface 21b, when viewed in the axial direction, are, for example, circular. The outer diameter of the outer circumferential surface 21a of the main body section 21 gradually increases towards the other side in the axial direction.

[0026] Several wings 22 are provided on the outer circumferential surface 21a. The several wings 22 are spaced apart from each other in the circumferential direction of the outer circumferential surface 21a. The several wings 22 project radially from the outer circumferential surface 21a.

[0027] Furthermore, a radially inner side of the rear surface 21b of the main body section 21 projects in the axial direction. In particular, the radial inner section of the rear surface 21b projects radially towards the shaft 8 (towards the compressor impeller 10, the right side of the Fig. 2) from the position where the turbine impeller 9 (blade 22) extends in the axial direction. For example, in the case of a radial turbine impeller, as in the Fig. Figure 2 shows the inner section of the rear surface 21b separated from the outermost circumferential section 22a (section where the outer diameter of the main body section 21 is greatest) of the turbine impeller 9, which is positioned at the outermost point in the radial direction.

[0028] Then the projecting section of the rear surface 21b of the main body section 21 is inserted into an end bore (which will be described later) of the shaft 8 and welded in place. In this way, the shaft 8 is joined to the rear surface 21b of the main body section 21 of the turbine impeller 9.

[0029] The Fig. Figure 3 is an explanatory drawing illustrating a welded structure of the turbine shaft 20. In the Fig. 3 is a cross-sectional structure with the center of wave 8 shown, which consists of the part of the Fig. 2 is removed, which is marked with a dashed line III.

[0030] As in the Fig. As shown in Figure 3, a welded surface 23 is formed on the rear surface 21b of the main body section 21. The welded surface 23 is, for example, ring-shaped. The welded surface 23 is welded to the shaft 8. The welded surface 23 projects in the axial direction (towards the compressor impeller 10, into the Fig. 2 and Fig. 3 to the right) from the outermost circumferential section 22a (see Fig. 2) the wings 22 which are provided on the main body section 21 which has been described above.

[0031] On a radial inner side of a section where the outer diameter of the main body section 21 is greatest (the section of maximum diameter of the main body section 21, and in the example of the turbine impeller 9 of a radial design, which is located in the Fig. As shown in Figure 2, the main body section 21 and the blades 22 extend radially outwards in approximately the same position as the outermost circumferential section 22a). At the section of maximum diameter of the main body section 21, the centrifugal force acting during operation (during rotation of the turbine shaft 20) increases. Therefore, the position of the welded section between the shaft 8 and the turbine impeller 9 is shifted axially from the section of maximum diameter of the main body section 21 towards the compressor impeller 10. In this case, the displacement of the welded section due to the centrifugal force is suppressed. This allows for the relief of a stress concentration.

[0032] On the rear surface 21b of the main body section 21, a projecting section 24 is formed on an inner side in the radial direction of the welded surface 23. The projecting section 24 extends axially from the welded surface 23. Furthermore, an end bore 25 is provided on an end surface 8a of the shaft 8. The end bore 25 is recessed axially by a welded surface 26, which will be described later. The projecting section 24 of the turbine impeller 9 is inserted into the end bore 25. With the projecting section 24 inserted into the end bore 25, the shaft 8 and the turbine impeller 9 are positioned such that their respective centers of mass are coaxial.

[0033] The weld surface 26 is formed on a radially outer side of the end bore 25 of the shaft 8. The projecting section 24 of the turbine impeller 9 is inserted into the end bore 25 of the shaft 8. In this way, when the welded surface 23 and the weld surface 24 are in contact, a front end surface 24a of the projecting section 24 is separated from a bottom surface 25a of the end bore 25. The positioning of the shaft 8 in the axial direction is achieved by the weld surface 26. For example, it is conceivable that the welded surface 23 and the weld surface 26 are perpendicular to the axial direction.

[0034] In this case, the outer circumferential sides of the weld surface 26 and the welded surface 23 are exposed. An electron beam or a laser beam is emitted onto the weld surface 26 and the welded surface 23 from the outer circumferential side in the circumferential direction. In this way, the weld surface 26 and the welded surface 23 are welded together.

[0035] Furthermore, a first sealing groove 27 and a second sealing groove 28 (sealing groove) are formed on the outer circumferential surface of the shaft 8. The first sealing groove 27 and the second sealing groove 28 are located on the right side (the other end side) in Fig. 3 is positioned with reference to the weld surface 26. The first sealing groove 27 and the second sealing groove 28 are arranged in the order of the first sealing groove 27 and the second sealing groove 28 from the side of the weld surface 26. Each of the first sealing groove 27 and the second sealing groove 28 is inserted into an inner circumferential side of a sealing ring.

[0036] The Fig. Figure 4 is an enlarged view of a portion of the dashed line extending from the Fig. 3 is removed. In the Fig. 4 is the welded section between the welded surface 26 of the shaft 8 and the welded surface 23 of the turbine impeller 9, indicated by an X-hatching. During the rotation of the turbine shaft 20, a displacement quantity occurs due to a centrifugal stress acting on the main body section 21 of the turbine impeller 9 (in the Fig. 4 (designated by a white arrow a), slightly larger than a displacement quantity due to the centrifugal stress acting on shaft 8 (in the Fig. 4 (indicated by a white arrow b). Here, for example, the turbine impeller 9 could be made of a nickel-based superalloy such as Inconel. The shaft 8 could be made of a high-strength carbon steel such as chromium-molybdenum steel.

[0037] The Fig. 5 and Fig. Figure 6 are drawings to illustrate a first comparative example. In the Fig. Figure 5 is a cross-sectional view of a position according to the Fig. 3 in the first comparative example. Fig. Figure 6 is an enlarged view of a part marked with a dashed line, which is taken from the Fig. 5 is removed.

[0038] As in the Fig. As shown in Figure 5, in the first comparative example, a projecting section S1a is provided on a shaft S1. An end bore T1a is provided in a turbine impeller T1. The projecting section S1a is inserted into the end bore T1a. When the shaft S1 and the turbine impeller T1 rotate, the displacement magnitude is increased due to the centrifugal stress acting on the turbine impeller T1 (in the Fig. 6 (indicated by a white arrow a) greater than the displacement magnitude due to the centrifugal stress acting on shaft S1 (in the Fig. 6 (indicated by a white arrow b).

[0039] As a result, the tensile stress acts near an outer circumferential surface S1b of the projecting section S1a and an inner circumferential surface T1b of the end bore T1a of the welded section (in the Fig. 6 (indicated by a circle with a dashed line).

[0040] In the present embodiment, the shaft 8 has the end bore 25. The turbine impeller 9 is provided with the projecting section 24. In this case, as described above, a Fig. 4. The upward displacement magnitude of the inner circumferential surface 25b of the end bore 25 is smaller than that of the outer circumferential surface 24b of the projecting section 24 of the turbine impeller 9. At this time, a compressive stress acts in the radial direction on the vicinity of the outer circumferential surface 24b of the projecting section 24 and the inner circumferential surface 25b of the end bore 25 (in the Fig. 4 (indicated by a circle with a dashed line) of the welded section. Therefore, even if the stress is concentrated near the outer circumferential surface 24b of the projecting section 24 and the inner circumferential surface 24b of the end bore 25 in the welded section due to the centrifugal force during the rotation of the turbine shaft 20, it is possible to prevent a force from being generated in a direction in which a gap formed between the outer circumferential surface 24b and the inner circumferential surface 25b propagates in the axial direction as a crack.

[0041] As in the Fig. As shown in Figure 3, the enlarged diameter section 29 can be formed on the outer circumferential surface of the shaft 8 between the weld surface 26 and the first sealing groove 27 (second sealing groove 28). The diameter of the enlarged diameter section 29 extends radially outwards from the side of the weld surface 26 to the first sealing groove 27. As shown in the Fig. Figure 3 shows a cross-sectional shape with the axial center of the shaft 8 (hereinafter referred to simply as a cross-sectional shape) of section 29 having an enlarged diameter, for example a curved line.

[0042] In other words, the section 29 with increased diameter is formed in a partition 8b. The partition 8b is positioned between the first sealing groove 27 and the weld surface 26 of the shaft 8. The thickness (annular cross-sectional area) perpendicular to the axial direction of the partition 8b increases towards the first sealing groove 27. Furthermore, the section 29 with increased diameter extends continuously, for example, from the outer circumferential end of the weld surface 26.

[0043] For example, when welded surface 23 and weld surface 26 are welded, the heat generated by the welding process is transferred from weld surface 26 to the first sealing groove 27 and the second sealing groove 28 in the shaft 8. Here, the dimensions of the first sealing groove 27 and the second sealing groove 28 require high accuracy. If the thermal deformation of the first sealing groove 27 and the second sealing groove 28 is significant, separate machining or similar processes are necessary to ensure accuracy. Therefore, it is desirable to minimize this thermal deformation. By providing section 29 with an increased diameter, the heat transferred from weld surface 26 to the first sealing groove 27 and the second sealing groove 28 is distributed radially. This allows the amount of heat transmitted axially to be minimized.As a result, thermal deformation of the first sealing groove 27 and the second sealing groove 28 due to heat transfer during welding can be mitigated.

[0044] The Fig. Figure 7 is an explanatory view to illustrate a second comparative example. As in the Fig. As shown in Figure 7, in the second comparative example, the maximum outer diameter of shaft S2 is roughly equal to the maximum outer diameter of shaft 8. The section 29 with the enlarged diameter is not formed in shaft S2.

[0045] In the present embodiment, the section 29 is provided with an increased diameter without changing the maximum outside diameter of the shaft 8 compared to the second comparative example. The weld surface 26, the welded surface 23, the projecting section 24, and the end bore 25 are positioned on an inner side in the radial direction compared to those of the second comparative example. In other words, the outer circumferential surface 24b of the projecting section 24 and the inner circumferential surface 25b of the end bore 25 are shifted inwards in the radial direction compared to the second comparative example to provide the section 29 with an increased diameter.

[0046] As in the first comparative example, it is assumed that the projecting section S1a is provided by the shaft S1, and the end bore T1a is provided in the turbine impeller T1. In this case, providing a section S1c of increased diameter in the shaft S1 results in a greater radial distance between the section of maximum diameter of the main body section 21 of the turbine impeller 9 and the projecting section S1a. Therefore, the difference in displacement of the outer circumferential surface S1b of the projecting section S1a and the inner circumferential surface T1b of the end bore T1a is increased by the centrifugal force during rotation of the turbine shaft 20. This results in an even greater tensile stress in the welded section.

[0047] In the present embodiment, the end bore 25 is provided in the shaft 8. The projecting section 24 is provided on the turbine impeller 9. A compression stress acts on the welded section. Therefore, this is also suitable for providing a section with an increased diameter without changing the maximum outer diameter of the shaft 8. Here, the projecting section 24 of the turbine impeller 9 has a fixed shape. Therefore, even if the centrifugal stress increases, it is unlikely that the displacement will increase. On the other hand, the inner circumferential surface 25b of the end bore 25 of the shaft 8 exhibits a greater rate of increase in displacement with respect to an increase in centrifugal stress than the outer circumferential surface 24b of the projecting section 24.

[0048] As a result, the difference in the displacement magnitude between the outer circumferential surface 24b of the projecting section 24 of the turbine impeller 9 and that of the inner circumferential surface 25b of the end bore 25 is reduced. Therefore, the compressive stress generated in the welded section can be further suppressed.

[0049] In this way, the end bore 25 is provided in the shaft 8. The projecting section 24 is provided on the turbine impeller 9. The section 29 of increased diameter is provided on the shaft 8. As a result, the effect of suppressing stress concentration at the welded section is synergistically improved. This makes it possible to suppress heat transfer to the first sealing groove 27 and the second sealing groove 28.

[0050] Furthermore, how in the Fig. As shown in Figure 3, a bottom surface 27a of the first sealing groove 27 and a bottom surface 28a of the second sealing groove 28 can be positioned on a radially outer side of the weld surface 26. In this case, the heat generated by welding the welded surface 23 and the weld surface 26 is transferred radially outwards and reaches the first sealing groove 27 and the second sealing groove 28. As a result, it is possible to ensure a long heat transfer path and to minimize the amount of heat reaching the first sealing groove 27 and the second sealing groove 28.

[0051] However, the second sealing groove 28 can be located on a right-hand side (the other end side) in the Fig. 3 with reference to the bottom surface 25a of the end bore 25. In this case, the thickness between the second sealing groove 28 and the end bore 25 is sufficiently ensured. This makes it possible to improve the strength.

[0052] A central bore 30, recessed in the axial direction, can be provided on the bottom surface 25a of the end bore 25 of the shaft 8. The central bore 30 is provided, for example, for mounting on a machining device at the time of machining the shaft 8, aligned with the center (axial center) of the shaft 8.

[0053] A curved section 30b can be formed on an inner circumferential surface 30a of the central bore 30. The curved section 30b has a curved cross-sectional shape. The cross-sectional shape of the curved section 30b is, for example, a curve in which the central surface projects radially inwards from both end faces. In the case that the curved section 30b is present, a stress concentration near the end bore 25 and the central bore 30 is mitigated.

[0054] This makes it possible to improve the strength of shaft 8.

[0055] Although the embodiment has been described with reference to the attached drawings, it is understood that the present disclosure is not limited to the embodiment described above. It is clear that those skilled in the art can imagine various modifications or variations within the described scope, and it is understood that these also fall within the technical scope.

[0056] For example, the embodiment described above describes the case in which both the first sealing groove 27 and the second sealing groove 28 are provided. However, the sealing groove is not limited to these. For example, only one sealing groove may be provided in the shaft 8, for instance, with the first sealing groove 27 not provided and only the second sealing groove 28 provided. Furthermore, in the case in which a sealing groove is positioned closer to the opposite end face than the end bore 25, the thickness between the sealing groove and the end bore 25 is sufficiently ensured, as described in the embodiment above. This allows for an improvement in strength.

[0057] Furthermore, the embodiment described above describes a case in which the section 29 of increased diameter is formed continuously from the outer circumferential end of the weld surface 26. However, the section 29 of increased diameter is not limited to this. For example, it is sufficient that an enlarged area is provided partially between the weld surface 26 and the first sealing groove 27. For example, the section 29 of increased diameter can be spaced from the weld surface 26 in the direction of the axis of rotation. In addition, the section 29 of increased diameter can, for example, be discontinuous. For example, a parallel section or similar can be provided within the section 29 of increased diameter.In the case where the section 29 of increased diameter is formed continuously from the outer circumferential end of the weld surface 26, machinability is improved. This makes it possible to improve productivity.

[0058] Furthermore, the embodiment described above describes the case in which the cross-sectional shape of the enlarged diameter section 29 is curved. However, the enlarged diameter section 29 can be linear, for example, as long as the diameter extends radially outwards from the weld surface 26 to the first sealing groove 27 and the second sealing groove 28.

[0059] Furthermore, the embodiment described above describes a case in which the projecting section 24 is positioned on an inner side of the enlarged diameter of section 29 in the radial direction. However, the projecting section 24 is not limited to this. For example, the projecting section 24 can extend closer to the compressor impeller 10 than a region corresponding to a radially inner side of the enlarged diameter of section 29.

[0060] Furthermore, the embodiment described above describes the case in which the bottom surface 27a of the first sealing groove 27 and the bottom surface 28a of the second sealing groove 28 are positioned on a radially outer side of the weld surface 26. However, the bottom surface 27a of the first sealing groove 27 and the bottom surface 28a of the second sealing groove 28 can also be positioned on a radially inner side of the weld surface 26. The bottom surface 27a of the first sealing groove 27 and the bottom surface 28a of the second sealing groove 28 can have the same position in the radial direction as that of the weld surface 26.

[0061] Furthermore, the embodiment described above describes the case in which the second sealing groove 28 is formed closer to the opposite end face than the end bore 25. However, the second sealing groove 28 can also be formed closer to one end face than the end bore 25. The second sealing groove 28 can have the same axial position as the end bore 25.

[0062] Furthermore, the embodiment described above describes the case in which the curved section 30b is formed on the inner circumferential surface 30a of the central bore 30. However, the curved section 30b is not an essential component.

[0063] Furthermore, the embodiment described above described the case in which the turbine impeller 9 is of a radial type. It should be noted that the turbine impeller 9 can be of a diagonal flow type or an axial flow type.

[0064] Furthermore, the embodiment described above describes the case in which the outer circumferential surface 21a and the rear surface 21b of the turbine impeller 9 have a circular outer diameter when viewed in the axial direction. However, the outer circumferential surface 21a and the rear surface 21b of the turbine impeller 9 are not limited to this. For example, the rear surface 21b need not be circular (a solid disk), but a notch (corrugation) can be provided on the rear surface 21b between a pair of the multiple blades 22.

[0065] Furthermore, the embodiment described above was presented as an example in which the turbine shaft 20 is provided in the turbocharger C. However, the turbine shaft 20 can also be provided in another turbine, such as a gas turbine.

[0066] The present disclosure can be applied to a turbine shaft with a shaft and an impeller and to a turbocharger. Reference symbol list C Turbocharger 8 wave 8a a final surface 9 turbine impellers (impellers) 20 turbine shaft 21 Main body section 21a outer circumferential surface 21b rear surface 22 wings 23 welded surface 24 projecting section 25 End bore 25a Soil surface 26 Welding surface 28 second sealing groove (sealing groove) 28a Soil surface 29 Section of enlarged diameter 30 Center bore 30a inner circumferential surface 30b curved section

Claims

[1] Turbine shaft (20) with: an impeller (9) having a projecting portion (24) provided on a rear surface (21b) of a main body portion (21) thereof and a welded surface (23) provided on the rear surface of the main body portion (21) on a radially outer side of the projecting portion (24) and extending in a radial direction; and a shaft (8) which an end bore (25) provided on an end surface thereof, wherein the projecting portion (24) is inserted into the end bore (25), a welding surface (26) provided in a radially outer side of the end bore (25) and welded to the welded surface (23) and extending in a radial direction, wherein a weld seam extends from an outer peripheral end of the welding surface (26) over an outer peripheral surface (24b) of the projecting portion (24) in the direction of a rotational axis of the turbine shaft, a sealing groove (28) provided at another end side with respect to the welding surface (26), and an enlarged diameter portion (29) formed between the welding surface (26) and the sealing groove (28), wherein a diameter of the enlarged diameter portion (29) gradually expands radially outward from the welding surface (26) side to the sealing groove (28) side. [2] Turbine shaft (20) according to claim 1, wherein a bottom surface of the sealing groove (28) is positioned on a radially outer side of the welding surface (26). [3] Turbine shaft (20) according to claim 1 or 2, wherein the sealing groove (28) is formed closer to the other end side than the end bore (25). [4] Turbine shaft (20) according to one of claims 1 to 3, further comprising: a center bore (30) provided on a bottom surface (25a) of the end bore (25) of the shaft (8) and recessed in an axial direction; a curved portion (30b) provided on an inner peripheral surface (30a) of the center bore (30) and having a curved cross-sectional shape with an axial center. [5] Turbocharger (C) with the turbine shaft (20) according to one of claims 1 to 4.

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