Shaft for turbocharger, and turbocharger

Abstract

A shaft 2 for a turbocharger TC comprises a first portion 21 disposed inside a bearing hole 51 of a housing 1. The bearing hole 51 is separated from a first space S1 that accommodates a turbine impeller 3 and from a second space S2 that accommodates a compressor impeller 4, and the first portion 21 includes, on a contact surface with a bearing B disposed inside the bearing hole 51, a coating Co that suppresses hydrogen embrittlement.

Description

Shafts for turbochargers and turbochargers

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-069210, filed April 22, 2024, the contents of which are incorporated herein by reference.

[0002] For example, a supercharger may be connected to the engine. For example, Patent Document 1 discloses a hydrogen engine equipped with a supercharger.

[0003] WO 2023 / 228570

[0004] Turbochargers connected to hydrogen engines can be exposed to hydrogen through various routes, which can cause hydrogen embrittlement in the turbocharger components.

[0005] An object of the present disclosure is to provide a shaft for a turbocharger and a turbocharger that can suppress hydrogen embrittlement.

[0006] In order to solve the above problem, a shaft for a turbocharger according to one aspect of the present disclosure includes a first portion disposed inside a bearing hole of a housing, the bearing hole being separated from a first space that accommodates a turbine impeller and a second space that accommodates a compressor impeller, and the first portion includes a coating that suppresses hydrogen embrittlement on a contact surface with a bearing disposed inside the bearing hole.

[0007] The shaft may include a second portion welded to the turbine impeller and free of the coating.

[0008] The shaft may include a third portion that is fitted into the central bore of the compressor impeller and that does not include a coating.

[0009] Another aspect of the present disclosure is a turbocharger comprising: a housing including a turbine impeller, a compressor impeller, a bearing, a first space that accommodates the turbine impeller, a second space that accommodates the compressor impeller, and a bearing hole that is separated from the first space and the second space and accommodates the bearing; and a shaft that is disposed inside the housing and rotatably supported by the bearing, the shaft being disposed inside the bearing hole and including a first portion that includes a coating that suppresses hydrogen embrittlement on a surface that contacts the bearing.

[0010] The shaft may include a second portion that is welded to the turbine impeller and does not include the coating.

[0011] The shaft may include a third portion that is fitted into the central bore of the compressor impeller and that does not include a coating.

[0012] The bearing may be a plain bearing.

[0013] The supercharger may include a thrust collar disposed around the shaft and receiving an axial load of the shaft, and a surface of the thrust collar receiving the axial load may include a material that suppresses hydrogen embrittlement.

[0014] According to the present disclosure, hydrogen embrittlement can be suppressed.

[0015] Fig. 1 is a schematic cross-sectional view of a turbocharger, and Fig. 2 is a schematic enlarged cross-sectional view of part A in Fig. 1.

[0016] An embodiment of the present disclosure will be described below with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. 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.

[0017] 1 is a schematic cross-sectional view of a turbocharger TC. The turbocharger TC is applied to a hydrogen engine (not shown). For example, the turbocharger TC includes a housing 1, a shaft 2, a turbine impeller 3, and a compressor impeller 4.

[0018] As will be described later, the turbine impeller 3 and the compressor impeller 4 rotate integrally with the shaft 2. Therefore, in the present disclosure, the axial direction, radial direction, and circumferential direction of the shaft 2, the turbine impeller 3, and the compressor impeller 4 may be simply referred to as the "axial direction," the "radial direction," and the "circumferential direction," respectively, unless otherwise specified. Also, in the present disclosure, the axis of the shaft 2, the turbine impeller 3, and the compressor impeller 4 may be simply referred to as the "axis" unless otherwise specified.

[0019] The housing 1 includes a bearing housing 5, a turbine housing 6, and a compressor housing 7. One end of the bearing housing 5 in the axial direction is connected to the turbine housing 6. The other end of the bearing housing 5 in the axial direction is connected to the compressor housing 7.

[0020] The bearing housing 5 includes a bearing hole 51. The bearing hole 51 extends in the axial direction within the bearing housing 5. The bearing hole 51 accommodates a bearing B. The bearing B rotatably supports the shaft 2. The shaft 2 passes through the bearing hole 51. The shaft 2 and the bearing B will be described in detail later.

[0021] A turbine impeller 3 is provided at a first end of the shaft 2 in the axial direction. The turbine impeller 3 rotates integrally with the shaft 2. The turbine housing 6 defines a first space S1 that houses the turbine impeller 3.

[0022] A compressor impeller 4 is provided at a second end of the shaft 2 opposite the first end in the axial direction. The compressor impeller 4 rotates integrally with the shaft 2. The compressor housing 7 defines a second space S2 that houses the compressor impeller 4.

[0023] The compressor housing 7 includes an air intake port 71 at an end opposite to the bearing housing 5 in the axial direction. The air intake port 71 is connected to an air cleaner (not shown).

[0024] The bearing housing 5 and the compressor housing 7 define a diffuser passage 72 therebetween. The diffuser passage 72 has an annular shape. The diffuser passage 72 is located radially outward from the compressor impeller 4. The diffuser passage 72 is in fluid communication with the intake port 71 via the compressor impeller 4.

[0025] The compressor housing 7 includes a compressor scroll passage 73. The compressor scroll passage 73 is located radially outward of the diffuser passage 72. The compressor scroll passage 73 is connected to the diffuser passage 72. The compressor scroll passage 73 is also in fluid communication with an intake port of a hydrogen engine (not shown).

[0026] When the compressor impeller 4 rotates, air is drawn into the compressor housing 7 through the intake port 71. The air is accelerated and pressurized by centrifugal force while passing through the compressor impeller 4. The air is further pressurized as it passes through the diffuser passage 72 and flows into the compressor scroll passage 73. The compressed air flows out from a discharge port (not shown) and is led to the intake port of the hydrogen engine. In the turbocharger TC, the portion including the compressor impeller 4 and the compressor housing 7 functions as a centrifugal compressor C.

[0027] The turbine housing 6 includes a discharge port 61 at an end opposite to the bearing housing 5 in the axial direction. The discharge port 61 is connected to an exhaust gas purification device (not shown).

[0028] The turbine housing 6 includes a connecting passage 62. The connecting passage 62 has an annular shape. The connecting passage 62 is located radially outward from the turbine impeller 3. The connecting passage 62 is in fluid communication with the discharge port 61 via the turbine impeller 3.

[0029] The turbine housing 6 includes a turbine scroll passage 63. The turbine scroll passage 63 is located radially outward of the connecting passage 62. The turbine scroll passage 63 is connected to the connecting passage 62. The turbine scroll passage 63 is also in fluid communication with a gas inlet (not shown). The gas inlet receives exhaust gas discharged from an exhaust manifold of the hydrogen engine.

[0030] Exhaust gas is guided from the gas inlet to the turbine scroll passage 63, and then through the connecting passage 62 and the turbine impeller 3 to the discharge port 61. The exhaust gas rotates the turbine impeller 3 as it passes through it. The rotational force of the turbine impeller 3 is transmitted to the compressor impeller 4 via the shaft 2. When the compressor impeller 4 rotates, the air is compressed as described above. The compressed air is then guided to the intake port of the hydrogen engine. In the turbocharger TC, a portion including the turbine impeller 3 and the turbine housing 6 functions as the turbine T.

[0031] Next, the shaft 2 and the bearing B will be described in detail.

[0032] FIG. 2 is a schematic enlarged cross-sectional view of part A in FIG.

[0033] In this embodiment, a plain bearing is used as bearing B. Specifically, in this embodiment, a full-floating bearing is used as bearing B. In other embodiments, for example, a semi-floating bearing may be used as bearing B.

[0034] In this embodiment, the bearing B includes a first bearing B1 and a second bearing B2. The number of bearings B is not limited to two, and may be one, or three or more. For example, in other embodiments, an integrated plain bearing may be used as the bearing B.

[0035] The first bearing B1 is disposed closer to the turbine impeller 3 than the second bearing B2. The second bearing B2 is disposed closer to the compressor impeller 4 than the first bearing B1. The first bearing B1 and the second bearing B2 are spaced apart from each other in the axial direction.

[0036] In this embodiment, the first bearing B1 is supported in the axial direction by a pair of positioning rings R1 fitted into grooves formed in the inner circumferential surface of the bearing hole 51. In this embodiment, the second bearing B2 is supported in the axial direction by a positioning ring R2 fitted into a groove formed in the inner circumferential surface of the bearing hole 51 and a thrust bearing 81, which will be described later. In other embodiments, instead of the positioning rings R1 and R2, a sleeve may be disposed between the first bearing B1 and the second bearing B2.

[0037] The first bearing B1 and the second bearing B2 are supported in the radial direction by the inner circumferential surface of the bearing hole 51. In this embodiment, the first bearing B1 and the second bearing B2 are plain bearings, and therefore the first bearing B1 and the second bearing B2 can slide in the circumferential direction relative to the inner circumferential surface of the bearing hole 51. For example, the first bearing B1 and the second bearing B2 are made of a copper material such as brass.

[0038] The bearing housing 5 includes a main oil passage 52. The main oil passage 52 extends in the axial direction. The main oil passage 52 extends parallel to the bearing hole 51. The main oil passage 52 is located above the bearing hole 51.

[0039] The bearing hole 51 and the main oil passage 52 open into a wall inside the bearing housing 5. A bearing retainer 83 (described later) is attached to the wall, and the opening of the main oil passage 52 is closed by the bearing retainer 83.

[0040] The main oil passage 52 communicates with a through hole 53. The through hole 53 is formed in the bearing housing 5. The through hole 53 extends from the outer wall of the bearing housing 5 to the main oil passage 52. Oil used in the hydrogen engine is supplied to the main oil passage 52 from an oil pump (not shown) via the through hole 53.

[0041] The bearing housing 5 includes a first oil passage 54 and a second oil passage 55. The first oil passage 54 and the second oil passage 55 each open to the main oil passage 52. Furthermore, the first oil passage 54 and the second oil passage 55 each open to the bearing hole 51. The first oil passage 54 and the second oil passage 55 each connect the main oil passage 52 and the bearing hole 51. The first oil passage 54 is provided at a position corresponding to the first bearing B1 and opens toward the first bearing B1. The second oil passage 55 is provided at a position corresponding to the second bearing B2 and opens toward the second bearing B2. Therefore, the first bearing B1 and the second bearing B2 are supplied with oil used in the hydrogen engine.

[0042] The bearing hole 51 is fluidly separated from the first space S1 that houses the turbine impeller 3 by a seal Se1. The seal Se1 is arranged between the bearing hole 51 and the first space S1 in the axial direction. The seal Se1 is arranged between the shaft 2 and the wall of the bearing housing 5 in the radial direction. The seal Se1 blocks the bearing hole 51 from exhaust gas flowing through the first space S1.

[0043] The bearing hole 51 is fluidly separated from the second space S2, which houses the compressor impeller 4, by a seal Se2. The seal Se2 is disposed axially between the bearing hole 51 and the second space S2. The seal Se2 is disposed radially between an oil thrower 84 disposed around the shaft 2 and the wall of the bearing housing 5. The seal Se2 blocks the bearing hole 51 from air flowing through the second space S2.

[0044] The shaft 2 includes a medium diameter portion 2a, a large diameter portion 2b, and a small diameter portion 2c.

[0045] In the axial direction, the medium diameter portion 2a extends in a region radially opposed to the bearing hole 51. In the axial direction, the medium diameter portion 2a is located between the large diameter portion 2b and the small diameter portion 2c. The medium diameter portion 2a has a cylindrical shape. The medium diameter portion 2a is inserted into the first bearing B1 and the second bearing B2. The medium diameter portion 2a is supported radially by the first bearing B1 and the second bearing B2. The medium diameter portion 2a is rotatably supported by the first bearing B1 and the second bearing B2. In this embodiment, the first bearing B1 and the second bearing B2 are sliding bearings, so the medium diameter portion 2a can slide circumferentially relative to the first bearing B1 and the second bearing B2. The medium diameter portion 2a has a constant outer diameter. However, the outer diameter of the medium diameter portion 2a does not have to be constant.

[0046] In the axial direction, the large diameter portion 2b extends from a first end (the end closest to the turbine impeller 3) of the medium diameter portion 2a toward the first space S1. For example, the large diameter portion 2b has a generally annular shape. The outer diameter of the large diameter portion 2b is larger than the outer diameter of the medium diameter portion 2a. For example, the outer diameter of the large diameter portion 2b is larger than the inner diameter of the bearing hole 51. For example, the large diameter portion 2b faces the wall of the bearing housing 5 that defines the bearing hole 51 in the axial direction.

[0047] In the axial direction, the small diameter portion 2c extends from the second end portion (the end portion closer to the compressor impeller 4) of the medium diameter portion 2a toward the second space S2. The small diameter portion 2c has a cylindrical shape. The outer diameter of the small diameter portion 2c is smaller than the outer diameter of the medium diameter portion 2a. The small diameter portion 2c has a constant outer diameter. However, the outer diameter of the small diameter portion 2c does not have to be constant.

[0048] A thrust bearing 81, a thrust collar 82, a bearing retainer 83, and an oil thrower 84 are provided on the shaft 2 in the axial direction between the second bearing B2 and the compressor impeller 4, in that order from closest to the second bearing B2. The shaft 2 is inserted into the thrust bearing 81, the thrust collar 82, and the oil thrower 84.

[0049] The thrust bearing 81 is disposed adjacent to the second bearing B2 in the axial direction and is in contact with the second bearing B2. The thrust bearing 81 also contacts the wall of the bearing housing 5 that defines the bearing hole 51 in the axial direction. The thrust bearing 81 is disposed around the medium diameter portion 2a. The thrust bearing 81 has an annular shape. In this embodiment, a plain bearing is used as the thrust bearing 81. Therefore, the thrust bearing 81 is capable of sliding in the circumferential direction relative to the wall of the bearing housing 5. For example, the thrust bearing 81 is made of a copper material such as brass.

[0050] The thrust collar 82 is disposed adjacent to the thrust bearing 81 in the axial direction and is in contact with the thrust bearing 81. The thrust collar 82 also contacts the step between the medium diameter portion 2a and the small diameter portion 2c in the axial direction. The thrust collar 82 is disposed around the small diameter portion 2c. The thrust collar 82 has an annular shape.

[0051] The bearing retainer 83 is disposed adjacent to the thrust collar 82 in the axial direction and is in contact with the thrust collar 82. The bearing retainer 83 is disposed around the oil thrower 84. The bearing retainer 83 is also fixed to the bearing housing 5. Therefore, the thrust bearing 81 and the thrust collar 82 are supported in the axial direction by the second bearing B2 and the bearing retainer 83. The bearing retainer 83 has an annular shape. The bearing retainer 83 includes an oil passage for guiding a portion of the oil flowing through the main oil passage 52 to the thrust collar 82.

[0052] The oil thrower 84 is disposed adjacent to the thrust collar 82 in the axial direction and is in contact with the thrust collar 82. One end of the oil thrower 84 is disposed inside the bearing retainer 83. The other end of the oil thrower 84 is disposed inside the seal Se2. The other end of the oil thrower 84 is in contact with the compressor impeller 4 in the axial direction. The oil thrower 84 has a generally cylindrical shape. The oil thrower 84 also includes a generally annular projection that protrudes radially.

[0053] 1 and 2, the thrust collar 82, oil thrower 84, and compressor impeller 4 on the small diameter portion 2c are pressed against the step between the medium diameter portion 2a and the small diameter portion 2c by bolts. In this way, the thrust collar 82, oil thrower 84, and compressor impeller 4 are fixed to the shaft 2 and rotate integrally with the shaft 2.

[0054] 2, when the shaft 2 moves axially toward the first space S1, the load in the axial direction is supported by the oil film pressure between the thrust bearing 81 and the thrust collar 82. When the shaft 2 moves axially toward the second space S2, the load in the axial direction is supported by the oil film pressure between the thrust collar 82 and the bearing retainer 83.

[0055] 1, as described above, the supercharger TC is applied to a hydrogen engine, and therefore the supercharger TC may be exposed to hydrogen through various routes.

[0056] For example, turbine T receives exhaust gas from a hydrogen engine. Therefore, components in turbine T may be exposed to unburned hydrogen in the exhaust gas. However, hydrogen engines typically operate primarily with lean burn. Therefore, most of the hydrogen is burned in the hydrogen engine, and the concentration of hydrogen in the exhaust gas is expected to be low.

[0057] In contrast, for example, the bearing bore 51 receives oil used in a hydrogen engine. In a hydrogen engine, the oil is exposed to blow-by gas leaking between the piston and the cylinder. The blow-by gas may contain pre-combustion hydrogen. Therefore, in a hydrogen engine, it is presumed that the oil absorbs the hydrogen in the blow-by gas. In this case, the components in the bearing bore 51 may be exposed to the oil containing hydrogen. Therefore, the components in the bearing bore 51 may suffer from aqueous embrittlement.

[0058] 2 , in this embodiment, as described above, the first bearing B1, the second bearing B2, and the thrust bearing 81 are plain bearings. Therefore, the bearings B1, B2, and 81 can slide relative to the surrounding components. Therefore, in this embodiment, it is presumed that hydrogen embrittlement may occur on the sliding surfaces between the bearings B1, B2, and 81 and the surrounding components.

[0059] As described above, in this embodiment, the first bearing B1, the second bearing B2, and the thrust bearing 81 are made of a copper material such as brass. In contrast, the components surrounding the bearings B1, B2, and 81 are made of steel. Although certain copper materials such as tough pitch copper can cause hydrogen embrittlement, steel is generally considered to be more susceptible to hydrogen embrittlement than copper materials such as brass. Therefore, in this embodiment, among the components within the bearing hole 51, hydrogen embrittlement is considered to be more likely to occur in the components surrounding the bearings B1, B2, and 81. In particular, the shaft 2 may rotate at high speeds. Therefore, it is assumed that hydrogen embrittlement is more likely to occur on the surface of the shaft 2.

[0060] To address this issue, in this embodiment, the shaft 2 includes a first portion 21 .

[0061] The first portion 21 is located inside the bearing hole 51. The first portion 21 includes the contact surfaces with the first bearing B1 and the second bearing B2. In this embodiment, the first portion 21 includes the surface of the medium diameter portion 2a. A coating Co is applied to the first portion 21 to suppress hydrogen embrittlement. For example, such a coating Co may be a known coating containing ceramic. The coating Co is not limited to this.

[0062] The shaft 2 includes a second portion 22. The second portion 22 includes a region to be connected to the turbine impeller 3. In this embodiment, the shaft 2 is connected to the turbine impeller 3 by welding. Therefore, the second portion 22 includes a region to be welded to the turbine impeller 3. In this embodiment, the second portion 22 includes an axial end surface of the large diameter portion 2b. For example, the welding may be electron beam welding. For example, the above-mentioned coatings, including ceramic, may be non-conductive. If the second portion 22 includes such a coating, the shaft 2 may not be weldable to the turbine impeller 3. Therefore, the second portion 22 does not include the coating Co.

[0063] The shaft 2 includes a third portion 23. The third portion 23 includes a region that is coupled to the compressor impeller 4. In this embodiment, the shaft 2 is coupled to the central hole of the compressor impeller 4 by fitting. Therefore, the third portion 23 includes a region that is fitted into the central hole of the compressor impeller 4. In this embodiment, the third portion 23 includes the circumferential surface of the small diameter portion 2c. Specifically, in this embodiment, the third portion 23 includes regions in the small diameter portion 2c that are inserted into the thrust collar 82, the oil thrower 84, and the compressor impeller 4. For example, if the above-mentioned coating is applied to the third portion 23, dimensional accuracy may decrease, and the shaft 2 may not be able to be inserted into the thrust collar 82, the oil thrower 84, and the compressor impeller 4. Therefore, the third portion 23 does not include the coating Co.

[0064] For example, the shaft 2 may be produced by the following method. First, the shaft 2 is formed from steel. For example, the shaft 2 may be formed by a removal process such as machining. Next, a coating Co is applied to the entire shaft 2. Next, the coating Co is removed from the second portion 22 and the third portion 23 by a removal process such as polishing.

[0065] Alternatively, the shaft 2 may be produced by the following method: First, the shaft 2 is formed from steel. For example, the shaft 2 may be formed by subtractive processing such as machining. Next, the second portion 22 and the third portion 23 are covered with a mask. Next, the entire shaft 2, including the mask, is coated with a coating Co. Next, the mask is removed from the second portion 22 and the third portion 23.

[0066] As described above, the thrust collar 82 rotates integrally with the shaft 2. In this embodiment, at least the end surface of the thrust collar 82 that contacts the thrust bearing 81 may include a Co coating to suppress hydrogen embrittlement, similar to the first portion 21. Alternatively, the entire thrust collar 82 may be formed of a material that suppresses hydrogen embrittlement. For example, such a material may be SUS316L. The material that suppresses hydrogen embrittlement is not limited to this.

[0067] As described above, the shaft 2 for the turbocharger TC according to this embodiment includes a first portion 21 disposed inside the bearing hole 51 of the housing 1. The bearing hole 51 is separated from the first space S1 that accommodates the turbine impeller 3 and the second space S2 that accommodates the compressor impeller 4. The first portion 21 includes a coating Co that suppresses hydrogen embrittlement on a contact surface with the bearing B disposed inside the bearing hole 51. As described above, in the turbocharger TC used in a hydrogen engine, it is presumed that components in the bearing hole 51 cause hydrogen embrittlement due to oil that has absorbed hydrogen in blow-by gas. According to the above configuration, the first portion 21 of the shaft 2 disposed inside the bearing hole 51 includes a coating Co that suppresses hydrogen embrittlement. Therefore, the above-described hydrogen embrittlement can be suppressed.

[0068] The shaft 2 also includes a second portion 22 that is welded to the turbine impeller 3 and does not include the coating Co. As described above, the coating Co may be non-conductive. However, according to the above configuration, the second portion 22 that is welded to the turbine impeller 3 does not include the coating Co, and therefore, electrical continuity between the turbine impeller 3 and the second portion 22 can be ensured during welding.

[0069] The shaft 2 also includes a third portion 23 that is fitted into the central hole of the compressor impeller 4 and does not include the coating Co. As described above, the coating Co can reduce dimensional accuracy. However, with the above configuration, the third portion 23 that is fitted into the central hole of the compressor impeller 4 does not include the coating Co, and therefore the third portion 23 can be easily inserted into the central hole of the turbine impeller 3 during assembly.

[0070] Moreover, the turbocharger TC according to this embodiment includes a housing 1 including a turbine impeller 3, a compressor impeller 4, a bearing B, a first space S1 that accommodates the turbine impeller 3, a second space S2 that accommodates the compressor impeller 4, and a bearing hole 51 that is separated from the first space S1 and the second space S2 and accommodates the bearing B, and a shaft 2 that is disposed inside the housing 1 and rotatably supported by the bearing B. The shaft 2 is disposed inside the bearing hole 51 and includes a first portion 21 that includes a coating Co that suppresses hydrogen embrittlement on a surface that contacts the bearing B. With this configuration, as described above, hydrogen embrittlement of the first portion 21 of the shaft 2 that is disposed inside the bearing hole 51 can be suppressed.

[0071] Furthermore, in the turbocharger TC, the bearing B is a plain bearing. Hydrogen embrittlement occurs on the surfaces where components slide against each other. Therefore, with the above configuration, hydrogen embrittlement of the shaft 2 that slides against the plain bearing can be suppressed.

[0072] The turbocharger TC also includes a thrust collar 82 that is disposed around the shaft 2 and receives a load in the axial direction of the shaft 2, and the surface of the thrust collar 82 that receives the load in the axial direction includes a material that suppresses hydrogen embrittlement (coating Co or the entire thrust collar 82). With this configuration, hydrogen embrittlement of the thrust collar 82 can be suppressed.

[0073] While one embodiment of the present disclosure has been described above with reference to the accompanying drawings, it goes without saying that the present disclosure is not limited to such an embodiment. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that such modifications also fall within the technical scope of the present disclosure.

[0074] For example, in the above embodiment, neither the second portion 22 nor the third portion 23 of the shaft 2 includes the coating Co. However, in other embodiments, at least one of the second portion 22 and the third portion 23 may include the coating Co. For example, if the reduction in dimensional accuracy due to the coating Co is not a problem, the coating Co may remain on the third portion 23.

[0075] The present disclosure provides ２ It can promote the use of hydrogen, which leads to reduced emissions, thereby contributing, for example, to Sustainable Development Goal (SDG) 7 "Ensure access to affordable, reliable, sustainable and modern energy" and SDG 13 "Take urgent action to combat climate change and its impacts."

[0076] REFERENCE SIGNS LIST 1 Housing 2 Shaft 3 Turbine impeller 4 Compressor impeller 21 First part 22 Second part 23 Third part 51 Bearing hole 82 Thrust collar B Bearing B1 First bearing B2 Second bearing Co Coating S1 First space S2 Second space TC Turbocharger

Claims

1. A shaft for a turbocharger, comprising: a first part disposed inside a bearing hole of a housing, the bearing hole being separated from a first space that houses a turbine impeller and a second space that houses a compressor impeller, the first part including a coating that suppresses hydrogen embrittlement on a contact surface with a bearing disposed inside the bearing hole.

2. A shaft for a turbocharger according to claim 1, wherein the shaft comprises a second portion welded to the turbine impeller and not including the coating.

3. A shaft for a turbocharger according to claim 1 or 2, wherein the shaft has a third portion that is fitted into a central hole of the compressor impeller and does not include the coating.

4. A turbocharger comprising: a turbine impeller; a compressor impeller; a bearing; a housing including a first space that accommodates the turbine impeller, a second space that accommodates the compressor impeller, and a bearing hole that is separated from the first space and the second space and accommodates the bearing; and a shaft that is disposed inside the housing and rotatably supported by the bearing, the shaft being disposed inside the bearing hole and including a first portion that includes a coating that suppresses hydrogen embrittlement on a surface that comes into contact with the bearing.

5. The turbocharger according to claim 4, wherein the shaft includes a second portion welded to the turbine impeller and free of the coating.

6. A turbocharger according to claim 4 or 5, wherein the shaft includes a third portion that is fitted into a central hole of the compressor impeller and does not include the coating.

7. A turbocharger according to claim 4 or 5, wherein the bearing is a plain bearing.

8. A turbocharger according to claim 4 or 5, further comprising a thrust collar disposed around the shaft and receiving a load in the axial direction of the shaft, and a surface of the thrust collar that receives the load in the axial direction includes a material that suppresses hydrogen embrittlement.

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