JP2014058884A - Turbocharger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbocharger the cost of which can be reduced and the performance of which can be improved.SOLUTION: A turbocharger 1 includes a compressor housing 2 and a bearing housing 3. A discharge scroll chamber 12 has such a shape that its cross sectional area is gradually larger toward a discharge port in the peripheral direction. The compressor housing 2 comprises a scroll piece 4 and a shroud piece 5 assembled with each other. The scroll piece 4 has an intake port forming part 41, an intake side recessed surface 42, and a scroll outer peripheral part 43. The shroud piece 5 has a shroud fitting-in part 51, an inner periphery side recessed surface 52, a shroud surface 53, and a diffuser surface 54. The bearing housing 3 includes an opposite face 31, an outer periphery annular fitting-in part 32, and an outer periphery side recessed surface 33. The cross sectional shape of the outer periphery side recessed surface 33 in a plane including the rotation axis of an impeller 13 is gradually changed along the peripheral direction.

Description

  The present invention relates to a turbocharger including a compressor housing and a bearing housing.

  A turbocharger mounted on an automobile or the like is configured to compress air taken in by a compressor and discharge the compressed air toward an internal combustion engine. In other words, the air flow path formed inside the compressor housing has a discharge scroll chamber into which the compressed air discharged from the impeller flows. The discharge scroll chamber guides the compressed air to the discharge port, and the compressed air is discharged from the discharge port. It is configured to discharge to the internal combustion engine side. In particular, the shape of the discharge scroll chamber greatly affects the performance of the compressor, and it is required to finish the shape appropriately according to the required performance.

  Here, as a method of manufacturing the compressor housing, for example, there is a method by gravity casting. In this case, since casting can be performed using a so-called core, the degree of freedom in shape is high and it is possible to deal with complicated shapes. However, since the casting cycle is long, the productivity is poor and the cost is high. In addition, when a sand mold or the like is used, the surface roughness increases, and there is a problem that the efficiency of the compressor decreases.

  On the other hand, there is a method of forming the compressor housing by die casting. In this case, since the casting cycle is shorter than that of gravity casting, the productivity is good and the cost is low. However, since it cannot be molded unless it has a shape that can be punched, the degree of freedom in shape is low, and it is not possible to cope with complicated shapes. Therefore, as disclosed in Patent Document 1, there is a compressor housing configured by assembling three pieces, that is, a scroll piece, a shroud piece, and an outer peripheral annular piece. Thereby, the shape freedom of the discharge scroll chamber of a compressor housing is ensured, making each piece the shape which is easy to shape | mold by die-casting.

  Moreover, in the turbocharger described in Patent Document 2, the compressor housing is constituted by two pieces of a scroll piece and a shroud piece. A curved surface is provided on the outer peripheral portion of the back plate disposed on the opposite side to the intake side of the compressor housing, and this curved surface is a part of the inner wall surface of the discharge scroll chamber.

Japanese Patent No. 4778097 Japanese Patent Laid-Open No. 2002-180841

However, the compressor housing described in Patent Document 1 has a large number of parts, a large number of manufacturing steps, and a high manufacturing cost. Further, unless the position accuracy of the outer peripheral annular piece is made extremely high, there is a possibility that the smooth flow of the compressed air discharged from the diffuser portion to the discharge scroll chamber may be hindered at the joint at the inner end portion.
Moreover, in the turbocharger described in Patent Document 2, the shape of the curved surface portion formed on the back plate is constant over the circumferential direction. For this reason, the degree of freedom of the shape of the discharge scroll chamber is limited, and there is a limit to the ideal shape.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a turbocharger capable of reducing cost and improving performance.

One aspect of the present invention is a turbocharger including a compressor housing having an air flow path on which an impeller is disposed, and a bearing housing that rotatably supports a rotor shaft that connects the impeller.
The air flow path has an intake port that sucks air toward the impeller, and a discharge scroll chamber that is formed in a circumferential direction on the outer peripheral side of the impeller and guides compressed air discharged from the impeller to a discharge port. The discharge scroll chamber has a shape in which the cross-sectional area gradually increases toward the discharge port in the circumferential direction,
The compressor housing comprises a scroll piece and a shroud piece assembled together,
The scroll piece includes a cylindrical intake port forming portion that forms the intake port, an intake side concave surface that forms a wall surface on the intake side in the discharge scroll chamber, and an outer periphery of the scroll that is disposed on the outer peripheral side of the discharge scroll chamber. And
The shroud piece includes a cylindrical shroud fitting portion to be fitted into the scroll piece, an inner circumferential concave surface constituting an inner circumferential wall surface in the discharge scroll chamber, a shroud surface facing the impeller, and the shroud A diffuser surface extending from the surface toward the discharge scroll chamber,
The bearing housing includes a facing surface that faces the diffuser surface, an outer peripheral annular insertion portion that is inserted into the scroll outer peripheral portion of the scroll piece, and an outer peripheral concave surface that forms an outer peripheral wall surface in the discharge scroll chamber. Prepared,
The outer peripheral concave surface is a turbocharger having a shape in which a cross-sectional shape by a plane including a rotation axis of the impeller is gradually changed along a circumferential direction (Claim 1).

  In the turbocharger, since the compressor housing can be constituted by two pieces of the scroll piece and the shroud piece, the number of parts of the compressor housing can be relatively reduced. As a result, the number of manufacturing steps for the turbocharger can be reduced, and the manufacturing cost can be reduced.

  Moreover, a part of wall surface of a discharge scroll chamber can be comprised by the said outer peripheral side concave surface of the said bearing housing. That is, a part of the wall surface of the discharge scroll chamber is formed in a concave shape by utilizing a part of the bearing housing that is originally required in the turbocharger. Therefore, the degree of freedom of shape of the discharge scroll chamber can be improved without increasing the number of parts.

  The outer peripheral concave surface has a shape in which the cross-sectional shape of the plane including the rotation axis of the impeller is gradually changed along the circumferential direction. Therefore, the shape of the outer peripheral wall surface in the discharge scroll chamber can be gradually changed along the circumferential direction. Thereby, the shape of the discharge scroll chamber can be made an ideal shape, and an ideal air flow in the compressor can be realized. As a result, the performance of the turbocharger can be improved.

  Moreover, the said outer peripheral side concave surface is formed in the bearing housing with the opposing surface which opposes the said diffuser surface. Therefore, a seam is not formed between the opposing surface and the outer peripheral concave surface. Therefore, a smooth flow of compressed air discharged from the space (diffuser portion) between the diffuser surface and the opposing surface to the discharge scroll chamber can be easily and reliably realized. From this point of view, it is possible to ensure improvement in performance of the turbocharger.

  As described above, according to the present invention, it is possible to provide a turbocharger capable of reducing cost and improving performance.

It is sectional drawing of the compressor part in Example 1, Comprising: It is the sectional view equivalent to the AA line of FIG. FIG. 4 is another cross-sectional view of the compressor portion according to the first embodiment, corresponding to a cross-sectional view taken along line BB in FIG. FIG. 3 is a plan view of the compressor housing as viewed from the intake side in the first embodiment. FIG. 3 is a cross-sectional view of the compressor housing in the first embodiment. FIG. 3 is a cross-sectional view of a part of the bearing housing in the first embodiment. FIG. 3 is an explanatory diagram illustrating an overall shape of a scroll chamber according to the first embodiment. 1 is a perspective view of a compressor housing in Embodiment 1. FIG. FIG. 3 is a perspective view of a bearing housing in the first embodiment. The side view of the bearing housing in Example 1. FIG. The front view of the bearing housing seen from the compressor side in Example 1. FIG. (A) CC sectional view taken along the line C-C in FIG. 10, (B) DD sectional view taken along the line D-D in FIG. 10, (C) E-E sectional view taken along the line E-D in FIG. FIG.

In the turbocharger, “circumferential direction” means the rotation direction of the impeller, and “axial direction” means the direction of the rotation axis of the impeller.
Further, it is preferable that the cross-sectional shape of the outer peripheral concave surface is formed such that the radius of curvature gradually increases toward the discharge port in the circumferential direction (Claim 2). In this case, the shape of the discharge scroll chamber can be made an ideal shape more easily. That is, the outer peripheral concave surface constituting a part of the wall surface of the discharge scroll chamber has the above-described shape, so that the cross-sectional area gradually increases toward the discharge port in the circumferential direction of the discharge scroll chamber. In the “shape”, the cross-sectional shape of each part is easily formed into an ideal shape. The radius of curvature is the radius of curvature when the cross-sectional shape of the outer circumferential concave surface is an arc, but in other cases than the arc, it means the average radius of curvature over the entire cross-sectional shape. To do.

  Moreover, it is preferable that the said outer peripheral side concave surface is formed so that the dimension of an axial direction may become large gradually as it goes to the said discharge port in the circumferential direction (Claim 3). Also in this case, similarly to the above, the shape of the discharge scroll chamber can be more easily made an ideal shape.

  Moreover, it is preferable that the said outer peripheral side concave surface is formed so that the dimension of a radial direction may become large gradually as it goes to the said discharge port in the circumferential direction (Claim 4). Also in this case, similarly to the above, the shape of the discharge scroll chamber can be more easily made an ideal shape.

Example 1
An embodiment of the turbocharger will be described with reference to FIGS.
As shown in FIG. 1, the turbocharger 1 of the present example includes a compressor housing 2 having an air flow path 10 in which an impeller 13 is disposed inside, and a bearing housing 3 that rotatably supports a rotor shaft 14 that connects the impeller 13. And.

  The air flow path 10 includes an intake port 11 that sucks air toward the impeller 13, a discharge scroll chamber 12 that is formed in the circumferential direction on the outer peripheral side of the impeller 13, and guides compressed air discharged from the impeller 13 to the discharge port 15. Have As shown in FIG. 6, the discharge scroll chamber 12 has a shape in which the cross-sectional area gradually increases from the side opposite to the discharge port 15 side in the circumferential direction toward the discharge port 15 side.

As shown in FIGS. 1, 2, 4, and 7, the compressor housing 2 includes a scroll piece 4 and a shroud piece 5 that are assembled together.
The scroll piece 4 is disposed on a cylindrical intake port forming portion 41 that forms the intake port 11, an intake side concave surface 42 that forms a wall surface on the intake side in the discharge scroll chamber 12, and an outer peripheral side of the discharge scroll chamber 12. And a scroll outer peripheral portion 43.
The shroud piece 5 includes a cylindrical shroud fitting portion 51 that is fitted into the scroll piece 4, an inner circumferential concave surface 52 that constitutes an inner circumferential wall surface in the discharge scroll chamber 12, and a shroud surface 53 that faces the impeller 13. And a diffuser surface 54 extending from the shroud surface 53 toward the discharge scroll chamber 12.

  As shown in FIGS. 1, 2, and 5, the bearing housing 3 includes a facing surface 31 that faces the diffuser surface 54, an outer circumferential annular fitting portion 32 that is fitted into the scroll outer circumferential portion 43 of the scroll piece 4, and a discharge scroll. The outer peripheral side concave surface 33 which comprises the outer peripheral wall surface in the chamber 12 is provided.

As shown in FIGS. 1, 2, 10, and 11, the outer peripheral concave surface 33 has a cross-sectional shape by a plane including the rotation axis of the impeller 13 (hereinafter simply referred to as “cross-sectional shape” is not particularly shown). As long as it refers to the cross-sectional shape by this plane, it has a shape that gradually changes along the circumferential direction.
More specifically, the cross-sectional shape of the outer circumferential concave surface 33 is formed such that the radius of curvature gradually increases toward the discharge port 15 in the circumferential direction.

  Further, the outer peripheral concave surface 33 is formed such that the axial dimension h gradually increases as it goes toward the discharge port 15 in the circumferential direction. Further, the outer peripheral concave surface 33 is formed so that the radial dimension w also gradually increases toward the discharge port 15 in the circumferential direction. 11A, 11B, 11C, and 11D, reference numerals 3a, 3b, 3c, and 3d in this order indicate the portion of the bearing housing 3 at a position far from the discharge port 15 as a compressed air path. A cross section is shown. That is, the reference numerals 3a, 3b, 3c, and 3d shown in FIG. 11 form part of the cross sections 12a, 12b, 12c, and 12d of the discharge scroll chamber 12 shown in FIGS. 1 and 2, respectively. It is a cross section of a part.

  Further, the intake-side concave surface 42 of the scroll piece 4 has a shape in which the cross-sectional shape gradually changes along the circumferential direction. Moreover, the inner peripheral concave surface 52 of the shroud piece 5 has a shape in which the cross-sectional shape gradually changes along the circumferential direction. The intake-side concave surface 42 and the inner peripheral-side concave surface 52 are also formed so that the cross-sectional shape gradually increases in curvature radius toward the discharge port 15 side in the circumferential direction.

  The turbocharger 1 rotates a turbine with exhaust gas discharged from an internal combustion engine such as an automobile, compresses intake air in the compressor using the rotational force, and sends the compressed air from the discharge port 15 to the internal combustion engine. It is configured. Therefore, although not shown, the turbocharger 1 includes a turbine housing on the opposite side of the compressor housing 2 that forms the outer shell of the compressor in the axial direction. An exhaust gas passage in which a turbine impeller is disposed is formed inside the turbine housing. The turbine impeller is fixed to the rotor shaft 14. That is, the impeller 13 of the compressor and the turbine impeller are connected by the rotor shaft 14. Thereby, it is comprised so that the impeller 13 of a compressor may rotate with rotation of a turbine impeller.

A bearing housing 3 that rotatably supports the rotor shaft 14 is disposed between the compressor housing 2 and the turbine housing. As shown in FIGS. 1, 2, 8, and 9, the bearing housing 3 is provided with a substantially disc-shaped flange portion 34 at one end in the axial direction, and on the compressor side surface of the flange portion 34, The opposing surface 31 and the outer peripheral concave surface 33 are each formed in an annular shape.
The bearing housing 3 is made of cast iron, and the facing surface 31 and the outer peripheral concave surface 33 are cut by machining such as a ball end mill using a machining center, for example.

  The opposing surface 31 and the outer peripheral concave surface 33 are formed continuously with each other. That is, although the opposing surface 31 is formed as a flat surface orthogonal to the axial direction, the outer peripheral concave surface 33 curves toward the compressor side continuously from the outer peripheral end, that is, without passing through a step or the like. It is formed as follows. And as above-mentioned, the outer peripheral side concave surface 33 is formed so that the cross-sectional shape may change gradually in the circumferential direction.

  The outer peripheral concave surface 33 of the bearing housing 3 formed in this way, the scroll outer peripheral portion 43 of the scroll piece 4 and the inner peripheral concave surface 52 of the shroud piece 5 which are formed so that the cross-sectional shape gradually changes in the circumferential direction. Thus, a discharge scroll chamber 12 is formed (FIGS. 1 and 2).

  As shown in FIG. 6, the discharge scroll chamber 12 is formed in a substantially circumferential shape, and the discharge port 15 projects from the discharge scroll chamber 12 in the circumferential tangential direction. And the discharge scroll chamber 12 is formed so that a cross-sectional area may become large gradually as it goes to the discharge port 15 along the circumferential direction. 1 and 2, reference numerals 12 a, 12 b, 12 c, and 12 d indicate a section of the discharge scroll chamber 12 at a position far from the discharge port 15 as a compressed air path in this order.

  Therefore, the intake side concave surface 42 of the scroll piece 4, the inner peripheral side concave surface 52 of the shroud piece 5, and the outer peripheral side concave surface 33 of the bearing housing 3, which form the discharge scroll chamber 12, are not rotationally symmetric. The cross-sectional shape gradually changes along the direction. As shown in FIGS. 1, 2, 10, and 11, the bearing housing 3 has the above-described cross-sectional dimensions (the axial dimension h and the radial dimension w) and the average radius of curvature of the outer circumferential concave surface 33. It has a shape that gradually increases along the circumferential direction. That is, the dimensions h and w and the average radius of curvature gradually increase toward the discharge port 15 in the circumferential direction.

  As shown in FIG. 10, a discharge communication recess 35 formed so as to connect the discharge scroll chamber 12 and the discharge port 15 is formed in a part of the flange portion 34 of the bearing housing 3 in the circumferential direction. Yes. The discharge communication recess 35 is formed so as to be parallel to the discharge port 15 between a portion where the axial dimension h of the outer peripheral side concave surface 33 is largest and a portion where it is smallest. That is, gradually from the first adjacent portion 351 to the second adjacent portion 352 with respect to the discharge communication recess 35 shown in FIG. 10 gradually in the circumferential direction over substantially the entire circumference excluding the portion where the discharge communication recess 35 is formed in the bearing housing 3. The dimensions h and w and the radius of curvature of the outer peripheral concave surface 33 are increased.

  Further, as shown in FIGS. 8 to 10, a positioning stage for determining the circumferential position of the bearing housing 3 and the compressor housing 2 at a position adjacent to the discharge communication recess 35 in the circumferential direction on the outer circumferential side of the outer circumferential concave surface 33. A portion 36 is formed. That is, a positioning step 46 is also formed in the compressor housing 2 at a position corresponding to the positioning step 36 of the bearing housing 3 as shown in FIG.

  The scroll piece 4 and the shroud piece 5 constituting the compressor housing 2 are both made of an aluminum die-cast product. As shown in FIG. 4, the scroll piece 4 has an intake port forming portion 41 formed in a cylindrical shape centered on the rotation axis of the impeller 13. Then, an end of the intake port forming portion 41 opposite to the intake side (hereinafter, the intake side is appropriately referred to as “front end side”, and the opposite side is appropriately referred to as “base end side”) extends to the outer peripheral side. Thus, the scroll wall surface forming part 420 having the intake side concave surface 42 is formed. And the scroll outer peripheral part 43 is provided in the outer peripheral part of the scroll wall surface formation part 420 so that it may extend to a base end side.

  In the shroud piece 5, a shroud insertion portion 51 is formed in a cylindrical shape centering on the rotation axis of the impeller 13, and an intake passage communicating with the intake port 11 is formed in the shroud insertion portion 51. The shroud fitting portion 51 is fitted inside the intake port forming portion 41 of the scroll piece 4.

  A shroud surface 53 is formed by forming the inner side surface of the shroud fitting portion 51 so as to spread outward from the base end side. The shroud surface 53 is connected to a diffuser surface 54 that spreads in a direction orthogonal to the axial direction on the outer peripheral side.

  As shown in FIGS. 1 and 2, the impeller 13 is disposed on the inner peripheral side of the shroud piece 5. The impeller 13 is formed by projecting a plurality of blades arranged in the circumferential direction from the outer peripheral surface of the hub. The plurality of blades are disposed to face the shroud surface 53 of the shroud piece 5.

  In assembling the compressor portion of the turbocharger 1, first, the shroud fitting portion 51 is press-fitted inside the intake port forming portion 41 so that the shroud piece 5 is assembled to the scroll piece 4, and the compressor shown in FIGS. A housing 2 is formed. As shown in FIGS. 1 and 2, the outer peripheral annular fitting portion 32 of the bearing housing 3 is used as the outer peripheral portion of the scroll piece 4 constituting the compressor housing 2 so that the impeller 13 is disposed inside the compressor housing 2. Press fit inside 43. At this time, the positioning step portion 46 of the scroll piece 4 is brought into contact with the positioning step portion 36 of the bearing housing 3 in the circumferential direction, thereby determining the circumferential position of the bearing housing 3 and the compressor housing 2.

  Thereby, the diffuser surface 54 of the shroud piece 5 and the facing surface 31 of the bearing housing 3 are arranged to face each other with a predetermined distance therebetween, so that the diffuser portion 16 is formed between them. On the outer peripheral side, the discharge scroll chamber 12 is formed by the intake side concave surface 42 of the scroll piece 4, the inner peripheral side concave surface 52 of the shroud piece 5, and the outer peripheral side concave surface 33 of the bearing housing 3.

Next, the function and effect of this example will be described.
In the turbocharger 1, since the compressor housing 2 can be configured by two pieces, that is, the scroll piece 4 and the shroud piece 5, the number of parts of the compressor housing 2 can be relatively reduced. As a result, the number of manufacturing steps for the turbocharger 1 can be reduced, and the manufacturing cost can be reduced.

  A part of the wall surface of the discharge scroll chamber 12 can be formed by the outer peripheral concave surface 33 of the bearing housing 3. That is, a part of the wall surface of the discharge scroll chamber 12 is formed in a concave shape by utilizing a part of the bearing housing 3 that is originally required in the turbocharger 1. Therefore, the degree of freedom of shape of the discharge scroll chamber 12 can be improved without increasing the number of parts.

  The outer peripheral concave surface 33 has a shape in which a cross-sectional shape by a plane including the rotation axis of the impeller 13 is gradually changed along the circumferential direction. Therefore, the shape of the outer peripheral wall surface in the discharge scroll chamber 12 can be gradually changed along the circumferential direction. Thereby, it becomes possible to make the shape of the discharge scroll chamber 12 into an ideal shape, and it is possible to realize an ideal air flow in the compressor. As a result, the performance of the turbocharger 1 can be improved.

  Further, the outer peripheral concave surface 33 is formed in the bearing housing 3 together with the facing surface 31 that faces the diffuser surface 54. Therefore, no seam is formed between the facing surface 31 and the outer peripheral concave surface 33. Therefore, a smooth flow of compressed air discharged from the diffuser unit 16 to the discharge scroll chamber 12 can be easily and reliably realized. From this point of view, it is possible to ensure the performance improvement of the turbocharger 1.

  Further, the cross-sectional shape of the outer circumferential concave surface 33 is formed such that the radius of curvature gradually increases toward the discharge port 15 in the circumferential direction, and the axial dimension h and the radial dimension w gradually increase. ing. Thereby, the shape of the discharge scroll chamber 12 can be made into an ideal shape more easily. That is, the outer peripheral concave surface 33 constituting a part of the wall surface of the discharge scroll chamber 12 has the above-described shape, so that the cross-sectional area gradually increases toward the discharge port 15 in the circumferential direction of the discharge scroll chamber 12. In the “shape that increases”, the cross-sectional shape of each part is easily formed into an ideal shape.

  As described above, according to this example, it is possible to provide a turbocharger capable of reducing cost and improving performance.

In the above embodiment, the scroll piece and the shroud piece are made of aluminum die-cast. However, the present invention is not limited to this, and these pieces can be formed by other materials and other production methods. . For example, the shroud piece may be formed of a resin molded product or the like.
Moreover, in the said Example, although the bearing housing was made from cast iron, it is not necessarily restricted to this.

DESCRIPTION OF SYMBOLS 1 Turbocharger 10 Air flow path 11 Intake port 12 Discharge scroll chamber 13 Impeller 14 Rotor shaft 15 Discharge port 2 Compressor housing 3 Bearing housing 31 Opposing surface 32 Outer periphery annular fitting part 33 Outer peripheral side concave surface 4 Scroll piece 41 Inlet opening formation part 42 Intake Side concave surface 43 Scroll outer peripheral portion 5 Shroud piece 51 Shroud fitting portion 52 Inner peripheral concave surface 53 Shroud surface 54 Diffuser surface

Claims (4)

A turbocharger comprising: a compressor housing having an air flow path on which an impeller is disposed; and a bearing housing that rotatably supports a rotor shaft that connects the impeller.
The air flow path has an intake port that sucks air toward the impeller, and a discharge scroll chamber that is formed in a circumferential direction on the outer peripheral side of the impeller and guides compressed air discharged from the impeller to a discharge port. The discharge scroll chamber has a shape in which the cross-sectional area gradually increases toward the discharge port in the circumferential direction,
The compressor housing comprises a scroll piece and a shroud piece assembled together,
The scroll piece includes a cylindrical intake port forming portion that forms the intake port, an intake side concave surface that forms a wall surface on the intake side in the discharge scroll chamber, and an outer periphery of the scroll that is disposed on the outer peripheral side of the discharge scroll chamber. And
The shroud piece includes a cylindrical shroud fitting portion to be fitted into the scroll piece, an inner circumferential concave surface constituting an inner circumferential wall surface in the discharge scroll chamber, a shroud surface facing the impeller, and the shroud A diffuser surface extending from the surface toward the discharge scroll chamber,
The bearing housing includes a facing surface that faces the diffuser surface, an outer peripheral annular insertion portion that is inserted into the scroll outer peripheral portion of the scroll piece, and an outer peripheral concave surface that forms an outer peripheral wall surface in the discharge scroll chamber. Prepared,
The turbocharger according to claim 1, wherein the concave surface on the outer peripheral side has a shape in which a cross-sectional shape by a plane including a rotation axis of the impeller is gradually changed along a circumferential direction.   The turbocharger according to claim 1, wherein the cross-sectional shape of the outer peripheral concave surface is formed such that a radius of curvature gradually increases toward the discharge port in the circumferential direction. .   3. The turbocharger according to claim 1, wherein the concave surface on the outer peripheral side is formed so that an axial dimension gradually increases toward the discharge port in the circumferential direction. 4. Charger.   The turbocharger according to any one of claims 1 to 3, wherein the outer peripheral concave surface is formed such that a radial dimension gradually increases toward the discharge port in the circumferential direction. Turbocharger characterized by

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