Patent Publication Number: US-11035377-B2

Title: Compressor housing for turbocharger and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Application No. 2018-099060, filed on May 23, 2018, entitled “COMPRESSOR HOUSING FOR TURBOCHARGER AND METHOD FOR MANUFACTURING THE SAME”. The contents of this application are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a compressor housing for a turbocharger, and a method for manufacturing the same. 
     Description of Related Art 
     A turbocharger installed in an engine compartment of a vehicle or the like is configured to compress sucked air in a compressor and discharge the compressed air to an internal combustion engine. That is, an air-flow path formed within a compressor housing includes a scroll chamber into which compressed air discharged from an impeller flows. The scroll chamber is configured to direct the compressed air to a discharge port and discharge the compressed air toward the internal combustion engine from the discharge port. 
     PRIOR ART LITERATURE 
     Patent Document 
     Patent Document 1
         JP-A-2016-084790       

     SUMMARY OF THE INVENTION 
     Engine compartments of vehicles and the like have been downsized and narrowed in recent years. Consequently, a turbocharger needs to be installed in a limited space of an engine compartment. As a result, shapes of discharge ports of compressor housings tend to be complicated. In order to deal with the complicated shapes, it is conceivable that compressor housings are molded by gravity casting or low-pressure casting. Since in these casting methods, a so-called core can be used for casting, a high degree of freedom in shaping can be ensured, which makes it possible to deal with complicated shapes. However, because of its long casting cycle, productivity is low and cost is high. Further, there is a problem in that when using, for example, a sand mold, an inner surface of a scroll rough or such is made rough, and which causes deterioration of the compressor efficiency. 
     On the other hand, compressor housings may be molded by die-casting. Since die casting has a shorter casting cycle than gravity casting or low-pressure casting, productivity is high and cost is low. However, die-casting can be applied only to a shape that can be die-cut from a mold (a shape without undercut). Thus, shaping freedom is low and complicated shapes cannot be dealt with. To solve the problem, a compressor housing including three pieces i.e., a scroll piece, a shroud piece, and a seal plate that are assembled together is disclosed in Patent Document 1. In this disclosure, each piece is shaped to be easily die-cast, and also a scroll chamber of the compressor housing can ensure the shaping freedom. 
     Further, in a configuration disclosed in Patent Document 1, the scroll piece includes a through part extending through the scroll piece in an axial direction, and an intake-side end of the through part constitutes a discharge port. A first intermediate wall surface extended from an intake-side wall surface that forms the scroll chamber, being bent toward an intake side in the axial direction, is smoothly connected with the discharge port. Meanwhile, a protruding part protruding in the axial direction is formed in the seal plate so as to be inserted into the through part of the scroll piece. The protruding part has a wall surface that is opposite an inner-side wall surface of the through part. The wall surface and the inner-side wall surface form an inner wall surface of an intermediate part through which the discharge port communicates with the scroll chamber. Consequently, the scroll piece having the discharge port formed therein, and the seal plate can be shaped to have no undercut and to be releasable from a mold. Therefore, there is no need to separately prepare a die for the scroll chamber and a die for the discharge port for die-casting, so that manufacturing cost can be reduced. 
     In the configuration disclosed in Patent Document 1, however, the seal plate made of aluminum die-cast constitutes a portion that corresponds to a compressor-side flange of a center housing. Therefore, the seal plate is less rigid than a flange that is integrally formed with a center housing made of cast iron. Therefore, noise tends to be generated by influence of vibration of a rotating body that includes an impeller, a rotor shaft, and the like. If increasing a thickness of the seal plate to improve its rigidity, it will be necessary to increase a length of the rotor shaft accordingly, thereby increasing the whole length of the rotating body. As a result, an increased mass of the rotating body lowers natural frequency, which causes an adverse effect in respect of vibration. Further, the increase of the length of the rotating body cause increase of material cost and thereby causing an adverse effect also in respect of manufacturing cost. 
     Further, in the configuration disclosed in Patent Document 1, the seal plate is fastened to the center housing at a position that is relatively close to a shaft center of the rotating body. Therefore, a sufficiently high fastening rigidity is difficult to obtain, and thus noise tends to be generated by influence of vibration of the rotating body. 
     The present invention has been made in view of such backgrounds to provide a compressor housing for a turbocharger that reduces noise generation and prevents an increase in manufacturing cost. 
     One aspect of the present invention provides a compressor housing for a turbocharger, which is configured to accommodate an impeller and is configured to be attachable to a center housing that accommodates a bearing device, the compressor housing including: 
     an intake port configured to suck air toward the impeller; 
     a scroll chamber formed in a circumferential direction on an outer-circumference side of the impeller, and configured to allow air discharged from the impeller to circulate; 
     a discharge port configured to discharge air circulating through the scroll chamber to an outside; and 
     an intermediate part through which the discharge port communicates with the scroll chamber, wherein 
     the compressor housing is composed of a scroll piece, a shroud piece, and an outer-circumferential annular piece that are dividedly formed and assembled in an axial direction, wherein 
     the scroll piece includes:
         the intake port formed through the scroll piece in the axial direction;   an intake-side wall surface formed on an outer-circumference side of the intake port, the intake-side wall surface constituting a wall surface of the scroll chamber on an intake side;   a through part formed through the scroll piece in the axial direction, an intake-side end of the through part constituting the discharge port;   a first intermediate wall surface extended from the intake-side wall surface, being bent toward the intake side to be parallel to the axial direction, and smoothly connected with the discharge port, the first intermediate wall surface constituting part of an inner wall surface of the intermediate part;   a scroll outer-circumferential part that covers an outer-circumference side of the scroll chamber; and   a joining part provided at the scroll outer-circumferential part to be joined to the center housing, the shroud piece includes:   a shroud press-fit part of a cylindrical shape press-fitted into the intake port;   an inner-circumference-side wall surface constituting a wall surface of the scroll chamber on the inner-circumference side;   a shroud surface opposed to the impeller; and   a diffuser surface extended from the shroud surface to the scroll chamber,       

     the outer-circumferential annular piece includes:
         an outer-circumferential annular press-fit part press-fitted into the scroll outer-circumferential part;   an outer-circumference-side wall surface constituting a wall surface of the scroll chamber on the outer-circumference side; and   a protruding part formed protruding toward the intake side and inserted into the through part in the axial direction, and wherein       

     the protruding part includes a second intermediate wall surface extended from the outer-circumference-side wall surface, being bent toward the intake side to be parallel to the axial direction, the second intermediate wall surface constituting part of the inner wall surface of the intermediate part, opposing to the first intermediate wall surface. 
     In the compressor housing for a turbocharger, the scroll piece, the shroud piece, and the outer-circumferential annular piece are assembled in the axial direction. The scroll piece includes the through part formed through the scroll piece in the axial direction, and the intake-side end of the through part constitutes the discharge port. 
     The first intermediate wall surface extended from the intake-side wall surface that forms the scroll chamber, being bent toward the intake side in the axial direction, is smoothly connected with the discharge port. Further, the protruding part is inserted into the through part. The protruding part is formed in the outer-circumferential annular piece, protruding in the axial direction that corresponds to an assembly direction. The protruding part includes the second intermediate wall surface opposing to the first intermediate wall surface. The first intermediate wall surface and the second intermediate wall surface form the inner wall surface of the intermediate part through which the discharge port is communicated with the scroll chamber. 
     Consequently, the scroll piece having the discharge port formed therein, and the outer-circumferential annular piece each can be shaped to be releasable from a mold in an insertion direction, that is, the axial direction (shaped to have no undercut). Therefore, the scroll piece can be molded by die-casting instead of gravity casting or low-pressure casting, and thus manufacturing cost can be reduced. Further, there is no need to separately prepare a die for the scroll chamber and a die for the discharge port for die-casting, so that manufacturing cost can be reduced. 
     Further, the scroll outer-circumferential part includes the joining part(s) to be joined to the center housing. The joining part and a compressor-side flange of the center housing, between which the outer-circumferential annular piece is interposed, are joined to each other, so that the compressor housing is fixed to the center housing. According to such a configuration, the scroll piece is joined to the center housing that is made of iron and is more rigid than conventional aluminum seal plates. Therefore, the thickness of a joint region between the scroll piece and the center housing does not need to be increased. As a result, high rigidity is secured without increasing the length of a rotating body, and thus noise due to vibration of the rotating body is reduced. Since a length of the rotating body does not need to be increased, an increase in material cost is restricted, and thus an increase in manufacturing cost is prevented. 
     As described above, the present invention provides a compressor housing for a turbocharger that reduces noise generation, and prevents an increase in manufacturing cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a compressor housing according to Embodiment 1; 
         FIG. 2  is a cross-sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 ; 
         FIG. 4  is a front perspective view that illustrates a step of press-fitting according to Embodiment 1; 
         FIG. 5  is a rear perspective view that illustrates the step of press-fitting according to Embodiment 1; 
         FIG. 6  is a cross-sectional view taken along line II-II in  FIG. 1  that illustrates the step of press-fitting; 
         FIG. 7  is a cross-sectional view taken along line II-II in  FIG. 1  that illustrates a step of cutting; 
         FIG. 8  is a cross-sectional view along line II-II in  FIG. 1  that illustrates a step of detaching; 
         FIG. 9  is a front perspective view that illustrates a step of press-fitting again according to Embodiment 1; and 
         FIG. 10  is a rear perspective view that illustrates the step of press-fitting according to Embodiment 1. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the above compressor housing for a turbocharger, the “circumferential direction” means a rotation direction of the impeller, and the “axial direction” means a direction of a rotating shaft of the impeller. The “intake side” means an opening side of the intake port, and a compressor-housing side in the axial direction of a rotor shaft serving as a rotating shaft of the impeller accommodated in the compressor housing. The center housing that pivotally supports the rotor shaft is located on a “side opposite to the intake side”. 
     The first intermediate wall surface and the second intermediate wall surface each have a semicircular cross section perpendicular to a flow-path direction in the intermediate part, and are opposed to each other to form the inner wall surface of the intermediate part that has a circular cross section perpendicular to the flow-path direction. Consequently, the intermediate part has a substantially circular cross section in the axial direction, and extends in the axial direction. 
     Another aspect of the present invention provides a method for manufacturing the compressor housing for a turbocharger according to claim  1 , the method including: 
     forming the scroll piece and an integral piece by die-casting, the integral piece integrally including a portion that is to be the shroud piece and a portion that is to be the outer-circumferential annular piece; 
     press-fitting the shroud press-fit part that constitutes part of the integral piece into the intake port of the scroll piece, and press-fitting the outer-circumferential annular press-fit part that constitutes part of the integral piece into the scroll outer-circumferential part of the scroll piece; and 
     after the press-fitting steps, cutting the integral piece to separate into the shroud piece and the outer-circumferential annular piece. 
     According to the method for manufacturing the compressor housing for a turbocharger, in the forming step, two pieces, i.e., the scroll piece, and the integral piece integrally including a portion that is to be the shroud piece and a portion that is to be the outer-circumferential annular piece are formed by die-casting. Therefore, productivity can be improved while suppressing the cost for die-casting as compared with a case where three pieces of the scroll piece, the shroud piece, and the outer-circumferential annular piece are separately molded by die-casting. 
     In the press-fitting step, a shrink range between the scroll outer-circumferential part of the scroll piece and the outer-circumferential annular press-fit part that constitutes part of the integral piece is set smaller than a shrink range between the intake port of the scroll piece and the shroud press-fit part that constitutes part of the integral piece. In this case, the integral piece is easily press-fitted into the scroll piece. 
     In the press-fitting steps, the a shrink range between the scroll outer-circumferential part of the scroll piece and the outer-circumferential annular press-fit part that constitutes part of the integral piece is set to an extent to allow the outer-circumferential annular piece to be removed after the cutting step, and 
     the method further comprises: 
     after the cutting step, detaching the outer-circumferential annular piece and removing cutting oil from the scroll piece and the outer-circumferential annular piece; and 
     after the detaching and removing step, press-fitting again the outer-circumferential annular piece into the scroll piece with a seal member interposed between the scroll piece and the outer-circumferential annular piece. In this case, sealability between the scroll piece and the outer-circumferential annular piece can be enhanced. 
     Embodiment 
     Embodiment 1 
     An embodiment of a compressor housing  1  for a turbocharger will be described referring to  FIGS. 1 to 6 . 
     The compressor housing  1  for a turbocharger is configured to accommodate an impeller  10 , and includes an intake port  11 , a scroll chamber  12 , and a discharge port  13 , as illustrated in  FIGS. 1 and 2 , and includes an intermediate part  14 , as illustrated in  FIG. 3 . As illustrated in  FIG. 2 , the compressor housing  1  for a turbocharger is configured to be attachable to a center housing  2  that accommodates a bearing device not illustrated. 
     As illustrated in  FIG. 2 , the intake port  11  sucks air toward the impeller  10 . 
     The scroll chamber  12  is formed in the circumferential direction on an outer-circumference side of the impeller  10 , and is configured to allow air discharged from the impeller  10  to circulate. 
     The discharge port  13  is configured to discharge air circulating through the scroll chamber  12  to an outside. 
     The intermediate part  14  allows the discharge port  13  and the scroll chamber  12  to communicate with each other, as illustrated in  FIG. 3 . 
     As illustrated in  FIGS. 4 and 5 , the compressor housing  1  is composed of a scroll piece  20 , a shroud piece  30 , and an outer-circumferential annular piece  40  that are dividedly formed and assembled in an axial direction Y. 
     As illustrated in  FIGS. 1 to 3 , the scroll piece  20  includes the intake port  11 , an intake-side wall surface  21 , a through part  22 , a first intermediate wall surface  23 , a scroll outer-circumferential part  24 , and joining parts  25 . The intake port  11  is formed through the scroll piece  20  in the axial direction Y. The intake-side wall surface  21  constitutes a wall surface of the scroll chamber  12  on an intake side Y 1 . The through part  22  is formed through the scroll piece  20  in the axial direction Y, and has an end on the intake side Y 1 , which constitutes the discharge port  13 . The first intermediate wall surface  23  is extended from the intake-side wall surface  21 , being bent to be parallel to the axial direction Y, and is smoothly connected with the discharge port  13 . 
     In other words, the first intermediate wall surface  23  is extended from the intake-side wall surface  21  and is bent toward the intake side Y 1  in a plane parallel to the axial direction Y, and is smoothly connected with the discharge port  13 , as illustrated in  FIG. 3 . The first intermediate wall surface  23  constitutes part of an inner wall surface  14   a  of the intermediate part  14 . The scroll outer-circumferential part  24  covers an outer-circumference side of the scroll chamber  12 . The joining parts  25  are provided at the scroll outer-circumferential part  24 , and are directly joined to joined portions  2   a  formed at the center housing  2 , as illustrated in  FIG. 2 . Consequently, the scroll piece  20  is directly fixed to the center housing  2 . Seal members may be interposed between the joining parts  25  and the joined portions  2   a.    
     As illustrated in  FIG. 2 , the shroud piece  30  includes a shroud press-fit part  31 , an inner-circumference-side wall surface  32 , a shroud surface  33 , and a diffuser surface  34 . The shroud press-fit part  31  is formed in a cylindrical shape, and is press-fitted into the intake port  11 . The inner-circumference-side wall surface  32  constitutes a wall surface of the scroll chamber  12  on an inner-circumference side. The shroud surface  33  is opposed to the impeller  10 . The diffuser surface  34  is extended from the shroud surface  33  to the scroll chamber  12 . 
     The shroud piece  30  also has an intake path  35  formed through the shroud press-fit part  31  and communicated with the intake port  11 . The shroud piece  30  also includes a facing surface  36  that is opposite the diffuser surface  34  (on the intake side Y 1 ). The facing surface  36  faces the scroll piece  20  in the axial direction Y. Meanwhile, the scroll piece  20  includes a contact portion  29  with which the facing surface  36  of the shroud piece  30  is made to contact in the axial direction Y, as illustrated in  FIG. 2 . The facing surface  36  is made to contact with the contact portion  29  of the scroll piece  20  in the axial direction Y, so that the shroud piece  30  is positioned in the axial direction Y. 
     As illustrated in  FIG. 3 , the outer-circumferential annular piece  40  includes an outer-circumference-side wall surface  41 , a protruding part  42 , and an outer-circumferential annular press-fit part  44 . The outer-circumference-side wall surface  41  constitutes a wall surface of the scroll chamber  12  on the outer-circumference side. The protruding part  42  is formed protruding toward the intake side Y 1  and is inserted into the through part  22  in the axial direction Y. The protruding part  42  includes a second intermediate wall surface  43  that is opposed to the first intermediate wall surface  23  and constitutes part of the inner wall surface  14   a  of the intermediate part  14 . The second intermediate wall surface  43  is extended from the outer-circumference-side wall surface  41 , being bent toward the intake side Y 1  to be parallel to the axial direction Y. In other words, as illustrated in  FIG. 3 , the second intermediate wall surface  43  is extended from the outer-circumference-side wall surface  41  and is bent toward the intake side Y 1  in a plane parallel to the axial direction Y. 
     The outer-circumferential annular press-fit part  44  is press-fitted into the scroll outer-circumferential part  24  of the scroll piece  20 . In the present embodiment, the outer-circumferential annular press-fit part  44  forms an outer-circumferential portion of the outer-circumferential annular piece  40 , and includes a flange  45  at an outer edge of the outer-circumferential annular press-fit part  44 , the flange  45  protruding in an outer-circumference direction of the outer-circumferential annular press-fit part  44 . A surface of the flange  45  on the intake side Y 1  constitutes a seal surface  45   a  in contact with an outer-circumferential end surface  24   a  that is an end surface of the scroll outer-circumferential part  24  on a side Y 2  opposite to the intake side Y 1 . The outer-circumferential end surface  24   a  and the seal surface  45   a  are parallel to each other. 
     The scroll piece  20 , the shroud piece  30 , and the outer-circumferential annular piece  40  are formed so as to withstand circulation of compressed air. As illustrated in  FIG. 2 , a rotor shaft  15  is pivotally supported in a rotatable way by the bearing device (not illustrated) accommodated in the center housing  2 . The rotor shaft  15  to which the impeller  10  is attached constitutes a rotating body  16  together with a rotor (not illustrated). 
     A method for manufacturing the compressor housing  1  according to the present embodiment includes a step S 1  of forming the scroll piece  20  illustrated in  FIGS. 4 and 5 , and an integral piece  50  by die-casting, the integral piece  50  integrally including a portion that is to be the shroud piece  30  and a portion that is to be the outer-circumferential annular piece  40 ; a step S 2  of press-fitting the shroud press-fit part  31  that constitutes part of the integral piece  50  illustrated in  FIG. 6  into the intake port  11  of the scroll piece  20  and press-fitting the outer-circumferential annular press-fit part  44  that constitutes part of the integral piece  50  into the scroll outer-circumferential part  24  of the scroll piece  20 ; and after the press-fitting step S 2 , a step S 3  of cutting the integral piece  50  illustrated in  FIGS. 6 and 7  to separate into the shroud piece  30  and the outer-circumferential annular piece  40 . 
     Hereinafter, the method will be described in detail. 
     First, in the forming step S 1 , the scroll piece  20  and the integral piece  50  are molded by die-casting, as illustrated in  FIGS. 4 and 5 . In the present embodiment, as illustrated in  FIG. 6 , the portion of the integral piece  50  that is to be the shroud piece  30  and the portion of the integral piece  50  that is to be the outer-circumferential annular piece  40  are connected with each other through an annular connecting portion  51  between the inner-circumference-side wall surface  32  and the outer-circumference-side wall surface  41 . 
     Next, in the press-fitting step S 2 , the integral piece  50  is press-fitted into the scroll piece  20  in the axial direction Y, as illustrated in  FIG. 6 . Specifically, while a phase of the discharge port  13  is aligned, as illustrated in  FIG. 4 , the shroud press-fit part  31  that constitutes part of the integral piece  50  is press-fitted into the intake port  11  of the scroll piece  20 , and the outer-circumferential annular press-fit part  44  that constitutes part of the integral piece  50  is press-fitted into the scroll outer-circumferential part  24 , as illustrated in  FIG. 6 . A shrink range between the scroll outer-circumferential part  24  and the outer-circumferential annular press-fit part  44  is smaller than a shrink range between the intake port  11  and the shroud press-fit part  31 . In the present embodiment, the shrink range between the scroll outer-circumferential part  24  and the outer-circumferential annular press-fit part  44  is set to an extent to loosely press-fit the outer-circumferential annular press-fit part  44  into the scroll outer-circumferential part  24  to be separated from each other later. 
     Then, as illustrated in  FIG. 6 , the facing surface  36  of a portion of the integral piece  50  that is to be the shroud piece  30  is made in contact with the contact portion  29  of the scroll piece  20  in the axial direction Y so that the integral piece  50  is positioned in the axial direction Y, and the press-fitting of the integral piece  50  is completed. Consequently, the intake-side wall surface  21 , the inner-circumference-side wall surface  32 , and the outer-circumference-side wall surface  41  form the scroll chamber  12  in the circumferential direction outside the impeller  10 . 
     Further, in the press-fitting step S 2 , the protruding part  42  is inserted into the through part  22  by press-fitting the integral piece  50 . As illustrated in  FIGS. 4 and 5 , the through part  22  is formed by a cylindrical portion  22   a  that has a substantially cylindrical shape extending in the axial direction Y. An end of the cylindrical portion  22   a  on the intake side Y 1  has a circular opening that forms the discharge port  13 . The vicinity of an end of the cylindrical portion  22   a  on a Y 2  side opposite the intake side Y 1  is cut off on a central C side. As illustrated in  FIG. 3 , the through part  22  has the first intermediate wall surface  23 . The first intermediate wall surface  23  is bent in a direction which shifts from an opening direction of the discharge port  13  (axial direction Y) to a formation direction in which the scroll chamber  12  is formed (circumferential direction perpendicular to the axial direction Y) so that the first intermediate wall surface  23  smoothly connects the discharge port  13  with the intake-side wall surface  21 . 
     As illustrated in  FIGS. 4 and 5 , the protruding part  42  protrudes toward the intake side Y 1 , and has an outer circumference surface  421  parallel to the axial direction Y. As illustrated in  FIG. 4 , the outer circumference surface  421  has a shape that fits in an inner wall of the cylindrical portion  22   a  that forms the through part  22 . The second intermediate wall surface  43  is formed on the inside of the protruding part  42 . The second intermediate wall surface  43  is bent in a direction which shifts from the axial direction Y to a circumferential direction perpendicular to the axial direction Y so that an end of the second intermediate wall surface  43  on the intake side Y 1  is smoothly connected with the outer-circumference-side wall surface  41 . 
     As illustrated in  FIG. 3 , the protruding part  42  is inserted into the through part  22  in the interference-fitting step S 2  so that the first intermediate wall surface  23  and the second intermediate wall surface  43  are opposed to each other. As a result, the inner wall surface  14   a  of the intermediate part  14  through which the scroll chamber  12  communicates with the discharge port  13  is formed. The first intermediate wall surface  23  and the second intermediate wall surface  43  each have a semicircular cross section perpendicular to a flow-path direction in the intermediate part  14 . The first intermediate wall surface  23  is disposed opposite the second intermediate wall surface  43 . As a result, the inner wall surface  14   a  of the intermediate part  14  is formed to have a substantially circular cross section perpendicular to the flow-path direction. Consequently, the intermediate part  14  has a tube-like shape. 
     Since the first intermediate wall surface  23  and the second intermediate wall surface  43  have the shapes described above, the intermediate part  14  communicates with the discharge port  13  at an end  42   a  of the intermediate part  14  on the intake side Y 1 , and communicates with, at a base  42   b  of the intermediate part  14  (an end on the side Y 2  that is opposite the intake side Y 1 ), the scroll chamber  12  formed in the circumferential direction, as illustrated in  FIG. 3 . The intermediate part  14  is bent in a direction which shifts from the opening direction of the discharge port  13  (axial direction Y) to the formation direction in which the scroll chamber  12  is formed (circumferential direction perpendicular to the axial direction Y) so that the intermediate part  14  smoothly connects the discharge port  13  and the scroll chamber  12 . 
     A pipe (not illustrated) through which compressed air discharged from the scroll chamber  12  is supplied to an internal combustion engine is connected to the discharge port  13 . A joint made of a deformable material may be interposed between the pipe and the discharge port  13 . 
     In the cutting step S 3  after the press-fitting step S 2 , the integral piece  50  is separated into the shroud piece  30  and the outer-circumferential annular piece  40  by cutting the connecting portion  51  of the integral piece  50  illustrated in  FIG. 6 , and a predetermined gap is formed between the shroud piece  30  and the outer-circumferential annular piece  40 , as illustrated in  FIG. 7 . 
     In the present embodiment, as illustrated in  FIGS. 8, 9, and 10 , after the cutting step S 3 , a step S 4  of detaching the outer-circumferential annular piece  40  that has been loosely press-fitted into the scroll outer-circumferential part  24 , and removing cutting oil that has been left in the cutting step S 3  is performed. Then, a step S 5  of press-fitting the outer-circumferential annular piece  40  into the scroll outer-circumferential part  24  again with a seal member  52  interposed between the outer-circumferential end surface  24   a  that is an end surface of the scroll outer-circumferential part  24  on the side Y 2  that is opposite the intake side Y 1  and the seal surface  45   a  that is a surface of the flange  45  on the intake side Y 1  is performed, as illustrated in  FIGS. 8 and 9 . In the step S 5 , the seal surface  45   a  is made in contact with the outer-circumferential end surface  24   a  so that the outer-circumferential annular piece  40  is positioned, and the press-fitting of the outer-circumferential annular piece  40  is completed. Consequently, the compressor housing  1  illustrated in  FIGS. 1 and 2  is obtained. 
     Next, effect of the compressor housing  1  according to the present embodiment will be described in detail. 
     In the compressor housing  1  according to the present embodiment, the scroll piece  20 , the shroud piece  30 , and the outer-circumferential annular piece  40  are assembled in the axial direction Y. The scroll piece  20  has the through part  22  formed therethrough in the axial direction Y, and an end of the through part  22  on the intake side Y 1  constitutes the discharge port  13 . The first intermediate wall surface  23  extended from the intake-side wall surface  21  that forms the scroll chamber  12 , being bent toward the intake-side in the axial direction Y, is smoothly connected with the discharge port  13 . Further, the protruding part  42  is inserted into the through part  22 . The protruding part  42  is formed protruding in the outer-circumferential annular piece  40  in the axial direction Y that corresponds to the assembly direction. The protruding part  42  includes the second intermediate wall surface  43  opposing to the first intermediate wall surface  23 . The first intermediate wall surface  23  and the second intermediate wall surface  43  form the inner wall surface  14   a  of the intermediate part  14  through which the discharge port  13  is communicated with the scroll chamber  12 . 
     Consequently, the scroll piece  20  including the discharge port  13 , and the outer-circumferential annular piece  40  can be shaped to be releasable from a mold (to have no undercut) in an insertion direction, that is, the axial direction Y. Therefore, the scroll piece  20  can be molded by die-casting instead of gravity casting or low-pressure casting, and manufacturing cost can be reduced. Further, a die for the scroll chamber  12  and a die for the discharge port  13  do not need to be separately prepared for die casting, and thus manufacturing cost can be reduced. Since the number of components does not increase, and assembly is not complicated as compared with conventional techniques, manufacturing cost does not increase. 
     The scroll outer-circumferential part  24  of the scroll piece  20  includes the joining parts  25  to be joined to the center housing  2 . The joining parts  25  and the joined portions  2   a  of the center housing  2 , between which the outer-circumferential annular piece  40  is interposed, are joined to each other. As a result, the compressor housing  1  can be fixed to the center housing  2 . Consequently, the scroll piece  20  is joined to the center housing  2  that is made of iron and is more rigid than conventional aluminum seal plates. Therefore, the thickness of a joint region between the scroll piece  20  and the center housing  2  does not need to be increased. As a result, high rigidity is secured without increasing the length of the rotating body  16  that includes the impeller  10  and the rotor shaft  15 , and thus noise due to vibration of the rotating body  16  is reduced. Since a length of the rotating body  16  does not need to be increased, an increase in material cost is restricted, and thus an increase in manufacturing cost is prevented. 
     Further, in the present embodiment, the first intermediate wall surface  23  and the second intermediate wall surface  43  each have a semicircular cross section perpendicular to a flow-path direction, and are opposed to each other to form the inner wall surface  14   a  of the intermediate part  14  that has a circular cross section perpendicular to the flow-path direction. Consequently, the discharge port  13  has a substantially circular cross section perpendicular to the flow-path direction, and thus has a cylindrical shape extending in the axial direction Y. Such a configuration prevents circulation of compressed air from being interrupted in the discharge port  13 . 
     In the present embodiment, the scroll piece  20  and the outer-circumferential annular piece  40  are made by aluminum die-casing. Since the scroll piece  20  and the outer-circumferential annular piece  40  are made of the same material, and thus have the same coefficient of thermal expansion, a gap is unlikely to be formed between seal portions (outer-circumferential end surface  24   a  and the seal surface  45   a ) of the scroll piece  20  and the outer-circumferential annular piece  40 . Therefore, air tightness of the compressor housing  1  can be improved. 
     The method for manufacturing the compressor housing  1  for a turbocharger according to the present embodiment includes the step S 1  of forming the scroll piece  20 , and the integral piece  50  by die-casting, the integral piece  50  integrally including a portion that is to be the shroud piece  30  and a portion that is to be the outer-circumferential annular piece  40 , the step S 2  of press-fitting the shroud press-fit part  31  that constitutes part of the integral piece  50  into the intake port  11  of the scroll piece  20 , and press-fitting the outer-circumferential annular press-fit part  44  that constitutes part of the integral piece  50  into the scroll outer-circumferential part  24  of the scroll piece  20 , and the step S 3  of, after the press-fitting step S 2 , cutting the integral piece  50  to separate into the shroud piece  30  and the outer-circumferential annular piece  40 . Consequently, in the forming step S 1 , two pieces, i.e., the scroll piece  20 , and the integral piece  50  integrally including a portion that is to be the shroud piece  30  and a portion that is to be the outer-circumferential annular piece  40  are formed by die-casting. Therefore, productivity can be improved while suppressing the cost for die-casting as compared with a case where three pieces of the scroll piece  20 , the shroud piece  30 , and the outer-circumferential annular piece  40  are separately molded by die-casting. 
     Further, in the press-fitting step S 2  according to the present embodiment, a shrink range between the scroll outer-circumferential part  24  of the scroll piece  20  and the outer-circumferential annular press-fit part  44  that constitutes part of the integral piece  50  is smaller than a shrink range between the intake port  11  of the scroll piece  20  and the shroud press-fit part  31  that constitutes part of the integral piece  50 . Consequently, the integral piece  50  is easily press-fitted into the scroll piece  20 , and the outer-circumferential annular piece  40  is easily removed from the integral piece  50 . 
     Further, in the interference-fitting step S 2  according to the present embodiment, the amount of interference between the scroll outer-circumferential part  24  of the scroll piece  20  and the outer-circumferential annular press-fit part  44  that constitutes part of the integral piece  50  allows the outer-circumferential annular piece  40  to be removed after the cutting step S 3 . The method for manufacturing the compressor housing  1  for a turbocharger according to the present embodiment further includes the removing step S 4  of, after the cutting step S 3 , removing the outer-circumferential annular piece  40  and removing cutting oil from the scroll piece  20  and the outer-circumferential annular piece  40 , and the second interference-fitting step S 5  of, after the removing step S 4 , interference-fitting the outer-circumferential annular piece  40  into the scroll piece  20  again with the seal member  52  interposed between the scroll piece  20  and the outer-circumferential annular piece  40 . According to such a method, sealability between the scroll piece  20  and the outer-circumferential annular piece  40  can be enhanced. 
     As described above, the present embodiment provides the compressor housing  1  for a turbocharger that reduces noise generation, and prevents an increase in manufacturing cost.