Patent Publication Number: US-11391177-B2

Title: Turbocharger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application Number 2020-079385 filed on Apr. 28, 2020. The entire contents of the above-identified application are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The disclosure relates to a turbocharger, in particular, a turbocharger in which a cooling water flow path is formed in a housing. 
     RELATED ART 
     Engines used in automobiles and the like may be equipped with a turbocharger to improve engine output and fuel efficiency. The turbocharger rotates an impeller of a compressor mechanically coupled to a turbine rotor via a rotor shaft, by rotating the turbine rotor by high-temperature fluid such as exhaust gas discharged from an engine. The turbocharger compresses a gas (for example, air) used for combustion in the engine by means of the impeller that is rotationally driven, and feeds the compressed gas to the engine. 
     Some turbochargers include a bearing housing that houses a bearing for rotatably supporting a rotor shaft, a turbine housing that houses a turbine rotor, and a compressor housing that houses an impeller (for example, JP 64-34435 UM-A). Because the working fluid, such as exhaust gas, supplied to the turbine side of the turbocharger is at a high temperature of 600° C. or higher, the movement of heat on the turbine side toward the compressor side occurs via the turbine housing, the bearing housing, the rotor shaft, and the like. 
     Various problems arise when heat on the turbine side is transferred to the compressor side. For example, when the gas in the compressor housing is heated by the heat transferred to the compressor side, it may cause a decrease in compressor efficiency. Further, lubricating oil that lubricates the equipment inside the turbocharger such as a bearing may be heated and caulked by heat from the turbine side. Further, the heat resistance of members such as a turbine housing and a compressor housing that transfer heat on the turbine side are also problematic. 
     In some turbochargers, a cooling water flow path through which cooling water flows is formed in a turbine housing or a bearing housing to suppress effects caused by heat on the turbine side. JP 64-34435 UM-A discloses a turbocharger provided with a ring-shaped cooling water flow path (water jacket) at a position on the turbine housing side of the bearing housing. JP 2018-71411 A discloses a turbocharger in which a bearing housing and a turbine housing are integrally manufactured by molding, and a ring-shaped cooling water flow path is provided at a part corresponding to the turbine housing. 
     SUMMARY 
     In recent years, as the engine increases in power, the temperature of the exhaust gas discharged from the engine and supplied to the turbine housing tends to increase. Therefore, there is a demand for a cooling water flow path that can be efficiently cooled. Note that the turbocharger described in JP 2018-71411 A has a structure in which heat is easily transferred from a turbine housing to a bearing housing because the bearing housing and the turbine housing are integrally formed. By configuring the bearing housing and the turbine housing as separate bodies, the contact heat resistance can be generated in these contact surfaces, so it is possible to suppress the transfer of heat from the turbine housing to the bearing housing. 
     In view of the above-described problem, an object of at least one embodiment of the present disclosure is to provide a turbocharger that can improve the cooling efficiency of the cooling water flow path and can reduce the movement of the heat on the turbine side toward the compressor side. 
     A turbocharger according to the present disclosure includes a turbine housing configured to house a turbine rotor provided on one side of a rotor shaft; and a bearing housing configured to house a bearing that rotatably supports the rotor shaft, in which at least one cooling water flow path through which cooling water flows is formed in at least one of the turbine housing and the bearing housing, and the at least one cooling water flow path is formed such that a plurality of flow path cross sections are present in, of a cross-section including an axis of the rotor shaft, a half cross-section divided by the axis. 
     In accordance with at least one embodiment of the present disclosure, a turbocharger is provided that can improve the cooling efficiency of the cooling water flow path and can reduce the movement of heat on the turbine side toward the compressor side. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The disclosure will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic configuration diagram schematically illustrating a configuration of an engine system including a turbocharger according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic sectional diagram of a turbocharger according to a first embodiment of the present disclosure. 
         FIG. 3  is an explanatory diagram for describing an example of a cooling water flow path illustrated in  FIG. 2 . 
         FIG. 4  is an explanatory diagram for describing an example of the cooling water flow path illustrated in  FIG. 2 . 
         FIG. 5  is an explanatory diagram for describing an example of the cooling water flow path illustrated in  FIG. 2 . 
         FIG. 6  is a schematic sectional diagram of a turbocharger according to a second embodiment of the present disclosure. 
         FIG. 7  is an explanatory diagram for describing an example of a cooling water flow path illustrated in  FIG. 6 . 
         FIG. 8  is a schematic sectional diagram of a turbocharger according to a third embodiment of the present disclosure. 
         FIG. 9  is an explanatory diagram for describing an example of a cooling water flow path illustrated in  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will be described hereinafter with reference to the appended drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions, and the like of components described in the embodiments or illustrated in drawings shall be interpreted as explanatory only and not intended to limit the scope of the present disclosure. 
     For instance, an expression of relative or absolute arrangement such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “centered”, “concentric” and “coaxial” shall not be construed as indicating only the arrangement in a strict literal sense, but also includes a state where the arrangement is relatively displaced by a tolerance, or by an angle or a distance within a range in which it is possible to achieve the same function. 
     For instance, an expression of an equal state such as “same”, “equal”, “uniform” and the like shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference within a range where it is possible to achieve the same function. 
     Further, for instance, an expression of a shape such as a rectangular shape, a cylindrical shape or the like shall not be construed as only the geometrically strict shape, but also includes a shape with unevenness, chamfered corners or the like within the range in which the same effect can be achieved. 
     On the other hand, an expression such as “comprising”, “including”, or “having” one component is not intended to be exclusive of other components. 
     The same configurations may be denoted by the same reference signs, and the description thereof may be omitted. 
     Turbocharger 
       FIG. 1  is a schematic configuration diagram schematically illustrating a configuration of an engine system including a turbocharger according to an embodiment of the present disclosure. 
     A turbocharger  1  according to some embodiments, as illustrated in  FIG. 1 , includes a rotor shaft  11 , a turbine rotor  12  mechanically coupled to one side (the right side in  FIG. 1 ) of the rotor shaft  11 , a compressor rotor  13  mechanically coupled to the other side of the rotor shaft  11  (the left in  FIG. 1 ), a bearing  14  that rotatably supports the rotor shaft  11 , and a housing  15  that houses them. 
     In the illustrated embodiment, as illustrated in  FIG. 1 , the housing  15  includes a turbine housing  16  configured to house the turbine rotor  12 , a bearing housing  17  configured to house the bearing  14 , and a compressor housing  18  configured to house the compressor rotor  13 . The bearing housing  17  is separated from the turbine housing  16  and the compressor housing  18 . The bearing housing  17  is disposed between the turbine housing  16  and the compressor housing  18 , and is integrally fastened to each of the turbine housing  16  and the compressor housing  18  by a fastening member such as, for example, a fastening bolt. 
     In the embodiment illustrated in  FIG. 1 , the compressor rotor  13  is provided with a supply line  21  for supplying gas (for example, combustion air) to a combustion device (for example, engine)  20 . The turbine rotor  12  is provided with an exhaust line  22  through which the exhaust gas is discharged from the combustion device  20 . The turbocharger  1  is configured to rotate the turbine rotor  12  by the energy of the exhaust gas introduced from the combustion device  20  into the turbine housing  16  through the exhaust line  22 . The compressor rotor  13  is mechanically coupled to the turbine rotor  12  via the rotor shaft  11  and thus is rotated in conjunction with the rotation of the turbine rotor  12 . The turbocharger  1  is configured to increase the pressure of the gas introduced into the compressor housing  18  through the supply line  21  by the rotation of the compressor rotor  13  and send the resultant gas to the combustion device  20 . 
     The turbine housing  16  is formed with: an exhaust gas introduction port  161  through which exhaust gas is introduced into the turbine housing  16 ; and an exhaust gas discharge port  162  through which exhaust gas that has passed through the turbine rotor  12  is discharged to the outside. The exhaust gas introduction port  161  opens in a direction that intersects (for example, orthogonally) with respect to an axis CA of the rotor shaft  11 . The exhaust gas discharge port  162  opens toward a front side XF in the axial direction. 
     The compressor housing  18  is formed with: a gas introduction port  181  through which gas is introduced into the compressor housing  18 ; and a gas discharge port  182  through which gas that has passed through the compressor rotor  13  is discharged to the outside. The gas introduction port  181  opens toward a rear side XR in the axial direction. The gas discharge port  182  opens in a direction that intersects (for example, orthogonally) with respect to the axis CA of the rotor shaft  11 . 
       FIG. 2  is a schematic sectional diagram of a turbocharger according to a first embodiment of the present disclosure. 
     As illustrated in  FIG. 2 , a scroll flow path  163 , which is a scroll exhaust gas flow path for sending, to the turbine rotor  12 , the exhaust gas introduced into the turbine housing  16  from the exhaust gas introduction port  161 ; and an exhaust gas discharge flow path  164 , which is an exhaust gas flow path for sending exhaust gas from the turbine rotor  12  to the exhaust gas discharge port  162  are formed inside the turbine housing  16 . 
     In the following description, as illustrated in  FIG. 2 , for example, an extending direction of the axis CA of the rotor shaft  11  is defined as an axial direction X, and a direction orthogonal to the axis CA is defined as a radial direction Y. In the axial direction X, a side (the right side in  FIG. 2 ) on which the turbine housing  16  is positioned with respect to the bearing housing  17  is referred to as the front side XF, and a side (the left side in  FIG. 2 ) on which the bearing housing  17  is positioned with respect to the turbine housing  16  is referred to as the rear side XR. 
     Variable Nozzle Device 
     In the illustrated embodiment, the turbocharger  1  is equipped with a variable nozzle device  23  within the housing  15 . The variable nozzle device  23  is disposed between the scroll flow path  163  and the turbine rotor  12  to surround the periphery of the turbine rotor  12  (the outer side in the radial direction Y). The variable nozzle device  23  is configured to define a nozzle flow path  165 , which is an exhaust gas flow path, between the scroll flow path  163  and the turbine rotor  12 . The variable nozzle device  23  is configured to adjust the flow path cross-sectional area of the nozzle flow path  165  by changing the blade angle of a nozzle vane  24  disposed in the nozzle flow path  165 . By increasing or decreasing the flow path cross-sectional area of the nozzle flow path  165 , the flow velocity and pressure of the exhaust gas sent from the scroll flow path  163  to the turbine rotor  12  can be changed. 
     The exhaust gas introduced into the turbine housing  16  from the exhaust gas introduction port  161  passes through the scroll flow path  163 , passes through the nozzle flow path  165 , and then is sent to the turbine rotor  12  to rotate the turbine rotor  12 . The exhaust gas that has rotated the turbine rotor  12  passes through the exhaust gas discharge flow path  164  and then is discharged from the exhaust gas discharge port  162  to the outside of the turbine housing  16 . 
     As illustrated in  FIG. 2 , the variable nozzle device  23  includes a nozzle mount  25  fixed to the housing  15 , a nozzle plate  26  defining a nozzle flow path  165  between the nozzle mount  25  and the nozzle plate  26 , at least one nozzle support  27  supporting the nozzle mount  25  and the nozzle plate  26  in a state of being spaced apart from each other, and at least one nozzle vane  24  rotatably supported between the nozzle mount  25  and the nozzle plate  26 . 
     The nozzle mount  25  includes an annular plate portion  251  that extends along a direction that intersects (for example, orthogonally) the axis CA. The nozzle mount  25  is supported within the housing  15 . In the illustrated embodiment, the nozzle mount  25  is fixed to the bearing housing  17  by the outer circumferential edge of the annular plate portion  251  being held between the turbine housing  16  and the bearing housing  17 . 
     The variable nozzle device  23  is supported within the housing  15  by the nozzle mount  25  being supported within the housing  15 . The nozzle plate  26  includes: a plate-side annular plate portion  261  that extends along a direction that intersects (for example, orthogonally) the axis CA; and a protruding portion  262  that protrudes from the inner circumferential edge of the plate-side annular plate portion  261  toward the front side XF in the axial direction X. 
     One side of the at least one nozzle support  27  is mechanically coupled to the annular plate portion  251  of the nozzle mount  25 , and the other side of the at least one nozzle support  27  is mechanically coupled to the plate-side annular plate portion  261  of the nozzle plate  26 . Thus, the nozzle plate  26  is supported by the at least one nozzle support  27  at a distance from the nozzle mount  25  in the axial direction X. In the illustrated embodiment, the at least one nozzle support  27  includes a plurality of the nozzle supports  27  disposed at intervals in the circumferential direction around the axis CA. 
     The nozzle flow path  165  described above is defined by: a mount-side flow path wall surface  252  located on the front side XF in the axial direction X of the annular plate portion  251  (nozzle mount  25 ); and a plate-side flow path wall surface  263  located on the rear side XR in the axial direction X of the plate-side annular plate portion  261  (nozzle plate  26 ). The plate-side flow path wall surface  263  is located on the front side XF relative to the mount-side flow path wall surface  252  and faces the mount-side flow path wall surface  252 . Each of the mount-side flow path wall surface  252  and the plate-side flow path wall surface  263  extends along a direction that intersects (for example, orthogonally) the axial direction X. 
     The at least one nozzle vane  24  is rotatably supported on the nozzle mount  25 . In the illustrated embodiment, the at least one nozzle vane  24  includes a plurality of the nozzle vanes  24  disposed at spaced apart positions along the circumferential direction around the axis CA. 
     An internal space  172  having an annular shape is formed inside by: a back surface (rear side XR surface)  253  of the annular plate portion  251  of the nozzle mount  25 ; and a groove portion  171  having an annular shape formed on the front side XF of the bearing housing  17 . The variable nozzle device  23  further includes a drive ring  28  and a lever plate  29 , as illustrated in  FIG. 2 . Each of the drive ring  28  and the lever plate  29  is disposed in the internal space  172 . The lever plate  29  is mechanically coupled to the nozzle vane  24  and the drive ring  28 . The drive ring  28  operates in conjunction with the plurality of nozzle vanes  24  via the lever plate  29 . Further, the drive ring  28  is mechanically coupled to an actuator (not illustrated) that rotates the drive ring  28  about the axis CA. By driving an actuator (not illustrated) to rotate the drive ring  28 , the plurality of nozzle vanes  24  rotate in conjunction with the rotation of the drive ring  28  and change the blade angle. 
     Cooling Water Flow Path 
     The turbocharger  1  according to some embodiments, as illustrated in  FIG. 2 , includes: the turbine housing  16  configured to house the turbine rotor  12  provided on one side of the rotor shaft  11 ; and the bearing housing  17  configured to house the bearing  14  that rotatably supports the rotor shaft  11 . As illustrated in  FIG. 2 , at least one cooling water flow path  3  through which cooling water flows is formed in at least one of the turbine housing  16  and the bearing housing  17 . The at least one cooling water flow path  3  described above is formed such that a plurality of flow path cross sections  30  are present in, of a cross-section including the axis CA of the rotor shaft  11 , a half cross-section divided by the axis CA, as illustrated in  FIG. 2 . 
     In the embodiment illustrated in  FIG. 2 , the at least one cooling water flow path  3  includes a bearing housing-side cooling water flow path  3 A formed in the bearing housing  17 . The bearing housing-side cooling water flow path  3 A is formed such that the plurality of flow path cross sections  30  are present in the above-described half cross-section. In the embodiment in  FIG. 2 , the plurality of flow path cross sections  30  are located radially outward relative to the bearing  14 . Furthermore, the plurality of flow path cross sections  30  are located on the rear side XR in the axial direction X relative to the internal space  172 . 
     According to the configuration described above, the at least one cooling water flow path  3  is formed such that the plurality of flow path cross sections  30  are present in the half cross-section. In this case, in the above-described half cross-section, the total length of the circumferential length of the flow path cross section  30  on the half cross-section can be increased, compared to the case where there is a single flow path cross section having the same flow path cross-sectional area as the total flow path cross-sectional area of the plurality of flow path cross sections  30 . By increasing the total length of the circumferential length of the flow path cross section  30  on the half cross-section, the contact area and the thermal conduction volume between the cooling water in the cooling water flow path  3  and the flow path wall surface that defines the cooling water flow path  3  can be increased, so that the cooling action by the cooling water in the cooling water flow path  3  is promoted. Thus, it is possible to improve the cooling efficiency of the cooling water flow path  3 . By improving the cooling efficiency of the cooling water flow path  3 , it is possible to reduce the movement of heat on the turbine side toward the compressor side. 
       FIGS. 3 to 5  are explanatory diagrams for describing an example of the cooling water flow path illustrated in  FIG. 2 .  FIGS. 3 to 5  illustrate a state as seen from one side of the axial direction X (for example, the front side XF). In some embodiments, as illustrated in  FIGS. 3 to 5 , the at least one cooling water flow path  3  described above includes an inlet flow path  4  configured to allow cooling water to flow therein, a first curved flow path  5  communicating with the inlet flow path  4 , a second curved flow path  6  communicating with the first curved flow path  5 , and an outlet flow path  7  configured to allow cooling water to flow thereout and that communicates with the second curved flow path  6 . Each of the first and second curved flow paths  5 ,  6  extends along the circumferential direction of the rotor shaft  11 . The second curved flow path  6  is disposed to be offset in the radial direction Y relative to the first curved flow path  5 . Note that the second curved flow path  6  may be disposed to be offset in the axial direction X relative to the first curved flow path  5 , or may be disposed to be offset in both the radial direction Y and the axial direction X relative to the first curved flow path  5 . 
     As illustrated in  FIGS. 3 to 5 , the inlet flow path  4  has one side connected to a cooling water supply port  41  and an other side  42  connected to the first curved flow path  5 . The outlet flow path  7  has one side connected to a cooling water discharge port  71  and an other side  72  connected to the second curved flow path  6 . In the illustrated embodiment, each of the cooling water supply port  41  and the cooling water discharge port  71  is formed on an outer surface  173  of the bearing housing  17 , as illustrated in  FIG. 2 . The cooling water flow path  3  is formed on the outer circumferential side of the bearing  14 . 
     The cooling water is supplied to the cooling water supply port  41  from a washing water supply source (not illustrated). The cooling water sent through the cooling water supply port  41  to the inlet flow path  4  flows through the first curved flow path  5 , the second curved flow path  6 , and the outlet flow path  7 , and is then discharged to the outside of the cooling water flow path  3  through the cooling water discharge port  71 . 
     As illustrated in  FIGS. 3 to 5 , at least a portion of the second curved flow path  6  in the circumferential direction when viewed from the axial direction X overlaps the first curved flow path  5 . When viewed from the axial direction X, the portion where the first curved flow path  5  and the second curved flow path  6  overlap has a circumferential range centered on the axis CA that is greater than or equal to 180 degrees and less than or equal to 360 degrees. It is preferable that the circumferential range is larger. Preferably, the circumferential range is 270 degrees to 360 degrees. 
     According to the configuration described above, the cooling water that has flowed into the cooling water flow path  3  through the inlet flow path  4  passes through the first curved flow path  5  and the second curved flow path  6  extending along the circumferential direction of the rotor shaft  11 , and then flows to the outside of the cooling water flow path  3  through the outlet flow path  7 . Because the second curved flow path  6  is disposed to be offset in the radial direction relative to the first curved flow path  5 , the cooling water in the first curved flow path  5  and the cooling water in the second curved flow path  6  can cool a wide range of the housing  15  (the bearing housing  17  in the illustrated example) in the radial direction, so that the movement of the heat on the turbine side toward the compressor side can be effectively suppressed. 
     Further, according to the configuration described above, at least a portion of the second curved flow path  6  in the circumferential direction when viewed from the axial direction X overlaps the first curved flow path  5 . Thus, in a portion where the first curved flow path  5  and the second curved flow path  6  overlap in the circumferential direction, the housing  15  (the bearing housing  17  in the illustrated example) can be intensively cooled by the cooling water in the first curved flow path  5  and the cooling water in the second curved flow path  6 . By disposing the overlapping portion in the circumferential range where the increase in the temperature of the housing  15  is significant, the housing  15  can be effectively cooled, and an increase in the temperature of the housing  15  can be effectively suppressed. 
     As illustrated in  FIGS. 3 to 5 , one direction in the circumferential direction is referred to as a first direction FD. Note that in the illustrated embodiment, the clockwise direction when viewed from the front side XF is referred to as the first direction FD, but in some other embodiments, the counterclockwise direction when viewed from the front side XF may be referred to as the first direction FD. 
     In some embodiments, as illustrated in  FIGS. 3 and 4 , the inlet flow path  4  is connected to a starting end  51  of the first curved flow path  5  in the first direction FD, and the outlet flow path  7  is connected to a starting end  61  of the second curved flow path  6  in the first direction FD. The at least one cooling water flow path  3  described above further includes a first contact flow path  8 A that connects a terminal end  52  of the first curved flow path  5  in the first direction FD with a terminal end  62  of the second curved flow path  6  in the first direction FD. 
     In the embodiment illustrated in  FIG. 3 , the first curved flow path  5  is located radially outward relative to the second curved flow path  6 . In the embodiment illustrated in  FIG. 4 , the first curved flow path  5  is located radially inward relative to the second curved flow path  6 . 
     Because the cooling water in the cooling water flow path  3  receives heat from the housing  15  when cooling the housing  15 , cooling effects are higher on the upstream side of the cooling water flow path  3  than on the downstream side. According to the configuration described above, the cooling water flow path  3  includes the first contact flow path  8 A that connects the terminal end  52  of the first curved flow path  5  in the first direction FD with the terminal end  62  of the second curved flow path  6  in the first direction FD. Thus, the cooling water flows through the first curved flow path  5  in the first direction FD, and then flows through the second curved flow path  6  to the side opposite to the first direction FD in the circumferential direction. The cooling water on the upstream side of the first curved flow path  5  can cool the upstream side (near the starting ends  51  and  61 ) of the first direction FD, and the cooling water on the downstream side of the first curved flow path  5  and on the upstream side of the second curved flow path  6  can cool the downstream side (near the terminal ends  52  and  62 ) of the first direction FD. Thus, according to the configuration described above, cooling can be effectively performed by the cooling water flow path  3  over a range from the upstream side to the downstream side in the first direction FD. 
     In some embodiments, as illustrated in  FIG. 5 , the inlet flow path  4  is connected to the starting end  51  of the first curved flow path  5  in the first direction FD, and the outlet flow path  7  is connected to the terminal end  62  of the second curved flow path  6  in the first direction FD. The at least one cooling water flow path  3  described above further includes a second contact flow path  8 B that connects the terminal end  52  of the first curved flow path  5  in the first direction FD and the starting end  61  of the second curved flow path  6  in the first direction FD. Note that in the embodiment illustrated in  FIG. 5 , the first curved flow path  5  is located radially outward relative to the second curved flow path  6 , but in some other embodiments, the first curved flow path  5  may be located radially inward relative to the second curved flow path  6 . 
     According to the configuration described above, the cooling water flow path  3  includes the second contact flow path  8 B that connects the terminal end  52  of the first curved flow path  5  in the first direction and the starting end  61  of the second curved flow path  6  in the first direction. Thus, after the cooling water flows through the first curved flow path  5  in the first direction, the cooling water flows through the second curved flow path  6  in the first direction similar to the first curved flow path  5 . The cooling water in the first curved flow path  5  and the cooling water in the second curved flow path  6  can cool the upstream side in the first direction relative to the downstream side. Thus, according to the configuration described above, by disposing the upstream side of the first curved flow path  5  or the second curved flow path  6  in the circumferential range where the increase in temperature of the housing  15  is significant, the housing  15  can be effectively cooled, and an increase in the temperature of the housing  15  can be effectively suppressed. 
     In some embodiments, for example, as illustrated in  FIG. 3 , the first curved flow path  5  described above is located radially outward relative to the second curved flow path  6  described above. Here, because the first curved flow path  5  is located on the upstream side in the flow direction of the cooling water with respect to the second curved flow path  6 , the cooling water in the first curved flow path  5  has a higher cooling effect than the cooling water in the second curved flow path  6 . According to the configuration described above, the first curved flow path  5  is located radially outward relative to the second curved flow path  6 , so that the cooling action of the cooling water flow path  3  on the outer side of the housing  15  (the bearing housing  17  in the example illustrated) in the radial direction can be increased. By increasing the cooling action on the outer side of the housing  15  in the radial direction, it is possible to effectively suppress the transfer of heat from the exhaust gas inside the scroll flow path  163  of the turbine housing  16  into the housing  15 . 
     In some embodiments, for example, as illustrated in  FIG. 4 , the first curved flow path  5  described above is located radially inward relative to the second curved flow path  6  described above. Here, because the first curved flow path  5  is located on the upstream side in the flow direction of the cooling water with respect to the second curved flow path  6 , the cooling water in the first curved flow path  5  has a higher cooling effect than the cooling water in the second curved flow path  6 . According to the configuration described above, the first curved flow path  5  is located radially inward relative to the second curved flow path  6 , so that the cooling action of the cooling water flow path  3  on the inner side of the housing  15  (the bearing housing  17  in the illustrated example) in the radial direction can be increased. By increasing the cooling action on the inner side of the housing  15  in the radial direction, it is possible to effectively suppress the transfer of heat on the turbine side to the compressor side and the bearing  14  through the rotor shaft  11 . 
       FIG. 6  is a schematic sectional diagram of a turbocharger according to a second embodiment of the present disclosure.  FIG. 7  is an explanatory diagram for describing an example of a cooling water flow path illustrated in  FIG. 6 . 
     In some embodiments, the at least one cooling water flow path  3  described above is formed such that the plurality of flow path cross sections  30  are present in, of a cross-section including the axis CA of the rotor shaft  11 , a half cross-section divided by the axis CA, as illustrated in  FIG. 6 . As illustrated in  FIGS. 6 and 7 , the at least one cooling water flow path  3  described above includes a one-side cooling water flow path  3 C and an other-side cooling water flow path  3 D. The one-side cooling water flow path  3 C is located on the one side (front side XF in the example illustrated) in the direction in which the axis CA extends, with respect to the other-side cooling water flow path  3 D. 
     As illustrated in  FIG. 7 , the one-side cooling water flow path  3 C includes a one-side inlet flow path  4 C configured to allow cooling water to flow therein, a one-side curved flow path  9 C that extends along the circumferential direction of the rotor shaft  11  and communicates with the one-side inlet flow path  4 C, and a one-side outlet flow path  7 C configured to allow cooling water to flow thereout and that communicates with the one-side curved flow path  9 C. 
     As illustrated in  FIG. 7 , the other-side cooling water flow path  3 D includes: an other-side inlet flow path  4 D configured to allow cooling water to flow therein; an other-side curved flow path  9 D that extends along the circumferential direction of the rotor shaft  11  and communicates with the other-side inlet flow path  4 D; and an other-side outlet flow path  7 D configured to allow cooling water to flow thereout and that communicates with the other-side curved flow path  9 D. 
     In the embodiment illustrated in  FIG. 7 , the one-side inlet flow path  4 C has one side connected to the cooling water supply port  41  described above, and the other side  42  connected to a starting end  91  of the curved flow path  9 C in the first direction FD. The one-side outlet flow path  7 C has one side connected to the cooling water discharge port  71  described above, and the other side  72  connected to a terminal end  92  of the curved flow path  9 C in the first direction FD. Each of the cooling water supply port  41  and the cooling water discharge port  71  is formed on the outer surface  173  of the bearing housing  17 , as illustrated in  FIG. 6 . The cooling water flow path  3  is formed on the outer circumferential side of the bearing  14 . The cooling water is supplied to the cooling water supply port  41  from a washing water supply source (not illustrated). The cooling water sent through the cooling water supply port  41  to the one-side inlet flow path  4 C flows through the curved flow path  9 C and the one-side outlet flow path  7 C, and then is discharged to the outside of the cooling water flow path  3  through the cooling water discharge port  71 . 
     In the embodiment illustrated in  FIG. 7 , the other-side inlet flow path  4 D has one side connected to the cooling water supply port  41  described above, and the other side  42  connected to the starting end  91  of the curved flow path  9 D in the first direction FD. The other-side outlet flow path  7 D has one side connected to the cooling water discharge port  71  described above, and the other side  72  connected to the terminal end  92  of the curved flow path  9 D in the first direction FD. Each of the cooling water supply port  41  and the cooling water discharge port  71  is formed on the outer surface  173  of the bearing housing  17 , as illustrated in  FIG. 6 . The cooling water flow path  3  is formed on the outer circumferential side of the bearing  14 . The cooling water is supplied to the cooling water supply port  41  from a washing water supply source (not illustrated). The cooling water sent through the cooling water supply port  41  to the other-side inlet flow path  4 D flows through the curved flow path  9 D and the other-side outlet flow path  7 D, and then is discharged to the outside of the cooling water flow path  3  through the cooling water discharge port  71 . 
     According to the configuration described above, the one-side cooling water flow path  3 C and the other-side cooling water flow path  3 D include the inlet flow paths  4 C,  4 D, the curved flow paths  9 C,  9 D, and the outlet flow paths  7 C,  7 D, respectively. Thus, the one-side cooling water flow path  3 C and the other-side cooling water flow path  3 D can cool the housing  15  by supplying cooling water through the respective inlet flow paths  4 C,  4 D. Because the one-side cooling water flow path  3 C is located on the one side in the direction in which the axis CA extends, relative to the other-side cooling water flow path  3 D, the housing  15  can be cooled over a wide range in the axial direction X, by these cooling water flow paths (the one-side cooling water flow path  3 C and the other-side cooling water flow path  3 D). 
       FIG. 8  is a schematic sectional diagram of a turbocharger according to a third embodiment of the present disclosure.  FIG. 9  is an explanatory diagram for describing an example of a cooling water flow path illustrated in  FIG. 8 . 
     In some embodiments, the at least one cooling water flow path  3  described above is formed such that the plurality of flow path cross sections  30  are present, of the cross-section including the axis CA of the rotor shaft  11 , in a half cross-section separated by the axis CA, as illustrated in  FIG. 8 . As illustrated in  FIGS. 8 and 9 , the at least one cooling water flow path  3  described above includes an outer cooling water flow path  3 E and an inner cooling water flow path  3 F. The outer cooling water flow path  3 E is located radially outward relative to the inner cooling water flow path  3 F. 
     As illustrated in  FIG. 9 , the outer cooling water flow path  3 E includes: an outer inlet flow path  4 E configured to allow cooling water to flow therein; an outer curved flow path  9 E that communicates with the outer inlet flow path  4 E and extends along the circumferential direction of the rotor shaft  11 ; and an outer outlet flow path  7 E configured to allow cooling water to flow thereout and that communicates with the outer curved flow path  9 E. 
     As illustrated in  FIG. 9 , the inner cooling water flow path  3 F includes: an inner inlet flow path  4 F configured to allow cooling water to flow therein; an inner curved flow path  9 F that communicates with the inner inlet flow path  4 F and extends along the circumferential direction of the rotor shaft  11 ; and an inner outlet flow path  7 F configured to allow cooling water to flow thereout and that communicates with the inner curved flow path  9 F. 
     As illustrated in  FIG. 9 , the outer curved flow path  9 E is located radially outward relative to the inner curved flow path  9 F. Then, when viewed from the axial direction X, at least a portion of the outer curved flow path  9 E in the circumferential direction overlaps the inner curved flow path  9 F. When viewed from the axial direction X, the portion where the outer curved flow path  9 E and the inner curved flow path  9 F overlap has a circumferential range centered on the axis CA that is greater than or equal to 180 degrees and less than or equal to 360 degrees. It is preferable that the circumferential range is larger. Preferably, the circumferential range is 270 degrees to 360 degrees. 
     In the embodiment illustrated in  FIG. 9 , the outer inlet flow path  4 E has one side connected to the cooling water supply port  41  described above, and the other side  42  connected to the starting end  91  of the outer curved flow path  9 E in the first direction FD. The outer outlet flow path  7 E has one side connected to the cooling water discharge port  71  described above, and the other side  72  connected to the terminal end  92  of the outer curved flow path  9 E in the first direction FD. Each of the cooling water supply port  41  and the cooling water discharge port  71  is formed on the outer surface  173  of the bearing housing  17 , as illustrated in  FIG. 8 . The cooling water flow path  3  is formed on the outer circumferential side of the bearing  14 . The cooling water is supplied to the cooling water supply port  41  from a washing water supply source (not illustrated). The cooling water sent through the cooling water supply port  41  to the outer inlet flow path  4 E flows through the outer curved flow path  9 E and the outer outlet flow path  7 E, and then is discharged to the outside of the cooling water flow path  3  through the cooling water discharge port  71 . 
     In the embodiment illustrated in  FIG. 9 , the inner inlet flow path  4 F has one side connected to the cooling water supply port  41  described above, and the other side  42  connected to the starting end  91  of the inner curved flow path  9 F in the first direction FD. The inner outlet flow path  7 F has one side connected to the cooling water discharge port  71  described above, and the other side  72  connected to the terminal end  92  of the inner curved flow path  9 F in the first direction FD. Each of the cooling water supply port  41  and the cooling water discharge port  71  is formed on the outer surface  173  of the bearing housing  17 , as illustrated in  FIG. 8 . The cooling water flow path  3  is formed on the outer circumferential side of the bearing  14 . The cooling water is supplied to the cooling water supply port  41  from a washing water supply source (not illustrated). The cooling water sent through the cooling water supply port  41  to the inner inlet flow path  4 F flows through the inner curved flow path  9 F and the inner outlet flow path  7 F, and then is discharged to the outside of the cooling water flow path  3  through the cooling water discharge port  71 . 
     According to the configuration described above, the outer cooling water flow path  3 E and the inner cooling water flow path  3 F include inlet flow paths  4 E,  4 F, curved flow paths  9 E,  9 F, and outlet flow paths  7 E,  7 F, respectively. Thus, the outer cooling water flow path  3 E and the inner cooling water flow path  3 F can cool the housing  15  by supplying cooling water through the inlet flow paths  4 E and  4 F. Because the outer cooling water flow path  3 E is located radially outward relative to the inner cooling water flow path  3 F, the housing  15  can be cooled over a wide range in the radial direction, by these cooling water flow paths (the outer cooling water flow path  3 E and the inner cooling water flow path  3 F). 
     In some embodiments, the at least one cooling water flow path  3  described above includes three or more cooling water flow paths  3  (for example,  3 C to  3 F, or the like), as illustrated in  FIG. 8 . As illustrated in  FIG. 9 , each of the three or more cooling water flow paths  3  includes: the inlet flow path  4  configured to allow cooling water to flow therein; a curved flow path  9  that communicates with the inlet flow path  4  and extends in the circumferential direction of the rotor shaft  11 ; and the outlet flow path  7  configured to allow cooling water to flow thereout and that communicates with the curved flow path  9 . 
     According to the configuration described above, each of the three or more cooling water flow paths  3  includes the inlet flow path  4 , the curved flow path  9 , and the outlet flow path  7 . Thus, each of the three or more cooling water flow paths  3  can cool the housing  15  by supplying cooling water through the respective inlet flow paths  4 . By increasing the number of cooling water flow paths  3 , the total length of the circumferential length of the flow path cross section  30  can be increased. By increasing the total length of the circumferential length of the flow path cross section  30 , it is possible to improve the cooling efficiency of the cooling water flow path  3 , and thus the movement of the heat on the turbine side toward the compressor side can be reduced. 
     In some embodiments, as illustrated in  FIGS. 2, 6, and 8 , the at least one cooling water flow path  3  described above includes the bearing housing-side cooling water flow path  3 A formed in the bearing housing  17 . In this case, the bearing  14  and the bearing housing  17  can be cooled by the cooling water in the bearing-side cooling water flow path  3 A. Thus, heat on the turbine side can be prevented from being transferred to the bearing and the compressor side. 
     As illustrated in  FIG. 8 , the cooling water flow path  3  in some embodiments described above may be formed in the turbine housing  16 . In some embodiments, as illustrated in  FIG. 8 , the at least one cooling water flow path  3  described above includes a turbine housing-side cooling water flow path  3 B formed in the turbine housing  16 . In the illustrated embodiment, the turbine housing-side cooling water flow path  3 B is formed in a portion of the turbine housing  16  that defines the exhaust gas discharge flow path  164 . Note that in the embodiment illustrated in  FIG. 8 , the at least one cooling water flow path  3  includes both the bearing-side cooling water flow path  3 A and the turbine housing-side cooling water flow path  3 B, but may include only the turbine housing-side cooling water flow path  3 B. 
     According to the configuration described above, the turbine housing  16  can be cooled by cooling water in the turbine housing-side cooling water flow path  3 B. Thus, heat on the turbine side can be prevented from being transferred to the bearing  14  and the compressor side. In addition, because the temperature increase in the turbine housing  16  can be suppressed, the heat resistance strength of the turbine housing  16  can be suppressed. By suppressing the heat resistance strength of the turbine housing  16 , it is possible to suppress the increase in weight and price of the turbine housing  16 . 
     The present disclosure is not limited to the embodiments described above and also includes a modification of the above-described embodiments as well as appropriate combinations of these modes. In some embodiments described above, the turbocharger  1  provided with the variable nozzle device  23  has been described as an example, but the present disclosure can also be applied to a turbocharger that does not include the variable nozzle device  23 . 
     The contents of some embodiments described above can be construed as follows, for example. 
     1) A turbocharger ( 1 ) according to at least one embodiment of the present disclosure includes: 
     a turbine housing ( 16 ) configured to house a turbine rotor ( 12 ) provided on one side of a rotor shaft ( 11 ); and 
     a bearing housing ( 17 ) configured to house a bearing ( 14 ) that rotatably supports the rotor shaft ( 11 ), in which 
     at least one cooling water flow path ( 3 ) through which cooling water flows is formed in at least one of the turbine housing ( 16 ) and the bearing housing ( 17 ), and the at least one cooling water flow path ( 3 ) is formed such that a plurality of flow path cross sections ( 30 ) are present in, of a cross-section including an axis (CA) of the rotor shaft ( 11 ), a half cross-section divided by the axis (CA). 
     According to the configuration of 1) above, the at least one cooling water flow path ( 3 ) is formed such that the plurality of flow path cross sections ( 30 ) are present in the half cross-section. In this case, in the above-described half cross-section, the total length of the circumferential length of the flow path cross section ( 30 ) on the half cross-section can be increased, compared to the case where there is a single flow path cross section having the same flow path cross-sectional area as the total flow path cross-sectional area of the plurality of flow path cross sections ( 30 ). By increasing the total length of the circumferential length of the flow path cross section ( 30 ) on the half cross-section, the contact area and the thermal conduction volume between the cooling water in the cooling water flow path ( 3 ) and the flow path wall surface that defines the cooling water flow path ( 3 ) can be increased, so that the cooling action by the cooling water in the cooling water flow path ( 3 ) is promoted. Thus, it is possible to further improve cooling efficiency by the cooling water flow path ( 3 ). By improving the cooling efficiency of the cooling water flow path ( 3 ), it is possible to reduce the movement of heat on the turbine side toward the compressor side. 
     2) In some embodiments, in the turbocharger ( 1 ) as described in 1) above, the at least one cooling water flow path ( 3 ) includes 
     an inlet flow path ( 4 ) configured to allow the cooling water to flow therein; 
     a first curved flow path ( 5 ) that communicates with the inlet flow path ( 4 ) and extends along a circumferential direction of the rotor shaft; 
     a second curved flow path ( 6 ) that is disposed to be offset in a radial direction relative to the first curved flow path ( 5 ), extends along the circumferential direction, and communicates with the first curved flow path ( 5 ); and 
     an outlet flow path ( 7 ) configured to allow the cooling water to flow thereout and that communicates with the second curved flow path ( 6 ), and 
     when viewed from an axial direction, at least a portion of the second curved flow path ( 6 ) in the circumferential direction overlaps the first curved flow path ( 5 ). 
     According to the configuration of 2) above, the cooling water that has flowed into the cooling water flow path ( 3 ) through the inlet flow path ( 4 ) passes through the first curved flow path ( 5 ) and the second curved flow path ( 6 ) extending along the circumferential direction of the rotor shaft ( 11 ), and then flows to the outside of the cooling water flow path ( 3 ) through the outlet flow path ( 7 ). Because the second curved flow path ( 6 ) is disposed to be offset in the radial direction relative to the first curved flow path ( 5 ), the cooling water in the first curved flow path ( 5 ) and the cooling water in the second curved flow path ( 6 ) can cool a wide range of the housing ( 15 ) in the radial direction, so that the movement of the heat on the turbine side toward the compressor side can be effectively suppressed. 
     Further, according to the configuration of 2) above, at least a portion of the second curved flow path ( 6 ) in the circumferential direction when viewed from the axial direction overlaps the first curved flow path ( 5 ). Thus, in a portion where the first curved flow path ( 5 ) and the second curved flow path ( 6 ) overlap in the circumferential direction, the housing ( 15 ) can be intensively cooled by the cooling water in the first curved flow path ( 5 ) and the cooling water in the second curved flow path ( 6 ). By disposing the overlapping portion in the circumferential range where the increase in the temperature of the housing ( 15 ) is significant, the housing ( 15 ) can be effectively cooled, and an increase in the temperature of the housing ( 15 ) can be effectively suppressed. 
     3) In some embodiments, in the turbocharger ( 1 ) described in 2) above, 
     when one direction of the circumferential direction is a first direction, 
     the inlet flow path ( 4 ) is connected to a starting end ( 51 ) of the first curved flow path ( 5 ) in the first direction, and 
     the outlet flow path ( 7 ) is connected to a starting end ( 61 ) of the second curved flow path ( 6 ) in the first direction, and 
     the at least one cooling water flow path ( 3 ) further includes a first contact flow path ( 8 A) connecting a terminal end ( 52 ) of the first curved flow path ( 5 ) in the first direction with a terminal end ( 62 ) of the second curved flow path ( 6 ) in the first direction. 
     Because the cooling water in the cooling water flow path ( 3 ) receives heat from the housing ( 15 ) when cooling the housing ( 15 ), cooling effects are higher on the upstream side of the cooling water flow path ( 3 ) than on the downstream side. According to the configuration of 3) above, the cooling water flow path ( 3 ) includes the first contact flow path ( 8 A) that connects the terminal end ( 52 ) of the first curved flow path ( 5 ) in the first direction with the terminal end ( 62 ) of the second curved flow path ( 6 ) in the first direction. Thus, the cooling water flows through the first curved flow path ( 5 ) in the first direction, and then flows through the second curved flow path ( 6 ) to the side opposite to the first direction in the circumferential direction. The cooling water on the upstream side of the first curved flow path ( 5 ) can cool the upstream side in the first direction, and the cooling water on the downstream side of the first curved flow path ( 5 ) and on the upstream side of the second curved flow path ( 6 ) can cool the downstream side in the first direction. Thus, according to the configuration described above, cooling can be effectively performed by the cooling water flow path ( 3 ) over a range from the upstream side to the downstream side in the first direction. 
     4) In some embodiments, in the turbocharger ( 1 ) described in 2) above, 
     when one direction of the circumferential direction is a first direction, 
     the inlet flow path ( 4 ) is connected to a starting end ( 51 ) of the first curved flow path ( 5 ) in the first direction, and 
     the outlet flow path ( 7 ) is connected to a terminal end ( 62 ) of the second curved flow path ( 6 ) in the first direction, and 
     the at least one cooling water flow path ( 3 ) further includes a second contact flow path ( 8 B) connecting a terminal end ( 52 ) of the first curved flow path ( 5 ) in the first direction and a starting end ( 61 ) of the second curved flow path ( 6 ) in the first direction. 
     According to the configuration of 4) above, the cooling water flow path ( 3 ) includes the second contact flow path ( 8 B) connecting the terminal end ( 52 ) of the first curved flow path ( 5 ) in the first direction with the starting end ( 61 ) of the second curved flow path ( 6 ) in the first direction. Thus, after the cooling water flows through the first curved flow path ( 5 ) in the first direction, the cooling water flows through the second curved flow path ( 6 ) in the first direction similar to the first curved flow path ( 5 ). The cooling water in the first curved flow path ( 5 ) and the cooling water in the second curved flow path ( 6 ) can cool the upstream side in the first direction relative to the downstream side. Thus, according to the configuration described above, by disposing the upstream side of the first curved flow path ( 5 ) or the second curved flow path ( 6 ) in the circumferential range where the increase in temperature of the housing ( 15 ) is significant, the housing ( 15 ) can be effectively cooled, and an increase in the temperature of the housing ( 15 ) can be effectively suppressed. 
     5) In some embodiments, in the turbocharger ( 1 ) described in any one of 2) to 4) above, the first curved flow path ( 5 ) is located radially outward relative to the second curved flow path ( 6 ). 
     Because the first curved flow path ( 5 ) is located on the upstream side in the flow direction of the cooling water with respect to the second curved flow path ( 6 ), the cooling water in the first curved flow path ( 5 ) has a higher cooling effect than the cooling water in the second curved flow path ( 6 ). According to the configuration of 5) above, the first curved flow path ( 5 ) is located radially outward relative to the second curved flow path ( 6 ), so that the cooling action of the cooling water flow path ( 3 ) on the outer side of the housing ( 15 ) in the radial direction can be increased. By increasing the cooling action on the outer side of the housing ( 15 ) in the radial direction, it is possible to effectively suppress the transfer of heat from the exhaust gas inside the scroll flow path ( 163 ) of the turbine housing ( 16 ) into the housing ( 15 ). 
     6) In some embodiments, the turbocharger ( 1 ) described in any one of 2) to 4) above, the first curved flow path ( 5 ) is located radially inward relative to the second curved flow path ( 6 ). 
     Because the first curved flow path ( 5 ) is located on the upstream side in the flow direction of the cooling water with respect to the second curved flow path ( 6 ), the cooling water in the first curved flow path ( 5 ) has a higher cooling effect than the cooling water in the second curved flow path ( 6 ). The first curved flow path ( 5 ) is located radially inward relative to the second curved flow path ( 6 ), so that the cooling action of the cooling water flow path ( 3 ) on the inner side of the housing ( 15 ) in the radial direction can be increased. By increasing the cooling action on the inner side of the housing ( 15 ) in the radial direction, it is possible to effectively suppress the transfer of heat on the turbine side to the compressor side and the bearing ( 14 ) through the rotor shaft ( 11 ). 
     7) In some embodiments, in the turbocharger ( 1 ) described in 1) above, 
     the at least one cooling water flow path ( 3 ) includes 
     a one-side cooling water flow path ( 3 C) including a one-side inlet flow path ( 4 C) configured to allow the cooling water to flow therein, a one-side curved flow path ( 9 C) that communicates with the one-side inlet flow path and extends along a circumferential direction of the rotor shaft ( 11 ), and a one-side outlet flow path ( 7 C) configured to allow the cooling water to flow thereout and that communicates with the one-side curved flow path ( 9 C); and 
     an other-side cooling water flow path ( 3 D) including an other-side inlet flow path ( 4 D) configured to allow the cooling water to flow therein, an other-side curved flow path ( 9 D) that communicates with the other-side inlet flow path ( 4 D) and extends along the circumferential direction of the rotor shaft, and an other-side outlet flow path ( 7 D) configured to allow the cooling water to flow thereout and that communicates with the other-side curved flow path ( 9 D), and 
     the one-side cooling water flow path ( 3 C) is located on one side in a direction in which the axis (CA) extends, relative to the other-side cooling water flow path ( 3 D). 
     According to the configuration 7) above, the one-side cooling water flow path ( 3 C) and the other-side cooling water flow path ( 3 D) include inlet flow paths ( 4 C,  4 D), curved flow paths ( 9 C,  9 D), and outlet flow paths ( 7 C,  7 D), respectively. Therefore, the one-side cooling water flow path ( 3 C) and the other-side cooling water flow path ( 3 D) can cool the housing ( 15 ) by supplying cooling water through the inlet flow paths ( 4 C,  4 D), respectively. Because the one-side cooling water flow path ( 3 C) is located on the one side in the direction in which the axis (CA) extends relative to the other-side cooling water flow path ( 3 D), the housing ( 15 ) can be cooled over a wide range in the axial direction by these cooling water flow paths ( 3 C,  3 D). 
     8) In some embodiments, in the turbocharger ( 1 ) described in 1) above, 
     the at least one cooling water flow path ( 3 ) includes 
     an outer cooling water flow path ( 3 E) including an outer inlet flow path ( 4 E) configured to allow the cooling water to flow therein, an outer curved flow path ( 9 E) that communicates with the outer inlet flow path ( 4 E) and extends along a circumferential direction of the rotor shaft, and an outer outlet flow path ( 7 E) configured to allow the cooling water to flow thereout and that communicates with the outer curved flow path ( 9 E); and 
     an inner cooling water flow path ( 3 F) including an inner inlet flow path ( 4 F) configured to allow the cooling water to flow therein, an inner curved flow path ( 9 F) that communicates with the inner inlet flow path ( 4 F) and extends along the circumferential direction of the rotor shaft, and an inner outlet flow path ( 7 F) configured to allow the cooling water to flow thereout and that communicates with the inner curved flow path ( 9 F), and 
     the outer cooling water flow path ( 3 E) is located radially outward relative to the inner cooling water flow path ( 3 F). 
     According to the configuration of 8) above, the outer cooling water flow path ( 3 E) and the inner cooling water flow path ( 3 F) include the inlet flow paths ( 4 E,  4 F), the curved flow paths ( 9 E,  9 F), and the outlet flow paths ( 7 E,  7 F), respectively. Thus, the outer cooling water flow path ( 3 E) and the inner cooling water flow path ( 3 F) can cool the housing ( 15 ) by supplying cooling water through the respective inlet flow paths ( 4 E,  4 F). Because the outer cooling water flow path ( 3 E) is located radially outward relative to the inner cooling water flow path ( 3 F), the housing ( 15 ) can be cooled over a wide range in the radial direction, by these cooling water flow paths ( 3 E,  3 F). 
     9) In some embodiments, in the turbocharger ( 1 ) described in 1) above, 
     the at least one cooling water flow path ( 3 ) includes three or more cooling water flow paths ( 3 ), each of the three or more cooling water flow paths ( 3 ) including 
     an inlet flow path ( 4 ) configured to allow the cooling water to flow therein, 
     a curved flow path ( 9 ) that communicates with the inlet flow path ( 4 ) and extends along a circumferential direction of the rotor shaft, and 
     an outlet flow path ( 7 ) configured to allow the cooling water to flow thereout and that communicates with the curved flow path ( 9 ). 
     According to the configuration 9) above, each of the three or more cooling water flow paths ( 3 ) includes the inlet flow path ( 4 ), the curved flow path ( 9 ), and the outlet flow path ( 7 ). Thus, each of the three or more cooling water flow paths ( 3 ) can cool the housing ( 15 ) by supplying cooling water through the respective inlet flow paths ( 4 ). By increasing the number of cooling water flow paths ( 3 ), the total length of the circumferential length of the flow path cross section ( 30 ) can be increased. By increasing the total length of the circumferential length of the flow path cross section ( 30 ), it is possible to improve the cooling efficiency of the cooling water flow path ( 3 ), and thus the movement of the heat on the turbine side toward the compressor side can be reduced. 
     10) In some embodiments, the turbocharger ( 1 ) according to any one of 1) to 9) described above, wherein the at least one cooling water flow path ( 3 ) includes a bearing housing-side cooling water flow path ( 3 A) formed in the bearing housing ( 17 ). 
     According to the configuration of ( 10 ) above, the bearing ( 14 ) and the bearing housing ( 17 ) can be cooled by the cooling water in the bearing-side cooling water flow path ( 3 A). Thus, heat on the turbine side can be prevented from being transferred to the bearing and the compressor side. 
     11) In some embodiments, in the turbocharger ( 1 ) according to any one of 1) to 10) described above, wherein the at least one cooling water flow path ( 3 ) includes a turbine housing-side cooling water flow path ( 3 B) formed in the turbine housing ( 16 ). 
     According to the configuration of 11) above, the turbine housing ( 16 ) can be cooled by cooling water in the turbine housing-side cooling water flow path ( 3 B). Thus, heat on the turbine side can be prevented from being transferred to the bearing ( 14 ) and the compressor side. In addition, because the temperature increase in the turbine housing ( 16 ) can be suppressed, the heat resistance strength of the turbine housing ( 16 ) can be suppressed. By suppressing the heat resistance strength of the turbine housing ( 16 ), it is possible to suppress the increase in weight and price of the turbine housing  16 ). 
     While preferred embodiments of the invention have been described as above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.