Patent Publication Number: US-2022220864-A1

Title: Cooling structure and turbocharger

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of International Application No. PCT/JP2020/032067, filed on Aug. 25, 2020, which claims priority to Japanese Patent Application No. 2019-196986 filed on Oct. 30, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND ART 
     Technical Field 
     The present disclosure relates to a cooling structure and a turbocharger. 
     Conventionally, a turbocharger includes a turbine housing, a bearing housing, and a compressor housing. A turbine impeller is accommodated in the turbine housing. A compressor impeller is accommodated in the compressor housing. The turbine impeller and the compressor impeller are connected by a shaft. The bearing housing accommodates the shaft and a bearing. The bearing supports the shaft. 
     A coolant flow path and a lubricant flow path are formed in the bearing housing. Coolant flows through the coolant flow paths. The coolant cools the bearing housing. Lubricant flows through the lubricant flow path. The lubricant is supplied to the bearing through the lubricant flow path. The lubricant lubricates the bearing. 
     Patent Literature 1 discloses a split-type bearing housing. The split-type bearing housing is divided by a dividing plane orthogonal to the axial direction of the shaft in a space between the bearing and the turbine impeller. The split-type bearing housing includes a first bearing housing and a second bearing housing. The first bearing housing is disposed on a compressor impeller side. The second bearing housing is disposed on a turbine impeller side. 
     A first coolant flow path is formed in the first bearing housing. A second coolant flow path is formed in the second bearing housing. When the first bearing housing and the second bearing housing are connected to each other, the first coolant flow path and the second coolant flow path form a single coolant flow path. 
     In the space between the bearing and the turbine impeller, a shaft accommodation space is formed to accommodate the shaft. A first shaft accommodation space is formed in the first bearing housing. A second shaft accommodation space is formed in the second bearing housing. When the first bearing housing and the second bearing housing are connected to each other, the first shaft accommodation space and the second shaft accommodation space form a single shaft accommodation space. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP H07-150962 A 
     SUMMARY 
     Technical Problem 
     However, a portion of the coolant flowing through the coolant flow paths may flow into the shaft accommodation space through the split surface. In the shaft accommodation space, the lubricant after lubricating the bearing is scattered. Therefore, there is a risk that the lubricant and the coolant are mixed in the shaft accommodation space. 
     An object of the present disclosure is to provide a cooling structure and a turbocharger that can reduce a mixture of a lubricant and a coolant. 
     Solution to Problem 
     In order to solve the above problem, a cooling structure according to one aspect of the present disclosure includes a housing including an inner cylindrical portion provided with an insertion hole through which a shaft is inserted; a coolant flow path formed radially outside the inner cylindrical portion in the housing; and a lid member disposed radially outside the inner cylindrical portion of the housing and adjacent to the coolant flow path. 
     The cooling structure may include: an inner end portion facing the housing in a radial direction and formed on an inner part of the lid member; an outer end portion facing the housing in the radial direction and formed on an outer part of the lid member; and an abutment surface formed in the housing and contacting either one of the inner end portion or the outer end portion in an axial direction of the shaft. 
     The cooling structure may include: an inner opposing surface of the housing, the inner opposing surface facing the inner end portion in the radial direction; an outer opposing surface of the housing, the outer opposing surface facing the outer end portion in the radial direction; and a sealing member disposed on either one of the inner opposing surface or the outer opposing surface. 
     The cooling structure may include a sealing member disposed on the abutment surface. 
     In order to solve the above problem, the turbocharger of the present disclosure includes the above cooling structure. 
     Effects of Disclosure 
     According to the present disclosure, it is possible to reduce a mixture of a lubricant and a coolant. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic cross-sectional view of a turbocharger. 
         FIG. 2  is an extraction of an area enclosed by dashed dotted lines in  FIG. 1 . 
         FIG. 3  is an extraction of an area enclosed by dashed lines in  FIG. 1 . 
         FIG. 4  shows a state in which a abutment surface contacts an inner end portion of a lid member. 
         FIG. 5  shows a state in which a sealing member is disposed on an outer opposing surface. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Specific dimensions, materials, and numerical values described in the embodiments are merely examples for a better understanding, and do not limit the present disclosure unless otherwise specified. In this specification and the drawings, duplicate explanations are omitted for elements having substantially the same functions and configurations by assigning the same sign. Furthermore, elements not directly related to the present disclosure are omitted from the figures. 
       FIG. 1  is a schematic cross-sectional view of a turbocharger TC. A direction indicated by an arrow L in  FIG. 1  is described as the left side of the turbocharger TC. A direction indicated by an arrow R in  FIG. 1  is described as the right side of the turbocharger TC. As shown in  FIG. 1 , the turbocharger TC comprises a turbocharger body  1 . The turbocharger body  1  includes a bearing housing  3 , a turbine housing  5 , and a compressor housing  7 . The turbine housing  5  is connected to the left side of the bearing housing  3  by a fastening bolt  9 . The compressor housing  7  is connected to the right side of the bearing housing  3  by a fastening bolt  11 . 
     A bearing hole  3   a  is formed in the bearing housing  3 . The bearing hole  3   a  passes through in the left-to-right direction of the turbocharger TC. A bearing  13  is arranged in the bearing hole  3   a . In  FIG. 1 , a semi-floating bearing is shown as an example of the bearing  13 . However, the bearing  13  may be any other radial bearing, such as a full-floating bearing or a rolling bearing. A shaft  15  is inserted into the bearing  13 . The shaft  15  is rotatably supported by the bearing  13 . A turbine impeller  17  is provided at the left end of the shaft  15 . The turbine impeller  17  is rotatably accommodated in the turbine housing  5 . A compressor impeller  19  is provided at the right end of the shaft  15 . The compressor impeller  19  is rotatably accommodated in the compressor housing  7 . The turbine impeller  17  and the compressor impeller  19  rotate integrally with the shaft  15 . 
     An inlet  21  is formed in the compressor housing  7 . The inlet  21  opens to the right side of the turbocharger TC. The inlet  21  is connected to an air cleaner (not shown). A diffuser flow path  23  is formed between the bearing housing  3  and the compressor housing  7 . The diffuser flow path  23  pressurizes air. The diffuser flow path  23  is formed in an annular shape from an inner side to an outer side in a radial direction of the shaft  15  (compressor impeller  19 ) (hereinafter simply referred to as the radial direction). The diffuser flow path  23  is connected to the inlet  21  via the compressor impeller  19  at the radially inner part. 
     A compressor scroll flow path  25  is formed in the compressor housing  7 . The compressor scroll flow path  25  is formed in an annular shape. The compressor scroll flow path  25  is, for example, located radially outside the compressor impeller  19 . The compressor scroll flow path  25  is connected to an intake port of an engine (not shown) and to the diffuser flow path  23 . 
     When the compressor impeller  19  rotates, air is sucked into the compressor housing  7  from the inlet  21 . The intake air is pressurized and accelerated while passing through blades of the compressor impeller  19 . The pressurized and accelerated air is pressurized in the diffuser flow path  23  and the compressor scroll flow path  25 . The pressurized air is discharged from a discharge port (not shown) and is led to the intake port of the engine. 
     A sealing plate  27  is disposed on a rear side (the left side in  FIG. 1 ) of the compressor impeller  19 . The sealing plate  27  has a disk shape. An outer diameter of the sealing plate  27  is larger than the maximum outer diameter of the compressor impeller  19 . However, the outer diameter of the sealing plate  27  may be equal to the maximum outer diameter of the compressor impeller  19 , or may be smaller than the maximum outer diameter of the compressor impeller  19 . A through hole is formed in the sealing plate  27  at the center of the radial direction. A shaft  15  is inserted into the through hole. 
     A fitting hole  3   b  is formed in the bearing housing  3  on a face closer to the compressor housing  7  (right side in  FIG. 1 ). The sealing plate  27  is fitted into the fitting hole  3   b . A bolt hole (not shown) is provided in the sealing plate  27  radially outward the through hole. The bolt hole penetrates in a rotational axis direction of the shaft  15  (hereinafter simply referred to as the axial direction). A threaded hole (not shown) is formed in the fitting hole  3   b  at a position facing the bolt hole in the axial direction. A fastening bolt (not shown) is inserted into the bolt hole. The fastening bolt is screwed into the threaded hole. The sealing plate  27  is fastened to the bearing housing  3  by the fastening bolt. 
     The bearing  13  accommodated in the bearing hole  3   a  of the bearing housing  3  is lubricated with a lubricant. The sealing plate  27  prevents the lubricant from leaking from the bearing housing  3  into the compressor housing  7  after lubricating the bearing  13 . It prevents the lubricant from leaking from the bearing housing  3  to the compressor housing  7 . 
     A heat shield  29  is disposed between the bearing housing  3  and the turbine housing  5 . The heat shield  29  has a disk shape. An outer diameter of the heat shield  29  is larger than the maximum outer diameter of the turbine impeller  17 . A through hole is formed in the heat shield  29  at the center of the radial direction. The shaft  15  is inserted into the through hole. The heat shield  29  is disposed at a position facing the turbine impeller  17  in the axial direction. The heat shield  29  is spaced apart from the turbine impeller  17  in the axial direction. 
     The heat shield  29  blocks radiated heat from the turbine impeller  17  to the bearing housing  3 . In other words, the heat shield  29  curbs transmission of the heat from an exhaust gas to the bearing housing  3 . The heat shield  29  curbs a temperature increase of the bearing  13  accommodated in the bearing hole  3   a  of the bearing housing  3 . As a result, a function of the bearing  13  is maintained. 
     An outlet  31  is formed in the turbine housing  5 . The outlet  31  opens to the left side of the turbocharger TC. The outlet  31  is connected to an exhaust gas purification device (not shown). A gap  33  is formed between the bearing housing  3  and the turbine housing  5 . In the gap  33 , a flow path x is formed where the exhaust gas passes through. The flow path x is formed in an annular shape from the inner side to the outer side in the radial direction of the shaft  15 . 
     A turbine scroll flow path  35  is formed in the turbine housing  5 . The turbine scroll flow path  35  is, for example, located radially outside the turbine impeller  17 . The flow path x is located between the turbine impeller  17  and the turbine scroll flow path  35 . The flow path x connects the turbine scroll flow path  35  with the outlet  31  via the turbine impeller  17 . 
     The turbine scroll flow path  35  is connected to a gas inlet (not shown). The exhaust gas discharged from an exhaust manifold of the engine (not shown) is led to the gas inlet. The exhaust gas led from the gas inlet to the turbine scroll flow path  35  is led to the outlet  31  through the flow path x and blades of the turbine impeller  17 . The exhaust gas led to the outlet  31  rotates the turbine impeller  17  while passing therethrough. 
     The rotational force of the turbine impeller  17  is transmitted to the compressor impeller  19  via the shaft  15 . As described above, the air is pressurized by the rotational force of the compressor impeller  19  and is led to the intake port of the engine. 
     As the flow rate of the exhaust gas introduced into the turbine housing  5  decreases, a rotational rate of the turbine impeller  17  decreases. As the rotational rate of the turbine impeller  17  decreases, the rotational rate of the compressor impeller  19  also decreases. When the rotational rate of the compressor impeller  19  decreases, it may not be possible to sufficiently increase the pressure of the air supplied to the intake port of the engine. 
     Therefore, a variable capacity mechanism  100  is disposed in the gap  33  in the turbine housing  5 . The variable capacity mechanism  100  comprises a shroud ring  101 , a nozzle ring  103 , nozzle vanes  105 , a drive mechanism  107 , and an actuator  109 . 
     The shroud ring  101  is disposed in the gap  33  on a side spaced apart from the bearing housing  3 . The shroud ring  101  includes a body portion  101   a  and a protruding portion  101   b . The body portion  101   a  is formed in a thin plate ring shape. The protruding portion  101   b  protrudes from an inner circumferential edge of the body portion  101   a  toward the outlet  31 . 
     Pin shaft holes  101   c  are formed in the body portion  101   a . The pin shaft hole  101   c  penetrates the body portion  101   a  in the axial direction. The plurality of pin shaft holes  101   c  (only one is shown in  FIG. 1 ) are formed at equal intervals in a circumferential direction of the body portion  101   a . However, the plurality of pin shaft holes  101   c  may be formed at unequal intervals in the circumferential direction of the body portion  101   a.    
     The nozzle ring  103  is disposed in the gap  33  on a side closer to the bearing housing  3 . The nozzle ring  103  faces the shroud ring  101  in the axial direction. The nozzle ring  103  is spaced apart from the shroud ring  101  in the axial direction. The flow path x is formed between the shroud ring  101  and the nozzle ring  103 . 
     The nozzle ring  103  includes a body portion  103   a . The body portion  103   a  is formed in a thin plate ring shape. The body portion  103   a  of the nozzle ring  103  has a diameter (outer diameter) substantially equal to that of the body portion  101   a  of the shroud ring  101 . 
     Pin shaft holes  103   b  are formed in the body portion  103   a . The pin shaft hole  103   b  penetrates the body portion  103   a  in the axial direction. The plurality of pin shaft holes  103   b  (only one is shown in  FIG. 1 ) are formed at equal intervals in the circumferential direction of the body portion  103   a . However, the plurality of the pin shaft holes  103   b  may be formed at unequal intervals in the circumferential direction of the body portion  103   a.    
     The pin shaft holes  103   b  are arranged so as to face the pin shaft holes  101   c  in the axial direction. A connecting pin  111  is inserted into the pin shaft holes  101   c  and  103   b . The shroud ring  101  is connected to the nozzle ring  103  by the connecting pin  111 . The connecting pin  111  maintains the shroud ring  101  and the nozzle ring  103  at a constant distance. 
     blade shaft holes  101   d  are formed in the body portion  101   a  of the shroud ring  101 . The blade shaft holes  101   d  are disposed radially inside the pin shaft holes  101   c  in the body portion  101   a . The blade shaft hole  101   d  penetrates the body portion  101   a  in the axial direction. The plurality of blade shaft holes  101   d  (only one is shown in  FIG. 1 ) are formed at equal intervals in the circumferential direction of the body portion  101   a.    
     Blade shaft holes  103   c  are formed in the body portion  103   a  of the nozzle ring  103 . The blade shaft holes  103   c  are disposed radially inside the pin shaft holes  103   b  in the body portion  103   a . The blade shaft hole  103   c  penetrates the body portion  103   a  in the axial direction. The plurality of blade shaft holes  103   c  (only one is shown in  FIG. 1 ) are formed at equal intervals in the circumferential direction of the body portion  103   a . The blade shaft holes  103   c  are disposed so as to face the blade shaft holes  101   d  in the axial direction. 
     A blade shaft  105   a  is integrally formed on the nozzle vane  105 . The blade shaft  105   a  extends from the nozzle vane  105  in the axial direction. The blade shaft  105   a  is inserted into the blade shaft holes  101   d  and  103   c . The blade shaft  105   a  is rotatably supported by the blade shaft holes  101   d  and  103   c . The nozzle vane  105  is disposed between the body portions  101   a  and  103   a  with the blade shaft  105   a  being inserted into the blade shaft holes  101   d  and  103   c . In other words, the nozzle vane  105  is disposed in the flow path x. The plurality of nozzle vanes  105  are arranged in the flow path x so as to being spaced apart from each other in the circumferential direction. The plurality of nozzle vanes  105  are arranged at equal intervals in a rotational direction (circumferential direction) of the turbine impeller  17 . However, the plurality of nozzle vanes  105  may be arranged at unequal intervals in the rotational direction of the turbine impeller  17 . 
     The drive mechanism  107  is connected to the actuator  109  and the blade shafts  105   a . The actuator  109  is, for example, a pneumatic actuator. The drive mechanism  107  converts a linear motion of the actuator  109  into a rotational motion. The actuator  109  drives the drive mechanism  107  to rotate the blade shafts  105   a.    
     When the blade shafts  105   a  rotate, the nozzle vanes  105  rotate integrally with the blade shafts  105   a . As the nozzle vanes  105  rotate, the distance between the plurality of nozzle vanes  105  arranged in the flow path x changes. As the distance between the plurality of nozzle vanes  105  changes, a flow path cross-sectional area of the flow path x changes. As the flow path cross-sectional area of the flow path x changes, a flow velocity of the exhaust gas flowing through the flow path x changes. 
     The variable capacity mechanism  100  changes the distance (hereinafter referred to as an opening degree) between the plurality of nozzle vanes  105  in accordance with the flow rate of the exhaust gas. For example, when the flow rate of the exhaust gas is small, the variable capacity mechanism  100  reduces the opening degree of the nozzle vanes  105  to increase the velocity of the exhaust gas. As such, the variable capacity mechanism  100  can increase the rotational rate of the turbine impeller  17  even when the flow rate of the exhaust gas is small. As a result, the variable capacity mechanism  100  can increase the rotational rate of the compressor impeller  19  even when the flow rate of the exhaust gas is small. 
       FIG. 2  is an extraction of an area enclosed by dashed dotted lines in  FIG. 1 .  FIG. 3  is an extraction of an area enclosed by dashed lines in  FIG. 1 . As shown in  FIGS. 2 and 3 , the bearing housing  3  comprises a bearing structure BS. The bearing structure BS includes an insertion hole  201 , a bearing  13 , a lubricant flow path  203 . 
     The insertion hole  201  penetrates the bearing housing  3  from the left end to the right end in  FIG. 1 . The shaft  15  is inserted into the insertion hole  201 . The insertion hole  201  faces the shaft  15  in the radial direction. The bearing hole  3   a  is formed in the center of the insertion hole  201 . The bearing hole  3   a  is a portion of the insertion hole  201  that faces the bearing  13  in the radial direction. The bearing  13  is accommodated in the bearing hole  3   a.    
     A groove  201   a  is formed in the insertion hole  201 . The groove  201   a  opens to the insertion hole  201 . An opening of the groove  201   a  is formed closer to the turbine impeller  17  with respect to the bearing hole  3   a . The opening of the groove  201   a  is formed between the bearing  13  and the turbine impeller  17 . 
     The groove  201   a  includes a radially extending portion  201   b  and an axially extending portion  201   c . The radially extending portion  201   b  faces the shaft  15  in the radial direction, and extends radially outward with respect to the shaft  15 . The radially extending portion  201   b  extends over the circumferential direction of the shaft  15  and is formed in an annular shape. The axially extending portion  201   c  extends in the axial direction of the shaft  15  from an outer circumferential edge of the radially extending portion  201   b . However, the groove  201   a  may only include the radially extending portion  201   b . In other words, the groove  201   a  may not include the axially extending portion  201   c . A scattering space S 1  is formed inside the groove  201   a . Details of the scattering space S 1  will be described later. 
     Lubricant is supplied to the lubricant flow path  203 . The lubricant flow path  203  opens (is connected) to the bearing hole  3   a . The lubricant flow path  203  leads the lubricant to the bearing hole  3   a . The lubricant flows from the lubricant flow path  203  into the bearing hole  3   a.    
     A bearing  13  is disposed in the bearing hole  3   a . The bearing  13  is formed in an annular shape. A through hole  13   a  is formed in the bearing  13 . The through hole  13   a  extends in the radial direction from an inner circumferential surface to an outer circumferential surface of the bearing  13 . The through hole  13   a  faces the lubricant flow path  203  in the radial direction. The lubricant flowing into the bearing hole  3   a  passes through the through hole  13   a , and flows into a space S 2  between the inner circumferential surface of the bearing  13  and the shaft  15 . 
     The lubricant flowing into the space S 2  moves in the axial direction (the left-to-right direction in  FIGS. 2 and 3 ) of the shaft  15 . In the bearing  13 , a pair of bearing surfaces  13   b ,  13   b  are formed on both right and left sides of the space S 2 . The lubricant is supplied between the pair of bearing surfaces  13   b ,  13   b  and the shaft  15 . The lubricant lubricates the pair of bearing surfaces  13   b ,  13   b . The shaft  15  is supported by the oil film pressure of the lubricant. The pair of bearing surfaces  13   b ,  13   b  receive a radial load of the shaft  15 . 
     The lubricant moves away from the space S 2  in the axial direction of the shaft  15  after lubricating the pair of bearing surfaces  13   b ,  13   b . A part of the lubricant moves from the bearings  13  toward the turbine impeller  17 . During rotation of the shaft  15 , a part of the lubricant is scattered in the radial direction of the shaft  15  as the shaft  15  rotates. 
     The lubricant scattered in the radial direction of the shaft  15  flows into the scattering space S 1 . The lubricant flowing into the scattering space S 1  falls vertically downward while moving in the rotational direction of the shaft  15  in the scattering space S 1  (groove  201   a ). The formation of the scattering space S 1  reduces the amount of lubricant that moves toward the turbine impeller  17 , compared to the case where the scattering space S 1  is not formed. 
     A projection  201   d  protruding radially inward is formed in the insertion hole  201 . The protrusion  201   d  is disposed closer to the turbine impeller  17  with respect to the scattering space S 1 . A large diameter portion  15   a  is formed in the shaft  15 . In the shaft  15 , the large diameter portion  15   a  is larger than a diameter of opposing portions that face the pair of bearing surfaces  13   b ,  13   b . The large diameter portion  15   a  faces the projection  201   d  in the radial direction. 
     The amount of lubricant moving toward the turbine Impeller  17  is reduced by disposing the projection  201   d  and the large diameter portion  15   a  closer to the turbine impeller  17  with respect to the scattering space S 1 , compared to the case where the protrusion  201   d  and the large diameter  15   a  are not disposed. 
     A sealing ring  205  is disposed closer the turbine impeller  11  with respect to the projection  201   d  and the large diameter portion  15   a . The sealing ring  205  is adjacent to the projection  201   d  and the large diameter portion  15   a . The sealing ring  205  prevents the lubricant from leaking from a gap between the protrusion  201   d  and the large diameter portion  15   a  toward the turbine impeller  17 . A cooling structure CS of the present embodiment will be described below with using  FIGS. 2 and 3 . 
     As shown in  FIGS. 2 and 3 , the bearing housing  3  includes the cooling structure CS. The cooling structure CS Includes a body (housing)  207  and a lid member  209 . The body  207  constitutes a part of the bearing housing  3 . The lid member  209  constitutes a part of the bearing housing  3 . The body  207  and the lid member  209  constitute the bearing housing  3 . The body  207  includes an inner cylindrical portion  207   a  in which the insertion hole  201  is formed. The groove  201   a  (the scattering space S 1 ) is formed in the inner cylindrical portion  207   a.    
     A coolant flow path  211  is formed in the body  207 . The coolant flow path  211  is formed radially outside the inner cylindrical portion  207   a . In other words, the inner cylindrical portion  207   a  is a part of the body  207  that is radially inside the coolant flow path  211 . In the inner cylinder  207   a , a partition wall  207   b  is formed between the coolant flow path  211  and the groove  201   a . The coolant flow path  211  and the groove  201   a  are partitioned by the partition wall  207   b . The coolant flow path  211  extends in the circumferential direction of the shaft  15 . In the body  207 , an opening  213  is formed closer to the turbine housing  5  with respect to the coolant flow path  211 . The opening  213  opens to the outside the body  207 . The opening  213  is continuous with the coolant flow path  211 . 
     A coolant (cooling water) passes through the coolant flow path  211 . The coolant cools the bearing housing (the body  207 ). The temperature of the bearing housing  3  is likely to be higher on a side closer to the turbine impeller  17  than on a side closer to the compressor impeller  19 . Accordingly, the coolant flow path  211  is formed on the side closer to turbine impeller  17  in the body  207 . Therefore, the coolant flow path  211  is formed on the turbine impeller  17  side of the body  207 . 
     The lid member  209  is formed in an annular shape. The lid member  209  is disposed radially outside the inner cylindrical portion  207   a . The lid member  209  is disposed in the opening  213 . The lid member  209  closes the opening  213 . In other words, the lid member  209  covers the opening  213 . 
     In this embodiment, the lid member  209  is press-fitted into the opening  213 . As such, the lid member  209  is joined to the body  207 . However, the lid member  209  is not limited thereto, and may be fastened, welded, or glued to the body  207 . 
     The lid member  209  is disposed adjacent to the coolant flow path  211  when press-fitted into the opening  213 . The left side of the lid member  209  in  FIG. 2  faces the external space (internal space of the turbine housing  5 ), and the right side of the lid member  209  in  FIG. 2  faces the coolant flow path  211 . In other words, the lid member  209  defines a part of the coolant flow path  211 . Accordingly, the coolant flow path  211  is formed by the two members, i.e., the body  207  and the lid member  209 . 
     The heat shield  29  is disposed on the left side of the lid member  209  in  FIG. 2 . The nozzle ring  103  is disposed on the left side of the heat shield  29  in  FIG. 2 . A spring washer SW is disposed between the lid member  209  and the heat shield  29 . The spring washer SW is connected to the lid member  209  and the heat shield  29 . The spring washer SW presses the heat shield  29  in a direction spaced apart from the lid member  209 . This pressure causes the heat shield  29  to contact the nozzle ring  103 . In other words, the heat shield  29  is pressed against the nozzle ring  103  by the spring washer SW. The heat shield  29  is held between the nozzle ring  103  and the lid member  209  by the spring washer SW. 
     The lid member  209  includes an inner end portion  209   a  and an outer end portion  209   b . The inner end portion  209   a  is formed on an inner part of the lid member  209 . The inner end portion  209   a  faces the body  207  in the radial direction. The outer end portion  209   b  is formed on an outer part of the lid member  209 . The outer end portion  209   b  faces the body  207  in the radial direction. 
     The opening  213  has an inner opposing surface  213   a , an outer opposing surface  213   b , and an abutment surface  213   c . The inner opposing surface  213   a  faces the inner end portion  213   a  of the lid member  209  in the radial direction. The outer opposing surface  213   b  faces the outer end portion  209   b  of the lid member  209  in the radial direction. The abutment surface  213   c  faces the outer end portion  209   b  in the axial direction, and contacts the outer end portion  209   b . The abutment surface  213   c  contacts the outer end portion  209   b  to position the lid member  209  in the axial direction. 
     The inner opposing surface  213   a  has a substantially cylindrical shape. The inner opposing surface  213   a  is located at a position where an inner circumference surface on an inner part of the coolant flow path  211  is extended in the axial direction. For example, the inner opposing surface  213   a  is flush with the inner circumferential surface on the inner part of the coolant flow path  211 . The abutment surface  213   c  has a substantially circular shape. The abutment surface  213   c  is located at a position where an inner circumferential surface on an outer part of the coolant flow path  211  is extended in a direction perpendicular to the axial direction. An inner end of the abutment surface  213   c  is continuous with the inner circumferential surface on the outer part of the coolant flow path  211 . The outer opposing surface  213   b  has a substantially cylindrical shape. The outer opposing surface  213   b  is continuous with an outer end of the abutment surface  213   c . The outer opposing surface  213   b  is located at a position extended from the outer end of the abutment surface  213   c  toward the turbine housing  5  in the axial direction. 
     The lid member  209  is composed of the same material as the body  207 . That is, the lid member  209  is composed of a material having the same coefficient of linear expansion as that of the body  207 . However, the lid member  209  may have a different coefficient of linear expansion from that of the body  207 . For example, the lid member  209  may be composed of a material having a higher coefficient of linear expansion than that of the body  207 . In such a case, when the temperature of the bearing housing  3  increases, the lid member  209  expands more than the body  207 . 
     In this state, the outer opposing surface  213   b  is pressed radially outward by the outer end portion  209   b . the outer end portion  209   b . As such, the coolant passing through the coolant flow path  211  is less likely to leak from a gap between the outer opposing surface  213   b  and the outer end portion  209   b.    
     In contrast, the inner end portion  209   a  moves (expands) in the direction spaced apart from the inner opposing surface  213   a . As such, a sealing member  215  is disposed on the inner opposing surface  213   a . The sealing member  215  is, for example, a sealing ring. The sealing member  215  is used to prevent the coolant from leaking from a gap between the inner opposing surface  213   a  and the inner end portion  209   a  toward the turbine housing  5 . 
     In the present embodiment, a sealing member  217  is also disposed on the abutment surface  213   c . The sealing member  217  is, for example, a sealing ring. The sealing member  217  is used to prevent the coolant from leaking from a gap between the abutment surface  213   c  and the outer end portion  2  toward the turbine housing  5 . However, the sealing members  215  and  217  are not essential. For example, when the body  207  and the lid member  209  are composed of the same material, the sealing members  215  and  217  may not be disposed on the inner opposing surface  213   a  and the abutment surface  213   c.    
     As described above, in the cooling structure CS of the present embodiment, the coolant flow path  211  is formed by two members, i.e., the main body  207  and the lid member  209 . In other words, the coolant flow path  211  is formed by two divided members. Conventionally, a coolant flow path has been formed by a single member by casting. 
     Specifically, a coolant flow path has been formed by a single component by placing a sand mold (core) in a mold to cast a bearing housing. This conventional casting method has a limitation in making a thickness of the wall forming the coolant flow path thinner, and this limits a shape and a cross-sectional area of the coolant flow path. 
     Furthermore, the conventional casting method has the limitation in making the thickness of the wall forming the coolant flow path thinner, and it is difficult to position the coolant flow path closer to a sealing ring provided on a shaft. As a distance between the coolant flow path and the sealing ring increases, the sealing ring is less likely to be cooled. When the sealing ring is less likely to be cooled, the temperature of the sealing ring increases more than the heat resistant temperature, and this may lead to a degradation of the sealing ring and a decrease of a sealing performance. 
     Furthermore, if the coolant flow path has a complicated structure in the conventional casting method, it is difficult to remove the casting sand after the bearing housing is formed. In addition, if the coolant flow path has a complicated shape or if the thickness of the wall forming the coolant flow path is made thinner in the conventional casting method, an acceptable tolerance range is narrowed and a yield rate may decrease. 
     In contrast, in the cooling structure CS of the present embodiment, the coolant flow path  211  is formed by the body  207  and the lid member  209 . Before the lid member  209  is attached to the body  207 , the coolant flow path  211  is exposed to the outside of the body  207  through the opening  213 . Accordingly, the coolant flow path  211  can be machined from the outside. Therefore, the cooling structure CS can reduce the restrictions on the shape and the cross-sectional area of the coolant flow path  211 . The coolant flow path  211  may be formed by machining instead of casting. Furthermore, the coolant flow path  211  may be formed by casting (i.e., formed by placing a core in a mold), and then may be formed by machining. 
     In the cooling structure CS of the present embodiment, the coolant flow path  211  is formed by the body  207  and the lid member  209 . This makes it easy, for example, to position the coolant flow path  211  closer to the sealing ring  205  provided on the shaft  15  by making the thickness of the lid member  209  thinner in the axial direction. Furthermore, this makes it easy to position the coolant flow path  211  closer to the sealing ring  205  by machining the coolant flow path  211  in the axial and radial directions. By positioning the coolant flow paths  211  closer to the sealing ring  205 , it is possible to prevent the temperature of the sealing ring  205  from increasing higher than the heat resistant temperature. 
     In the cooling structure CS of the present embodiment, the coolant flow path  211  is exposed to the outside of the body  207  through the opening  213  before the lid member  209  is attached to the body  207 . Accordingly, even when the bearing housing  3  is formed by casting, it is easy to remove the casting sand from the coolant flow path  211 . Furthermore, the coolant flow path  211  can be formed by machining since it is exposed to the outside of the body  207  through the opening  213 . Therefore, the cooling structure CS of the present embodiment can expand the tolerance range in casting, and thereby improving the yield rate. 
     In the cooling structure CS of the present embodiment, the lid member  209  adjacent to the coolant flow path  211  is disposed radially outside the inner cylindrical portion  207   a  of the body  207 . Accordingly, the split surfaces (the joint surfaces) of the body  207  and the lid member  209  are not exposed to the insertion hole  201  (the groove  201   a ). In other words, the split surfaces (the joint surfaces) of the body  207  and the lid member  209  do not communicate with the insertion hole  201  (the groove  201   a ). If the split surfaces of the body  207  and the lid member  209  communicate with the insertion hole  201  (groove  201   a ), a part of the coolant passing through the coolant flow path  211  may flow into the scattering space S 1  through the split surfaces. If the coolant flows into the scattering space S 1 , the lubricant in the scattering space S 1  may be mixed with the coolant, and the lubricant may be diluted. If the lubricant is diluted, for example, it may cause an engine to fail when the turbocharger TC is mounted on a vehicle or a ship. 
     In contrast, when the lid member  209  adjacent to the coolant flow path  211  is arranged radially outside the inner cylinder  207   a , the split surfaces of the two members do not connect the coolant flow path  211  with the scattering space S 1 . Accordingly, the coolant passing through the coolant flow path  211  does not flow into the scattering space S 1  through the split surfaces of the two members. As a result, the cooling structure CS of this embodiment can prevent (reduce) the mixture of the coolant and the lubricant, the dilution of the lubricant, and the failure of the engine. 
     The cooling structure CS of the present embodiment comprises the abutment surface  213   c  that can contact the outer end portion  209   b  of the lid member  209  in the axial direction. As such, when the lid member  209  is press-fitted into the body  207 , the abutment surface  213   c  can position the lid member  209  in the axial direction. However, the abutment surface  213   c  may contact with the inner end portion  209   a  of the lid member  209  in the axial direction. 
       FIG. 4  shows a state in which an abutment surface  313   c  contacts an inner end portion  309   a  of a lid member  309 . As shown in  FIG. 4 , the coolant flow path  211  and an opening  313  are formed in the body  307 . The lid member  309  is press-fitted into the opening  313 . 
     The opening  313  includes an inner opposing surface  313   a , an outer opposing surface  313   b , and the abutment surface  313   c . The inner opposing surface  313   a  faces the inner end portion  309   a  of the lid member  309  in the radial direction. The outer opposing surface  313   b  faces an outer end portion  309   b  of the lid member  309  in the radial direction. The abutment surface  313   c  faces the inner end portion  309   a  in the axial direction and contacts the inner end portion  309   a . The abutment surface  313   c  can position the lid member  309  in the axial direction by contacting the inner end portion  309   a . In this way, the abutment surface  213   c ,  313   c  may contact either one of the inner end portion  309   a  or the outer end portion  209   b  in the axial direction. 
     The outer opposing surface  313   b  has a substantially cylindrical shape. The outer opposing surface  313   b  is located at a position where an inner circumferential surface on an outer part of the coolant flow path  211  is extended in the axial direction. For example, the outer opposing surface  313   b  is flush with the inner circumferential surface on the outer part of the coolant flow path  211 . The abutment surface  313   c  has a substantially circular shape. The abutment surface  313   c  is located at a position where the inner circumferential surface on the inner part of the coolant flow path  211  is extended in a direction perpendicular to the axial direction. An outer end of the abutment surface  313   c  is continuous with the inner circumferential surface on the inner part of the coolant flow path  211 . The inner opposing surface  313   a  has a substantially cylindrical shape. The inner opposing surface  313   a  is continuous with an inner end of the abutment surface  313   c . The inner opposing surface  313   a  is located at a position extended from the inner end of the abutment surface  313   c  toward the turbine housing  5  in the axial direction. 
     If the lid member  309  is made of a material having a smaller coefficient of linear expansion than that of the body  307 , the body  307  expands greater than the lid member  309  as the temperature of the bearing housing  3  increases. 
     In this state, the inner end portion  309   a  is pressed radially outward by the inner opposing surface  313   a . Accordingly, the coolant passing through the coolant flow path  211  is less likely to leak from a gap between the inner opposing surface  313   a  and the inner end portion  309   a.    
     In contrast, the outer opposing surface  313   b  moves in a direction spaced apart from the outer end portion  309   b . As such, a sealing member  315  is disposed on the outer opposing surface  313   b . The sealing member  315  is, for example, a sealing ring. The sealing member  315  is used to prevent the coolant from leaking from a gap between the outer opposing surface  313   b  and the outer end portion  309   b  toward the turbine housing  5 . In this manner, the sealing member  215 ,  315  may be provided on either one of the inner opposing surface  213   a  or the outer opposing surface  313   b . As such, it is possible to prevent the coolant from leaking from the coolant flow path  211  toward the turbine housing  5 , even when the materials of the body  207 ,  307  and the lid member  209 ,  309  are different from each other. 
     The sealing members  215  and  315  are not limited to a sealing ring. The sealing members  215  and  315  may be, for example, a liquid gasket. 
       FIG. 5  shows a state in which a sealing member  415  is disposed on an outer opposing surface  413   b . As shown in  FIG. 5 , the coolant flow path  211  and an opening  413  are formed in a body  407 . A lid member  409  is screwed to the opening  413 . 
     The opening  413  includes the inner opposing surface  313   a , an outer opposing surface  413   b , and the abutment surface  313   c . The inner opposing surface  313   a  faces the inner end portion  309   a  of the lid member  409  in the radial direction. The outer opposing surface  413   b  faces an outer end portion  409   b  of the lid member  409  in the radial direction. The abutment surface  313   c  faces the inner end portion  309   a  in the axial direction, and contacts the inner end portion  309   a.    
     As shown in  FIG. 5 , the outer opposing surface  413   b  is provided with a female threaded portion FS threaded on an inner circumference surface. The outer end portion  409   b  is provided with a male threaded portion MS threaded on the outer circumference surface. The lid member  409  and the body  407  are screwed together by rotating the lid member  409  with respect to the body  407  with the female screw portion FS and the male screw portion MS being engaged. This makes it easier to assemble the bearing housing  3  (lid member  409  and body  407 ), compared to the case where the lid member  209  and body  207  are press-fitted together. 
     A sealing member  415  is disposed between the female threaded portion FS and the male threaded portion MS. The sealing member  315  is, for example, a liquid gasket. The sealing member  415  prevents the coolant from leaking from a gap between the female threaded portion FS and the male threaded portion MS toward the turbine housing  5 . 
     As described above, in the cooling structure CS of this embodiment, the sealing member  217  is disposed on the abutment surface  213   c  (see  FIGS. 2 and 3 ). As such, the sealing member  217  prevents the coolant from leaking from a gap between the abutment surface  213   c  and the outer end portion  209   b  toward the turbine housing  5 . 
     Although the embodiments of the present disclosure have been described above with reference to the accompanying drawings, the present disclosure is not limited thereto. It is obvious that a person skilled in the art can conceive of various examples of variations or modifications within the scope of the claims, which are also understood to belong to the technical scope of the present disclosure. 
     In the above embodiment, the abutment surface  213   c ,  313   c  is formed on the body  207 ,  307 ,  407 . However, the present disclosure is not limited thereto, and the body  207 ,  307 ,  407  may not include the abutment surface  213   c ,  313   c . Furthermore, in the above embodiment, the sealing member  215 ,  315 ,  415  is disposed on the inner opposing surface  213   a ,  313   a  or on the outer opposing surface  213   b ,  313   b ,  413   b . However, the present disclosure is not limited, and the sealing members  215 ,  315 ,  415  may not be disposed on the inner opposing surface  213   a ,  313   a  or on the outer opposing surface  213   b ,  313   b ,  413   b . In addition, in the above embodiment, the sealing member  217  is disposed on the abutment surface  213   c ,  313   c . However, the present disclosure is not limited thereto, and a sealing member  217  may not be disposed on the abutment surface  213   c ,  313   c . For example, the lid member  209 ,  309 ,  409  may be welded to the body  207 ,  307 ,  407 .