Abstract:
A circular ring-shaped shroud plate is arranged between a scroll passage and a turbine chamber. The shroud plate has a through-hole that penetrates therethrough in a direction along an axis of a turbine shaft. A variable nozzle is supported in an openable/closable manner on the shroud plate by a shaft inserted through the through-hole. A gap between the shroud plate and a turbine housing in the direction along the axis is partitioned into a first space that communicates with an outlet of exhaust gas that faces the through-hole and is provided upstream of a turbine wheel with respect to the flow of exhaust gas, and a second space that communicates with the scroll passage, by a disc spring that is so arranged as to surround the turbine wheel.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a turbocharger in which a variable nozzle mechanism that makes variable the flow velocity of exhaust gas blown onto a turbine wheel by causing a variable nozzle to operate in an opening/closing manner is incorporated. 
         [0003]    2. Description of the Related Art 
         [0004]    As a turbocharger that is mounted on an engine, there is a turbocharger in which a variable nozzle mechanism that makes variable the flow velocity of exhaust gas blown onto a turbine wheel by causing a variable nozzle to operate in an opening/closing manner is incorporated. 
         [0005]    For example, in a turbocharger described in Japanese Patent Application Publication No. 2009-144545 (JP-2009-144545 A), as shown in  FIG. 5 , a turbine shaft  71  is rotatably supported by a bearing housing  72 . A turbine housing  73  is arranged on one side of the bearing housing  72  (on the left side in  FIG. 5 ) in a direction along an axis L 1  of the turbine shaft  71 . The turbine housing  73  has a turbine chamber  74  at a central portion thereof, and has a convolute scroll passage  75  around the turbine chamber  74 . A turbine wheel  76  that rotates in the aforementioned turbine chamber  74  is provided on the turbine shaft  71 . In addition, in this turbocharger  70 , an exhaust gas E that has flowed along the scroll passage  75  after being discharged from an engine is blown onto the turbine wheel  76 , and the turbine wheel  76  is rotationally driven. As a result of this, a compressor wheel (not shown) that is coaxial with the turbine wheel  76  rotates integrally with the turbine wheel  76 , so that the engine is supercharged (intake air is compressed and delivered to the engine). 
         [0006]    An annular support member  79  having a plurality of through-holes  78  that penetrate therethrough in the direction along the aforementioned axis L 1  (a lateral direction in  FIG. 5 ) is arranged in an annular communication passage  77  between the aforementioned scroll passage  75  and the aforementioned turbine chamber  74 . Shafts  81  are turnably inserted through the through-holes  78  respectively, and variable nozzles  82  are fixed to the shafts  81  respectively. In addition, each of the variable nozzles  82  is operated in an opening/closing manner by being turned integrally with a corresponding one of the shafts  81 . The flow velocity of the exhaust gas E that is blown onto the turbine wheel  76  is changed, the rotational speed of the turbocharger  70  is changed, and the boost pressure (the intake pressure) of the engine is adjusted. 
         [0007]    An annular sealing member  83  is so arranged as to surround the turbine wheel  76 , in a gap G between the support member  79  and the turbine housing  73 , in the direction along the aforementioned axis L 1 . The aforementioned gap G is sealed upstream of the aforementioned through-holes  78  with respect to the flow of exhaust gas by this sealing member  83 . Thus, the exhaust gas E in the scroll passage  75  is restrained from leaking out through the gap G. 
         [0008]    However, in the turbocharger  70  described in the aforementioned Japanese Patent Application Publication No. 2009-144545 (JP-2009-144545 A), when the exhaust gas E leaks out to the gap G through between the through-holes  78  and the shafts  81  as indicated by an arrow in  FIG. 5  in the process of passing through between adjacent ones of the variable nozzles  82  from the scroll passage  75 , the exhaust gas E flows along the gap G downstream with respect to the flow of exhaust gas. In addition, this exhaust gas E is discharged from an outlet  84 , which is located at a downstream end of the gap G downstream of the turbine wheel  76  with respect to the flow of exhaust gas, without passing the turbine wheel  76 . Thus, the amount of the exhaust gas E that is blown onto the turbine wheel  76  decreases by an amount of the discharged exhaust gas. As a result, the rotational speed of the turbocharger  70  may become low, and the boost pressure of the engine may decrease. 
       SUMMARY OF THE INVENTION 
       [0009]    The invention provides a turbocharger capable of restraining the boost pressure from decreasing as a result of exhaust gas that leaks out from between a through-hole and a shaft. 
         [0010]    A turbocharger in accordance with a first aspect of the invention includes a turbine housing, a turbine wheel, an annular support member, a plurality of variable nozzles, and an annular sealing member. The turbine housing has a convolute scroll passage around a turbine chamber. The turbine wheel is provided on a turbine shaft, rotates in the turbine chamber, and is rotationally driven when exhaust gas that has flowed along the scroll passage after being discharged from an engine is blown thereonto. The annular support member is arranged between the scroll passage and the turbine chamber, and has through-holes, which penetrate in a direction along an axis of the turbine shaft, at a plurality of spots around the turbine wheel. The plurality of the variable nozzles are supported in an openable/closable manner on the support member by shafts inserted through the respective through-holes, and make variable a flow velocity of exhaust gas blown onto the turbine wheel through changes in opening degrees thereof. The annular sealing member is so arranged as to surround the turbine wheel, and partitions a gap between the support member and the turbine housing in the direction along the axis into a first space that communicates with an outlet of exhaust gas, which faces the through-holes and is provided upstream of the turbine wheel with respect to flow of exhaust gas, and a second space that communicates with the scroll passage. 
         [0011]    According to the, aforementioned configuration, in the turbocharger, exhaust gas that has flowed along the scroll passage of the turbine housing passes through between adjacent ones of the variable nozzles and is blown onto the turbine wheel in the turbine chamber, and the turbine wheel is rotationally driven. The variable nozzles are opened/closed with the shafts inserted through the through-holes of the support member serving as fulcrums, so that the opening degrees of the variable nozzles are changed. As a result of this, the flow velocity of exhaust gas that is blown onto the turbine wheel is changed, the rotational speed of the turbocharger is changed, and the boost pressure of the engine is adjusted. 
         [0012]    In the aforementioned turbocharger, there is a gap between the support member and the turbine housing. However, this gap is sealed by the annular sealing member upstream of the aforementioned through-holes with respect to the flow of exhaust gas. 
         [0013]    By the way, when exhaust gas leaks out to the gap through between the through-holes and the shafts in the process of passing through between adjacent ones of the variable nozzles, the exhaust gas flows downstream along the gap. This exhaust gas passes through an outlet of the aforementioned gap, and is returned upstream of the turbine wheel with respect to the flow of exhaust gas. This exhaust gas is blown onto the turbine wheel together with the exhaust gas that has passed through between the adjacent ones of the variable nozzles, and is devoted to rotationally driving the turbine wheel. In this manner, the exhaust gas that has temporarily leaked out from between the through-holes and the shafts is used to rotate the turbine wheel. Therefore, in comparison with a turbocharger in which exhaust gas is discharged downstream of a turbine wheel with respect to the flow of exhaust gas, the rotational speed of the turbocharger is less likely to decrease, and the boost pressure is further restrained from decreasing. 
         [0014]    In the aforementioned configuration, a passage that establishes communication between the first space and operation ranges of the variable nozzles may be provided, and the outlet may be constituted by an opening region of the passage in the operation ranges. 
         [0015]    According to the aforementioned configuration, the exhaust gas that has leaked out to the first space from between the through-holes and the shafts flows through the passage that establishes communication between the first space and the operation ranges of the variable nozzles. This exhaust gas passes through the opening region (the outlet) of the passage in the operation ranges, and flows to the operation ranges. Then, the aforementioned exhaust gas is blown onto the turbine wheel together with the exhaust gas that has passed through between adjacent ones of the variable nozzles. 
         [0016]    In the aforementioned configuration, the turbine housing may be provided with a bulge portion that extends toward a side of a bearing housing that rotatably supports the turbine shaft and is located between the support member and the turbine wheel in a state of being spaced apart from the support member, and the passage may be constituted by a space between the support member and the bulge portion. 
         [0017]    According to the aforementioned configuration, when exhaust gas leaks out to the first space through between the through-holes and the shafts in the process of passing through between the adjacent ones of the variable nozzles, the exhaust gas flows downstream along the gap. This exhaust gas passes through the passage between the support member and the bulge portion of the turbine wheel, and is thereby guided in the direction along the axis. Then, the exhaust gas flows from the outlet of the passage to the operation ranges of the variable nozzles. 
         [0018]    In this manner, the space between the bulge portion and the support member is utilized as the aforementioned passage that establishes communication between the gap and the operation ranges. Therefore, it is unnecessary to provide the passage separately. In the aforementioned configuration, the turbocharger may further include an annular plate that is arranged opposite the support member across the variable nozzles and is integrally coupled to the support member. The sealing member may be constituted by a disc spring that is arranged in such a state as to surround the turbine wheel in the gap, and the disc spring may be in contact, at one of an outer peripheral edge portion thereof and an inner peripheral edge portion thereof, with the support member and in contact, at the other of the outer peripheral edge portion thereof and the inner peripheral edge portion thereof, with the turbine housing, in a state of being elastically deformed such that a dimension of the disc spring in the direction along the axis decreases, thereby urge the support member toward a side of a bearing housing that supports the turbine shaft, press the plate against the bearing housing, and partition the gap into the first space and the second space as the sealing member. 
         [0019]    According to the aforementioned configuration, the disc spring urges the support member toward the side of the bearing housing through a spot where the disc member is in contact, on one of the outer peripheral edge portion thereof and the inner peripheral edge portion thereof, with the support member. As a result of this, the annular plate that is integrally coupled to the support member is also urged toward the same side, and is pressed against the bearing housing. Due to this pressing, the support member, the variable nozzles, and the plate are positioned in a floating state without being fixed to the bearing housing and the turbine housing. 
         [0020]    Besides, one of the outer peripheral edge portion of the disc spring and the inner peripheral edge portion of the disc spring is in contact with the support member, and the other of the outer peripheral edge portion of the disc spring and the inner peripheral edge portion of the disc spring is in contact with the turbine housing, so that the gap is partitioned into the downstream space (the first space) that leads to the through-holes and the outlet, and the upstream space (the second space) that does not lead thereto. Thus, the exhaust gas that has directly flowed from the scroll passage into the space upstream of the gap is sealed by the disc spring, and is inhibited from leaking out to the downstream space. Besides, the exhaust gas that has leaked out to the downstream space from between the through-holes and the shafts is inhibited from flowing into the upstream space by the sealing member. 
         [0021]    In this manner, a single member (the disc spring) serves both as an urging member that urges the support member and as the sealing member that seals the gap. Therefore, the number of parts of the turbocharger is smaller than in the case where the urging member and the sealing member are constituted by different members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The features, advantages, and technical and industrial significance of this invention will be described in the following detailed description of example embodiments of the invention with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0023]      FIG. 1  is a view showing one embodiment of the invention, and is a partial cross-sectional view showing an overall configuration of a turbocharger in which a variable nozzle mechanism is incorporated; 
           [0024]      FIGS. 2A and 2B  are views showing part of the variable nozzle mechanism in the embodiment of the invention,  FIG. 2A  is a lateral view as viewed from the left side of  FIG. 1 , and  FIG. 2B  is a lateral view as viewed from the right side of  FIG. 1 ; 
           [0025]      FIG. 3  is a partial cross-sectional view showing the variable nozzle mechanism of  FIG. 1  and a peripheral region thereof on an enlarged scale; 
           [0026]      FIG. 4  is a partial cross-sectional view showing a cross-sectional structure of a cross-section that is different from those of  FIGS. 1 and 3 , as to the variable nozzle mechanism and the peripheral region thereof in the embodiment of the invention; and 
           [0027]      FIG. 5  is a partial cross-sectional view showing a variable nozzle mechanism and a peripheral region thereof in a conventional turbocharger on an enlarged scale. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0028]    One embodiment as a concrete form of the invention will be described hereinafter with reference to  FIGS. 1 to 4 . A vehicle is mounted with an engine that burns the mixture of air that is sucked into a combustion chamber through an intake passage, and fuel that is supplied to the combustion chamber. This engine is provided with a turbocharger  10  shown in  FIG. 1 . In this turbocharger  10 , a turbine shaft  11  is rotatably supported on a bearing housing  12  by a bearing  13 . A turbine housing  14  is adjacently arranged on one side of the bearing housing  12  (on the right side in  FIG. 1 ) in a direction along an axis L 1  of the turbine shaft  11  (hereinafter referred to as “an axial direction”). A compressor housing (not shown) composed of a plurality of members is adjacently arranged on the other side (on the left side in  FIG. 1 ) of the bearing housing  12 . The turbine housing  14  and the compressor housing are fastened to the bearing housing  12 . In addition, this bearing housing  12 , this turbine housing  14 , and this compressor housing constitute a housing of the turbocharger  10 . 
         [0029]    A cylindrical turbine chamber  15  that extends in the aforementioned axial direction is formed at a central portion of the turbine housing  14 . In the turbine housing  14 , a convolute scroll passage  16  is formed around the turbine chamber  15 . The turbine chamber  15  and the scroll passage  16  communicate with each other via a communication passage  17  (see  FIG. 3 ). 
         [0030]    Incidentally, an inner wall surface  12 A that faces the communication passage  17  in the bearing housing  12 , and an inner wall surface  14 A that faces the communication passage  17  in the turbine housing  14  are perpendicular to or almost perpendicular to the aforementioned axis L 1 . 
         [0031]    A turbine wheel  26  that rotates in the turbine chamber  15  is fixed on one end (on the right side in  FIG. 1 ) of the turbine shaft  11 . A compressor wheel (not shown) that rotates in the compressor housing is fixed on the other end (on the left side in  FIG. 1 ) of the turbine shaft  11 . 
         [0032]    In addition, in the turbocharger  10  having the aforementioned basic configuration, an exhaust gas E that has flowed along the scroll passage  16  after being discharged from an engine is blown onto the turbine wheel  26  through the communication passage  17 , so that the turbine wheel  26  is rotationally driven. This rotation is transmitted to the compressor wheel via the turbine shaft  11 . As a result, in the engine, air that is sucked in through a negative pressure that is generated in the combustion chamber in accordance with the movement of a piston is forcibly delivered (supercharged) to the combustion chamber through the rotation of the compressor wheel of the turbocharger  10 . In this manner, the efficiency of filling the combustion chamber with air is enhanced. 
         [0033]    A variable nozzle mechanism  30  is incorporated in the aforementioned turbocharger  10 . The variable nozzle mechanism  30  changes the exhaust gas flow area of the communication passage  17 , and makes variable the flow velocity of the exhaust gas E that is blown onto the turbine wheel  26 . The variable nozzle mechanism  30  is a mechanism for adjusting the rotational speed of the turbocharger  10  to adjust the amount of air that is forcibly delivered to the combustion chamber. 
         [0034]    Next, the overall configuration of this variable nozzle mechanism  30  will be described.  FIG. 2A  shows part of the variable nozzle mechanism  30  (a nozzle plate  31  and the like) as viewed from the left side of  FIG. 1 , and  FIG. 2B  shows part of the variable nozzle mechanism  30  (the nozzle plate  31  and the like) as viewed from the right side of  FIG. 1 . As shown in  FIGS. 1 ,  2 A, and  2 B, the variable nozzle mechanism  30  is equipped with the nozzle plate  31  and a unison ring  35 , which are arranged in the communication passage  17 . This nozzle plate  31  and this unison ring  35  assume the shape of a circular ring around the aforementioned axis L 1 . Besides, the nozzle plate  31  is also referred to simply as a plate. 
         [0035]    On the nozzle plate  31 , a plurality of shafts  32  are arranged substantially at equal angular intervals on the circle around the aforementioned axis L 1 . The respective shafts  32  extend parallel to the axis L 1 , and are turnably inserted through the nozzle plate  31 . Each of variable nozzles (nozzle vanes)  33  is fixed to a corresponding one of the shafts  32  in one region thereof (on the right side in  FIG. 1 ) that is exposed from the nozzle plate  31 . In  FIG. 1 , one of the variable nozzles  33  is indicated by an alternate long and two short dashes line. Besides, a proximal end portion of each of arms  34  is fixed to a corresponding one of the shafts  32  at the other end thereof (on the left in  FIG. 1 ) that is exposed from the nozzle plate  31 . 
         [0036]    The unison ring  35  has recess portions  36  at a plurality of spots on an inner peripheral face thereof. A distal end portion of each of the aforementioned arms  34  is engaged with a corresponding one of these recess portions  36 . The unison ring  35  is rotated from the outside of the turbocharger  10  via a link  37  (see  FIG. 1 ) or the like. That is, an arm  39  is fixed to a turning shaft  37 A of the link  37 , and a distal end portion of the arm  39  is engaged with a recess portion  40  that is provided in an inner peripheral face of the unison ring  35 . In addition, when the unison ring  35  is turned around the aforementioned axis L 1  via the link  37 , the turning shaft  37 A, the arm  39  and the like from outside the turbocharger  10 , the respective arms  34  that are engaged with the plurality of the recess portions  36  of the unison ring  35  are turned (opened/closed) around the shafts  32  in a state of being synchronized with one another. Due to the turning of each of the shafts  32 , the opening degree of a corresponding one of the variable nozzles  33  changes, and the aforementioned exhaust gas flow area of the communication passage  17  is changed. Then, the flow velocity of the exhaust gas E that is blown onto the turbine wheel  26  through between the adjacent ones of the variable nozzles  33  is adjusted. 
         [0037]    For example, in  FIG. 2A , when the arm  39  is turned counterclockwise by the link  37  or the like with the turning shaft  37 A serving as a fulcrum, the unison ring  35  thereby turns in a direction indicated by each of arrows in  FIGS. 2A and 2B . Due to the aforementioned turning of the unison ring  35 , each of the shafts  32  turns counterclockwise in  FIG. 2A , and turns clockwise in  FIG. 2B . As a result of the aforementioned turning of each of the shafts  32 , a corresponding one of the variable nozzles  33  turns to the closing side, and the flow velocity of the exhaust gas E that is blown onto the turbine wheel  26  becomes high. Contrary to the above, when the variable nozzles  33  turn to the opening side, the flow velocity of the exhaust gas E that is blown onto the turbine wheel  26  becomes low. 
         [0038]      FIG. 3  shows the variable nozzle mechanism  30  in  FIG. 1  and a peripheral region thereof on an enlarged scale. Besides,  FIG. 4  shows a cross-sectional structure of the variable nozzle mechanism  30  and the peripheral region thereof along a cross-section that is different from those of the aforementioned  FIGS. 1 and 3  (a cross-section that extends past later-described spacers  47 ) on an enlarged scale. As shown in  FIGS. 3 and 4 , the variable nozzle mechanism  30  is equipped with a support member that is arranged in the aforementioned communication passage  17 , in addition to the aforementioned configuration. This support member is constituted by a shroud plate  41  that assumes the shape of a circular ring around the aforementioned axis L 1 . The shroud plate  41  is arranged on such a side as to move away from the bearing housing  12  (on the right side of each of  FIGS. 3 and 4 ) with respect to the nozzle plate  31 . Through-holes  42  that penetrate in the axial direction are drilled through the shroud plate  41  at a plurality of spots on a circle around the aforementioned axis L 1 . On the other hand, each of the shafts  32  for a corresponding one of the variable nozzles  33  is exposed from the corresponding one of the variable nozzles  33  to the shroud plate  41  side. The exposed region of this shaft  32  is turnably inserted through a corresponding one of the aforementioned through-holes  42 . Accordingly, each of the variable nozzles  33  is supported on the nozzle plate  31  and the shroud plate  41  in such a manner as to be capable of turning integrally with a corresponding one of the shafts  32 . 
         [0039]    The shroud plate  41  is coupled to the nozzle plate  31  by a plurality of pins  46  that are arranged at substantially equal angular intervals on the circle around the aforementioned axis L 1 . The diameter of this circle is larger than the diameter of the circle on which the plurality of the aforementioned shafts  32  are arranged. Accordingly, each of the pins  46  is located at a spot that is farther from the axis L 1  than a corresponding one of the shafts  32 . Each of the pins  46  is press-fitted in the nozzle plate  31 , and is press-fitted in a corresponding one of holes  45  that are drilled in the shroud plate  41 . 
         [0040]    Each of the pins  46  is covered with a corresponding one of the circular tube-like spacers  47  between the nozzle plate  31  and the shroud plate  41 . These spacers  47  ensure a gap that is as thick as the variable nozzles  33 , between the nozzle plate  31  and the shroud plate  41 . Due to the aforementioned coupling, the nozzle plate  31  and the shroud plate  41  are joined integrally with each other to constitute “an assembly body  48 ”. In this assembly body  48 , the range sandwiched by the nozzle plate  31  and the shroud plate  41  is a range (an operation range A) where each of the variable nozzles  33  turns (opens/closes) together with a corresponding one of the shafts  32 . 
         [0041]    Furthermore, in the turbocharger  10 , a sealing member is arranged in a gap G between the shroud plate  41  of the assembly body  48  and the inner wall surface  14 A of the turbine housing  14 , around the turbine wheel  26 . This sealing member is constituted by a disc spring  50  that is formed in the shape of a circular ring by an elastic body such as a metal plate or the like. This gap G is provided in consideration of, for example, the possibility of ensuring an installation space of the assembly body  48  between the bearing housing  12  and the turbine housing  14  even when the turbine housing  14  or the like is thermally deformed (contracted or expanded) during a transition between a cold state and a hot state, or even when the accuracies of component parts of the turbocharger  10  are dispersed. 
         [0042]    The disc spring  50  seals the aforementioned gap G upstream of the through-holes  42  with respect to the flow of exhaust gas. Besides, the disc spring  50  also has the function of urging the assembly body  48  in the axial direction to press the assembly body  48  against the inner wall surface  12 A of the bearing housing  12 . The disc spring  50  is so formed in a conical (tapered) shape as to approach the inner wall surface  14 A of the turbine housing  14  as the distance to a central portion of the disc spring  50  decreases. 
         [0043]    An outer peripheral edge portion  52  of the disc spring  50  assumes the shape of a circular ring around the axis L 1 , and is in contact with the shroud plate  41  at a spot that is farther from the axis L 1  than all the holes  45 . As described above, each of the holes  45  is located at a spot that is farther from the axis L 1  than a corresponding one of the through-holes  42 . Therefore, the aforementioned outer peripheral edge portion  52  is in contact with the shroud plate  41  at a spot that is farther from the axis L 1  than all the through-holes  42 . An inner peripheral edge portion  51  of the disc spring  50  assumes the shape of a circular ring around the axis L 1 , and is in contact with the inner wall surface  14 A of the turbine housing  14 . In this case, the inner peripheral edge portion  51  is in contact with the inner wall surface  14 A at a spot that is nearer to the turbine wheel  26  than all the through-holes  42 . 
         [0044]    Due to the application of a load to the aforementioned inner peripheral edge portion  51  and the aforementioned outer peripheral edge portion  52 , the disc spring  50  is bent (elastically deformed) in such a direction that the dimension of the disc spring  50  in the axial direction thereof decreases. The disc spring  50  urges, at the outer peripheral edge portion  52  thereof, the assembly body  48  (the shroud plate  41 ) toward the bearing housing  12  side. Due to this urging, the nozzle plate  31  is pressed against the inner wall surface  12 A of the bearing housing  12 . 
         [0045]    Furthermore, a bulge portion  18  that extends toward the bearing housing  12  side in a state of being slightly spaced apart from the shroud plate  41  toward the turbine wheel  26  side is formed integrally with the turbine housing  14 . The bulge portion  18  assumes the shape of a circular ring around the axis L 1 , is located between the shroud plate  41  and the turbine wheel  26 , and constitutes part of the inner wall surface of the aforementioned turbine chamber  15 . In addition, a passage  43  that establishes communication between the gap G and the operation ranges A of the variable nozzles  33 , namely, those regions of the variable nozzles  33  which are located downstream of the shafts  32  respectively with respect to the flow of exhaust gas is constituted by an annular space that extends parallel to the axis L 1  between the shroud plate  41  and the bulge portion  18 . A downstream end of this passage  43  (an opening region in the operation ranges A) constitutes an outlet  44  of the exhaust gas E in the gap G. Accordingly, the outlet  44  is located upstream of the turbine wheel  26  with respect to the flow of exhaust gas. 
         [0046]    As described above, the turbocharger  10  in accordance with this embodiment of the invention is configured. Next, the operation of this turbocharger  10  will be described. The exhaust gas E that is generated through the operation of the engine flows into the turbocharger  10  in the process of flowing through an exhaust passage, and flows along the scroll passage  16  of the turbine housing  14 . This exhaust gas E passes through between the adjacent ones of the variable nozzles  33 , and is blown onto the turbine wheel  26  in the turbine chamber  15 . Due to the blowing of this exhaust gas E, the turbine wheel  26  is rotationally driven. As a result of this, the compressor wheel that is coaxial with the turbine wheel  26  rotates integrally with the turbine wheel  26  to supercharge the engine. 
         [0047]    The variable nozzles  33  are turned through the operation of the link  37  or the like from outside the turbocharger  10 , and the opening degrees of the variable nozzles  33  are thereby changed. As a result of this, the flow velocity of the exhaust gas E that is blown onto the turbine wheel  26  is changed, the rotational speed of the turbocharger  10  is changed, and the boost pressure of the engine is adjusted. 
         [0048]    It should be noted herein that although the aforementioned turbocharger  10  has the gap G between the shroud plate  41  and the turbine housing  14 , this gap G is sealed by the disc spring  50  upstream of the aforementioned through-holes  42  with respect to the flow of exhaust gas. That is, in the turbocharger  10 , between the assembly body  48  (the shroud plate  41 ) and the inner wall surface  14 A of the turbine housing  14 , the disc spring  50  is elastically deformed in the axial direction, and is incorporated with elastic energy accumulated therein. 
         [0049]    The shroud plate  41  with which the outer peripheral edge portion  52  of the disc spring  50  is held in contact is constantly urged in the axial direction by forces that act to discharge elastic energy of the disc spring  50  (an elastic restoration force and an urging force). The urging force of this disc spring  50  is transmitted to the nozzle plate  31  via the spacers  47  and the pins  46 . Due to the transmission of this urging force, the assembly body  48  is displaced toward the bearing housing  12  side, and part of the nozzle plate  31  is pressed against the inner wall surface  12 A of the bearing housing  12 . Due to this pressing, the assembly body  48  is positioned in a floating state without being fixed to both the housings  12  and  14 . 
         [0050]    Besides, the outer peripheral edge portion  52  of the disc spring  50  is in contact with the shroud plate  41  at a spot that is farther from the axis L 1  than the through-holes  42 , and the inner peripheral edge portion  51  of the disc spring  50  is in contact with the inner wall surface  14 A of the turbine housing  14 . The disc spring  50 , which is in such a state of contact, partitions the gap G into a downstream space S 1  that leads to the through-holes  42 , the holes  45 , and the passage  43  (the outlet  44 ), and an upstream space S 2  that does not lead to the through-holes  42 , the holes  45 , and the passage  43  (the outlet  44 ). Thus, the exhaust gas E that has directly flowed from the scroll passage  16  into the upstream space S 2  is sealed by the disc spring  50 , and is inhibited from leaking out to the downstream space S 1 . 
         [0051]    By the way, in order for each of the variable nozzles  33  to turn integrally with a corresponding one of the shafts  32 , this corresponding one of the shafts  32  is turnably inserted through the corresponding one of the through-holes  42 . Therefore, a sizable gap is created between each of the shafts  32  and an inner wall surface of a corresponding one of the through-holes  42 . Thus, the exhaust gas E may leak out to the gap G (the space S 1 ) through between the through-holes  42  and the shafts  32  in the process of passing through between the adjacent ones of the variable nozzles  33 . This exhaust gas E flows downstream with respect to the flow of exhaust gas along the gap G (the space S 1 ). The exhaust gas E flows through the passage  43  that establishes communication between the aforementioned gap G (the space S 1 ) and the operation ranges A of the variable nozzles  33 , downstream of the shafts  32  with respect to the flow of exhaust gas. This exhaust gas E is guided to the operation ranges A through the opening region (the outlet  44 ) of the passage  43  in the operation ranges A, and is returned upstream of the turbine wheel  26  with respect to the flow of exhaust gas. This exhaust gas E is blown onto the turbine wheel  26  together with the exhaust gas E that has passed through the adjacent ones of the variable nozzles  33 , and is devoted to rotationally driving the turbine wheel  26 . 
         [0052]    According to the embodiment of the invention described above in detail, the following effects are obtained. (1) In the turbocharger  10  in which the variable nozzle mechanism  30  is incorporated and the disc spring  50  is arranged as a sealing member in the gap G between the shroud plate  41  of the assembly body  48  and the inner wall surface  14 A of the turbine housing  14 , the outlet  44  of the exhaust gas E in the gap G is provided upstream of the turbine wheel  26  with respect to the flow of exhaust gas. 
         [0053]    Thus, even when the exhaust gas E temporarily leaks out to the gap G (the space S 1 ) from between the shafts  32  and the through-holes  42  of the shroud plate  41  that supports the variable nozzles  33  in the variable nozzle mechanism  30 , the exhaust gas E can be returned from the outlet  44  upstream of the turbine wheel  26  with respect to the flow of exhaust gas, and can be used to rotate the turbine wheel  26 . As a result, the rotational speed of the turbocharger  10  is made less likely to decrease, and the boost pressure can be more restrained from decreasing, in comparison with a turbocharger in which the exhaust gas E is discharged downstream of the turbine wheel  26  with respect to the flow of exhaust gas (Japanese Patent Application Publication No. 2009-144545 (JP-2009-144545 A). 
         [0054]    (2) The passage  43  that establishes communication between the gap G and the operation ranges A of the variable nozzles  33  is provided, and the opening region of this passage  43  in the operation ranges A serves as the outlet  44 . Thus, the exhaust gas E that has leaked out to the gap G (the space S 1 ) from between the through-holes  42  and the shafts  32  is guided to the sides of the operation ranges A of the variable nozzles  33  by the passage  43 , and is caused to flow to the operation ranges A from the outlet  44 . The exhaust gas E can thereby be returned upstream of the turbine wheel  26  with respect to the flow of exhaust gas. 
         [0055]    (3) The turbine housing  14  is provided with the bulge portion  18  that extends toward the bearing housing  12  side and is located between the shroud plate  41  and the turbine wheel  26  in a state of being spaced apart from the shroud plate  41 , and the passage  43  is constituted by the annular space between the shroud plate  41  and the bulge portion  18 . 
         [0056]    Thus, the exhaust gas E that has leaked out to the gap G (the space S 1 ) through between the through-holes  42  and the shafts  32  can be guided to the sides of the operation ranges A of the variable nozzles  33  by the passage  43  between the shroud plate  41  and the bulge portion  18 , and can be caused to flow from the outlet  44  to the operation ranges A. 
         [0057]    In this manner, the space between the bulge portion  18  and the shroud plate  41  is utilized as the passage  43  that establishes communication between the gap G and the operation ranges A. Therefore, there is no need to provide the passage  43  separately. 
         [0058]    Besides, the shroud plate  41  is separated from the turbine housing  14  (the bulge portion  18 ). Therefore, even when the turbine housing  14  is deformed through heat or the like, the influence of the deformation can be prevented or restrained from being exerted on the shroud plate  41 . 
         [0059]    (4) The annular nozzle plate  31  is arranged opposite the shroud plate  41  across the variable nozzles  33 , and the shroud plate  41  is joined integrally with the nozzle plate  31  by the pins  46  and the spacers  47 . In the gap G, the disc spring  50  is arranged in a state of surrounding the turbine wheel  26 . With the disc spring  50  elastically deformed such that the dimension thereof in the direction along the axis L 1  decreases, the outer peripheral edge portion  52  of the disc spring  50  is held in contact with the shroud plate  41 , and the inner peripheral edge portion  51  of the disc spring  50  is held in contact with the inner wall surface  14 A of the turbine housing  14 . 
         [0060]    Thus, the shroud plate  41  can be urged by the disc spring  50 , the nozzle plate  31  can be pressed against the inner wall surface  12 A of the bearing housing  12 , and the assembly body  48  can be positioned in a floating state without being fixed to the bearing housing  12  and the turbine housing  14 . 
         [0061]    Besides, the gap G is partitioned by the disc spring  50  into the downstream space S 1  that leads to the through-holes  42  and the outlet  44 , and the upstream space S 2  that does not lead to the through-holes  42  and the outlet  44 . Thus, the exhaust gas E that has directly flowed from the scroll passage  16  into the upstream space S 2  is sealed by the disc spring  50 , and can be inhibited from leaking out to the downstream space S 1 . Besides, the exhaust gas E that has leaked out to the downstream space S 1  from between the through-holes  42  and the shafts  32  can be inhibited from flowing into the upstream space S 2  by the disc spring  50 . 
         [0062]    In this manner, the single member (the disc spring  50 ) serves both as an urging member that urges the shroud plate  41  and as a sealing member that seals the gap G. Therefore, the number of parts of the turbocharger  10  can be made smaller than in the case where the urging member and the sealing member are constituted by different members. 
         [0063]    (5) The outer peripheral edge portion  52  of the disc spring  50  is held in contact with the shroud plate  41  at a spot that is farther from the axis L 1  than the holes  45  of all the pins  46 . Thus, even when the exhaust gas E that flows between the adjacent ones of the variable nozzles  33  leaks out to the gap G from between the holes  45  of the shroud plate  41  and the pins  46 , it is possible to return the exhaust gas E from the outlet  44  upstream of the turbine wheel  26  with respect to the flow of exhaust gas, and use the exhaust gas E to rotate the turbine wheel  26 . As a result, the rotational speed of the turbocharger  10  can be made less likely to decrease, and the boost pressure can be further restrained from decreasing. 
         [0064]    (6) Through the urging force of the disc spring  50  alone, the assembly body  48  of the variable nozzle mechanism  30  is positioned by being pressed against the bearing housing  12 . Thus, the assembly body  48  can be configured in a relatively small size, the temperature differences among the component parts of the assembly body  48  can be reduced, and the degree of thermal deformation at high temperatures can be reduced. 
         [0065]    Besides, the assembly body  48  is not forcibly fixed on the outer diameter side of the nozzle plate  31  or the like. Therefore, the restriction on deformation can be reduced, and the degree of thermal deformation can be reduced. In view of these facts, even when the clearance between the nozzle plate  31  and the variable nozzles  33  or the clearance between the shroud plate  41  and the variable nozzles  33  is reduced, the stiffening or the like of the variable nozzles  33  at high temperatures is avoided. The stiffening of the variable nozzles  33  is a phenomenon that the variable nozzles  33  become unlikely to move or immovable through contact with the nozzle plate  31  and the shroud plate  41  when turning (opening/closing). As a result, the turbo performance can be improved. That is, the turbine efficiency can be enhanced. 
         [0066]    Incidentally, the invention can be embodied into other embodiments thereof, which will be described below. The outlet  44  of the exhaust gas E in the gap G may be provided at a spot that is different from the spot of the foregoing embodiment of the invention, on the condition that the outlet  44  be located upstream of the turbine wheel  26  with respect to the flow of exhaust gas. This spot may be a spot that is located more upstream with respect to the flow of exhaust gas and nearer to the shafts  32  than in the foregoing embodiment of the invention. Besides, this spot may be located upstream of the shafts  32  with respect to the flow of exhaust gas. 
         [0067]    The shroud plate  41  may be arranged in contact with the bulge portion  18 . In addition, the passage  43  having the outlet  44  may be provided in a boundary region between the shroud plate  41  and the bulge portion  18 . 
         [0068]    The shroud plate  41  in the foregoing embodiment of the invention may be provided with the passage  43  having the outlet  44 . The bulge portion  18  may be provided integrally with the shroud plate  41  instead of being provided integrally with the turbine housing  14 , and the shroud plate  41  having this bulge portion  18  may be provided with the passage  43  having the outlet  44 . 
         [0069]    The bulge portion  18  may be provided with the passage  43  having the outlet  44 . The passage  43  may not necessarily be provided parallel to the axis L 1 , but may be provided inclined with respect to the axis L 1 . 
         [0070]    The passage  43  may not necessarily be annular. Passages  43  may be provided on the circle around the axis L 1  at a plurality of spots that are spaced apart from one another in the circumferential direction. Contrary to the foregoing embodiment of the invention, the disc spring  50  may be held in contact, at the inner peripheral edge portion  51  thereof, with the shroud plate  41 , and may be held in contact, at the outer peripheral edge portion  52  thereof, with the inner wall surface  14 A of the turbine housing  14 . In this case, however, the inner peripheral edge portion  51  of the disc spring  50  is held in contact with the shroud plate  41  upstream of the through-holes  42  with respect to the flow of exhaust gas. 
         [0071]    The disc spring  50  needs to be held in contact with the shroud plate  41  upstream of the through-holes  42  with respect to the flow of exhaust gas. However, the disc spring  50  may be held in contact with the turbine housing  14  at any spot thereof. For example, the disc spring  50  may be held in contact with the turbine housing  14  upstream of the through-holes  42  with respect to the flow of exhaust gas. 
         [0072]    In the case where the amount of the exhaust gas E that flows from between the pins  46  and the holes  45  is negligibly small, the disc spring  50  may be held in contact with the shroud plate  41  downstream of the holes  45  (but upstream of the through-holes  42 ) with respect to the flow of exhaust gas. 
         [0073]    The sealing member may be constituted by a member other than the member that urges the assembly body  48  of the variable nozzle mechanism  30 . For example, the sealing member may be constituted by a gasket instead of being constituted by the disc spring.