A turbocharger includes a first scroll member made of sheet metal, extending in a circumferential direction of an impeller shaft, having an opening that is opened to the bearing housing, and forming a part of a wall surface of the first turbine scroll passage, a second scroll member made of sheet metal, extending in the circumferential direction of the impeller shaft, having an opening that is opened to the bearing housing, and forming a part of a wall surface of the second turbine scroll passage, and a closing member closing the opening of the first scroll member and forming the wall surface of the first turbine scroll passage on the side thereof adjacent to the bearing housing, and closing the opening of the second scroll member and forming the wall surface of the second turbine scroll passage on the side thereof adjacent to the bearing housing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2019-056681 filed on Mar. 25, 2019, the entire disclosure of which is incorporated herein by reference.

BACKGROUND ART

The present disclosure relates to a turbocharger.

A housing of a turbocharger includes a bearing housing that rotatably supports an impeller shaft, a turbine housing that is connected to one end of the bearing housing and in which exhaust gas discharged from an internal combustion engine flows, and a compressor housing that is connected to the other end of the bearing housing and in which intake air to be introduced to the internal combustion engine flows.

A turbine chamber is formed in the turbine housing. The turbine chamber accommodates a turbine impeller that is connected to one end of the impeller shaft and that rotates integrally with the impeller shaft by exhaust gas introduced into the turbine chamber. In addition, a turbine scroll passage that is a part of a passage that guides the exhaust gas flowing into the turbine housing to the turbine chamber is formed in the turbine housing.

A compressor impeller that is connected to the other end of the impeller shaft and rotates integrally with the turbine impeller is accommodated in the compressor housing. When the turbine impeller is rotated by the exhaust gas discharged from the internal combustion engine and the compressor impeller rotates integrally with the turbine impeller via the impeller shaft, the intake air flowing through the compressor housing is compressed by the rotation of the compressor impeller, and such compressed intake air is supplied to the internal combustion engine. The intake efficiency of the internal combustion engine is enhanced and the performance of the internal combustion engine is improved by such supercharging of the intake air to the internal combustion engine by the turbocharger.

A catalyst purifying exhaust gas is disposed downstream of the turbine housing of the turbocharger in a direction in which the exhaust gas flows. Purification of exhaust gas by the catalyst is accomplished by increasing the temperature of the catalyst to its activation temperature or higher. In a case where the temperature of exhaust gas is low, the temperature of the catalyst may not increase to the activation temperature or higher, and thus exhaust gas may not be sufficiently purified.

In general, since it is necessary to ensure rigidity, the turbine housing is formed so as to have thick walls by casting, so that the turbine housing has a great mass and a great heat capacity. Thus, the heat of exhaust gas flowing through the turbine housing tends to reduce, thereby decreasing the temperature of the exhaust gas, while the exhaust gas flows through the turbine housing. As a result, it takes long to increase the temperature of the catalyst to the activation temperature or higher. This prevents increasing the temperature of the catalyst to the activation temperature or higher early when it is required to warm up the catalyst early, such as a cold start of the internal combustion engine.

International Publication No. WO 2015/097872 discloses a turbocharger in which a wall surface of a turbine scroll passage is formed by a passage forming plate of sheet metal. The passage forming plate suppresses the heat transfer from exhaust gas to the turbine housing. As a result, the temperature decrease of the exhaust gas while the exhaust gas flows through the turbine housing is suppressed.

In addition, the turbocharger of the above-cited Publication has a twin scroll structure in which a first turbine scroll passage and a second turbine scroll passage are formed. The first turbine scroll passage and the second turbine scroll passage extend annularly around the turbine chamber. In the internal combustion engine provided by a four cylinder engine, exhaust gas discharged from the first cylinder and fourth cylinder flows through the first turbine scroll passage, and exhaust gas discharged from the second cylinder and the third cylinder flows through the second turbine scroll passage. The turbocharger having twin scroll structure suppresses interference of pulsation of exhaust gas discharged from each cylinder. As a result, the performance of the turbocharger during the low speed operation may be improved. The wall surface of the first turbine scroll passage is formed by a first passage forming plate made of sheet metal. The wall surface of the second turbine scroll passage is formed by a part of the first passage forming plate different from a part thereof forming the first turbine scroll passage, and a second passage forming plate made of sheet metal.

However, the shape of the first passage forming plate becomes complex in a case where the wall surface of the first turbine scroll passage and a part of the wall surface of the second turbine scroll passage are formed by the first passage forming plate. This makes it difficult to form the first passage forming plate by press working.

The present disclosure is directed to providing a turbocharger in which a scroll structure can be easily formed.

SUMMARY

In accordance with an aspect of the present disclosure, there is provided a turbocharger including a housing including a bearing housing that rotatably supports an impeller shaft, and a turbine housing that is connected to one end of the bearing housing in a rotation axis direction of the impeller shaft and in which exhaust gas discharged from an internal combustion engine flows, a first inlet port through which the exhaust gas flows into the turbine housing, a second inlet port through which the exhaust gas flows into the turbine housing, a turbine chamber formed in the turbine housing, a turbine impeller accommodated in the turbine chamber, and rotating integrally with the impeller shaft by the exhaust gas flowing into the turbine chamber, a first turbine scroll passage that is formed in the turbine housing around a part of an outer periphery of the turbine chamber, and through which the exhaust gas flowing into the turbine housing through the first inlet port is introduced to the turbine chamber, a second turbine scroll passage that is formed in the turbine chamber around a part of the outer periphery of the turbine chamber and through which the exhaust gas flowing into the turbine housing through the second inlet port is introduced to the turbine chamber, and an annular communication passage that is formed in the turbine housing and provides communication between the first turbine scroll passage and the turbine chamber and between the second scroll passage with the turbine chamber. The turbocharger has a twin entry scroll structure in which the second turbine scroll passage communicates with the turbine chamber through a part of the communication passage that is different from a part of the communication passage through which the first turbine scroll communicates with the turbine chamber. The turbocharger includes a first scroll member, a second scroll member, and a closing member. The first scroll member is made of sheet metal, extends in a circumferential direction of the impeller shaft, has an opening that is opened to the bearing housing, and forms a part of a wall surface of the first turbine scroll passage. The second scroll member is made of sheet metal, extends in the circumferential direction of the impeller shaft, has an opening that is opened to the bearing housing, and forms a part of a wall surface of the second turbine scroll passage. The closing member closes the opening of the first scroll member and forms the wall surface of the first turbine scroll passage on the side thereof adjacent to the bearing housing, and closes the opening of the second scroll member and forms the wall surface of the second turbine scroll passage on the side thereof adjacent to the bearing housing.

Other aspects and advantages of the present disclosure will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following will describe an embodiment of a turbocharger according to the present disclosure with reference toFIGS. 1 to 5.

FIG. 1depicts a turbocharger10having a housing11that includes a bearing housing20, a turbine housing30, and a compressor housing40. The bearing housing20, the turbine housing30, and the compressor housing40are made of cast iron. Exhaust gas discharged from an internal combustion engine E flows inside the turbine housing30. Intake air to be led to the internal combustion engine E flows inside the compressor housing40. The internal combustion engine E of the present embodiment is a four-cylinder engine in which first, second, third, fourth cylinders C1, C2, C3, C4are arranged in series. Combustion takes place in the first cylinder C1, the third cylinder C3, the fourth cylinder C4, and the second cylinder C2in this order. A first exhaust manifold M1is connected to the first cylinder C1and the fourth cylinder C4, and a second exhaust manifold M2is connected to the second cylinder C2and the third cylinder C3.

The bearing housing20rotatably supports an impeller shaft12. A turbine impeller13is connected to one end of the impeller shaft12in the rotation axis direction of the impeller shaft12. Specifically, the impeller shaft12has a fitting recess12athat is formed in one end surface in the rotation axis direction of the impeller shaft12, and the turbine impeller13has a fitting projection13athat is formed extending toward the impeller shaft12and may be fitted to the fitting recess12aof the impeller shaft12. With the fitting projection13aof the turbine impeller13fitted to the fitting recess12aof the impeller shaft12, the turbine impeller13is attached to the impeller shaft12by welding or the like so that the turbine impeller13is rotatable integrally with the impeller shaft12. A compressor impeller14is connected to the other end of the impeller shaft12in the rotation axis direction of the impeller shaft12.

The turbine housing30is connected to one end of the bearing housing20in the rotation axis direction of the impeller shaft12. The compressor housing40is connected to the other end of the bearing housing20in the rotation axis direction of the impeller shaft12.

The bearing housing20includes a bearing housing body portion21having a tubular shape. The bearing housing body portion21has an insertion hole21hthrough which the impeller shaft12is inserted. The bearing housing body portion21rotatably supports the impeller shaft12inserted through the insertion hole21hvia a radial bearing15. The axial direction of the bearing housing body portion21coincides with the rotation axis direction of the impeller shaft12.

The bearing housing body portion21has a projection21cthat has a tubular shape and protrudes from one end surface21alocated at the one end of the bearing housing body portion21in the rotation axis direction of the impeller shaft12. The insertion hole21his opened at an end surface21dof the projection21c. A C-ring17is interposed between the inner peripheral surface of the insertion hole21hand the outer peripheral surface of the impeller shaft12. The C-ring17serves as a sealing member. The bearing housing body portion21has a recessed portion21ethat is formed recessed in the other end surface21blocated in the other end of the bearing housing body portion21in the rotation axis direction of the impeller shaft12. The insertion hole21his opened at the bottom surface of the recessed portion21e. The diameter of the recessed portion21eis greater than that of the insertion hole21h. The axis of the recessed portion21ecoincides with the axis of the insertion hole21h. A thrust bearing16is accommodated in the recessed portion21e. The thrust bearing16is accommodated in the recessed portion21ein contact with the bottom surface of the recessed portion21e.

The bearing housing20includes a first flange portion22that projects outwardly in the radial direction of the impeller shaft12from one end of the outer peripheral surface of the bearing housing body portion21in the axial direction thereof, and a second flange portion23that projects outwardly in the radial direction of the impeller shaft12from the other end of the outer peripheral surface of the bearing housing body portion21in the axial direction thereof. The first flange portion22and the second flange portion23have a ring shape. A projected section24having a ring shape that projects outward in the radial direction is formed at the end of the outer peripheral surface of the first flange portion22opposite from the second flange portion23. The projected section24has an end surface24athat is located opposite from the second flange portion23and is continuous with the one end surface21aof the bearing housing body portion21.

The compressor housing40has a compressor housing body portion41having a bottomed cylindrical shape. The compressor housing body portion41has a bottom wall41ahaving a substantially disc-shape and a cylindrical peripheral wall41bformed extending from the periphery of the bottom wall41ain the rotation axis direction of the impeller shaft12. One end surface of the peripheral wall41bopposite from the bottom wall41ais opened. The compressor housing40is connected to the other end of the bearing housing20in the rotation axis direction of the impeller shaft12with the end of the peripheral wall41bof the compressor housing40having an opening and the second flange portion23of the bearing housing20fixed by bolts (not shown). The opening of the peripheral wall41bis closed by the other end surface21bof the bearing housing body portion21and the end surface of the second flange portion23located opposite from the first flange portion22. In other words, the opening of the peripheral wall41bis closed by the end surface of the bearing housing20located at the other end of the bearing housing20in the rotation axis direction of the impeller shaft12.

The compressor housing40further has a compressor tubular portion42projecting opposite side of the bottom wall41afrom the peripheral wall41b. The compressor tubular portion42has an intake port42a. The intake port42aextends in the rotation axis direction of the impeller shaft12. The axis of the intake port42acoincides with the rotation axis of the impeller shaft12.

A compressor impeller chamber43, a diffuser passage44, and a compressor scroll passage45are formed in the compressor housing40, The compressor impeller chamber43is in communication with the intake port42a, and accommodates the compressor impeller14. The compressor scroll passage45is formed extending around the outer periphery of the compressor impeller chamber43in a swirl shape. The diffuser passage44extends around the compressor impeller chamber43in an annular shape, and provides communication between the compressor impeller chamber43and the compressor scroll passage45.

A compressor shroud46having a tubular shape is disposed in the compressor housing40. The compressor shroud46includes a tubular portion46aextending along the inner peripheral surface of the compressor tubular portion42, and a ring portion46bthat is formed continuous with the tubular portion46a, extending along the inner bottom surface of the bottom wall41ain an annular shape. The compressor impeller chamber43is a space surrounded by the tubular portion46aof the compressor shroud46and the recessed portion21eof the bearing housing20.

The compressor impeller14has a shaft insertion hole14hthat extends in the rotation axis direction of the impeller shaft12and through which the impeller shaft12is inserted. The other end of the impeller shaft12in the rotation axis direction thereof projects out in the compressor impeller chamber43. The compressor impeller14is attached to the impeller shaft12by a nut (not shown) or the like so as to be rotatable integrally with the impeller shaft12with a portion of the impeller shaft12projecting out in the compressor impeller chamber43inserted into the shaft insertion hole14h. An end of the compressor impeller14on the bearing housing20side is supported by the thrust bearing16via a seal ring collar and a thrust collar (neither shown). The thrust bearing16receives a load in the thrust direction acting on the compressor impeller14.

The ring portion46bof the compressor shroud46has a surface46cfacing the bearing housing20, which is a flat surface extending in the radial direction of the impeller shaft12. The diffuser passage44is formed between the surface46cof the ring portion46band a part of the end surface of the bearing housing20that is located at the other end in the rotation axis direction of the impeller shaft12and facing the surface46cof the ring portion46bin the rotation axis direction of the impeller shaft12.

A compressor scroll member47having an annular shape is disposed in the compressor housing40. The compressor scroll member47extends around the compressor shroud46. The compressor scroll passage45is formed by the outer peripheral surface of the ring portion46bof the compressor shroud46, the inner bottom surface of the bottom wall41aof the compressor housing body portion41, and the inner peripheral surface of the compressor scroll member47. It is noted that the compressor scroll member47and the compressor shroud46need not be necessarily formed separately from the compressor housing40, but may be formed integrally with the compressor housing40.

As shown inFIGS. 2 and 3, the turbine housing30has a turbine housing body portion31having an annular shape surrounding the turbine impeller13. The turbine housing body portion31has an outer peripheral wall31a, an inner peripheral wall31b, and a connecting wall31c. The outer peripheral wall31aand the inner peripheral wall31bextend in the rotation axis direction of the impeller shaft12. The inner peripheral wall31bis located inward of the outer peripheral wall31ain the radial direction of the impeller shaft12. The connecting wall31cconnects an end of the outer peripheral wall31alocated on the side thereof opposite from the bearing housing20in the rotation axis direction of the impeller shaft12and an end of the inner peripheral wall31blocated on the side thereof opposite from the bearing housing20in the rotation axis direction of the impeller shaft12, in the radial direction of the impeller shaft12. The connecting wall31chas a curved in an arc, which is convex away from the bearing housing20. The surface of the turbine housing body portion31opposite from the connecting wall31chas an opening. In other words, the turbine housing body portion31is opened to the bearing housing20.

The outer peripheral wall31ahas an end surface31dthat is located on the side thereof that is adjacent to the bearing housing20in the rotation axis direction of the impeller shaft12. The inner peripheral wall31bhas an end surface31ethat is located on the side thereof that is adjacent to the bearing housing20in the rotation axis direction of the impeller shaft12. The end surface31dof the outer peripheral wall31aprojects further than the end surface31eof the inner peripheral wall31btoward the bearing housing20in the rotation axis direction of the impeller shaft12. A flange31fis formed in the outer peripheral surface of the outer peripheral wall31aat an end thereof that is opposite from the connecting wall31c. The flange31fhas a ring shape projecting radially outwardly from the outer peripheral surface of the outer peripheral wall31a. An end surface31gof the flange31flocated on the side thereof that is opposite from the connecting wall31cis formed continuously with the end surface31dof the turbine housing body portion31.

The turbine housing30includes a turbine tubular portion32, extending from the inner peripheral wall31bof the turbine housing body portion31in a direction opposite from the bearing housing20. The turbine tubular portion32has a shape whose diameter increases as separated away from the bearing housing20. An end of the turbine tubular portion32opposite from the turbine housing body portion31is connected to a downstream exhaust pipe (not shown). The downstream exhaust pipe connects between the turbocharger10and a catalyst (not shown) disposed downstream of the turbine housing30in a direction in which exhaust gas flows. The catalyst purifies exhaust gas. Increasing the temperature of the catalyst to its activation temperature or higher, the catalyst purifies exhaust gas.

The turbine housing30is connected to the one end of the bearing housing20in the rotation axis direction of the impeller shaft12by fixing the flange31fand the projected section24with bolts B1in a state that the end surface31gof the flange31fof the turbine housing body portion31and the end surface24aof the projected section24of the bearing housing20are in contact with each other.

As shown inFIG. 3, a first inlet port33aand a second inlet port33bare formed in the turbine housing30to introduce exhaust gas discharged from the internal combustion engine E into the turbine housing30. The first inlet port33ais connected to the second exhaust manifold M2, and the second inlet port33bis connected to the first exhaust manifold M1. A turbine chamber34is formed in the turbine housing30. The turbine impeller13is accommodated in the turbine chamber34.

As shown inFIGS. 2 and 3, the turbine housing30has a first turbine scroll passage35through which exhaust gas flowing into the turbine housing30from the first inlet port33ais introduced to the turbine chamber34, and a second turbine scroll passage36through which exhaust gas flowing into the turbine housing30from the second inlet port33bis introduced to the turbine chamber34. The first turbine scroll passage35and the second turbine scroll passage36are formed around the outer periphery of the turbine chamber34, respectively. The first turbine scroll passage35surrounds about a half of the circumference of the turbine chamber34in the circumferential direction of the impeller shaft12. In other words, the first turbine scroll passage is formed in the turbine housing30around a part of the outer periphery of the turbine chamber34. The second turbine scroll passage36surrounds about a half of the circumference of the turbine chamber34in the circumferential direction of the impeller shaft12where it is not surrounded by the first turbine scroll passage35. In other words, second turbine scroll passage36is formed in the turbine housing30around a part of the outer periphery of the turbine chamber34.

A communication passage37having an annular shape is formed in the turbine housing30. The communication passage37provides communication between the first turbine scroll passage35and the turbine chamber34, and also between the second turbine scroll passage36and the turbine chamber34. The communication passage37surrounds the entire circumference of the turbine chamber34. In the radial direction of the impeller shaft12, the communication passage37is located between the turbine chamber34and the first turbine scroll passage35or between the turbine chamber34and the second turbine scroll passage36. About a half of the communication passage37in the circumferential direction thereof communicates with the first turbine scroll passage35, and the remaining half of the communication passage37communicates with the second turbine scroll passage36. Thus, the first turbine scroll passage35is in communication with the turbine chamber34through about the half of the communication passage37in the circumferential direction thereof, and the second turbine scroll passage36is in communication with the turbine chamber34through the remaining half of the communication passage37in the circumferential direction thereof. In other words, the second turbine scroll passage36communicates with the turbine chamber34through a part of the communication passage37that is different from a part of the communication passage37through which the first turbine scroll passage35communicates with the turbine chamber34. Thus, the turbocharger10has a twin entry scroll structure.

As shown inFIG. 2, the turbine housing30has a connecting passage38through which the second inlet port33band the second turbine scroll passage36are in communication with each other. The connecting passage38is formed around the outer periphery of the turbine chamber34. The connecting passage38surrounds about a half circumference of the turbine chamber34where it is surrounded by the first turbine scroll passage35. Thus, the connecting passage38extends along the first turbine scroll passage35. The turbine housing30has an outlet port39through which exhaust gas flowing through the turbine chamber34is discharged to the outside the turbine housing30.

A turbine shroud portion51is provided in the turbine housing30. The turbine shroud portion51includes a tubular portion51aextending along the outer surface of the inner peripheral wall31bof the turbine housing body portion31opposite from the outer peripheral wall31a, and a ring portion51bextending in an annular shape along the end surface31eof the turbine housing body portion31while continuing to the tubular portion51a.

As shown inFIGS. 4 and 5, the turbocharger10includes a first scroll member52made of sheet metal. The thickness of the first scroll member52is smaller than that of the turbine housing30. The first scroll member52is formed by pressing a metal sheet. The first scroll member52has a first ring part53and a first passage forming part54that is continuous with the outer peripheral edge of the first ring part53and is located outward of the first ring part53. As shown inFIGS. 2 and 3, the first ring part53has a flat plate shape extending in the radial direction of the impeller shaft12. The first ring part53is an inner peripheral end portion of the first scroll member52.

The first passage forming part54is formed extending over the half of the first ring part53in the circumferential direction thereof. The first passage forming part54includes a first outer peripheral portion54a, a first inner peripheral portion54b, and a first connecting portion54c. The first outer peripheral portion54aand the first inner peripheral portion54bextend in the rotation axis direction of the impeller shaft12. The first inner peripheral portion54bis located inward of the first outer peripheral portion54a. The first connecting portion54cconnects an end of the first outer peripheral portion54aopposite from the bearing housing20in the rotation axis direction of the impeller shaft12and an end of the first inner peripheral portion54bopposite from the bearing housing20in the rotation axis direction of the impeller shaft12. In other words, the first connecting portion54cconnects the first outer peripheral portion54aand the first inner peripheral portion54bin a radial direction of the impeller shaft12. The first connecting portion54chas a curved in an arc, which is convex away from the bearing housing20. A surface of the first passage forming part54opposite from the first connecting portion54cis opened. In other words, the first passage forming part54is opened to the bearing housing20. A first rib54dis formed at the end of the first outer peripheral portion54aopposite from the first connecting portion54c. The first rib54dprojects radially outwardly. The first rib54dis an outer peripheral end portion of the first scroll member52, and the tip end portion54xof the first rib54dis an outer peripheral side edge portion of the first scroll member52.

As shown inFIG. 5, the distance from the first outer peripheral portion54ato the first inner peripheral portion54bin the radial direction of the first ring part53reduces toward the other end542from the one end541in the circumferential direction of the first passage forming part54. In addition, the distance from the first rib54dto the first connecting portion54cin the rotation axis direction of the impeller shaft12reduces toward the other end542from the one end541in the circumferential direction of the first passage forming part54.

The turbocharger10includes a first inlet port forming member55that has a half cylindrical shape, and is formed integrally with the first scroll member52. The first inlet port forming member55includes a first bottom portion55athat is continuous with the first connecting portion54cat the one end541of the first passage forming part54in the circumferential direction thereof. The first bottom portion55ahas a first through hole55hhaving a semicircular shape. The first inlet port forming member55includes a first outer wall55bthat is formed standing from one edge of the first bottom portion55aand continuous with the first outer peripheral portion54a, and a first inner wall55cthat is formed standing from the other edge of the first bottom portion55athat is opposite from the one edge from which the first outer wall55bthat is formed standing and continuous with the first inner peripheral portion54b. The first inner wall55chas a recess that is recessed toward the first bottom portion55ain a part of one end of the first inner wall55copposite from the first bottom portion55aat a position adjacently to the first inner peripheral portion54b. A surface of the first inlet port forming member55opposite from the first bottom portion55ais opened. In other words, the first inlet port forming member55is opened to the bearing housing20. The first outer wall55bhas a first rib section55dat an end opposite from the first bottom portion55athat projects in a direction away from the first inner wall55cand formed continuously with the first rib54d.

As shown inFIGS. 4 and 5, the turbocharger10includes a second scroll member56made of sheet metal. The thickness of the second scroll member56is smaller than that of the turbine housing30. The second scroll member56is formed by pressing a metal sheet. The second scroll member56has a second ring part57and a second passage forming part58that is continuous with the outer peripheral edge of the second ring part57and is located outward of the second ring part57. The second passage forming part58has an annular shape. As shown inFIGS. 2 and 3, the second ring part57has a plate shape extending in the radial direction of the impeller shaft12. The second ring part57is an inner peripheral end portion of the second scroll member56.

The second passage forming part58includes a second outer peripheral portion58a, a second inner peripheral portion58b, and a second connecting portion58c. The second outer peripheral portion58aand the second inner peripheral portion58bextend in the rotation axis direction of the impeller shaft12. The second inner peripheral portion58bis located inward of the second outer peripheral portion58a. The second connecting portion58cconnects an end of the second outer peripheral portion58aopposite from the bearing housing20in the rotation axis direction of the impeller shaft12and an end of the second inner peripheral portion58bopposite from the bearing housing20in the rotation axis direction of the impeller shaft12. In other words, the second connecting portion58cconnects the second outer peripheral portion58aand the second inner peripheral portion58bin the radial direction of the impeller shaft12. The second connecting portion58chas a shape curved in an arc, which is convex away from the bearing housing20. The second inner peripheral portion58band the second connecting portion58care formed extending the entire circumference around the second ring part57, and the second outer peripheral portion58aextends the three quarter around the second ring part57. In other words, the second outer peripheral portion58ais not formed in a part of the circumference of the second passage forming part58. A surface of the second passage forming part58opposite from the second connecting portion58cis opened. In other words, the second passage forming part58is opened to the bearing housing20. A second rib58dis formed at the end of the second outer peripheral portion58aopposite from the second connecting portion58c. The second rib58dprojects radially outwardly. The second rib58dis an outer peripheral end portion of the second scroll member56, and the tip end portion58xof the second rib58dis an outer peripheral side edge portion of the second scroll member56.

The distance from the second outer peripheral portion58ato the second inner peripheral portion58bin the radial direction of the second ring part57is always greater than the distance from the first outer peripheral portion54ato the first inner peripheral portion54bin the radial direction of the first ring part53. The distance from the second rib58dto the second connecting portion58cin the rotation axis direction of the impeller shaft12gradually reduces along the second ring part57. The distance from the second rib58dto the second connecting portion58cin the rotation axis direction of the impeller shaft12is always greater than the distance from the first rib54dto the first connecting portion54c.

The turbocharger10includes a second inlet port forming member59that has a half cylindrical shape, and is formed integrally with the second scroll member56. The second inlet port forming member59includes a second bottom portion59athat is continuous with the second connecting portion58cin the circumferential direction of the second passage forming part58. The second bottom portion59ahas a second through hole59hhaving a circular shape. The second inlet port forming member59includes a second outer wall59bthat is formed standing from one edge of the second bottom portion59a, and a second inner wall59cthat is formed standing from the other edge of the second bottom portion59aon the side opposite from the edge from which the second outer wall59bis formed standing. The second outer wall59bis continuous with one end of the second outer peripheral portion58ain the circumferential direction thereof. The second inner wall59cis continuous with a part of the second connecting portion58cof the second passage forming part58where the second outer peripheral portion58ais not formed, and a part of the second inner wall59cis continuous with one end of the second rib58dopposite from the second outer peripheral portion58ain the circumferential direction thereof. A surface of the second inlet port forming member59opposite from the second bottom portion59ais opened. In other words, the second inlet port forming member59is opened to the bearing housing20. The second outer wall59bhas a second rib section59dat an end opposite from the second bottom portion59athat projects in a direction away from the second inner wall59cand formed continuously with the second rib58d. The second inlet port forming member59has a shape in which the distance between the second outer wall59band the second inner wall59cbecomes greater from the opening connected to the one end of the second outer peripheral portion58ain the circumferential direction to the other opening. At a part where the distance between the second outer wall59band the second inner wall59cis large, such distance is greater than the distance between the first outer wall55band the first inner wall55c.

As shown inFIG. 2, the first scroll member52and the second scroll member56extend in the circumferential direction of the impeller shaft12, respectively. The first passage forming part54extends in a swirl shape and outward of the turbine chamber34over a half circumference thereof in the circumferential direction of the impeller shaft12. The second passage forming part58extends in a swirl shape and outward of the turbine chamber34over the entire circumference thereof in the circumferential direction of the impeller shaft12.

The second passage forming part58of the second scroll member56is disposed in a space surrounded by the outer peripheral wall31a, the inner peripheral wall31b, and the connecting wall31cof the turbine housing body portion31. A gap is formed between the inner surface of the outer peripheral wall31aand the outer surface of the second outer peripheral portion58a. A gap is formed between the inner surface of the inner peripheral wall31badjacent to the outer peripheral wall31aand the outer surface of the second inner peripheral portion58b. A gap is formed between the inner surface of the connecting wall31cand the outer surface of the second connecting portion58c, That is, the second passage forming part58of the second scroll member56is accommodated in the turbine housing body portion31with the second passage forming part58spaced from the turbine housing body portion31. A space between the second passage forming part58and the turbine housing body portion31serves as a first heat insulation layer71. The second ring part57of the second scroll member56overlaps the end surface31eof the turbine housing body portion31in the rotation axis direction of the impeller shaft12, The second rib58dcorresponds to a free end of the second scroll member56. The tip end portion58xof the second rib58dis spaced from the outer peripheral wall31aof the turbine housing body portion31in the radial direction of the impeller shaft12. The outer peripheral wall31ais a facing member that faces the tip end portion58xof the second rib58d. The tip end portion58xof the second rib58dcorresponds to a free end edge portion.

The first passage forming part54of the first scroll member52is accommodated in a space surrounded by the second outer peripheral portion58a, the second inner peripheral portion58b, and the second connecting portion58cof the second passage forming part58of the second scroll member56. A gap is formed between the inner surface of the second outer peripheral portion58aand the outer surface of the first outer peripheral portion54a. A slight gap is formed between the inner surface of the second inner peripheral portion58badjacent to the second outer peripheral portion58aand the outer surface of the first inner peripheral portion54b. A gap is formed between the inner surface of the second connecting portion58cand the outer surface of the first connecting portion54c. Thus, the first passage forming part54of the first scroll member52is accommodated in the second passage forming part58with the first passage forming part54of the first scroll member52spaced from the second passage forming part58of the second scroll member56. The first ring part53of the first scroll member52overlaps the second ring part57of the second scroll member56in the rotation axis direction of the impeller shaft12. The first rib54dcorresponds to a free end of the first scroll member52. In addition, the tip end portion54xof the first rib54dfaces the second rib58dof the second scroll member56with the tip end portion54xspaced from the second rib58dof the second scroll member56in the radial direction of the impeller shaft12. The second rib58dis a facing member that faces the tip end portion54xof the first rib54d. The tip end portion54xof the first rib54dis a free end edge portion.

As shown inFIG. 5, the first scroll member52lays on the second scroll member56so that the distance from the second rib58dto the second connecting portion58cin the rotation axis direction of the impeller shaft12gradually reduces from the one end541to the other end542of the first passage forming part54in the circumferential direction thereof. The first inlet port forming member55is accommodated in a space surrounded by the second bottom portion59a, the second outer wall59b, and the second inner wall59cof the second inlet port forming member59. At a part where the distance between the second outer wall59band the second inner wall59cis large, the first inlet port forming member55is located adjacent to the second inner wall59c, and the outer surface of the first outer wall55bis spaced from the inner surface of the second outer wall59b.

The first through hole55hof the first inlet port forming member55is in communication with about the half of the second through hole59hof the second inlet port forming member59. The first through hole55hand the second through hole59hmay be opened and closed by a valve (not shown). The valve closes the first through hole55hand the second through hole59hduring the normal operation of the turbocharger10. The valve reduces the amount of exhaust gas flowing into the turbine chamber34by opening the first through hole55hand the second through hole59hwhen there is a fear that the impeller shaft12may over-rotates in a case where excessive amount of exhaust gas flows into the turbine chamber34.

As shown inFIGS. 2 and 3, a first elastic member72is interposed between the second outer peripheral portion58aof the second passage forming part58and the outer peripheral wall31aof the turbine housing body portion31in the radial direction of the impeller shaft12. The first elastic member72has an annular shape, and is mounted on the second outer peripheral portion58aof the second passage forming part58. In the present embodiment, the first elastic member72is provided by a wire mesh, and is welded to the second outer peripheral portion58aof the second passage forming part58by micro spot welding. The first elastic member72is disposed between the second outer peripheral portion58aof the second passage forming part58and the outer peripheral wall31aof the turbine housing body portion31in a state that is pressed and deformed. The second outer peripheral portion58aof the second passage forming part58is supported by the turbine housing body portion31via the first elastic member72.

The first ring part53of the first scroll member52and the second ring part57of the second scroll member56are disposed between the other end surface512of the ring portion51bof the turbine shroud portion51located adjacent to the tubular portion51a, and the end surface31eof the turbine housing body portion31in the rotation axis direction of the impeller shaft12.

The turbocharger10has a passage forming plate60having an annular shape and disposed between the bearing housing20and the first scroll member52, and between the bearing housing20and the second scroll member56in the rotation axis direction of the impeller shaft12. The passage forming plate60is made of sheet metal, and the thickness of the passage forming plate60is smaller than that of the turbine housing30. The passage forming plate60is disposed outward of the turbine impeller13in the radial direction of the impeller shaft12. The passage forming plate60covers an opening S1of the first passage forming part54, a part S2of an opening of the second passage forming part58where it is not closed by the first passage forming part54and a gap S3between the first outer peripheral portion54aof the first passage forming part54and the second outer peripheral portion58aof the second passage forming part58, which are shown inFIGS. 2, 3, and 5, from the bearing housing20side. Thus, the passage forming plate60corresponds to a closing member that covers the opening of the first passage forming part54and the opening of the second passage forming part58. In addition, as shown inFIG. 3, the passage forming plate60covers the opening of the first inlet port forming member55and the opening of the second inlet port forming member59from the bearing housing20side. The passage forming plate60includes a first end surface60a, and a second end surface60b. The first end surface60afaces the one end surface21aof the bearing housing body portion21of the bearing housing20, and the second end surface60bpartially faces the first connecting portion54cof the first passage forming part54, the second connecting portion58cof the second passage forming part58, the first bottom portion55aof the first inlet port forming member55, and the second bottom portion59aof the second inlet port forming member59.

The passage forming plate60includes an outer peripheral end portion60cthat is disposed between the one end surface21aof the bearing housing body portion21of the bearing housing20and the first rib54d, and the between the one end surface21aof the bearing housing body portion21of the bearing housing20and the second rib58d. The outer peripheral end portion60cof the passage forming plate60is spaced from the one end surface21aof the bearing housing body portion21, and in contact with the first rib54dand the second rib58d. Thus, the outer peripheral end portion60cof the passage forming plate60is a free end. In addition, the passage forming plate60includes an outer peripheral edge portion60dthat faces the outer peripheral wall31aof the turbine housing body portion31with a gap formed therebetween in the radial direction of the impeller shaft12. In other words, the outer peripheral edge portion60dof the passage forming plate60is spaced from the outer peripheral wall31aof the turbine housing body portion31.

A plurality of spacers61is interposed between an inner peripheral end portion60eof the passage forming plate60and the ring portion51bof the turbine shroud portion51in the rotation axis direction of the impeller shaft12. The spacers61are arranged at predetermined intervals in the circumferential direction of the communication passage37. The spacers61maintains a space between the one end surface511of the ring portion51bof the turbine shroud portion51and the second end surface60bof the passage forming plate60in the rotation axis direction of the impeller shaft12.

A second elastic member73is interposed between the outer peripheral end portion60cof the passage forming plate60and the bearing housing body portion21of the bearing housing20in the rotation axis direction of the impeller shaft12. The second elastic member73is disposed at a position where the outer peripheral end portion60cof the passage forming plate60is located in the radial direction of the impeller shaft12. The second elastic member73has an annular shape and is attached to the first end surface60aof the passage forming plate60. In the present embodiment, the second elastic member73is provided by a wire mesh, and is welded to the first end surface60aof the passage forming plate60by micro spot welding. The second elastic member73is disposed between the one end surface21aof the bearing housing body portion21of the bearing housing20and the first end surface60aof the passage forming plate60in a state that is pressed and deformed. The outer peripheral end portion60cof the passage forming plate60is supported by the bearing housing20via the second elastic member73.

A plate spring62having an annular shape is interposed between the first end surface60aof the passage forming plate60and the one end surface21aof the bearing housing body portion21of the bearing housing20in the rotation axis direction of the impeller shaft12. The plate spring62is disposed inward of the first passage forming part54and the second passage forming part58in the radial direction of the impeller shaft12. An inner peripheral part of the plate spring62is in contact with the one end surface21aof the bearing housing body portion21of the bearing housing20, and an inner peripheral edge of the plate spring62faces the outer peripheral surface of the projection21cin the radial direction of the impeller shaft12. An outer peripheral part of the plate spring62is in contact with part of the first end surface60aof the passage forming plate60forming the inner peripheral end portion60e.

The plate spring62is held between the bearing housing body portion21of the bearing housing20and the passage forming plate60in a state where the plate spring62is compressed in the rotation axis direction of the impeller shaft12with respect to the pre-deformed original shape. Thus, the plate spring62urges the inner peripheral end portion60eof the passage forming plate60in a direction opposite from the bearing housing20, that is, toward the spacer61, by its reaction force to return to the pre-deformed original shape. Accordingly, the second ring part57of the second scroll member56, the first ring part53of the first scroll member52, the ring portion51bof the turbine shroud portion51, the spacer61, and the inner peripheral end portion60eof the passage forming plate60are pressed against the end surface31eof the turbine housing body portion31, and supported by end surface31e. The first scroll member52and the second scroll member56are supported by the turbine housing30with the first ring part53and the second ring part57held between the other end surface512of the ring portion51bof the turbine shroud portion51and the end surface31eof the turbine housing body portion31. Thus, the first ring part53is a fixed end in the first scroll member52and the second ring part57is a fixed end in the second scroll member56. The inner peripheral end portion60eof the passage forming plate60is held between the bearing housing body portion21of the bearing housing20and the spacer61via the plate spring62.

The turbine chamber34is a space surrounded by the inner peripheral surface of the tubular portion51aof the turbine shroud portion51, the end surface21dof the projection21c, and the surface of the plate spring62on the passage forming plate60side. The communication passage37is a space formed between the one end surface511of the ring portion51bof the turbine shroud portion51and a part of the second end surface60bof the passage forming plate60forming the inner peripheral end portion60e. Thus, the part of the second end surface60bof the passage forming plate60forming the inner peripheral end portion60eforms the wall surface of the communication passage37on the bearing housing20side, and the one end surface511of the ring portion51bof the turbine shroud portion51forms the wall surface of the communication passage37on the side opposite from the bearing housing20.

As shown inFIG. 3, the first inlet port33ais a space surrounded by the inner surface of the first bottom portion55a, the inner surface of the first outer wall55b, the inner surface of the first inner wall55cof the first inlet port forming member55, and a part of the second end surface60bof the passage forming plate60facing the first bottom portion55aof the first inlet port forming member55. The second inlet port33bis a space surrounded by the outer surface of the first bottom portion55a, the outer surface of the first outer wall55b, the outer surface of the first inner wall55cof the of the first inlet port forming member55, the surface of the first rib section55dfacing the first bottom portion55a, the inner surface of the second bottom portion59a, the inner surface of the second outer wall59b, the second inner wall59cof the second inlet port forming member59, and the second end surface60bof the passage forming plate60.

As shown inFIG. 2, the first turbine scroll passage35is a space surrounded by the inner surface of the first outer peripheral portion54aof the first passage forming part54, the inner surface of the first inner peripheral portion54b, the inner surface of the first connecting portion54cof the first passage forming part54, and a part of the second end surface60bof the passage forming plate60facing the first passage forming part54. Thus, the passage forming plate60forms the wall surface of the first turbine scroll passage35on the bearing housing20side. The cross sectional area of the first turbine scroll passage35gradually reduces from an end thereof adjacent to the first inlet port33atowards an end thereof adjacent to the turbine chamber34in the circumferential direction of the impeller shaft12.

The connecting passage38is a space surrounded by the outer surface of the first passage forming part54of the first scroll member52, the inner surface of the second passage forming part58of the second scroll member56, and a part of the second end surface60bof the passage forming plate60covering the gap S3between the first outer peripheral portion54aand the second outer peripheral portion58a. The cross sectional area of the connecting passage38is constant from an end thereof adjacent to the second inlet port33btoward and end thereof adjacent to the second turbine scroll passage36in the circumferential direction of the impeller shaft12.

As shown inFIG. 3, the second turbine scroll passage36is a space surrounded by the inner surface of the second outer peripheral portion58a, the inner surface of the second inner peripheral portion58b, a part of the inner surface of the second connecting portion58cof the second passage forming part58of the second scroll member56not facing the first scroll member52, and a part of the second end surface60bof the passage forming plate60facing the second scroll member56. The cross sectional areal of the second turbine scroll passage36gradually reduces from an end thereof adjacent to the connecting passage38toward an end thereof adjacent to the turbine chamber34in the circumferential direction of the impeller shaft12.

The turbocharger10includes an outlet port forming member63having a tubular shape that is disposed inside the turbine tubular portion32and forms a wall surface of the outlet port39. The outlet port forming member63is made of sheet metal, and the thickness of the outlet port forming member63is smaller than that of the turbine housing30. Thus, the passage forming plate60forms the wall surface of the second turbine scroll passage36on the bearing housing20side. The outer peripheral surface of the outlet port forming member63is spaced from the inner peripheral surface of the turbine tubular portion32. A space between the outer peripheral surface of the outlet port forming member63and the inner peripheral surface of the turbine tubular portion32serves as the second heat insulation layer74.

The following will describe the operation of the present embodiment.

Exhaust gas discharged from the second cylinder C2and the third cylinder C3of the internal combustion engine E through the second exhaust manifold M2is led to the first turbine scroll passage35through the first inlet port33a. The exhaust gas led to the first turbine scroll passage35is introduced into the turbine chamber34through the communication passage37. Exhaust gas discharged from the first cylinder C1and the fourth cylinder C4of the internal combustion engine E through the first exhaust manifold M1is led to the second turbine scroll passage36through the second inlet port33band the connecting passage38. The exhaust gas led to the second turbine scroll passage36is introduced to the turbine chamber34through the communication passage37. While the exhaust gas flows through the connecting passage38and the second turbine scroll passage36, the first heat insulation layer71suppresses transfer of heat from the exhaust gas to the turbine housing body portion31of the turbine housing30.

With the exhaust gas introduced into the turbine chamber34, the turbine impeller13rotates. With the rotation of the turbine impeller13, the compressor impeller14rotates integrally with the turbine impeller13via the impeller shaft12. With the rotation of the compressor impeller14, intake air introduced into the compressor impeller chamber43through the intake port42ais compressed, which is decelerated while passing through the diffuser passage44, and velocity energy of the intake air is converted to pressure energy. Then, the high-pressured intake air is discharged to the compressor scroll passage45, and is supplied to the internal combustion engine E. Such supercharging of the intake air to the internal combustion engine E by the turbocharger10enhances the intake efficiency of the internal combustion engine E to thereby improve the performance of the internal combustion engine E. Exhaust gas flowing through the turbine chamber34flows out from the outlet port39and is led to the catalyst through the downstream exhaust pipe, and is purified by the catalyst. The second heat insulation layer74suppresses the heat transfer from the exhaust gas to the turbine tubular portion32of the turbine housing30while exhaust gas flowing through the outlet port39.

The following will describe the effects of the present embodiment.

(1) Part of the wall surface of the first turbine scroll passage35is formed by the first scroll member52made of sheet metal, and part of the wall surface of the second turbine scroll passage36is formed by the second scroll member56made of sheet metal. The shapes of the first scroll member52and the second scroll member56may be simplified by providing a member forming the part of the wall surface of the first turbine scroll passage35and a member forming the part of the wall surface of the second turbine scroll passage36, separately. This configuration facilitates manufacturing the first scroll member52and the second scroll member56by pressing. As a result, the scroll structure may be manufactured easily.
(2) The first scroll member52and the second scroll member56may be assembled by only placing the first passage forming part54of the first scroll member52in a space surrounded by the second outer peripheral portion58aof the second passage forming part58, the second inner peripheral portion58b, and the second connecting portion58cof the second scroll member56.
(3) The connecting passage38is formed between the first connecting portion54cof the first passage forming part54and the second connecting portion58cof the second passage forming part58, and is disposed side by side with the first turbine scroll passage35in the rotation axis direction of the impeller shaft12. This configuration permits securing the cross sectional area of the connecting passage38in the rotation axis direction of the impeller shaft12, so that the area of the connecting passage38where it is disposed side by side with the first turbine scroll passage35in the radial direction of the impeller shaft12may be small. Therefore, the turbocharger10may be downsized in the radial direction of the impeller shaft12.
(4) The first scroll member52and the second scroll member56are supported by the turbine housing30with the first ring part53and the second ring part57held between the ring portion51bof the turbine shroud portion51and the inner peripheral wall31bof the turbine housing body portion31. Therefore, the positional relationship between the first scroll member52and the second scroll member56may be determined without integrating the first scroll member52and the second scroll member56by welding.
(5) In the first scroll member52, the first rib54dis a free end, and the tip end portion54xof the first rib54dfaces the second rib58dof the second scroll member56in a state that the tip end portion54xis spaced from the second rib58d. This configuration allows the heat expansion of the first scroll member52, which occurs when the first scroll member52is warmed by the heat of the exhaust gas flowing through the first turbine scroll passage35. Similarly, in the second scroll member56, the second rib58dis a free end, and the tip end portion58xof the second rib58dfaces the outer peripheral wall31aof the turbine housing body portion31in a state that the tip end portion58xis spaced from the outer peripheral wall31a. This configuration allows the heat expansion of the second scroll member56, which occurs when the second scroll member56is warmed by the heat of the exhaust gas flowing through the second turbine scroll passage36and the connecting passage38. As a result, the deformation of the first scroll member52and the second scroll member56, which may be caused by excessive stress locally acting on the first scroll member52and the second scroll member56may be suppressed.
(6) The twin entry structure of the turbocharger10suppresses the interference of the pulsation of the exhaust gas. As a result, the performance of the turbocharger10during the low speed operation may be improved.
(7) The surface roughness of the wall surface of the first turbine scroll passage35may be reduced by forming the wall surface of the first turbine scroll passage35by the first scroll member52made of sheet metal, as compared with the case where the wall surface of the first scroll member52is formed by the turbine housing30made of cast iron. Additionally, the surface roughness of the respective wall surfaces of the second turbine scroll passage36and the connecting passage38may be reduced by forming the wall surfaces of the second turbine scroll passage36and the connecting passage38by the second scroll member56made of sheet metal, as compared with the case where the wall surface of the second turbine scroll passage36and the connecting passage38is formed by the turbine housing30made of cast iron. This increases the efficiency of the turbocharger10.
(8) The first heat insulation layer71is provided between the second passage forming part58of the second scroll member56and the turbine housing body portion31. The provision of the first heat insulation layer71suppresses transfer of the heat of the exhaust gas flowing through the connecting passage38and the second turbine scroll passage36to the turbine housing body portion31. Further, the second heat insulation layer74is provided between the outlet port forming member63and the turbine tubular portion32. This permit using cast iron, which has inferior heat resistance but is lower in price than cast steel, as a material for the turbine housing30. As a result, the manufacturing cost of the turbocharger10may be reduced.

The present embodiment may be modified in various manners, as exemplified below. The above-described embodiment and the modification may be implemented in combination with each other within the scope of the present disclosure.

The shapes of the first scroll member52and the second scroll member56may be modified into those shown inFIGS. 6 through 9.

InFIG. 6, the outer surface of the first connecting portion54cof the first scroll member52is in contact with the inner surface of the second connecting portion58cof the second scroll member56in the rotation axis direction of the impeller shaft12. It is noted that the shape of the second scroll member56shown inFIG. 6is the same as the second scroll member56of the above-described embodiment. In this case, the connecting passage38is formed between the outer surface of the first outer peripheral portion54aof the first scroll member52and the outer surface of the second outer peripheral portion58aof the second scroll member56, and between a radially outward part of the outer surface of the first connecting portion54cand a radially outward part of the outer surface of the second connecting portion58c. Thus, a large part of the connecting passage38is formed outward of the first turbine scroll passage35in the radial direction of the impeller shaft12.

InFIG. 7, the first passage forming part54of the first scroll member52includes a peripheral wall portion54ethat extends in the rotation axis direction of the impeller shaft12, a curved portion54fthat has a curved shape and is formed continuous with an end of the peripheral wall portion54eopposite from the bearing housing20. The peripheral wall portion54ehas a first rib54dprojecting outwardly in the radial direction of the impeller shaft12and in an end of the peripheral wall portion54eadjacent to the bearing housing20. It is noted that the shape of the second scroll member56shown inFIG. 7is the same as the second scroll member56of the above-described embodiment.

The turbocharger10has a welded portion A where an end of the curved portion54fof the first scroll member52opposite from the peripheral wall portion54eand the radially central part of the second connecting portion58cof the second scroll member56are welded. The first scroll member52and the second scroll member56are integrated together with the welded portion A. The first scroll member52and the second scroll member56are supported by the turbine housing30with the second ring part57held between the end surface31eof the turbine housing body portion31and the other end surface512of the ring portion51bof the turbine shroud portion51.

Thus, the first turbine scroll passage35is a space surrounded by the inner surface of the second inner peripheral portion58bof the second scroll member56, the radially inner part of the inner surface of the second connecting portion58c, the inner surface of the peripheral wall portion54eof the first scroll member52, the inner surface of the curved portion54f, and the second end surface60bof the passage forming plate60. Since a part of the second scroll member56forms a part of the wall surface of the first turbine scroll passage35, a part where the first scroll member52and the second scroll member56overlap is reduced, as compared with the above-described embodiment. As a result, the weight of the turbocharger10may be reduced. The connecting passage38is formed between the outer surface of the peripheral wall portion54eof the first scroll member52and the inner surface of the second outer peripheral portion58aof the second scroll member56, and between the outer surface of the curved portion54fof the first scroll member52and the inner surface of the second connecting portion58cof the second scroll member56.

In the first scroll member52shown inFIG. 8, the first ring part53and the first inner peripheral portion54bare omitted, as compared with the above-described embodiment. The shape of the second scroll member56shown inFIG. 8is the same as the second scroll member56of the above-described embodiment. The turbocharger10has a welded portion A where an end of the first connecting portion54cof the first scroll member52opposite from the first outer peripheral portion54aand the second inner peripheral portion58bof the second scroll member56are welded. The first scroll member52and the second scroll member56are integrated together with the welded portion A. The first scroll member52and the second scroll member56are supported by the turbine housing30with the second ring part57held between the end surface31eof the turbine housing body portion31and the other end surface512of the ring portion51bof the turbine shroud portion51.

In this case, the first turbine scroll passage35is a space surrounded by the inner surface of the second inner peripheral portion58bof the second scroll member56, the inner surface of the first outer peripheral portion54a, the inner surface of the first connecting portion54cof the first scroll member52, and the second end surface60bof the passage forming plate60. Since a part of the second scroll member56forms a part of the wall surface of the first turbine scroll passage35, a part where the first scroll member52and the second scroll member56overlap is reduced, as compared with the above-described embodiment. As a result, the weight of the turbocharger10may be reduced. The connecting passage38is formed between the outer surface of the first outer peripheral portion54aof the first scroll member52and the inner surface of the second outer peripheral portion58aof the second scroll member56, and between the outer surface of the first connecting portion54cof the first scroll member52and the inner surface of the second connecting portion58cof the second scroll member56.

In the second scroll member56shown inFIG. 9, the second ring part57is omitted, and the length of the second outer peripheral portion58ais the same as that of the second inner peripheral portion58bin a half of the circumference in the circumferential direction of the impeller shaft12. Although not shown in the illustration, the length of the second inner peripheral portion58bis smaller than that of the second outer peripheral portion58ain the remaining half of the circumference in the circumferential direction of the impeller shaft12. In addition, the first rib54dis omitted in the first scroll member52shown inFIG. 9, and the distance of the first outer peripheral portion54aof the first passage forming part54from an end thereof opposite from the first connecting portion54cto the first connecting portion54cis the same as the distance of the second outer peripheral portion58aof the second passage forming part58from an end thereof opposite from the second connecting portion58cto the second connecting portion58c. The turbocharger10has a welded portion A where an end of the first outer peripheral portion54aof the first scroll member52opposite from the first connecting portion54cand an end of the second inner peripheral portion58bof the second scroll member56opposite from the second connecting portion58care welded. The first scroll member52and the second scroll member56are integrated together by the welded portion A.

The first passage forming part54of the first scroll member52and the second passage forming part58of the second scroll member56are arranged side by side in the radial direction of the impeller shaft12, and accommodated in a space surrounded by the outer peripheral wall31a, the inner peripheral wall31b, and the connecting wall31cof the turbine housing body portion31. The first scroll member52is disposed inward of the second scroll member56in the radial direction of the impeller shaft12. The first outer peripheral portion54aof the first scroll member52and the second inner peripheral portion58bof the second scroll member56overlap in the radial direction of the impeller shaft12. The first scroll member52and the second scroll member56are supported by the turbine housing30with the first ring part53held between the end surface31eof the turbine housing body portion31and the other end surface512of the ring portion51bof the turbine shroud portion51.

The first turbine scroll passage35is a space surrounded by the inner surface of the first outer peripheral portion54a, the inner surface of the first inner peripheral portion54b, the inner surface of the first connecting portion54cof the first scroll member52, and the part of the second end surface60bof the passage forming plate60facing the first connecting portion54c. The connecting passage38is a space surrounded by the inner surface of the second outer peripheral portion58a, the inner surface of the second inner peripheral portion58b, the inner surface of the second connecting portion58cof the second scroll member56, and the part of the second end surface60bof the passage forming plate60facing the second connecting portion58c. Although not shown in the illustration, the second turbine scroll passage36is a space surrounded by the inner surface of the second outer peripheral portion58a, the inner surface of the second inner peripheral portion58b, the inner surface of the second connecting portion58cof the second scroll member56, and the part of the second end surface60bof the passage forming plate60facing the second connecting portion58c. The second turbine scroll passage36is in communication with the communication passage37through a gap formed between the end of the second inner peripheral portion58bwhere the length thereof is smaller than the second outer peripheral portion58aand the second end surface60bof the passage forming plate60.

In the configuration shown inFIGS. 7 through 9, the first scroll member52and the second scroll member56are integrated by welding. As compared with the case where the first scroll member52and the second scroll member56are not integrally formed, the first scroll member52and the second scroll member56are more easily handled during the manufacture of the turbocharger10.

The structure for supporting the first scroll member52and the second scroll member56may be modified in a manner shown inFIGS. 10 and 11. The configuration of the bearing housing20and the turbine housing30will be described in detail in the following, but the description of the configuration the same as the above embodiment will be omitted. In addition, although the shapes of the first scroll member52and the second scroll member56are the same as those of the above-described embodiment inFIGS. 10 and 11, the first scroll member52and the second scroll member56may have the shapes shown inFIGS. 6 through 9.

As shown inFIGS. 10 and 11, the bearing housing body portion21of the bearing housing20has a large diameter portion211, and a small diameter portion212that is continuous with one end of the large diameter portion211in the rotation axis direction of the impeller shaft12. The outer diameter of the small diameter portion212is smaller that of the large diameter portion211. The small diameter portion212is located adjacently to the turbine housing30in the rotation axis direction of the impeller shaft12. The bearing housing body portion21has a projected portion213having a tubular shape and projecting from an small diameter side end surface21fof the small diameter portion212in the rotation axis direction of the impeller shaft12. The projected portion213is formed so that the diameter of the projected portion213reduces as away from the small diameter portion212in the rotation axis direction of the impeller shaft12. The insertion hole21his opened at the end surface213aof the projected portion213. The C-ring17, which serves as a sealing member, is interposed between the inner peripheral surface of the insertion hole21hof the projected portion213and the outer peripheral surface of the impeller shaft12. A projection213bhaving an annular shape is formed projecting from the end surface213aof the projected portion213around the insertion hole21hin the end surface213aof the projected portion213. The bearing housing20has a annular connecting flange214having a ring shape that projects outwardly in the radial direction of the impeller shaft12from the outer peripheral surface of the small diameter portion212.

The turbine housing body portion31of the turbine housing30has a connecting projection311projecting outwardly in the radial direction of the impeller shaft12from an end of the outer peripheral surface of the outer peripheral wall31aadjacent to the bearing housing20. The turbine housing body portion31has a groove portion312recessed in the inner peripheral portion of the end surface31d. The groove portion312is opened at the inner peripheral surface of the outer peripheral wall31a. The groove portion312includes an inner bottom surface312aextending in the radial direction of the impeller shaft12, and an inner peripheral surface312bextending in the rotation axis direction of the impeller shaft12.

The bearing housing20has a closing plate25that has a ring shape and covers the opening of the turbine housing body portion31. The closing plate25has a standing portion251having a ring shape that stands from the inner peripheral edge of the closing plate25toward the bearing housing20, and a connecting protrusion252projecting from the outer peripheral edge of an end surface251aof the standing portion251in the radial direction of the impeller shaft12.

The passage forming plate60is disposed between the closing plate25and the first scroll member52and between the closing plate25and the second scroll member56in the rotation axis direction of the impeller shaft12. The passage forming plate60includes an outer peripheral plate portion601, an inner peripheral plate portion602, and a connecting plate603connecting the inner peripheral edge of the outer peripheral plate portion601and the outer peripheral edge of the inner peripheral plate portion602. The outer peripheral plate portion601and the inner peripheral plate portion602extend in the radial direction of the impeller shaft12. One end surface of the outer peripheral plate portion601is in contact with one end surface25aof the closing plate25on the side thereof adjacent to the turbine housing body portion31. The other end surface of the outer peripheral plate portion601is in contact with the second rib58d. A large part of the one end surface of the inner peripheral plate portion602faces the one end surface25aof the closing plate25in a state that the large part of the one end surface of the inner peripheral plate portion602is spaced from the one end surface25a. A radially inner part of the other end surface of the inner peripheral plate portion602faces the ring portion51bof the turbine shroud portion51, and a radially outer part of the other end surface of the inner peripheral plate portion602faces the first passage forming part54of the first scroll member52. In addition, the part of the other end surface of the inner peripheral plate portion602that forms the radially outer end is in contact with the first rib54d.

The closing plate25is connected to the bearing housing body portion21with the connecting flange214of the bearing housing body portion21of the bearing housing20and the connecting protrusion252of the closing plate25held by the fastening force of the clamping member26. With the closing plate25connected to the bearing housing20, the closing plate25is located so as to surround the projected portion213of the bearing housing20.

A cover member27is disposed between n outer surface of the projected portion213of the bearing housing20and an inner peripheral surface of the closing plate25in the radial direction of the impeller shaft12. The cover member27is a heat insulator. The cover member27has a shape that extends along the outer surface of the projected portion213of the bearing housing20and is disposed spaced from the outer surface of the projected portion213. An inner peripheral portion of the cover member27is fixed to the end surface213aof the projected portion213, and an inner peripheral edge of the cover member27faces the outer peripheral surface of the projection213bin the radial direction of the impeller shaft12. The outer peripheral portion of the cover member27is held between the small diameter side end surface21fof the bearing housing body portion21and the end surface251aof the standing portion251. The outer peripheral edge of the cover member27faces the inner peripheral surface of the connecting protrusion252.

The outer peripheral end portion of the closing plate25and the radially outer end portion of the outer peripheral plate portion601are disposed between the inner bottom surface312aof the groove portion312of the turbine housing body portion31and the washer W in the rotation axis direction of the impeller shaft12. The one end surface of the closing plate25on the turbine housing30side is in contact with the one end surface of the outer peripheral plate portion601of the passage forming plate60. The other end surface of the closing plate25on the side opposite from the turbine housing30is in contact with the washer W. A surface of the washer W facing the closing plate25is in contact with the end surface31dof the turbine housing body portion31. The other end surface of the outer peripheral plate portion601of the passage forming plate60opposite from the closing plate25is in contact with the inner bottom surface312aof the groove portion312. The outer peripheral edge of the closing plate25and the outer peripheral edge of the outer peripheral plate portion601face the inner peripheral surface312bof the groove portion312. A mounting bolt B2is inserted through the washer W and screwed into the connecting projection311of the outer peripheral wall31awith the closing plate25and the outer peripheral plate portion601of the passage forming plate60disposed between the turbine housing body portion31and the washer W.

The outer peripheral part of the closing plate25and the radially outer end portion of the outer peripheral plate portion601of the passage forming plate60are held between the washer W and the turbine housing body portion31in the rotation axis direction of the impeller shaft12. Thus, the closing plate25and the turbine housing body portion31are connected, thereby connecting the turbine housing30to the one end of the bearing housing20in the rotation axis direction of the impeller shaft12. The passage forming plate60is supported by the bearing housing20and the turbine housing30.

As shown inFIG. 10, the turbine shroud portion51may be connected to the inner peripheral wall31bof the turbine housing body portion31by the mounting bolt B2with the first ring part53and the second ring part57disposed between the end surface31eof the turbine housing body portion31and the other end surface512of the ring portion51bof the turbine shroud portion51. Specifically, the ring portion51bof the turbine shroud portion51has a mounting hole51hthrough which the shaft portion of the mounting bolt B2may be inserted, and a recessed portion51cthat is recessed in one end surface511. The mounting hole51his opened at the bottom surface of the recessed portion51c. In addition, the first ring part53and the second ring part57have mounting holes53hand57h, respectively, through which the shaft portion of the mounting bolt B2may be inserted. Further, a mounting portion31his formed in the inner peripheral wall31bof the turbine housing body portion31. The mounting bolt B2may be screwed into the mounting portion31h. The mounting bolt B2is inserted through the mounting hole51hof the ring portion5b, the mounting hole53hof the first ring part53, the mounting hole57hof the second ring part57, and screwed into the mounting portion31hof the inner peripheral wall31b. Since the head of the mounting bolt B2is received in the recessed portion51c, the mounting bolt B2is not projected out from the one end surface511of the ring portion51b.

In this case, the first ring part53and the second ring part57are held between the ring portion51bof the turbine shroud portion51and the inner peripheral wall31bof the turbine housing body portion31with axial force caused by screwing the mounting bolt B2acting on the ring portion51bof the turbine shroud portion51, with the result that the first ring part53and the second ring part57are supported by the turbine housing30. Thus, the ring portion51bneed not be urged toward the turbine housing body portion31by, for example, the plate spring62. In addition, the spacers61for securing a space between the passage forming plate60and the ring portion51bof the turbine shroud portion51may be omitted. As a result, the configuration of the turbocharger10may be simplified.

As shown inFIG. 11, the turbocharger10may include an external threaded portion513formed in the outer peripheral surface of the tubular portion51aof the turbine shroud portion51, and an internal threaded portion313formed in the surface of the inner peripheral wall31bof the turbine housing body portion31opposite from the outer peripheral wall31a. The turbine shroud portion51is connected to the turbine housing30by screwing the external threaded portion513of the tubular portion51ainto the internal threaded portion313of the inner peripheral wall31bwith the first ring part53and the second ring part57disposed between the end surface31eof the turbine housing body portion31and the other end surface512of the ring portion51bof the turbine shroud portion51.

In this case, the first ring part53and the second ring part57are held between the ring portion51bof the turbine shroud portion51and the inner peripheral wall31bof the turbine housing body portion31with axial force caused by screwing the tubular portion51aof the turbine shroud portion51, with the result that the first ring part53and the second ring part57are supported by the turbine housing30. Thus, the ring portion51bneed not be urged toward the turbine housing body portion31by, for example, the plate spring62. In addition, the spacers61for securing a space between the passage forming plate60and the ring portion51bof the turbine shroud portion51may be omitted. As a result, the configuration of the turbocharger10may be simplified.

As shown inFIG. 12, the end of the second inlet port forming member59opposite from the second passage forming part58may be disposed at a position about 180 degree shifted relative to the end of the first inlet port forming member55opposite from the first passage forming part54in the circumferential direction of the first ring part53and the second ring part57. In other words, the dimension of the second inlet port33bmay be reduced. In this case, the connecting passage38is not formed, and the second inlet port33bdirectly communicates with the second turbine scroll passage36.

The structure for supporting the first scroll member52and the second scroll member56may be modified as follows.

For example, the first scroll member52is supported by holding the first ring part53between the end surface31eof the turbine housing body portion31and the other end surface512of the tubular portion51aof the turbine shroud portion51. The second scroll member56may be modified so that the length of the second rib58dis increased outwardly in the radial direction of the impeller shaft12, and the second ring part57is omitted, as compared with the above-described embodiment. Thus, the second scroll member56is supported with the second rib58dheld by the bearing housing20and the end surface31dof the turbine housing body portion31. It is noted that the second rib58dmay be held with or without the passage forming plate60by the bearing housing20and the end surface31dof the turbine housing body portion31.

In a configuration in which both the first ring part53of the first scroll member52and the second ring part57of the second scroll member56are held by the turbine housing body portion31and the turbine shroud portion51, a gap between the turbine impeller13and the turbine shroud portion51is set in consideration with dimensional tolerance for the first ring part53and the second ring part57in the thickness direction thereof. On the other hand, in a configuration in which only the first ring part53of the first scroll member52is held by the turbine housing body portion31and the turbine shroud portion51, a gap between the turbine impeller13and the turbine shroud portion51is set in consideration with dimensional tolerance for the first ring part53in the thickness direction thereof. In other words, the gap between the turbine impeller13and the turbine shroud portion51may be set without considering the dimensional tolerance of the second ring part57. Therefore, the dimensional tolerance for the gap between the turbine impeller13and the turbine shroud portion51may be reduced, thereby improving the performance of the turbocharger10.

In the above configuration, the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cis an inner peripheral end portion of the second scroll member56and a free end. The tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cis a free end edge portion, and the turbine shroud portion51is a facing member that faces the tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58c. The tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cfaces the turbine shroud portion51with the tip of the end portion of the second inner peripheral portion58bspaced from the turbine shroud portion51.

It is noted that the second inner peripheral portion58bmay be disposed so that the inner surface of the second inner peripheral portion58bis in contact with the first inner peripheral portion54bof the first scroll member52, and the outer surface of the second inner peripheral portion58bis in contact with the inner peripheral wall31bof the turbine housing body portion31. “The inner peripheral end portion of the second scroll member56being a free end” includes a state that the inner peripheral end portion is in contact with the surrounding parts, but slidable thereon, and the heat expansion of the second scroll member56in the radially inward side of the second scroll member56is not hindered.

The structure for supporting the first scroll member52and the second scroll member56may be modified as follows.

For example, the second scroll member56is supported by holding the second ring part57between the end surface31eof the turbine housing body portion31and the other end surface512of the tubular portion51aof the turbine shroud portion51. The first scroll member52may be modified so that the length of the first rib54dis increased outwardly in the radial direction of the impeller shaft12and the first ring part53is omitted, as compared with the above-described embodiment. Thus, the first scroll member52is supported with the first rib54dheld by the bearing housing20and the end surface31dof the turbine housing body portion31. It is noted that the first rib54dmay be held with or without the passage forming plate60by the bearing housing20and the end surface31dof the turbine housing body portion31.

In this case, since only the second ring part57of the second scroll member56is held by the turbine housing body portion31and the turbine shroud portion51, a gap between the turbine impeller13and the turbine shroud portion51is set in consideration with dimensional tolerance of the second ring part57in the thickness direction thereof. In other words, the gap between the turbine impeller13and the turbine shroud portion51may be set without considering the dimensional tolerance for the first ring part53in the thickness direction thereof. Therefore, the dimensional tolerance for the gap between the turbine impeller13and the turbine shroud portion51may be reduced, thereby improving the performance of the turbocharger10.

In this configuration, the end portion of the first inner peripheral portion54bopposite from the first connecting portion54cis an inner peripheral end portion of the first scroll member52and a free end. A tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54cis a free end edge portion, and the passage forming plate60is a facing member that faces a tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54c. The tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54cfaces the second end surface60bof the passage forming plate60with the tip of the end portion of the first inner peripheral portion54bspaced from the second end surface60bof the passage forming plate60.

The outer surface of the first inner peripheral portion54bmay be in contact with the inner surface of the second inner peripheral portion58bof the second scroll member56. “The inner peripheral end portion of the first scroll member52being a free end” includes a state that the inner peripheral end portion is in contact with the surrounding parts, but slidable thereon, and the heat expansion of the first scroll member52in the radially inward side of the first scroll member52is not hindered.

The structure for supporting the first scroll member52and the second scroll member56may be modified as follows.

For example, the first scroll member52is modified so that the length of the first rib54dis increased outwardly in the radial direction of the impeller shaft12and the first ring part53is omitted, as compared with the above-described embodiment. The second scroll member56is modified so that the second rib58dextend outwardly in the radial direction of the impeller shaft12and the second ring part57is omitted, as compared with the above described embodiment. The first rib54dand the second rib58dare held by the bearing housing20and the end surface31dof the turbine housing body portion31with the first rib54dand the second rib58doverlapped in the rotation axis direction of the impeller shaft12, thereby supporting the first scroll member52and the second scroll member56.

In this configuration, the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cis an inner peripheral end portion of the second scroll member56and a free end. The tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cis a free end edge portion, and the turbine shroud portion51is a facing member that faces the tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58c. The tip of the end portion of the second inner peripheral portion58bopposite from the second connecting portion58cfaces the turbine shroud portion51with the tip of the end portion of the second inner peripheral portion58bspaced from the turbine shroud portion51.

The end portion of the first inner peripheral portion54bopposite from the first connecting portion54cis an inner peripheral end portion of the first scroll member52, and a free end. A tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54cis a free end edge portion, and the passage forming plate60is a facing member that faces a tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54c. The tip of the end portion of the first inner peripheral portion54bopposite from the first connecting portion54cfaces the second end surface60bof the passage forming plate60with the tip of the end portion of the first inner peripheral portion54bspaced from the second end surface60bof the passage forming plate60.

If the first scroll member52may be formed by the pressing, the distance from the first outer peripheral portion54ato the first inner peripheral portion54bin the radial direction of the first ring part53need not be constant in the rotation axis direction of the impeller shaft12, The distance from the first outer peripheral portion54ato the first inner peripheral portion54bin the radial direction of the first ring part53may be increased from the first connecting portion54ctoward the opening. That is, the first scroll member52may have a shape in which the diameter of the opening increases from the first connecting portion54cto the opening in the rotation axis direction of the impeller shaft12.

Similarly, if the second scroll member56may be formed by pressing, the distance from the second outer peripheral portion58ato the second inner peripheral portion58bin the radial direction of the second ring part57need not be constant in the rotation axis direction of the impeller shaft12. The distance from the second outer peripheral portion58ato the second inner peripheral portion58bin the radial direction of the second ring part57may be increased from the second connecting portion58ctoward the opening. That is, the second scroll member56has a shape that the diameter of the opening increases from the second connecting portion58cto the opening in the rotation axis direction of the impeller shaft12.

The turbocharger10may include a plurality of fixed vanes that is fixed to the turbine shroud portion51. The fixed vanes are spaced from each other in the circumferential direction of the communication passage37. In this case, the fixed vanes maintain the distance between the one end surface511of the ring portion51bof the turbine shroud portion51and the second end surface60bof the passage forming plate60in the rotation axis direction of the impeller shaft12, so that the spacers61may be omitted.

The turbocharger10may include a plurality of variable vanes that are rotatably supported by the turbine shroud portion51and the passage forming plate60, and a plurality of link members that drives the variable vanes. The variable vanes and the link members are spaced from each other, respectively, in the circumferential direction of the communication passage37. The variable vanes are disposed between the passage forming plate60and the turbine shroud portion51in the rotation axis direction of the impeller shaft12. The link members are disposed between the passage forming plate60and the bearing housing body portion21of the bearing housing20in the rotation axis direction of the impeller shaft12. Each of the link members drives its associated variable vane so as to change the angular position of the vane relative to the ring portion51b, thereby changing the cross sectional area of the communication passage37. The flow rate of exhaust gas introduced to the turbine chamber34may be adjusted by changing the cross sectional area of the communication passage37.

In the turbocharger10, the passage forming plate may be omitted, and the openings of the first scroll member52and the second scroll member56may be covered by the bearing housing20. In this case, the bearing housing20serves as a closing member. The one end surface21aof the bearing housing body portion21of the bearing housing20forms a wall surfaces of the first turbine scroll passage35, the second turbine scroll passage36, and the connecting passage38on the bearing housing20side.

The gap S3between the first outer peripheral portion54aof the first passage forming part54and the second outer peripheral portion58aof the second passage forming part58may be covered by the first rib54dof the first passage forming part54of the first scroll member52. In this case, the connecting passage38is a space surrounded by the outer surface of the first passage forming part54, the inner surface of the second passage forming part58, and the surface of the first rib54don the first connecting portion54cside.

The first rib54dof the first passage forming part54of the first scroll member52may be disposed so that the first rib54dis spaced from the outer peripheral end portion60cof the passage forming plate60. The first rib54dmay be in contact with the surrounding parts of the first scroll member52on the side opposite from the outer peripheral end portion60cof the passage forming plate60. The first rib54dof the first passage forming part54of the first scroll member52shown inFIGS. 10 and 11may be spaced from the outer peripheral plate portion601of the passage forming plate60. On the opposite side from the outer peripheral plate portion601of the passage forming plate60, the first rib54dmay be in contact with the surrounding parts of the first scroll member52.

“The outer peripheral end portion of the first scroll member52being an free end” includes a state that the outer peripheral end portion is in contact with the surrounding parts but is slidable thereon, and the heat expansion of the first scroll member52in the radially outer side of the first scroll member52is not hindered.

The second rib58dof the second passage forming part58of the second scroll member56may be disposed so that the second rib58dis spaced from the outer peripheral end portion60cof the passage forming plate60. The second rib58dmay be in contact with parts disposed around the second scroll member56on the side opposite from the outer peripheral end portion60cof the passage forming plate60.

“The outer peripheral end portion of the second scroll member56being an free end” includes a state that the outer peripheral end portion is in contact with the surrounding parts but is slidable thereon, and the heat expansion of the second scroll member56in the radially inward side of the second scroll member56is not hindered.

The first elastic member72interposed between the outer peripheral wall31aof the turbine housing body portion31and the second outer peripheral portion58aof the second passage forming part58of the second scroll member56in the radial direction of the impeller shaft12may be omitted.

The first elastic member72need not be provided by a mesh wire, but by other elastic members.

The method for fixing the first elastic member72to the second outer peripheral portion58aof the second passage forming part58is not limited to micro spot welding. For example, the first elastic member72may be fixed to the second outer peripheral portion58aof the second passage forming part58by adhesion using adhesive or riveting.

The second elastic member73interposed between the first end surface60aof the passage forming plate60and the one end surface21aof the bearing housing body portion21of the bearing housing20in the rotation axis direction of the impeller shaft12may be omitted.

The second elastic member73need not necessarily be provided by a wire mesh but by other elastic members.

The method for fixing the second elastic member73to the first end surface60aof the passage forming plate60is not limited to micro spot welding. For example, the second elastic member73may be fixed to the first end surface60aof the passage forming plate60by adhesion using adhesive or riveting.

The turbine shroud portion51need not necessarily be provided separately from the turbine housing30, but may be formed integrally with the turbine housing30. In this case, the wall surface of the communication passage37opposite from the bearing housing20is formed by the turbine housing30.

The first inlet port forming member55need not necessarily be formed integrally with the first scroll member52, but may be formed separately from the first scroll member52.

The second inlet port forming member59need not necessarily be formed integrally with the second scroll member56, but may be formed separately from the second scroll member56.

The internal combustion engine E may be provided by a gasoline engine or a diesel engine. The internal combustion engine E is not limited to a four-cylinder engine, but may be a six-cylinder engine. The arrangement of the cylinders in the internal combustion engine is not limited to an in-line arrangement, but may be a V-shape arrangement.

The materials for the bearing housing20, the turbine housing30, and the compressor housing40are not limited to cast iron, but may be a cast steel.