A turbocharger includes a semi-floating metal. The semi-floating metal is provided with a supply opening configured to supply oil to an inner bearing section. The turbocharger is provided with: an oil supply path which extends from inside of a bearing housing to the supply opening, and feeds the oil to be supplied to the inner bearing section; a removal section which changes a flowing direction of the oil supplied from an upstream side to separate minute foreign matter in the oil; and a conveyance path and a retaining region which collect the minute foreign matter separated by the removal section so as to prevent the minute foreign matter from mixing again with the oil flowing toward the supply opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbocharger which includes a turbine and a compressor.

2. Description of the Related Art

A turbocharger including a turbine and a compressor has been widely used as a supercharger for improving a performance of an internal combustion engine. In the turbocharger, a turbine wheel (turbine impeller) constituting the turbine and a compressor wheel (compressor impeller) constituting the compressor are connected to each other by a rotating shaft. An exhaust gas from the internal combustion engine is fed into the turbine side. The exhaust gas thus fed rotates the turbine wheel and thereby rotates the compressor wheel. Air is forced to flow into a cylinder of the internal combustion engine by the rotation of the compressor wheel, whereby a gas pressure inside the cylinder is raised and virtual displacement is increased.

The above-described turbocharger needs to rotate and drive the turbine and the compressor at a high speed. As a consequence, the rotating shaft is also rotated at a high speed. It is therefore extremely important to ensure lubrication between the rotating shaft and a housing that houses the rotating shaft. Japanese Patent Application Laid-Open Publication No. 2010-96120 (PTL 1) cited below proposes a bearing device for a turbocharger, which is intended to remove foreign matter in oil that serves as a lubricant.

In the bearing device of PTL 1, a detour is provided in the vicinity of an oil inlet inside a housing and a filter is disposed in the detour. Foreign matter in the oil is removed by the filter, and the oil from which the foreign matter is removed is then supplied from the inlet to rolling bearings.

SUMMARY OF THE INVENTION

In the related art described above, the rolling bearings hold the rotating shaft. Accordingly, a particular problem seems not to occur even when the oil is supplied through the detour where the filter is disposed. On the other hand, the application of the above-described related art without alteration is not preferable when the type of the bearing is changed to a fluid bearing which is a plain bearing.

A fluid bearing includes a bearing member such as a semi-floating metal bearing disposed between a rotating shaft and a housing, and is designed to form an oil film by forcing oil into the clearance between the housing and the bearing member at a high pressure, and to form an oil film by forcing the oil into the clearance between the rotating shaft and the bearing member at a high pressure. The formation of the oil films between these components as described above enables the rotating shaft to rotate at a high speed.

If a filter as in the related art is provided for such a fluid bearing, the filter causes a reduction of pressure, which may complicate the formation of the oil films between the components. In order to supply the oil at a sufficient pressure to the fluid bearing, a supply pressure of the oil has to be increased or a screen of the filter has to be made coarse. Nonetheless, the installation of a specific device for increasing the supply pressure of the oil should be avoided. For this reason, the increase range in the supply pressure of the oil is limited. On the other hand, if the screen of the filter is made coarse, then foreign matter is more likely to flow into the fluid bearing side. In this context, the filter method is not always effective in order to remove the foreign matter from the oil inside the turbocharger that employs the fluid bearing. In addition, if the filter method is employed, it is necessary to conduct maintenance work such as the replacement or cleaning of the filter due to the necessity of disposing the filter in an oil supply path.

In the case of the fluid bearing, it is not preferable to provide the filter on the oil supply path in the fluid bearing, but the necessity of removing the foreign matter from the oil is higher than in the case of the rolling bearing. The fluid bearing is configured to exert the function as the bearing by use of the oil films formed between the components. Accordingly, each clearance between the components is so small that the entry of even minute foreign matter may cause a trouble. To be more precise, the minute foreign matter moving between the components may damage opposed surfaces of the components or the minute foreign matter stuck between the components may block a flow of the oil between the components. The occurrence of these phenomena may lead to seizure due to the shortage of the oil or the locking of the rotating shaft, and may cause a reduction in supercharging pressure or the occurrence of abnormal noise from the turbocharger.

The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide a turbocharger which employs a fluid bearing to support a rotating shaft that connects a turbine and a compressor to each other, and is capable of minimizing the entry of minute foreign matter into the fluid bearing without blocking a function of the fluid bearing.

An aspect of the present invention is a turbocharger including: a turbine wheel constituting a turbine; a compressor wheel constituting a compressor; a rotating shaft connecting the turbine wheel and the compressor wheel to each other; a housing which houses at least the rotating shaft; and a semi-floating metal bearing forming a fluid bearing between the rotating shaft and the housing. The semi-floating metal bearing is provided with a supply opening configured to supply oil to an inner bearing section formed between the semi-floating metal bearing and the rotating shaft. The turbocharger is provided with an oil supply path extending from inside of the housing to the supply opening and configured to feed the oil to be supplied to the inner bearing section. In addition, the oil supply path is provided with a removal section configured to change a flowing direction of the oil supplied from an upstream side to separate minute foreign matter in the oil. The turbocharger is provided with a collecting section configured to collect the minute foreign matter separated by the removal section so as to prevent the minute foreign matter from mixing again with the oil flowing toward the supply opening.

In the turbocharger, the collecting section may include: a retaining region configured to retain the minute foreign matter separated by the removal section, so as to prevent the minute foreign matter from mixing again with the oil flowing toward the supply opening; and a conveyance path configured to move the minute foreign matter, separated by the removal section, from the removal section to the retaining region. The conveyance path may be joined to the removal section at a position different from a main flow path on which the oil flows from the removal section toward the supply opening.

In the turbocharger, an oil reservoir space configured to temporarily retain the oil may be formed between the housing and the semi-floating metal bearing. In addition, the retaining region and the conveyance path may be formed in the oil reservoir space.

In the turbocharger, the retaining region may be formed below the removal section and the supply opening.

In the turbocharger, a guide wall surface configured to guide the minute foreign matter to the conveyance path may be formed between the removal section and the supply opening.

In the turbocharger, the removal section may include a separation wall surface opposed to the flow of the oil supplied from the upstream side.

In the turbocharger, the separation wall surface may be formed on an outer peripheral surface of the semi-floating metal bearing.

In the turbocharger according to claim7, an oil reservoir space configured to temporarily retain the oil may be formed between the housing and the semi-floating metal bearing. The housing may be provided with an upstream side supply opening configured to supply the oil to the oil reservoir space. The separation wall surface may be formed by locating the upstream side supply opening and the supply opening at different positions.

The above-mentioned configurations can be combined with one another unless the configurations are not technically incompatible with one another. When the configurations are combined, their combinations can exert the operations and effects that are intrinsic to the respective configurations.

According to the present invention, it is possible to provide a turbocharger which employs a fluid bearing to support a rotating shaft that connects a turbine and a compressor to each other, and is capable of minimizing the entry of minute foreign matter into the fluid bearing without blocking a function of the fluid bearing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the accompanying drawings. To make the descriptions understood easily, the same constituents in the drawings are denoted by the same reference numerals as much as possible and overlapped descriptions will be omitted.

A turbocharger representing an embodiment of the present invention will be described with reference toFIG. 1.FIG. 1is a schematic cross-sectional view of a turbocharger TC which is the embodiment of the present invention. As shown inFIG. 1, the turbocharger TC of the embodiment includes a bearing housing2, a turbine3provided with a turbine wheel (turbine impeller)31, a compressor4provided with a compressor wheel (compressor impeller)41, a rotating shaft5, and a semi-floating metal bearing6.

The turbine wheel31is a key component that constitutes the turbine3, and is housed in a turbine housing32. The compressor wheel41is a key component that constitutes the compressor4, and is housed in a compressor housing42. The turbine wheel31and the compressor wheel41are connected to each other by the rotating shaft5. The rotating shaft5is rotatably held by the semi-floating metal bearing6interposed between the bearing housing2and the rotating shaft5.

The turbine housing32includes a turbine side scroll chamber which is not clearly shown inFIG. 1. The turbine side scroll chamber is a chamber which houses the turbine wheel31. The turbine side scroll chamber is provided with an inlet port for supplying an exhaust gas from an internal combustion engine to the inside of the chamber, and an outlet port for discharging the supplied exhaust gas. The turbine wheel31is rotated by the exhaust gas supplied from the inlet port, whereby the rotating shaft5is rotated and driven.

The compressor housing42includes a compressor side scroll chamber which is not clearly shown inFIG. 1. The compressor side scroll chamber is a chamber which houses the compressor wheel41. The compressor side scroll chamber is provided with an inlet port for supplying air to the inside of the chamber, and an outlet port for feeding the supplied air to the internal combustion engine. The compressor wheel41is rotated in response to the rotating shaft5that is rotated and driven. With the rotation of the compressor wheel41, the air is taken in from the inlet port and is compressed inside the compressor side scroll chamber. The compressed air is fed from the outlet port to the internal combustion engine.

The bearing housing2houses the semi-floating metal bearing6which rotatably holds the rotating shaft5. The semi-floating metal bearing6is a component which has a substantially cylindrical shape. The semi-floating metal bearing6is fixed to the bearing housing2by use of a thrust pin7. The semi-floating metal bearing6is fixed to the bearing housing2in such a manner as to be movable in a radial direction of the semi-floating metal bearing6but not to be movable or rotatable in its axial and rotational directions.

The semi-floating metal bearing6is formed as a member having stepped shapes on both of its inner and outer peripheral surfaces. The inner peripheral surface of the semi-floating metal bearing6includes: an inside small diameter portion62aformed on one end; an inside small diameter portion63aformed on the other end; and an inside large diameter portion61aformed at a central portion between the inside small diameter portion62aand the inside small diameter portion63a. An inner diameter of the inside small diameter portion62aand an inner diameter of the inside small diameter portion63aare formed substantially equal to each other. The inside large diameter portion61ais formed to have an inner diameter which is larger than the inner diameters of the inside small diameter portion62aand the inside small diameter portion63a.

The outer peripheral surface of the semi-floating metal bearing6includes: an outside large diameter portion62bformed on one end; an outside large diameter portion63bformed on the other end; and an outside small diameter portion61bformed at a central portion between the outside large diameter portion62band the outside large diameter portion63b. An outer diameter of the outside large diameter portion62band an outer diameter of the outside large diameter portion63bare formed substantially equal to each other. The outside small diameter portion61bis formed to have an outer diameter which is smaller than the outer diameters of the outside large diameter portion62band the outside large diameter portion63b.

The rotating shaft5is inserted in the inner peripheral surface side of the semi-floating metal bearing6. A small diameter portion51, and large diameter portions52and53provided in such a manner as to sandwich the small diameter portion51, are formed at part of the rotating shaft5that is inserted in the inner peripheral surface side of the semi-floating metal bearing6. Each of the large diameter portions52and53is formed to have an outer diameter which is larger than an outer diameter of the small diameter portion51. The large diameter portion52is located at a position opposed to the inside small diameter portion62aand the large diameter portion53is located at a position opposed to the inside small diameter portion63a. A clearance between the large diameter portion52and the inside small diameter portion62ais extremely small, and an oil film is formed by forcing oil at a high pressure into the small clearance. Similarly, a clearance between the large diameter portion53and the inside small diameter portion63ais extremely small, and an oil film is formed by forcing the oil at the high pressure into the small clearance.

A diameter enlarged portion5A is provided between the large diameter portion52of the rotating shaft5and the turbine wheel31. The diameter enlarged portion5A is formed integrally with the rotating shaft5in such a manner as to be in intimate contact with the large diameter portion52. The oil forming the oil film by being forced into the clearance between the large diameter portion52and the inside small diameter portion62apasses through a gap between the diameter enlarged portion5A and the semi-floating metal bearing6as well as a gap between the diameter enlarged portion5A and the bearing housing2, and flows back to an oil pan which is not clearly shown in the drawing.

A thrust cup member5B is provided between the large diameter portion53of the rotating shaft5and the compressor wheel41. The thrust cup member5B is fitted into the rotating shaft5in such a manner as to be in intimate contact with the large diameter portion53. The oil forming the oil film by being forced into the clearance between the large diameter portion53and the inside small diameter portion63apasses through a gap between the thrust cup member5B and the semi-floating metal bearing6as well as a gap between the thrust cup member5B and the bearing housing2, and flows back to the oil pan which is not clearly shown in the drawing.

As described above, the small diameter portion51is provided between the large diameter portion52and the large diameter portion53of the rotating shaft5. Meanwhile, the inside large diameter portion61ais provided between the inside small diameter portion62aand the inside small diameter portion63aof the semi-floating metal bearing6. Accordingly, the small diameter portion51of the rotating shaft5and the inside large diameter portion61aof the semi-floating metal bearing6are respectively arranged at such positions to face each other, and an inside oil reservoir space8ais thus formed.

A supply opening61cis formed in the semi-floating metal bearing6in order to supply the oil to the inside oil reservoir space8a. The supply opening61cis formed penetrating the semi-floating metal bearing6from the inside large diameter portion61ato the outside small diameter portion61b. In this embodiment, the supply opening61cis formed in such a manner as to be located on the opposite side of the rotating shaft5from the thrust pin7, or in other words, to be located above the rotating shaft5inFIG. 1.

Housing inner walls21,22, and23are formed at portions of the bearing housing2which the semi-floating metal bearing6is housed in. The housing inner wall22and the housing inner wall23are formed while interposing the housing inner wall21in between.

The housing inner wall22forms a circular cross section and a part of the cross section is provided facing the outside large diameter portion62bof the semi-floating metal bearing6while the rest of the cross section is provided facing the outside small diameter portion61bof the semi-floating metal bearing6. A clearance between the housing inner wall22and the outside large diameter portion62bis extremely small, and an oil film is formed by forcing the oil at the high pressure into the small clearance.

The housing inner wall23forms a circular cross section with the diameter equal to that of the housing inner wall22, and a part of the cross section is provided facing the outside large diameter portion63bof the semi-floating metal bearing6while the rest of the cross section is provided facing the outside small diameter portion61bof the semi-floating metal bearing6. A clearance between the housing inner wall23and the outside large diameter portion63bis extremely small, and an oil film is formed by forcing the oil at the high pressure into the small clearance.

The housing inner wall21forms a circular cross section with the diameter larger than those of the housing inner walls22and23, and is provided at a position to face the outside small diameter portion61bof the semi-floating metal bearing6. As a consequence, an outside oil reservoir space8bis formed between the housing inner wall21and the outside small diameter portion61b.

A housing side supply opening26(an upstream side supply opening) for supplying the oil to the outside oil reservoir space8bis formed in the bearing housing2. An oil feed passage25is formed in the bearing housing2so as to communicate with the housing side supply opening26. The oil with the high pressure is supplied to the oil feed passage25, passed through the housing side supply opening26, and supplied to the outside oil reservoir space8b.

The housing side supply opening26is formed at a position opposed to the outside small diameter portion61bof the semi-floating metal bearing6. The supply opening61cformed in the semi-floating metal bearing6and the housing side supply opening26are formed in different positions so as not to be opposed to each other. As a consequence, the oil supplied to the outside oil reservoir space8bhits the outside small diameter portion61bof the semi-floating metal bearing6, whereby a flowing direction of the oil is changed and the oil flows toward the supply opening61c. The above-mentioned flow of the oil forms an oil supply path FL which extends from the oil feed passage25to the inside oil reservoir space8a. In this embodiment, minute foreign matter contained in the oil is prevented from going into the semi-floating metal bearing6by utilizing the above-mentioned change in the direction of the oil on the oil supply path FL.

Next, how the minute foreign matter is removed will be described in detail with reference toFIG. 2.FIG. 2is an enlarged cross-sectional view enlarging a bearing section inFIG. 1. As shown inFIG. 2, the oil supplied from the oil feed passage25passes through the housing side supply opening26and is supplied to the outside oil reservoir space8b. Since the housing side supply opening26is opposed to the outside small diameter portion61bof the semi-floating metal bearing6, the oil supplied from the housing side supply opening26to the outside oil reservoir space8bhits the outside small diameter portion61band its flowing direction is changed. Since the outside oil reservoir space8bis filled with the oil, a main flow of the oil, in which most of the oil flows even though not forming a fast flow, flows toward the supply opening61calong the oil supply path FL.

Meanwhile, minute foreign matter CT contained in the oil taps into the flow of the oil and is conveyed from the oil feed passage25to the outside oil reservoir space8bthrough the housing side supply opening26. As described previously, the flowing direction of the oil supplied to the outside oil reservoir space8bis changed substantially at a right angle along the oil supply path FL. Here, the minute foreign matter CT contained in the oil has a higher specific gravity than the oil. Accordingly, the minute foreign matter CT does not follow the change in the flowing direction of the oil but falls along the outer peripheral surface of the outside small diameter portion61bby inertia. Hence, the minute foreign matter CT moves downward inFIG. 2(in a direction from the housing side supply opening26toward the thrust pin7). The minute foreign matter CT moving downward is retained in a lower part of the outside oil reservoir space8b.

As a result of applying the above-described configuration, a portion near an outlet of the housing side supply opening26, part of the outside small diameter portion61bopposed to the housing side supply opening26, and part of the outside oil reservoir space8blocated in between collectively function as a removal section RA for separating the minute foreign matter CT from the oil. Meanwhile, the lower part of the outside oil reservoir space8bfunctions as a retaining region SA which retains the minute foreign matter CT separated from the oil, so as to prevent the minute foreign matter CT from mixing again with the oil which flows toward the supply opening61c. In the meantime, the part of the outside oil reservoir space8bjoining the removal section RA and the retaining region SA functions as a conveyance path TA, which causes the minute foreign matter CT separated by the removal section RA to move from the removal section RA to the retaining region SA. Accordingly, the retaining region SA and the conveyance path TA function as a collecting section which collects the minute foreign matter CT separated from the oil in the removal section RA, so as to prevent the minute foreign matter CT from mixing again with the oil which flows toward the supply opening61c.

As described above, in this embodiment, the oil supply path FL is provided with the removal section RA which is configured to separate the minute foreign matter CT in the oil by changing the flowing direction of the oil. Thus, it is possible to remove the minute foreign matter CT in the oil without providing a filter on the oil supply path FL. Since the minute foreign matter CT is separated by changing the flowing direction of the oil without using the filter, a supply pressure of the oil supplied to the fluid bearing is not reduced more than needed, and hence the function of the fluid bearing is not blocked. Meanwhile, the minute foreign matter CT separated from the oil is collected by the conveyance path TA and the retaining region SA which serve as the collecting section, so as to prevent the minute foreign matter CT from mixing again with the oil that flows toward the supply opening61cconfigured to supply the oil to a space (i.e., an inner bearing section) between the large diameter portions52and53as well as the inside small diameter portions62aand63a. Thus, it is possible to inhibit the minute foreign matter CT from mixing again with the oil and flowing toward the inner bearing section.

As described above, in this embodiment, the retaining region SA which retains the minute foreign matter CT separated from the oil by the removal section RA so as to prevent the minute foreign matter CT from mixing again with the oil that flows toward the supply opening61c, and the conveyance path TA which causes the minute foreign matter CT separated by the removal section RA to move from the removal section RA to the retaining region SA, are formed collectively as the collecting section. As shown inFIG. 2, the conveyance path TA is joined to the removal section RA at a position which is different from the main flow path (a flow path along the arrow indicated inFIG. 2as the oil feed passage) on which the oil flows from the removal section RA toward the supply opening61c. Specifically, in the example shown inFIG. 2, the main flow path extends from the left side of the removal section RA in the drawing, while the conveyance path TA extends from a portion below the removal section RA in the drawing.

The retaining region SA which retains the minute foreign matter CT so as to prevent the minute foreign matter CT from mixing again with the oil flowing toward the supply opening61c, and the conveyance path TA which causes the minute foreign matter CT to move from the removal section RA to the retaining region SA, are formed as described above. Accordingly, it is possible to locate the removal section RA securely away from the retaining region SA and thereby to surely retain the removed minute foreign matter CT. In addition, the conveyance path TA is joined to the removal section RA at the position different from the main flow path on which the oil flows from the removal section RA toward the supply opening61c. Thus, it is possible to guide the minute foreign matter CT, which has been separated from the oil flowing on the main flow by the removal section RA, to the retaining region SA through the conveyance path TA without returning the minute foreign matter CT to the main flow path side.

Moreover, in this embodiment, the outside oil reservoir space8bconfigured to temporarily retain the oil is formed between the bearing housing2and the semi-floating metal bearing6. In addition, the retaining region SA and the conveyance path TA are formed in the outside oil reservoir space8b.

Since the conveyance path TA and the retaining region SA are formed in the outside oil reservoir space8bas described above, it is possible to downsize the turbocharger TC and to form the conveyance path TA and the retaining region SA closer to the supply opening61c. As a consequence, the removal section RA can also be located closer to the supply opening61c, so that the minute foreign matter CT can be separated from the oil at a position closer to the supply opening61c. Since the minute foreign matter CT is separated from the oil at the position closer to the supply opening61c, it is possible to minimize a possibility of the entry of minute foreign matter CT which occurs between the removal section RA and the supply opening61c.

In this embodiment, the retaining region SA is formed below the removal section RA and the supply opening61c. By locating the retaining region SA below the removal section RA, it is possible to achieve the configuration to cause the minute foreign matter CT separated by the removal section RA to fall by its own weight along the outer peripheral surface of the outside small diameter portion61b, and to surely gather in the retaining region SA. In addition, although the retaining region SA is formed in the outside oil reservoir space8b, the minute foreign matter CT retained in the retaining region SA can even more surely be inhibited from moving toward the supply opening61csince the retaining region SA is located below the supply opening61c.

In this embodiment, the removal section RA includes a separation wall surface which is opposed to the flow of the oil supplied from the upstream side. Here, a portion of the outside small diameter portion61bin the removal section RA, which is the portion of the outer peripheral surface of the semi-floating metal bearing6opposed to the housing side supply opening26, corresponds to the separation wall surface in the above-described embodiment.

As described above, the removal section RA has the separation wall surface and the separation wall surface is located opposite the flow of the oil supplied from the upstream side. Accordingly, the entire flow of the oil supplied form the upstream side can surely be changed.

Furthermore, since the separation wall surface is formed on the outer peripheral surface of the semi-floating metal bearing6, it is possible to form the smaller turbocharger TC as compared to the case of additionally providing an independent wall surface, and moreover, to separate the minute foreign matter CT from the oil at the position closer to the supply opening61c.

In this embodiment, the separation wall surface is formed by locating the housing side supply opening26and the supply opening61cat different positions. Since the separation wall surface is formed by locating the housing side supply opening26and the supply opening61cat the different positions as described above, the separation wall can be formed easily and surely on the outer peripheral surface of the semi-floating metal bearing6.

Next, a first modified example of the embodiment will be described with reference toFIG. 3.FIG. 3is an enlarged cross-sectional view showing the first modified example of the invention depicted inFIG. 2. The modified example shown inFIG. 3uses a semi-floating metal bearing6L which is prepared by providing the semi-floating metal bearing6with a guide protrusion61dand a guide recess61e.

The guide protrusion61dis formed in the removal section RA. To be more precise, the guide protrusion61dis provided in the vicinity of the supply opening61cand beside the housing side supply opening26. A surface of the guide protrusion61ddirected to the housing side supply opening26forms a guide wall surface61da. Even if the minute foreign matter CT tries to flow toward the supply opening61c, the minute foreign matter CT is blocked by the guide wall surface61daand is guided toward the conveyance path TA.

The guide recess61eis formed in the removal section RA. To be more precise, the guide recess61eis provided in the vicinity of the supply opening61cand beside the housing side supply opening26, and is adjacent to the housing side supply opening26side of the guide protrusion61d. A surface of the guide recess61edirected to the housing side supply opening26forms a guide wall surface61ea. Even if the minute foreign matter CT tries to flow toward the supply opening61c, the minute foreign matter CT is blocked by the guide wall surface61eaand is guided toward the conveyance path TA.

Although both the guide protrusion61dand the guide recess61eare provided in this example, it is possible to provide any one of the guide protrusion61dand the guide recess61einstead.

Next, a second modified example of the embodiment will be described with reference toFIG. 4andFIG. 5.FIG. 4is an enlarged cross-sectional view showing the second modified example of the embodiment depicted inFIG. 2.FIG. 5is a cross-sectional view showing an A-A cross section inFIG. 4. The modified example shown inFIG. 4andFIG. 5uses a semi-floating metal bearing6M which is prepared by changing the position of the supply opening61cof the semi-floating metal bearing6.

A supply opening61caof the semi-floating metal bearing6M is provide on the side opposite of the rotating shaft5from the housing side supply opening26. As shown inFIG. 5, the minute foreign matter CT going into the outside oil reservoir space8bfrom the housing side supply opening26slips along the outside of the semi-floating metal bearing6M and is retained at the bottom of the outside oil reservoir space8b. The supply opening61caof the semi-floating metal bearing6M is formed at a lower part of the semi-floating metal bearing6M. Accordingly, the oil supply path FL goes upward into the inside oil reservoir space8aat this part. The oil supply path FL runs relatively close to the retaining region SA where the minute foreign matter CT is retained. Nonetheless, the oil supply path FL is designed to pass above the retaining region SA so as not to bring in the minute foreign matter CT. Furthermore, the flowing direction of the oil supply path FL is arranged in such a way as to run relatively close to the retaining region SA and then to go upward into the inside oil reservoir space8a. Thus, it is possible to reduce the bringing in of the minute foreign matter CT more effectively.

Next, a third modified example of the embodiment will be described with reference toFIG. 6.FIG. 6is an enlarged cross-sectional view showing the third modified example of the embodiment depicted inFIG. 2. The modified example shown inFIG. 6uses a semi-floating metal bearing6N which is prepared by changing the position of the supply opening61cof the semi-floating metal bearing6, and a bearing housing2N which is prepared by providing the bearing housing2with a separation wall member28.

A supply opening61cbof the semi-floating metal bearing6N is provided at a position in front of the housing side supply opening26. The bearing housing2N is provided with the separation wall member28. The separation wall member28is an L-shaped component which is provided on the housing inner wall21. The separation wall member28is provided in such a way as to intervene between the housing side supply opening26and the supply opening61cb. Accordingly, a separation wall surface28aof the separation wall member28is provided opposite to the housing side supply opening26.

The oil going into the outside oil reservoir space8bfrom the housing side supply opening26hits the separation wall surface28aof the separation wall member28and then meanders. Thereafter, the oil hits the outside small diameter portion61b, which is the outer peripheral surface of the semi-floating metal bearing6N, and flows toward the supply opening61cb. During this meandering process, the minute foreign matter CT is separated from the flow of the oil. Accordingly, the removal section RA includes the separation wall surface28a. The minute foreign matter CT separated from the flow of the oil by the removal section RA passes through the conveyance path TA and is retained in the retaining region SA.

Next, a fourth modified example of the embodiment will be described with reference toFIG. 7andFIG. 8.FIG. 7is an enlarged cross-sectional view showing the fourth modified example of the embodiment depicted inFIG. 2.FIG. 8is a cross-sectional view showing a B-B cross section inFIG. 7. The modified example shown inFIG. 7andFIG. 8uses a bearing housing2P which is prepared by changing an internal flow path in the bearing housing2.

A housing side supply opening26aof the bearing housing2P is provided opposite to the supply opening61cof the semi-floating metal bearing6. A separation chamber26ris formed between the oil feed passage25and the housing side supply opening26aof the bearing housing2P. When viewed in the direction of illustration inFIG. 7, an end portion25aof the oil feed passage25is joined to a portion near the center of the separation chamber26r. Meanwhile, the housing side supply opening26ais joined to one end portion of the separation chamber26r. Accordingly, the oil supplied to the separation chamber26rhits a bottom surface of the separation chamber26r, whereby the flowing direction of the oil is changed. Hence, the oil flows to the housing side supply opening26aand then to the supply opening61cdirectly. The above-described flow of the oil defines the oil supply path FL that extends from the oil feed passage25to the inside oil reservoir space8a.

To be more precise, the oil supplied from the oil feed passage25is passed through the end portion25aand is supplied to the separation chamber26r. Since the end portion25aof the oil feed passage25is opposed to the bottom surface of the separation chamber26r, the supplied oil hits the bottom surface of the separation chamber26rand its flowing direction is changed. Since the separation chamber26ris filled with the oil, a main flow of the oil, in which most of the oil flows even though not forming a fast flow, flows toward the housing side supply opening26aand the supply opening61calong the oil supply path FL.

Meanwhile, the minute foreign matter CT contained in the oil taps into the flow of the oil and is conveyed from the oil feed passage25to the separation chamber26r. As described previously, the flowing direction of the oil supplied to the separation chamber26ris changed substantially at a right angle along the oil supply path FL. In this example, the other end of the separation chamber26rfrom the one end portion where the housing side supply opening26ais formed is joined to the outside oil reservoir space8bwithout using the housing side supply opening26a(seeFIG. 8). The minute foreign matter CT contained in the oil has a higher specific gravity than the oil. Accordingly, the minute foreign matter CT does not follow the change in the flowing direction of the oil but falls along the bottom surface of the separation chamber26rby inertia. Hence, the minute foreign matter CT moves to the outside oil reservoir space8b. Thereafter, the minute foreign matter CT moving downward is retained in the lower part of the outside oil reservoir space8b.

In this modified example, an upper portion of the separation chamber26rfunctions as the removal section RA. As described above, the minute foreign matter CT separated from the flow of the oil at the upper portion of the separation chamber26rreaches the outside oil reservoir space8bvia the separation chamber26r. Accordingly, a lower portion of the separation chamber26rand part of the outside oil reservoir space8bcollectively function as the conveyance path TA.

The embodiment of the present invention has been described with reference to specific examples. It is to be noted, however, that the present invention is not limited only to these specific examples. In other words, a person skilled in the art can add design changes to any of these specific examples as appropriate, and such changes are also encompassed by the scope of the present invention as long as the changed examples retain the features of the present invention. For example, the elements included in any of the above-described examples, as well as layouts, materials, conditions, shapes, sizes, and the like of the elements are not limited only to those specified in the examples but can be changed as appropriate. In addition, any elements in the above-described examples can be used in combination as long as such combinations are technically feasible. Such combinations are also encompassed by the scope of the present inventions as long as the combined examples retain the features of the present invention.