Bearing structure and turbocharger

A bearing structure includes: a shaft provided with a turbine impeller; a pair of rolling bearings accommodated in a bearing hole and each including: an inner ring provided to the shaft; and an outer ring having a damper portion formed on an outer periphery of the outer ring; an opposing surface opposed to, from a turbine impeller side, a lateral surface of the outer ring of the rolling bearing provided on the turbine impeller side; and a first oil supply groove formed in the opposing surface and opposed to at least the damper portion and the lateral surface of the outer ring.

BACKGROUND ART

Technical Field

The present disclosure relates to a bearing structure and a turbocharger.

Related Art

In some cases, a turbocharger may include rolling bearings, for example, as described in Patent Literature 1. The rolling bearings are provided on a turbine side and a compressor side, respectively.

CITATION LIST

Patent Literature

Patent Literature 1: JP 6168739 B

SUMMARY

Technical Problem

In the turbocharger, the temperature on the turbine side is liable to be higher than the temperature on the compressor side. Therefore, there is a demand for improving a cooling performance for the rolling bearing provided on the turbine side.

The present disclosure has an object to provide a bearing structure and a turbocharger capable of improving a cooling performance for a rolling bearing provided on a turbine side.

Solution to Problem

In order to solve the above-mentioned problem, according to one aspect of the present disclosure, there is provided a bearing structure, comprising: a shaft provided with a turbine impeller; a pair of rolling bearings accommodated in a bearing hole and each including: an inner ring provided to the shaft; and an outer ring having a damper portion formed on an outer periphery of the outer ring; an opposing surface opposed to, from a turbine impeller side, a lateral surface of the outer ring of the rolling bearing provided on the turbine impeller side; and a first oil supply groove formed in the opposing surface and opposed to at least the damper portion and a lateral surface of the outer ring.

The outer ring may be rotatable with respect to a bearing housing in which the bearing hole is formed.

The first oil supply groove may extend to at least a position opposed to, in an axial direction of the shaft, an innermost portion in a radial direction of the lateral surface of the outer ring, and wherein the opposing surface may include an opposing portion that continues to the first oil supply groove in a circumferential direction of the shaft and that is closest to the lateral surface of the outer ring on the opposing surface.

The bearing structure may comprise a second oil supply groove formed in an inner peripheral surface of the bearing hole and opposed to the damper portion, and extending in the axial direction of the shaft to the first oil supply groove.

The bearing structure may comprise: a first oil passage formed in the inner peripheral surface of the bearing hole and opened toward the rolling bearing provided on the turbine impeller side; a second oil passage formed in the inner peripheral surface of the bearing hole and opened toward the rolling bearing provided on a compressor impeller side; and a third oil passage formed in the inner peripheral surface of the bearing hole and opened between the first oil passage and the second oil passage.

The pair of rolling bearings may be angular bearings having a face-to-face duplex configuration.

In order to solve the above-mentioned problem, according to one aspect of the present disclosure, the turbocharger includes the bearing structure described above.

Effects of Disclosure

According to the present disclosure, it is possible to improve a cooling performance for a rolling bearing provided on a turbine side.

DESCRIPTION OF EMBODIMENTS

Now, with reference to the attached drawings, an embodiment of the present disclosure is described. Dimensions, materials, and specific numerical values, and the like described in the embodiment are merely examples used for facilitating the understanding, and do not limit the present disclosure otherwise particularly noted. Elements having substantially the same functions and configurations herein and in the drawings are denoted by the same reference symbols to omit redundant description thereof, and illustration of elements with no direct relationship to the present disclosure is omitted.

FIG. 1is a schematic sectional view for illustrating a turbocharger TC. In the following, a direction indicated by the arrow L illustrated inFIG. 1corresponds to a left side of the turbocharger TC. A direction indicated by the arrow R illustrated inFIG. 1corresponds to a right side of the turbocharger TC. As illustrated inFIG. 1, the turbocharger TC includes a turbocharger main body1. The turbocharger main body1includes a bearing housing20. A turbine housing3is coupled to the left side of the bearing housing20by a fastening mechanism2. A compressor housing5is coupled to the right side of the bearing housing20by fastening bolts4.

A protrusion21is formed on an outer peripheral surface of the bearing housing20. The protrusion21is formed on the turbine housing3side. The protrusion21protrudes in a radial direction of the bearing housing20. A protrusion3ais formed on an outer peripheral surface of the turbine housing3. The protrusion3ais formed on the bearing housing20side. The protrusion3aprotrudes in a radial direction of the turbine housing3. The protrusions21and3aare band-fastened by the fastening mechanism2. The fastening mechanism2is, for example, formed of a G coupling configured to clamp the protrusions21and3a.

A bearing hole22is formed in the bearing housing20. The bearing hole22penetrates in a right-and-left direction of the turbocharger TC. A pair of rolling bearings6are provided in the bearing hole22. The shaft7is rotatably supported by the rolling bearings6. A turbine impeller8is provided at a left end portion of the shaft V. The turbine impeller8is rotatably accommodated in the turbine housing3. A compressor impeller9is provided at a right end portion of the shaft7. The compressor impeller9is rotatably accommodated in the compressor housing5.

An intake port10is formed in the compressor housing5. The intake port10is opened on the right side of the turbocharger TC. The intake port10is connected to an air cleaner (not shown). A diffuser flow passage11is defined by the bearing housing20and the compressor housing5coupled to each other by the fastening bolts4. The diffuser flow passage11increases pressure of air. The diffuser flow passage11is formed in an annular shape from an inner side toward an outer side in a radial direction of the shaft7(hereinafter simply referred to as “radial direction”). The diffuser flow passage11communicates with the intake port10on the inner side in the radial direction via the compressor impeller9.

A compressor scroll flow passage12is formed inside the compressor housing5. The compressor scroll flow passage12has an annular shape. The compressor scroll flow passage12is located on an outer side in the radial direction with respect to the compressor impeller9. The compressor scroll flow passage12communicates with an intake port of an engine (not shown). The compressor scroll flow passage12also communicates with the diffuser flow passage11. When the compressor impeller9rotates, the air is sucked from the intake port10into the compressor housing5. The sucked air is accelerated by an effect of a centrifugal force in the process of flowing through blades of the compressor impeller9. The accelerated air is pressurized by the diffuser flow passage11and the compressor scroll flow passage12. The pressurized air flows out from an exhaust port (not shown) and is led to the intake port of the engine.

An exhaust port13is formed in the turbine housing3. The exhaust port13is opened on the left side of the turbocharger TC. The exhaust port13is connected to an exhaust gas purification device (not shown). A flow passage14and a turbine scroll flow passage15are formed in the turbine housing3. The turbine scroll flow passage15has an annular shape. The turbine scroll flow passage15is located on an outer side with respect to the turbine impeller8in a radial direction. The flow passage14is located between the turbine impeller8and the turbine scroll flow passage15.

The turbine scroll flow passage15communicates with a gas inlet port (not shown). Exhaust gas discharged from an exhaust manifold (not shown) of the engine is led to the gas inlet port. The turbine scroll flow passage15also communicates with the flow passage14. The exhaust gas led from the gas inlet port to the turbine scroll flow passage15is led to the exhaust port13via the flow passage14and spaces between blades of the turbine impeller8. The exhaust gas led to the exhaust port13rotates the turbine impeller8in the process of flowing therethrough.

A rotational force of the turbine impeller8is transmitted to the compressor impeller9via the shaft7. When the compressor impeller9rotates, the air is pressurized as described above. In such a manner, the air is led to the intake port of the engine.

FIG. 2is an extracted view for illustrating a portion indicated by two-dot chain lines ofFIG. 1. As illustrated inFIG. 2, the turbocharger TC includes a bearing structure S. In the bearing structure S, a branch-origin oil passage23is formed in the bearing housing20. The branch-origin oil passage23extends in an axial direction of the shaft7(rotation axis direction, hereinafter referred to simply as “axial direction”). The branch-origin oil passage23extends substantially parallel to the bearing hole22. The branch-origin oil passage23is located on an upper side in the vertical direction, with respect to the bearing hole22.

The bearing hole22and the branch-origin oil passage23are opened in an opening surface24of the bearing housing20. The opening surface24extends, for example, perpendicular to the axial direction. A seal plate40is mounted to the opening surface24. The seal plate40has a substantially annular shape. The seal plate40closes an opening of the branch-origin oil passage23. An inner diameter of the seal plate40is smaller than an inner diameter of the bearing hole22. A part of the seal plate40on an inner side in the radial direction protrudes toward an inner side in the radial direction with respect to the bearing hole22.

A through hole25is opened with respect to the branch-origin oil passage23. The through hole25is formed in the bearing housing20. The through hole25extends from an outside of the bearing housing20to the branch-origin oil passage23. Oil fed out from an oil pump (not shown) is supplied from the through hole25to the branch-origin oil passage23.

A first oil passage26, a second oil passage27, and a third oil passage28are formed in the bearing housing20. The first oil passage26, the second oil passage27, and the third oil passage28are opened with respect to the branch-origin oil passage23. The first oil passage26, the second oil passage27, and the third oil passage28are also opened with respect to an inner peripheral surface of the bearing hole22. The first oil passage26, the second oil passage27, and the third oil passage28allow the branch-origin oil passage23and the bearing hole22to communicate with each other.

The first oil passage26is formed on the left side ofFIG. 2(on the turbine impeller8side, or on the side of a turbine-side bearing50described later), with respect to the second oil passage27. The third oil passage28is formed between the first oil passage26and the second oil passage27. The third oil passage28is opened between the first oil passage26and the second oil passage27in the inner peripheral surface of the bearing hole22.

An oil discharging hole29ais formed in a lower wall portion29of the bearing housing20. The lower wall portion29is located on a lower side ofFIG. 2(lower side in the vertical direction) with respect to the bearing hole22. The lower wall portion29forms a part of (the inner peripheral surface of) the bearing hole22. The oil discharging hole29apenetrates through the lower wall portion29in a direction perpendicular to the axial direction. The oil discharging hole29ais opened in the inner peripheral surface of the bearing hole22. A position of the oil discharging hole29ain the axial direction is, for example, between the first oil passage26and the second oil passage27(between the pair of rolling bearings6).

A side wall portion30is formed on the bearing housing20. The side wall portion30protrudes from the inner peripheral surface of the bearing hole22toward an inner side in the radial direction. The side wall portion30has an annular shape. A right end surface31(opposing surface) of the side wall portion30inFIG. 2(compressor impeller9side) extends, for example, in the radial direction. The side wall portion30is formed integrally with the bearing housing20. However, the side wall portion30may be a member that is separate from the bearing housing20and may be mounted to the bearing housing20.

Further, the shaft7is inserted through the bearing hole22. The shaft7includes a large-diameter portion7a, a middle-diameter portion7b, and a small-diameter portion7c. An outer diameter of the middle-diameter portion7bis smaller than an outer diameter of the large-diameter portion7a. The middle-diameter portion7bis located on the right side ofFIG. 2(compressor impeller9side) with respect to the large-diameter portion7a. An outer diameter of the small-diameter portion7cis smaller than the outer diameter of the middle-diameter portion7b. The small-diameter portion7cis located on the compressor impeller9side with respect to the middle-diameter portion7b. A position of the middle-diameter portion7bin the axial direction is located between the side wall portion30and the seal plate40.

A first step surface7dand a second step surface7eare formed on the shaft7. The first step surface7dradially extends from an outer peripheral surface of the large-diameter portion7ato an outer peripheral surface of the middle-diameter portion7b. The second step surface7eradially extends from the outer peripheral surface of the middle-diameter portion7bto an outer peripheral surface of the small-diameter portion7c. A tapered surface Tal is formed on the middle-diameter portion7bside of the outer peripheral surface of the large-diameter portion7a. An outer diameter of the tapered surface Tal decreases as closer to the middle-diameter portion7b. A part of the tapered surface Tal having the smallest outer diameter continues to the first step surface7d.

The rolling bearings6are arranged in the bearing hole22. Two rolling bearings6are provided in the bearing hole22. The two rolling bearings6are apart from each other in the axial direction. In the following description, when the two rolling bearings6are distinguished, the rolling bearing6arranged on the left side ofFIG. 2(turbine impeller8side) is referred to as “turbine-side bearing50”. The rolling bearing6arranged on the right side ofFIG. 2(compressor impeller9side) is referred to as “compressor-side bearing60”.

The turbine-side bearing50includes an inner ring51, an outer ring52, rolling elements53, and a cage54. The inner ring51is mounted to the outer peripheral surface of the middle-diameter portion7bof the shaft7. The inner ring51rotates integrally with the shaft V. The outer ring52is provided on an outer side in the radial direction with respect to the inner ring51. The outer ring52is opposed to the inner peripheral surface of the bearing hole22. A plurality of rolling elements53are arranged between the outer ring52and the inner ring51. The cage54retains the plurality of rolling elements53.

Similarly, the compressor-side bearing60includes an inner ring61, an outer ring62, rolling elements63, and a cage64. The inner ring61is mounted to the outer peripheral surface of the middle-diameter portion7bof the shaft7. The inner ring61rotates integrally with the shaft7. The outer ring62is provided on an outer side in the radial direction with respect to the inner ring61. The outer ring62is opposed to the inner peripheral surface of the bearing hole22. A plurality of rolling elements63are arranged between the outer ring62and the inner ring61. The cage64retains the plurality of rolling elements63.

The rolling bearings6are, for example, angular bearings. Connection lines indicated by broken lines inFIG. 2each connect a position at which the outer ring52,62of the rolling bearing6is closest to (or is brought into abutment against) the rolling element53,63and a position at which the inner ring51,61is closest to (or is brought into abutment against) the rolling element53,63. The connection lines each indicate a contact angle of the rolling bearing6. The connection lines are inclined with respect to a surface perpendicular to the axial direction of the shaft7. The connection line of the turbine-side bearing50is inclined in a direction spaced away from the compressor-side bearing60, as closer to the outer side in the radial direction. The connection line of the compressor-side bearing60is inclined in a direction spaced away from the turbine-side bearing50, as closer to the outer side in the radial direction.

In the inner ring51of the turbine-side bearing50, a thickness of an outer lateral surface51aon the large-diameter portion7aside is smaller than a thickness of an inner lateral surface51bon the compressor-side bearing60side. In the inner ring61of the compressor-side bearing60, a thickness of an outer lateral surface61aon the seal plate40side is smaller than a thickness of an inner lateral surface61bon the turbine-side bearing50side. However, the thickness of the outer lateral surface51a,61amay be larger than the thickness of the inner lateral surface51b,61bor may be equal to the thickness of the inner lateral surface51b,61b.

In the outer ring52of the turbine-side bearing50, a thickness of an outer lateral surface52a(lateral surface) on the side wall portion30side is approximately equal to a thickness of an inner lateral surface52bon the compressor-side bearing60side. In the outer ring62, a thickness of an outer lateral surface62aon the seal plate40side is approximately equal to a thickness of an inner lateral surface62bon the turbine-side bearing50side. However, the thickness of the outer lateral surface52a,62amay be larger or smaller than the thickness of the inner lateral surface52b,62b.

The inner ring51(outer lateral surface51a) of the turbine-side bearing50is brought into abutment against the first step surface7d. The inner ring51is brought into abutment against the first step surface7dfrom the right side ofFIG. 2(compressor impeller9side). An outer diameter of the first step surface7dis approximately equal to an outer diameter of the outer lateral surface51aof the inner ring51. However, the outer diameter of the first step surface7dmay be larger or smaller than the outer diameter of the outer lateral surface51a.

The outer ring52(outer lateral surface52a) of the turbine-side bearing50is opposed to the end surface31of the side wall portion30in the axial direction. The end surface31is opposed to the outer lateral surface52aof the outer ring52from the left side ofFIG. 2(turbine impeller8side).

A spacer70is provided between the inner ring51and the inner ring61. The spacer70has an annular shape. The shaft7is inserted through the spacer70. The spacer70is opposed to the inner lateral surface51bof the inner ring51and the inner lateral surface61bof the inner ring61in the axial direction. An outer diameter of the spacer70is approximately equal to the outer diameter of the inner lateral surface51b,61bof the inner ring51,61. However, the outer diameter of the spacer70may be larger or smaller than the outer diameter of the inner lateral surface51b,61bof the inner ring51,61. Further, a spring and spring stoppers may be provided in place of the spacer70.

An oil thrower member80is mounted to the small-diameter portion7cof the shaft7. The oil thrower member80causes oil to scatter toward the outer side in the radial direction, after lubricating the compressor-side bearing60. An insertion portion81of the oil thrower member80is inserted through the seal plate40. The seal plate40is located on the outer side in the radial direction with respect to the insertion portion81. The seal plate40is opposed to the outer ring62(outer lateral surface62a) in the axial direction.

An outer diameter of the insertion portion81is larger than the outer diameter of the outer lateral surface61aof the inner ring61of the compressor-side bearing60. However, it is only required that the outer diameter of the insertion portion81be larger than at least an inner diameter of the outer lateral surface61a. The insertion portion81is brought into abutment against the outer lateral surface61a. The inner ring61is brought into abutment against the insertion portion81from the left side ofFIG. 2(turbine impeller8side).

The turbine-side bearing50(inner ring51), the spacer70, the compressor-side bearing60(inner ring61), the oil thrower member80, and the compressor impeller9are mounted to the shaft7from the end portion of the shaft7on the compressor impeller9side in the order of the turbine-side bearing50, the spacer70, the compressor-side bearing60, the oil thrower member80, and the compressor impeller9. Fastening bolts are fastened to the end portion of the shaft7on the compressor impeller9side. A compressive force (axial force) acts on those members in the axial direction. The turbine-side bearing50, the spacer70, the compressor-side bearing60, the oil thrower member80, and the compressor impeller9rotate integrally with the shaft7.

A damper portion55is formed on an outer peripheral surface52cof the outer ring52of the turbine-side bearing50. The damper portion55includes an annular groove55a, an inner parallel surface55b, an outer parallel surface55c, and a cutout portion55d. The annular groove55a, the inner parallel surface55b, the outer parallel surface55c, and the cutout portion55deach have an annular shape. The annular groove55adivides the outer peripheral surface52cin the axial direction. A surface located closer to the compressor-side bearing60with respect to the annular groove55acorresponds to the inner parallel surface55b. A surface located closer to the side wall portion30with respect to the annular groove55acorresponds to the outer parallel surface55c. The cutout portion55dis formed on the side wall portion30side of the outer parallel surface55c. The outer parallel surface55cis shorter than the inner parallel surface55bin the axial direction by the length corresponding to the cutout portion55d.

The first oil passage26is opened toward the turbine-side bearing50in the inner peripheral surface of the bearing hole22. The first oil passage26is opposed to the outer side of the annular groove55ain the radial direction. Oil is supplied from the first oil passage26to the annular groove55a. The oil spreads throughout the entire periphery of the annular groove55a. The oil flows from the annular groove55atoward the inner parallel surface55bside and the outer parallel surface55cside. The oil tends to flow toward the side of the outer parallel surface55chaving a small length. Therefore, a cooling effect on the side wall portion30side is improved. Vibration of the shaft7is curbed by the oil supplied between the inner peripheral surface of the bearing hole22and each of the inner parallel surface55band the outer parallel surface55c.

Here, the turbine-side bearing50is described in detail. The compressor-side bearing60also has the same configuration. A damper portion65is formed on the outer peripheral surface62cof the outer ring62. The damper portion65includes an annular groove65a, an inner parallel surface65b, an outer parallel surface65c, and a cutout portion65d. The second oil passage27is opened toward the compressor-side bearing60in the inner peripheral surface of the bearing hole22. The second oil passage27is opposed to the outer side of the annular groove65ain the radial direction. The vibration of the shaft7is suppressed by the oil supplied between the inner peripheral surface of the bearing hole22and each of the inner parallel surface65band the outer parallel surface65c.

In such a manner, the damper portions55and65are formed on the outer rings52and62, respectively. Therefore, support member configured to support the turbine-side bearing50and the compressor-side bearing60and function as the damper portions are not required. The outer rings52and62are smaller in weight than such a support member. Accordingly, the damper function is improved.

The illustrated shape of each of the damper portions55and65is merely an example. The damper portions55and65may have any shape as long as the vibration is curbed by the oil supplied between the bearing hole22and each of the outer rings52and62. In order to allow the outer peripheral surfaces52cand62cof the outer rings52and62to function as the damper portions55and65, the bearing hole22may be processed.

The curbing effect for the vibration of the shaft7can be changed by changing the lengths of the inner parallel surfaces55band65band the outer parallel surfaces55cand65cin the axial direction, without changing the overall shapes of the outer rings52and62. Therefore, the damper portions55and65can be designed easily. Part of the oil passing through the damper portions55and65is supplied to the rolling elements53and63of the turbine-side bearing50and the compressor-side bearing60and thereafter is discharged from the oil discharging hole29a.

The rolling bearings6are angular bearings, and therefore receive a thrust load of the shaft7. When the thrust load acts on the shaft7leftward ofFIG. 2, the outer ring52of the turbine-side bearing50presses the side wall portion30. When the thrust load acts on the shaft7rightward ofFIG. 2, the outer ring62of the compressor-side bearing60presses the seal plate40. Movement of the shaft7caused by the thrust load is stopped by the side wall portion30and the seal plate40.

No rotation stopper is provided to the outer rings52and62. When the outer rings52and62do not press the side wall portion30and the seal plate40, the outer rings52and62are relatively rotatable (freely rotatable) in a circumferential direction of the shaft7with respect to the bearing housing20(bearing hole22). When the shaft7rotates, the inner rings51and61rotate integrally with the shaft7. The rolling elements53and63rotate along with rotation of the inner rings51and61. The rolling elements53and63move in a circumferential direction of the inner rings51and61, respectively. The outer rings52and62rotate in the circumferential direction of the shaft7along with the rotation and movement of the rolling elements53and63or along with a flow of the oil. The rotation speed of the outer ring52is lower than the rotation speed of the inner ring51. The vibration curbing effect is improved by arranging the outer rings52and62relatively rotatable.

The pair of rolling bearings6have a face-to-face duplex configuration. Therefore, there is no need to provide a spacer (seat for outer rings) between the outer ring52and the outer ring62. The outer rings52and62cannot be preloaded. Therefore, the outer ring52and62can rotate easily. As a result, the vibration curbing effect of the damper portions55and65is improved.

In the bearing structure S, the temperature on the left side ofFIG. 2(turbine impeller8side or turbine-side bearing50side) is liable to be higher than the temperature on the right side (compressor impeller9side or compressor-side bearing60side). Therefore, the third oil passage28is formed. The shaft7, the spacer70configured to rotate integrally with the shaft7, and the inner ring51are located on an extension of the third oil passage28.

Through the shaft7, the spacer70configured to rotate integrally with the shaft7, and the inner ring51, a part of the bearing structure S that is liable to be higher in temperature is efficiently cooled. In particular, since the amount of oil required for lubricating the rolling bearings6is small, mechanical losses are caused if a large amount of oil is supplied to the turbine-side bearing50. By forming the third oil passage28, a cooling effect for a high-temperature part can be improved without excessively increasing the amount of oil supplied to the turbine-side bearing50. Further, the temperature of the oil supplied to the rolling bearings6is increased. By forming the third oil passage28, the high-temperature part can be efficiently cooled with the low-temperature oil from the branch-origin oil passage23.

If a spacer is provided between the outer ring52and the outer ring62, the spacer will face the third oil passage28. The spacer will block the supply of oil from the third oil passage28to the high-temperature part. The pair of rolling bearings6have the face-to-face duplex configuration, and hence there is no need to provide the spacer. As a result, the oil can be supplied easily from the third oil passage28to the high-temperature part.

FIG. 3is a sectional view taken along the line ofFIG. 2. InFIG. 3, only the bearing housing20is illustrated. InFIG. 3, a first oil supply groove31ais illustrated with coarse cross hatching, and a second oil supply groove22ais illustrated with fine cross hatching, which will be described later. As illustrated inFIG. 3, the first oil passage26has a substantially crescent shape as seen from the axial direction. The first oil passage26extends from the inner peripheral surface of the bearing hole22toward the outer side in the radial direction. A curvature radius of an inner peripheral surface of the first oil passage26is smaller than the inner diameter of the bearing hole22.

In the side wall portion30of the bearing housing20, the first oil supply groove31ais formed on the end surface31on the turbine-side bearing50side (near side on the drawing sheet ofFIG. 3). The first oil supply groove31aextends in, for example, the radial direction. The first oil supply groove31ais formed at a position turned by a predetermined angle α from a connection line connecting a center of the bearing hole22and a center of the branch-origin oil passage23. When a rotation direction of the shaft7is a clockwise inFIG. 3, the first oil supply groove31ais located on a forward side in the rotation direction of the shaft7with respect to the connection line. When the rotation direction of the shaft7is a counterclockwise inFIG. 3, the first oil supply groove31ais located on a backward side in the rotation direction of the shaft7with respect to the connection line. When the up-and-down direction ofFIG. 3corresponds to the vertical direction, the first oil supply groove31ais formed at a position turned by the predetermined angle α in the circumferential direction of the shaft7from a vertical plane passing through the center of the bearing hole22.

A phase of the second oil supply groove22adescribed later is formed so as to correspond to a phase of the first oil supply groove31a. The thickness of a wall portion between the second oil supply groove22aand the branch-origin oil passage23is sufficiently secured by shifting the phase of the first oil supply groove31awith respect to the above-mentioned connection line. However, as long as the strength of the wall portion does not become insufficient, the first oil supply groove31aand the second oil supply groove22amay be formed so that the above-mentioned vertical plane is positioned at a center thereof. Further, the first oil passage26described above may be formed into an annular shape. In this case, the first oil supply groove31aand the second oil supply groove22amay be formed at any position in the circumferential direction of the shaft7.

The first oil supply groove31ais formed, for example, by cutting from the center side of the bearing hole22with using a tool having a diameter smaller than an inner diameter of the side wall portion30. However, the first oil supply groove31amay be formed by other means.

An opposing portion31bis formed on the end surface31of the side wall portion30. The opposing portion31bcontinues to the first oil supply groove31ain the circumferential direction of the shaft7. The opposing portion31bis, for example, a remaining part of the end surface31at which the first oil supply groove31ais not formed. A part of the end surface31opposed to the outer lateral surface52ain the axial direction has a portion at which the first oil supply groove31ais not formed. In the end surface31, the opposing portion31bis closest to the outer lateral surface52aof the outer ring52.

As described above, the thrust load causes the outer ring52to press the end surface31. When the opposing portion31bis not formed, the outer ring52is brought into abutment against a bottom surface of the first oil supply groove31a. As a result, the first oil supply groove31ais closed by the outer ring52. By forming the opposing portion31b, the outer ring52is positioned in the axial direction by the opposing portion31b.

The opposing portion31bextends in the circumferential direction of the shaft7over about one-eighth (equal to or smaller than one-half, or equal to or smaller than one-fourth) of the entire periphery. Therefore, even when the outer ring52is pressed against the end surface31, the outer ring52is less liable to incline.

FIG. 4is a sectional view for illustrating the bearing structure S. InFIG. 4, a cross section of the bearing structure S taken along the line IV-IV ofFIG. 3is illustrated. That is, the upper portion above the center axis of the shaft7inFIG. 4corresponds to a cross section illustrated inFIG. 3obtained by shifting the phase in the circumferential direction of the shaft7by the predetermined angle α.

As illustrated inFIG. 4, the first oil supply groove31ais opposed to at least the damper portion55and the outer lateral surface52aof the outer ring52. Here, an outermost part in the radial direction of the first oil supply groove31acontinues to the inner peripheral surface of the bearing hole22. The outermost part in the radial direction of the first oil supply groove31ais flush with the damper portion55of the outer ring52, or is located on the outer side in the radial direction with respect to the damper portion55. The first oil supply groove31aextends to at least a position opposed to, in the axial direction, an innermost part in the radial direction of the outer lateral surface52aof the outer ring52. The first oil supply groove31aextends to a position on the inner side in the radial direction with respect to the outer ring52. The first oil supply groove31aextends to an end portion of the end surface31on the innermost side in the radial direction. However, it is only required that a part of the first oil supply groove31abe opposed to the outer lateral surface52ain the axial direction.

By forming the first oil supply groove31a, the amount of oil that flows from the damper portion55toward the outer lateral surface52aside increases. The cooling effect for the high-temperature part is improved. The oil flows in the axial direction on the turbine impeller8side by the amount corresponding to a depth of the first oil supply groove31a. Therefore, the cooling effect is improved.

The second oil supply groove22ais formed in the inner peripheral surface of the bearing hole22. The second oil supply groove22ais opposed to the outer parallel surface55cand the cutout portion55dof the damper portion55. The second oil supply groove22ais located on the outer side of the outer parallel surface55cin the radial direction. The second oil supply groove22aextends in the axial direction from the first oil passage26to the first oil supply groove31a. However, it is only required that the second oil supply groove22aextend to at least the first oil supply groove31a, and the second oil supply groove22amay be apart from the first oil passage26in the axial direction.

By forming the second oil supply groove22a, the amount of oil that flows from the damper portion55toward the outer lateral surface52aside increases. The cooling effect for the high-temperature part is improved. Further, with the rotation of the outer ring52, the oil can spread easily throughout the entire inner peripheral surface of the bearing hole22. Therefore, the entire inner peripheral surface of the bearing hole22is cooled.

Although the embodiment of the present disclosure has been described above with reference to the attached drawings, it is understood that the present disclosure is not limited to the above-mentioned embodiment. It is obvious that a person skilled in the art can conceive of various alternations and modifications within the scope of claims, and those examples are construed as falling within the technical scope of the present disclosure.

In the above-mentioned embodiment, description is given of the case in which the two rolling bearings6are provided apart from each other in the axial direction in the bearing hole22. However, three or more rolling bearings6may be arranged.

In the above-mentioned embodiment, description is given of the case in which the first oil supply groove31aand the second oil supply groove22aare formed only on the turbine-side bearing50side. However, the first oil supply groove31aand the second oil supply groove22amay be similarly formed also on the compressor-side bearing60side.

In the above-mentioned embodiment, description is given of the case in which the outer rings52and62are rotatable with respect to the bearing housing20in which the bearing hole22is formed. However, as long as the damper portions55and65are provided to the outer rings52and62, respectively, the movement of the outer rings52and62in the rotation direction may be restricted.

In the above-mentioned embodiment, description is given of the case in which the opposing portion31bis formed on the end surface31of the side wall portion30. However, the opposing portion31bis not essential.

In the above-mentioned embodiment, description is given of the case in which the second oil supply groove22ais formed on the inner peripheral surface of the bearing hole22. However, the second oil supply groove22ais not essential.

In the above-mentioned embodiment, description is given of the case in which, in addition to the first oil passage26and the second oil passage27, the third oil passage28is formed in the bearing housing20. However, the third oil passage28is not essential.

In the above-mentioned embodiment, description is given of the case in which the pair of rolling bearings6are angular bearings having the face-to-face duplex configuration. However, the rolling bearings6may be rolling bearings other than the angular bearings (for example, deep-groove ball bearings or self-aligning ball bearings). Further, the pair of rolling bearings6may have a back-to-back duplex configuration.

INDUSTRIAL APPLICABILITY

The present disclosure can be used for a bearing structure and a turbocharger.