Floating bush bearing device and supercharger provided with the same

A floating-bush bearing device (1) for rotatably supporting a rotational shaft (2), includes: a floating bush (3) having a cylindrical shape and including a bearing hole (33) into which the rotational shaft (2) is to be inserted; and a bearing housing (4) which rotatably houses the floating bush (3). At least one of an inner peripheral surface (31) of the floating bush (3), an outer peripheral surface (32) of the floating bush (3), or an inner peripheral surface (41) of the bearing housing (4) includes, in a cross section in an axial direction thereof, a plurality of land portions (311, 321, 411) having a true arc shape which is a part of a true circular shape, and a plurality of recess portions (312, 322, 412) being disposed at a position recessed from the land portions, the recess portions being configured such that a distance between the recess portions and a virtual true circular line (31a, 32a, 41a) passing through the land portions increases in a direction opposite from a rotational direction of the rotational shaft (2) from end portions (311b, 321b, 411b) of the land portions opposite from the rotational direction of the rotational shaft.

TECHNICAL FIELD

The present disclosure relates to a floating bush bearing device for rotatably supporting a rotational shaft and a supercharger provided with the floating bush bearing device.

BACKGROUND ART

In relation to bearing devices for rotatably supporting a rotational shaft, a floating bush bearing device is known, which includes a floating bush having a cylindrical shape and including a bearing hole into which a rotational shaft can be inserted (see Patent Document 1, for instance). Such a floating bush bearing device supplies a gap between a floating bush and a rotational shaft with lubricant oil to form an oil film, and rotatably supports the rotational shaft with the oil film formed in the gap.

Furthermore, in the floating bush bearing device disclosed in Patent Document 1, the circularity of the inner peripheral surface of the floating bush is changed into a polygonal shape to enhance the centering effect, thus improving the oscillation stability.

CITATION LIST

Patent Literature

SUMMARY

Problems to be Solved

However, the present inventors found that, if the circularity is changed into a polygonal shape by machining the entire area of the inner peripheral surface of a floating bush like the floating bush bearing device disclosed in Patent Document 1, oscillation that does not synchronize with rotation of the rotational shaft (hereinafter, non-synchronous oscillation) is likely to occur. The present inventors conducted intensive researches to find out the reason for the above, and found that the non-synchronous oscillation is caused by machining tolerance that exists over the entire area of the inner peripheral surface of the floating bush when the inner peripheral surface of the floating bush is entirely machined.

At least one embodiment of the present invention was made in view of the above problem of the typical arts, and an object is to provide a floating bush bearing device with an excellent oscillation stability and a supercharger including the floating bush bearing device.

Solution to the Problems

(1) A floating-bush bearing device for rotatably supporting a rotational shaft according to at least one embodiment of the present invention comprises: a floating bush having a cylindrical shape and including a bearing hole into which the rotational shaft is to be inserted; and a bearing housing which rotatably houses the floating bush. At least one of an inner peripheral surface of the floating bush, an outer peripheral surface of the floating bush, or an inner peripheral surface of the bearing housing includes, in a cross section in an axial direction thereof, a plurality of land portions having a true arc shape which is a part of a true circular shape, and a plurality of recess portions being disposed at a position recessed from the land portions, the recess portions being configured such that a distance between the recess portions and a virtual true circular line passing through the land portions increases in a direction opposite from a rotational direction of the rotational shaft from end portions of the land portions opposite from the rotational direction of the rotational shaft.

The land portions have a true arc shape, which is a part of a true circular shape, and thus it is possible to control the tolerance of the land portions to be smaller than the tolerance of the recess portions. Thus, according to the above embodiment (1), with at least one of the inner peripheral surface of the floating bush, the outer peripheral surface of the floating bush, or the inner peripheral surface of the bearing housing being formed to include the above land portions in a cross section in the axial direction, it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability.

Furthermore, the recess portions disposed at positions recessed from the land portions are configured such that a distance from the virtual true circular line passing through the land portions increases from the end portions of the land portions opposite to the rotational direction of the rotational shaft toward a direction opposite to the rotational direction of the rotational shaft. With such recess portions, the gap in the circumferential direction become uneven, which provokes shortage of lubricant oil at sections where the gaps are large. If the lubricant oil falls short as described above partially in the circumferential direction, the axis eccentricity ratio increases and thereby the oscillation stability increases, according to the findings of the present inventors. Thus, according to the above embodiment (1), with at least one of the inner peripheral surface of the floating bush, the outer peripheral surface of the floating bush, or the inner peripheral surface of the bearing housing being formed to include the above recess portions in a cross section in the axial direction thereof, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

(2) In some embodiments, in the above described floating bush bearing device (1), the inner peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush.

According to the above embodiment (2), the gap between the rotational shaft and the land portions of the inner peripheral surface of the floating bush is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability. Furthermore, a large section of the gap is formed between the rotational shaft and the inner peripheral surface of the floating bush, and thereby it is possible to provoke shortage of lubricant oil in the large section of the gap to enhance the oscillation stability.

(3) In some embodiments, in the above described floating bush bearing device (1) or (2), the outer peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush.

According to the above embodiment (3), the gap between the land portion of the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability. Furthermore, a large section of the gap is formed between the land portion of the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing, and thereby it is possible to provoke shortage of lubricant oil in the large section of the gap to enhance the oscillation stability.

(4) In some embodiments, in the floating bush bearing device according to any one of the above (1) to (3), the inner peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The outer peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The land portions on the inner peripheral surface of the floating bush and the land portions on the outer peripheral surface of the floating bush are formed in regions which overlap with each other in a circumferential direction. The recess portions on the inner peripheral surface of the floating bush and the recess portions on the outer peripheral surface of the floating bush are formed in regions which overlap with each other in the circumferential direction.

With the above embodiment (4), the gap between the rotational shaft and the land portion of the inner peripheral surface of the floating bush and the gap between the land portion of the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing are controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability. Furthermore, large sections of the gaps are formed between the rotational shaft and the inner peripheral surface of the floating bush and between the land portion of the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing, and thereby it is possible to provoke shortage of lubricant oil in the large sections of the gap to enhance the oscillation stability.

(5) In some embodiments, in the floating bush bearing device according to any one of the above (2) to (4), the floating bush includes an oil supply hole formed through a peripheral wall of the floating bush having a cylindrical shape. The oil supply hole is formed at a position which overlaps with an end portion of the land portions on a side of the rotational direction of the rotational shaft, or an end portion of the recess portions on a side opposite from the rotational direction of the rotational shaft, as seen in the axial direction.

With the above embodiment (5), the oil supply hole is formed on a position where the distance from the true circular line is greatest, or in the vicinity of the position, on the recess portion. Thus, with the oil supply hole formed on such a position, it is possible to increase the flow rate of lubricant oil that flows from the outer peripheral side of the floating bush toward the inner peripheral side of the floating bush.

(6) In some embodiments, in the floating bush bearing device according to any one of the above (1) to (5), the inner peripheral surface of the bearing housing is formed to include each of the land portions and the recess portions in a cross section in the axial direction of the bearing housing.

With the above embodiment (6), the gap between the land portion of the inner peripheral surface of the bearing housing and the outer peripheral surface of the floating bush is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability. Furthermore, a large section of the gap is formed between the inner peripheral surface of the bearing housing and the outer peripheral surface of the floating bush, and thereby it is possible to provoke shortage of lubricant oil in the large section of the gap to enhance the oscillation stability.

(7) In some embodiments, in the floating bush bearing device according to any one of the above (1) to (6), the land portions and the recess portions formed on at least one of the inner peripheral surface of the floating bush, the outer peripheral surface of the floating bush, or the inner peripheral surface of the bearing housing are formed continuously over the axial direction of the bearing housing or the floating bush. The recess portions are formed so that a distance between the recess portions and the virtual true circular line changes in the axial direction.

With the above embodiment (7), the distance between the recess portion and the virtual true circular line changes in the axial direction. With such recess portions, the gap in the axial direction become uneven, which provokes shortage of lubricant oil at sections where the gaps are large. Thus, with at least one of the inner peripheral surface of the floating bush, the outer peripheral surface of the floating bush, or the inner peripheral surface of the bearing housing being formed to include the above recess portions, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

(8) In some embodiments, in the floating bush bearing device (7), the recess portions are formed so that the distance between the recess portions and the virtual true circular line increases from a first end side toward a second end side in the axial direction.

With the above embodiment (8), the gap in the axial direction become uneven, which provokes shortage of lubricant oil at sections where the gaps are large. Thus, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

(9) In some embodiments, in the floating bush bearing device (7) or (8), the inner peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The outer peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. Each of the recess portions on the inner peripheral surface of the floating bush and the recess portions on the outer peripheral surface of the floating bush is formed so that a distance between the recess portion and the virtual true circular line increases from a first end side toward a second end side in the axial direction.

With the above embodiment (9), large sections of the gaps are formed on the second end side in the axial direction, between the rotational shaft and the inner peripheral surface of the floating bush, and between the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing. Thus, it is possible to provoke shortage of lubricant oil at the large sections of the gap to enhance the oscillation stability.

(10) In some embodiments, in the floating bush bearing device (7) or (8), the inner peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The outer peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The recess portions on the inner peripheral surface of the floating bush are formed so that a distance between the recess portions and the virtual true circular line increases from a first end side toward a second end side in the axial direction. The recess portions on the outer peripheral surface of the floating bush are formed so that a distance between the recess portions and the virtual true circular line increases from the second end side toward the first end side in the axial direction.

With the above embodiment (10), a large section of the gap is formed on the second end side in the axial direction, between the rotational shaft and the inner peripheral surface of the floating bush. Further, a large section of the gap is formed on the first end side in the axial direction, between the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing. Thus, it is possible to provoke shortage of lubricant oil at the large sections of the gap to enhance the oscillation stability.

(11) In some embodiments, in the floating bush bearing device (7), the floating bush includes an oil supply hole formed through a peripheral wall of the floating bush having a cylindrical shape. The inner peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The recess portions on the inner peripheral surface of the floating bush is formed so that a distance between the recess portions and the virtual true circular line increases from a first end side and a second end side in the axial direction toward the oil supply hole.

According to the above embodiment (11), the recess portion on the inner peripheral surface of the floating bush is configured such that the gap is greatest in the vicinity of the oil supply hole, and decreases toward the first end side and the second end side from the oil supply hole in the axial direction. Thus, it is possible to provoke shortage of lubricant oil at the large section of the gap to enhance the oscillation stability. Furthermore, lubricant oil supplied between the rotational shaft and the inner peripheral surface of the floating bush is less likely to leak from the first end side and the second end side in the axial direction, and thus it is possible to avoid an event in which lubricant oil falls short over the entire length in the circumferential direction and the axial direction.

(12) In some embodiments, in the floating bush bearing device according to any one of the above (7) to (11), the floating bush includes an oil supply hole formed through a peripheral wall of the floating bush having a cylindrical shape. The outer peripheral surface of the floating bush is formed so as to include each of the land portions and the recess portions in a cross section in the axial direction of the floating bush. The recess portions on the outer peripheral surface of the floating bush are formed so that a distance between the recess portions and the virtual true circular line increases from a first end side and a second end side in the axial direction toward the oil supply hole.

According to the above embodiment (12), the recess portion on the outer peripheral surface of the floating bush is formed so that the gap is greatest in the vicinity of the oil supply hole, and decreases from the first end side and the second end side toward the oil supply hole in the axial direction. Thus, it is possible to provoke shortage of lubricant oil at the large section of the gap to enhance the oscillation stability. Furthermore, lubricant oil supplied between the rotational shaft and the inner peripheral surface of the floating bush is less likely to leak from the first end side and the second end side in the axial direction, and thus it is possible to avoid an event in which lubricant oil falls short over the entire length in the circumferential direction and the axial direction. Moreover, it is possible to increase the flow rate of lubricant oil supplied to the inner peripheral side of the floating bush.

(13) In some embodiments, in the floating bush bearing device according to any one of the above (1) to (6), a center line of the inner circumferential surface of the floating bush is inclined from a center line of the rotational shaft, or a center line of the outer peripheral surface of the floating bush is inclined from a center line of the inner peripheral surface of the bearing housing.

According to the above embodiment (3), the gap between the rotational shaft and the inner peripheral surface of the floating bush, or the gap between the outer peripheral surface of the floating bush and the inner peripheral surface of the bearing housing are uneven in the axial direction, which provokes shortage of lubricant oil at the large sections of the gap. Thus, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

(14) In some embodiments, in the floating bush bearing device according to any one of the above (1) to (13), the recess portions formed on the inner peripheral surface of the floating bush are formed by machining the inner peripheral surface of the floating bush having a true circular shape, the recess portions formed on the outer peripheral surface of the floating bush are formed by machining the outer peripheral surface of the floating bush having a true circular shape, or the recess portions formed on the inner peripheral surface of the bearing housing are formed by machining the inner peripheral surface of the bearing housing having a true circular shape.

According to the above embodiment (14), the recess portion if formed by machining the inner peripheral surface and the outer peripheral surface of a typical floating bush having a true circular shape and the inner peripheral surface of a bearing housing. Thus, for instance, extensive reconstruction of an ongoing production line is not necessary, which is advantageous in terms of productivity and costs.

(15) A supercharger according to at least one embodiment of the present invention comprises: a rotational shaft; a compressor wheel coupled to an end portion of the rotational shaft; and the floating bush bearing device according to any one of the above (1) to (14).

According to the above embodiment (15), it is possible to provide a supercharger having an excellent oscillation stability.

Advantageous Effects

According to at least one embodiment of the present invention, it is possible to provide a floating bush bearing device with an excellent oscillation stability and a supercharger including the floating bush bearing device.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.

Further, in the description below, some the same features are associated with the same reference numerals and not described again.

FIGS. 1 to 5are each a cross-sectional view of a cross section of a floating bush bearing device according to an embodiment of the present invention, taken along the axial direction.FIG. 6Ais an explanatory diagram for explaining a cross-sectional shape of a land portion and a recess portion, in a floating bush bearing device according to an embodiment of the present invention.FIG. 6Bis an explanatory diagram for explaining a relative position of a land portion and a recess portion formed on an inner peripheral surface and an outer peripheral surface of a floating bush, in a floating bush bearing device according to an embodiment of the present invention.

A floating bush bearing device1(1A to1E) according to an embodiment of the present invention is a device for rotatably supporting the rotational shaft2, and includes a floating bush3and a bearing housing4as depicted inFIGS. 1 to 5.

The floating bush3is a cylindrical member having a bearing hole33into which the rotational shaft2is insertable. A gap10between an inner peripheral surface31of the floating bush3and the rotational shaft2is supplied with lubricant oil that forms an oil film, and the oil film formed in the gap10rotatably supports the rotational shaft2.

A bearing housing4is a member for rotatably housing the floating bush3. Lubricant oil is also supplied to a gap20between an outer peripheral surface32of the floating bush3and an inner peripheral surface41of the bearing housing4to form an oil film, and the oil film formed in the gap20rotatably supports the floating bush3which rotates along with the rotational shaft2in the same direction as the rotational direction R of the rotational shaft2.

Furthermore, as depicted inFIGS. 1 to 5, at least one of the inner peripheral surface31of the floating bush3, the outer peripheral surface32of the floating bush3, or the inner peripheral surface41of the bearing housing4is formed to include a plurality of land portions311,321,411, and a plurality of recess portions312,322,412in a cross section in the axial direction. The land portions311,321,411have a true arc shape, which is a part of a true circular shape. The recess portions312,322,412are at positions recessed from the land portions311,321,411. The recess portions312,322,412are configured such that a distance from a virtual true circular line31a,32a,41apassing through the land portions311,321,411increases from end portions311b,321b,411bof the land portions311,321,411opposite to the rotational direction R of the rotational shaft2toward a direction opposite to the rotational direction R of the rotational shaft2.

The tolerance of the land portions311,321,411having a true arc shape, which is a part of a true circular shape, can be controlled to be small compared to the tolerance of the recess portions312,322,412. Thus, according to this embodiment, with at least one of the inner peripheral surface31of the floating bush3, the outer peripheral surface32of the floating bush3, or the inner peripheral surface41of the bearing housing4being formed to include the above land portions311,321,411in a cross section in the axial direction, it is possible to suppress non-synchronous oscillation due to tolerance to enhance the oscillation stability.

Furthermore, the recess portions312,322,412disposed at positions recessed from the land portions311,321,411are configured such that a distance from the virtual true circular line31a,32a,41apassing through the land portions311,321,411increases from the end portions of the land portions311,321,411opposite to the rotational direction R of the rotational shaft2toward a direction opposite to the rotational direction R of the rotational shaft2. With such recess portions312,322,412, the gap10,20in the circumferential direction become uneven, which provokes shortage of lubricant oil at sections where the gap10,20are large. If the lubricant oil falls short as described above partially in the circumferential direction, the axis eccentricity ratio increases and thereby the oscillation stability increases, according to the findings of the present inventors. Thus, according to this embodiment, with at least one of the inner peripheral surface31of the floating bush3, the outer peripheral surface32of the floating bush3, or the inner peripheral surface41of the bearing housing4being formed to include the above recess portions312,322,412in a cross section in the axial direction thereof, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

In the depicted embodiment, four land portions311,321,411, and four recess portions312,322,412are formed at a regular interval in the circumferential direction. Further, the recess portions312,322,412are formed into an arc shape, which is a part of a true circular shape, of an ellipse shape, or of an oval shape, for instance. However, the number of the land portions311,321,411and the recess portions312,322,412in the circumferential direction is not particularly limited. Further, the shape of the recess portions312,322,412is not limited to an arc shape. The shape may be a part of a polygon composed of a plurality of straight lines “a” to “e” as depicted inFIG. 6A(a), or may be formed of a single line “f” as depicted inFIG. 6A(b).

Furthermore, in the depicted embodiment, an expression θ1<θ2 is satisfied, where θ1 is an angular range showing a region in which the land portions311,321,411are formed, and θ2 is an angular range showing a region in which the recess portion312,322,412are formed. However, the relationship between θ1 and θ2 is not limited to θ1<θ2. The relationship may be θ1=θ2 as depicted inFIG. 6A(b), or θ1>θ2, though not depicted.

In some embodiments, as depicted inFIGS. 1, 4, and 5, in the floating bush bearing device1(1A,1D,1E), the inner peripheral surface31of the floating bush3may be formed to include each of the land portions311and the recess portions312in a cross section in the axial direction of the floating bush3.

In the depicted embodiment ofFIG. 1, the land portion311is formed from the end portion311ato the end portion311bin a direction opposite to the rotational direction R. The recess portion312is formed from the end portion312ato the end portion312bin a direction opposite to the rotational direction R. The end portion311bof the land portion311is at the same position as the end portion312aof the recess portion312.

According to this embodiment, the gap10between the rotational shaft2and the land portion311of the inner peripheral surface31of the floating bush3is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance to enhance the oscillation stability. Furthermore, large sections are formed in the gap10between the rotational shaft2and the inner peripheral surface31of the floating bush3, and thereby it is possible to provoke shortage of lubricant oil in the large sections of the gap10to enhance the oscillation stability.

In some embodiments, as depicted inFIGS. 2, 4, and 5, in the floating bush bearing device1(1B,1D,1E), the outer peripheral surface32of the floating bush3may be formed to include each of the land portions321and the recess portions322in a cross section in the axial direction of the floating bush3.

In the depicted embodiment ofFIG. 2, the land portion321is formed from the end portion321ato the end portion321ba direction opposite to the rotational direction R. The recess portion322is formed from the end portion322ato the end portion322bin a direction opposite to the rotational direction R. The end portion321bof the land portion321is at the same position as the end portion322aof the recess portion322.

According to this embodiment, the gap20between the land portion321of the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance to enhance the oscillation stability. Furthermore, large sections are formed in the gap20between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4, and thereby it is possible to provoke shortage of lubricant oil in the large sections of the gap20to enhance the oscillation stability.

In some embodiments, as depicted inFIGS. 4, and 5, in the floating bush bearing device1(1D,1E), the inner peripheral surface31of the floating bush3may be formed to include each of the land portions311and the recess portions312in a cross section in the axial direction of the floating bush3. Furthermore, the outer peripheral surface32of the floating bush3may be formed to include each of the land portion321and the recess portion322in a cross section in the axial direction of the floating bush3. Further, the land portion311of the inner peripheral surface31of the floating bush3and the land portion321of the outer peripheral surface32of the floating bush3are formed in regions that overlap with each other in the circumferential direction. Further, the recess portion312of the inner peripheral surface31of the floating bush3and the recess portion322of the outer peripheral surface32of the floating bush3are formed in regions that overlap with each other in the circumferential direction.

Herein, “the land portion311and the land portion321are formed in regions that overlap with each other in the circumferential direction” refers to an embodiment depicted inFIG. 6B. Specifically, as depicted inFIG. 6B, the angular range θ1representing a region in which the land portion311is formed and the angular range θ1representing a region in which the land portion321is formed have the same angle. In other words, the center point O of the land portion311having a true arc shape and the center point O of the land portion321having a true arc shape are at the same position. Furthermore, the center point O, the end portion311aof the land portion311and the end portion321aof the land portion321are on the same radial line. Furthermore, the center point O, the end portion311bof the land portion311and the end portion321bof the land portion321on the same radial line.

Furthermore, “the recess portion312and the recess portion322are formed in regions that overlap with each other in the circumferential direction” refers to an embodiment depicted inFIG. 6B. Specifically, as depicted inFIG. 6B, the angular range θ2representing a region in which the recess portion321is formed and the angular range θ2representing a region in which the recess portion322is formed have the same angle. Furthermore, the center point O, the end portion312aof the recess portion312and the end portion321aof the recess portion322are on the same radial line. Furthermore, the center point O, the end portion312bof the recess portion312and the end portion321bof the recess portion322are on the same radial line.

According to this embodiment, the gap10between the rotational shaft2and the land portion311of the inner peripheral surface31of the floating bush3and the gap20between the land portion321of the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4are controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance to enhance the oscillation stability. Furthermore, large sections of the gaps10,20are formed between the rotational shaft2and the inner peripheral surface31of the floating bush3and between the land portion321of the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4, and thereby it is possible to provoke shortage of lubricant oil in the large sections of the gap to enhance the oscillation stability.

In some embodiments, as depicted inFIGS. 1, 2, 4 and 5, in the floating bush bearing device1(1A,1B,1D,1E), the floating bush3includes an oil supply hole34formed through a peripheral wall3A of the floating bush3having a cylindrical shape. Further, the oil supply hole34is disposed on a position overlapping with the end portion311a,321aof the land portion311,321on the side of the rotational direction R of the rotational shaft2, or with the end portion312bof the recess portion312,322on the opposite side from the rotational direction R of the rotational shaft2, as seen in the axial direction.

In the depicted embodiment, the oil supply hole34is formed on a position overlapping with the end portion311a,321aof the land portion311,321on the side of the rotational direction R of the rotational shaft2, as seen in the axial direction. In other words, the oil supply hole34is disposed on the position closest to the side of the rotational direction R on the land portion311,321. However, though not depicted, the oil supply hole34may be formed on a position overlapping with the end portion312b,322bof the recess portion312,322on the opposite side from the rotational direction R of the rotational shaft2, as seen in the axial direction. In other words, the oil supply hole34may be formed on the position most opposite from the side of the rotational direction R on the recess portion312,322

In the depicted embodiment, four oil supply holes34are formed at a regular interval in the circumferential direction. However, the number of oil supply holes34is not particularly limited.

According to this embodiment, the oil supply hole34is formed on a position where the distance from the true circular line31a,32ais greatest, or in the vicinity of the position, on the recess portion312,322. Thus, with the oil supply hole34formed on such a position, it is possible to increase the flow rate of lubricant oil that flows from the outer peripheral side of the floating bush3toward the inner peripheral side of the floating bush3.

In some embodiments, as depicted inFIGS. 3 and 5, in the floating bush bearing device1(1C,1E), the inner peripheral surface41of the bearing housing4may be formed to include each of the land portion411and the recess portion412in a cross section in the axial direction of the bearing housing4.

In the depicted embodiment, the land portion411is formed from the end portion411aon the side of the rotational direction R of the rotational shaft2to the end portion411bon the opposite side from the rotational direction R. The recess portion412is formed from the end portion412aon the side of the rotational direction R of the rotational shaft2to the end portion412bon the opposite side from the rotational direction R. The end portion411bof the land portion411on the opposite side from the rotational direction R is at the same position as the end portion412aof the recess portion412on the side of the rotational direction R.

According to this embodiment, the gap20between the land portion411of the inner peripheral surface41of the bearing housing4and the outer peripheral surface32of the floating bush3is controlled with high accuracy, and thereby it is possible to suppress non-synchronous oscillation due to tolerance, and to enhance the oscillation stability. Furthermore, a large section of the gap20is formed between the inner peripheral surface41of the bearing housing4and the outer peripheral surface32of the floating bush3, and thereby it is possible to provoke shortage of lubricant oil in the large section of the gap20to enhance the oscillation stability.

FIGS. 7 to 12are an axial-directional cross-sectional view of a cross section of a floating bush bearing device according to an embodiment of the present invention, taken along the axial direction.

In some embodiments, as depicted inFIGS. 7 to 12, in the floating bush bearing device1(1F,1G,1H,1I,1J,1K), the land portion311,321,411and the recess portion312,322,412formed on at least one of the inner peripheral surface31of the floating bush3, the outer peripheral surface32of the floating bush3, or the inner peripheral surface41of the bearing housing4, are formed continuously over the axial direction of the bearing housing4or the floating bush3. Further, the recess portion312,322,412is formed so that the distance d (d1, d2, d3) between the recess portion312,322,412and the virtual true circular line31a,32achanges in the axial direction.

In the embodiment depicted inFIGS. 7 to 12, the virtual true circular line31a,32a,41athat passes through the land portion311,321,411extends parallel to the axis CL in the axial direction. That is, the distance d (d1, d2, d3) from the true circular line31a,32achanges in the axial direction only at the recess portion312,322,412, and the cross-sectional shape of the land portion311,321,411does not change in the axial direction.

According to this embodiment, the distance d (d1, d2, d3) between the recess portion312,322,412and the virtual true circular line31a,32achanges in the axial direction. With such recess portions312,322,412, the gap10,20in the axial direction become uneven, which provokes shortage of lubricant oil at sections where the gaps10,20are large. Thus, with at least one of the inner peripheral surface31of the floating bush3, the outer peripheral surface32of the floating bush3, or the inner peripheral surface41of the bearing housing4being formed to include the above recess portions312,322,412, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

In some embodiments, as depicted inFIGS. 7 to 9, in the floating bush bearing device1(1F,1G,1H), the recess portion312,322,412is formed so that the distance d (d1, d2, d3) between the recess portion312,322,412and the virtual true circular line31a,32a,41aincreases from the first end side Y1toward the second end side Y2in the axial direction.

In the depicted embodiment, the upper side in the drawing is the first end side Y1, and the lower side in the drawing is the second end side Y2. Furthermore, in the embodiment depicted inFIG. 7, on the inner peripheral surface31of the floating bush3, the distance d1between the recess portion312and the virtual true circular line31aincreases from the first end side Y1toward the second end side Y2in the axial direction. Furthermore, in the embodiment depicted inFIG. 8, in addition to the configuration depicted inFIG. 7, on the outer peripheral surface32of the floating bush3, the distance d2between the recess portion322and the true circular line32aincreases from the first end side Y1toward the second end side Y2in the axial direction. Furthermore, in the embodiment depicted inFIG. 9, on the inner peripheral surface41of bearing housing4, the distance d3between the recess portion412and the virtual true circular line41aincreases from the first end side Y1toward the second end side Y2in the axial direction.

According to this embodiment, the gaps10,20in the axial direction become uneven, which provokes shortage of lubricant oil at sections where the gap10,20are large. Thus, it is possible to provoke shortage of lubricant oil to enhance the oscillation stability.

In some embodiments, as depicted inFIG. 8, in the floating bush bearing device1(1G), the inner peripheral surface31of the floating bush3is formed to include each of the land portion311and the recess portion312in a cross section in the axial direction of the floating bush3. Furthermore, the outer peripheral surface32of the floating bush3is formed to include each of the land portion321and the recess portion322in a cross section in the axial direction of the floating bush3. Furthermore, each of the recess portion312on the inner peripheral surface31of the floating bush3and the recess portion322on the outer peripheral surface32of the floating bush3is formed so that the distance d (d1, d2) between the recess portion312,322and the virtual true circular line31a,32aincreases from the first end side Y1toward the second end side Y2in the axial direction.

According to this embodiment, large sections of the gaps10,20are formed on the second end side Y2in the axial direction, between the rotational shaft2and the inner peripheral surface31of the floating bush3, and between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4. Thus, it is possible to provoke shortage of lubricant oil at the large sections of the gaps10,20to enhance the oscillation stability.

In some embodiments, as depicted inFIG. 10, in the floating bush bearing device1(1I), the inner peripheral surface31of the floating bush3is formed to include each of the land portion311and the recess portion312in a cross section in the axial direction of the floating bush3. Furthermore, the outer peripheral surface32of the floating bush3is formed to include each of the land portion321and the recess portion322in a cross section in the axial direction of the floating bush3. Furthermore, the recess portion312on the inner peripheral surface31of the floating bush3is formed so that the distance d1between the recess portion312and the virtual true circular line31aincreases from the first end side Y1toward the second end side Y2in the axial direction. The recess portion322on the outer peripheral surface32of the floating bush3is formed so that the distance d2between the recess portion322and the virtual true circular line32aincreases from the second end side Y2toward the first end side Y1in the axial direction.

According to this embodiment, a large section of the gap10is formed on the second end side Y2in the axial direction, between the rotational shaft2and the inner peripheral surface31of the floating bush3. Further, a large section of the gap20is formed on the first end side Y1in the axial direction, between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4. Thus, it is possible to provoke shortage of lubricant oil at the large sections of the gaps10,20to enhance the oscillation stability.

In some embodiments, as depicted inFIGS. 11 and 12, in the floating bush bearing device1(1J,1K), the floating bush3includes an oil supply hole34formed through the peripheral wall3A of the floating bush3having a cylindrical shape. Furthermore, the inner peripheral surface31of the floating bush3is formed to include each of the land portion311and the recess portion312in a cross section in the axial direction of the floating bush3. Furthermore, the recess portion312on the inner peripheral surface31of the floating bush3is formed so that the distance d1between the recess portion312and the virtual true circular line31aincreases from the first end side Y1and the second end side Y2toward the oil supply hole34in the axial direction.

In the depicted embodiment, the oil supply hole34is formed in the central part of the floating bush3in the axial direction. Further, at the central part of the bearing housing4in the axial direction, a lubricant-oil supply hole44for supplying lubricant oil to the gap20on the inner peripheral surface41of the bearing housing4and the outer peripheral surface32of the floating bush3is formed.

According to this embodiment, the recess portion312on the inner peripheral surface31of the floating bush3is configured such that the gap10is greatest in the vicinity of the oil supply hole34, and decreases toward the first end side Y1and the second end side Y2from the oil supply hole34in the axial direction. Thus, it is possible to provoke shortage of lubricant oil at the large section of the gap10and enhance the oscillation stability. Furthermore, lubricant oil supplied between the rotational shaft2and the inner peripheral surface31of the floating bush3is less likely to leak from the first end side Y1and the second end side Y2in the axial direction, and thus it is possible to avoid an event in which lubricant oil falls short over the entire length in the circumferential direction and the axial direction.

In some embodiments, as depicted inFIG. 12, in the floating bush bearing device1(1K), the floating bush3includes the oil supply hole34formed through the peripheral wall3A of the floating bush3having a cylindrical shape. Furthermore, the outer peripheral surface32of the floating bush3is formed to include each of the land portion321and the recess portion322in a cross section in the axial direction of the floating bush3. Furthermore, the recess portion322on the outer peripheral surface32of the floating bush3is formed so that the distance d2between the recess portion322and the virtual true circular line32aincreases from the first end side Y1and the second end side Y2toward the oil supply hole34in the axial direction.

According to this embodiment, the recess portion322on the outer peripheral surface32of the floating bush3is formed so that the gap20is greatest in the vicinity of the oil supply hole34, and decreases from the first end side Y1and the second end side Y2toward the oil supply hole34in the axial direction. Thus, it is possible to provoke shortage of lubricant oil at the large section of the gap20to enhance the oscillation stability. Furthermore, lubricant oil supplied between the rotational shaft2and the inner peripheral surface31of the floating bush3is less likely to leak from the first end side Y1and the second end side Y2in the axial direction, and thus it is possible to avoid an event in which lubricant oil falls short over the entire length in the circumferential direction and the axial direction. Thus, it is possible to increase the flow rate of lubricant oil supplied to the inner peripheral side of the floating bush3.

In some embodiments, as depicted inFIG. 13, in the floating bush bearing device1(1L,1M), the center line CL1of the inner peripheral surface31of the floating bush3is inclined with respect to the center line CL of the rotational shaft2. Furthermore, as depicted inFIGS. 13 and 14, the center line CL2of the outer peripheral surface32of the floating bush3is inclined with respect to the center line CL3of the inner peripheral surface41of the bearing housing4.

In the embodiment depicted inFIG. 13, the inner peripheral surface31and the outer peripheral surface32of the floating bush3are formed in parallel with each other, and are inclined with respect to the rotational shaft2and the bearing housing4. Accordingly, the gap10between the rotational shaft2and the inner peripheral surface31of the floating bush3and the gap20between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4are uneven in the axial direction. Furthermore, in the embodiment depicted inFIG. 14, the center line CL3of the inner peripheral surface41of the bearing housing4is inclined with respect to each of the center line CL of the rotational shaft2, the center line CL1of the inner peripheral surface31of the floating bush3, and the center line CL2of the outer peripheral surface32of the floating bush3. Accordingly, the gap20between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4are uneven in the axial direction.

According to this embodiment, the gap10between the rotational shaft2and the inner peripheral surface31of the floating bush3, or the gap20between the outer peripheral surface32of the floating bush3and the inner peripheral surface41of the bearing housing4are uneven in the axial direction, which provokes shortage of lubricant oil at the large sections of the gap10,20. Thus, it is possible to provoke shortage of lubricant oil and enhance the oscillation stability.

In some embodiments, in the floating bush bearing device1(1A to1M) depicted inFIGS. 1 to 14described above, the recess portion312formed on the inner peripheral surface31of the floating bush3is formed by machining the inner peripheral surface of the floating bush having a true circular shape. Furthermore, the recess portion322formed on the outer peripheral surface32of the floating bush3is formed by machining the outer peripheral surface of the floating bush having a true circular shape. Furthermore, the recess portion412formed on the inner peripheral surface41of the bearing housing4is formed by machining the inner peripheral surface of the bearing housing having a true circular shape.

The type of machining may be selected from various methods, such as pressing, roller pressing, cutting and grinding, depending on the type and shape of an object to be machined.

According to this embodiment, the recess portion312,322,412is formed by machining the inner peripheral surface and the outer peripheral surface of a typical floating bush having a true circular shape and the inner peripheral surface of a bearing housing. Thus, extensive reconstruction of an ongoing production line is not necessary, which is advantageous in terms of productivity and costs.

FIG. 15is a schematic diagram of an embodiment of a turbocharger including a floating bush bearing device of the present invention. As depicted inFIG. 15, the supercharger100in the present embodiment is configured as a turbocharger100awhich includes a rotational shaft2, a compressor rotor102and a turbine rotor104coupled to the opposite ends of the rotational shaft2, and the above described floating bush bearing device1rotatably supporting the rotational shaft2.

The compressor rotor102is disposed in an intake passage of the engine, while the turbine rotor104is disposed in an exhaust passage of the engine. The turbine rotor104is rotated by exhaust gas discharged from the engine, and thereby the compressor rotor102is coaxially driven to compress air flowing through the intake passage and supply the supercharged air to the engine.

With this configuration, it is possible to provide a turbocharger100aincluding a floating bush bearing device with an excellent oscillation stability and a reduced bearing loss.

The supercharger100of the present invention is not limited to the above described turbocharger100a. As depicted inFIG. 16, the supercharger100may be configured as an electric supercharger100bincluding an electric motor106instead of the turbine rotor104, so that the electric motor106rotates the rotational shaft2and drives the compressor rotor102.

The embodiments of the present invention have been described above. However, the present invention is not limited thereto, and various modifications may be applied as long as they do not depart from the object of the present invention

INDUSTRIAL APPLICABILITY

At least one embodiment of the present invention can be suitably applied to, for instance, a small supercharger to be mounted to an automobile engine, as a floating bush bearing device that rotatably supports a rotational shaft.

DESCRIPTION OF REFERENCE NUMERALS