Turbomachine

1. A turbomachine, comprising:

a rotational shaft;

a pair of thrust collars disposed around the rotational shaft;

a thrust bearing disposed around the rotational shaft at an axial directional position between the pair of thrust collars; and

an annular channel disposed around the rotational shaft in an annular shape, for draining lubricant oil after lubricating a sliding portion between the thrust bearing and the thrust collars,

wherein the annular channel includes:

an oil-drain port portion forming a lower region of the annular channel, for discharging the lubricant oil inside the annular channel downward; and

an oil-guide channel portion disposed above the oil-drain port portion so as to form an upper region of the annular channel and configured to guide the lubricant oil from the sliding portion in a circumferential direction of the rotational shaft to the oil-drain port portion, and

wherein the oil-guide channel portion forming the upper region of the annular channel has an asymmetric shape with respect to a rotational direction of the rotational shaft, the oil-guide channel portion having a minimum flow-path cross sectional area at a first position on an upstream side in the rotational direction, and a maximum flow-path cross sectional area at a second position on a downstream side of the first position, and

wherein the oil-guide channel portion is configured such that the flow-path cross sectional area increases monotonically and continuously from the first position toward the second position along the rotational direction.

2. The turbomachine according to claim 1 ,

wherein a flow-path width of the oil-guide channel portion in a radial direction of the rotational shaft is greater at the second position than at the first position.

3. The turbomachine according to claim 2 ,

wherein an outer peripheral edge of the oil-guide channel portion has an arc shape having a center offset from an axial center of the rotational shaft.

4. The turbomachine according to claim 3 ,

wherein the center of the arc shape is at a position offset from the axial center at least in a horizontal direction from an upstream region toward a downstream region of the oil-guide channel portion in the rotational direction.

5. The turbomachine according to claim 1 ,

wherein a flow path of the oil-guide channel portion in an axial direction of the rotational shaft is greater at the second position than at the first position.

6. The turbomachine according to claim 1 ,

wherein a flow-path cross sectional area of the oil-guide channel portion is smaller at a most upstream position in the rotational direction than at a most downstream position in the rotational direction.

7. The turbomachine according to claim 1 ,

wherein an outer peripheral edge of the oil-guide channel portion has a shape formed by: a combination of one or more curves; a combination of a plurality of lines; or a combination of one or more lines and one or more curves.

8. The turbomachine according to claim 1 , further comprising a bearing housing for housing the thrust bearing,

wherein the annular channel includes a first oil-drain channel formed by a space surrounded by a first end surface of the thrust bearing and a bearing groove formed on an inner wall surface of the bearing housing facing the first end surface.

9. The turbomachine according to claim 1 , further comprising an oil deflector disposed so as to face a second end surface of the thrust bearing and an end surface of the thrust collar disposed on a side of the second end surface, the end surface being opposite from a sliding surface between the thrust collar and the thrust bearing,

wherein the annular channel includes a second oil-drain channel formed by a space surrounded by the oil deflector, the thrust collar, and the thrust bearing.

10. The turbomachine according to any one of claim 1 , further comprising:

an impeller configured to rotate with the rotational shaft;

a working-fluid flow path in which the impeller is disposed and through which a working fluid flows; and

a partition wall separating the working-fluid flow path and a bearing space housing the thrust bearing and the pair of thrust collars,

wherein the annular channel includes a third oil-drain channel formed by a space surrounded by at least the partition wall.

11. The turbomachine according to claim 1 ,

wherein a relational expression V×S>Q is satisfied, where V is a flow rate of the lubricant oil at each position in the oil-guide channel portion, S is a flow-path cross sectional area S at each position in the oil-guide channel portion, and Q is a supply amount of the lubricant oil to the thrust bearing.

12. The turbomachine according to claim 11 , wherein the turbomachine is a turbocharger including a turbine and a compressor disposed on either side of the rotational shaft.

13. The turbomachine according to claim 1 , wherein the turbomachine is a turbocharger including a turbine and a compressor disposed on either side of the rotational shaft.