Journal bearing and rotating machine

1. A journal bearing, comprising:

a carrier ring to be arranged on an outer peripheral side of a rotation shaft;

a pad to be swingably arranged on the outer peripheral side of the rotation shaft and an inner peripheral side of the carrier ring; and

an oil supply nozzle configured to supply oil to a portion between the rotation shaft and the pad,

wherein the pad includes:

an inner peripheral surface opposed to the rotation shaft;

an outer peripheral surface opposed to the carrier ring via a gap; and

an upstream end surface which is formed on an upstream side of the inner peripheral surface in a rotating direction of the rotation shaft, and connects the inner peripheral surface and the outer peripheral surface to each other,

wherein the inner peripheral surface includes:

a partially cylindrical surface; and

a recessed portion which is arranged on an upstream side of the partially cylindrical surface, and forms an opening space for storing the oil,

wherein the opening space includes:

an oil inlet port which is opened at the upstream end surface, and is configured to introduce the oil to the opening space; and

an oil outlet port opened so as to be opposed to the rotation shaft,

wherein the pad includes a backflow prevention portion configured to prevent the oil in the opening space from flowing back to the oil inlet port,

wherein the oil supply nozzle is arranged to be adjacent to the pad in a circumferential direction,

wherein the backflow preventing portion includes a bottom surface that defines an outer peripheral side of the opening space, and

wherein a radial distance between the bottom surface and the rotation shaft decreases toward the upstream side.

2. The journal bearing according to claim 1 , wherein the radial distance between the bottom surface and the rotation shaft decreases toward the upstream side in a stepwise manner.

3. The journal bearing according to claim 1 ,

wherein the recessed portion includes:

a first side surface that defines one axial end side of the opening space; and

a second side surface that defines another axial end side of the opening space,

wherein the backflow preventing portion includes a division wall that divides the opening space in an axial direction,

wherein the division wall includes:

a first wall surface opposed to the first side surface; and

a second wall surface opposed to the second side surface, and

wherein an axial distance between the first side surface and the first wall surface and an axial distance between the second side surface and the second wall surface decrease toward the upstream side.

4. The journal bearing according to claim 1 ,

wherein the backflow preventing portion includes a protrusion formed on the recessed portion, and

wherein a radial height of the protrusion increases toward the upstream side.

5. The journal bearing according to claim 1 ,

wherein the backflow preventing portion includes a protrusion formed on the recessed portion, and

wherein an axial width of the protrusion increases toward the upstream side.

6. The journal bearing according to claim 1 ,

wherein the backflow preventing portion includes a plurality of protrusions formed on the recessed portion, and

wherein an arrangement density of the plurality of protrusions increases toward the upstream side.

7. The journal bearing according to claim 1 , wherein the backflow preventing portion includes a recess formed in the recessed portion.

8. The journal bearing according to claim 1 , wherein a cutout portion that extends in the circumferential direction is formed at an axial end portion of the inner peripheral surface.

9. The journal bearing according to claim 1 ,

wherein, in an axial center portion of the inner peripheral surface, a groove portion that extends in the circumferential direction is formed on a downstream side of the recessed portion in the rotating direction of the rotation shaft, and

wherein a protruding portion that closes an end portion of the groove portion on the upstream side is formed on the recessed portion.

10. A rotating machine, comprising:

the journal bearing of claim 1 ; and

the rotation shaft.

11. A journal bearing, comprising:

a carrier ring to be arranged on an outer peripheral side of a rotation shaft;

a pad to be swingably arranged on the outer peripheral side of the rotation shaft and an inner peripheral side of the carrier ring; and

an oil supply nozzle configured to supply oil to a portion between the rotation shaft and the pad,

wherein the pad includes:

an inner peripheral surface opposed to the rotation shaft,

an outer peripheral surface opposed to the carrier ring via a gap; and

an upstream end surface which is formed on an upstream side of the inner peripheral surface in a rotating direction of the rotation shaft, and connects the inner peripheral surface and the outer peripheral surface to each other,

wherein the inner peripheral surface includes:

a partially cylindrical surface; and

a recessed portion which is arranged on an upstream side of the partially cylindrical surface, and forms an opening space for storing the oil,

wherein the opening space includes:

an oil inlet port which is opened at the upstream end surface, and is configured to introduce the oil to the opening space; and

an oil outlet port opened so as to be opposed to the rotation shaft,

wherein the pad includes a backflow prevention portion configured to prevent the oil in the opening space from flowing back to the oil inlet port,

wherein the opening space includes two axial end sides, and the backflow preventing portion includes:

a first side surface that defines a first one of the two axial end sides of the opening space; and

a second side surface that defines a second one of the two axial end sides of the opening space, and

wherein an axial distance between the first side surface and the second side surface decreases toward the upstream side.

12. The journal bearing according to claim 11 , wherein the axial distance between the first side surface and the second side surface decreases toward the upstream side in a stepwise manner.

13. The journal bearing according to claim 11 , wherein a maximum value of the axial distance between the first side surface and the second side surface is equal to an axial dimension of the partially cylindrical surface.

14. The journal bearing according to claim 11 ,

wherein the recessed portion includes a bottom surface that defines an outer peripheral side of the opening space,

wherein a radial distance between the bottom surface and the rotation shaft increases toward the upstream side, and

wherein an end portion of the bottom surface on the upstream side is connected to an end portion of the outer peripheral surface on the upstream side.

15. A journal bearing, comprising:

a carrier ring to be arranged on an outer peripheral side of a rotation shaft;

a pad to be swingably arranged on the outer peripheral side of the rotation shaft and an inner peripheral side of the carrier ring; and

an oil supply nozzle configured to supply oil to a portion between the rotation shaft and the pad,

wherein the pad includes:

an inner peripheral surface opposed to the rotation shaft;

an outer peripheral surface opposed to the carrier ring via a gap; and

an upstream end surface which is formed on an upstream side of the inner peripheral surface in a rotating direction of the rotation shaft, and connects the inner peripheral surface and the outer peripheral surface to each other,

wherein the inner peripheral surface includes:

a partially cylindrical surface; and

a recessed portion which is arranged on an upstream side of the partially cylindrical surface, and forms an opening space for storing the oil,

wherein the opening space includes:

an oil inlet port which is opened at the upstream end surface, and is configured to introduce the oil to the opening space; and

an oil outlet port opened so as to be opposed to the rotation shaft,

wherein the pad includes a backflow prevention portion configured to prevent the oil in the opening space from flowing back to the oil inlet port,

wherein the backflow preventing portion includes a backflow preventing member separate from the pad, and

wherein the backflow preventing member is mounted to the pad so as to cover a part of the oil inlet port.