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A rotating machine comprising such as an axial power turbine or a turbocharger has a housing with a bearing cavity and a chamber separated by a first wall. A shaft is rotatable about an axis in the bearing cavity, extends through an opening in the first wall and is mounted for rotation on a bearing

A rotating machine comprising such as an axial power turbine or a turbocharger has a housing with a bearing cavity and a chamber separated by a first wall. A shaft is rotatable about an axis in the bearing cavity, extends through an opening in the first wall and is mounted for rotation on a bearing assembly provided in the bearing cavity. An oil sealing arrangement including an oil diffuser device is arranged on the shaft for displacing oil away from the shaft as it rotates. This restricts the flow of oil to the opening. The oil diffuser device defines a diffuser passage between the bearing assembly and the first wall, the passage extending outwardly of the axis.

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1. A rotating machine comprising: a housing defining a bearing cavity and a chamber separated by a first wall;a shaft rotatable about an axis in the bearing cavity and extending through an opening in the first wall, the shaft being mounted for rotation on a bearing assembly provided in the bearing c

1. A rotating machine comprising: a housing defining a bearing cavity and a chamber separated by a first wall;a shaft rotatable about an axis in the bearing cavity and extending through an opening in the first wall, the shaft being mounted for rotation on a bearing assembly provided in the bearing cavity;an oil sealing arrangement for displacing oil away from the shaft as it rotates thereby restricting the flow of oil to the opening;the oil sealing arrangement comprising an oil diffuser device defining an oil diffuser passage disposed between opposed surfaces of the bearing assembly and the first wall, the oil diffuser passage being configured for guiding and diffusing oil flow, the oil diffuser passage extending outwardly of the axis and having a radially inner first portion that extends in a first direction with a dominant radial component and a second portion outboard of the radially inner portion and extending in a second direction with a greater axial component than the first direction; andwherein the oil diffuser device comprises a fixed member that is designed not to rotate with the shaft and defines a first surface, and a rotatable member for rotation with the shaft and defines a second surface, the first and second surfaces facing each other and defining the oil diffuser passage between them. 2. A rotating machine according to claim 1, wherein the oil diffuser passage has an outlet end distal from the shaft that extends in a direction away from the first wall. 3. A rotating machine according to claim 2, wherein the first portion of the oil diffuser passage has an inlet end that extends in a substantially radial direction. 4. A rotating machine according to claim 1, wherein the first surface has a first portion that extends in the first direction and a second portion that extends in the second direction, and the second surface has a first portion that extends in the first direction and a second portion that extends in the second direction. 5. A rotating machine according to claim 1, wherein the axial distance between the first and second surfaces increases with radial distance from the shaft. 6. A rotating machine according to claim 1, wherein the fixed member is defined by the housing. 7. A rotating machine according to claim 1, wherein the rotatable member of the diffuser device is substantially disc-shaped with a bore in which the shaft is received. 8. A rotating machine according to claim 7, wherein an outer periphery of the second surface of the rotatable member is curved in a direction away from the first wall. 9. A rotating machine according to claim 8, wherein the rotatable member is disposed in the bearing cavity such that there is a small annular clearance between its outer periphery and a neighbouring wall of the housing. 10. A rotating machine according to claim 1, wherein the oil sealing arrangement further comprises a labyrinth member disposed around the shaft for defining at least one oil collection chamber between the oil diffuser device and the first wall. 11. A rotating machine according to claim 10, wherein the at least one oil collection chamber is defined between the labyrinth member and a wall portion of the bearing cavity and is arranged to collect oil that passes through said small annular clearance. 12. A rotating machine according to claim 10, wherein the labyrinth member has at least one surface that is inclined with respect to the shaft axis for directing collected oil away from the shaft towards a drain. 13. A rotating machine according to claim 10, wherein there is provided a plurality of oil collection chambers arranged to receiving oil in sequence. 14. A rotating machine according to claim 1, wherein the sealing assembly further comprises at least one seal ring disposed around the shaft within the opening to seal the shaft with respect to the first wall. 15. A rotating machine according to claim 1 and in the form of a turbomachine. 16. A rotating machine according to claim 15, wherein the turbomachine is a turbocharger including a turbine or compressor housing defining the chamber, and a bearing housing defining said bearing cavity. 17. A rotating machine according to claim 15, wherein the turbomachine is a power turbine including a turbine housing defining the chamber, and a bearing housing defining said bearing cavity. 18. A rotating machine according to claim 1, wherein the oil diffuser passage is sized so as to ensure that when the oil emerges from the outlet the flow has decelerated such that the gravitational and surface tension forces dominate and cause the oil to pour from the outlet of the oil diffuser passage. 19. A rotating machine comprising: a housing defining a bearing cavity and a chamber separated by a first wall;a shaft rotatable in the bearing cavity about an axis and extending through an opening in the first wall, the shaft being mounted for rotation on a bearing assembly provided in the bearing cavity;an oil sealing arrangement for displacing oil away from the shaft as it rotates thereby restricting the flow of oil to the opening;the oil sealing arrangement comprising an oil diffuser device defining a substantially annular oil diffuser passage for guiding and diffusing the flow of oil towards an outlet, the oil diffuser passage being disposed between the bearing assembly and the first wall,the oil diffuser passage having a radially inner first portion that extends in a first direction with a dominant radial component and a second portion outboard of the radially inner portion and extending in a second direction with a greater axial component than the first direction, andthe oil diffuser passage extending outwardly of the axis and being defined between first and second surfaces spaced apart such that, as the shaft rotates, oil flows along the oil diffuser passage as a body in contact with the first and second surfaces and decelerates such that gravitational and surface tension forces dominate and cause the oil to pour from the outlet of the oil diffuser passage.