Lubrication oil system for a reduction gearbox

1. A reduction gear box for a gas turbine engine comprising a casing; at least one reduction epicyclic gear stage, within the casing, the reduction gear stage comprising at least an array of gears meshing together with at least one gear mounted for rotation on a gear carrier and at least one bearing associated therewith; a lubricating oil delivery system provided within the casing and surrounding a portion of the gear carrier, the oil delivery system comprising a conduit; a closed oil reservoir; a first metered opening communicating the conduit with the reservoir and at least one metered outlet opening communicating the reservoir with the gear carrier and the bearing such that the reservoir is filled with oil in normal flight operating conditions and the oil trapped in the reservoir is released to the carrier and bearing when a temporary drop in the oil system pressure occurs.

2. The reduction gearbox as defined in claim 1 wherein the oil delivery system is defined partially within a portion of the casing and the reservoir is a cavity defined in the portion of the casing.

3. The reduction gear box as defined in claim 2 wherein an annular oil distribution channel is defined on the casing in contact with the gear carrier and the bearing and the metered outlet opening is in communication with the annular channel.

4. The reduction gear box as defined in claim 3 comprising at least three of said metered outlet opening communicating the reservoir with the annular channel.

5. The reduction gearbox as defined in claim 3 wherein the gear carrier includes a cylindrical component journalled within the casing and communicating with the annular channel.

6. The reduction gear box as defined in claim 5 wherein the at least one gear is a planet gear within a planetary gear stage and the planetary gear is journalled to the bearing mounted to the gear carrier.

7. The reduction gear box as defined in claim 6 wherein the oil is pumped to the planetary gear by the gear carrier.

8. An oil supply system for a reduction gearbox in a gas turbine engine, the reduction gearbox of the type having at least one reduction epicyclic gear stage, within the casing, the reduction gear stage comprising at least an array of gears meshing together with at least one gear mounted for rotation on a gear carrier and a bearing associated therewith, the engine being subject to normal flight and negative “g” flight conditions; the oil supply system comprising an oil reserve system consisting of a closed reservoir provided adjacent the gear carrier, a restricted inlet opening associated with the reservoir for allowing oil to enter and fill the reservoir in normal flight conditions and a plurality of metered outlet openings to feed the oil from the reservoir to the gear carrier when a negative “g” condition occurs.

9. The oil supply system as defined in claim 8 wherein the closed reservoir is a cavity formed in the casing of the reduction gearbox.

10. The oil supply system as defined in claim 9 wherein there are at least three metered outlet openings.

11. A method of supplying lubricating oil to a reduction gearbox wherein the gearbox includes reduction gear stages and a gear carrier mounting at least a gear rotatable in the gear carrier and an associated bearing, the method comprising:

forming a closed reservoir radially outwardly of the gear carrier within the reduction gear box, and a restricted opening to the reservoir for delivering lubricating oil through;

forming an annular oil channel surrounding the gear carrier and in oil communication therewith;

providing metered openings to communicate the reservoir with the annular oil channel so that the oil trapped in the reservoir is distributed into the oil channel to the gear carrier when a temporary pressure drop occurs in the oil delivery system.

12. The method as defined in claim 11 wherein forming the reservoir comprises forming the reservoir as a cavity defined in the casing of the gearbox.