TECHNICAL FIELD
The invention relates generally to aircraft engines and more particularly to an pressure lubrication system of aircraft engines.
BACKGROUND OF THE ART
Engines in aircraft normally require high quality lubrication which can be achieved only by forced circulation or pressure lubrication systems. This requires a tank from which the lubricating fluid is supplied, a pump and a circulation network for movement of the lubricating fluid between the tank and the various bearings of the engine. In a conventional oil-filled tank used only for normal flight, oil is drawn off through an outlet at the bottom of the tank to ensure a continuous supply at all times. However, to obtain a continuous supply of oil from the tank in an aircraft which turns at steep angles or flies inverted, outlets must be placed at various positions in the periphery of the tank, or movable parts must be used in order that at least one outlet will be in the lowest part of the tank and thus submerged no matter what orientation is assumed by the tank with respect to the downward sense of the vertical. The conventional tank therefore requires a complicated configuration.
Accordingly, there is a need to provide an improved pressure lubrication system of aircraft engines which may be useful for inverted flight and/or other flight attitudes.
SUMMARY
In one aspect, the described subject matter provides an aircraft engine oil system comprising: a tank for containing oil, having in a upright orientation, a top and a bottom, and a geometrical center defined as a centroid of the tank shape, the tank configured to have an oil level surface above the geometrical center when the oil has a required minimum volume and to have the oil level surface spaced apart from the top of the tank when the oil has a required maximum volume; an oil inlet communicating with an oil pump, the inlet being located in the geometrical center of the tank and being submerged in the oil for delivery of the oil under a pressure differential between the tank to the oil system; and an oil return communicating with the tank for returning oil from the oil system back to the tank.
In another aspect, the described subject matter provides a pressure lubrication system for an aircraft engine, comprising: a lubrication fluid circulation network; a tank for containing a lubrication fluid, having in a upright orientation, a top and a bottom; a fluid returning tube communicating with the tank and the lubrication fluid circulation network for returning the lubrication fluid from the lubrication fluid circulation network back to the tank; and a pump for pumping the lubrication fluid into the lubrication fluid circulation network, the pump having an inlet positioned inside the tank in a location such that the pump inlet is submerged in the lubrication fluid in the tank regardless of the tank orientation.
Further details of these and other aspects of the described subject matter will be apparent from the detailed description and drawings included below.
DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures depicting aspects of the described subject matter, in which:
FIG. 1 is a schematic cross-sectional view of a turbofan gas turbine engine as an exemplary application of the described subject matter;
FIG. 2 is a schematic illustration of a lubrication fluid circulation network for use in the engine of FIG. 1, with a cross-sectional view of a tank of the lubrication fluid circulation network showing the configuration of the tank in an upright orientation;
FIG. 3 is a schematic illustration of the lubrication fluid circulation network, with a cross-sectional view of the tank of FIG. 2 showing the tank in an inverted orientation;
FIG. 4 is a schematic illustration of the lubrication fluid circulation network, with a cross-sectional view of the tank of FIG. 2 showing the tank in a 90° orientation;
FIG. 5 is a schematic illustration of the lubrication fluid circulation network, with a cross-sectional view of the tank of FIG. 2 showing the tank in a 270° orientation;
FIG. 6 is a schematic longitudinal cross-sectional view of the tank of FIG. 2, showing front and rear ends of the tank; and
FIG. 7 is a schematic illustration of a cross-section of a tank having a non-axisymmetric triangular shape, according to another embodiment.
DETAILED DESCRIPTION
FIG. 1 schematically illustrates a turbofan gas turbine engine which is mounted on an aircraft, and which includes a housing or nacelle 10, a core casing 13, a low pressure spool assembly seen generally at 12 which includes a fan assembly 14, a low pressure compressor assembly 16 and a low pressure turbine assembly 18, and a high pressure spool assembly seen generally at 20 which includes a high pressure compressor assembly 22 and a high pressure turbine assembly 24. The core casing 13 surrounds the low and high pressure spool assemblies 12 and 20 in order to define a main fluid path (not indicated) therethrough. In the main fluid path there is provided a combustor 25 in which a combustion process takes place and produces combustion gases to power the high and low turbine assemblies 24 and 18. A pressure lubrication system generally indicated at 26 is provided to generate pressure lubricant circulation for engine components such as bearings of the low and high pressure spool assemblies 12 and 20.
Referring to FIGS. 1 and 2, the pressure lubrication system 26 such as a pressure oil system generally includes a lubrication fluid circulation network 28 through the engine bearing chambers (not shown) for distribution of lubrication fluid to the bearings, and a tank 30 (such as an oil tank) to define a capacity for containing the lubrication fluid as a source of the lubrication fluid supply of the lubrication fluid circulation network 28. A pump 32 is provided for pumping the lubrication fluid from the tank 30 into the lubrication fluid circulation network 28. The pump 32 which may be positioned either inside or outside of the tank 30, has an inlet 34 for intake of the lubrication fluid in the tank 30. The inlet 35 may be positioned in a central area inside the tank 30, such as in a geometrical center (or centroid) of the tank 30, when the pump 32 is positioned inside the tank 30. A fluid returning tube 35 may be provided to communicate the tank 30 with the fluid lubrication fluid circulation network 28 for directing a returning flow of the lubrication fluid from the lubrication fluid circulation network 28 into the tank 30.
It is known that in geometry, the centroid or geometric center of a plane figure or two-dimensional shape X is the intersection of all straight lines that divide X into two parts of equal moment bout the line. Informally, it is the “average” of all points of X. The definition extends to any object X in n-dimension space: its centroid is the intersection of all hyperplanes that divide X into two parts of equal moment.
The tank 30 therefore may be of any suitable shape, such as a rectangular configuration as shown in FIG. 2. The tank 30 as shown in FIG. 2 is in an upright orientation which is a normal orientation during engine operation when the aircraft is grounded or in cruise flight, and has top and bottom walls 36, 38, opposed side walls 40 and 42 and front and rear walls 44, 46 (see FIG. 6). The tank 30 defines the capacity of the tank 30 such that a lubrication fluid level surface 48 in the tank 30 is spaced apart from the top wall 36 of the tank 30 when the lubrication fluid has a required maximum volume for the tank 30 and a lubrication fluid level surface 50 in the tank 30 is in a predetermined location above the inlet 34 when the lubrication fluid has a required minimum volume for the tank 30, in order to have the pump inlet 34 submerged in the lubrication fluid.
FIGS. 2-5 illustrate four typical orientations of the tank 30 and lubrication fluid circulation network 28 when the aircraft changes attitude during flight. As already mentioned, FIG. 2 illustrates an upright orientation of the tank 30 when the aircraft is grounded or in cruise flight. FIG. 3 illustrates an inverted orientation of the tank 30 during an inverted flight of the aircraft. FIG. 4 illustrates a 90° rotated orientation of the tank 30 during a 90° knife-edge flight of the aircraft. FIG. 5 illustrates a 270° rotated orientation of the tank 30 during a 270° knife-edge flight of the aircraft.
As shown in FIGS. 2-5, the pump inlet 34 is always submerged in the lubrication fluid contained in the tank 30 because the inlet 34 is positioned in this central area inside the tank 30 and therefore the lubrication fluid level surface 50 in the tank 30 is always above the location of the pump inlet 34 even when the lubrication fluid remaining in the tank 30 is at the required minimum volume, regardless of the tank orientation (upright, inverted, 90° or 270° orientations).
It is noted that the pump inlet 34 may be positioned off the geometric center of the tank 30 provided that the lubrication fluid level surface 50 (when at the minimum volume of the fluid) in the tank 30 is always above the location of the pump inlet 34 in any tank orientation, thereby ensuring lubrication fluid supply to the pressure lubrication system 26 of the engine in any flight attitude.
The pump 32 may be positioned outside the tank 30. A fluid passage (not indicated) may be provided extending through a wall of the tank 30 to communicate the tank 30 with the pump 32 for delivery of the lubrication fluid from the tank through the pump 32 to the lubrication fluid circulation network 28, under a pressure differential generated by the pump. In this embodiment, the fluid passage has an open end (same as the inlet 34 shown in FIG. 2) defining a passage entry which is positioned in the same location as the pump inlet 34, as previously described with reference to FIG. 2. In that previously described embodiment wherein the pump 32 is provided within the tank 30, the fluid passage for delivery of lubrication fluid from the tank 30 to the lubrication fluid circulation network 28, is defined by the internal passage of the pump 32, optionally with input and/or output tube extensions.
As shown in FIGS. 2-5, there is always a space within the tank 30 above the lubrication fluid level surface 50, even when the lubrication fluid is in the required maximum volume, regardless of the tank orientation.
The system 26 may be further provided with a pair of vent tubes 52 and 54 each having an inlet 52a and 54a respectively, positioned inside the tank 30, and an outlet 52b and 54b respectively, positioned outside the tank 30. The vent tubes 52 and 54 are configured and positioned to have the inlet 52a (or 54a) of one vent tube located in a space above the lubrication fluid level surface 48 for ventilation when in the fluid has a required maximum volume, and to have the outlet 54b (or 52b) of the other vent tube located above the lubrication fluid level surface 48 in order to prevent lubrication fluid from escaping the tank 30, regardless of the tank orientation, as illustrated in FIGS. 2-5.
In one embodiment as shown in FIG. 2, both of the tubes 52 and 54 may be configured in an L-shape including an inlet section having an open end defining inlets 52a and 54a respectively, and an outlet section having an open end defining the outlets 52b and 54b respectively. The inlet and outlet sections of each tube are in a substantially perpendicular relationship.
The vent tube 52 is affixed to the tank 30 such that the inlet section extends through the bottom wall 38 of the tank 30 in an upright direction to position inlet 52a adjacent to the top and side walls 36, 40 inside of the tank 30. The outlet section of the vent tube 52 is positioned outside of the bottom wall 38 of the tank 30 such that the outlet 52b is positioned below the bottom wall 38 and adjacent to the side wall 42 outside of the tank 30. This configuration and positioning of the vent tube 52 ensures that its inlet 52a will always be positioned above the lubrication fluid level surface 48 in the tank 30, even when in the fluid has a required maximum volume, regardless of whether the tank is upright as shown in FIG. 2 or in the 270° rotated orientation as shown in FIG. 5. Therefore when the tank 30 is in these two tank orientations, the vent tube 52 will be free of lubrication fluid therein and is available for ventilation of the tank 30.
The vent tube 54 is affixed to the tank 30 similar to that of vent tube 52, but is positioned in an opposite direction relative to the direction of the vent tube 52. Therefore, in the upright tank orientation as shown in FIG. 2, the vent tube 54 has its inlet 54a positioned inside the tank 30, adjacent the bottom wall 38 and the side wall 42 of the tank 30, and has its outlet 54b outside of the tank 30, above the top wall 36 and adjacent the side wall 40 of the tank 30. Therefore, the inlet 54a of the vent tube 54 is positioned in the space within the tank 30, above the lubrication fluid level surface 48 even when in the required maximum volume, regardless of whether the tank is inverted as shown in FIG. 3 or in the 90° rotated orientation as shown in FIG. 4. Therefore, the vent tube 54 will be free of lubrication fluid therein and available for ventilation of the tank 30 during these two tank orientations in which the vent tube 52 is not available for ventilation because its inlet 52a is submerged in the lubrication fluid.
It is understood that vent tube 54 is not available for ventilation of the tank 30 during the tank orientations shown in FIGS. 2 and 5 because the inlet 54a is submerged in the lubrication fluid.
When the inlet 52a of the vent tube 52 is submerged in the lubrication fluid in the tank 30 (when the tank is inverted as shown in FIG. 3 or in a 90° rotated orientation as shown in FIG. 4) the outlet 52b is located above the tank 30 and above the lubrication fluid level surface 48 in the tank 30. Therefore, the vent tube 52 in these two tank orientations will not cause lubrication fluid leakage from the tank. Similarly, the vent tube 54 will not cause lubrication fluid leakage from the tank 30 when the tank is upright as shown in FIG. 2 or in the 270° rotated orientation as shown in FIG. 5.
The fluid returning tube 35 in this embodiment includes an outlet section (not indicated) affixed to the tank 30, extending through the top wall 36 into the inside of the tank 30, for example, downwardly along the side wall 40, to position an outlet 35a in a location at an inner corner between the side wall 40 and the bottom wall 38 of the tank 30. Lubrication fluid returning from the lubrication fluid circulation network 28 into the tank 30, is driven by a pressure differential in the system rather than by gravity. Therefore, the fluid returning tube 35 may be otherwise attached to the tank 30 to position outlet 35a in any location within the tank without difficulty for proper functioning during any tank orientation as shown in FIGS. 2-5.
In FIG. 2, while the tank 30 is in the upright orientation, lubrication fluid in the tank 30 will enter the vent tube 54 through inlet 54a and remain in the inlet section of the vent tube 54 while the vent tube 52 will be free of oil. During an instant transient period of time while the tank orientation changes from the upright orientation as shown in FIG. 2 to the inverted orientation as shown in FIG. 3 or to the 270° rotated orientation as shown in FIG. 5, a small amount of residual lubrication fluid in tube 54 will drain out from the outlet 54b which will be positioned below the tank 30 in the two latter tank orientations. A temporary fluid spillage may occur in a transient period of time during every tank orientation change when a previously “sleeping” vent tube 52 or 54, is emptied of the small amount of fluid in order to be free of lubrication fluid and available for ventilation. Therefore, an apparatus or device for collecting the temporary fluid spillage may be provided.
As shown in FIGS. 2-6, a housing 56 of any shape (a cylindrical shape is shown in the drawings) may be provided to accommodate the tank 30 such that the outlets 52b and 54b of the respective vent tubes 52 and 54 are positioned within the housing 56. The housing 56 defines at least one opening 58 (see FIG. 6) for venting air. The opening 58 is disposed in a location of the housing, for example at the respective opposed front and rear ends 60a, 60b of the housing. The opening 58 may be positioned radially spaced apart from a periphery of a vertical and transverse cross-section of the housing 56. As an example of the housing, this feature is shown in the figures as two circular openings 58 defined in the opposite front and rear ends 60a and 60b of the cylindrical housing 56, coaxial to the peripheral wall (not indicated) of the housing 56. Therefore, the housing 56 defines a capacity for collecting the lubrication fluid resulting from the temporary fluid spillage during the tank orientation transition period. Any other alternative types of apparatus or arrangements for collecting the temporary fluid spillage may be used with the tank 30 and the vent tubes 52 and 54, without affecting the principle in which the tank 30 or the pressure lubrication system 26 works for inverted flight.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departure from the scope of the described subject matter. For example, a turbofan gas turbine engine is illustrated in the drawings and described as an exemplary application of the described subject matter. However, the described subject matter is applicable to other aircraft engines. As above-mentioned, a rectangular tank and a cylindrical housing which are convenient for description and illustration, are used as an example to illustrate the described subject matter. However, the tank and housing may be of any shapes. For example, the tank according to another embodiment, may have a non-axisymmetric shape such as a triangle, as illustrated in FIG. 7. The geometrical center of the tank is the centroid of the triangle and is determined by the three dividing line also as shown in FIG. 7. The method to locate the centroid of the triangle is known and will not be discussed herein. Still other modifications which fall within the scope of the described subject matter will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.
Patent Application
20110315484
