Interruption tolerant lubrication system

A lubrication system for a turbine engine or other application includes a first or primary branch 12 and a second or secondary branch 14, a main pump 16, a lubricant distributor 18 for receiving lubricant from the main pump and distributing the lubricant to the branches, and a auxiliary pump 30 in the second branch downstream of the distributor. The system is operable in a normal mode of operation in which lubricant flows from a lubricant source into the primary and secondary branches 12, 14 and is also operable in a backup mode of operation in which lubricant backflows from the primary branch into the secondary branch.

TECHNICAL FIELD

This invention relates to lubrication systems and particularly to a multi-branch lubrication system capable of diverting lubricant from a branch with tolerance for lubricant starvation to a branch with less tolerance for lubricant starvation.

BACKGROUND

Aircraft gas turbine engines include a number of components requiring lubrication. Examples of such components include rotor shaft rolling element bearings, gear teeth and journal bearings for supporting gears. These components may be supplied with lubricant by different, parallel branches of a lubrication system. Certain of these components may be relatively intolerant to lubricant starvation. Other components may have relatively more tolerance for lubricant starvation.

In a conventional lubrication system, events such as aircraft maneuvers can result in lubricant starvation of both the starvation tolerant components and the starvation intolerant components. As a result, the starvation intolerant components may suffer significant damage requiring subsequent replacement of those components. In more extreme situations, the starvation intolerant components may be rendered inoperative. Accordingly, it is desirable to have a lubrication system architecture that continues to deliver lubricant, at least temporarily, to the starvation intolerant components.

SUMMARY

One embodiment of the lubrication system described herein includes a first relatively starvation tolerant branch, a second relatively starvation intolerant branch, a main pump, a lubricant distributor for receiving lubricant from the main pump and distributing the lubricant to the branches, and a auxiliary pump in the second branch downstream of the distributor.

A related lubrication system architecture includes a first branch for delivering lubricant to components having, as a whole, a relatively higher tolerance for lubricant starvation and a second branch for delivering lubricant to components having, as a whole, a relatively lower tolerance for lubricant starvation. The system architecture also includes means for backflowing lubricant from the first branch into the second branch in the event that the lubrication requirement of at least the second branch cannot be satisfied.

A related method of supplying lubricant includes flowing the lubricant from a lubricant source into primary and secondary branches and, in the event that the lubricant is inadequate to satisfy the lubrication requirement of at least the secondary branch, backflowing lubricant from the primary branch into the secondary branch.

The foregoing and other features of the various embodiments of the lubrication system, architecture and lubrication method will become more apparent from the following detailed description and the accompanying drawings.

DETAILED DESCRIPTION

FIG. 1shows an aircraft gas turbine engine10and an associated multi-branch lubrication system and system architecture. The system includes a first branch12and a second branch14. A main pump16draws lubricant from a tank, not shown, or other source of lubricant. The pump pumps the lubricant to a lubricant distributor18, such as a manifold or distribution valve, which receives the lubricant and distributes it to the branches. Each branch has a destination20,22. In the illustrated system, a component requiring lubrication resides at each destination. Examples of such components are a rotor shaft roller bearing24and a journal bearing26for rotatably supporting a gear. In many typical applications a lubricant recovery system, not shown, recovers the lubricant from the components, and returns it to the lubricant source.

The components24,26have differing degrees of tolerance for lubricant starvation. For example, the journal bearing26is less tolerant of lubricant starvation and the roller bearing24is more tolerant of lubricant starvation. Because the first branch serves a component that is relatively more tolerant to lubricant starvation, the first branch, and the component, may be referred to as being tolerant to lubricant starvation. Because the second branch serves a component that is relatively less tolerant to lubricant starvation, the second branch, and the component, may be referred to as being intolerant to lubricant starvation. By referring to a component or branch as starvation tolerant we do not mean that the component or branch can operate indefinitely without adequate lubricant. By referring to a component or branch as starvation intolerant we do not mean that the component or branch cannot operate for at least a brief time without a normal quantity of lubricant. Instead, tolerance or intolerance for lubricant starvation are relative rather than absolute attributes of the components and branches. In addition, lubricant starvation does not necessarily mean that a component or branch is completely deprived of lubricant, but merely that the component or its associated branch is receiving less lubricant than is satisfactory.

The system also includes an auxiliary pump30in the second branch downstream (in the direction of normal lubricant flow indicated by the fluid flow arrows) of the distributor18and upstream of destination22and its associated journal bearing26. The auxiliary pump resides in the second branch because the second branch is the branch serving the component with relatively less tolerance for lubricant starvation. Because of the presence of the auxiliary pump, branch14may be referred to as a secondary branch. Branch12may therefore be referred to as a primary branch. Designating branch14as a secondary branch does not imply that branch14or component26are in any way less important than the primary branch12and component24.

As seen inFIG. 1, the system is operable in a normal mode in which lubricant flows from the main pump, through the distributor18into the branches12,14and ultimately to the destinations20,22. The auxiliary pump30operates concurrently with the main pump16. The system branches12,14, and more specifically the components24,26served by those branches each have an individual lubrication requirement. The branches collectively have an aggregate lubrication requirement. The individual and aggregate lubrication requirements are satisfied by the lubrication system during operation in the normal mode.

As seen inFIG. 2, the system is also operable in a backup mode. Operation in the backup mode occurs when the flow of lubricant from the main pump16is inadequate to satisfy at least the lubrication requirement of the lubricant intolerant branch14, more specifically, the lubrication requirements of the components26served by that branch. This condition may correspond to an aircraft maneuver that temporarily impairs the ability of the lubrication system to deliver a satisfactory quantity of lubricant. Or the condition requiring operation in the backup mode may be a more severe and/or persistent event such as a leak, rupture or blockage in the lubrication system. The “X” symbol just downstream of the main pump inFIG. 2signifies the inability of the system to satisfy the lubrication requirements irrespective of the reason for such inability. In the backup mode, the auxiliary pump30urges a reverse flow or backflow of lubricant from the first branch12into the second branch14as indicated by the fluid flow arrows. As a result, the starvation tolerant component24in the starvation tolerant branch12experiences a greater deprivation of lubricant than would otherwise be the case. However the starvation intolerant component26in the starvation intolerant branch14receives more lubricant than would otherwise be the case. Specifically, the second branch receives enough lubricant to satisfy its minimum lubrication requirements. The minimum lubrication requirements may include a minimum lubricant quantity and/or a minimum duration or time during which lubricant must be supplied.

In order to operate as just described, the primary branch12, i.e. the branch with greater starvation tolerance, is configured to have an available lubricant capacity sufficient to satisfy the minimum lubrication requirements of the less starvation tolerant secondary branch14. The capacity of the branch12is a function of the volume of lubricant contained in the conduits and other elements of the branch. However a designer will recognize that the entire volume of lubricant in the primary branch12may not be available, or at least not readily available, for reverse flow into the secondary branch14. Availability may be limited by the presence of hardware or features in a branch that prevent or impede reverse lubricant flow in the branch. For example, a check valve32in branch12would limit the available lubricant capacity to the lubricant contained in the branch between the distributor18and the check valve. The system designer will size and locate the elements and features of the primary branch in order to ensure the availability of sufficient lubricant capacity to satisfy the minimum lubrication requirements of the starvation intolerant secondary branch.

For simplicity, the above example describes a system having only two branches, each of which serves only one component. More generally, and as seen inFIG. 3, the system may have three or more branches each serving one or more components. The components of a given branch may be arranged in series, in parallel, or in any series/parallel combination.FIG. 3shows such a system having m starvation tolerant branches and n starvation intolerant branches. Each starvation intolerant branch includes an auxiliary pump30. During normal operation, the main pump16pumps lubricant to all the branches. During operation in the backup mode, i.e. when the main pump cannot satisfy the lubrication requirements of at least the starvation intolerant branches, the auxiliary pumps cause lubricant to backflow from the starvation tolerant branches (branches1through m) into the starvation intolerant branches (branches m+1 through m+n).

FIG. 4shows a lubrication system architecture. For simplicity, a system architecture with only two branches is shown, however the principles described herein are applicable to system architectures with three or more branches. The illustrated system includes a first branch12serving a first group36of components24and a second branch14serving a second group38of components26. The components of the first group36are, as a whole, more tolerant of lubricant starvation. The components of the second group38are, as a whole, less tolerant of lubricant starvation. The second branch includes a auxiliary pump30or other means for backflowing lubricant from the first branch to the second branch. As described above, during normal operation the pump delivers lubricant to both branches. During backup operation, i.e. when the lubrication requirements of at least the second branch cannot be satisfied, the auxiliary pump30causes lubricant to backflow from the first branch into the second branch.

The above described first group36of components having a higher starvation tolerance and second group38of components having a lower starvation tolerance may be defined in a number of ways. For example, and as seen inFIG. 5, even the least starvation tolerant member24aof the first group36may have more starvation tolerance than the most starvation tolerant component26dof the second group38. Under this definition, there is no tolerance overlap between the groups. However, as seen inFIG. 6, a designer may also choose to define the groups such that at least one member of the starvation tolerant first group (e.g. component24a) has less starvation tolerance than at least one member (e.g. component26d) of the starvation intolerant second group. The designer nevertheless considers group36to be more starvation tolerant as a whole than group38. In other words, when all factors are considered, group36is more starvation tolerant than group38, notwithstanding the overlap seen inFIG. 6. Such groupings may be necessary because of, for example, constraints on the relative positioning and interrelationships between components. In other words, constraints other than the intrinsic starvation tolerance of the individual components may dictate that component24abe in starvation tolerant group36rather than in group38. Such a grouping may be justified if, for example, component24a, is not highly critical to the continued satisfactory operation of the engine. In general, the grouping of components into starvation tolerant and starvation intolerant branches may account for not only a component's intrinsic ability to continue operating in a lubricant starved state, but also its criticality to continued operation of the engine10, the difficulty and expense of replacing or repairing it if it sustains damage and other relevant factors. Moreover, althoughFIG. 6depicts only a small overlap involving only one component from each group, the overlap may be more extensive and may involve more than one component from at least one of the groups.

Although the lubrication system, architecture and method have been described in the context of an aircraft gas turbine engine, it is nevertheless applicable to other machinery having multibranch lubrication systems.

Although this disclosure refers to specific embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the subject matter set forth in the accompanying claims.