Patent Description:
Gas turbine engines often have multiple gearboxes that require lubrication. These gas turbines have a variety of drawbacks, limitations, and disadvantages. Accordingly, there is a need for inventive systems, methods, components, and apparatuses described herein.

United States patent application <CIT> discloses a lubrication system for a turbine engine. The lubrication system comprises first lubrication system which includes a first turbine engine component that is fluidly coupled with a first lubricant heat exchanger and a second lubricant circuit which includes a second turbine engine component that is fluidly coupled with a second lubricant heat exchanger. The second lubricant circuit is fluidly separate from the first lubricant circuit.

European patent application <CIT> discloses a lubrication system for a gas turbine engine. The lubrication system comprises first and second lubrication systems for supplying the gearbox. The first lubrication system supplying oil from the oil tank and the second lubrication system for supplying oil form the sump when it reaches a predetermined level.

United states patent application <CIT> discloses a lubrication system for a drive system of a tilt rotor aircraft. The lubrication system having first and second lubrication systems that are connected to the drive gearboxes for the tilt rotor aircraft. The lubrication system having a failsafe reservoir in case of failure.

The present disclosure provides a gas turbine engine as set out in the appended claims.

In a first aspect the present disclosure provides a gas turbine engine for an aircraft, the gas turbine engine comprising: a shaft fixed to a compressor of the gas turbine engine; at least one of a turboprop and a turbofan; a power gearbox having a power output shaft fixed to the at least one of the turboprop and the turbofan, wherein the power gearbox receives an input rotation from the shaft; an auxiliary gearbox having an auxiliary output shaft powering at least one auxiliary component of the gas turbine engine; a first lubrication system; and a second lubrication system that is separated from the first lubrication system, wherein the first lubrication system circulates a first lubricant through the power gearbox, and the second lubrication system circulates a second lubricant through the auxiliary gearbox. The gas turbine engine has a failsafe valve that, when actuated, provides a fluid connection between the first lubrication system and the second lubrication system, and the first lubrication system and the second lubrication system lack a fluid connection when the failsafe valve is closed. The first lubrication system (<NUM>) lacks a filter.

The embodiments may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale. Moreover, in the figures, like-referenced numerals designate corresponding parts throughout the different views.

By way of an introductory example, a power gearbox may drive at least one of a turboprop and a turbofan in a gas turbine engine. A first lubrication system may be dedicated to the power gearbox. A separate second lubrication system may lubricate and/or cool other components, such as other gearboxes of the gas turbine engine.

One interesting feature of the devices, systems, and methods described below may be that the separate and isolated lubrication systems allow for optimal lubricant selection for critical components of the gas turbine engine, thereby increasing the lifespan of certain components and reducing the maintenance burden.

Another interesting feature of the devices, systems, and methods described below may be that the separate and isolated lubrication systems save valuable space within the confines of the gas turbine engine, thereby providing room for other components.

Another interesting feature of the devices, systems, and methods described below may be that the separate and isolated lubrication systems can save valuable space within the confines of the gas turbine engine, thereby providing room for other components.

Another interesting feature of the devices, systems, and methods described below may be that the separate and isolated lubrication systems reduce the need for filtering and/or increase the lifespan of a lubricant within at least one of the lubrication systems.

<FIG> is a cross-sectional view of a gas turbine engine <NUM>. In some examples, the gas turbine engine <NUM> may supply power to and/or provide propulsion of an aircraft. Examples of the aircraft may include a helicopter, an airplane, an unmanned space vehicle, a fixed wing vehicle, a variable wing vehicle, a rotary wing vehicle, an unmanned combat aerial vehicle, a tailless aircraft, a hover craft, and any other airborne and/or extraterrestrial (spacecraft) vehicle. Alternatively or in addition, the gas turbine engine <NUM> may be utilized in a configuration unrelated to an aircraft such as, for example, an industrial application, an energy application, a power plant, a pumping set, a marine application (for example, for naval propulsion), a weapon system, a security system, a perimeter defense or security system.

The gas turbine engine <NUM> may take a variety of forms in various embodiments. Though depicted as an axial flow engine, in some forms the gas turbine engine <NUM> may have multiple spools and/or may be a centrifugal or mixed centrifugal/axial flow engine. In some forms, the gas turbine engine <NUM> may be a turboprop, a turbofan, a geared turbofan, or a turboshaft engine. Furthermore, the gas turbine engine <NUM> may be an adaptive cycle and/or variable cycle engine. Other variations are also contemplated.

The gas turbine engine <NUM> may include an intake section <NUM>, a compressor section <NUM>, a combustion section <NUM>, a turbine section <NUM>, and an exhaust section <NUM>. During operation of the gas turbine engine <NUM>, fluid received from the intake section <NUM>, such as air, travels along the direction D1 and may be compressed within the compressor section <NUM>. The compressed fluid may then be mixed with fuel and the mixture may be burned in the combustion section <NUM>. The combustion section <NUM> may include any suitable fuel injection and combustion mechanisms. The hot, high pressure fluid may then pass through the turbine section <NUM> to extract energy from the fluid and cause a shaft <NUM> of a turbine <NUM> in the turbine section <NUM> to rotate, which in turn drives the compressor section <NUM>. Discharge fluid may exit the exhaust section <NUM>.

As noted above, the hot, high pressure fluid passes through the turbine section <NUM> during operation of the gas turbine engine <NUM>. As the fluid flows through the turbine section <NUM>, the fluid passes between adjacent blades of the turbine <NUM> causing the shaft <NUM> to rotate. The rotating turbine <NUM> may turn a shaft <NUM> in a rotational direction D2, for example. The shaft <NUM> may rotate around an axis of rotation, which may correspond to a centerline X of the turbine <NUM> in some examples.

The gas turbine engine <NUM> may also include a turbofan <NUM> (or alternatively a turboprop, not shown) located upstream from the compressor section <NUM>. The turbofan <NUM> may receive fluid from the intake section <NUM> and direct it downstream. A portion of the fluid passing through the turbofan <NUM> may enter the compressor section <NUM> while another portion of the fluid may bypass the compressor section <NUM>. To better direct fluid passing through the turbofan <NUM>, the turbofan may be surrounded by a shroud <NUM>. The shroud <NUM> may be a component which encircles the turbofan <NUM>. Examples of the shroud <NUM> may include a duct or a cylindrical shell. The shroud <NUM> may extend over other portions of the gas turbine engine <NUM>, such as the compressor section <NUM>.

The turbofan <NUM> may be coupled to the shaft <NUM> through a power gearbox <NUM> (e.g., where the power gearbox <NUM> includes an output shaft fixed to the turbofan <NUM>. The power gearbox <NUM> may be any component which mechanically transforms rotations D2 of the shaft <NUM> into rotations of the turbofan <NUM>. Examples of the power gearbox <NUM> may include a coaxial helical inline gearbox, a bevel helical gearbox, or a planetary gearbox (also known as an epicyclic gear train). The turbofan <NUM>, shroud <NUM>, and power gearbox <NUM>, may be supported by struts <NUM> coupled to different points of the gas turbine engine <NUM>. For example, as illustrated in <FIG>, the struts may extend between the power gearbox <NUM> and the shroud <NUM>, and between the shroud <NUM> and the compressor section <NUM>. The struts <NUM> may extend between other portions of the gas turbine engine <NUM> as well.

<FIG> illustrates a cross-sectional view of the power gearbox <NUM>. The power gearbox <NUM> may include a plurality of gears <NUM> which rotate in response to the rotation of the shaft <NUM>. The gears <NUM> may be any object which is capable of mechanically transferring rotation of one component to another component. For example, the gears <NUM> may transfer the rotation of the shaft <NUM> to a rotation of the turbofan <NUM> depicted in <FIG>. Non-limiting examples of the gears <NUM> may include spur gears, helical gears, or herringbone gears forming a planetary gear train. The plurality of gears <NUM> may rotate a ring gear <NUM> which encircles the plurality of gears <NUM>. The ring gear <NUM> may be any component which, through interaction with the plurality of gears, rotates at a reduced rate compared to the rotation of the shaft <NUM>. Examples of the ring gear <NUM> may include a spur ring gear, a helical ring gear, or a herringbone ring gear. The ring gear <NUM> may be included in other embodiments of the power gearbox <NUM>. Several examples of non-limiting gearbox embodiments are shown in United States patent application <CIT>.

Referring to <FIG>, the gas turbine engine <NUM> may additionally include one or more accessory drives, such as the depicted accessory drive <NUM>. The accessory drive <NUM> may provide power to certain engine components, including auxiliary components such as starters, integrated drive generators (IDG), fuel pumps or other pumps, hydraulic components, lubrication/scavenge components (such as pumps), a de-oiler, generators (for aircraft services and/or engine control), or any other suitable component(s). The accessory drive <NUM> may include an internal gearbox <NUM> (or inlet gearbox) that transforms rotation of the shaft <NUM> (shown in <FIG>) into rotation of components within a transfer gearbox <NUM> (e.g., where the transfer gearbox <NUM> is mechanically coupled to the internal gearbox <NUM>). The internal gearbox <NUM> may include a bevel gear for direct drive by the shaft <NUM> (shown in <FIG>), though an idler shaft or gear may additionally be included, and the transfer gearbox <NUM> may include any gear structure for transferring associated mechanical energy downstream. In particular, the transfer gearbox <NUM> may be mechanically coupled to at least one auxiliary gearbox <NUM>, and the transfer gearbox <NUM> may supply the auxiliary gearbox <NUM> with mechanical energy for powering auxiliary components. The auxiliary gearbox <NUM> may be fixed to the shroud <NUM> (<FIG>) or another portion of the gas turbine engine housing/casing, but it may alternatively be located in a different location. The auxiliary gearbox <NUM> may be coupled to one or more auxiliary components.

As shown in <FIG>, the gas turbine engine <NUM> includes a first lubrication system <NUM> devoted to the power gearbox <NUM> and a second lubrication system <NUM> devoted to the accessory drive <NUM> (including its gearboxes). Optionally, the second lubrication system <NUM> may also provide lubrication to the auxiliary components <NUM> and/or other turbomachinery components <NUM> (e.g., high-power electronic components, gears, bearings, and/or any other contact-based mechanical components requiring lubrication or cooling).

The first lubrication system <NUM> may include a variety of components related to lubrication and cooling. For example, certain included components may include (but are not limited to) a first lubrication pump <NUM>, a first oil tank <NUM>, a first oil cooler <NUM>, and a first oil filter <NUM>. Certain components may be omitted, and/or others may be included.

During operation, the first pump <NUM> may provide the pressure necessary to circulate a first lubricant L1 through the first lubrication system <NUM>. The first lubricant L1 may include any suitable fluid capable of reducing frictional interaction between mechanical components, such as oil. In the depicted example, the first lubricant L1 may flow from the first pump <NUM> to the first oil tank <NUM> (via piping <NUM>) to the first oil tank <NUM>. Examples of the first pump <NUM> may include fixed displacement pumps or variable displacement pumps, such as a rotary vane pump, a piston pump, or a centrifugal pump. In certain exemplary embodiments, the first pump <NUM> is driven by the power gearbox <NUM>.

The piping <NUM> may include a first supply line <NUM> arranged to direct the first lubricant L1 from the first oil tank <NUM>, through the heat exchanger or first oil cooler <NUM> (e.g., to transfer heat away from the first lubricant L1), and then to the power gearbox <NUM>. The heated first lubricant L1 may then flow through the first oil filter <NUM> and then back to the first pump <NUM>. As will be appreciated by those skilled in the art, certain components may be duplicated, omitted, or re -arranged such that the sequence of the loop changes (e.g., the first oil cooler <NUM> may be located between the power gearbox <NUM> and the first pump <NUM>, for example).

Similarly, the second lubrication system <NUM> may include a variety of components related to lubrication and cooling. For example, certain included components may include (but are not limited to) a second lubrication pump <NUM>, a second oil tank <NUM>, a second oil cooler <NUM>, a second supply line <NUM>, a second return line <NUM>, and a second oil filter <NUM>. Certain components may be omitted, and/or others may be included.

During operation, the second pump <NUM> may provide the pressure necessary to cause a second lubricant L2 to flow through the second lubrication system <NUM>. As discussed in more detail below, the second lubricant L2 may have different characteristics than the first lubricant L1 (or not). In the depicted example, the second lubricant L2 may flow from the second pump <NUM> to the second oil tank <NUM> (via piping <NUM>). The piping <NUM> may include a plurality of parallel lines arranged to direct the second lubricant L2 from the second oil tank <NUM> to certain gearboxes and/or certain auxiliary component(s) <NUM>. For example, as shown, the second pump <NUM> directs the second lubricant L2 through a first conduit C1 to the internal gearbox <NUM> for lubrication and cooling. The second lubricant L2 may flow directly from the internal gearbox <NUM> to the transfer gearbox <NUM> (or alternatively tubing may be included therebetween). Similarly, the second lubricant L2 may flow directly from the transfer gearbox <NUM> to the auxiliary gearbox <NUM> (or alternatively tubing may be included therebetween). Optionally, a second parallel conduit C2 may be included to direct the second lubricant L2 for lubrication and/or cooling of the auxiliary component <NUM>, but in other embodiments, this second conduit C2 may be in series with the first conduit C1 (or excluded entirely). The second lubricant L2 may then flow through the second oil filter <NUM> and back to the second pump <NUM>. As will be appreciated by those skilled in the art, certain components may be duplicated, omitted, or re-arranged such that the sequence of the loop changes (e.g., the heat exchanger <NUM> may be located just before the second pump <NUM>, for example).

A feature of the embodiment of <FIG> is that the first lubrication system <NUM> is wholly separate from the second lubrication system <NUM> when the gas turbine engine <NUM> is in a normal operational state. That is, the first lubricant L1 of the first lubrication system <NUM> does not flow through the piping <NUM> of the second lubrication system <NUM>, and vice versa, during normal operation. This feature may be advantageous for several reasons. For example, in certain applications, an optimal oil for cooling the power gearbox <NUM> may be different from an optimal oil for cooling one or more of the components of the accessory drive <NUM> and/or other turbomachinery components <NUM>. For example, one of the first lubrication system <NUM> and the second lubrication system <NUM> may include a respectively high (e.g., at least <NUM>% higher, such as at least <NUM>% higher, than the respective other lubrication system) of at least one of the following: viscosity, water content, calorific content, specific gravity, a different characteristic typically selected with an engine oil, and/or a combination thereof.

Additionally or alternatively, desirable oil conditions may be different in each lubrication system. For example, it may be advantageous for the first lubrication system <NUM> to operate with the first lubricant L1 at a higher pressure than the second lubricant of the second lubrication system <NUM>. For example, one of the first lubrication system <NUM> may have an operational oil pressure (e.g., during idle speed) that is at least <NUM> psi higher than an operational oil pressure in the second lubrication system <NUM> at the same engine speed at least at one location within the respective circuits, such as at least <NUM> psi higher, at least <NUM> psi higher, at least <NUM> psi higher, etc. (e.g., any reasonable pressure differential based on the engine design). The opposite is also true (e.g., the second lubrication system <NUM> may have a higher operational pressure than the first oil system <NUM> at least at one location in the respective circuits). Similarly, it may be advantageous for the first lubricant L1 and the second lubricant L2 to function at different temperatures (e.g., having an average temperature difference of at least about <NUM> degrees Celsius), different mass and/or volumetric flow rates (e.g., where one flow rate is at least <NUM>% higher than the other).

Separating the first lubricant L1 and the second lubricant L2 also may provide advantages from a filtering perspective. For example, the power gearbox <NUM>, which may include extreme tolerances from a quality perspective, may have a respectively-high cleanliness level relative to certain components cooled and lubricated by the second lubrication system <NUM>. Since the loading on bearings and gears within the power gearbox <NUM> can be extremely high (making precise and clean lubrication critical), keeping the first lubricant L1 within a dedicated circuit for the power gearbox <NUM> may isolate the first lubricant L1 from components associated with lower cleanliness. This may increase the lifespan of the first lubricant L1 (and also the power gearbox <NUM>) relative to other embodiments. Additionally, changing the second lubricant L2 may be accomplished without changing the relatively clean first lubricant L1, which may reduce maintenance costs particularly in applications where the first lubrication system <NUM> requires significantly more lubricant than the second lubrication system <NUM> (e.g., due to high demands of the power gearbox <NUM>). Further, it is contemplated that the first lubrication system <NUM> may exclude a filter altogether, which may reduce weight and increase available space for other components.

Advantageously, separating the first lubrication system <NUM> from the second lubrication system <NUM> may also allow for a more efficient design that saves space relative to other embodiments. For example, since the first lubrication system <NUM> and the second lubrication system <NUM> do not need to interconnect (and may include separate pumps, filters, etc.), each separate lubrication system can be designed to strategically fit in spaces near their respective components, saving valuable space within the housing of the gas turbine engine. Further, certain components that are typical in other embodiments of gas turbine engines may be omitted altogether (saving weight, space, and cost). For example, the present teaching may allow for the omission of a bifurcation panel generally included in existing gas turbine engines, which is commonly nested in a congested location at the aft end of the fan and used to bifurcate oil between different components (such as a power gearbox and auxiliary components).

The separation systems are connected via tubing <NUM> that includes a failsafe valve <NUM>. As shown, the tubing <NUM> may connect the first pump <NUM> to the second lubrication system <NUM> such that, if the second pump <NUM> fails (or the second lubrication system <NUM> otherwise fails, such as due to loss of lubrication fluid), the first pump <NUM> may circulate the first lubrication fluid L1 through the second lubrication system <NUM> to avoid system failure. While not shown, it is contemplated that the second pump <NUM> could be used similarly to circulate the second lubrication fluid L2 through the first lubrication system <NUM> during an emergency situation. The failsafe valve <NUM> may remain closed in normal operational states, but may open to connect the systems to prevent system failure in rare circumstances.

Referring to <FIG>, in some embodiments, the first lubrication system <NUM> may include an integrated oil pump <NUM> within the power gearbox <NUM> (e.g., while optionally excluding a wholly separate pump dedicated to the first lubrication system <NUM>, such as the first pump <NUM> shown in <FIG>). Notably, the power gearbox <NUM> of <FIG> includes five (<NUM>) planetary gears <NUM> rather than four (as in the embodiment of <FIG>), but the integrated pump described herein may be applicable to both emboldens (in addition to others). Such an integrated oil pump <NUM> may replace the first pump <NUM> shown in <FIG>, for example, thereby saving space, weight, and overall cost of the gas turbine engine. As depicted by <FIG>, the power gearbox <NUM> may include the ring gear <NUM> (shown as a dashed line) that rotates (e.g., upon movement of the planetary gears <NUM>) to drive at least one lubrication supply element <NUM> fixed to an outer housing <NUM>. The lubrication supply element <NUM> may include a small oil pump that includes a single (or plurality) of lubrication gerotors, vanes, and/or gears within a relatively small housing, for example. The lubrication supply element <NUM> provides the first lubrication L1 to the gears and bearings of the power gearbox <NUM>. The power gearbox <NUM> may also include at least one scavenge elements <NUM>, which also may be driven by rotation of the ring gear <NUM>. Similarly, the scavenge elements <NUM> may include a relatively small version of an oil pump and include of a singular, or plurality of, gerotors, vanes or gears. These units also have an integral drive-shaft that can motor the oil pump. When the first lubricant is scavenged by the scavenge elements <NUM>, it may then move through a return line <NUM> to an oil tank <NUM> and then back to the lubrication supply element <NUM> through a supply line <NUM>. While not shown, additional elements may be included (e.g., a filter, heat exchanger, an additional pump, etc.). Advantageously, the present embodiment allows the power gearbox <NUM> to provide the pumping function itself through the integrated oil pump <NUM>, and without a separate pumping device.

While the embodiment of <FIG> shows a single lubrication supply element <NUM>, more than one may be included. Further, while two scavenge elements <NUM> are shown, more or fewer may be included. <FIG> shows another arrangement of the gas turbine engine <NUM> similar to the embodiment of <FIG> above but with a different pump configuration. As shown in <FIG>, the first lubrication system <NUM> and the second lubrication system <NUM> are wholly separate (and the first lubricant L1 and second lubricant L2 do not intermix). However, rather than two separate pumps (e.g., the first pump <NUM> and the second pump <NUM> shown in <FIG>), a single pumping unit <NUM> provides the energy for circulating lubricant through each of the first lubrication system <NUM> and the second lubrication system <NUM>. The pumping unit <NUM> preferably includes two separate pumping chambers such that the first lubricant L1 and the second lubricant L2 o not intermix. Providing a single pumping body may save space, reduce weight, and provide relatively high energy efficiency relative to other embodiments. In particular, it is contemplated that the pumping unit <NUM> (e.g., all pumping chambers) may be powered by the power gearbox <NUM>. Other power sources may additionally or alternatively be used. For example, any of the pumps discussed herein may be powered by electric motor(s). <FIG> shows an exemplary method for operating one or more of the embodiments described above. For example, at a first step <NUM>, the above-described first lubricant L1 may be supplied to the first lubrication system <NUM>. Similarly, at a second step <NUM>, the second lubricant L2 may be supplied to the second lubrication system <NUM>. As discussed above, the first lubrication system <NUM> may circulate the first lubricant L1 through the power gearbox <NUM>, the second lubrication system L2 may circulate the second lubricant L2 through at least one auxiliary component <NUM>, and the first lubricant L2 may be wholly excluded from the second lubrication system <NUM>.

Claim 1:
A gas turbine engine (<NUM>) for an aircraft, the gas turbine engine comprising:
a shaft (<NUM>) fixed to a compressor (<NUM>) of the gas turbine engine;
at least one of a turboprop and a turbofan (<NUM>);
a power gearbox (<NUM>) having a power output shaft fixed to the at least one of the turboprop and the turbofan, wherein the power gearbox receives an input rotation from the shaft;
an auxiliary gearbox (<NUM>) having an auxiliary output shaft powering at least one auxiliary component of the gas turbine engine;
a first lubrication system (<NUM>); and
a second lubrication system (<NUM>) that is separated from the first lubrication system,
wherein the first lubrication system circulates a first lubricant (L1) through the power gearbox;
characterised in that:
the second lubrication system circulates a second lubricant (L2) through the auxiliary gearbox; and the gas turbine engine has a failsafe valve (<NUM>) that, when actuated, provides a fluid connection between the first lubrication system (<NUM>) and the second lubrication system (<NUM>), and the first lubrication system (<NUM>) and the second lubrication system (<NUM>) lack a fluid connection when the failsafe valve (<NUM>) is closed, and
wherein the first lubrication system (<NUM>) lacks a filter.