# Patent

## Title
Close coupled gearbox assembly for a tip turbine engine

## Abstract

A gearbox assembly (90) closely couples a fan-turbine rotor assembly (25) and an axial compressor rotor (46) to reduce the overall engine length and minimizes the number of engine bearings.

## Background
This invention was made with government support under Contract No.: F33657-03-C-2044. The government therefore has certain rights in this invention.


BACKGROUND OF THE INVENTION
The present invention relates to a tip turbine engine, and more particularly to a gearbox assembly between a bypass fan rotor and an axial compressor rotor.
An aircraft gas turbine engine of the conventional turbofan type generally includes a forward bypass fan, a compressor, a combustor, and an aft turbine all located along a common longitudinal axis. A compressor and a turbine of the engine are interconnected by a shaft. The compressor is rotatably driven to compress air entering the combustor to a relatively high pressure. This pressurized air is then mixed with fuel in a combustor and ignited to form a high energy gas stream. The gas stream flows axially aft to rotatably drive the turbine which rotatably drives the compressor through the shaft. The gas stream is also responsible for rotating the bypass fan. In some instances, there are multiple shafts or spools. In such instances, there is a separate turbine connected to a separate corresponding compressor through each shaft. In most instances, the lowest pressure turbine will drive the bypass fan.
Although highly efficient, conventional turbofan engines operate in an axial flow relationship. The axial flow relationship results in a relatively complicated elongated engine structure of considerable longitudinal length relative to the engine diameter. This elongated shape may complicate or prevent packaging of the engine into particular applications.
A recent development in gas turbine engines is the tip turbine engine. Tip turbine engines locate an axial compressor forward of a bypass fan which includes hollow fan blades that receive airflow from the axial compressor therethrough such that the hollow fan blades operate as a centrifugal compressor. Compressed core airflow from the hollow fan blades is mixed with fuel in an annular combustor and ignited to form a high energy gas stream which drives the turbine integrated onto the tips of the hollow bypass fan blades for rotation therewith as generally disclosed in U.S. Patent Application Publication Nos.: 20030192303; 20030192304; and 20040025490.
The tip turbine engine provides a thrust to weight ratio equivalent to conventional turbofan engines of the same class within a package of significantly shorter length.
A gearbox assembly provides a speed differential between the fan-turbine rotor assembly and the axial compressor. Integration of the fan-turbine rotor assembly and the axial compressor provides an engine design challenge.
Accordingly, it is desirable to provide a gearbox assembly which integrates the fan-turbine rotor assembly and the axial compressor without greatly increasing the overall engine length and minimizes the number of engine bearings to reduce complexity and increase reliability.
SUMMARY OF THE INVENTION
A gearbox assembly for a tip turbine engine according to the present invention includes a sun gear shaft which rotates with an axial compressor and a planet carrier which rotates with a fan-turbine rotor assembly to provide a speed differential therebetween. By attaching a fan-turbine rotor flange directly to the gearbox assembly, the fan-turbine rotor assembly is closely coupled thereto which reduces the overall engine length and minimizes the number of engine bearings to reduce complexity and increases reliability.



BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:
FIG. 1 is a partial sectional perspective view of a tip turbine engine;
FIG. 2 is a longitudinal sectional view of a tip turbine engine along an engine centerline; and
FIG. 3 is an expanded view of a gearbox assembly.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 illustrates a general perspective partial sectional view of a tip turbine engine type gas turbine engine 10. The engine 10 includes an outer nacelle 12, a nonrotatable static outer support structure 14 and a nonrotatable static inner support structure 16. A multitude of fan inlet guide vanes 18 are mounted between the static outer support structure 14 and the static inner support structure 16. Each inlet guide vane preferably includes a variable trailing edge 18A.
A nose cone 20 is preferably located along the engine centerline A to smoothly direct airflow into an axial compressor 22 adjacent thereto. The axial compressor 22 is mounted about the engine centerline A behind the nose cone 20.
A fan-turbine rotor assembly 24 is mounted for rotation about the engine centerline A aft of the axial compressor 22. The fan-turbine rotor assembly 24 includes a multitude of hollow fan blades 28 to provide internal, centrifugal compression of the compressed airflow from the axial compressor 22 for distribution to an annular combustor 30 located within the nonrotatable static outer support structure 14.
A turbine 32 includes a multitude of tip turbine blades 34 (two stages shown) which rotatably drive the hollow fan blades 28 relative to a multitude of tip turbine stators 36 which extend radially inwardly from the static outer support structure 14. The annular combustor 30 is axially forward of the turbine 32 and communicates with the turbine 32.
Referring to FIG. 2, the nonrotatable static inner support structure 16 includes a splitter 40, a static inner support housing 42 and a static outer support housing 44 located coaxial to said engine centerline A.
The axial compressor 22 includes the axial compressor rotor 46 from which a plurality of compressor blades 52 extend radially outwardly and a compressor case 50 fixedly mounted to the splitter 40. A plurality of compressor vanes 54 extends radially inwardly from the compressor case 50 between stages of the compressor blades 52. The compressor blades 52 and compressor vanes 54 are arranged circumferentially about the axial compressor rotor 46 in stages (three stages of compressor blades 52 and compressor vanes 54 are shown in this example). The axial compressor rotor 46 is mounted for rotation upon the static inner support housing 42 through a forward bearing assembly 68 and an aft bearing assembly 62.
The fan-turbine rotor assembly 24 includes a fan hub 64 that supports a multitude of the hollow fan blades 28. Each fan blade 28 includes an inducer section 66, a hollow fan blade section 72 and a diffuser section 74. The inducer section 66 receives airflow from the axial compressor 22 generally parallel to the engine centerline A and turns the airflow from an axial airflow direction toward a radial airflow direction. The airflow is radially communicated through a core airflow passage 80 within the fan blade section 72 where the airflow is centrifugally compressed. From the core airflow passage 80, the airflow is turned and diffused toward an axial airflow direction toward the annular combustor 30. Preferably the airflow is diffused axially forward in the engine 10, however, the airflow may alternatively be communicated in another direction.
A gearbox assembly 90 aft of the fan-turbine rotor assembly 24 provides a speed increase between the fan-turbine rotor assembly 24 and the axial compressor 22. Alternatively, the gearbox assembly 90 could provide a speed decrease between the fan-turbine rotor assembly 24 and the axial compressor rotor 46. The gearbox assembly 90 is mounted for rotation between the static inner support housing 42 and the static outer support housing 44. The gearbox assembly 90 includes a sun gear shaft 92 which rotates with the axial compressor 22 and a planet carrier 94 which rotates with the fan-turbine rotor assembly 24 to provide a speed differential therebetween. The gearbox assembly 90 is preferably a planetary gearbox that provides co-rotating or counter-rotating rotational engagement between the fan-turbine rotor assembly 24 and an axial compressor rotor 46. The gearbox assembly 90 is mounted for rotation between the sun gear shaft 92 and the static outer support housing 44 through a forward bearing 96 and a rear bearing 98. The forward bearing 96 and the rear bearing 98 are both tapered roller bearings and both handle radial loads. The forward bearing 96 handles the aft axial loads while the rear bearing 98 handles the forward axial loads. The sun gear shaft 92 is rotationally engaged with the axial compressor rotor 46 at a splined interconnection 100 or the like.
In operation, air enters the axial compressor 22, where it is compressed by the three stages of the compressor blades 52 and compressor vanes 54. The compressed air from the axial compressor 22 enters the inducer section 66 in a direction generally parallel to the engine centerline A and is turned by the inducer section 66 radially outwardly through the core airflow passage 80 of the hollow fan blades 28. The airflow is further compressed centrifugally in the core airflow passage 80 of the hollow fan blades 28 by rotation of the hollow fan blades 28. From the core airflow passage 80, the airflow is turned and diffused by the diffuser section 74 axially forward in the engine 10 into the annular combustor 30. The compressed core airflow from the hollow fan blades 28 is mixed with fuel in the annular combustor 30 and ignited to form a high-energy gas stream. The high-energy gas stream is expanded over the multitude of tip turbine blades 34 mounted about the outer periphery of the fan blades 28 to drive the fan-turbine rotor assembly 24, which in turn drives the axial compressor 22 through the gearbox assembly 90. Concurrent therewith, the fan-turbine rotor assembly 24 discharges fan bypass air axially aft to merge with the core airflow from the turbine 32 in an exhaust case 106. A multitude of exit guide vanes 108 are located between the static outer support housing 44 and the nonrotatable static outer support structure 14 to guide the combined airflow out of the engine 10 to provide forward thrust. An exhaust mixer 110 mixes the airflow from the turbine blades 34 with the bypass airflow through the fan blades 28.
Referring to FIG. 3, the gearbox assembly 90 is mounted for rotation between the static inner support housing 42 and the static outer support housing 44. The gearbox assembly 90 includes the sun gear shaft 92 which rotates with the axial compressor rotor 46 and the planet carrier 94 which rotates with the fan-turbine rotor assembly 24 to provide a speed differential therebetween.
A multitude of planet gears 112 are mounted upon independent planet shafts 114 through a forward planet bearing 116 and an aft planet bearing 118 which supports each planet shaft 114. The forward planet bearing 116 and the aft planet bearing 118 are supported within the planet carrier 94. The planet carrier 94 is supported within the static outer support housing 44 through the gearbox thrust bearing 96 and a gearbox radial bearing 98. The static outer support housing 44 defines a ring gear 120. The ring gear 120 is preferably formed from a first static outer support housing 44a and a second static outer support housing 44b which define a first and a second ring gear portion 120a, 120b. The first static outer support housing 44a and the second static outer support housing 44b are assembled together through a multitude of fasteners 45 (one shown) such as bolts or the like to facilitate assembly and maintenance of the gearbox assembly 90.
A sun gear 122 extends from the sun gear shaft 92 and the ring gear 120 is formed in the first static outer support housing 44a and the second static outer support housing 44b. The sun gear 122 and the ring gear 120 are in meshing engagement with the planet gears 112 to provide a speed differential between the axial compressor 22 and the fan-turbine rotor assembly 24. It should be understood that various gear assembly arrangements including co-rotating and counter-rotating gear systems will also be used with the present invention.
The fan-turbine rotor assembly 24 includes an axial fan-turbine hub section 124 which mounts the fan-turbine rotor assembly 24 to the planet carrier 94 through a multitude of fasteners 126 (one shown) such as a bolt or the like. The multitude of fasteners 126 are arranged such that at least each of the planet shafts 114 receive a fastener 126 at least partially therein.
By attaching the axial fan-turbine hub section 124 to the gearbox assembly 90, the fan-turbine rotor assembly 24 is closely coupled thereto which reduces the overall engine length. Also, by attaching the axial fan-turbine hub section 124 to the gearbox assembly 90, the number of engine bearings are minimized which reduces complexity and increases reliability.
It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.
The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A tip turbine engine comprising:
a nonrotatable support structure mounted about an engine centerline, said nonrotatable support structure includes an inner static support housing and an outer static support housing located coaxial to said engine centerline;
a planetary gearbox assembly mounted between said inner static support housing and said outer static support housing, said planetary gearbox assembly including a sun gear shaft and a planet carrier rotatable about said engine centerline;
an axial compressor mounted for rotation with said sun gear shaft about said engine centerline; and
a fan-turbine rotor assembly mounted aft of said axial compressor, said fan-turbine rotor mounted to said planet carrier for rotation therewith through an axial fan hub section.

2. The tip turbine engine as recited in claim 1, further comprising an axial fan-turbine hub section which extends from said fan turbine rotor hub, said axial fan turbine hub bolted to said planet carrier.

3. The tip turbine engine as recited in claim 1, further comprising a bearing between said outer static support housing and said planet carrier.