# Patent

## Title
Ring gear mounting arrangement with oil scavenge scheme

## Abstract

In one exemplary embodiment, an epicyclic gear train for a turbine engine includes a first shaft that is rotatable about an axis. A ring gear includes first and second portions each having an inner periphery with teeth. The first and second portions are secured to one another at a radial interface. At least one of the first and second portions includes a flange that extends radially outward. The flange is fixed to the first shaft in an axial direction by a fastening element. A carrier supports star gears that mesh with the ring gear. A sun gear meshes with the star gears and is coupled to a second shaft.

## Background
REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser. No. 11/504,220, filed on 15 Aug. 2006.


BACKGROUND OF THE INVENTION
This invention relates to a ring gear used in an epicyclic gear train of a gas turbine engine.
Gas turbine engines typically employ an epicyclic gear train connected to the turbine section of the engine, which is used to drive the turbo fan. In a typical epicyclic gear train, a sun gear receives rotational input from a turbine shaft through a compressor shaft. A carrier supports intermediate gears that surround and mesh with the sun gear. A ring gear surrounds and meshes with the intermediate gears. In arrangements in which the carrier is fixed against rotation, the intermediate gears are referred to as “star” gears and the ring gear is coupled to an output shaft that supports the turbo fan.
Typically, the ring gear is connected to the turbo fan shaft using a spline ring. The spline ring is secured to a flange of the turbo fan shaft using circumferentially arranged bolts. The spline ring includes splines opposite the flange that supports a splined outer circumferential surface of the ring gear. The ring gear typically includes first and second portions that provide teeth facing in opposite directions, which mesh with complimentary oppositely facing teeth of the star gears.
An epicyclic gear train must share the load between the gears within the system. As a result, the splined connection between the ring gear and spline ring is subject to wear under high loads and deflection. Since the spline connection requires radial clearance, it is difficult to get a repeatable balance of the turbo fan assembly. Balance can also deteriorate over time with spline wear.
SUMMARY OF THE INVENTION
In one exemplary embodiment, an epicyclic gear train for a turbine engine includes a first shaft that is rotatable about an axis. A ring gear includes first and second portions each having an inner periphery with teeth. The first and second portions are secured to one another at a radial interface. At least one of the first and second portions includes a flange that extends radially outward. The flange is fixed to the first shaft in an axial direction by a fastening element. A carrier supports star gears that mesh with the ring gear. A sun gear meshes with the star gears and is coupled to a second shaft.
In a further embodiment of the above, the teeth on the first portion are angled in a first direction. The teeth on the second portion are angled in a second direction opposite the first direction. A rotational direction of the ring gear forces the first and second portions toward one another at the radial interface.
In a further embodiment of any of the above, the first and second portions each have a generally S-shaped outer circumferential surface opposite the teeth that provide a first thickness and a second thickness axially inward from the first thickness. The second thickness is greater than the first thickness.
In a further embodiment of any of the above, the first and second portions each include a recess facing one another to provide an internal annular cavity.
In a further embodiment of any of the above, the flange and the teeth of at least one of the first and second portions provide a unitary structure.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cross-sectional view of a front portion of a gas turbine engine illustrating a turbo fan, epicyclic gear train and a compressor section.
FIG. 2 is an enlarged cross-sectional view of the epicyclic gear train shown in FIG. 1.
FIG. 3 is an enlarged cross-sectional view of an example ring gear similar to the arrangement shown in FIG. 2.
FIG. 4 is a view of the ring gear shown in FIG. 3 viewed in a direction that faces the teeth of the ring gear in FIG. 3.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
A portion of a gas turbine engine 10 is shown schematically in FIG. 1. The turbine engine 10 includes a fixed housing 12 that is constructed from numerous pieces secured to one another. A compressor section 14 having compressor hubs 16 with blades are driven by a turbine shaft 25 about an axis A. A turbo fan 18 is supported on a turbo fan shaft 20 that is driven by a compressor shaft 24, which supports the compressor hubs 16, through an epicyclic gear train 22.
In the example arrangement shown, the epicyclic gear train 22 is a star gear train. Referring to FIG. 2, the epicyclic gear train 22 includes a sun gear 30 that is connected to the compressor shaft 24, which provides rotational input, by a splined connection. A carrier 26 is fixed to the housing 12 by a torque frame 28 using fingers (not shown) known in the art. The carrier 26 supports star gears 32 using journal bearings 34 that are coupled to the sun gear 30 by meshed interfaces between the teeth of sun and star gears 30, 32. Multiple star gears 32 are arranged circumferentially about the sun gear 30. Retainers 36 retain the journal bearings 34 to the carrier 26. A ring gear 38 surrounds the carrier 26 and is coupled to the star gears 32 by meshed interfaces. The ring gear 38, which provides rotational output, is secured to the turbo fan shaft 20 by circumferentially arranged fastening elements, which are described in more detail below.
Referring to FIGS. 3 and 4, the ring gear 38 is a two-piece construction having first and second portions 40, 42. The first and second portions 40, 42 abut one another at a radial interface 45. A trough 41 separates oppositely angled teeth 43 (best shown in FIG. 4) on each of the first and second portions 40, 42. The arrangement of teeth 43 forces the first and second portions 40, 42 toward one another at the radial interface 45. The back side of the first and second portions 40, 42 includes a generally S-shaped outer circumferential surface 47 that, coupled with a change in thickness, provides structural rigidity and resistance to overturning moments. The first and second portions 40, 42 have a first thickness T1 that is less than a second thickness T2 arranged axially inwardly from the first thickness T1. The first and second portions 40, 42 include facing recesses 44 that form an internal annular cavity 46.
The first and second portions 40, 42 include flanges 51 that extend radially outward away from the teeth 43. The turbo fan shaft 20 includes a radially outwardly extending flange 70 that is secured to the flanges 51 by circumferentially arranged bolts 52 and nuts 54, which axially constrain and affix the turbo fan shaft 20 and ring gear 38 relative to one another. Thus, the spline ring is eliminated, which also reduces heat generated from windage and churning that resulted from the sharp edges and surface area of the splines. The turbo fan shaft 20 and ring gear 38 can be rotationally balanced with one another since radial movement resulting from the use of splines is eliminated. An oil baffle 68 is also secured to the flanges 51, 70 and balanced with the assembly.
Seals 56 having knife edges 58 are secured to the flanges 51, 70. The first and second portions 40, 42 have grooves 48 at the radial interface 45 that form a hole 50, which expels oil through the ring gear 38 to a gutter 60 that is secured to the carrier 26 with fasteners 61 (FIG. 2). The direct radial flow path provided by the grooves 48 reduces windage and churning by avoiding the axial flow path change that existed with splines. That is, the oil had to flow radially and then axially to exit through the spline interface. The gutter 60 is constructed from a soft material such as aluminum so that the knife edges 58, which are constructed from steel, can cut into the aluminum if they interfere. Referring to FIG. 3, the seals 56 also include oil return passages 62 provided by first and second slots 64 in the seals 56, which permit oil on either side of the ring gear 38 to drain into the gutter 60. In the example shown in FIG. 2, the first and second slots 64, 66 are instead provided in the flange 70 and oil baffle 68, respectively.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. An epicyclic gear train for a turbine engine comprising:
a first shaft rotatable about an axis;
a ring gear including first and second portions each having an inner periphery with teeth, the first and second portions secured to one another at a radial interface, and at least one of the first and second portions including a flange extending radially outward, the flange fixed to the first shaft in an axial direction by a fastening element;
a carrier supporting star gears that mesh with the ring gear; and
a sun gear meshing with the star gears and coupled to a second shaft.

2. The epicyclic gear train according to claim 1, wherein the teeth on the first portion are angled in a first direction, and the teeth on the second portion are angled in a second direction opposite the first direction, a rotational direction of the ring gear forcing the first and second portions toward one another at the radial interface.

3. The epicyclic gear train according to claim 1, the first and second portions each have a generally S-shaped outer circumferential surface opposite the teeth that provide a first thickness and a second thickness axially inward from the first thickness, the second thickness greater than the first thickness.

4. The epicyclic gear train according to claim 3, wherein the first and second portions each include a recess facing one another to provide an internal annular cavity.

5. The epicyclic gear train according to claim 1, wherein the flange and the teeth of the at least one of the first and second portions provide a unitary structure.

6. The epicyclic gear train according to claim 5, wherein the fastening element is a nut and a bolt.

7. The epicyclic gear train according to claim 5, wherein the flange is axially constrained and affixed to the first shaft without splines.