U.S. patent application number 13/486810 was filed with the patent office on 2012-09-20 for gas turbine engine gear train.
Invention is credited to Michael E. McCune, Lawrence E. Portlock, Frederick M. Schwarz.
Application Number | 20120237336 13/486810 |
Document ID | / |
Family ID | 46828606 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120237336 |
Kind Code |
A1 |
McCune; Michael E. ; et
al. |
September 20, 2012 |
GAS TURBINE ENGINE GEAR TRAIN
Abstract
An epicyclic gear train includes a carrier that supports star
gears that mesh with a sun gear. A ring gear surrounds and meshes
with the star gears. The star gears are supported on respective
journal bearings. Each of the journal bearings includes a
peripheral journal surface and each of the star gears includes a
radially inner journal surface that is in contact with the
peripheral journal surface of the respective journal bearing. The
epicyclic gear train has a gear reduction ratio of greater than or
equal to about 2.3
Inventors: |
McCune; Michael E.;
(Colchester, CT) ; Portlock; Lawrence E.;
(Bethany, CT) ; Schwarz; Frederick M.;
(Glastonbury, CT) |
Family ID: |
46828606 |
Appl. No.: |
13/486810 |
Filed: |
June 1, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13340737 |
Dec 30, 2011 |
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13486810 |
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11504220 |
Aug 15, 2006 |
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13340737 |
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Current U.S.
Class: |
415/122.1 ;
475/331 |
Current CPC
Class: |
F05D 2220/36 20130101;
F05D 2260/34 20130101; F16H 57/0423 20130101; F16H 2057/085
20130101; F02C 7/36 20130101; F05D 2260/40311 20130101; F01D 5/027
20130101; F02K 3/06 20130101; F16H 1/28 20130101; F05D 2240/70
20130101; F16H 57/0486 20130101; F02C 3/107 20130101; F05D
2260/4031 20130101 |
Class at
Publication: |
415/122.1 ;
475/331 |
International
Class: |
F01D 15/12 20060101
F01D015/12; F16H 57/08 20060101 F16H057/08 |
Claims
1. A gear apparatus, comprising: an epicyclic gear train including
a carrier supporting star gears that mesh with a sun gear, and a
ring gear surrounding and meshing with the star gears, the star
gears being supported on respective journal bearings, each of the
journal bearings including a peripheral journal surface and each of
the star gears including a radially inner journal surface in
contact with the peripheral journal surface of the respective
journal bearing, wherein the epicyclic gear train has a gear
reduction ratio of greater than or equal to about 2.3.
2. The gear apparatus as recited in claim 1, wherein the radially
inner journal surface of each of the star gears is in contact with
the peripheral journal surface of the respective journal bearing
along an axial length with respect to a rotational axis of the
respective star gear.
3. The gear apparatus as recited in claim 1, wherein the radially
inner journal surface of each of the star gears is in contact with
the peripheral journal surface of the respective journal bearing
along a substantially full axial length of the respective star gear
with respect to a rotational axis of the respective star gear.
4. The gear apparatus as recited in claim 1, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
2.3.
5. The gear apparatus as recited in claim 1, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
about 2.5.
6. The gear apparatus as recited in claim 1, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
2.5.
7. A turbine engine comprising: a turbine shaft; a fan; and an
epicyclic gear train coupled between the turbine shaft and the fan,
the epicyclic gear train including a carrier supporting star gears
that mesh with a sun gear, and a ring gear surrounding and meshing
with the star gears, each of the star gears being supported on a
respective journal bearing, each journal bearing including a
peripheral journal surface and each of the star gears including a
radially inner journal surface in contact with the peripheral
journal surface of the respective journal bearing, wherein the
epicyclic gear train has a gear reduction ratio of greater than or
equal to about 2.3.
8. The turbine engine as recited in claim 7, wherein the radially
inner journal surface of each of the star gears is in contact with
the peripheral journal surface of the respective journal bearing
along an axial length with respect to a rotational axis of the
respective star gear.
9. The turbine engine as recited in claim 7, wherein the radially
inner journal surface of each of the star gears is in contact with
the peripheral journal surface of the respective journal bearing
along a substantially full axial length of the respective star gear
with respect to a rotational axis of the respective star gear.
10. The turbine engine as recited in claim 7, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
2.3.
11. The turbine engine as recited in claim 7, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
about 2.5.
12. The turbine engine as recited in claim 7, wherein the epicyclic
gear train has a gear reduction ratio of greater than or equal to
2.5.
13. The turbine engine as recited in claim 7, wherein the fan
defines a bypass ratio of greater than about ten (10) with regard
to a bypass airflow and a core airflow.
14. The turbine engine as recited in claim 7, wherein the fan
defines a bypass ratio of greater than about 10.5:1 with regard to
a bypass airflow and a core airflow.
15. The turbine engine as recited in claim 7, wherein the fan
defines a bypass ratio of greater than ten (10) with regard to a
bypass airflow and a core airflow.
16. The turbine engine as recited in claim 7, wherein the fan
defines a pressure ratio that is less than about 1.45.
17. The turbine engine as recited in claim 7, wherein the fan
defines a pressure ratio that is that is less than 1.45.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present disclosure is a continuation application of U.S.
patent application Ser. No. 13/340,737, filed on Dec. 30, 2011,
which is a continuation-in-part of U.S. patent application Ser. No.
11/504,220, filed Aug. 15, 2006.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a ring gear used in an epicyclic
gear train of a gas turbine engine.
[0003] 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.
[0004] 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.
[0005] 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
[0006] A disclosed example gear apparatus according to a
non-limiting exemplary embodiment includes an epicyclic gear train
including a carrier supporting star gears that mesh with a sun
gear, and a ring gear surrounding and meshing with the star gears,
the star gears being supported on respective journal bearings. Each
of the journal bearings including a peripheral journal surface and
each of the star gears including a radially inner journal surface
in contact with the peripheral journal surface of the respective
journal bearing. The epicyclic gear train including a gear
reduction ratio of greater than or equal to about 2.3.
[0007] In a further embodiment of the foregoing gear apparatus, the
radially inner journal surface of each of the star gears is in
contact with the peripheral journal surface of the respective
journal bearing along an axial length with respect to a rotational
axis of the respective star gear.
[0008] In a further embodiment of the foregoing gear apparatus, the
radially inner journal surface of each of the star gears is in
contact with the peripheral journal surface of the respective
journal bearing along a substantially full axial length of the
respective star gear with respect to a rotational axis of the
respective star gear.
[0009] In a further embodiment of the foregoing gear apparatus, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to 2.3.
[0010] In a further embodiment of the foregoing gear apparatus, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to about 2.5.
[0011] In a further embodiment of the foregoing gear apparatus, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to 2.5.
[0012] A disclosed turbine engine according to another non-limiting
exemplary embodiment includes a turbine shaft, a fan, and an
epicyclic gear train coupled between the turbine shaft and the fan,
the epicyclic gear train including a carrier supporting star gears
that mesh with a sun gear, and a ring gear surrounding and meshing
with the star gears. Each of the star gears is supported on a
respective journal bearing and each journal bearing includes a
peripheral journal surface and each of the star gears includes a
radially inner journal surface in contact with the peripheral
journal surface of the respective journal bearing. The epicyclic
gear train including a gear reduction ratio of greater than or
equal to about 2.3.
[0013] In a further embodiment of the foregoing turbine engine, the
radially inner journal surface of each of the star gears is in
contact with the peripheral journal surface of the respective
journal bearing along an axial length with respect to a rotational
axis of the respective star gear.
[0014] In a further embodiment of the foregoing turbine engine the
radially inner journal surface of each of the star gears is in
contact with the peripheral journal surface of the respective
journal bearing along a substantially full axial length of the
respective star gear with respect to a rotational axis of the
respective star gear.
[0015] In a further embodiment of the foregoing turbine engine, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to 2.3.
[0016] In a further embodiment of the foregoing turbine engine, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to about 2.5.
[0017] In a further embodiment of the foregoing turbine engine, the
epicyclic gear train has a gear reduction ratio of greater than or
equal to 2.5.
[0018] In a further embodiment of the foregoing turbine engine the
fan defines a bypass ratio of greater than about ten (10) with
regard to a bypass airflow and a core airflow.
[0019] In a further embodiment of the foregoing turbine engine, the
fan defines a bypass ratio of greater than about 10.5:1 with regard
to a bypass airflow and a core airflow.
[0020] In a further embodiment of the foregoing turbine engine, the
fan defines a bypass ratio of greater than ten (10) with regard to
a bypass airflow and a core airflow.
[0021] In a further embodiment of the foregoing turbine engine, the
fan defines a pressure ratio that is less than about 1.45.
[0022] In a further embodiment of the foregoing turbine engine, the
fan defines a pressure ratio that is that is less than 1.45.
[0023] Although different examples have the specific components
shown in the illustrations, embodiments of this invention are not
limited to those particular combinations. It is possible to use
some of the components or features from one of the examples in
combination with features or components of another of the
examples.
[0024] These and other features disclosed herein can be best
understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] 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.
[0026] FIG. 2 is an enlarged cross-sectional view of the epicyclic
gear train shown in FIG. 1.
[0027] FIG. 3 is an enlarged cross-sectional view of an example
ring gear similar to the arrangement shown in FIG. 2.
[0028] 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
[0029] 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.
[0030] 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.
[0031] The star gears 32 are supported on respective ones of the
journal bearings 34, Each of the journal bearings 34 includes a
peripheral journal surface 34a and each of the star gears 32
includes a radially inner journal surface 32a that is in contact
with the peripheral journal surface 34a of the respective journal
bearing 34. The radially inner journal surface 32a of each of the
star gears 32 is in contact with the peripheral journal surface 34a
of the respective journal bearing 34 along an axial length L, with
respect to a rotational axis of the respective star gear 32, which
is substantially parallel to the axis A. In this example, the
radially inner journal surface 32a of each of the star gears 32 is
in contact with the peripheral journal surface 34a of the
respective journal bearing 34 along a substantially full axial
length L of the respective star gear 32. Thus, the journal bearings
34 provide a "line" contact. In comparison, a ball bearing would
provide a "point" contact. The "line" contact between the journal
bearings 34 and the star gears 32 distributes loads on the journal
bearings 34, rather than focusing the load at a single point, and
thereby enhances the durability of the epicyclic gear train 22.
[0032] In one disclosed, non-limiting embodiment, the engine 10 has
a bypass ratio that is greater than about six (6) to ten (10), the
epicyclic gear train 22 is a planetary gear system or other gear
system with a gear reduction ratio of greater than about 2.3 or
greater than about 2.5, and a low pressure turbine of the engine 10
has a pressure ratio that is greater than about 5. In one disclosed
embodiment, the engine 10 bypass ratio is greater than about ten
(10:1) or greater than about 10.5:1, the turbofan 18 diameter is
significantly larger than that of the low pressure compressor of
the compressor section 14, and the low pressure turbine has a
pressure ratio that is greater than about 5:1. In one example, the
epicyclic gear train 22 has a gear reduction ratio of greater than
about 2.3:1 or greater than about 2.5:1. It should be understood,
however, that the above parameters are only exemplary of one
embodiment of a geared architecture engine and that the present
invention is applicable to other gas turbine engines including
direct drive turbofans.
[0033] A significant amount of thrust is provided by a bypass flow
B due to the high bypass ratio. The fan 18 of the engine 10 is
designed for a particular flight condition--typically cruise at
about 0.8M and about 35,000 feet. The flight condition of 0.8 M and
35,000 ft, with the engine at its best fuel consumption--also known
as "bucket cruise TSFC"--is the industry standard parameter of 1 bm
of fuel being burned divided by 1 bf of thrust the engine produces
at that minimum point. "Low fan pressure ratio" is the pressure
ratio across the fan blade alone. The low fan pressure ratio as
disclosed herein according to one non-limiting embodiment is less
than about 1.45. "Low corrected fan tip speed" is the actual fan
tip speed in ft/sec divided by an industry standard temperature
correction of [(Tambient deg R)/518.7) 0.5]. The "Low corrected fan
tip speed" as disclosed herein according to one non-limiting
embodiment is less than about 1150 ft/second.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] Although an 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.
* * * * *