U.S. patent application number 12/866499 was filed with the patent office on 2011-03-03 for epicyclic gear system having two arrays of pinions mounted on flexpins with compensation for carrier distortion.
This patent application is currently assigned to THE TIMKEN COMPANY. Invention is credited to Gerald P. Fox, Randy P. Kruse, Milos Malec, James Maloof, Jaroslav Suchanek.
Application Number | 20110053730 12/866499 |
Document ID | / |
Family ID | 40548728 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110053730 |
Kind Code |
A1 |
Fox; Gerald P. ; et
al. |
March 3, 2011 |
Epicyclic Gear System Having Two Arrays Of Pinions Mounted On
Flexpins With Compensation For Carrier Distortion
Abstract
An epicyclic gear system (A) includes sun and ring gears (2, 4)
and planet pinions (6, 8) arranged in two side-by-side arrays (a,
b) between the sun and ring gears, there also being a carrier (10,
50) to which planet pinions are coupled through flexpins (30). The
carrier has primary and secondary walls (20, 22) between which the
pinions are located and webs (24) connecting the walls. The
flexpins for one array of pinions are cantilevered from the primary
wall and the flexpins for the other array of pinions are
cantilevered from the secondary wall. When the gear system
operates, the carrier along its primary wall is subjected to an
externally applied torque which transfers through the system at the
planet pinions of the two arrays. The load path (pa) for the
pinions at the primary wall is shorter than the load path (pb) for
the pinions at the secondary wall, and this disparity causes the
carrier to distort. To compensate for this distortion so that the
pinions of the two arrays will mesh more evenly with the sun and
ring gears, the flexpins of the first array are offset angularly
with respect to the flexpins of the second array, or the teeth of
the pinions in the first array are narrower than the teeth of the
pinions of the second array, or the primary wall of the carrier has
areas (40, 44) of weakness where the flexpins of the first array
are cantilevered from it, or the flexpins of the first array are
more flexible than the flexpins of the second array. As a
consequence, the pinions of the two arrays mesh better under load
with the sun and ring gears and share the transfer of torque more
evenly.
Inventors: |
Fox; Gerald P.; (Massillon,
OH) ; Kruse; Randy P.; (North Canton, OH) ;
Suchanek; Jaroslav; (Ujezd u Brna, CZ) ; Malec;
Milos; (Velka Bites, CZ) ; Maloof; James;
(Clinton, OH) |
Assignee: |
THE TIMKEN COMPANY
Canton
OH
|
Family ID: |
40548728 |
Appl. No.: |
12/866499 |
Filed: |
February 12, 2009 |
PCT Filed: |
February 12, 2009 |
PCT NO: |
PCT/US09/33896 |
371 Date: |
November 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61028274 |
Feb 13, 2008 |
|
|
|
61125715 |
Apr 28, 2008 |
|
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Current U.S.
Class: |
475/347 |
Current CPC
Class: |
F16H 57/082 20130101;
F16H 1/2836 20130101 |
Class at
Publication: |
475/347 |
International
Class: |
F16H 57/08 20060101
F16H057/08 |
Claims
1. An epicyclic gear system comprising: a sun gear having an axis;
a ring gear surrounding the sun gear and having an axis that
coincides with the axis of the sun gear; first planet pinions
meshing with the sun and ring gears in a first array; second planet
pinions meshing with the sun and ring gears in a second array that
is offset axially from the first array; and a carrier having first
flexpins coupled to the first planet pinions and second flexpins
coupled to the second planet pinions, the carrier further having a
coupling region at which torque is applied to the carrier when the
gear system is subjected to a load, with the torque transferring
between the coupling region and the first flexpins through first
load paths and between the coupling region and the second flexpins
through second load paths that are longer than the first load
paths, and with the difference in lengths of the load paths causing
a distortion in the carrier, and means for compensating for the
distortion to enable the first and second pinions to mesh more
evenly with the sun and ring gears when torque is applied to the
carrier.
2. An epicyclic gear system according to claim 1 wherein the means
for compensating comprises an angular offset of the first flexpins
from the second flexpins in the absence of torque applied to the
carrier.
3. An epicyclic gear system according to claim 1 wherein the means
for compensating comprises the teeth on the first pinions being
narrower than the teeth on the second pinions.
4. An epicyclic gear system according to claim 1 wherein the means
for compensating enables the first flexpins and the second flexpins
to undergo substantially the same deflection when torque is
transferred in spite of distortion in the carrier caused by
differences in the length of the load paths.
5. An epicyclic gear system according to claim 4 wherein the means
for compensating comprises areas of weakness in the carrier at the
first flexpins.
6. An epicyclic gear system according to claim 4 wherein the means
for compensating comprises the first flexpins being more flexible
than the second flexpins.
7. An epicyclic gear system according to claim 1 wherein the
carrier has first and second walls and webs connecting the walls;
and wherein the first flexpins are cantilevered from the first wall
and the second flexpins are cantilevered from the second wall.
8. An epicyclic gear system according to claim 7 wherein the means
for compensating includes areas of weakness in the first wall where
the first flexpins are cantilevered from the first wall.
9. An epicyclic gear system according to claim 8 wherein the areas
of weakness are formed by slots or grooves in the first wall.
10. An epicyclic gear system according to claim 9 wherein the slots
or grooves are arcuate and follow the contour of the first
flexpins.
11. An epicyclic gear system according to claim 9 wherein the slots
or grooves lie along a circle that circumscribes the axes of the
first flexpins.
12. An epicyclic gear system comprising: a sun gear having an axis;
a ring gear surrounding the sun gear and having an axis that
coincides with the axis of the sun gear; first planet pinions
meshing with the sun and ring gears in a first array; second planet
pinions meshing with the sun and ring gears in a second array that
is offset axially from the first array; and a carrier including: a
first wall; a second wall spaced axially from the first wall; webs
connecting the first and second walls; first flexpins cantilevered
from the first wall and projecting into the first pinions; sleeves
interposed between the first flexpins and the first pinions and
being cantilevered from the ends of the first flexpins that are
remote from the first wall; second flexpins cantilevered from the
second wall and projecting into the second pinions; more sleeves
interposed between the second flexpins and the second pinions and
being cantilevered from the ends of the second flexpins that are
remote from the second wall; and a coupling region at which the
carrier is subjected to a torque when a load is transferred through
the gear system, with that torque transferring to the first pinions
through first load paths that pass through the first flexpins and
transferring to the second pinions through second load paths that
pass through the second flexpins, the second load paths being
longer than the first load paths and causing a greater distortion
of the carrier along the second load paths than along the first
load paths when a load is transferred through the gear system; and
means for compensating for the greater distortion along the second
load paths than along the first load paths to enable the first and
second pinions to mesh more evenly with the sun and ring gears in
spite of the distortion.
13. An epicyclic gear system according to claim 12 wherein the
means for compensating comprises an angular offset of the first
flexpins from the second flexpins in the absence of torque applied
to the carrier.
14. An epicyclic gear system according to claim 12 wherein the
means for compensating comprises the teeth on the first pinions
being narrower than the teeth on the second pinions.
15. An epicyclic gear system according to claim 12 wherein the
means for compensating includes areas of weakness in the first wall
where the first flexpins are cantilevered from the first wall.
16. An epicyclic gear system according to claim 15 wherein the
areas of weakness are formed by slots or grooves in the first wall
adjacent the first flexpins.
17. An epicyclic gear system according to claim 16 wherein the
slots or grooves are arcuate and follow the contour of the first
pins.
18. An epicyclic gear system according to claim 16 wherein the
slots or grooves lie along a circle that circumscribes the axes of
the first flexpins.
19. An epicyclic gear system according to claim 12 wherein the
means for compensating comprises the first flexpins being more
flexible than the second flexpins.
20. An epicyclic gear system comprising: a sun gear having an axis;
a ring gear surrounding the sun gear and having an axis that
coincides with the axis of the sun gear; first planet pinions
meshing with the sun and ring gears in a first array; second planet
pinions meshing with the sun and ring gears in a second array that
is offset axially from the first array; and a carrier having first
flexpins coupled to the first planet pinions and second flexpins
coupled to the second planet pinions, the carrier further having a
coupling region at which torque is applied to the carrier when the
gear system is subjected to a load, with the torque transferring
between the coupling region and the first flexpins through first
load paths and between the coupling region and the second flexpins
through second load paths, the first load paths being stiffer than
the second load paths with the difference in the stiffness of the
load paths causing a distortion in the carrier, and means for
compensating for the distortion to enable the first and second
pinions to mesh more evenly with the sun and ring gears when torque
is applied to the carrier.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application derives priority from and otherwise claims
the benefit of U.S. provisional application 61/028,274, filed 13
Feb. 2008, and U.S. provisional application 61/125,715, filed 28
Apr. 2008, both of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] This invention relates in general to epicyclic gear systems,
and more particularly to an epicyclic gear system having its planet
pinions arranged in two arrays on flexpins with compensation for
carrier distortion.
BACKGROUND ART
[0003] The typical epicyclic gear system has a sun gear, a ring
gear surrounding the sun gear, and planet pinions located between
and engaged with the sun and ring gears, and in addition, it has a
straddle-type carrier that provides pins about which the planet
pinions rotate, with the pins being anchored at both ends in the
carrier. A gear system so configured has the capacity to transfer a
large amount of power in a relatively compact configuration--or in
other words, it has a high power density.
[0004] But heavy loads tend to distort the carrier and its pins and
skew the axis about which the planet pinions rotate. Under such
conditions, the planet pinions do not mesh properly with the sun
and ring gears. This causes excessive wear in the planet pinions
and the sun and ring gears, generates friction and heat, and
renders the entire system overly noisy.
[0005] A planetary system in which the planet pinions are supported
on and rotate about so-called flexpins mitigates the skewing. In
this regard, a flexpin for a planet pinion at one end is anchored
in and cantilevered from the wall of a carrier of which it is a
part. The other end of the flexpin has a sleeve fitted to it, with
the sleeve extending back over, yet otherwise spaced from the
flexpin. The sleeve supports the planet pinion, in that it serves
as a component of a bearing for the pinion. In other words, flexpin
technology employs a double cantilever to offset the skewing that
would otherwise occur. See U.S. Pat. No. 6,994,651 and U.S. Pat.
No. 7,056,259, which are incorporated herein by reference, for a
further discussion of flexpin technology.
[0006] The cantilevers produce high stresses in the flexpins, and
to have more moderate stresses, some carriers have two walls with
flexpins anchored in each of the walls and, of course, a separate
planetary pinion around each flexpin. This doubles the number of
flexpins to share the torque transferred through the system and
thus reduces the unit load applied to each flexpin. The planet
pinions are arranged in two arrays between the walls, there being
for each pinion in the one array and corresponding pinion aligned
with it in the other array. Spaces exist between pairs of
corresponding pinions and webs extend between the two walls in
these spaces. The carrier, whether it rotates or not, is subjected
to an externally applied torque at one of its walls. The planet
pinions transmit torque through the system, but the lengths of the
load paths from the flexpins on the two walls differ, the load
paths from the flexpins on the primary wall, which is subjected to
the external torque, being considerably shorter than the load paths
from the flexpins on the other or secondary wall. This renders the
array, identified with the shorter load paths stiffer than the
array identified with the longer load paths. The carrier undergoes
a distortion that causes the flexpins on the secondary wall
displace angularly with respect to the flexpins on the primary
wall, reference being to the axis of the planetary system. Since
the planet pinions of the two arrays mesh with the sun and ring
gears, the displacement causes an uneven sharing of the torque
transmitted at the teeth where the pinions mesh with the sun and
ring gears.
DESCRIPTION OF THE INVENTION
[0007] FIG. 1 is a perspective view, partially broken away and in
section, of an epicyclic gear system having its planet pinions
arranged in two arrays on flexpins and otherwise being constructed
in accordance with and embodying the present invention;
[0008] FIG. 2 is another perspective view of the gear system, again
partially broken away and in section;
[0009] FIG. 3 is a partial sectional view showing one of the
carrier walls and a flexpin on that wall;
[0010] FIG. 4 is an exploded perspective view of a flexpin, its
sleeve, bearing and planet pinion, for either one of the
arrays;
[0011] FIG. 5 is an elevational view of the carrier of the gear
system, and showing load paths of uneven lengths and distortions,
greatly exaggerated, caused by those uneven load paths;
[0012] FIGS. 6, 6A, and 6B are schematic views showing an angular
offset between the flexpins of the two arrays to compensate for the
distortion of the carrier and the resulting planet pinion and ring
gear mesh;
[0013] FIG. 7 is a perspective view of the carrier and also showing
the angular offset;
[0014] FIGS. 8, 8A, and 8B are schematic views showing narrower
teeth for the pinions of one of the arrays to compensate for the
distortion of the carrier; and
[0015] FIG. 9 is a perspective view of a carrier provided with
areas of weakness in its primary wall to impart equivalent
deflective characteristics to the flexpins of its two arrays;
[0016] FIG. 10 is a perspective view of an alternative carrier with
areas of weakness in its primary wall;
[0017] FIG. 11 is a perspective view of a carrier that has the
flexpins of differing flexibility to impart equivalent deflective
characteristics;
[0018] FIG. 12 is a longitudinal sectional view of the flexpins for
the alternative carrier of FIG. 11; and
[0019] FIG. 13 is an elevational view of the carrier having a hub
for transferring torque to it.
BEST MODES FOR CARRYING OUT THE INVENTION
[0020] Referring now to the drawings, an epicyclic gear system A
(FIGS. 1 & 2) that is organized about a central axis X includes
a sun gear 2, a ring gear 4 that surrounds the sun gear 2 and
shares the axis X with the sun gear 2, and planet pinions 6 and 8
that are arranged in two rows or arrays a and b between the sun and
ring gears 2 and 4. The planet pinions 6 and 8 of the two arrays a
and b mesh with both the sun and ring gears 2 and 4, but rotate
about axes Y that are offset from, yet parallel to, the central
axis X. In addition, the gear system A has a carrier 10 that
supports the planet pinions 6 and 8 and establishes the offset axes
Y about which they rotate. The sun gear 2, ring gear 4, and carrier
10 represent components, any two of which may rotate while the
third is typically held fast.
[0021] The epicyclic gear system A depicted is well suited for use
in wind turbines that harness the wind and convert it into
electrical energy. However, it lends itself as well to other
applications in which torque is applied at any one of the
components and torque is delivered at either of the remaining two
components, while the third component is held fast. In a wind
turbine in which the epicyclic gear system A serves as the
transmission for increasing the relatively low angular velocity of
a wind-powered rotor to a higher velocity suitable for an
electrical generator small enough to fit into the nacelle of the
wind turbine, the wind-powered rotor is coupled to the carrier 10,
the sun gear 2 is connected to a shaft 12 that is coupled through
more gearing to the electrical generator, and the ring gear 5
remains fixed. The carrier 10 and sun gear 2 rotate in the same
direction.
[0022] The carrier 10 has two walls between which the planet
pinions 6 and 8 are confined--a primary wall 20 and a secondary
wall 22--and also axially directed webs 24 that extend between the
walls 20 and 22 and connect them rigidly together. The webs 24
create within the carrier 10 pockets that are occupied by the
planet pinions 6 and 8, there being a pinion 6 and a pinion 8 in
each pocket. To facilitate installation of the planet pinions 6 and
8 within the carrier 10, the webs 24 are formed integral with the
secondary wall 22 and initially separate from the primary wall 20,
only to be secured to the primary wall 20 with screws 26 during
assembly. Likewise, the webs 24 may be formed integral with the
primary wall 20 and separate from the secondary wall 22. The shaft
12 for the sun gear 2 extends through one or both of the carrier
walls 20 and 22. The planet pinions 6 and 8 rotate within the
pockets between the walls 20 and 22, yet project radially outwardly
beyond the webs 24 for engagement with the sun gear 2 and ring gear
4. The primary wall 20 has a flange 28 that projects radially
outwardly beyond the webs 24. The flange 28 serves as a location or
coupling region at which torque is applied to the carrier 10.
[0023] The planet pinions 6 and 8 rotate about flexpins 30 and
sleeves 32 (FIGS. 3 & 4), the former of which project from the
carrier walls 20 and 22, there being a separate flexpin 30 and
sleeve 32 for each planet pinion 6 and 8. Each flexpin 30 is
anchored in or otherwise secured firmly to the wall 20 or 22 along
which its planet pinion 6 or 8 is located such that it is
cantilevered from the wall 20 or 22. The sleeve 32 encircles the
flexpin 30, yet is spaced outwardly from the flexpin 30, except at
the end of the flexpin 30 that is remote from the wall 20 or 22
from which it projects. Here the sleeve 32 is attached firmly to
its flexpin 30 such that it is cantilevered from the flexpin 30,
completing a double cantilever so to speak. Each planet pinion 6 or
8 encircles the sleeve 32 for its flexpin 30, there being a bearing
34 between the pinion 6 or 8 and the sleeve 32. The bearing 34 may
take the form of an antifriction bearing in which the inner
raceways are carried by the sleeve itself, or the sleeve may form
part of a simple plain bearing. The flexpin 30 between the location
at which it is cantilevered from its wall 20 or 22 and the location
where its sleeve 32 is cantilevered from the pin 30 may have a
groove 36 that imparts greater flexibility to the flexpin 30.
[0024] During the operation of the gear system A, with torque
transferring through it, the flexpins 30 undergo flexures that
offset their ends circumferentially with respect to the axis X. In
other words, the remote end of each flexpin 30 lags slightly behind
or advances slightly ahead of the end that are anchored in or to
the carrier wall 20 and 22, reference being to the circumferential
direction about the axis X. The sleeve 32, being cantilevered from
the remote end of the pin 30, imparts a moment that causes the end
of the pin 30 to flex in the opposite direction. Owing to this
capacity of the pins 30 to flex, under two cantilevers, the sleeves
32 remain parallel to the central axis X, and, of course, the axes
Y about which the planet pinions 6 and 8 rotate likewise remain
parallel to the axis X.
[0025] When torque is applied to the carrier 10 at the flange 28 on
its primary wall 20, that torque transfers between the flange 28
and to the pinions 6 of the array a in relatively short load paths
p.sub.a (FIG. 5) that are basically confined to the primary wall 20
and the flexpins 30 on that wall 20. The torque also transfers
between the flange 28 and the pinions 8 of the array b in
significantly longer load paths p.sub.b that pass through the
primary wall 20, the webs 24, the secondary wall 22, and the
flexpins 30 on that wall 22. Were the carrier 10 a traditional
carrier, the torque transferred through the shorter load paths
p.sub.a may cause some distortion of the primary wall 20, but it is
for all intents and purposes inconsequential. The torque
transferred through the longer load paths p.sub.b would effect a
much greater distortion in the more flexible secondary wall 22 and
webs 24. This would render the array a having the shorter load path
p.sub.a stiffer than the array b having the longer load paths
p.sub.b. With the axis X serving as a reference, the distortion
would offset the flexpins 30 of the array b circumferentially with
respect to the flexpins 30 of the array a. If under no load the
pins 30 of the array a were to align with the pins 30 of the array
b, once a load is applied to the carrier 10, thereby effecting a
transfer of torque, the flexpins 30 of the array b will no longer
align with the flexpins 30 in the array a. The planet pinions 6 of
the array a and the planet pinions 8 of the array b would not mesh
evenly with the sun gear 2 and ring gear 4. The uneven mesh would
cause the planet pinions 6 of the array a to carry a greater load
than the planet pinions 8 of the array b when the torque
transferred through the system A reaches the torque at which the
system A is designed to operate.
[0026] To compensate for the distortion of the carrier 10 and
thereby overcome the deficiency, the carrier 10 is constructed such
that when no torque is transmitted through it, the planet pinions 6
of the array a are indexed or offset circumferentially by an angle
.theta. with respect to the planet pinions 8 of the array b (see
arrows in FIG. 7). Thus, when the epicyclic gear system A is set in
operation with a light torque applied at the carrier flange 28 and
delivered through the shaft 12, the planet pinions 8 of the array b
will engage first with the sun gear 2 and ring gear 4. As the
torque increases, the carrier 10 undergoes distortions along its
secondary wall 22 and at its webs 24 of the less stiff array b, and
those distortions bring the planet pinions 8 of the array b closer
to alignment with their counterpart pinions 6 in the array a. At
the torque at which the system A is designed to operate, the
flexpins 30 of the array b align with their counterparts in the
array a and the planet pinions 6 and 8 mesh generally evenly with
the sun gear 2 and ring gear 4. The planet pinions 6 and 8 of the
two arrays a and b then share the transfer of torque generally
evenly.
[0027] In any gear system, a backlash or clearance exists between
the teeth where two gears mesh. In the system A, a clearance
l.sub.b (FIG. 6A) exists where any planet pinion 8 engages the ring
gear 4, that is to say, at the tooth on the planet pinion 8 that
projects between a pair of successive teeth in the ring gear 4 and
on the sun gear 2 as well. At no load or very light loads, the
teeth of the planet pinions 6 in the array a do not actually engage
the teeth of the ring gear 4 in the sense that the leading faces
actually contact teeth of the ring gear 4, that is to say, a
clearance exists on both sides of each meshed tooth. This derives
from a smaller clearance l.sub.a (FIG. 6B) where the planet pinions
6 mesh with the ring gear 4, and that lesser clearance l.sub.a
exists by reason of a slight angular offset .theta. of the flexpins
30 for the planet pinions 8 of the array b from the flexpins 30 of
the array a, resulting in an offset clearance l.sub..theta.. That
offset clearance l.sub..theta. should conform to the following
relationship:
l.sub.b.gtoreq.l.sub.b=l.sub..theta.+l.sub.a
As the torque applied at the carrier flange 28 increases, so does
the clearance l.sub.a in the array a. When the torque reaches that
at which the system A is designed to operate, the clearance l.sub.a
in the array a and the clearance l.sub.b in the array b are
substantially the same, and the planet pinions 6 and 8 mesh
essentially evenly with the ring gear 4. Since the mesh is even,
the planet pinions 6 and 8 share the torque evenly, that is to say,
the magnitude of the torque transferred through the planet pinions
6 of the array a is substantially the same as the magnitude of the
torque transferred through the pinions 8 of the array b. The
conditions and compensation that exists at the mesh between the
planet pinions 6 and 8 and the ring gear 4 also exist at the mesh
between the planet pinions 6 and 8 and the sun gear 2.
[0028] While the screws 26 hold the carrier 10 together in that
they pass through the primary wall 20 and thread into the webs 24
or otherwise clamp the webs 24 and the walls 20 and 22 together,
they might not provide the precision required to establish the
angle .theta. between the pins 30 of the array a and the pins 30 of
the array b. The precision may be achieved with dowels 38 (FIG. 7)
that fit tightly into the primary wall 20 and into the webs 23,
assuming that the secondary walls 22 and the web 24 are formed
integral.
[0029] In the alternative, the compensation for distortion of the
carrier 10 may be provided by making the teeth of the planet gears
6 in the array a circumferentially narrower than the teeth of the
planet gears 8 in the array b (FIG. 8B), resulting in a larger
backlash for the planet pinions 6 than for the planet pinions 8. As
a consequence, when no or little torque is transmitted, the teeth
of the planet pinions 8 engage the sun and ring gears 2 and 4 in
the sense that they actually contact the teeth of the sun and ring
gears 2 and 4. But the planet pinions 6, while meshing with the sun
and ring gears 2 and 4, do not actually engage those gears 2 and 4.
In other words, the teeth of the planet gears 6, where they mesh
with the sun and ring gears 2 and 4, do not actually contact the
teeth on the sun and ring gears 2 and 4. Instead, they are narrow
enough to fit between successive teeth on the sun and ring gears 2
and 4 with a clearance l.sub.a at each of the leading and trailing
faces at the point of mesh. The clearance l.sub.a should conform
generally to the following relationship:
l.sub.b<2l.sub.a
[0030] As the torque increases, the secondary wall 22 and the web
24 of the more flexible array b flex enough to displace the
flexpins 30 for the pinions 8 of the array b angularly with respect
to the flexpins 30 for the pinions 6 of the array a. The narrower
teeth of the pinions 6 actually engage the teeth of the sun and
ring gears 2 and 4 in the sense that they contact the teeth of the
sun and ring gears 2 and 4. At this juncture, torque transfers
through the planet pinions 6 and 8 of both arrays a and b. When the
torque transferred reaches the magnitude for which the system A is
designed to operate, the flexure of the secondary wall 22 and webs
24 is such that the planet pinions 6 and the planet pinions 8 share
the torque transfer essentially equally, that is to say, one-half
transfers through the pinions 6 of the array a and the other half
transfers through the pinions 8 of the array b. This alternative
provides compensation irrespective of the direction in which the
external torque is applied to the carrier 10.
[0031] In another alternative, compensation for the distortion
along the secondary wall 22 and webs 24 is provided by rendering
the primary wall 20 more flexible where the flexpins 30 for that
wall 20 emerge from it. This, in effect, allows the flexpins 30 on
the primary wall 20, when the gear system A transmits torque, to
undergo about the same amount of deflection as the flexpins 30 on
the secondary wall 22. To this end, the primary wall 20 at each
flexpin 30 has an area of weakness in the form of a pair of arcuate
cutouts or slots 40 (FIG. 9) of equal radius and length, with their
centers being at the axes Y for the flexpin 30. The slots 40, which
open out of both faces of the wall 20, are arranged 180.degree.
apart with their centers generally located along a circle C that
circumscribes the axes Y of the several pins 30 and having its
center at the central axis X. In other words, one slot 40 lies
circumferentially ahead of the pin 30 and the other slot 40 lies
circumferentially behind the pin 30. Thus, the slots 40 impart more
flexibility to the primary wall 20 where the flexpins 30 extend
from it than does the secondary wall 22 where the flexpins 30
emerge from it. This selective weakness approach gives the flexpins
30 of the primary wall 20 essentially the same deflective
characteristics as the flexpins 30 on the secondary wall 22. This
in turn renders the two arrays a and b equally stiff--or equally
flexible--so that the pinions 6 of the array a and the pinions 8 of
the array b mesh evenly with the sun gear 2 and ring gear 4 and the
pinions 6 and 8 share the torque transferred essentially
evenly.
[0032] The primary wall 20 may also be rendered more flexible at
its flexpins 30 with arcuate grooves 44 (FIG. 10) that open out of
only one face of the primary wall 20 instead of both faces as do
the slots 40. Like the slots 40, the grooves 44 should leave the
flexpins 30 of the primary wall 20 with essentially the same
deflective characteristics as the flexpins 30 of the secondary wall
22, so that the pinions 6 and 8 of the arrays a and b share the
torque generally evenly.
[0033] Neither the slots 40 nor the grooves 44 need to be arcuate
in configuration, but they should render the primary wall 20 more
flexible to the sides of the flexpins 30 along which they are
located. Shapes other than slots or grooves will also suffice if
they enable the flexpins 30 with which they are identified to
deflect more easily in the circumferential direction, reference
being to the central axis X. For example, the primary wall 20 may
have a region of thinner cross section, not necessarily resembling
an arc, at the side or sides of each flexpin 30. The shapes,
whether they be the slots 40 or the grooves 44 or some other
configuration, may reside only to one side of each flexpin 30 in
the primary wall 20.
[0034] In lieu of compensating at the primary wall 20 for the
variations in the lengths of the two load paths p.sub.a and
p.sub.b, the compensation may be at the flexpins 30 themselves. An
alternative carrier 50 (FIGS. 11 & 12) has a primary wall 20
and a secondary wall 22, with webs 24 extending between the two
walls 20 and 22. The primary wall 20 is devoid of any slots 40 or
grooves 44 or other shapes designed to impart greater flexibility
to the wall 20 itself. However, the pinions 6 of the array a rotate
about flexpins 30a that differ from flexpins 30b about which the
pinions 8 of the array b rotate. The difference resides in the
flexibility of the pins 30a and 30b themselves; the pins 30a for
the array a are more flexible than the pins 30b for the array b. To
this end, each pin 30a and 30b has (FIG. 12) a base 52 where it is
fitted into the wall 20 and 22 from which the pins 30a and 30b
extends and a head 54 at the opposite end of the pins 30a and 30b.
Between its base 52 and its head 54, each pin 30a and 30b has an
intervening shank 56. The sleeve 32 that surrounds the pin 30a and
30b is fitted to its head 54 and may even be formed integral with
the head 54. The shank 56 tapers downwardly from the base 52 and
from the head 54 to a necked-in region 58. The diameter for the
necked-in region 58 of each pin 30b that projects from the
secondary wall 22 exceeds the diameter for the necked-in region 58
for each pin 30a that projects from the primary wall 20. This
imparts greater flexibility to the pins 30a. The arrangement is
such that the deflection of the pins 30b occasioned by the
distortion of the secondary wall 22 and webs 32 under load equals
the deflection of the more flexible pins 30a, so that the pinions 6
and 8 that are carried by the pins 30a and 30b, respectively, share
the load evenly, that is to say their pinions 6 and 8 transfer
essentially the same amount of torque.
[0035] The flexpins 30a may be rendered more flexible than the
flexpins 30b without reducing the diameter of their necked-in
regions 58. For example, the flexpins 30 may be hollow or partially
hollow, while the flexpins 30b are solid throughout. Also, the
flexpins 30a may be formed from a material that flexes more easily
than the material from which the flexpins 30b are formed. Then
again, a combination of the foregoing, including variance in
diameters of the necked-in regions 58, may be employed. The object
is to render the flexpins 30a more flexible than the flexpins 30b
irrespective of the manner in which it is achieved.
[0036] In the carrier 10, the same effect may be achieved by making
the grooves 36 in the flexpins 30 at the primary wall 20 deeper
than the grooves 36 in the flexpins 30 at the secondary wall 22.
Indeed, by so configuring the flexpins 30 of the primary wall 20,
the arcuate slots 40 or grooves 44 may be eliminated or diminished
in size.
[0037] The carrier 50 with flexpins 30a and 30b of different
flexibility in its primary wall 20 may be provided with arcuate
slots 40 or grooves 44 or other shapes to impart greater
flexibility to the primary wall 20 at its flexpins 30a. In that
arrangement, the desired deflective characteristics for the
flexpins 30a of the array a are derived from both the primary wall
20 and the greater flexibility of the flexpins 30a that project
from the wall 20. This arrangement for balancing the deflection of
the flexpins 30a and 30b represents a combination of the selected
wall weakness approach and the variance-in-pin stiffness
approach.
[0038] The external torque need not be applied to either carrier 10
or 50 through a flange at the periphery of its primary wall 20, but
instead elsewhere on the wall 20, such as through a hub 64 (FIG.
13) that serves as a coupling region on the wall 20. Again the load
path p.sub.b for the array b is longer than the load path p.sub.a
for the array a. Similar distortions in the secondary wall 22 and
webs 24 occur.
* * * * *