One-piece planetary gear for a rotary actuator and method of assembling a rotary actuator with a one-piece planetary gear

A geared rotary actuator (1 or 1') and method of assembling the same, with the geared rotary actuator (1 or 1') including a plurality of one-piece planetary gears (12 or 12'), each including a first set of gear teeth (19) meshing with a sun gear (11), and at least two additional sets of gear teeth (17, 18 or 17') respectively forming an inboard set of gear teeth and an outboard set of gear teeth respectively adapted to mesh with sets of gear teeth (13 or 13', 14 or 14'), of outboard and inboard ring gears. At least one tooth of the sets of gears (17, 18, 19 or 17', 19') are axially aligned along a length of the one-piece planetary gears (12 or 12') so as to enable the inboard ring to be moved axially past the outboard set of gear teeth (17 or 17') to mesh with the inboard set of gear teeth (18 or 17').

TECHNICAL FIELD 
The present invention relates to a planetary gear arrangement for a rotary 
actuator and method of assembling a rotary actuator and, more 
particularly, to a one-piece planetary gear and method of assembling a 
rotary actuator utilizing the one-piece planetary gear to accommodate an 
inboard gear mesh between a center and outboard mesh. 
BACKGROUND ART 
Rotary mechanical actuators have been utilized to fold wings of military 
aircraft in a unique folding geometry which permits a smaller actuator 
package to provide an effective higher torque moment combined with maximum 
extension. In military aircraft such as, for example, A-6 or A-12, a wing 
fold geometry having a fold angle of about 167.degree. is required, with 
the rotary actuator utilizing counter rotating output arms combined with 
linkages that can extend to more than twice an original envelope, that is, 
the actuator arms rotate 366.degree. for a 167.degree. rotation of a wing 
resulting in approximately a two-to-one mechanical torque advantage, 
thereby resulting in a lower weight since weight of the actuator is in 
proportion to a torque. 
Rotary actuator systems generally include a valve, hydraulic motor, 
hydraulic brake, simple and differential planetary gear assembly as well 
as a stop means. 
The differential planetary gear assembly for the rotary actuator system 
generally incorporates two different gear ratios, with the first ratio 
resulting in a negative value between large arms of the actuator and the 
center portion of the actuator while a second ratio results in a positive 
value between the small arms and center portion of the actuator. 
Consequently, in the proposed rotary actuator systems, with respect to the 
center portion of the actuator, the smaller side arms rotate in one 
direction while the larger arm rotates in an opposite direction, with the 
gears in the differential planetary gear arrangement being cageless and 
balanced. 
Moreover, geared rotary actuator generally only have one mesh on either 
side of a center gear mesh. During assembly, the planet gears are 
positioned around the support rings, and the ring gears are slid into 
place over the planet/support ring assembly. To facilitate assembly, a 
pitch diameter on the center mesh is larger than a pitch diameter of the 
end mesh. 
If an additional gear mesh is added to one side of the center mesh, 
assembly problems arise. More particularly, if the inboard mesh pitch 
diameter must, for some reason, be smaller than the outboard mesh and 
center mesh, the inboard mesh ring gear could be prevented from sliding 
over the outboard planet gears due to the larger outboard pitch diameter. 
One disadvantage in planetary gear arrangements for rotary actuator systems 
of the aforementioned type resides in the fact that the planetary gears 
are splined in the actuator. The splines lengthen the actuator to provide 
a sufficient torque carrying capability; however, lengthening of the 
rotary actuator adds to the weight. Additionally, the provision of splined 
connections is expensive by virtue of the required machining operations 
for the planetary gears and the spline shaft. 
U.S. Pat. No. 4,721,016 proposes a multi-staged geared rotary actuator for 
positioning aircraft flight control surfaces such as, for example, leading 
edge flaps, wherein a support of axially-aligned tubular planet gear 
shafts in successive stages is achieved by means extending through the 
axially-aligned tubular planet gear shafts which supports the ends of the 
planet gear shafts and reacts against bending forces applied to the ends 
of the tubular gear shafts to reduce deflection and maximize gear mesh of 
gears carried on the planet gear shafts for maximum torque transmission. 
While the above-proposed multiple-stage geared rotary actuator is effective 
for advantageously controlling a positioning of aircraft flight control 
surfaces, the proposed actuator is not faced with any assembly limitations 
in spite of the use of a multi-partite planetary gear construction. 
A compound gear arrangement is proposed in U.S. Pat. No. 4,751,855, also 
intended for use as a geared hinge for aircraft, each comprising a 
plurality of substantially axially aligned gear trains each having two 
relatively rotatable output ring gears surrounding a sun gear input 
element and two planet gear elements, with the planet gear elements being 
coupled for rotation in unison by the sun gear element and meshing with 
respective ones of the ring gears. The sun gear elements of adjacent gear 
trains are drivingly coupled by a means which permits an axial 
misalignment between the sun gear elements. 
While the above-proposed compound gear arrangement solves a flexibility 
problem, by virtue of the proposed constructional features, no particular 
assembly problem exists in the proposed compound gear arrangement. 
DISCLOSURE OF INVENTION 
The aim underlying the present invention essentially resides in providing a 
one-piece planetary gear for a rotary actuator and a method of assembling 
a rotary actuator utilizing a one-piece planetary gear which avoids, by 
simple means, shortcomings and disadvantages encountered in the prior art 
and which facilitates the assembly of a geared rotary actuator. 
In accordance with the present invention, a geared rotary actuator is 
provided which includes a sun gear coupled to a driven shaft, with a 
one-piece planetary gear means being provided and including a first mesh 
or set of gear teeth meshing with the sun gear in addition to at least two 
additional gear mesh or sets of gear teeth forming an inboard and outboard 
gear mesh, and with at least one tooth of each of the sets of gear teeth 
on the one-piece planetary gear means being axially aligned along the 
one-piece planetary gear means. An inboard ring gear is provided having a 
first operating pitch diameter including teeth meshing with the gear teeth 
of the inboard mesh, and an outboard ring gear having a second operating 
pitch diameter, larger than the first pitch diameter, is provided with 
gear teeth meshing with the outboard gear mesh. 
In accordance with the method of assembling a rotary geared actuator in 
accordance with the present invention having a sun gear, a plurality of 
one-piece planet gear means having a set of gear teeth meshing with the 
sun gear, and at least two additional sets of gear teeth, with at least 
one tooth of the gear teeth sets being axially aligned along inboard and 
outboard gear teeth sets of the additional sets of gear teeth, and with a 
first ring gear having a first operating pitch diameter which has teeth 
meshing with the inboard set of teeth and a second ring gear having a 
second operating pitch diameter larger than the first diameter having gear 
teeth meshing with the outboard set of gear teeth, a plurality of the 
one-piece planet gears are aligned with the aligned teeth in a position 
such that the aligned gear teeth are in a mesh position with the ring 
gears, a first ring gear is axially moved past the outboard set of gear 
teeth to mesh with the inboard set of gear teeth, and the second ring gear 
is moved axially to mesh with the outboard set of gear teeth. The first, 
second and third ring gears are provided with a suitable modified tooth 
profile so as to enable the teeth of the ring gear to be slid past the 
respective set of teeth of the planet gears. 
By virtue of the above-noted features of the rotary actuator and method of 
assembling the same in accordance with the present invention, it is 
possible to ensure that the planets are positioned around the support 
rings in such a manner that the ring gears can be readily slid into place 
over the planet/support ring assembly without any danger of the inboard 
mesh ring gear being prevented from sliding over the outboard planets due 
to the larger outboard pitch diameter. 
The rotary actuator and method of assembly of such rotary actuator is 
readily applicable to any situation wherein the actuator has a torque 
input on a sun gear and a plurality of planet gears, with each planet gear 
having a plurality of gear mesh. 
Moreover, it is not necessary in accordance with the present invention to 
have an identical number of teeth on the planet gears or the ring gears at 
the outboard or inboard positions as long as there is meshing between the 
respective sets of gear teeth. 
Additionally, the planetary gears may, in a conventional manner be provided 
with a carrier; however, such carrier is not necessary. 
Additionally, by virtue of the features of the present invention, the 
one-piece planetary gear assembly may be provided with a constant number 
of teeth or a variable number of teeth for planet gear or the ring gears. 
The above and other objects, features and advantages of the present 
invention will become more apparent from the following description when 
taken in connection with the accompanying drawings which show, for the 
purpose of illustration only, several embodiments in accordance with the 
present invention.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings wherein like reference numerals used 
throughout the various views to designate like parts and, more 
particularly, to FIGS. 1 and 2, according to these figures, a rotary 
actuator generally designated by the reference numeral 1 for enabling, for 
example, a folding of a wing structure generally designated by the 
reference character W of aircraft such as, for example, an A-6 or A-12 
aircraft, is mounted on the wing structure W, in a conventional manner, 
whereby the wing structure W is displaceable from a folded position (FIG. 
1) to a spread position (FIG. 2). A linkage system including, for example, 
link members 3, 4 are interposed between the rotary actuator 1 and the 
wing structure W for transmitting a rotary motion of the rotary actuator 1 
to the wing structure W to enable a folding and unfolding of the wing 
structure W. 
As shown in FIG. 4, the rotary actuator 1 includes a differential gear 
assembly generally designated by the reference numeral 10 comprising an 
input means such as, for example, a shaft S, a sun gear 11, a plurality of 
one-piece planetary gears generally designated by the reference numeral 
12, a plurality of ring gears 13, 14, 15, 16, respectively meshing with 
gear teeth 17, 18, 19, 20 provided on each of the planetary gears 12. 
The differential gear 10 in FIG. 4 drives link members 40, 41, 42, 43, 44 
by way of the planetary gears 12 and sun gear 11, with the link member 40 
being suitably secured by, for example, bolt means (not shown) with the 
wing structure at inboard and outboard positions of the wing structure in 
a conventional manner. The link members 41, 43 drive the outboard wing 
structure to fold the same up past a vertical position, with the link 
member 42 being connected in a conventional manner to the inboard wing 
structure, and the link members 40 and 44 forming a conventional hinge 
point for the wing structure. As shown in FIG. 3, the ink members 40 and 
44 are connected to each other by a tie bar 40a. 
The geared rotary actuator of FIGS. 3 and 4 is a standard GRA configuration 
with an additional set of gear teeth or gear mesh provided at the ring 
gear 13 and acting as a ground for the planetary system. 
As shown in FIG. 5, wherein the number of gear teeth for the respective 
center, inboard, and outboard gear mesh are parenthetically indicated, the 
center mesh has one more tooth than the outboard mesh of the planet and 
the inboard mesh planet has one less tooth. By virtue of the fact that the 
ring gear 13 acts as a ground for the planetary system, the center ring 
gear 15 is caused to travel in the opposite direction from the inboard 
ring gears 14, 16. 
As shown most clearly in FIG. 5, the inboard gear meshes have a smaller 
operating pitch diameter than the center gear mesh and the outboard gear 
mesh and the operating pitch diameter of the center mesh must be larger 
than the outboard mesh for the ring gear 15 to travel in the opposite 
direction to the ring gears 14, 16 thereby creating the assembly problem 
of trying to push a smaller operating pitch diameter of the ring gears 14, 
16 over the larger operating pitch diameter of the outboard mesh. 
While traditionally this problem has been solved by providing a two-piece 
planetary gear construction, in accordance with the present invention, 
each of the planetary gears 12 is fashioned as a one-piece planetary gear 
including a plurality of gear meshes or sets of gear teeth 17, 18, 19, 20 
as shown most clearly in FIGS. 6 and 7. 
To ensure assembly of the geared rotary actuator in accordance with the 
present invention, the number of gear teeth on each ring gear 13, 14, 15, 
16 must be the same so that the gears can align for assembly in the 
preferred embodiment. Moreover, the number of teeth on the sun gear 11 
must follow the standard GRA assembly rule, namely: 
EQU (N.sub.1 +N.sub.2).div.N.sub.p =INTEGER 
where: 
N.sub.1 =number of teeth of center ring gear; 
N.sub.2 =number of teeth of sun gear; and 
N.sub.p =number of planets. 
Additionally, as shown in FIG. 7, at least one tooth of each of the sets or 
mesh of gear teeth along an entire length of the planetary gear 12 must be 
in alignment. Additionally, the inboard gear mesh and outboard gear mesh 
tooth profiles must be modified so that the inboard ring gear 14 or 16 can 
slide past the outboard planet tooth. 
In the illustrated example of FIG. 5, the same pitch gears were chosen for 
the inboard and outboard gear meshes. Using standard gear proportions, the 
inboard ring gear pitch diameter would have been the same as the outboard 
pitch diameter. Standard gear modifications for tight centers are applied 
so as to obtain the same center distances for all meshes as much as 
practicable without violating any good design constructions. Since the 
operating pitch diameter diminishes proportionally to the correct value, 
by a careful selection of the original tooth form, the final outboard 
planet tooth form will be smaller than the inboard planet tooth form and 
other tooth form modifications also satisfy this requirement. 
As can readily be appreciated, the number of teeth shown in FIG. 5 is 
merely for illustrative purposes, and if the above noted criteria are met, 
gear assemblies with different number of teeth will also assemble equally 
well and, for example, as shown in FIG. 5A, the number of teeth of the set 
of gear teeth of the center ring gear may be greater than the number of 
teeth in the outboard ring gear. Furthermore, by careful selection of the 
geometry of the respective teeth, it may be possible to utilize the same 
cutter for both inboard and outboard planetary teeth in some instances. 
Moreover, while FIGS. 4 and 5 provide an example of a rotary actuator 
wherein an outboard mesh is provided only on the left side of the figure, 
it is also possible in accordance with the present invention to provide a 
second outboard mesh to the right of the respective figures. 
Alternatively, as shown most clearly in FIGS. 8 and 9, a rotary actuator 
generally designated by the reference numeral 1' may be provided wherein a 
differential gear assembly generally designated by the reference numeral 
10' comprises a sun gear 11, a plurality of one-piece planetary gears 
generally designated by the reference numeral 12', and a plurality of ring 
gears 13', 14', 15', 16' respectively meshing with gear teeth 17', 19' and 
20' provided on each of the planetary gears 12'. The rotary actuator 1' 
differs from the rotary actuator 1 in that the number of teeth of the 
respective ring gears 13', 14', 15', 16', as parenthetically shown in FIG. 
9 differ while the number of gear teeth of the respective sets of gear 
teeth on the one-piece planetary gear 12' are the same. Additionally, to 
facilitate manufacturing of the planetary gear 12', the inboard and 
outboard sets of gear teeth 17' are fashioned as continuous to the 
structure, i.e., having an axial length enabling engagement with the ring 
gears 13', 14'; however, such continuous gear mesh is not necessary. 
Moreover, to obtain the gear ratio illustrated in FIG. 9, outboard 
planetary teeth in the three of the six planetary gears 12' were removed 
for assembly limitations. However, other tooth numbers would not require 
such removal. 
As shown in FIG. 10, in assembling the rotary actuator 1, in accordance 
with the method of the present invention, the planetary gears 12 are 
arranged about a circumference of the sun gear 11 securely mounted on the 
shaft S, with the assembled cluster of planetary gears 12 and sun gear 11 
being held in a proper positional relationship by suitable conventional 
means such as, for example, a planet support (not shown). The plurality of 
the one-piece planetary gears 12 are positioned such that the at least one 
aligned gear tooth of each of the sets of gear teeth 17, 18, 19, 20 are in 
a mesh position with respect to the ring gears 13, 14, 15, 16. 
The ring gear 16 is axially moved from the right of FIG. 10 to mesh with 
the inboard set of gear teeth 20. The ring gear 15 is axially moved past 
the outboard set of gear teeth 17, inboard set of gear teeth 18 and meshes 
with the center set of gear teeth 19, with the gear ring 14 being axially 
moved past the outboard set of gear teeth 17 and meshing with the inboard 
set of gear teeth 18 as shown in FIG. 11. Then the ring gear 13 is moved 
axially to mesh with the outboard set of gear teeth 17 completing the 
assembly of the differential as shown most clearly in FIG. 12. 
By virtue of the features of the subject matter of the present invention, 
it is possible to produce and assemble a geared rotary actuator in an 
extremely simple manner without any problem relating to an assembly of the 
inboard mesh ring gear sliding over the outboard planetary gear mesh even 
with the outboard planetary gear mesh having a larger outboard pitch 
diameter. 
While we have shown and described several embodiments in accordance with 
the present invention, it is understood that the same is not limited 
thereto but is susceptible to numerous changes and modifications as known 
to one of ordinary skill in the art, and we therefore do not wish to be 
limited to the details shown and described herein, but intend to cover all 
such modifications as are encompassed by the scope of the appended claims.