Note: Descriptions are shown in the official language in which they were submitted.
3~32
COMPOUND EPICYCLIC COG BELT SPEED REDUCER
The present invention relates to speed reducers
and, more specifically, to a compound epicyclic speed
reducer having a high velocity ratio, such as at least
1,000:1, and usable for an e~tended period at high
input speed for the driving shaft, such as at least
3,000 revolutions per minute.
A speed reducer having a high velocity ratio
between the driving and driven components of the reducer
is required in applications where it is desired to
increase -the output torque o~ the driven comp~nent
greatly o~er the input torque of the driving component,
or where it is desired to decrease the output speed of
the driven component greatly over the input speed of
the driving component.
For achieving a high velocity ratio, "ordinary"
gear trains, that is, trains using gears rotatable
about axes stationary relative to each other, are
undesirable because many sets of gears in series are
required to achieve a high ~elocity ratio. While a
higher velocity ratio can be achieved with fewer parts
by use of worms, worms require precise machining and,
in general t have a lower power transmission efficiency
than spur gears.
Epicyclic gear trains offer the advantage of
requiring fewer sets of gears to achieve a high velocity
ratio, resulting in less weight without substantial
reduction in power transmission efficiency as compared
to ordinary gear trains. However, the gears o epicyclic
speed reducers must be precisely machined and precisely
positioned. In addition, there is moxe difficulty in
,~
adjusting the velocity ratio from any designed value
for an epicyclic speed reducer than ~or an ordinary
speed reducer because changing the size of any one gear
in an epicyclic speed reducer usually requires
repositioning at least some oE the other gears.
Some of the problems with epicyclic speed
reducers can be overcome by exotic design. For example,
in the device of U.S. patent No. 3,481,222, issued in
the name o Baron on February 12, 1969, a "floating"
orbiting planet shaft is provided so -that the planet
gears need not be positioned quite so precisely with
respect to the sun gears as in an epicyclic speed
reducer having a firmly positioned planet shaft.
A problem common to both ordinary and epicyclic
speed reducers using meshing gears is that maximum
lnput speed is limited. In producing electric motors
of a given power rating, for example, the power to cost
and power to weight ratios are substantially higher for
a high-speed motor, such as a motor having an output
speed in the range o~ 3,000 to 20,000 rpm, than Eor a
low-speed motor, such as a motor having an output speed
in the range of 1,000 to 31 rpm, so that an inexpen
sive high velocity ratio speed reducer capable of
handling high input speed would be desirable. Conven-
tional speed reducers using meshing gears simply cannot
be driven above about 3,000 rpm for extended periods
because of heat build-up resulting in rapid wear -- at
least without the additional expense of high precision
machining and/or exotic and expensive gear materials
and lubricants or lubrication systems. At high speed,
lubricant is flung from the gears by centrifugal force.
Heat build-up and rapid wear at high speed is even more
of a problem with worms. A practical upper limit for
the input speed of worm gear reducers is about 2,000
rpm.
Lubrication problems also can be overcome
somewhat by exotic design. For example, the "~lart
reduction pulley", which has a meshing gear epicyclic
reducer, uses "splash lubrication" in which lubricant
flung from spinning gears contacts the inner periphery
of the specially designed reducer housing and splashes
back onto the rotating gears. Nevertheless, even the
Hart reduction pulley is recommended for use with a
motor having an output speed of only 1,750 rpm.
Naturally, total cost is a primary considera-
tion in the selection of an electric motor-speed
reducer combination producing a desired output speed
and torque. In genexal, where low output speed is
required, the cost of the speed reducer portion is
much greater than the cost of the electric motor
portion. Up to now, to achieYe a desired low output
speed, the combination of a high-speed motor and a
high velocity ratio speed reducer capable of handling
high input speed has not been cost effective, because
the additional expense of the high input speed, high
velocity ratio speed reducer is substantially greater
~ than the cost savings resulting from using a high-
; speed motor. Again, it is apparent that an inexpensive
high velocity ratio speed reducer capable of handling
high input speed is desirable.
For a specific application, ordinary and
epicyclic gear trains can be used in combination. For
example, the device of Canadian patent No. 824,402,
issued in the name of Zucchellini on October 7, 1969,
Z
uses an epicyclic reduce~ drivin~ a worm to achieve
exact positioning of a slide that can carry machine
tools. The devices of Canadian patent No. 922,926,
issued in the name of Lemmens on March 20, 1973, and
Canadian patent No. 935,668, issued in the name of
Roper on October 23, 1973, use variable pitch pulley
belt drives connected to the input shaft or the input
and output shafts of an epicyclic speed reducer for
providing an infinitely variable transmission.
Ordinary and epicyclic gearing also can be
connected in series to overcome a disadvantage of
either system when used alone. In the Hart reduction
pulley, an initial speed reduction is achieved by an
open V-belt drive connecting the oùtput pulle~ of a
motor and the input pulley of an epicyclic speed
reducer. The result is that the total velocity ratio
can be altered through a limited range by changing the
velocity ratio of the open V-belt drive without changing
the velocity ratio of the epicyclic speed reducer.
The Hart reduction pulley Ealls into a
further class of speed reducers that includes the
devices of Canadian patent No. ~56,655, issued in the
name of Helling on May 17, 1949, and the following
United States patents:
Morini No. 3,115,794, issued December 31, 1963; and
Philpott et al. No. 3,842,685, issued October 22, 1974.
Each of these devices uses some type of endless loop
force-transmitting element, such as a belt or a chain,
in conjunction with an epicyclic speed reducer. Also,
in each of these devices input power is applied directly
to the carrier member for the orbiting planet shaft of
the epicyclic reducer. An advantage of using endless
loop force-transmitting elements that is not recognized
in any of these patents is that higher input speed can
be accommodated by speed reducers using endless loop
force-transmitting elements rather than meshing gears;
and a disadvantage o each of these devices that is
not recognized in any of the patents i5 the decreased
maximum input speed permitted by driviny a carrier
member directly.
The principal object of the present invention
is to provide a compact and light speed reducer having
a high velocity ratio, such as at least 1,000:1,
providing high power transmission e~ficiency, such as
about 90 percent, and usable for an extended period at
high input speed, such as at least 3,000 rpm.
It also is an object to provide such a speed
reducer in a form adaptable to a variety of applications
including use in various motor-speed reducer combina-
tions, and in reverted or nonreverted, constant velocity
ratio or variable velocity ratio, constant output
torque or regulated maximum output torque, and instan-
taneous or gradual start-up applications.
The foregoing objects can be accomplished by
a compound epicyclic speed reducer comprising: a
frame; a reaction sun; means for maintaining said
reaction sun stationary relative to said frame; an
output sun coaxial with said reaction sun, the common
axis of said two suns defining a primary axis; at
least two planets, one for each o-f said suns, including
a reaction planet and an output planet; planet shaft
means for carrying said planets for conjoint rotation;
an idler carrier assembly rotatably supporting said
planet shaft means spaced from and extending sub-
~ t~ 2
stantiall~ parallel to said primary axis, the axis of
said planet shaft means supported by sald idler carrier
assembly defining a secondary axis; at least two
endless loop force-transmitting elements connecting,
respectively, said reaction sun and said reaction
planet, and said output sun and said ou~put planet;
and rotary input means for driving said planet shaft
means and thereby effecting conjoint rotation of said
two planets about said secondary axis, rotation of
said reaction planet effecting rotation of said idler
carrier assembly about sai.d primary axis for orbiting of
said planet shaft means and said planets about said
primary axis, and rotation of said output planet about
said secondary axis in combination with orbiting of said
output planet about said primary axis eEfecting rotation
of said output sun.
Such objects also can be accomplished by a
compound epicyclic speed reducer comprising: a frame;
at least two suns; means mounting said suns on said
frame in coaxial relationship, the common axis of said
two suns defining a primary axis; means for maintaining
one of said suns stationary relative to said frame; at
least two planets, one for each of said suns; planet
shaft means for carrying said planets for conjoint
rotation; an idler carrier assembly rotatably supporting
said planet shaft means spaced from and extending sub-
stantially parallel to said primary axis, the axis of
said planet shaft means supported by said idler carrier
assembly d2fining a secondary axis; at least two
endless loop force-transmitting elements connecting,
respectively, one of said suns and one of said planets,
and the other of said suns and the other of said
z
planets; rotary input means for e:Efecting rotation of
said plane~ shaft means and thereby effecting conjoint
rotation of said two planets about said secondary axis,
rotation of said planets effecting rotation of said
idler carrier assembly about said primary axis for
orbiting of said planet shaft and said planets about -
said primary axis; and a rotary output member rotatably
mounted on said frame and driven by rotation of said
planets about said secondary axi.s in combination with
orbiting of said planets about said primary axis.
Such objects also can be accomplished by
rotary drive mechanism comprisiny a high-speed electric
motor having a rotary output member rotating a-t a speed
of at least 3,000 rpm~ and a compound epicyclic speed
reducer having a velocity ratio of at least 1,000:1 and
including: an input shaft rotatable about a first axis
by rotation of said motor rotary output member; an
output shaft coaxial with the input shaft and rotatable
relative thereto; three suns, all concentric about said
first axis, including a stationary reaction sun, an
input sun rotatable with said input shaft and an output
sun rotatable with said output shaft; three planets/
including a reaction planet for said reaction sun, an
input planet for said input sun and an output planet for
said output sun; planet shaft means carrying said three
planets for conjoint rotation; an idler carrier member
mounting said planet shaft means spaced from and extending
substantially parallel to said first axis for orbiting
of said planet shaft means about the primary axis; and
three endless loop force-transmitting elements for
connecting, respectively, said reaction sun and said
3Z
reaction planet, said input sun and said input planet,
and said cutput sun and said output planet.
In drawings which illustra-te embodiments of
the invention,
Figure 1 is a somewhat diagrammatic end
elevation of a compound epic~clic cog belt speed
reducer in accordance with t.he present invention, and
Figure 2 is a somewhat diagrammatic vertical ~ection
taken along line 2--2 of Figure 1,
: 10 Figures 3 and 4 are corresponding somewhat
diagrammatic fragmentary vertical axial sections of
modified forms of speed reducers in accordance with the
present invention showing alternative mountings of an
electric motor at the input sides of the reducers,
Figure 5 is a somewhat diagrammatic fragmen-
tary enlarged vertical axial ssction of another embodi-
ment of speed reducer in accoxdance with the present
invention having a modified planet carrier assembly,
Figure 6 is a somewhat diagrammatic vertical
axial section of another embodiment of speed reducer in
accordance with the present invention having maximum
output torque control mechanism, and Figure 7 is a
somewhat diagrammatic end elevation of the speed
reducer of Figure 6,
Figure 8 is a somewhat diagrammatic vertical
axial section of another embodiment of speed reducer in
accordance with the present invention having a manually-
controlled variable diameter reaction sun for changing
the velocity ratio of the reducer, and Figure 9 is a
somewhat diagrammatic fragmentary section taken along
line 9--9 of Figure 8,
Figure 10 is a somewhat diagrammatic fragmen-
tary vertical axial section o~ another embodiment o~
speed reducer in accordance with the present invention
having a power-controlled variable diameter reaction sun;
Figure 11 is a somewhat diagrammatic fragmentary
vertical axial section of another embodiment of speed
reducer in accordance with the present invention having
alternative reaction suns fc~r variable speed control,
Figure 12 is a somewhat diagrammatic vertical
axial section of another embodiment of speed reducer
in accordance with the present invention, illustrating
a nonreverted ~orm,
Figure 13 is a somewhat diagrammatic vertical
axial section of another embodiment of speed reducer
in accordance with the present invention, illustrating
an "electric wheel" application in which the spee~
reducer is built into the hub of a wheel and an electric
; motor is mounted outside the hub, and
Figure 14 is a somewhat diagrammatic vertical
axial section of a speed reducer in accordance with
the present invention, illustrating a "drum motor"
application in which the speed reducer and an electric
motor are mounted inside a drum for rotating the drum.
; The compound epicyclic speed reducer in
accordance with the present invention shown in Figures
1 and 2 includes a mounting base 1 supporting a closed,
substantially cylindrical housing 2 having opposite
end discs 3 and 4 joined by through-bolts 5. The
bolts are the reducer.
Input shaft 6 carries an input sun 11 generally
at the axial center of the reducer, and output shaft 8
carries an output sun 12 inside the housing adjacent
to the output end disc 4. A reaction sun 13 is mounted
stationarily in the housing 2 adjacent to the input
end disc 3 by screws 14 and has an axial bore 15
throuyh which the input sha~t 6 passes freely. All of
the suns are coaxial about the primary axis of the
reducer.
Elongated parallel carrier plates 16, spaced
apart axially of the reducer, have corresponding
central portions located at opposite sides o~ the
input sun 11 and project generally diametrally of the
reducer to form an idler planet carrier assembly. The
central portions of such carrier plates are journaled
on input shaft 6 by bearings 17 so as to be ~reel~
rotatable relative to the input shaft. Corresponding
swinging ends of the plates are joined by crossbars
18. A spacer tube 19 encircling to the input shaft
generally inside the bore 15 through the reaction sun
prohibits substantial movement of the idler carrier
assembly axially of the input shaft.
A planet shaft 20 is journaled in corresponding
end portions of the carrier plates 16 by bearings 21
and is fxeely rotatable relative to the carrier plates.
Such shaft defines an axis -- the secondary axis of
the reducer -- parallel to the primary axis and orbital
about the primary axis by rotation of the carrier
assembly. An input planet 22, an output planet 23 and
a reaction planet 24 all are fixed to shaft 20 at
axially spaced locations radially aligned, respectively,
with input sun 11, output sun 12 and reaction sun 13.
Each planet is connected to its associated sun by an
endless loop force--transmitting element 25, 26 or 27.
Preferably, all of the suns and planets are
cog wheels or sheaves and all of the endless loop
force-transmitting elements are cog belts. Nevertheless,
in an application requ.iring high torque ~ransference
or in an applicakion where h:igh temperature or stress
would shorten the life of cog belts, the planets and
suns can be sprockets and the endless loop ~orce-
transmitting elements can be chains~
In operation, rotation of input sun 11 by
rotation of input shaft 6 necessarily effects rotation
of input planet 22 by force transference by the input
endless loop Eorce-transmitting element 25. Since all
of the pl~nets are :~ixed to planet shaft 20 to rotate
conjointly, reaction planet 24 is rotated by rotation
of input planet 22 and, consequently, is driven orbitally
around the stationary reaction sun 13 ~y force trans~
ference by the reaction endlests loop force-
transmitting element 27. Planet shaft 20, the other
planets and the idler carrier assembly are swung
around the primary axis of the reducer with the reaction
planet. Rotation of output planet 23 about the secondary
axis and orbiting of such planet about the primary
axis effects rotation of output sun 12, and the output
shaft 8 carrying such sun, by force transference by
the output endless loop force-transmitting element 26,
but at a much slower speed than the rotational speed
of the input shaft.
The velocity ratio R of the speed reducer,
that is, the rotative speed of input shaft 6 relative
to the rotative speed of output shaft 8, depends on
the relative sizes of the suns and planets and can be
determined by the following equation in which it is
assumed that all suns and planets are of the same
pitch (same number of teeth per unit circumference)
11
32
and in which "Ni" represents the number of teeth on a
sun or planet "i" as designated in the above description:
3 1 N13N22
N2 4N1 1
13 23
2~ 12
For illustration, input sun 11, output planet 23 and
reaction planet 24 all can have the same number of
teeth "x", the relative numbers of teeth o~ the input
sun 11 and the input planet 22 can be about 1:2, or
x:2x, and the relative numbers of teeth of the input
planet 22 and the reaction sun 13 can be about 1:2, or
2x:4x, as shown in the drawings, in which case the
velocity ratio equation can be reduced to the following:
17 (2x)(4x)
R = 1 (x)(x) _ - l3
(x)(N12) 12
22 In this instance the velocity ratio R is totally
dependent on the relative sizes of the output sun 12
and the reaction sun 13. If such suns are the same
size, the velocity ratio is infinite, that is, the
output shaft ~ will not rotate regardless of whether
or not the input shaft is rotated; if the output sun
is larger than *he reaction sun, the velocity ratio i5
negative, that is, the output shaft will rotate in the
opposite sense from the sense of rotation of the input
shaft; and if the output sun is smaller than the
reaction sun, the velocity ratio is positive, that is,
the output shaft will rotate in the same sense as the
sense of rotation of the input shaft.
rro obtain a high ~elocity ratio, either
positive or negative, the outpu-t sun should be only
slightly larger or smaller than the reaction sun.
Where cog wheels are used, the output sun can ha~e
only one more or one less tooth than the reaction sun.
For example, in a represenative installation the
output sun can be a cog wheel having 150 teeth and the
reaction sun can be a cog wheel having 151 teeth, in
which case the velocity xatio is about 1,050:1.
The velocity ratio can be changed substantially
by changing the size of one or more of the suns or
planets slightly, particularly the output sun or the
reaction sun. For example, adding one tGoth to the
reaction sun, so that the reaction sun has 152 teeth,
cogs, without changing the size of the output sun, so
that the output sun still has 150 teeth, results in a
velocity ratio of about 525:1, that is, a 50 percent
reduction in the velocity ratio. Such a slight change
can be accomplished easily without altering the ~rame
size or design by substituting one cog wheel for
another. In contrast, in known systems using rneshing
sun and planet gears, the velocity ratio cannot be
changed wi.thout providing cne or more new or additional
sets of precisely machined gears, which often necessitates
a change i.n ~rame size or design.
The most important advantage o~ a speed
: reducer in accordance with the present invention is
that such reducer can handle ~ery high input speed for
an extended period. Sets of wheels or sprockets
connected by endless loop force-transmitting elements
can be dri.ven àt a much higher speed than meshing
gears of the same size, primarily because by use of
13
flexible endless loop force-transmitting elements
transmitted force is spread throu~h several wheel or
sprocket teeth, rather than being concentrated on one
or two gear teeth as in meshing gears. In addition,
spreading transmit-ted force through several teeth
allows use of li~hter wheel ox spxocket materials
having less strength than would be required for
meshing gears transferring the same force.
To accomn~odate the fastest input speed
possi~le, the input sun always should be effectively
smaller than, or at least no larger than, the input
planet so that the planet shaft rotates at a slower
speed relative to the carrier assembly than the input
shaft. Preferably the input planet is two to ten
times larger than the input sun. In the embodiment of
the invention shown in Figures 1 and 2, the reduction
ratio Rp from the input shaft 6 to the planet shaft
20, that is, the rotative speed of the input shaft
relative to the rotative speed of the planet shaft,
can be determined b~ the following equati~n:
N13N22
~12 4N.
Rp = N~
1 ~ N
and, as in the previous illustration, if input sun 11,
output planet 23 and re~ction planet 24 have "x"
teeth, input planet 22 has 2x teeth, and reaction sun
13 has 4x teeth, the equation can be reduced as follows:
Rp = ~ = 7 = 2.33:1.
14
Accordin~ly, the planet shaft would rotate at somewhat
less than one-half the spee~ of rotation of the input
shaft and in the same sense as the input shaft.
Similarly, it is preEerred that the reaction
planet be substantially smaller than the reaction sun,
such as no greater than one-half the size of khe
reaction sun, so that the idler carrier assembly
rotates e~en slowerO The reduction ratio Rc from the
input sha~t to the carriex assembly, that is, the
rotative speed o~ the input shaft ralati~e to the
rotative speed of the carrier assembly, can be determined
by the ollowing equation:
N13M22
R = 1 - --
16 which, assuming the same relative sizes o~ the suns
and planets as before, reduces to
R - - 7:1
Accordingly, the carrier assembly would rotate at one-
seventh the speed of xotation of the i.nput shaft, one-
third the speed of the speed of rotation of the planet
shaft, and in the opposite sense from the sense of
rotation of the input shaft and planet shaft.
Using small planets also reduces the inertia
of the carrier assembly so that less power is required
to start the carrier assembly rotating.
In prior art devices in which a planet
carrier assembly is ~otated directly and, in affect,
serves as the input component of the reducer, maximum
input speed is limited because the planets and planet
shaft carried by the carrier assembly rotate faster
than, or at about the same speed as, the carrier
9~
assembly. Accordingly, in such prior art devices it
is the maximum speed o~ rotation of the planet shaft
or carrier member that determines the m~imum input
speed, whereas in the present invention ma~imum input
speed is limited only by the maximum permissible speed
of rotation of the input shaft. Considering that in
the present invention the input shaft rotates several
times faster than the plane-t shaft, it will be recognized
that the speed reducer of the present invention can
handle an input speed several times faster, such as
10,000 rpm or even faster, than prior epicyclic speed
reducers having carrier members driven directly.
Specialized applications of the speed reducer
of the present invention are shown in Figures 3 through
14. As shown in Figure 3, the housing input end disc
3 can have an outward projecting mounting flange 28 on
which the base 29 of a standard ~rame motor 30 can be
stationarily mounted with the motor output shaft 31 in
registration with the speed reducer input sha~t 6.
Such two shafts can be directly connected by a coupling
32.
Alternatively r as shown in Figure 4, the
housing input end disc 3 can have outward projecting
mounting brackets 33 spaced on opposite sides o~ the
input shaf-t 6 such that a flange frame motor 34 can be
stationarily mounted on such brackets with its output
shaft 35 in registration with the speed reducer input
shaft 6 and connected to such input shaft by a coupling
36.
For very high speed or high torque applications,
it is preferred that the carrier assembly be balanced,
that is, have its center of gravity on the primary
16
axis. In the duplex carrier assembly shown in Fiyure
5, two sets of planets are carried, respectively, by
two separate planet sha~ts 20 journaled in opposite
end portions o~ the carrier plates 16 by bearings 17.
Each set o planets includes an input planet 22, an
output planet 23 and a reaction planet 24, each o the
same size as the corresponding planet of the other
set. The input shaft 6 carries two identical input
suns ll side-by-side between the carrier plates. ~ach
input sun is radially aligned with one o the input
planets and is connected thereto by an endless loop
force-transmitting element 25. A single endless loop
force-transmitting element 27 operahly connects the
two reaction planets 24 and the reaction sun 13.
Similarly, a single endless loop force-transmitting
element would connect the two output planets 23 and
the output sun (not shown). In other respects, the
embodiment of the present invention shown in Figure 5
is identical to the embodiment shown in Figures 1 and
2. While two sets o~ planets are shown in Figure 5,
three or more sets could be provided, preferably
spaced uniformly circumferentially around the primar~
axis of the reducer.
The embodiment o the present invention
shown in Figures 6 and 7 al~o uses a substantially
cylindrical housing 2 h~ving opposite input and output
end discs 3 and 4, respectively. Rather than being
; fixed to the input end disc, the reaction sun 13 is
fixed on a sleeve 37 journaled in a bearing 38 carried
in an aperture through the center of the input end
disc. A brake disc 39 also is ~ixed to the sleeve,
but outside of the housing, and a clamping brake
17
mechanism 40 is provided to clamp or release the brake
disc, thereby resistin~ rotation of the reaction sun
or permitting it to rotate Ereely.
The input sha~t 6 of such reducer extends
through the bore of sleeve 37 and, as in the previous
embodiments, has its inner end portion received in a
bearing lO carried in a blind axial bore in the inner
end of vutput shaft 8 extending through the housing
output end disc 4. The input sun 11 carried by the
input shaft is connected to the input planet 22 carried
by the planet shaft 20 b~ an endless loop force-
transmitting element 25. Such planet shaft is supported
for orbiting about the primary axis of the reducer by
an idler carrier disc 41 journaled on sleeve 37 by a
bearing 42 and freely rotatable relative to such
sleeve. A suitable fastener, such as a nut, at the
inner end portion o~ slee~e 37 prevents sliding of the
carrier disc axially of such sleeve. The output
planet 23 and the reaction planet 24 are carried at
the opposite end portions of the planet shaft 2~ in
radial alignment with their corresponding output and
reaction suns 12 and 13, respectively, and are connected
to such suns by endless loop force-transmitting elements
26 and 27, respectively.
A further modi~ication of the embodiment
shown in ~igures 6 ancl 7 is the provision of a clamping
brake mechanism 43 for the idler carrier disc 41.
Such brake is carried at the inner periphery of housing
2 and is actuatable to securely clamp the carrier
disc, and thereby pre~ent its rotation, and is releasable
for allowing free rotation of the caxrier disc.
1~
82
In use, with brake 40 ac-tuated for preventing
rotation of the brake disc 39 and the reaction sun 13,
and with brake 43 released ~or permitting free rotation
of the carrier disc, the embodiment o~ Figure 7 operates
the same as the embodiment of Figures l and ~. ~owever,
the speed reducer o~ Figure 6 can be converted from
epicyclic to ordinary operation by simultaneously
releasing brake 40 for permitting free rotation of the
reaction sun and applying brake 43 for preventing
rotation of the carrier disc. In this instance, the
primary and secondary axes o~ the reducer remain
stationary relative to each other and the reducer acts
as a two-stage ordinary speed reducer. The velocity
ratio is the product of the ratios of the input and
output sets, that is, the product of N22/Nll and
Nl2/N23. Thls product will be several times less than
the velocity ratio in epicyclic operation.
Brake 40 and brake disc 39 also can be used
in cooperation to determine the maximum output torque
transferable by output shaft ~. With brake 43 released,
the frictional resistance applied by brake 40 to the
brake disc can be selected at any desired ~alue so
that the reaction sun will slip if the applied torque
exceeds a predetermined value. This would be beneficial,
for example, if the load driven by the output shaft
becomes jammed, preventin~ rotation of the output
shaft, whereupon the brake disc would slip in its
brake and permit rotation of the reaction sun before
the reducer or the motor drivin~ the input shaft is
damaged.
Brake 40 and brake disc 39 also can be used
in cooperation for ~radual, as opposed to instantaneous,
19
"3~
start-up. As discussed above, the present in~ention
permits us~ of light, inexpensive high-speed electric
motors for driving input shaft 6. It can take such a
motor a substantial period to reach its designed
operating speed, and if a substantial load is applied
immediately, the motor coulcl stall before the operatiny
speed is reached. With bra~e 43 released ~or allowing
free rotation of the carrier disc 41 and with brake 40
released enabling free rotation of brake disc 39 and
reaction sun 24, e~en if a substantial load is applied
to the output shaft, very little torque need be applied
to the input sha~t to start the carrier member revolving
because the reaction sun is free to rota-te. As the
motor reaches its designed output speed, brake 40 can
be applied gradually, whereupon the output shaft
begins to turn, until finally the brake is fully
applied resulting in the reaction sun heing held
stationary relative to the housing and the output
shaft being rotated at maximum speed in epicyclic
operation.
The embodiment of the present invention
shown in Figures 8 and 9 is ~ery similar to the embodi-
ment shown in Figures 6 and 7, the major differences
being that the reaction sun 13 in Figures 8 and 9 is
fixed to the housing input end disc 3 and is of variable
effecti~e circumferential extent for changing the
velocity ratio of the reducer. ~s best seen in Figure
9, the reaction sun 13 includes a central core portion
45 surrounded by a somewhat resilient annular outer
strip 46. The adjacent ends of the annular strip do
not abut, but rather define a narrow ~ap 47 at the top
of the reaction sun. ~uch ends are movable toward and
away from each other for reducing or increasiny the
effective circumferential extent of the reaction sun
by manually turning a worm 48 meshing with a worm gear
49 formed integral with a sleeve nut 50. The sleeve
nut, serving as a turnbuckle, receives oppositely
threaded screws 51 projecting from plates 52 rigidly
attached to the innex peripheries of the opposite end
portions of the annular strip 46.
Rotation of worm gear ~9 in one direction
will reduce the effective size of the reaction sun
while rotation of the worm gear in the opposite direction
will increase the effective size of the sun. As
previously discussed, even a slight change in the
effective size of the reaction sun effects a substan-
tially change in the velocity ratio of the reducer.
As shown in Figure 9, an idler pulley 53 can be provided
to tension the reaction endless loop force-
transmitting element 27 despite changes in the effective
size of the reaction sun.
As shown in Figure 10, the modifications of
Figures 6 and 7 and Figures 8 and 9 can be combined.
The embodiment of Figure 10, like the embodiment of
Figures 6 and 7, has a brake disc 39 and reaction sun
13 both fixed to a sleeve 37 rotatably mounted in the
housing input end disc 3. The construction of the
reaction sun of the embodiment of Figure 10 is substan-
tially identical to the construction of the reaction
sun in Figures 8 and 9, with the exception that an
electric motor 54 is provided for turning worm 48 to
adjust the effective circumferential extent of the
reaction sun. Power to the electric motor 5~ is
supplied through slip rings 55. Accordingly, the
velocity ra~io of the spee~ reducer can be adjusted
from a remote location for speed control of the output
shaft.
The embodiment o~ the present invention
shown in Figure 11 has two reaction suns 13' and 13l'
in side-by-side arrangement, each ha~ing its own
associated brake disc 39' or 39". The diameters of
the two reaction suns are slightly different. The
reaction sun 13' adjacent to the housing input end
disc 3 is fixed to a sleeve 56 carrying the clutch
disc 3~' and extending through the central aperture in
such end disc. The other ~eaction sun 13" is fixed to
a sleeve 58 extending through the bore of sleeve 56
and carrying the other brake disc 39". Both sleeves
are freely rotatable relative to each other and relati~e
to the housing input end disc.
The planet shaft 2~ carried by the idler
carrier assembly (not shown) has two reaction planets
24' and 24" connected to their corresponding reaction
suns by endless loop f~rce-transmitting elements 27'
and 271lo Separate brakes (not shown) are provided for
the two brake discs. In all other respects, the
embodiment of Figure 11 is identical to the embodiment
of Figures 6 and 7.
In operation, one or the other of the brake
discs is fixed by actuation o~ its associated brake
for maintaining the corresponding reaction sun stationary
while the other brake disc and reaction sun are free
to rotate. Accordingly, either of two velocity ratios
can be selected depending on which brake disc and
reaction sun are maintained stationary.
~l~L5~Z
Figure 12 illustrates a "nonre~erte~" embodi-
ment of the present invention, that is, an embodiment
in which the input and output members are not coaxial,
using a substantially cylindrical housing 2 having
opposite end discs 59 and 60. An output sleeve 8' is
journaled in bearings 9' carried in an aperture throuyh
the center oF end disc 60 and is freely rotatable
relative to such end disc. Inside the housing, an
output sun 12 is f.ixed to the output sleeve and a
reaction sun 13 having a large central bore 15 recei~ing
the sleeve is ~ixed to the housing end disc 60. The
suns are coaxial about the axis of the output sleeve --
the primary axis of the reducer. An idler carrier
disc 41 is rotatably mounted on the inner end portion
of the output sleeve by a bearing 42. Sliding of the
carrier disc axially of the output sleeve is prevented
by a fastener such as a nut 61.
A light, high-speed electric motor 62 is
mounted at the outer margin of the idler carrier disc
with its output shaft projecting parallel to but
spaced ~rom the axis o~ output sleeve 8'. The motor
shaft serves as the planet shaft 20' for the output
planet 23 and the reaction planet 24 aligned, respect-
ively, with output sun 12 and reaction sun 13. Such
planets are fixed to the output shaft for conjoint
rotation and are connected to their respective suns by
endless loop force-transmitting elements 26 and 27.
Power to the electric mo~or is supplied
through slip rings 55 mounted on a stationary sleeve
63 projec-ting inward from housing end disc 59 and
coaxial with the output sleeve 8'. The speed reducer
of Figure 12 can be conveniently mounted with a separate
23
shaft 64 ex-tendin~ through the bores of sleeves 8' and
63, which shaft can be stationary or movable without
interferring wi-th operation o~ the reducer. ~lterna-
tively, output sleeve 8' can have internal threads
complemental to external threads of shaft 64, and
sha~t 64 can be nonrotatable, such that rotation of
the output sleeve moves shaft 64 axially through the
reducer.
In operation, rotation of reaction planet 2
by rotation of the motor output shaft 20' effects
rotation of the entire carrier assembly, including the
motor, about the stationary reaction sun 13. Rotation
of output planet 23 about the axis of the motor output
shaft and orbitin~ of such planet about the primary
axis of the reducer effects rotation of output sun 12
and output shaft 8' carr~ing such sun. The velocity
ratio R of the speed reducer, that is, the rotative
speed of the motor output shaft acting as the planet
sha~t 20' as compared to the rotative speed of output
shaft 8' can be shown to be represented by the following
equation:
24
R 1 Nl3N23
N24 12
If the t~o planets are the same size, each havin~ "x"
teeth, and the relative numbexs o~ teeth of the reaction
planet 24 and the reaction sun 13 is 1:8, or lx:8x,
the velocity ratio equation can be reduced to the
following:
982
1 ~ x .~ 7
R ~ - N 3x = N~3
xN12 12
This equation is the same a~; the reduced equation for
the embodiment of Figures 1 and 2. Accordin~lY, if
the output sun is a co~ wheel having 150 teeth and the
reaction sun is a cog wheel having 151 teeth, the
velocity ratio is 1,050:1.
Figure 13 illustrates an "electric wheel"
application using an electric motor and a speed
reducer in accordance with the present invention for
drivin~ each wheel of an electric ~ehicle such as an
electric wheelchair ox an electric automobile. The
reducer is housed inside the substantially cylindrical
central hub 2 of a vehicle wheel 65. Such hub is
rotatably mounted on a nonrotatable axle 66 having an
axial bore 67. The output shaft of a high-speed
electric motor 68 mounted stationarily relative to the
axle extends through the axle bore and serves as the
input shaft 6' of the reducer. The inner end portion
of such shaft carries the input sun 11. There is no
output shaft, bu-t rather the output sun 12 is fixed to
a side of hub 2. The reaction sun 13 is fixed to the
inner end portion of axle 66. All of the suns are
coaxial.
A carrier disc ~1 is journaled on the axle
and is freely rotatable relative thereto. Such
carrier disc carries a planet shaft 20 extending
parallel to the primary axis of the reducer and having
an input planet 22, an output planet 23 and a reaction
planet 24 in radial ali~nment with their xespective
suns. The planets are connected to the suns by
endless loop force-transmitting elements 25, 26 and
27. As in the previous embodiments, all of the
planets rotate con~ointl~.
The operation of the embodiment of Figure 13
is substantially the sa~e as the operation o~ the
embodiment of Figures 1 and 2. Rotation o$ the input
sun 11 by rotation of the m~to~ oukput shaft effects
rotation of the wheel hub 2 and wheel 65 relati~e to
the nonrotatable axle 66 carrying the reaction sun.
The velocity ratio of the embodiment of
Figure 13 can be changed by removing the output
endless loop force-transmittiny element 23, so that
there is no force transference between the output
planet and sun, and fixing carrier disc 41 to hub 2.
In this instance, the wheel 65 rotates at the same
speed as the speed of rotation of the carrier disc,
which is faster than the speed of rotation of the
output sun 12 with belt 23 connected and the carrier
disc free to rotate relative to the hub. Speed shift
mechanism, similar to the embodiment of Figures 6 and
7, can be incorporated to select between the two types
of operation. Rather than being fixed to an end of
the hub, output sun 12 can be rotatable relative to
the hub, and a brake or lock provided -to prevent or
allow rotation of the output sun relative to the hub.
A further brake or lock $or the carrier disc would be
required to prevent rotation of the carrier disc
relative to the hub when the output sun is rotatable
and to allow rotation of the carrier disc rela-tive to
the hub when the output sun is fixed.
26
~l.5~9~3~
Figure 14 illustrates a "drum motor" applica~
tion using an electric motor and a speed reducer in
accordance with the present invenkion in which the
high-speed electric motor 69 is mounked inside a
cylindrical drum 2, such as a roller drum or a drum
dri~ing a belt conveyor. Such drum has opposite end
discs 70 and 71. Motor 69 is mounted inside the drum
by a mounting sleeve 72 rotatably recelved in an
aperture through the center of drum end disc 70. As
diagrammatically illustrated at -the right of Figure
14, the motor mounting sleeve is rigidly attached to
the frame 72 on which the drum motor is mounted for
preventing rotation of the electric motor~ The power
connection 74 for the motox e~tends lengthwise through
the axial bore of the stationary mounting sleeve 72.
The rotating motor output shaft extends
axially of the drum 2 toward drum end disc 71 and
serves as the input shaft 6" of the reducer. The free
end portion of the input shaft is received in a bore
in the inner end of a reaction shaft 75 rotatably
mounted in a central aperture in end disc 71. The
input sun 11 rotates with input shaft 6"; the output
sun 12 is fixed to the inner side of end disc 70; and
the reaction sun 13 is fixed to the inner end portion
: of reaction shaft 75.
An idler carrier disc 41 is rota$ably
mounted on sleeve 75 and supports a planet shaft 20
extending parallel $o the primary axis o~ the reducer
and carrying an input planet 22, an output planet 23
and a reaction planet 24 radially aligned with their
respective suns. Corresponding suns and planets are
connected by endless loop force-transmitting elements
25, 26 and 27.
As diagrammatically illustrated at the left
of Figure 14, a brake 76 carried by the stationary
frame 73 supporting the drum motor normally is clamped
for preventing rotation of reaction shaft 75 and
reaction sun 13 relative to the frame. Rotation of
the input sun 11 by rotation of shaft 6" effects
rotation of all of the planets conjointly, and rotation
of the reaction planet 24 effects rotation o-f the
entire carrier assembly around the stationary .reaction
sun 13. Rotation and orbiting of the output planet 23
effects rotation of the output sun 12, and the drum to
which it is attached, relative to the frame. The
drum-driving engagement of the input sun 11 wi-th the
output sun 12 can be disconnected by releasing brake
76 for allowing rotation of the reaction sun relative
to -the frame~
In each embodiment of the invention, the
suns and planets of the epicyclic speed reducer are
connected by endless loop force-transmitting elements,
and input power is transferred directly to a planet
shaft supported b~ an idler carrier member, permitting
hiyh input speed and easy adjustment of the velocity
ratio of the reducer by substitution of one planet or
sun for another~
28
